predicting truck load spectra under weight limit changes and its application to steel bridge fatigue

Maximum towing capabilities are for properly equipped vehicles with required equipment and a 150-lb. driver and passenger and vary based on cargo, vehicle configuration, accessories, option content and number of passengers. See label on door jamb for carrying capacity of a specific vehicle. For additional information, see your Ford Dealer.2022 FORD BRONCO SPORTREQUIRED EQUIPMENTIncludes items that must be installed.* Your New Vehicle Limited Warranty (see your dealer for a copy) may be voided if you tow without them.For trailers over 1,500 pounds – Class II Trailer Tow Package (53B)*Check with your dealer for additional requirements, restrictions and limited warranty details.Included with Trailer Tow Package – Option Code 53BS ee chart at right for the weight-carrying capacity of this hitchreceiver. (This capacity also is shown on a label affixed to each receiver.)FACTORY-INSTALLED TRAILER HITCH RECEIVER OPTIONball mounting, and other appropriate equipment to tow both the trailer and its cargo load.Refer to the Trailer Towing Selector chart for Maximum Loaded Trailer Weight for this vehicle.HITCH RECEIVER WEIGHT CAPACITYBronco Sport (Option Code)(53B)Trailer Wiring Harness (4-Pin) XXTrailer Sway Control X XAVAILABLE TRAILER TOWING PACKAGENote: C ontent may vary depending on model, trim and/or powertrain. Seeyour Ford Dealer for specific content information for all light trucks that will be used for towing to help ensure easy, proper connection of trailer lights.Bronco Sport Badlands in Area 51 color.Optional features shown with available Ford Accessories.3. Badlands™ model only.Notes: • C ertain states require electric trailer brakes for trailers over a specified weight. Be sure to checkstate regulations for this specified weight. WARNING: Do not tow a trailer fitted with electric trailer brakes unless your vehicle is fitted with a compatible aftermarket electronic trailer brake controller. Failure to follow this instruction could result in the loss of control of your vehicle, personal injury or death. For additional information and assistance, we recommend that you contact an authorized dealer.• Bronco Sport calculated with SAE J2807® method.• Combined weight of vehicle and trailer cannot exceed listed GCWR. • Do not exceed the Maximum Loaded Trailer Weight listed.TRAILER TOWING SELECTORFrontal Area is the total area in square feet that a moving vehicle and trailer exposes to air resistance. The chart above shows the limitations that must be considered in selecting a vehicle/trailer combination. Exceeding these limitations may significantly reduce the performance of your towing vehicle.FRONTAL AREA CONSIDERATIONSTrailer Frontal AreaLoad should be balanced from side-to-side to optimize handling and tire wear Load must be firmly secured to prevent shifting during cornering or braking, which could result in a sudden loss of controlBefore StartingBefore setting out on a trip, practice turning, stopping and backing up your trailer in an area away from heavy trafficKnow clearance required for trailer roof Check equipment (make a checklist) Backing UpBack up slowly, with someone spotting near the rear of the trailer to guide you Place one hand at bottom of steering wheel and move it in the direction you want the trailer to goMake small steering inputs – slight movement of steering wheel resultsin much greater movement in rear of trailerBrakingAllow considerably more distance for stopping with trailer attached Remember, the braking system of the tow vehicle is rated for operation at the GVWR, not GCWRIf your tow vehicle is an F-150, F-Series Super Duty®, Transit or Expedition and your trailer has electric brakes, the optional Integrated Trailer Brake Controller (TBC) assists in smooth and effective trailer braking by powering the trailer’s electric or electric-over-hydraulic brakes with proportional output based on the towing vehicle’s brake pressureIf you are experiencing trailer sway and your vehicle is equipped with electric brakes and a brake controller, activate the trailer brakes with the brake controller by hand. Do not apply the tow vehicle brakes as this can result in increased sway TurningWhen turning, be sure to swing wideenough to allow trailer to avoid curbsand other obstructions.Towing On HillsDownshift the transmission to assistbraking on steep downgrades and toincrease power (reduce lugging) whenclimbing hillsWith TorqShift® transmission, selecttow/haul mode to automaticallyeliminate unwanted gear search whengoing uphill and help control vehiclespeed when going downhillParking With A TrailerWhenever possible, vehicles withtrailers should not be parked on agrade. However, if it is necessary, placewheel chocks under the trailer’s wheels,following the instructions below.Apply the foot service brakes and holdHave another person place the wheelchocks under the trailer wheels on thedowngrade sideOnce the chocks are in place, releasebrake pedal, making sure the chockswill hold the vehicle and trailerApply the parking brakeS hift automatic transmission into park,or manual transmission into reverseWith 4-wheel drive, make sure thetransfer case is not in neutral (if ap-plicable)Starting Out Parked On A GradeApply the foot service brake and holdStart the engine with transmission inpark (automatic) or neutral (manual)Shift the transmission into gear andrelease the parking brakeRelease the brake pedal and move thevehicle uphill to free the chocksApply the brake pedal while anotherperson retrieves the chocksAcceleration And PassingThe added weight of the trailer candramatically decrease the accelerationof the towing vehicle – exercise caution.When passing a slower vehicle, be sureto allow extra distance. Remember, theadded length of the trailer must clearthe other vehicle before you can pullback inSignal and make your pass on levelterrain with plenty of clearanceIf necessary, downshift for improvedaccelerationDriving With An AutomaticOverdrive TransmissionWith certain automatic overdrivetrans missions, towing – especiallyin hilly areas – may cause excessiveshifting between overdrive and thenext lower gear.To eliminate this condition and achievesteadier performance, overdrive can belocked out (see vehicle Owner’sManual)I f excessive shifting does not occur, useoverdrive to help enhance performanceOverdrive may also be locked out toobtain engine braking on downgradesWhen available, select tow/haul modeto automatically eliminate unwantedgear search and help control vehiclespeed when going downhillDriving With Cruise ControlTurn off the cruise control with heavyloads or in hilly terrain. The cruisecontrol may turn off automaticallywhen you are towing on long, steepgrades. Use caution while driving onwet roads and avoid using cruise controlin rainy or winter weather conditions.Spare Tire UseA conventional, identical full-sizespare tire is required for trailertowing (mini, compact anddissimilar full-size spare tiresshould not be used; always replacethe spare tire with a new road tireas soon as possible).On The RoadAfter about 50 miles, stop in aprotected location and double-check:Trailer hitch attachmentLights and electrical connectionsTrailer wheel lug nuts for tightnessEngine oil – check regularly throughoutyour tripHigh Altitude OperationYour vehicle may have reducedperformance when operating at highaltitudes and when heavily loadedor towing a trailer. While driving atelevation, in order to match drivingperformance as perceived at sea level,reduce GVWs and GCWs by 2% per1,000 ft. elevation.Powertrain/Frontal AreaConsiderationsThe charts in this Guide show theminimum powertrain needed to achievean acceptable towing performance forthe listed GCW of tow vehicle and trailerUnder certain conditions, however,(e.g., when the trailer has a large frontalarea that adds substantial air drag orwhen trailering in hilly or mountainousterrain) it is wise to choose a vehiclewith a higher ratingTowing performance is maximized witha low-drag, rounded front design trailerSelecting A Trim SeriesYour specific vehicle’s tow capabilitycould be reduced based on weight ofselected trim series and option content.Note: For additional trailering informationpertaining to your vehicle, refer to thevehicle Owner’s Manual.Photography, illustrations and information presented herein were correct when approved for publishing. Ford Motor Company reserves the right to discontinue or change at any time the specifications or designs without incurring obligation. Some features shown or described are optional at extra cost. Some options are required in combination with other options. Consult your dealer for the latest, most complete information on models, features, prices and availability.Many of the recreational vehicles shown in this brochure are modified or manufactured by companies other than Ford Motor Company. Ford assumes no responsibility for such modifications or manufacturing.© 2021 Ford Motor Company. All rights reserved.。

2023-2024学年人教版高中英语高考模拟班级：__________ 姓名：__________ 考号：__________一、填空题（本大题共计3小题，每题3分，共计9分）1.With only her thoughts for________（陪伴），she walked slowly along the seafront.【答案】company【解析】答案：company.for company陪伴，作伴，是固定搭配。

故填：company.2.（1）I'm not ______（完全）happy with about his advice.2.（2） I've finished this magazine. Can I ______（交换）with you? 2.（3）I haven't been ______（在户外）for a long time.2.（4）He didn't want to write down a ______（系列）of facts in his diary.2.（5）How can Linda ______（恢复）from the illness in the dirty room?2.（6）I would be ______（感激的）if you could give me some advice.2.（7）We have a ______（德语）lesson every Wednesday.2.（8）This is a kind of magazine aimed at ______（青少年）.2.（9）He broke the glass on ______（故意）.2.（10）Nobody could ______（忽视）these problems.2.（11）Not having seen him for a long time, I can hardly ______（认出）him.2.（12）I know from the young man's ______（口音）that he is from the South.2.（13）You'd better find a ______（本地人）to tell you how to get there.2.（14）They went ______（直接）home without stopping at the gas station, for it was too late.2.（15）Chinese is our ______（官方的）language.2.（16）There are a lot of ______（流利的）English speakers in Hong Kong.2.（17）I lost my ______（身份）card on the way to Beijing.2.（18）Zhenghe made seven ______（航海）to the Indian Ocean in the Ming Dynasty.2.（19）There are ______（频繁的）contacts between the peoples of the two countries.2.（20）After months of discussion, a peace agreement is ______（逐渐地）taking shape.【答案】（1）entirely【解析】（1）entirely 考查副词。

Defects and in-service fatigue life of truck wheelsM.Carboni a,*,S.Beretta a ,A.Finzi ba Dipartimento di Meccanica,Politecnico di Milano,Via La Masa 34,20158Milan,Italyb Gianetti Ruote S.p.A.,Via Stabilimenti 1,20020Ceriano Laghetto (MI),ItalyReceived 6June 2002;accepted 26June 2002AbstractTruck wheels are usually assessed against fatigue by experimental tests based on standardised load sequences (CARLOS load spectra)which reproduce a typical service life of the real component.The present paper deals with the effect of defects,caused by the manufacturing process,on the fatigue life of wheels subjected to block loading tests.The research was prompted by premature service failures of a batch of truck wheels.The investigation firstly dealt with fatigue and crack growth tests for the quality control of the material and then with the detection of defects at the origin of the unexpected failures.The data have been used to assess the acceptability of defects and to estimate life under proof tests using current crack propagation models.#2002Elsevier Science Ltd.All rights reserved.Keywords:Defects;Wheels;Fatigue strength;Automotive failures1.IntroductionTruck wheels are classified as ‘‘safety components’’and,for this reason,they are subjected to particular attention during fatigue design in order to guarantee an appropriate in-service durability together with the need of a light-weight design.In fatigue assessment of wheels,the commonly accepted procedure by man-ufacturers is to pass two durability tests,namely the ‘‘radial fatigue test’’and the ‘‘cornering fatigue test’’[1–3].These tests are conventionally defined and are based on simple load conditions not representing the real in-service behaviour of components.Another widely used type of test is based on standardised load spectra (grouped under the name ‘‘CARLOS’’:CAR LOading Spectra)consisting of a preset sequence of lateral and vertical forces obtained by extrapolation of loads measured directly on components during typical manoeuvrings (straight driving,braking,cornering,parking,...)both on-road and off-road.In the special case of truck wheels,LBF (Germany)has developed ‘‘Eurocycle’’[4,5],an accelerated test spectrum able to represent,in a 65km route,2032km of typical exercise of truck wheels on European roads.Load spectra are applied to the real component,during fatigue tests,by a special Biaxial Test Facility [5,6].Particularly,in this machine the 1350-6307/03/$-see front matter #2002Elsevier Science Ltd.All rights reserved.P I I :S 1350-6307(02)00036-5Engineering Failure Analysis 10(2003)45–/locate/engfailanal*Corresponding author.Tel.:+39-02-2399-8253;fax:+39-02-2399-8202.E-mail address:carboni@mecc.polimi.it (M.Carboni).46S.Beretta et al./Engineering Failure Analysis10(2003)45–57wheel,fully assembled with hub,spindle,bearings and tire,turns inside a slightly larger steel cylinder,that rotates by means of an electric motor,and is simntaneously loaded by two servo-hydraulic actuators(ver-tical and horizontal)according to the load sequence included in‘‘Eurocycle’’.Proceeding in this way,the experimental durability check of a given wheel is carried out subjecting,by the biaxial test facility,a minimum lot of three components that have to survive to at least246‘‘Eurocycle’’blocks,corresponding to about500000km of service.The typical problems of the components,in terms of fatigue strength,are essentially three:i)disk failure caused by fretting-fatigue in the attachment face zone;ii)crack nucleation and propagation at the edge of the ventilation holes where the maximum circumferential stress exists(at45 to the axial direction);iii) fatigue failure of the welded joint between disk and rim.The design approach to these different problems, from the point of view of the test based on simple load conditions,is based on FEM analyses with the aim of defining the linear damage[7]or the elasto-plastic behaviour of the component[8]under the simple load conditions.Considering load spectra,a simple approach to design[4–6]can be directly exploited with experimental tests:after a design verification with strain-gauge measurements of the maximum stresses under simple load conditions,fatigue strength of the component is essentially assessed by durability tests based on ‘‘Eurocycle’’load spectra using the biaxial facility.In order to obtain wheel prototypes‘‘designed against load spectra’’,a computational model has been recently developed by Gianetti Ruote[9].It consists of a FEM analysis of the52load sequences constituting‘‘Eurocycle’’in order to achieve from them a simula-tion of the stress histories of the critical points of the wheel.Based on these analyses it is then possible to estimate the fatigue damage and to design the wheel for the proof tests using a critical Miner index obtained from data on previous wheel and specimen fatigue test spectra.Such a procedure permits one to refine the design procedure to a life evaluation of the prototypes,which will be subjected to‘‘Eurocycle’’under the biaxial test facility,very close to the experimental evidence[10,11].It is necessary to remark that both these approaches(direct experiments or FEM calculations)are not fully able to account for the process variability and the influence of defects(of any origin:metallurgical, technological,etc...)on fatigue strength of wheels during the design procedure[12].From this point ofresearch.view,some in-service premature failures(Fig.1)of a34.8kN wheel have prompted the present Array Fig.1.Introduction to the wheel problem:(a)solid model of the wheel;(b)particulars of the premature failures.First of all,the fatigue behaviour of two lots of material(thefirst coming from the batch of premature failures and the other from a standard batch)has been investigated in terms of S–N and crack propagation curves with the aim to verify the homogeneity of the material properties between the batches.The typical defects present in different lots of the component have then been evaluated.Since fractographic observa-tion has shown that the fractures could be ascribed to the presence of defects due to the hole punching procedure of the ventilation hole,the research addressed the analysis of the acceptability of these defects. The material data have eventually allowed us to define of criteria to assess defect acceptability.2.Investigation of the causes of premature service failuresThe wheels under investigation have a nominal capacity of34.8kN with a rim diameter of57.15mm. Wheels are produced in a Fe430D steel whose mechanical properties are:ultimate tensile strength450 MPa,yield stress320MPa and rotating bending(R=À1)fatigue limit225MPa[11].2.1.Fatigue experimentsFatigue tests have been carried out on two different lots of wheels in order to investigate the presence of significant differences in fatigue properties.To this aim,fatigue specimens are similar to the‘‘key-hole’’type and have been extracted from the attachment face of the wheels by machining(Fig.2).FEM analyseshave permitted us to determine the relation between the applied load and the maximum stress at the notch root[13].Two series of specimens(one extracted from the batch of wheels which failed in service and the other from a standard production batch)have been subjected to fatigue tests(stress ratio R=0.1)in order to determine the S–N diagrams of the two wheel batches.The fatigue limits of the two specimen series have been investigated using‘‘Short Stair-case’’sequences.Thefinite life region has been investigated using equally spaced stress levels between280and320MPa,which corresponds to the monotonic yield strength. Fatigue tests have been carried out on a servo-hydraulic testing machine at a frequency of30Hz.The specimens have been gripped by universal joints to avoid any secondary bending.The results of the fatigue tests are shown in Fig.3in terms of the maximum stress applied to the speci-men.The tests have substantially shown that the fatigue behaviour of the two lots is very similar and that the fatigue limit,at R=0.1,isÁS R=0.1=264MPa(Fig.3).The fatigue life scatter can be ascribed to the presence of non-metallic Ca inclusions with dimensions up to100m m[13].2.2.Crack growth testsIn order to evaluate the crack propagation curve of the Fe430D steel and to check the material homo-geneity of the two wheel batches,crack growth tests have been performed using two small CT specimens per wheel batch.Specimens,whose dimensions were50Â50Â10mm(precrack25mm),have been machined from the wheels.Test were carried out at constantÁP with R=0.1at an operating frequency of 20Hz.Crack propagation was measured on both the specimen faces using plastic replicas that were even-tually observed under an optical microscope at100Âmagnification.Growth rate was then obtained withthe secant method [14].During propagation tests,closure measurements have been carried out using two different methods of ‘‘global compliance’’:by an extensometer at the notch edge and by a ‘‘BackFace’’strain gauge.A further test series has been carried out on another CT specimen,coming from the standard batch,in order to determine the ÁK th value using the ÁK -decreasing technique [14].The relevant results obtained from the tests are shown in Fig.4:the results show that also from the propagation point of view there is no differences between the two different lots of material.Closure mea-surements gave an average ÁK eff/ÁK of 0.64for ÁK <15MPa p m.The crack propagation threshold at R =0.1was found to be ÁK th =6.9MPa p m.2.3.Defect analysisIn order to analyse the causes of the premature in-service failures,some fractographic observations have been firstly carried out.These observations have evidenced the presence of tearings,presumably due to hole punching,at the fracture origin.To measure the entity of the found defects,polished sections have been extracted from the two different lots of wheels already examined.The polished sections have been extracted in a radial direction with respect to the ventilation hole,in the same position where the failures took place (see Fig.5a ).Particularly,polished sections revealed the presence of narrow defects (Fig.5b )whose typical sections are shown in Fig.5c and d .Because of the elongated shape,defect size was measured in terms of depth.The defect data have then been analysed using Weibull distributions (Fig.6):the result is that the data coming from the lot of the premature failures are described by a defect population different from that of the standard production wheels.The characteristic value of the defect depth is about 60m m for thestandardFig.4.Propagation properties of the material:crack propagation curves of the analysed lots.S.Beretta et al./Engineering Failure Analysis 10(2003)45–5749production wheels and about 200m m for the wheels of the batch with premature failures.The same ana-lysis was carried out on the wheels that suffered premature in-service failures.In this case the average dimension of defects at ventilation holes (excluding fractured holes)was about 600m m.3.Defect size and fatigue strength of Fe430D steelThe first step for the defect acceptability analysis has been the establishment of a relationship between defect size and fatigue strength for the Fe430D steel at R =À1,which is the typical stress ratio of stress spectrum at wheel ventilation holes [10].This has been done by analysing material data and by carrying out fatigue tests on micronotched specimens.The analysis of the effect of defects on fatigue strength can be done by treating defects as small cracks:the fatigue limit is then the threshold cyclic stress for the non-propagation of these small cracks [15].Considering irregular defects,the maximum stress intensity factor at the tip can be calculated with Mur-akami’s equation [15]:ÁK I ¼0:65ÁÁ Áffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Áffiffiffiffiffiffiffiffiffiarea p q ð1Þwhere p area (root square of the defect section in a direction perpendicular to the applied stress)is the geometric parameter defined byMurakami.Fig.5.Typical defect aspect (a and b)due to punching operations as observed (c and d)by an optical microscope from lapped sections.50S.Beretta et al./Engineering Failure Analysis 10(2003)45–57By using steel data obtained at R =0.1,namely the fatigue limit and the ÁK th ,together with Eq.(1)it is possible to depict the so-called ‘‘Kitagawa–Takahashi diagram’’[15]and to obtain the ‘‘El-Had-dad parameter’’[16](or alternatively ‘‘fictitious crack size’’)p area o equal to 450m m (Fig.7).Since the shape of the Kitagawa diagram does not change with stress ratio [17]and the p area o parameter is expected to remain the same also at a stress ratio R =À1,the relationship between fatigue strength at R =À1and crack size (expressed in terms of p area)could be described by the El-Haddad equation[16]:Á w ¼Á wo Áffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiarea o p ffiffiffiffiffiffiffiffiffiffiffiarea o p þffiffiffiffiffiffiffiffiffiareap s p area <10Áp area o ð2Þwhere Á wo (fatigue limit on smooth specimens at R =À1)is equal to 225MPa [11].Eq.(2)is valid only in the short crack region,that is p area <10.p area o [16].3.1.Experiments on micro-notched specimensIn order to verify the validity of Eq.(2)we decided to carry out fatigue test series on micro-notched specimens.Particularly,two series of ‘‘dog-bone’’specimens were micro-notched by means of a pair of micro-drills equivalent to defects with p area of 143and 443m m (Fig.8).Successively,two series of fatigue limit tests with short ‘‘stair-case’’sequences were carried out on a resonant bending machine.Fatigue tests were interrupted if a specimen had survived 107cycles.Fig.9shows a details of experimental tests:in particular can be seen a non-propagating crack at the tip of a run-out specimen.The presence of these non-propagating cracks confirms that micro-notches can be treated as small cracks.The fatigue limit of 143m m and 443m m defects were respectively 392and 348.8MPa.These results are in good accordance with the predictions of Eq.(2)(Fig.7),that was eventually adopted for analysing the detrimental influence of defects on the service life of wheels.4.Effect of defects on wheel lifeThe final phase of the research consisted of estimating the effect of defects on the life of a wheel subjected to the ‘‘Eurocycle’’load spectrum.The analysis was carried out in terms of fatigue damage calculation and crack propagation.4.1.Fatigue damageFirst of all,how can the defects measured with the lapped sections be drawn in the determined Kitagawa diagram?As we said earlier,for the particular shape of these defects,it is more opportune to consider,as a characteristic parameter,the depth than the p area.But to apply Eqs.(1)and (2)it is necessary to find out a good way to characterize defects geometry also by the second parameter.Murakami [15]suggested that for narrow and lengthy defects the best characterization in terms of p area is to assume,for the defect itself,a rectangular shape presenting dimensions ‘‘a ’’and 10a (Fig.10),where ‘‘a ’’is the depth of the given defect.Proceeding in this way,the standard production batch (characteristic depth equal to 60m m)presents p area=189m m corresponding,using the obtained Kitagawa Diagram,to a fatigue limit (R =À1)of 198MPa,while the batch of premature failures (characteristic depth equal to 200m m)presents p area=632m m corresponding to a fatigue limit (always R =À1)of 152MPa.The edge of the ventilation hole is subjected,during the ‘‘Eurocycle’’test on the wheel,to a stress time history with a stress ratio of approximately À1[11].In Fig.11a the stress history measured by a strain gage glued near the edge of the ventilation hole is reported.Considering that fatigue design of wheels is based on fatigue damage whose critical value has been obtained by wheel biaxial fatigue tests,it is then possible to evaluate approximately the effect of defects in terms of increment of damage due to the variation of the fatigue limit (Fig.10b ).4.2.Propagation of defectsThe analysis of defect propagation has been carried out by means of dedicated software:‘‘NASGRO’’developed by different International Research Institutes [18].NASGRO has been chosen because,until now,it has shown the best correlations of experimental results and because it includes a powerful version of the ‘‘Yield Strip’’model proposed by Newman [19].The experimental tests of crack propagation have been executed at R =0.1,while the ‘‘Eurocycle’’spec-trum is mainly at R =À1.This problem is solved by NASGRO by the application,to describe the propa-gation law,of the followingexpression:Fig.8.Geometry of the micronotched ‘‘dog-bone’’specimens used to validate the obtained Kitagawa Diagram and particulars of the introduced artificial defects.S.Beretta et al./Engineering Failure Analysis 10(2003)45–5753d a d N ¼C 1Àf 1ÀR ÁK n 1ÀÁK th ÁK p1ÀK max K crit qð3Þwhere the ‘‘f ’’parameter represents a measure of the closure effect on propagation and it is used to gen-eralise the crack propagation curve to different R values.‘‘f ’’depends on the constraint factor ‘‘ ’’that currently is well defined for aluminium alloys,but not yet for steels [19,20],even if its value,for the Fe430D,has been recently [21]found to be equal to 2.5.The difficulties of the analysis of the system wheel by means of NASGRO come principally from two considerations:i)the system geometry is too complicated;ii)the ventilation hole during use is subjected to a combination of axial and bending stresses [4].Recent research [22]has shown the possibility of repre-senting the ventilation hole by a ‘‘companion specimen’’.Particularly,it has been seen that a holed plate,subjected at the edge of the hole to the strain history of the ventilation hole,presents a durability similarto Fig.9.Details of experimental results on micronotched specimens:(a)crack surface for a p area=443m m micronotch (broken during the test);(b)particular of the same starting defect;(c)starting micronotch for a p area=143m m (run-out);(d)particular of the non-propagating crack for the samespecimen.Fig.10.Assumption of the characteristic parameter p area for the particular morphology of the defects found from the lapped sections.54S.Beretta et al./Engineering Failure Analysis 10(2003)45–57Fig.11.Effect of defects on wheel life:(a)stress history measured by a strain gauge glued near the edge of the ventilation hole;(b)evaluation in terms of increment of damage due to the variation of the fatigue limit;(c)assumption of the geometry of the system for the defect propagation approach.S.Beretta et al./Engineering Failure Analysis 10(2003)45–5755that of the wheels.On the basis of these results,the analysis has been carried out modelling holed plates,subjected to the Eurocycle load history measured at the ventilation hole,with different dimensions of starting defects (Fig.11c ).4.3.Life predictions and comparison with experimentsFig.12shows the results,in terms of normalised life and depth of the starting defect,of the damage calculation and of the defect propagation.From this figure,it is possible to see that the two methods yield quite different results.In order to define which of the two is the best at describing the behaviour of the batch of the premature failures,it is necessary to know that the in-service life of this batch (characterised by an average maximum defect of 600–700m m)has been about one tenth of the design life (the ‘‘In-service’’dash in Fig.12).Assuming ‘‘1’’the life of the wheels of standard production (characterised by a maximum defect of 100m m),it is evident that the NASGRO analysis is very near to the one tenth of life shown by the batch of premature failures.However,the damage calculation leads to a conservative design,suggesting a life,for the maximum defects,of about one thousandth.As a further comparison,some wheels of the batch of premature failures have been tested on the biaxial machine.These wheels have shown a defects distribution at the ventilation hole characterised by a max-imum defect of about 150–200m m and a life half of the design one.The ‘‘Biaxial’’dash in Fig.12shows the region covered by the wheels which failed during biaxial tests and in this case the NASGRO analysis seems to be nearer to experimentalevidences.Fig.12.Obtained results in terms of damage calculation and defect propagation.56S.Beretta et al./Engineering Failure Analysis 10(2003)45–57S.Beretta et al./Engineering Failure Analysis10(2003)45–5757 5.ConclusionsThe analysis has been presented of a component subjected to random fatigue in the presence of defects coming from the production procedure.First of all has been characterised the fatigue and crack propaga-tion behaviour of the material,then typical defects have been inserted and their influence on the fatigue limit,strength and crack propagation speed has been investigated,thus defining the limit of acceptability of the defects and the residual life of the component subjected to random fatigue.References[1]ISO3006Road vehicles—passenger car wheels—fatigue testing methods,vol.2.Switzerland:1976.[2]Richard C,Rice M.SAE fatigue design book.2nd ed.SAE Publication;1988.[3]Wright DH.Testing automotive materials and components.SAE Publication;1993.[4]Grubisic V,Fischer G.Procedure for optimal lightweight design and durability testin of wheels.Int J Vehicle Des.1984;6.[5]Grubisic V,Fischer G.Automotive wheels,methods and procedure optimal design and testing.SAE Technical Paper1983;830135.[6]Grubisic V,Fischer G,Heinritz M.Design optimisation of forged wheel hubs for commercial vehicles.SAE Technical Paper1984;841706.[7]Landgraf RW,Thangjitham S,Ridder RL.Automotive wheel assembly:a case study in durability design.Case studies for fatigueeducation ASTM STP12501994.[8]Kocabicak U,Firat M.Numerical analysis of wheel cornering fatigue tests.Eng.Fail.Anal.2001;8.[9]Finzi A,Piazza L.Fatigue life prediction in wheels design.Marc Users Scientific Technical Conference,Genova,1999.[10]Carboni M,Beretta S,Clerici P,Finzi A,Piazza L.A fatigue design procedure for truck wheels.ATA2000;53(9/10).[11]Carboni M.Analisi dell’affaticamento di ruote per autocarri.MSc thesis,Politecnico di Milano1997.[12]McGrath PJ,Hattingh DG,James MN,Els-Botes A.Effects of forming process on fatigue performance of wheel centre discs.Proceedings ECF13,San Sebastia n,2000.[13]Beretta S,Carboni M,Clerici P.Caratterizzazione a fatica di diverse forniture di lamiere per la costruzione di ruote.Report ofresearch contract between Politecnico di Milano and Gianetti Ruote no.8/99,Milano,2000.[14]ASTM E647-95a.Standard test method for measurement of fatigue crack growth rates.Philadelphia:ASTM;1994.[15]Murakami Y,Endo M.Effect of defects,inclusions and inhomogeneities on fatigue strength.Int.J.Fatigue1994;16.[16]El-Haddad MH,Smith KN,Topper TH.Fatigue crack propagation of short cracks.J Eng Mater Struct ASME Trans1979;101.[17]Hertzberg RW.Deformation and fractures mechanics of engineering materials.New York:J.Wiley&Sons;1995.[18]AAVV NASGRO.Developed by different research institutes:NASA,ESA,NLR and Lockheed;2000.[19]Newman Jr JC.A crack closure model for predicting fatigue crack growth under aircraft spectrum loading ASTM STP748.Philadelphia:ASTM;1981.[20]Skorupa M.Empirical trends and prediction models for fatigue crack growth under variable amplitude loading.ECN-R-96–0071996.The Netherlands:Petten:Netherlands Energy Research Foundation ECN.[21]Beretta S,Carboni M,Machniewicz T,Skorupa M.Correlation between experiments and Strip Yield results on fatigue crackgrowth in a structural steel.Proceedings ECF14,Krakow,2002.[22]Cantini S,Cerini G.Danneggiamento a fatica di ruote per autocarro.MSc thesis,Politecnico di Milano,1998.。

《目的论视角下新车发布会口译策略研究》篇一一、引言随着全球汽车市场的蓬勃发展，新车发布会的举办已成为各大汽车品牌展示其最新产品、技术及品牌理念的重要平台。

在这一过程中，口译作为沟通的桥梁，其重要性不言而喻。

本文以目的论为视角，对新车发布会口译策略进行研究，旨在提高口译的准确性和效率，为汽车行业的新车发布会口译实践提供理论支持。

二、目的论视角下的口译特点目的论（Skopos Theory）是翻译学中的重要理论，认为翻译是一项具有明确目的性的交际活动。

在新车发布会的口译中，其特点主要表现在以下几个方面：1. 传达信息的准确性：口译需准确传达发布会上涉及的新车性能、技术特点、品牌理念等关键信息。

2. 语言的即时性：口译需在短时间内完成信息的转换，确保双方沟通的即时性。

3. 文化背景的适应性：口译需考虑不同文化背景下的语言差异，以适应不同国家消费者的需求。

三、新车发布会口译策略研究基于目的论视角，本文提出以下新车发布会口译策略：1. 预译前准备：在发布会前，口译员需充分了解新车的性能、技术特点、品牌背景等关键信息，以及发布会的主旨和目标。

此外，还需了解目标国家的文化背景和语言习惯，以便更好地进行跨文化交际。

2. 精确理解原语：在口译过程中，要确保准确理解原语的含义，避免因误解或歧义导致信息传递失误。

为此，口译员需具备扎实的语言基础和丰富的专业知识。

3. 即时翻译与二次翻译相结合：在确保信息准确性的前提下，口译员可采用即时翻译与二次翻译相结合的方式。

对于关键信息，可进行即时翻译，以确保信息的即时性；对于非关键信息或需要进一步解释的内容，可进行二次翻译或适当调整表达方式。

4. 适应文化差异的翻译：针对不同国家的文化差异，口译员需灵活运用翻译策略，如归化、异化等，以适应目标国家的文化背景和语言习惯。

同时，还需注意避免因直译或过度归化而导致的误解或歧义。

5. 互动与反馈：在口译过程中，口译员需与发言人保持良好互动，及时获取反馈信息。

Off-road-capable truck Ford F- Raptor review The Ford F-150 Raptor is a high-performance, off-road-capable truck that has been designed to tackle any terrain with ease. This truck is not only rugged and tough, but it is also equipped with advanced technology and features that make it a joy to drive. In this review, we will take a closer look at the Ford F-150 Raptor and examine its features, performance, and overall value.First and foremost, the Ford F-150 Raptor is a beast of a truck. It boasts a powerful 3.5-liter V6 engine that delivers 450 horsepower and 510 lb-ft of torque. This engine is paired with a 10-speed automatic transmission that provides smooth and responsive shifts. The Raptor also features a four-wheel-drive system that allows it to conquer any terrain, whether it be mud, sand, or rocks. The truck's suspension has been specially designed to handle rough terrain, with Fox Racing shocks that offer 13 inches of travel in the front and 14 inches in the rear.One of the standout features of the Ford F-150 Raptor is its off-road capability. This truck has been designed to handle even the toughest terrain, with features like skid plates, tow hooks, and a locking rear differential. The Raptor also comes equipped with a Terrain Management System that allows drivers to select different driving modes depending on the terrain they are traversing. The system offers six different modes, including Normal, Sport, Weather, Mud/Sand, Baja, and Rock Crawl. Each mode adjusts the truck's throttle response, transmission shift points, and traction control to optimize performance in different conditions.But the Ford F-150 Raptor is not just a rugged off-road truck. It also offers a comfortable and well-appointed interior that is loaded with features. The cabin is spacious and comfortable, with plenty of room for passengers and cargo. The seats are supportive and offer a good driving position, while the dashboard is well laid out and easy to use. The Raptor also comes with a host of advanced technology features, including a touchscreen infotainment system, Apple CarPlay and Android Auto compatibility, and a premium sound system.In terms of safety, the Ford F-150 Raptor is equipped with a range of advanced features that help to keep drivers and passengers safe on the road. These include adaptive cruise control, lane departure warning, blind spot monitoring, and automatic emergency braking. The truck also features a high-strength steel frame and a range of airbags to provide added protection in the event of a collision.Overall, the Ford F-150 Raptor is an impressive truck that offers a winning combination of performance, capability, and comfort. It is a great choice for anyone who needs a rugged off-road vehicle that can handle any terrain, while also offering a comfortable and well-appointed interior. The Raptor is not cheap, with a starting price of around $54,000, but it is worth the investment for anyone who needs a truck that can tackle tough conditions with ease. If you are in the market for an off-road-capable truck, the Ford F-150 Raptor is definitely worth considering.。

Customer Supplier ProjectDocument Public EES KISSsoft GmbH Weid 10, P.O. Box 121 6313 Menzingen Switzerland www.EES-KISSsoft.ch Title: -No.: -Date: 16.4.08Manager: Hanspeter Dinner@: h.dinner@EES-KISSsoft.chVersion: 0 Autor: HD Date: 16.4.08 Approved: HD Date: 16.4.08 EES KISSsoft GmbH ++41 41 755 09 54 (Phone)P.O. Box 121 ++41 41 755 09 48 (Fax)Weid 10 ++41 79 821 25 41 (Mobile)6313 Menzingen h.dinner@EES-KISSsoft.chSwitzerland www.EES-KISSsoft.chA gear set in a light commercial vehicle transmission (nominal power of only 35kW) should be analysed with respect to resulting lifetime using a load spectrum. For a test of the gear set, it has to be determined whether all steps in the load spectrum need to be considered or whether certain steps in the load spectrum could be neglected. In the later case, this would mean that the time needed for testing the gear could be reduced. If it is found that the gear set has a lifetime higher than the required lifetime, it is of interest to find out the maximum permissible torque for which the lifetime would just be met. This would then allow the gear set to be used also in another transmission, connected to a more powerful engine. 1 Gear data Given a gear set as follows: z1=17, z2=33, mn=3.00mm, beta=14deg RH, alpha=17.5deg, facewidth=20mm, ref profile1.40/0.30/1.10, a=78mm, x1=0.30, n1=1300RpM, Tnom=275NmLoad spectrum is given as follows:Speed of gear 1 Time Torque of gear 1650 10h 125% of nominal torque 975 20h 80% of nominal torque 1300 30h 100% of nominal torque 1300 30h 75% of nominal torque 1625 10h50% of nominal torque Because we use a load spectrum, set KA=1.00Required safety factorsSH=0.90, SF=1.1G e a r l i f e t i m e c a l c u l a t i o n w i t h l o a d s p e c t r u m2 Questions1)What is the resulting lifetime?2)What is determining the lifetime of the gear set (flank or root? gear 1 or gear 2?)3)Which load step contributes most to the damage of the gear4)If the gear set has to operate for only 1000h, what is the maximum nominal torque thatcan be transmitted instead of the 275Nm above?3 Solution3.1 Basic gear data input, definition of load spectrumStart with an empty file for all other settings not mentioned above.Enter basic gear data as follows:Enter the reference profile as follows:Go to database tool and open a new load spectrum definitionEnter the load spectrum as follows, then save the load spectrum:to select the load spectrum as shown below:The fact that a load spectrum is used can now be seen by the symbol as shown below:Now, define the required safety factors in the module specific settings:3.2 Answer to question 1)Finally, you can calculate the resulting life time by pressing next to the required lifetimeto find the resulting lifetime of 3223h3.3 Answer to question 2)We can now, based on the above lifetime, calculate the safety factors. Of course, the lowestsafety factor is now as specified in the module specific settings, required safety factors:In this example, the flank safety factor of gear 1 is equal to the required safety factor of 0.90.All other safety factors are higher than the required safety factors. This means the that flank ofgear 1 is the determining the lifetime of the gear set.3.4 Answer to question 3)Check in the report “Lifetime”There, you will find the partial damages for each load step in the load spectrum:The first step in the load spectrum contributes most, the third step is also important. The other steps contribute nothing to the total damage! This means that for example to test the gears, these load levels need not be tested at all!3.5 Answer to question 4)If the gear set has to run for only 1000h, it obviously can take more torque that the 275Nm specified above. You can calculate the nominal torque that can be transmitted (still considering the load spectrum) by entering the 1000h as a lifetime and then pressing the button next to the field for torque. Then, the nominal torque transmittable (considering the load spectrum), for a required lifetime of 1000h and for the required safety factors, will be returned, here with 311Nm:This means that the gear set could also be used in a transmission rated for slightly higher power rating than 40kW.。

2018年第6期 AUTOMOBILE APPLIED TECHNOLOGY 汽辛仿真与‘10. 16638/ki. 1671-7988. 2018. 06. Oil某铝制乘用车白车身疲劳寿命计算夏德伟，刘丽霞，徐志强，齐飞(辽宁忠旺集团有限公司北京技术与发展中心，北京100020)摘要：对该款铝制乘用车白车身利用Hypermesh建立了其有限元模型，在此基础上结合六分力轮测得的短波路路 况下的载荷谱数据，利用N code对该车进行了疲劳寿命计算。

在计算过程中，相比于通用的计算步骤，文中通过 建立简化的悬架模型，提出了一个简化方法。

最后，根据计算结果指出在该类型乘用车设计中，针对疲劳需要重点 关注的位置。

关键词：乘用车；疲劳计算中图分类号：U467文献标识码：B文章编号：1671-7988(2018)06-29-04The fatigue life calculation of the body-in-white of an aluminum passenger carXia Dewei, Liu Lixia, Xu Zhiqiang, Qi Fei(Liaoning Zhongwang Group Co.,Ltd Beijing Technology&Development Center,Beijing100020)Abstract: The finite element model of the white body of aluminum passenger car was established by using Hypermesh.Based on this,the load spectrum data of the short-wave road measured by six-force wheel was used to calculate the fatigue life of the car with Ncode.In the calculation process,compared with the common calculation steps,this paper presents a simplified method by establishing a simplified suspension model.Finally,according to the results of t he calculation,we point out the positions that need more attention for fatigue calculation in this type of passenger car design.Keywords: passenger car; fatigue calculationCLC NO.: U467 Document Code: B Article ID: 1671-7988(2018)06-29-04引言更换更轻质的白车身材料是新能源车发展的一种重要手 段，铝合金因其轻质、可塑性强、回收性好等优良的性能被 广泛使用。

Self-driving robotaxis are taking off in China在中国，自动驾驶出租车有新突破The world has been inching toward fully autonomous cars for years. In China, one company just got even closer to making it a reality.多年来，世界一直在向全自动驾驶汽车缓慢前进。

在中国，有一家公司离实现这一目标更近了一步。

On Thursday, AutoX, an Alibaba (BABA)-backed startup, announced it had rolled out fully driverless robotaxis on public roads in Shenzhen. The company said it had become the first player in China to do so, notching an important industry milestone.周四，阿里巴巴(Alibaba)支持的初创公司AutoX宣布，它已在深圳的公共道路上推出了全自动无人驾驶出租车。

该公司表示，它已成为中国首家这样做的公司，创下了一个重要的行业里程碑。

Previously, companies operating autonomous shuttles on public roads in the country were constrained by strict caveats, which required them to have a safety driver inside.此前，在中国的公共道路上运营无人驾驶汽车的公司受到了严格的限制，要求它们必须有一名司机在车内以保证安全。

This program is different. In Shenzhen, AutoX has completely removed the backup driver or any remote operators for its local fleet of 25 cars, it said. The government isn't restricting where in the city AutoX operates, though the company said they are focusing on the downtown area.不过这个项目与以往不同。

Chapter9Load Spectra9.1Introduction9.2Different types of loads on a structure in service9.3Description of load histories9.4Determination of load spectra9.4.1The qualitative approach9.4.2The quantitative approach9.5Load spectra and service-simulation fatigue tests9.6Major topics of the present chapterReferences9.1IntroductionThe fatigue loads on a structure in service are generally referred to as the load spectrum.The description of load spectra and methods to obtain load spectra are discussed in the present chapter.A survey of various aspects of fatigue of structures was presented as aflow diagram in introductory chapter (Chapter1,Figure1.2).A reduced diagram is presented here in Figure9.1 to illustrate the significance of load spectra for fatigue design analysis of a structure.Without information on the anticipated load spectrum,the analysis of the fatigue performance of a structure is impossible.Furthermore, verification tests to support the analysis are often necessary for economic or safety reasons.The load spectrum must be consulted for planning such validation tests.Sometimes the load spectrum is changed after a number of years by a modified use of the structure,which is different from the initial expectations. The load spectrum must then be considered again.Fatigue load spectra should also be reviewed if fatigue failures occur in service.The load spectrum of a structure should give information about the load-time history,which is the variation of the load as a function of time,259260Chapter9Fig.9.1Load spectra as input for the fatigue performance of a structure.P(t).The present knowledge of the fatigue phenomenon as it occurs in technical materials(see Chapter2)clearly indicates that the significant points of a P(t)load history are the maxima and minima,P max and P min,see Figure9.2.At these load levels,reversal of cyclic slip occurs in the material, either at the material surface or in the crack tip plastic zone.These reversals are decisive for the fatigue damage accumulation in a structure.Several practical questions arise:1.Is it necessary to know the full sequence of all turning points of the loadhistory?2.Are all similar structures in service subjected to the same load history,or in other words,how unique is a certain load history for a structure?3.Are small cycles of interest,or is the fatigue damage contribution ofthese cycles negligible?4.Is it important whether loads are applied at a high or a low loading rate(wave shape)?5.Long periods at zero load(rest periods,structure not in use)or longperiods at a significant load level(average load in service if dynamicFig.9.2Characteristic occurrences of a load-time history P(t).Load Spectra261 loads do not occur during that period),are these periods important for the fatigue damage accumulation?The last two questions are pointing to problems of time dependent phenomena,e.g.corrosion,creep,or diffusion processes in the material which might affect the fatigue process.In the literature,these problems are frequently discussed as effects of the load frequency(cycles per minute)and the cyclic wave shape,see Section2.5.7(e.g.Figure2.30).Before the above problems can be discussed,an essential question is:Is the load history known which a structure will experience in service,or can it be estimated?Even more,how can the load history be described,and can it be measured?In the present chapter,load histories of different types of structure are discussedfirst(Section9.2),which reveals essential differences between the statistical nature of load histories.Methods for the description of a load history and statistical compilations of load spectrum data are presented in Section9.3.The determination of load spectra is discussed in Section9.4. Service-simulation load histories are addressed in Section9.5.The major aspects of the present chapter are summarized in Section9.6.9.2Different types of loads on a structure in serviceWhich loads occur on a structure in service?Answers to this question depend on the type of structure and how the structure is used.First some exemplary cases are discussed in a qualitative way to illustrate the variety of problem settings.Different types of loads can then be defined.1.Pressure vesselMany pressure vessels used in the industry and other production facilities are used in a simple way.The pressure is built up to a specific working level, maintained at that level,and then released to zero.If such a pressure cycle occurs aboutfive times a day,the load spectrum contains approximately 40000cycles in a life period of20years.Fatigue problems could arise.A number of questions can easily be formulated.Is the pressure always the same.Are the number of pressurization cycles user dependent?Is the duration of a pressure cycle important?Is the gas or liquid inside the pressure vessel aggressive?Anyhow,a number of questions to be considered if fatigue critical notches,usually inlets and joints,occur in the pressure vessel.262Chapter9Fig.9.3(a)Axle loads on a railway bridge in10kN intervals.Fig.9.3(b)Load spectrum of axle load level exceedings for data in Figure9.3a.Load Spectra263 2.BridgeThe variety of bridges is large.A simple steel railway bridge is considered here.It is loaded in bending by each passage of a train.The load spectrum in a specific case of the Dutch Railways was depending on the number of train axles passing the bridge each day and the weight applied by the axles to the bridge.The load spectrum was predicted by considering the variety of trains that would use the bridge[1].The prediction is shown as a bar chart(histogram)in Figure9.3a,which gives the number of axle loads in intervals of10kN.The load spectrum was checked later,see the measured data in Figure9.3a.It turns out that the scatter of the axle loads was larger than predicted.The same data are compared in Figure9.3b by plotting the numbers of load level exceedings,i.e.the number of times that a specific load level is exceeded in24hours.Low load levels are exceeded many times,while high load levels occur less frequently.The results in Figure9.3b show a reasonable agreement between the measured data and predictions. Some agreement should be present if the utilization of a structure is well defined and known in advance.This applies to the example of Figure9.3 of trains used in accordance with a specified time table.However,for other moving vehicles such a prediction can be more difficult.mp postModern aluminium street light posts are predominantly loaded by wind forces coming from different directions and varying intensities.For a lamp post as shown in Figure9.4,it leads to bending and torsion load cycles with maxima stress levels near the base of the ually,an opening is made in the pillar close to the base for making electrical connections.Although a cover is closing the opening,stress concentrations are present in that area and fatigue cracks have occurred.A correlation between the function of the street light and load spectrum does not exist.The load spectrum depends on the weather conditions,which should be described in statistical terms. Weather conditions depend on the geographical location.These conditions can be more severe along a sea cost where humidity and salt concentration can also adversely affect the fatigue behavior.Another obvious aspect involved is the dynamic response of the pillar on the windfluctuations.It cannot be expected that the wind load spectrum on the street light and the stress spectrum at the fatigue critical location are linearly related.Dynamic response calculation techniques are well developed,but it may be advisable to measure the stress spectrum on a representative location of the structure.264Chapter9Fig.9.4Lamp post in Pijnacker(the Netherlands).4.Motor-car The load spectrum on a car can be very complex.It obviously depends on two major inputs:(i)the driver,and(ii)the condition of the roads to be used.A single load spectrum applying to all cars of the same type is impossible.Moreover,an average load spectrum applicable to most cars is meaningless.Fatigue failures are associated with severe driving and poor roads which applies to a small percentage of cars.However,a small percentage is still a large number of cars.It implies that a relatively severe load spectrum must be considered for the fatigue performance.The fatigue problem of motor-cars is also associated with the complexity of the structure with several components which can be fatigue critical.In addition,loads on a car act on the wheels in three different directions(x,y,z)with different frequencies and phase angles.Inertial forces on theflexible structure are also complex.All these conditions imply that a load spectrum cannot easily be defined.It is for these reasons that the motor-car industry is relying on experience,measurements and experiments.Load Spectra265Fig.9.5Slow load variation of the wing bending moment during a singleflight,with fast superimposed turbulence loads and ground loads.5.Wing of transport aircraftThe aerodynamic lift on the wing of an aircraft is carrying the aircraft weight.The distributed lift on the wing exerts a bending moment with a maximum at the root of the wing.On the ground,the lift is zero and the aircraft is supported by the undercarriage.Eachflight thus implies a cycle of the bending moment on the wing,see the heavy line in Figure9.5.Bending of the wing introduces tension stresses in the lower wing skin structure and compression in the upper wing skin structure.The tension skin is well recognized as a fatigue critical part of the wing.The once perflight cycle on the tension skin is a very slow cycle with an almost quasi-static variation of the load.However,the wing is also subjected to much faster load cycles, see Figure9.5.Inflight,these cycles occur in turbulent air(gusty weather) predominantly during the climb and descent period at low altitudes.The turbulence at cruising altitude is usually very limited,and load variations are small(a small change due to fuel consumption).Also maneuver loads can be significant,depending on the type of aircraft.During take-off and landing, high-frequency cycles are introduced by runway roughness,touch-down on the ground,and spin up of the wheels.In addition to wing bending,torsional moments are also exerted on the wing.The loading picture is fairly complex, which is only schematically illustrated by Figure9.5.The above examples illustrate a variety of different loads.Two major types of characteristic groups of loads must be recognized:266Chapter91.Deterministic loads.2.Stochastic loads.A load is considered to be deterministic if it can be defined as a specific occurrence,from which it is known that it will occur with a magnitude that can be estimated.Deterministic loads should follow from the planned utilization of a structure.The load cycle of a pressure vessel is fully deterministic.Manoeuvers of ships and transport aircraft are predominantly deterministic.Many loads on a motor-car,a bridge,or a crane are predictable and have a deterministic character.However,depending on how such structures are used,loads cannot always be considered to be deterministic. Obviously,joyriding a car can lead to unpredictable loads.Stochastic loads have an essentially statistical nature.They cannot be predicted to occur with a certain magnitude at a given moment.Good examples are wind forces on a street light pillar,forces exerted by waves of the sea on ships and drilling platforms,turbulence on an aircraft,and loads on motor-cars due to poor road conditions.A description of stochastic loads can only be done in a statistical way,i.e.in terms of the probability that something will happen.Stochastic loads are also referred to as random loads. In many cases,the statistical properties of stochastic loads are not very well known,although long-term measurements have provided useful data,e.g.for sea waves and wind forces.Stochastic and deterministic loads can also occur simultaneously on the same structure.An example is shown in Figure9.5with random turbulence and runway roughness loads superimposed on the deterministic once-per-flight load cycle.The problem is how to combine these loads for fatigue evaluations.The superimposed loads increase the severity of the flight because the maximum load occurring during aflight becomes more severe,and the same is true for the minimum load.This aspect will be reconsidered in the following section on describing load histories.Another aspect of random loads is that the intensity is not always the same.The statistical properties are not necessarily constant.This is easily understood by considering random loads depending on the weather conditions.Stormy weather can induce severe random loads on a lamp post, but more frequently occurring milder weather conditions can also contribute to fatigue.It has led to a second differentiation between load histories: (i)Stationary load histories.(ii)Non-stationary load histories.In thefirst case,the statistical properties do not vary as a function of time, whereas in the second case,these properties can vary during the serviceLoad Spectra267Fig.9.6Results of counting maxima of a symmetric load time history(varying amplitude). usage of a structure.Although the terms stationary and non-stationary load histories are usually associated with stochastic loads,they can also apply to deterministic loads,e.g.by changing the use of a structure.9.3Description of load historiesLevel crossing count methodsA load-time history is defined by a sequence of maxima and minima if time-dependent phenomena are not considered:P max,1,P min,1,P max,2,P min,2, etc.Such a sequence is usually reduced to a statistical representation in order to have a useful survey of the fatigue loads.In the past,several counting techniques were developed for this purpose based on counting level crossings for a number of load levels or counting peak values above a number of load levels.The historical development(see[2])will not be followed here,but basic aspects of statistical count procedures are considered.A simple load sequence is shown in Figure9.6,a load signal with a varying amplitude.Approximately similar maxima and minima occur around a mean level,indicated as level0.In view of the symmetry around this level,it is sufficient to consider the maxima ually,load spectra are presented as numbers of peak values occurring above a load level j denoted as n exc,j.In the present case,this number is equal to the number of positive level crossings(going from a minimum to a maximum)of load level j.268Chapter 9(a)Number of peaks inintervals (b)Number of peaks exceeding level j (c)Probability of exceeding level jFig.9.7Peak counting results of the load-time history sample in Figure 9.6.Numbers are counted in Figure 9.6for levels j =0to j =4,see the numbers n exc ,j in the row to the far right of this figure.The number of peak values in an interval (n peak ,i )is then obtained as the difference between the numbers of level crossings of the two enclosing levels of the interval:n peak ,i =n exc ,j =i −1−n exc ,j =i (9.1)These numbers have been plotted in Figure 9.7a,which is a histogram of the number of peak loads in the intervals.The numbers of peak values above load level j are plotted in Figure 9.7b.A curve is drawn through these counting results.These exceeding numbers are normalized in Figure 9.7c by dividing n exc ,j by the total number of peaks (n 0)above the zero reference level (j =0),see Figure 9.7c.The values obtained are related to the probability of a peak value occurring above level j ,or:Pr (peak >level j)=n exc ,jn 0(9.2)In Figure 9.6,a short load-time history was used to illustrate the counting technique.A long load-time history with a stationary character will lead to an exceeding probability curve with a stationary character.In statistical terms,the curve becomes an estimate of the probability function of the occurrence of peak values.The bar chart of the number of loads in load level intervals is associated with the probability density function .Load spectra are usually presented as load exceeding curves as shown in Figure 9.7b.They must then be related to a certain time in service.A second example of a load history is given in Figure 9.8.The load variation is no longer symmetric in this case,but a reference level can again be determined with alternating maxima and minima above and below this level respectively.Counting can occur in load intervals for the minima and maxima separately,which leads to two load spectra for the maxima andFig.9.8A non-symmetric load-time history.Separate counts of maxima and minima.Fig.9.9An irregular load-time history.minima as presented in Figure9.8b.The number of maxima and minima must be equal(the number is27in Figure9.8a).The two spectra for the maximum and the minimum peak values in Figure9.8b give indications about the size of the positive and negative peak values,and about how often they occur.This information may be instructive for afirst evaluation of the severity of a non-symmetric load spectrum,and also for comparing load spectra of different severities.The two load-time histories in Figures9.6and9.8contain only maxima above the reference level and minima below this level.However,the situation is different for a more irregular load-time history as shown in Figure9.9. In Figures9.6and9.8,the number of positive level crossings of level j (n exc,j)was equal to the number of peak values above level j.However, in Figure9.9,level j in thefirst part of the load history is associated with one positive level crossings whereas the corresponding number of positive peaks larger than level j is equal to three.Actually,it is not difficult to see that the number of positive level crossings is equal to the number of maxima above that level reduced by the number of minima above that level.As a consequence,Equation(9.1)is no longer applicable and the numbers of peakvalues in an interval cannot be derived unambiguously from level crossingcounts.Of course,the peak values can be counted in a number of intervals and the counting results can still be presented in statistical graphs.But it may be questioned whether this is meaningful.In Figure9.9,four maxima are counted in interval i,but they are due to small load variations.These peak values cannot be associated with four loads with an amplitude P a,i.A load sequence as shown in Figure9.9is more irregular than the load sequences of Figures9.6and9.8.The irregularity of a load-time history can be defined by an irregularity factor which is the ratio of the number of peak values and the number of level crossings of the reference level:k=number of peak valuesnumber of level crossings of the reference level(9.3)The irregularity factor is obviously equal to1for constant-amplitude loading,but also for a load-time history with an amplitude modulation in Figure9.6.The factor remains equal to1in Figure9.8for the non-symmetric load-time history with alternately positive and negative load amplitudes.If the irregularity factor is equal to1,the magnitude of load excursions with respect to the reference level can be indicated by a single load parameter. However,this is not possible for an irregular load-time history for which k>1.The value of k in Figure9.9is2.5which implies a high irregularity. In such cases,an apparent need is present to consider load variations between successive peak values in terms of load ranges which is discussed later. Flat and steep load spectraIf the irregularity of a load-time history is limited(i.e.with an irregularity factor not too much above1),useful statistical data on peak loads can still be presented in the format of a one-parameter load spectrum.In such a case, the shape of the load spectrum is of interest.Two significantly different shapes are shown in Figure9.10.As mentioned before in the discussion on Figure9.7b,such spectra should be associated with certain periods in service,e.g.hours or years,or also the number of times of using the structure (missions).Load spectra should preferably cover long periods in order to be representative for the variability of the load-time history.The load level in the twofictitious spectra in Figure9.10(1000hours in service)are expressed as a percentage of the maximum load occurring in that period.Figure9.10 shows a steep load spectrum and aflat load spectrum.In a steep spectrum, the number of high loads is small and the number of low loads is large.As an illustration,high loads with a peak value exceeding80%of the maximumFig.9.10Two different types of load spectra.load of the steep spectrum in Figure9.10occur onlyfive times,whereas the number of low loads with a peak value below20%of the maximum load is 100000−3200=96800cycles which is97%of all cycles.The opposite is true for theflat load spectrum.Again in Figure9.10,the80%load level is exceeded10000times,whereas the number of small cycles below20% of the maximum load is relatively small:100000−85000=15000cycles which is15%of all rge and small cycles have special effects on fatigue as discussed in Chapters10and11,see also Section9.5.Range counting methodsFrom a fatigue damage point of view,load amplitudes are more significant than mean loads.The amplitude is half the range between a minimum load and the subsequent maximum load.Load ranges represent important characteristic values of a load-time history exerted on a structure or applied in a fatigue tests.Load ranges of a load-time history can be counted,but since ranges are defined by a minimum and a maximum,a two-parametercounting methods must be adopted.Results can then be presented in matrix(a)Matrix presentation ofbad ranges occurring betweendifferent load intervals(b)Range countings of theload-time history ofFigure9.6(c)Range countings of theload-time history ofFigure9.8Fig.9.11Two-dimensional load range countings in matrix format.format as is illustrated by Figure9.11.A range is counted in the matrix at the corresponding interval in which the range was starting(listed at the left-hand side of the matrix)and the interval in which the range is completed(listed at the top side of the matrix).As indicated in Figure9.11a,a positive load range coming from a minimum and going to a maximum,is counted in the upper right triangle of the matrix.Negative load ranges,coming from a maximum and going to a minimum,are counted in the lower left triangle of the matrix. The counting results of the load-history samples in Figures9.6and9.8are given in Figures9.11b and9.11c respectively.It should be noted that the counting results in Figure9.11b are along a diagonal of the matrix.This should be expected because for this load-history(Figure9.6)each peak load is followed by an opposite peak load of approximately the same magnitude. This is not true for the load history in Figure9.8,which leads to more distributed counting results in the matrix of Figure9.11c.The matrix is thus characteristic for the random nature of the load history.It is a two-parameter counting method,and for each range the mean value can easily be calculated because the minima and the maxima of the ranges are known.The accuracy is limited because counting of peak values does not indicate the exact location of a peak in an interval.However,smaller intervals can improve the accuracy.(a)Range countes(b)Rainflow counts(c)Rainflow countsFig.9.12Intermediate load reversal as part of a larger range.The rainflow count methodIn principle,range counting includes counting of all successive load ranges, also small load variations occurring between adjacent larger ranges.It might be thought that small load variations can be disregarded in view of a negligible contribution to fatigue damage.A fundamental counting problem arises if a small load variation occurs between larger peak values. This situation is illustrated in Figure9.12.A two-parameter range counting procedure will count the ranges AB,BC and CD,and store this information in a matrix.Now,consider the situation that the intermediate range BC would not occur.Then,the large range AD would be counted only.Fatigue damage is related to load ranges.It should be expected that the fatigue damage of the large range AD alone is larger than for the three separate ranges AB, BC and CD.This has led to the so-called rainflow counting method of Endo [5].12The intermediate small load reversal BC is counted as a separate cycle and then removed from the major load range AD.This larger range can then be counted as a separate load range,see Figure9.12b.If four successive peak values are indicated by P i,P i+1,P i+2and P i+3,the rainflow count requirement for counting and removing a small range from a larger range isP i+1<P i+3and P i+2>P i(9.4a) If the intermediate small load reversal occurs in a descending load range,see Figure9.12c,the requirement isP i+1>P i+3and P i+2<P i(9.4b)12A similar eliminating concept for small intermediate ranges was described by Anne Burns in1956[6].The Strain-Range-Counter developed by the Vickers aircraft industry was counting in accordance with this method.Fig.9.13Successive rainflow counts.In words:the peak values of the intermediate small load reversal should be inside the range of the two peak values of the larger range.Successive rainflow counts are indicated in Figure9.13.In Figure9.13afive rainflow counts can be made.After counting and removing these small cycles, Figure9.13b is obtained.In thisfigure again three rainflow counts can be made,but now of larger ranges.Removing these cycles lead to Figure9.11c in which again two still larger load reversals can be counted and removed.In thefinal residue,Figure9.11d,no further counts are possible.The ranges of the residue must be counted separately at the end of the counting procedure. The rainflow count results can be stored in a similar two-parameter matrix as discussed before(Figure9.11).The rainflow count procedure has found some support[7]by considering cyclic plasticity.A short load sequence is given in Figure9.14a,which leads to counting two intermediate load reversals by the rainflow count method,as indicated in thisfigure.The corresponding plastic behavior is schematically indicated in Figure9.14b,which could apply to local plasticity at the material surface during the initiation period,or to crack tip plasticity during crack growth.The intermediate load reversals c1and c2are causing hysteresisloops inside the major hysteresis of the major cycle between A and B.It is(a)Load history sample with(b)Correspondingtwo intermediate load reversals plastic deformation loopsFig.9.14Hysteresis loops associated with rainflow counts.thus assumed that the intermediate plasticity loops do not affect the major loop.This reasoning gives somewhat speculative support to the rainflow counting method.Some more comments on counting methodsAs discussed in the previous text,statistical information of load-time history obtained by counting of level crossings,peak values,or ranges can be presented in a graph or a matrix.A graph represents a one-parameter distribution function while a matrix corresponds to a two-parameter dis-tribution and thus gives more information.However,one significant aspect was not yet rmation about the sequence in which the counts were made is lost by these counting procedures.The matrix in Figure9.11 collects numbers of ranges between successive peak values,but information about the sequence of the ranges is not obtained.Some indirect information about sequences is retained in the rainflow count method.Each range counted by the rainflow procedure and stored in the matrix combines two peak values which may have been separated by intermediate load reversals in the original load-time history.However, these smaller ranges should have occurred between those two peak values in order to satisfy the rainflow count equation(9.4).Intermediate larger ranges did not occur because of the counting condition in the same equation.Anyway,the question must be considered whether the sequence is important。