A new technique for viewing deformation zones at crack tips

A new technique has been developed to examine and view the deformation zone that occurs at a crack tip during loading. The technique, referred to as the “image-distortion technique”, is based on the optical distortion that results on a highly polished surface ahead of a crack when it is strained. The “image distortion” is a direct result of the thickness change occurring at the crack tip. While the technique was developed using monotonic loading, it is believed that it also will be applicable to cyclic-loading crack-tip studies. Additional studies are underway that will yield strain fields at the crack tip from the observed images of the deformation zones.