Research On Mesoscopic Simulation And Acoustic Emission Characteristics Of Metal Plastic Materials In Tensile Process

Deformation and fracture of metal plastic material is the main failure mode inpetrochemical equipments. The metal plastic material’s macro mechanics propertiesmainly depend on the development of its internal defects that produced in theprocesses of molding, machining and using. It’s the development trend of solidmechanics that combine the macromechanics and mesomechanics research methodto establish the corresponding macroscopic and mesoscopic fracture theory. Theprocess of acoustic emission (AE) for material is a phenomena accompanied with themechanics process and material internal structure evolution. With the developmentand improvement perennial, the AE technique has became an effective tool formaterials research. In particularly, the application of AE plays an important role boththeoretical and practical for describing the evolution of micro defects of metal plasticmaterials in tensile process and observing the behavior of material injury andevaluating the safety and reliability performance of materials.This paper was supported by Natural Science Foundation of HeilongjiangProvince 《Study on metal components’ mesoscopic damage mechanism underlow-cycle fatigue and acoustic emission evaluation method》. Based on themeso-damage theoretical model and AE characteristic of void damage evolution, wetook the void defects in metal materials as the starting point to establish the AEquantitative evaluation of metal plastic materials. We carried out the tensileexperiment on Q345steel and20steel Φ8mm notched bar specimen and got the AEinformation from yield to fracture process. The Meso-damage parametersdistribution of the tensile notched specimen was simulated with theGurson-Tvergaard-Needleman model and their void growth ratio numerical solutionswere achieved by ABAQUS finite element software. Through the combining theresults of AE testing experiment with numerical simulation, the quantitativeevaluation formula that takes void growth ratio as damage variable in the process ofAE cumulative hits for the metal plastic materials was established.Metal plastic material micromechanical damage mechanism is the process ofvoids nucleation, growth and convergence. The changing of AE cumulative hitsdirectly corresponds to the different injury stages of material. The void growth ratiois a micromechanics parameter which builts on the micro voids damage mechanism of metal plastic materials. And it is the bridge that contacted between the mesodamage characteristic and maco damage parameters. Its variation directly reflects thestages of deterioration of material. The notched front of void growth ratio’snumerical evolution under different damage states of Q345steel and20steelnotched specimens was achieved by numerical simulation. By constructing thefunction between AE cumulative hits and void growth ratio of metal plastic material,the results show that the material from yield to fracture process can be divided intotwo stages, namely linear damage and nonlinear damage stage. As a result, thedamage critical transition point of AE cumulative hits values of Q345steel and20steel were defined. This critical transition value could be used as material’s damagefracture of AE recognition feature and safety evaluation threshold value.