Plastic Wave Propagation in Hopkinson Bar
The focus of this chapter (cf. [MB-02]) is an analysis of the experimental Hopkinson bar technique when such a device consists of a short tensile or shearing specimen surrounded by two very long elastic bars (explained in detail in [AM-79]). Unlike commonly applied bypass analysis which attempts to draw conclusions from behaviour of elastic bars, an attempt is made to take into account real plastic waves inside the specimen with a few hundred reflections. A quasi-rate-independent tensor function model for AISI 316H calibrated in [Mic97] is applied in its simplest yet nonlinear version. Some special slightly perturbed elastic incident and reflected waves in elastic bars serve here to simulate starting solutions. The numerical results show a good agreement with experimentally observed homogeneous strain state throughout the specimen during the process. Lindholm’s procedure for finding specimen stress and strain by such a bypass procedure is criticized. An iterative procedure aimed to improve such a procedure is briefly discussed. In this chapter, we wish to revisit standard techniques for analysis of the Hopkinson bar testing technique taking into account plastic wave propagation inside the standard (extremely short) tension specimen as well as elastic waves propagating along the very long incident-reflected wave bar as well as the transmitted wave bar. The strains inside the specimen are large up to 60%. The evolution equation for plastic stretching tensor as calibrated in [Mic97] on the basis of experiments performed in the dynamic testing laboratory of JRC-Ispra, Italy ([AM-79, AMP91, AMM91]) is applied. The tests have been performed using classical tension specimen as well as bicchierrino shear specimen1 made of austenitic stainless steel AISI 316H in the range of strain rates [10 -3, 103]s -1.
KeywordsPlastic Strain Stress Rate Equivalent Plastic Strain Initial Yield Stress Deformation Gradient Tensor
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