Investigation Of The Dynamic Response Of Typical Metals Subjected To Shock Loading With Crystal Plasticity Model

The dynamic plastic deformation of metals subjected to shock loading is an ultrafast dynamic process,and an assembly point of interdisciplinary science.A detailed understanding of the dynamic response of metals under shock loading is critical to many technical applications,e.g.high-speed impact phenomena,vehicular crash tests,and the development of armor.The crystal plasticity originates from the evolution of defects on microscale and mesoscale.Due to the lack of in situ diagnostic techniques,it's still hard to recognize the evolution laws of the defects during an ultrafast process.Measurement of the velocity profiles is the main method to obtain high-time-resolution deformation information of materials under shock loading.From the features of the velocity profiles,we can infer the deformation details.However,if we don't understand the dynamic constitutive behavior of the material well,we can't get much information from the velocity profiles.In this sense,an accurate constitutive model is the key to the interpretation of the velocity profiles and the investigation of the dynamic plastic deformation.A number of constitutive models have been established to address the dynamic response of metals under shock loading.However,the existing models can't capture the common features of different metals,such as the "Swegle-Grady fourth power law",or distinguish the different features of different metals,such as the different temperature dependence of the dynamic yield stress of FCC metals and BCC metals,because these models haven't taken into account the deformation mechanisms comprehensively,or haven't established accurate governing equations for each deformation mechanism.In this work,we have established a universal constitutive model for both FCC and BCC metals under the thermoelastic viscoplastic frame,in which dislocation homogeneous nucleation,multiplication,trapping,annihilation,and deformation twinning are comprehensively considered.Particularly,the governing equation of dislocation multiplication is determined by dimension analysis method.The essence of the equation is that the multiplication rate is proportional to the plastic dissipation rate.This model has successfully reproduced the features of the velocity profiles of typical FCC metals and BCC metals under different applied stresses or different environment temperatures.Three typical features of the velocity profiles are investigated,including the temperature effect of the Hugoniot Elastic Limit(HEL),the power law characteristics of the plastic front and the quasi-elastic behavior of the release and reloading process.The conclusions are listed in the following:Firstly,it's found that the thermal hardening behavior of FCC metals results from the phonon drag hardening,while the shear modulus mechanism is proved to be suitable for mesoscopic materials.Regarding to BCC metals,the thermal softening behavior is attributed to the thermal softening of the Peierls stress,while the thermal hardening behavior of vanadium is attributed to the forest hardening induced by thermally activated dislocation homogeneous nucleation.Secondly,we proposed a third power scaling,which matches better with recent experiments rather than the classical fourth power scaling,to describe the power law characteristics of the plastic front with the applied stress.We demonstrated that the power law characteristic of the plastic front originates from the particular stress dependence of the plasticity behaviors.Thirdly,we provided a dislocation-based explanation of the quasi-elastic behavior of the release and reloading process.It's found that the quasi-elastic behavior results from the immobilization of the mobile dislocation during the release or the reloading process.