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.
Superplastic forming: an analytical approach
Abstract Gas pressure forming is the most common and widely practiced method of evaluating practical superplastic forming characteristics. In order to carry out the forming operation under constant strain-rate conditions, a mathematical model is necessary to govern the pressure-time path. In the present analysis, a simple and straightforward equation has been developed relating the required gas pressure to the material parameters such as flow stress, strain rate, and also the sheet and die geometries. Another equation has been derived to predict the thickness variations between the pole and the equator of a hemisphere. The effectiveness of these equations has been validated by monitoring the progress of forming at the different stages of blowing Ti6.5Al3.3Mo1.6Zr alloy hemispheres and thereby measuring the radii of curvature and thicknesses at pole and equator.
Testing digital circuits using a Mixed-Signal Automatic Test Equipment
This paper presents the results of parametric testing of digital ICs using a dedicated Mixed Signal Automatic Testing Equipment. Due to the prohibitive price of the ATE equipment and dedicated Device Interface Board (DIB) for digital Integrated Circuits (ICs), a DIB for analog circuits was used to perform the testing. Despite the challenges presented by the experiments, the results prove to be accurate for the performed tests, according to the data sheet of the digital ICs and production test data provided by the manufacturer.