Dynamic mechanical properties and fracture behavior of a 304L stainless steel GTAW joint under shear conditions

This paper employs the torsional split-Hopkinson bar to investigate the dynamic shear deformation behavior and fracture characteristics of a 304L stainless steel Gas Tungsten Arc Welded (GTAW) joint at room temperature under strain rates in the range of 8 x 10(2) s(-1) I to 2.8 x 10(3) s(-1). The experimental results indicate that the strain rate has a significant influence on the mechanical properties and fracture response of the tested GTAW joints. It is found that the flow stress, total shear strain to failure, work hardening exponent and strain rate sensitivity all increase with increasing strain rate, but that the activation volume decreases. The observed dynamic shear deformation behavior is modeled using the Kobayashi-Dodd constitutive law, and it is shown that the predicted results are in good agreement with the experimental data. Observation of the fractured specimens indicates that the fracture features are closely related to the preceding flow behavior. At all values of strain rate, it is noted that the specimens all fracture within their fusion zones, and that the primary failure mechanism is one of extensive localized shearing. The fracture surfaces are characterized by the presence of many dimples, which suggests a ductile fracture mode. It is shown the strain rate has a significant influence upon the appearance of the dimpled surface. A higher strain rate tends to reduce the size of the dimples and to increase their density. Finally, it is determined that the presence of weld inclusions also influences the appearance of the fracture. These inclusions cause the initiation of micro-voids, which grow and coalesce within the fusion zone, and eventually form a continuous fracture surface.