Material characterization of duplex stainless steel by superplastic free bulging test
Macroscopic superplastic behaviour of metallic or non metallic materials is usually represented by the strain rate sensitivity, and it can be determined by tensile tests at elevated temperature. However, a uniaixal stress state occurs in the test whilst a multiaixal stress state is induced in actual superplastic forming processes. The difference of the stress state might affect the reliability of the strain rate sensitivity obtained from the tension test. In the current study, the material characterization of duplex stainless steel, UNS S31803, has been carried out to determine the strain rate sensitivity throughout superplastic free bulging test under constant pressure. The measured height of bulged plate during the test was transformed into strain rate and stress corresponding to height at each time by theoretical considerations. The strain rate sensitivities were calculated for each pressure level. After calculating the strain rate sensitivity and strength coefficient for each test case, the flow stress equations have been employed in the finite element simulation to verify the experiments. The bulged height obtained from the simulation showed a reasonable agreement with the experimental findings. In the future, if a study on the effect of fillet radius of test tool and microstructure evolution is carried out, it is thought that the reliability of the material characterization by superplastic free bulging test can be enhanced.
Dimensional analysis of superplastic bulge forming
Abstract Free-Bulge Forming (FBF), due to its simplicity, has been widely used as the main featuring test for superplastic forming (SPF) for a large range of materials. Numerous tests have been performed analytically, experimentally and numerically as a way to determine relevant properties of the material and to characterize the whole process. Nevertheless, the high number of variables involved in a SPF process hampers its analysis. This work applies Dimensional Analysis to reduce the number of variables to facilitate the characterization of SPF processes by analyzing the most relevant dimensionless parameters and developing a broad spectrum model of the FBF as a function of them.
Advanced processing methods for titanium
Among the topics discussed are recent advancements in Ti near-net shape technology, vacuum hot pressing of large, near-net shape spar fittings, Ti alloy sheet forming, superplastic forming/diffusion bonding of Ti alloys, the influence of H additions on the high temperature superplasticity of Ti alloys, the effects of processing on the fatigue life of Ti-6Al-4V castings, and the laser welding of a Ti alloy. Also considered are aspects of speed machining of Ti, the microstructures and mechanical properties of laser-welded Ti alloys, and the failure characteristics of cutting tools for Ti alloy machining at high speeds.