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B339•ApplicationStainless Steel Ball and StemTechnical dataFunctional dataValve Size 1.5" [40]Fluidchilled or hot water, up to 60% glycol Fluid Temp Range (water)0...250°F [-18...120°C]Body Pressure Rating 400 psi Close-off pressure ∆ps 200 psiFlow characteristic A-port equal percentage, B-port modified for constant common port flow Servicing maintenance-free Flow Pattern 3-way Mixing/Diverting Leakage rate0% for A – AB, <2.0% for B – AB Controllable flow range 75°Cv29 Body pressure rating note 400 psiCv Flow RatingA-port: as stated in chart B-port: 70% of A – AB Cv MaterialsValve body Nickel-plated brass body Stem seal EPDM (lubricated)SeatPTFEPipe connection NPT female ends O-ring EPDM (lubricated)Ballstainless steel Suitable actuatorsNon-SpringARB(X)Safety notesWARNING: This product can expose you to lead which is known to the State of California to cause cancer and reproductive harm. For more information go to Product featuresThis valve is typically used in air handling units on heating or cooling coils, and fan coil unit heating or cooling coils. Some other common applications include Unit Ventilators, VAV box re-heat coils and bypass loops. This valve is suitable for use in a hydronic system with variable or constant flow.B339 Flow/Mounting detailsDimensionsDimensional drawingsARB, ARXA B C D E F H1H210.0" [254] 4.4" [112]7.2" [184] 5.7" [146] 1.7" [44] 2.3" [58]0.8" [20]0.6" [15]ARB N4, ARX N4A B C D E F11.4" [289] 4.4" [112]9.3" [236]7.8" [198] 3.1" [80] 3.1" [80]ARQB, ARQXA B C D E F H1H29.9" [251] 4.4" [112]7.8" [199] 6.3" [161] 2.3" [58] 2.3" [58]0.8" [20]0.8" [20]AFRB, AFRXA B C D E F10.8" [275] 4.4" [112]7.9" [201] 6.4" [162] 2.3" [58] 2.3" [58]AFRB N4, AFRX N4A B C D E F13.0" [330] 4.4" [112]11.2" [284]9.7" [246] 3.7" [95] 3.7" [95]A B C D E F10.8" [275] 4.4" [112]7.9" [201] 6.4" [162] 2.3" [58] 2.3" [58]ARQB, ARQXA B C D E F H1H29.9" [251] 4.4" [112]7.8" [199] 6.3" [161] 2.3" [58] 2.3" [58]0.8" [20]0.8" [20]AFRB N4, AFRX N4A B C D E F13.0" [330] 4.4" [112]11.2" [284]9.7" [246] 3.7" [95] 3.7" [95]AFRX24-MFT95 Modulating, Spring Return, 24 V, 0 to 135 Ω InputTechnical dataElectrical data Nominal voltage AC/DC 24 VNominal voltage frequency50/60 HzPower consumption in operation7.5 WPower consumption in rest position 3 WTransformer sizing10 VA (class 2 power source)Electrical Connection18 GA appliance cable, 3 ft [1 m], with 1/2" conduitconnectorOverload Protection electronic throughout 0...95° rotationFunctional data Operating range Y0...135 ΩOperating range Y note Honeywell Electronic Series 90, input 0...135 ΩPosition feedback U 2...10 VPosition feedback U note Max. 0.5 mAPosition feedback U variable VDC variableDirection of motion motor selectable with switchDirection of motion fail-safe reversible with cw/ccw mountingManual override 5 mm hex crank (3/16" Allen), suppliedAngle of rotation90°Running Time (Motor)default 150 s, variable 70...220 sRunning time motor variable70...220 sRunning time fail-safe<20 s tamb = 68°F [20°C]Angle of rotation adaptation off (default)Noise level, motor45 dB(A)Noise level, fail-safe62 dB(A)Position indication MechanicalSafety data Degree of protection IEC/EN IP54Degree of protection NEMA/UL NEMA 2 UL Enclosure Type 2Agency Listing cULus acc. to UL60730-1A/-2-14, CAN/CSAE60730-1:02, CE acc. to 2014/30/EU and 2014/35/EU; Listed to UL 2043 - suitable for use in airplenums per Section 300.22(c) of the NEC andSection 602.2 of the IMCQuality Standard ISO 9001Ambient temperature-22...122°F [-30...50°C]Storage temperature-40...176°F [-40...80°C]Ambient humidity max. 95% r.H., non-condensingServicing maintenance-freeWeight Weight 4.1 lb [1.9 kg]Materials Housing material Galvanized steel and plastic housingAFRX24-MFT95 AccessoriesGateways Description TypeGateway MP to BACnet MS/TP UK24BACGateway MP to LonWorks UK24LONGateway MP to Modbus RTU UK24MODService tools Description TypeZK4-GENConnection cable 10 ft [3 m], A: RJ11 6/4 ZTH EU, B: 3-pin Weidmüller and supplyconnectionZTH USService Tool, with ZIP-USB function, for parametrisable and communicativeBelimo actuators, VAV controller and HVAC performance devicesElectrical installationINSTALLATION NOTESProvide overload protection and disconnect as required.Actuators may also be powered by 24 VDC.Actuators and controller must have separate transformers.Consult controller instruction data for more detailed information.Resistor value depends on the type of controller and the number of actuators. No resistor is used for oneactuator. Honeywell® resistor kits may also be used.To reverse control rotation, use the reversing switch.Actuators may be controlled in parallel. Current draw and input impedance must be observed.Meets cULus requirements without the need of an electrical ground connection.Warning! Live Electrical Components!During installation, testing, servicing and troubleshooting of this product, it may be necessary to workwith live electrical components. Have a qualified licensed electrician or other individual who has beenproperly trained in handling live electrical components perform these tasks. Failure to follow all electricalsafety precautions when exposed to live electrical components could result in death or serious injury.High Limit Control Low Limit ControlTypical and Override Control Multiple ActuatorsAFRX24-MFT95Multiple Actuators with Minimum Position Potentiometer Multiple Actuators Used with W973, W7100 and T775。
Elastomeric Bearings, Dampers and Isolators: “Comfort, Care and Feeding”By LORD Corporation, Rotary Wing Business UnitWhat should you expect an elastomeric component to do in your aircraft? And how can you help them to last longer and perform optimally? Helicopters are recognized as one of the great engi-neering marvels of our time. In fact, there are thosewho would argue that their ability to function is scarcely believable. In spite of critics and nay-sayers, however, there continues to be a steady growth of owners, operators and passengers of helicopters all over the world. Many technical hurdles have been successfully conquered in order to achieve this commercial success. Elastomeric components are part of that solution.The most serious issues with regard to the operationof helicopters are those involving reliability/maintain-ability, noise and vibration. Elastomeric bearings, isolators and dampers have been enabling devices in the development of quieter, more comfortable and more reliable aircraft, reducing both Direct Operating Cost (DOC), and interior noise and vibration, and thereby increasing the acceptability of helicopter transportation.How is this so?A bearing is a mechanical device that accommodates dynamic motions. The term “bearing” is often used to refer to shaft-supports, which allow continuous rotation. Elastomeric bearings also allow rotational motion, but are limited to oscillatory motions (from 10 to 90 degrees, or up to ±1 inch). They also offer some clear advan-tages over “hard bearings.”• The elastomer layer(s) add a “spring” effect, tending to restore the angular motion back to the undefl ected position.• Elastomeric bearings have no “clearance,” andtherefore no “chatter” or possible fretting, and alsono increase in clearance as they wear. This results in smooth performance throughout the life of the part.• The degradation of elastomeric bearings is gradual and fail-safe.• Elastomeric bearings are maintenance-free. Onesignifi cant specifi c example: Unlike hard bearings, elastomerics are unaffected by airborne particles of sand and dirt, which notoriously cause accelerated wear in hard bearings.• On-condition removal criteria are determined during bench-testing. This allows the wear patterns andlimits to be quantifi ed and helps avoid prematureremoval of adequately functioning parts, saving DOC.• The elastomer in the bearing smooths the operation of the dynamic system, which inherently reduces vibra-tion and often improves control system response.An Isolator is a device installed in a load path to mini-mize the transmission of dynamic loads or motions through it. Isolators can be made with various elas-tomers or with an elastomer/fl uid (LORD Fluidlastic®) device, creating optimal isolation at the primary vibration frequencies.Dampers are used to attenuate dynamic motions in the aircraft, most often in the rotor. Elastomeric damperscan be used with or without special fl uids, which have the added advantages of more damping force for a given dynamic motion and consistent performance within wide ranges of temperature and dynamic motions. Both Elastomeric and LORD Fluidlastic dampers have demonstrated superior performance and cost effective-ness, with smaller size and weight, when compared tohydraulic dampers.Figure 1 – Collection of LORD Elastomeric Bearings used in helicopters, including shear restraints used in bearingless rotors, main rotor bearings and pitch linkrod end bearingsHow to Care for ElastomericsThe three types of elastomeric helicopter components have similar inspection and care guidelines. Through long-term testing at LORD Corporation as well as inspec-tion of returned-from-service parts from civilian and military aircraft, the primary forms of degradation have been identifi ed:• Elastomer fatigue from dynamic loading• Overload or inappropriate loading (Foreign ObjectDamage, Tool Damage or Tension Loading)• Oil or other incompatible fl uid contamination• Environmental degradation (effects of heat, ozone)• Loss of fl uid or pressure in LORD Fluidlastic Isolators or DampersHow can you identify these degradation modes, and which ones can you prevent?FatigueElastomer fatigue is the normal degradation mode of a bearing in oscillatory loading. A part can experience a surprising amount of crumbing, cracking and rubber loss before there is noticeable performance impact.As an elastomeric component is used, small surface cracks eventually form, starting in the highest strain region of the part. The crack edges rub together, growing slowly, and the abrasion causes what is most typically observed as “crumbing” (like eraser crumbs). See Figure 2. The cracks continue to grow and join together over time, and small segments of elastomer may also be extruded from the layer(s). Eventually, either a substantialFigure 2 – Typical fatigue “crumbing”This part is still completely functional.portion of the rubber will be extruded, or the cracks will grow to a removable condition. Other indications the part should be removed include increased vibration, touching or cracked metal shims. The applicable Component Repair & Overhaul (CR&O) Manual or Maintenance Manual is the defi nitive source for specifi c removal criteria for each application.Dampers, which are often made with higher damped LORD BTR® elastomer, show the same degradation modes. Fatigue damage is generally not preventable, but is a function of the amount of time that the aircraft is operating at the most strenuous conditions.Overload or Tension LoadingElastomeric parts are designed to operate generally in COMPRESSION, and/or SHEAR. Main Rotor Bearings, for example, normally carry loads in compression, and accommodate motion in shear. Compression loading occurs when the forces on the part are in a direction that tends to “squash” the material. In fact, elastomeric parts may show “bulging” of the elastomer around the edges when they are loaded. Shear loading occurs when the load on the part tends to stretch the elastomer in a direc-tion perpendicular to its smallest dimension or parallel to the “bond line.” See Figure 3.In the event that a part is placed in TENSION (which occurs when the elastomer is stretched, like a rubber band or a balloon), the elastomer has less strength, and will tend to crack and wear much more quickly. Both bearings and dampers are designed to avoid being placed in tension. When a part experiences a shearor tension load for which it was not designed, the tearFigure 3 – Shear sample before load is appliedstrength of the elastomer or the metal-to-rubber bond may be exceeded. This may result in large clean cracks in the layers, complete separation of the layers, or damaged metal shims (bending or cracking).Damage to a part during installation – due to contact with a sharp object, placing the part in tension or applying inappropriate forces or motions – can shorten the lifeof the elastomeric component. Special care should be taken to prevent the slicing, puncturing or gouging ofthe elastomer or bond line in any elastomeric part. Also whenever possible, it is desirable to remove any large static loads from elastomeric bearings when the aircraft is in storage. Blade folding and tie-down, for example, may include very high cocking motions to some rotor bearings. Finally, care should also be taken to protect the edges of the thin metal laminates (shims) from nicks or other damage, since this can signifi cantly reduce the fatigue life of the part. Figure 4 shows a part that expe-rienced overload after the elastomer section had been damaged.Oil or Other Incompatible Fluid ContaminationElastomeric materials have been developed to improve resistance to various aircraft fl uids, solvents and deter-gents. Still, petroleum-based oils, fuels, hydraulic fl uids and greases can have a devastating effect on the elas-tomer and the bond, and can very quickly cause weak-ening, swelling and extrusion.Figure 4 – Helicopter Landing Gear Mount that has experienced damage from a tool Parts exposed to oils, greases and hydraulic fl uids should be washed in mild detergent and water or dena-tured alcohol to prevent further damage. In the event of exposure to more volatile fl uids such as fuel, solvents or cleaning fl uids, the parts should be dried, and the fl uid allowed to evaporate. To prevent this serious and avoid-able degradation, special care should be taken to cover the elastomer surface when cleaning equipment nearby.Environmental Degradation (Effects of Heat, Ozone)Daily exposure to sunlight, heat and ozone can also cause surface cracking, often appearing perpendicular to the load in the elastomer. These surface cracks are small, and are not cause for removal. As the part is cycled, these may become sites for initiation of the expected fatigue cracks. Electric generators and motors as well as bright sunlight increase the presence of ozone.Most elastomers contain waxes designed to offer protec-tion from ozone. The waxes are designed to come to the surface of the part over time and provide a protective layer, (called wax bloom), which often appears gray or brown, and may fl ake or crumb as the part is exercised.Excessive heat will cause most bearings and isolators to become brittle on the exposed surfaces. (Heat does not normally cause the elastomer to “melt” or soften). The rubber-to-metal adhesives are also sensitive to heat, and performance of the part can be degraded as a resultFigure 5 – Engine isolator with severe oil contaminationNote the wavy edges and the de-bonded layers. This part is no longeroperational.of prolonged exposure to high temperatures. Prolonged exposure or storage at high temperatures (above 125°F [52°C]) also may contribute to stiffening of the elas-tomer, as well as compression or torsion “set” or “drift” in parts that have steady static loads. Certainly, material and adhesive selections are determined based on the expected environment and usage of the parts. If youhave an environment that could be considered unusual, it may be necessary to perform more frequent inspections.LORD BTR elastomers have been developed to reduce the effects of heat, chemicals and ozone, and they are used where there is known exposure to these effects.Loss of Fluid or Pressure in LORD Fluid-lastic Isolators or DampersLORD Fluidlastic devices have many of the same wear modes as typical elastomerics. They are completely sealed, and there is generally no requirement to monitor, fi ll, pressurize or meddle with the fl uid. The fl uids used are not harmful, in the event of accidental exposure. There is generally no provision for anyone other than LORD Corporation to repair, refi ll or maintain the part. For certain applications in which dynamic performance is considered critical, pressure or leak detection methods have been incorporated or are being requested toprovide positive assurance that the dampers or isolators are completely functional. The applicable CR&O Manuals or Maintenance Manuals provide all of the information necessary for such applications.SummaryElastomeric and LORD Fluidlastic Dampers, Isola-tors and Bearings have become important elements of the modern helicopter. They offer unique advantages in performance, enabling several new rotor design concepts, while reducing DOC, noise and vibration.Their inspection and appropriate replacement are key to obtaining maximum life and usage from each one.LORD Suggested Removal CriteriaWhile an understanding of the degradation modes of elastomeric bearings is valuable in and of itself, the critical question posed by most operators is “How do I determine if the bearing is still serviceable?” The photos presented in this article are intended to help you decide in the majority of cases.Because of the wide variety of applications, bearing geometry and operators, there may not be a simple answer. In every case in which removal criteria exist in a maintenance manual, it should be followed. However, when the elastomeric bearing is not covered by a main-tenance manual, the following general guidelines may be used:• If the bearing is visibly degraded to such a degree that it allows excessive motion or vibration, remove and replace it.• If the bearing has visible compression set, and it appears this will lead to diffi culty in installation or increased vibration, remove and replace it.Figure 6 – Typical ozone “checking” on a partFigure 7 – Unacceptable fatigue and fl uidcontamination on Turboprop Engine Mounting (DeHavilland Dash 8)The small cracks have no measurable depth.LORD provides valuable expertise in adhesives and coatings, vibration and motion control, and magnetically responsive technologies. Ourpeople work in collaboration with our customers to help them increase the value of their products. Innovative and responsive in an ever-changing marketplace, we are focused on providing solutions for our customers worldwide . . . Ask Us How.LORD Corporation World Headquarters 111 Lord DriveCary, NC 27511-7923 U.S.A.Customer Support Center +1 877 ASK LORD (275 5673)©2006 LORD Corporation Printed in U.S.A. OD LL6504 (Rev.2 2/06)• If enough elastomer has been extruded to allow the shims to touch or if there are any cracked shims, remove and replace the bearing.• If the bearing is separated (due to fatigue or bond line damage) over more than 25% of the bonded area, remove and replace it.• If the bearing is “oil” contaminated to a slight degree, it should be cleaned with a water-based detergent, rinsed and dried. If the contamination damage is extensive, removal and replacement are required.• If the bearing exhibits a very unusual damagecondition, it should be returned to the OEM Product Support Organization for further analysis.Fluidlastic and BTR are registered trademarks and “Ask Us How” is a trademark of LORD Techmark, Inc., a subsidiary of LORD Corporation.Figure 8 – Acceptable fatigue on Helicopter Nodal Beam (Bell 214 Type)Figure 9 – Acceptable heat exposure on EngineMounting for Turboprop Aircraft (DeHavilland Dash 8)Again, the best removal criteria are always based on the maintenance manual and experience. However, when in doubt, take it out!Where to Go for More InformationLORD has complete maintenance manual instructions available for most helicopter and fi xed wing aircraft applications. If a maintenance manual is not available, our team of product support specialists will respond to your request.。
Important Notice:Our recommendations, if any, for the use of this product are based on tests believed to be reliable. Since the use of this product is beyond the control of the manufacturer, no guarantee or warranty, expressed or implied, is made as to such use or effects incidental to such use, handling or possession or the results to be obtained, whether in accordance with the directions or claimed so to be. The manufacturer expressly disclaims responsibility therefore. Furthermore, nothing contained herein shall be construed as a recommendation to use any product in conflict with existing laws and/or patents covering any material or use.2020 Bruck Street, Columbus, Ohio 43207CUSTOMER SERVICE 1-800-669-4583TECH SERVICE 1-800-347-GLUE Application GuidelinesPhysical Properties (Typical)Application temperature Above 55°F.Open assembly time 5 minutes (70°F./50%RH)Total assembly time 10-15 minutes (70°F./50%RH)Minimum required spread Approximately 6 mils or 250 square feet per gallonRequired clamping pressure Enough to bring joints tightly together (generally,100-150 psi for softwoods, 125-175 psi for medium woods and 175-250 psi for hardwoods)Methods of application Plastic bottles for fine applications; glue may also be spread with a roller spreader or brush.Cleanup Damp cloth while glue is wet. Scrape off and sand dried excess. Type Cross-linking polyvinyl acetate State LiquidColor Light brown Dried film Brown Solids 48%Viscosity 4,000 cps pH 3.0Calculated VOC : 5.5 g/L Weight/gallon 9.1lbs .Chalk temperature* Approx. 55°F.Flashpoint >200°F.Freeze/thaw stability StableStorage life 12 months in tightly closed containers at 75°F.© 2007 Franklin International. All rights reserved. (Rev. 01/07)Titebond ®IIDark Wood GlueUnits per Packages Cat. No.SizePackageWeightper Pallet37038 oz. Bottle 128160370416 oz. Bottle 12161003705Gallon Jug220633707 5 Gallon Plastic Pail 15124Ordering InformationLimitationsTitebond II Dark Wood Glue is not for continuous submersion or for use below the waterline. Not for structural or load bearing applications. Do not use when temperature, glue or materials are below 55°F. Freezing may not affect the function of the product but may cause it to thicken. Agitation should restore product to original form. Because of variances in the surfaces of treated lumber, it is a good idea to test for adhesion. Not FDA approved for indirect food contact. Read MSDS before use. KEEP FROM FREEZING. KEEP OUT OF THE REACH OF CHILDREN.Product Features •Passes ANSI Type II water-resistance•Designed for interior and exterior applications •Excellent sandability •Unaffected by finishes•Ideal for radio frequency (R-F) gluing systems •Easy cleanup with water*Chalk temperature indicates the lowest recommended temperature at which the glue, air and materials can be during application, to assure a good bond.Bond Strength ASTM D-905(on hard maple)Temperature Strength psi% wood failureRoom Temperature 3,750 72150°F. Overnight 1,7506。
备战 2021 高考英语原汁原味外刊热点话题阅读特辑day9: The Marine plastic problem is bound to get worse海洋塑料问题注定会越来越严重课前导读： 《科学》杂志上发表的一项新研究表明，流入世界海洋的塑料数量将急剧上升，对于这一趋势，那些试图减少塑料垃圾的努力将无济于事。
精彩英文 The annual inflow of plastic could nearly triple from 2016 to 2040, the study found, and even if companies and governments meet all their commitments to tackle plastic waste, it would reduce the projection for 2040 by only 7%, still a more-than twofold increase in volume. The study’s authors, the nonprofit Pew Charitable Trust and sustainability consulting firm Systemiq Ltd., set out a range of measures to stem the flow and called on businesses and governments to do more to reduce the use of plastic. They developed what they say is a first-of-its-kind model of the global plastics-supply chain—from production to consumption to disposal—using data and input from 17 experts from various regions. Consumer and regulatory pressure has prompted many of the world’s biggest consumer-goods companies to commit to making all their packaging reusable, recyclable or compostable within the next five years. Businesses have also pledged to use more recycled content in their packaging, often touting suchpromises to woo shoppers. Waste-reduction advocates say those commitments aren’t enough because they focus on recycling plastic, rather than making and using less of it. Companies like Walmart Inc.,Nestle and Procter & GambleCo. say they plan to eliminate unnecessary packaging and use more refillable containers, but few have set measurable targets for doing so. 【报刊词汇预习】 1. annual 每年的 adj 2. triple 三倍的 adj. 3. inflow 流入 n. 4. commitment 承诺 n. 5. tackle 处理 vt. 6. projection 投影 n. 7. volume 体积 n. 8. twofold 双重的 adj. 9. nonprofit 非营利性 adj. 10. sustainability 持续性/səˌsteɪnəˈbɪləti/ 11. consulting 咨询的 adj. 12. stem 阻止 vt 13. a first-of-its-kind 首创的 adj. 14. plastics-supply 塑料供应的 adj. 15. disposal 处置 n 16. data 数据 n 17. input~ (into/to sth)~ (of sth)投入资源（指时间、知识、思想等）；投入；输入 vt/nHer specialist input to the discussions has been very useful. 她在这些讨论中提供的专家建议很有 助益。
一次性塑料制品的问题英语作文高中全文共3篇示例，供读者参考篇1The Issue of Single-Use Plastic ProductsIntroductionIn recent years, the issue of single-use plastic products has become a major concern for environmentalists, policymakers, and the general public. These products, which are used just once before being thrown away, are causing significant harm to the environment, wildlife, and human health. In this essay, we will explore the problems associated with single-use plastic products and discuss potential solutions to address this pressing issue.Environmental ImpactOne of the most significant problems with single-use plastic products is their impact on the environment. These products are made from non-biodegradable materials, which means that they do not break down naturally over time. As a result, they end up in landfills, rivers, oceans, and other natural habitats, where they can take hundreds of years to decompose. In the meantime, theycan release harmful chemicals into the environment, pollute the soil and water, and endanger wildlife.For example, plastic bags are often mistaken for food by marine animals such as sea turtles and seabirds, leading to the entanglement and ingestion of these animals. This can have devastating consequences for their health and well-being, and can even lead to death. Similarly, plastic bottles and straws can end up in rivers and oceans, where they can harm fish, seabirds, and marine mammals.Human Health ImpactIn addition to their environmental impact, single-use plastic products can also have negative effects on human health. Many of these products contain harmful chemicals such as phthalates, bisphenol A (BPA), and styrene, which have been linked to a variety of health problems, including cancer, reproductive issues, and developmental disorders. When these chemicals leach out of plastic products and into our food, water, and air, they can pose a serious risk to human health.Furthermore, the production and disposal of single-use plastic products can also contribute to air and water pollution, which can have far-reaching effects on human health. For example, the incineration of plastic products can release toxicgases and chemicals into the atmosphere, while the accumulation of plastic waste in landfills can contaminate groundwater and soil.Potential SolutionsIn order to address the issue of single-use plastic products, it is important to adopt a multi-faceted approach that includes policy changes, consumer education, and technological innovations. One potential solution is to ban or restrict the production and use of certain single-use plastic products, such as plastic bags, straws, and utensils. Several countries and cities around the world have already implemented such bans, with positive results.Another important solution is to promote the use of reusable alternatives to single-use plastic products, such as reusable bags, water bottles, and food containers. By encouraging consumers to choose these more sustainable options, we can reduce the demand for single-use plastic products and decrease their impact on the environment.Furthermore, efforts should be made to improve recycling infrastructure and increase the recycling rate of plastic products. This can help to reduce the amount of plastic waste that ends up in landfills and oceans, and can promote a more circulareconomy in which plastic products are reused and recycled rather than discarded.ConclusionIn conclusion, the issue of single-use plastic products is a complex and pressing problem that requires urgent action. By addressing the environmental and health impacts of these products, we can create a more sustainable future for ourselves and future generations. Through a combination of policy changes, consumer education, and technological innovations, we can work together to reduce the use of single-use plastic products and protect our planet for years to come.篇2The Problem of Disposable Plastic ProductsIntroductionDisposable plastic products have become a ubiquitous part of our daily lives. From water bottles to food packaging to shopping bags, these convenient items have made our lives easier in many ways. However, their widespread use also comes with a number of negative consequences that cannot be ignored. In this essay, we will explore the environmental, social, andhealth problems associated with disposable plastic products and discuss potential solutions to these issues.Environmental ImpactOne of the biggest problems with disposable plastic products is their impact on the environment. Plastic is a highly durable material that takes hundreds or even thousands of years to decompose. As a result, plastic waste accumulates in landfills, rivers, and oceans, posing a serious threat to wildlife and ecosystems. Marine animals often mistake plastic debris for food, leading to ingestion and entanglement that can be fatal. Additionally, plastic waste releases harmful chemicals into the environment as it breaks down, further exacerbating environmental pollution.Social and Economic ImpactThe production and disposal of disposable plastic products also have social and economic consequences. Many developing countries lack proper waste management infrastructure, leading to widespread plastic pollution in these regions. In addition, the extraction and production of plastic materials contribute to air and water pollution, disproportionately affecting low-income communities. Furthermore, the use of disposable plastic products promotes a culture of convenience and instantgratification that can have negative implications for our overall well-being.Health ImpactIn addition to their environmental and social impacts, disposable plastic products also pose a threat to human health. Some plastic materials contain harmful chemicals such as BPA and phthalates, which have been linked to a variety of health problems including cancer, reproductive disorders, and hormonal imbalances. These chemicals can leach out of plastic products and into our food and water, putting consumers at risk of exposure. Ingesting or inhaling microplastics, which are small plastic particles that have been found in various foods and beverages, can also have negative effects on human health.Potential SolutionsIn order to address the problems associated with disposable plastic products, we must take a multipronged approach that involves individuals, businesses, and governments. One possible solution is to reduce our reliance on single-use plastics by choosing reusable alternatives whenever possible. This could include using a refillable water bottle, bringing your own shopping bags, and avoiding products with excessive plastic packaging. Businesses can also play a role by phasing outdisposable plastic products in favor of more sustainable alternatives. For example, restaurants and cafes can switch to compostable or biodegradable packaging, while retailers can offer incentives for customers to bring their own containers.Governments can also implement policies to reduce plastic pollution, such as banning certain types of single-use plastics, imposing taxes on plastic products, and investing in recycling infrastructure. Many countries have already taken steps to address the issue of disposable plastic products, and more initiatives are being proposed at the national and international levels. By working together to reduce our consumption of disposable plastic products and transition to a more sustainable way of living, we can help protect our environment, improve public health, and promote social equity.ConclusionDisposable plastic products have become a pervasive part of our modern lifestyle, but their convenience comes at a high cost to the environment, society, and our health. By acknowledging the problems associated with these products and taking action to reduce their impact, we can help create a more sustainable future for generations to come. Whether through individual choices, corporate responsibility, or government intervention,each of us has a role to play in addressing the challenges posed by disposable plastic products. It is only by working together that we can overcome these obstacles and create a cleaner, healthier planet for all.篇3The Issue of Single-Use Plastic ProductsIntroductionIn recent years, the issue of single-use plastic products has gained significant attention due to the growing awareness of the harm they pose to the environment and human health.Single-use plastic products, such as bags, bottles, straws, and utensils, are designed for convenience but have long-lasting negative impacts on our planet. This essay will explore the problems associated with single-use plastic products and propose solutions to address this urgent issue.Environmental ImpactOne of the most pressing issues with single-use plastic products is their contribution to environmental pollution. Plastic waste does not biodegrade but breaks down into smaller pieces called microplastics, which can be ingested by animals and enter the food chain. Marine animals, such as turtles, whales, andseabirds, often mistake plastic for food, leading to choking, starvation, and other fatal consequences. Additionally, plastic pollution poses a threat to ecosystems, affecting the balance of marine and terrestrial environments.Furthermore, the production and disposal of single-use plastic products contribute to greenhouse gas emissions and the depletion of natural resources. The production of plastic requires fossil fuels and energy-intensive processes, leading to carbon dioxide emissions and environmental degradation. Moreover, plastic waste often ends up in landfills or incineration facilities, releasing toxic substances and pollutants into the air, soil, and water.Health ImpactAside from environmental concerns, single-use plastic products also have adverse effects on human health. Many plastics contain harmful chemicals, such as bisphenol A (BPA) and phthalates, which can leach into food and beverages, particularly when exposed to heat or sunlight. These chemicals have been linked to various health problems, including hormonal disruptions, reproductive issues, and cancer. In addition, plastics that break down into microplastics can contaminate watersources and food supplies, posing a risk to human health through ingestion or inhalation.Social ImpactThe issue of single-use plastic products also has social implications, particularly in developing countries where waste management infrastructure is limited. Plastic pollution can exacerbate poverty, hinder economic development, and harm community health and well-being. Informal waste pickers, often marginalized individuals and families, may be exposed to hazardous materials while scavenging through plastic waste for recycling or disposal. Moreover, plastic pollution can impact tourism, fishing, and other industries reliant on clean and healthy environments, leading to economic losses and social disruptions.Policy ResponseTo address the challenge of single-use plastic products, governments, businesses, and individuals must take collective action to reduce plastic consumption, promote recycling and waste management, and encourage sustainable alternatives. Policy measures, such as plastic bans, taxes, and incentives, can help to reduce the production and consumption of single-use plastics. Many countries have already implemented restrictionson plastic bags, straws, and other disposable items to curb plastic pollution and foster a circular economy.Businesses can also play a crucial role in addressing the issue of single-use plastic products by redesigning packaging, transitioning to biodegradable materials, and investing in recycling and waste management solutions. Many companies are adopting sustainable practices, such as refillable containers, compostable packaging, and product take-back programs, to reduce their environmental footprint and meet consumer demand for eco-friendly products.Individual ActionsAs consumers, we can make a difference by making conscientious choices in our daily lives to reduce plastic waste and promote sustainability. Simple actions, such as carrying reusable bags, bottles, and utensils, avoiding single-use plastics, recycling and composting waste, and supporting local businesses and initiatives, can have a positive impact on the environment and society. By raising awareness, advocating for policy changes, and inspiring others to adopt sustainable practices, we can collectively contribute to a cleaner, healthier, and more sustainable future for generations to come.ConclusionIn conclusion, the issue of single-use plastic products is a complex and multifaceted challenge that requires comprehensive solutions at the global, national, and local levels. By recognizing the environmental, health, and social impacts of plastic pollution, we can take proactive steps to reduce our reliance on single-use plastics, promote sustainable alternatives, and create a more resilient and regenerative society. Together, we can address the issue of single-use plastic products and work towards a more sustainable and inclusive future for all.。
A 高分子化学和高分子物理UNIT 1 What are Polymer?第一单元什么是高聚物？What are polymers? For one thing, they are complex and giant molecules and are different from low molecular weight compounds like, say, common salt. To contrast the difference, the molecular weight of common salt is only 58.5, while that of a polymer can be as high as several hundred thousand, even more than thousand thousands. These big molecules or ‘macro-molecules’ are made up of much smaller molecules, can be of one or more chemical compounds. To illustrate, imagine that a set of rings has the same size and is made of the same material. When these things are interlinked, the chain formed can be considered as representing a polymer from molecules of the same compound. Alternatively, individual rings could be of different sizes and materials, and interlinked to represent a polymer from molecules of different compounds.什么是高聚物？首先，他们是合成物和大分子，而且不同于低分子化合物，譬如说普通的盐。
第23卷第21期岩石力学与工程学报23(21)：3577～3583 2004年11月Chinese Journal of Rock Mechanics and Engineering Nov.，2004岩土材料弹塑性损伤模型及变形局部化分析*杨强陈新周维垣(清华大学水利水电工程系北京 100084)摘要常规的弹塑性模型由于没有考虑到损伤和塑性的耦合作用，难以模拟破坏时由于内部损伤的累积导致的变形局部化剪切带的形成过程，因而，不能很好地反映实际结构的细观破坏机理。
作者采用一种宏细观结合的思路，基于细观损伤力学提出了一个适用于岩土材料弹塑性损伤模型，研究均质材料在外部环境作用下由于损伤和塑性的耦合导致的局部化剪切带的形成过程。
对基体材料服从Drucker-Prager准则的球形孔洞体胞单元提出了一个塑性损伤屈服面，为了反映岩土材料在拉应力和压应力作用下不同的孔洞形成机理，分别采用了球形拉应力和塑性应变的成核机制来建立孔隙率的演化方程，根据塑性损伤屈服面和孔隙率的演化方程，导出了关联流动法则下的岩土材料塑性损伤本构方程。
将笔者提出的岩土材料弹塑性损伤模型，通过用户子程序嵌入到大型商业有限元软件MRAC中。
为了研究塑性和损伤的耦合作用，分别采用Gurson弹塑性损伤模型和Mises弹塑性模型，对Tvergaard 关于自由表面有周期性分布微小形状缺陷的半无限大板在平面应变拉伸作用下剪切带的形成进行了数值模拟，计算结果表明弹塑性损伤本构模型在模拟变形局部化方面具有明显的优势。
采用作者提出的岩土材料弹塑性损伤模型，对平面应力条件下有一个缺陷单元的均质岩土材料单轴受压试件的局部化剪切破坏进行了数值模拟。
关键词岩土力学，岩土材料，体积孔隙率，Drucker-Prager准则，成核机制分类号 TU 452 文献标识码 A 文章编号1000-6915(2004)21-3577-07ELASTO-PLASTIC DAMAGE MODEL FOR GEOMATERIALSAND STRAIN LOCALIZAION ANALYSESYang Qiang，Chen Xin，Zhou Weiyuan(Department of Hydraulic and Hydropower Engineering，Tsinghua University， Beijing 100084 China)Abstract Elasto-plastic models can not explain the micro mechanism of shear band formation caused by damage evolution in ductile material due to the neglecting of the interaction between damage and plastic flow. An elasto-plastic damage model for geo-materials based on micromechanics is proposed and the micro mechanism of shear band formation in homogeneous geo-material is studied. A macroscopic yield criterion for porous geo-materials with matrices of Drucker-Prager yield criterion is given，and a plastic strain-controlled void nucleation model as well as a tensile volumetric stress-controlled nucleation model are proposed for the compressive and tensile stresses，respectively. Moreover，the constitutive relationship of the elasto-plastic damage model with plastic normality flow rule is deduced. This elasto-plastic damage model for geo-materials is embeded into the commercial FEM software MARC as a user’s subroutine. A tensile plane strain specimen with initial shape imperfection on its upper bound which was first analyzed by Tvergaard is investigated through the elasto-plastic damage model and Mises elasto-plastic model，respectively. It is shown that the shear band development is only found in Gurson elasto-plastic damage model. Shear band formation due to void nucleation and growth in a plane stress specimen of homogeneous geo-material with one defect element subjected to uniaxial compression is 2003年12月8日收到初稿，2004年2月8日收到修改稿。
