Research On Test Method For Impact Dynamic Shear Mechanical Properties Of Metal Materials

Because shear failure occurs frequently and easily with the shear strain rate at more than10⁵s^-1 under the strong impulse load,requirements of higher standards have been proposed for the shear mechanical property test of metal materials.In the past,split Hopkinson pressure bars（SHPB）technology was commonly used in the shear test of metal materials to obtain the mechanical properties with the shear strain rate at less than 10⁴s^-11 for metal materials through the special design of sample and compression bars.Alternatively,light gas gun technology can be applied to load the samples with the strain rate at over 10⁵s^-1,but it introduces a lot of inconveniences for the experiments due to its limitations.In view of the above problems,in this study,we employs the direct striking of Hopkinson bars（DIHPB system）to load the double shear specimens,so as to obtain shear mechanical properties with shear strain rate at above 10⁵s^-11 for metal materials.The main work and conclusions are as follows:（1）In the dynamic experiment,the shear strain-shear stress curve under the loading of low velocity has been obtained,which fits well with the experimental results of the Hopkinson pressure bar,indicating that the two test methods are consistent at low strain rates.DIHPB system can accurately evaluate the dynamic mechanical properties of materials.Shear stress-time curves of the three metal materials have been obtained under the condition of high-speed loading of the struck bar.The deformation process of the solid material has been visually observed by using a high-speed camera.（2）The dynamic loading process of double shear specimens has been numerically simulated using the finite element software ABAQUS/Explicit,and the result suggests that the stress-strain fields are uniformly distributed in the main area of the shear zone under the strike of low velocity.Based on the experiment,shear stress-shear strain curves and equivalent stress-equivalent strain curves agree well with the simulated curves.Experimental transmission strain-time curves fit well with the first part of the simulated curve under high-speed strike,and the linear fitting of the shear strain curves has substantiated that shear strain rate of the materials could reach as high as over 10⁵s^-1 under high-speed strike.（3）With the metallographic microscope and the scanning Electron Microscope（SEM）,the failure analysis has been performed for the recycled specimen fractures,and the failure behavior and its mechanism of TC4 and 603 steels have been studied under different strain rates.It is shown that ductile fracture and brittle fracture mechanism of TC4 lead to the material failure under quasi-static loading,while the failure mode of the materials is ductile fracture under dynamic loading.For the 603 steel,ductile fracture is presented under both quasi-static loading and dynamic loading.