Dynamic Strength of Materials

Abstract

The methods used in practice for the acquisition and interpretation of experimental data pertaining to the resistance of materials to plastic-strain (shearstrength) are based on the concepts of the nature of motion of a material possessing strength and the features of high-rate deformation discussed in Chap. 1. These methods are briefly described below. Additional information on this topic is available to the reader in monographs [1-3], review [4], and the original papers cited in [1-4]. Comparison between the Shock Hugoniot and the Hydrostatic Compression IsothermGiven two assumptions: (1) material strength is isotropic, and (2) the difference between isothermal hydrostatic compression and the mean stress σ ii /3 is small, the dynamic yield strength is calculated to be the difference between the stress σ 1 on the elastic-plastic shock Hugoniot and the pressure P on the hydrostatic compression isotherm (given in terms of specific volume V (or strain ε)) as Y d = 3(σ 1 − P )/2. This approach to the estimation of Y d is limited to cases wherein the stresses σ 1 are relatively low, and the temperature rise during shock compression is modest (resulting in a thermal component of pressure that is low in comparison to the total pressure).For the aluminum alloy Al-2024, [5] recommends that for shock pressures in the 2.7 GPa ≤ σ 1 ≤ 9.4 GPa range, one should use the following relations for σ 1 (ε) (the normal stress component in a plane wave shock) and P (ε) (the hydrostatic compression) in calculations of the dynamic yield strength: σ 1 = 0.18 + 72.06ε − 347.1ε 2 (GPa); P = 75.9ε + 201ε 2 (GPa). This method for the evaluation of Y d , among other things, requires a highly accurate determination of the curves σ 1 (ε) and P (ε) since minor changes in ε can lead to significant changes in σ 1 and P .