Uniaxial Creep, Cyclic Creep and Relaxation of AISI Type 304 Stainless Steel at Room Temperature. An Experimental Study

摘要

A servocontrolled testing machine and strain measurement at the gage length were used to study the uniaxial rate(time)-dependent behavior of AISI Type 304 Stainless Steel at room temperature. The creep strain accumulated in a given period of time depends strongly on the stress rate preceding the creep test. In constant stress rate zero-to-tension loading the creep strain accumulated in a fixed time period at a given stress level is always higher during loading than during unloading. Continued cycling causes an exhaustion of creep ratchetting which depends on the stress rate. Periods of creep and relaxation introduced during completely reversed plastic cycling show that the curved portions of the hysteretic loop exhibit most of the inelasticity. In the straight portions creep and relaxation are small and there exists a region commencing after unloading where the behavior is similar to that at the origin for virgin materials. This region does not extend to zero stress. The results are at variance with creep theory and with viscoplasticity theories which assume that the yield surface expands with the stress. They support the theory of viscoplasticity based on total strain and overstress. (Author)