EFFECT OF TENSILE STRESS AND RESIDUAL STRESS ON THE SPONTANEOUS STRAY FIELD SIGNALS FROM THE SUR

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CHINESE JOURNAL OF MECHANICAL ENGINEERING Vo1.20,No.6,2007 ・29・ 

DONG Lihong National Key Laboratory for Remanufacturing, Academy ofArmored Force Engineering, Beijing 100072,China 

Basic Course Department, Ordnance Engineering College, Shijiazhuang 050003,China 

XU Binshi DONG Shiyun National Key Laboratory for Remanufactudng, Academy ofArmored Force Engineering, Beijing 100072,China 

CHEN Qunzhi Aeronautical Technology Research Cen ̄c Beijing 100076,China 

WANG Dan YIN Dawei National Key Laboratory for Remanufactudng, Academy ofArmored Force Engineering, Beijing 100072,China 

0 INTRoDUCTIoN 

EFFECT OF TENSILE STRESS AND RESI DUAL STRESS ON TH E SPONTAN EOUS STRAY FI ELD SIGNALS FROM THE SURFACE OF 0.45%C STEEL木 

Abstract:In order to explore the quantitative method of meta1 magnetic memory testin MMMT) and clarify the relationship between爿D(y),the norma1 component of spontaneous stray field,and applied stress or residua1 stress.the static tensile tests Of 0.45%C stee1 sheet specimens are carried out on a scrvo hydraulic MTS8 10 machine.HD(y)values are measured during the test process by an EMS一2003 meta1 magnetic memory diagnostic apparatus and a non—magnetic electric control displacement instrument.Residua1 stresses of some points on the surface of a specimen are measured by a Stress Tech X—Stress 3000 X—ray difraction instrument.The results show that the same variation rules of爿 value versus applied tensile stress are presented under the difierent conditions of 

1oad—on and 1oad—off.However,the same rule does not exist between the (y)value and residua1 stress.The variation of Cv)value reflects the history ofapplied tensile stress. Key words:Meta1 magnetic memory Spontaneous stray field Tensile stress Residua1 stress 

It is well known that a magnetic field and stress can affect the structure of magnetic domain and magnetic properties of ferromagnetic steels greatly.At present both the methods of magnetic Barkhausen noise and magnetic acoustic emission testing measure the variations of magnetic parameters under the effects of external magnetic field and stress to evaluate residual stress.microstructure and fatigue damage .However,such methods require the co—application of magnetic attachments. AIthough the interaction between stress and magnetization process has been studied extensively since the phenomenon of mangetostriction was first reported by JOULEt .no important 

achievements were given in this field,especially under stress alone without an external magnetic field. Since metal magnetic memory testing(MMMT、was presented on the 50th intemational welding conference.researches on the variation of spontaneous strav field signals induced by stress become the foCUS again.The phenomenon of metal magnetic memory was firstly observed in Russia at the beginning Of 1 980’s.spontaneous stray field would occur on the stress concentration zones of ferromagnetic components surface under the effect of applied loads in the earth magnetic field where normal component Ho(Y)of spontaneous stray field is zero.Even after removal of the applied load.the strav field can still exist on this position.So the potential dangerous areas of ferromagnetic materials can be found by measuring the distribution of normal component of straV fieldt J.Howeve ̄the physical mechanism 

Of MMMT phenomenon was not clear and some researchers still doubted it.So the variation of normal component of spontaneous stray field under the applied stress played a highly important role in clarifying the mechanism Of MMMT for its application. This project is supported by National Natural Science Foundation of China (No.50235030,No.50505052).Received September 15,2006;received in revised form May 10,2007;accepted July 31,2007 The variation of normal component ∽of magnetic field on the surface of flat—sheet type specimen under the conditions of load—on and load—off state respectively and residual stress are presented in this paper.Their relationships are also discussed. 1 EXPERIMENTAL DETAILS 1.1 Specimen preparation The test material is 0.45%C steel which is used very commonly as mechanical parts in engineering.Fig.1 shows the specimen configuration.Its surface roughness Ra is 1.6 gm.Two horizontal parallel lines were drawn on the surface of test specimen with 10 mm space vertically,which were named by line l andline 2. Fig.1 Specimen configuration Ten points with constant 1 0 mm intervals on every horizontal line were chosen to measure their magnetic signals. 1-2 Experimental equipments The tensile test was carried out with a servo hydraulic MTS8 1 0 system whose static error was±0.5%.Spontaneous stray field signals were measured by an EMS一2003 metal magnetic memory apparatus and a three—dimensional non—magnetic electric control displacement instrument.The key part of magnetic memory testing system is a Hall sensor with high sensitivity of 1 A/m which can measure normal component CV)signals.The three—dimensional non—magnetic electric control displacement