Ly12 Aluminum Annealed Under Strong Dynamic Load Shear Modulus And Yield Strength

The shear modulus and yield strength as a function of shock stress play a unique role in constitutive relation investigations of materials. In this thesis, the self-consistent method proposed by J. R. Asay and L. C. Chhabildas (so called AC method) for measuring the yield strengths of materials under shock loading were systematically formulated, including the fundamental principle, experimental techniques, data reduction and analyses, and yield strengths of annealed LY12 Al under shock loading were measured using the AC method. In addition, the shear moduli for the annealed LY12 Al up to 80 GPa were obtained based on the measured sound velocity data. The experiment and data reduction techniques were reasonably improved in the AC method, and the understanding of the AC method framework was deepened through this thesis work. (1) One-stepped sample and single-flyer instead of the usual two-stepped sample and two-layer combined flyer are used in loading-unloading experiments. This experimental configuration not only can meet the physical requirements, but also simplify the wave interaction of loading-unloading process. It is found that the location of elastic-plastic transition is more accurately identified based on the acquired Lagrangian sound velocity (C^L) against particle velocity (u), relative to based on the Lagrangian sound velocity against engineering strain (ε).(2) Sound velocity and shear modulus data of annealed LY12 Al at four different stress-loaded levels were attained by loading-unloading experiments. In comparison with the corresponding results of unannealed LY12 Al given by Y. Yu, we found that the sound velocities and shear moduli of annealed LY12 Al were closed to those of the unannealed LY12 Al in the experimental stress range. But we also found that the shear stress (τ₀ + τ_C) at pre-compressed state is obviously lower, relative to the unannealed LY12 Al. In combination with the reported sound velocity data, we gained a correlation of the Euler longitudinal sound velocity (C_l) with the axial stress (σ_x) by the quadratic fitting: C_l= -3.117×10^-4σ_x²+0.075σ_x+7.042. The measured Euler bulk sound velocities are in agreement with those calculated from the Hugoniot and Griineisen equation of state of Al. The comparison of shear modulus data shows that the corrected SCG model is the best onecapable of describing the variation of the measured shear modulus of Al with shock stress, although the SCG model and the finite strain theory are applicable at lower pressures.(3) Comparative experiments of the one-stepped LY12 Al sample with the two-stepped one shock-loaded by TC4/LY12 Al two-layer flyer were performed at the same stress-loaded levels. Experimental results show that large disparities exist for both experimental situations, indicating that the isentropic reloading assumption is not reliable in the case of one-stepped sample experiments. Two-stepped samples should be used in loading-reloading experiments.(4) The longitudinal sound velocity and shear stress (rc - r0) data in loading-reloading experiments were also obtained. In combination with the shear stress (zc + r0) acquired in loading-unloading experiments, the stress strength of 0.6 GPa at 20.0 GPa shock stress is constrained. Furthermore, the hydrostatic pressure corresponding to the 20.0 GPa shock stress is obtained by taking the strength correction into account.