Studies of Fracture in the High Voltage Electron Microscope

Abstract

Experimental techniques for the study of in-situ crack propagation and fracture have been developed for use in the 500 kV electron microscope at the University of Virginia. The investigations are concerned with the problems of defining the mechanism of crack propagation on a microstructural scale and the relationship of thin film vs bulk behavior. By restricting ourselves to ductile fracture, the features to be seen if bulk behavior dominates are necking, shear, and hole formation in front of the propagating cracks.In-situ straining of the specimens was accomplished using a hydraulically loaded tensile stage designed and built for use with one of the radial access ports provided in the microscope.Two types of specimens have been investigated: (i) single crystal ribbons of silver grown from solution using an ionic reduction technique and (ii) annealed polycrystalline sheet stainless steel. The former served primarily for studying the fundamental aspects of ductile fracture while with the latter the influence of grains and grain boundaries on fracture was investigated.