Study on metal instability using stress wave propagation technique

This thesis aims to investigate the necking phenomenon in the metal samples in response to the loading speed. Several experiments with three repetitions were conducted in order to investigate the loading speed on the mechanical behavior of the samples. Two different kinds of steel (i.e. DKP and stainless steel 304) were utilized with two different thicknesses as 1 and 2 mm, respectively. Dimensions used in the manufacture of the samples, which would be tensile tested in different strain rates, were chosen according to ASTM-E8. Numerical simulations and validation procedure were conducted in a commercial finite element package, ABAQUS/Explicit. Validated finite element processes were used to expand the domain of the study to predict the location of the necking in the samples under various loading rates. Stress analyses were performed to investigate the stress propagation inside the samples along with the strain propagation values to determine the onset of necking. Several load-displacement diagrams were plotted to indicate the changes in loading history of the samples in different loading rates. Theoretical backgrounds and the formulation for the necking phenomenon and stress wave propagation, were also studied. It was found out that the stress propagation technique is more powerful than other prevalent techniques. The advantage of the method is its capability in the simulation of necking and the prediction of its location in the samples under high rate loading. It can also consider the transition from dimple failure to slip failure obtained from post-necking investigations.