A model study of cavity growth in superplasticity using single premachined holes

Abstract

Experiments were conducted on a superplastic copper alloy to investigate the growth of single holes machined in the gage length prior to testing. Specimens were deformed in tension in the three regions of flow associated with superplastic materials. Within each flow region, three distinct stages of hole growth were identified. Initially, in stage 1, the hole simultaneously increases in length along the tensile axis but decreases in the dimension measured perpendicular to the tensile axis ("transverse contraction"). Subsequently, in stage 2, the hole grows both along and perpendicular to the tensile axis ("transverse growth"). Finally, in stage 3, a crack nucleates on either side of the hole and propagates to cause failure ("crack propagation"). It is shown that the transitions between the different stages of growth is dependent upon the initiation and development of macroscopic necking adjacent to the hole.