Dynamic Compressive And Tensile Constitutive Behavior Of Lanthanum

This paper studies on the dynamic compressive and tensile constitutive behavior ofLanthanum, the main contents are as follows:1) The high strain rate compressive constitutive equation of La metal was determined andchecked:Both compressive tests, static on Material Test System (MTS) and dynamic on splitHopkinson pressure bar (SHPB), were carried out for La metal. The effects of strain rate andtemperature in the first loading of SHPB tests were separately given. The effect of strain rateconnected with the evolution of the microstructure and the effect of temperature involved withmelting point were represented by J-C type empirical constitutive equation. The determinedconstitutive equation of La metal was checked by using the numerical simulation of SHPB tests.The reflected and transmitted pulses of SHPB tests computed with the determined constitutiveequation for La metal specimens can be consistent with the experimental data to a certain extent.2) The determined high strain rate compressive constitutive equation of La metal was adjustedto describe the large strain of La metal:The multi-compressive loadings in SHPB tests for La metal specimens, which were recordedby a high speed camera, were used to investigate the constitutive equation of La metal at largedeformation and the dependence of the constitutive equation of La metal on deformation history.Assuming that the flow stressσ eof La metal as a function of the strain ε, strain rate ε and thetemperature T maintains its form with variable parameters during multi-compression of La metalin SHPB tests, the constitutive equation of La metal determined in the first loading of SHPB testswas adjusted in numerically simulating large deformations of La metal specimens generated bymulti-compression in SHPB tests and recorded by the high-speed camera.3)The dynamic compressive constitutive behavior of La metal under multiple SHPB testsloading was revealed:For some recovered La metal specimens, which were deformed uniformly, multiple-SHPBtests were performed, and the compressive constitutive behaviors of La metal under multipleSHPB tests were also revealed.4) The La metal specimens recovered from SHPB tests were investigated by using scanning electron microscope (SEM):The results of SEM investigation of the recovered La metal specimens for typical testsshowed that there is a variety of deformation microstructures dependent on strain rate, temperatureand stress state. Physically, one classifies the obstacles into short range (thermally activatedbarriers) and long range (athermal barriers). The thermally activated barriers can be overcome bythermal energy. The response of materials at high strain rates is intimately connected with theevolution of the microstructure, However, it is difficult to describe the deformation historydependence of the dynamic constitutive equation by using physically based models.5) The high strain rate tensile constitutive equation of La metal was determined and checkedfor sheet specimens:Both tensile tests, static on MTS and split Hopkinson tensile bar (SHTB) for La metal sheetswere carried out for La metal. It was found that La metal specimens fractured during the firstloading of SHTB tests. The numerical simulated reflected and transmitted pulses in SHTB testsinvolving the fracture of La metal specimens at a certain strain could be consistent with theexperimental pulses.6) The dynamic fracture mechanism of La metal was investigated:The La metal sheets recovered from SHTB tests were investigated by using SEM. It wasfound that the fracture mechanism of La metal is brittle essentially, however, the fracturemechanism transforms from brittle to ductile as the tensile strain rate increased. Void nucleation,growth and coalescence could be observed in some SEM investigation of La metal sheetsrecovered from SHTB tests at high strain rates.