Experimental study on viscoplastic behavior of SUS 304 stainless steel after axial cyclic preloading

Abstract

Structural materials used in such products as airplanes and pressure vessels in nuclear reactors are usually subjected to cyclic loadings and to abrupt accidental overloadings. An accurate estimate of strength properties of cyclic prestrained materials under accidental overloading can be very useful for the purposes of design safety and cost reduction. In this report, viscoplastic behavior of Type 304 stainless steel after axial cyclic preloading of various types was investigated experimentally at room temperature. The difference between flow stress levels depending on strain rate decreases considerably after cyclic preloading. However, the relaxation stress drop increases rather than decreasing with an increase of flow stress even after cyclic preloading. No consistency in viscoplastic behavior, which is shown by the customary viscoplastic theories, can be found. Plastic modulus Ep depends on the flow stress level for the case of comparatively small cyclic preloading. Ep becomes much smaller and constant after strong cyclic preloading. Thus much larger plastic strain may occur when an abrupt overload is applied. A very strong linear relationship between Ep and plastic work per cycle is found.