Effect Of Microstructure On Acoustic Emission Characteristics During The Stretching Of Metallic Materials

Metal materials are widely used in various engineering fields due to their advantages such as high strength,good plasticity and excellent toughness.As a dynamic nondestructive testing technology,acoustic emission detection technology has the greatest advantage that the data signal comes from the defects of the material itself,and has a high sensitivity to the change of the microstructure of the material.Therefore,the acoustic emission detection technology can effectively detect the micro damage in the process of material deformation.The acoustic emission mechanism and signal characteristics of materials are the basis of the application of acoustic emission detection technology.The existing acoustic emission theory research is flawless perfect enough,and it cannot effectively guide people’s understanding of acoustic emission.In this paper,the microscopic grain morphology of DC05 steel plate was changed by heat treatment.Single tensile test was carried out on the steel plate by using the New SANS tensile testing machine,and the acoustic emission signal in the steel plate stretching process was measured by using the PCI-2 dual-channel acoustic emission detector.Also,this paper analyzed the impact of microscopic organizational morphology on acoustic emission characteristic signals.With the help of metallographic observation combined with metallurgical principles,the physical nature of the acoustic emission source is explained,which has important theoretical and practical value for the promotion and application of acoustic emission technology.By heat-treating the DC05 steel plates at 750℃,800℃,850℃,900℃,and 950℃,the grain size of the materials at 750℃ and 800℃ is not significantly increased.At 850℃,900℃,950℃,the grain size of the material is significantly increased.Uniaxial tensile tests were performed on the obtained specimens with different microstructures.It was found that the increase in grain size had little effect on the elastic modulus of the material,but with the increase of grain size,the yield strength,ultimate strength and elongation of the material decreased.The acoustic emission characteristics of DC05 steel during tensile process were studied.Combined with the metallographic observation and the metallurgical principle,the mechanism of the acoustic emission source in each stage of stretching was explained.The variation of the acoustic emission characteristics of the specimens after heat treatment at different temperatures(750℃,800℃,850℃,900℃,and 950℃)was compared and the cause of the change was analyzed: When the heat treatment temperature was lower(750 ℃,800 ℃),due to the reduction in the amount of ferrite produced by heat treatment,the grain size of the material changed little,so the acoustic emission energy,amplitude,and ring count signals generated during the stretching of the specimen are weak,and the energy accumulation and the ringing curve has a lower cumulative curve;with the increase of heat treatment temperature(850℃,900℃,950℃),the grain size of the material increases significantly,and the grain dislocation slip movement strengthens during the tensile plastic deformation of the specimen.As a result,the acoustic emission energy,amplitude,and ring count signals generated during the stretching of the specimen become stronger,and the energy accumulation curve and the cumulative count of the ring curve move upper.