High Strain Rate Thermo-Inelasticity of Damaged AISI 316H

Abstract

Two groups of AISI 316 H specimens, previously subjected either to creep or low cycle fatigue, are examined by tension at 550 C in the strain-rate range 1/210 3,103 s1. The specimens previously treated by creep suffered various levels of creep strains while the specimens predamaged by LCF had various LCF strain critical cycle numbers (as a measure of initial life time). A third group of virgin specimens was tested in the same strain rate range but at diverse room temperatures from 20 to 550 C. First dissipation function is determined and then some memory type unified evolution equations are analyzed and calibrated for as-received, creep-damaged and LCF-damaged specimens, covering stress, strain, strain rate and temperature relations and accounting for strain and strain-rate hardening. The material constants entering the equations are damage-dependent. Comparisons with some empirical and microstructural models are made. Our analysis based on modeling and experimental data is compared with Lemaitre's strain equivalence principle. Standard damage mechanics models are then matched with effective field homogenization method.