Inelastic Deformation And Damage At High Temperature Progress Report April 1 1991 March 31 1992

Combined experimental and theoretical investigations into the inelastic deformation and damage behavior of engineering alloys at elevated temperatures are being pursued. The analysis of previously performed strain rate change and relaxation tests on modified 9Cr-1Mo steel showed the need for inclusion of a recovery of state term in the growth laws for the state variables of the viscoplasticity theory based on overstress (VBO). Recovery of state terms were introduced and the experimental results were satisfactorily simulated. The finite deformation theory of VBO has been developed further to include a convected derivative rationale for the choice of the objective stress rate. The reversing direct current voltage drop measurements during low cycle fatigue at elevated temperature were improved. A passive filter bank and new positioning devices for the coils were installed. Tests at 650°C and lasting several days showed excessive, uncontrollable temperature changes. It was decided to drop the test temperature to 538°C which is close to the operating temperature of Type 304 Stainless Steel. The temperature fluctuations in torsion tests were within ±3°C which was considered satisfactory. Testing will continue at 538°C.