CONICET | Buscador de Institutos y Recursos Humanos

THE INFLUENCE OF DYNAMIC STRAIN AGING ON STRESS RELAXATION AND LOW CYCLE FATIGUE BEHAVIOUR OF STAINLESS STEELS Martina Avalos, Iris Alvarez-Armas and Alberto F. Armas Instituto de Física Rosario (IFIR), Bv. 27 de Febrero 210 bis, 2000 Rosario, Argentina The term (DSA), denotes a process of aging that takes place during plastic deformation. Over a particular strain rate and temperature range, the interactions between solute atoms and dislocations result in a strong pinning of dislocations, responsible for strain aging. Higher stress levels are required to produce further straining of the material, either to pull dislocations free from the pinning atoms or to nucleate fresh dislocations. Thus, the main effects of dynamic strain aging on the mechanical properties of materials during cyclic tests are an inverse dependence of the peak tensile stress on strain rate, an unusual increase in cyclic hardening and a serrated flow known as the Portevin-Le Chatelier (PLC) effect. In this investigation it was proposed to perform stress relaxation tests (SRT) as an alternative approach for investigating which elements might be responsible for dynamic strain aging. In stress relaxation tests, the crosshead motion of the testing machine is suddenly stopped during the tensile or compression part of the fatigue hysteresis loop at a desired strain, and the stress is allowed to relax over a period of time. The stress decreases with time, and a relaxation curve is obtained. From the study of the SRT curves, it is possible to estimate parameters characterizing thermal activated processes. Considering that DSA is a phenomenon that affects deformation dynamics, it is reasonable to assume that it affects the dynamics of SRT curves as well as the low-cycle fatigue response. Low-cycle fatigue constitutes a technological problem in structural parts or industrial equipment and it is particularly important at intermediate temperatures. The temperature dependence of low-cycle fatigue is an important aspect for material exposed to service above room temperature. If the regime of temperatures is stated into the DSA temperature range, the influence of DSA on the mechanical behavior of the alloy became an important matter, as well. The aim of this work is to analyzed the dynamic strain aging effects through the stress relaxation tests and study the influence of the DSA on the cyclic behavior of different stainless steels .