Experimental validation for the quasi-shear wave behavior of LiF single crystal along a low-symmetry orientation under uniaxial shock loading.

To investigate the quasi-shear wave behavior and the underlying microscopic mechanism of an anisotropic solid under dynamic deformation beyond its Hugoniot elastic limit, LiF single crystals are shock-compressed along the [310] low-symmetry crystallographic orientation via normal plate-impact method. Interfacial velocity profiles are measured with a Doppler pin system. Peak normal stresses in samples vary between 1.91 GPa and 3.23 GPa. Under the lowest stress in this study, the resultant wave profile shows typical elastoplastic two-wave structures. In the second lowest stress experiment, an irregularity of the plastic wave or the inelastic deformation wave appears in the wave profile. At two higher stresses, a third wave is found following the elastoplastic two waves propagating along the normal direction. Our observations of three-wave structures in the [310] LiF are in excellent agreement with the simulation result of literature. This fact confirms that the immobilization of dislocations and rotation of slip planes are responsible for the microscopic mechanism of the three-wave propagations in the [310] LiF under uniaxial shock loading. The mechanism of the elastoplastic two-wave to anomalous three-wave structures evolution of material under different peak normal stresses will also be discussed.