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Failure of man-made structures and machine components becomes eminent when they exceed their useful life. Such incidents, however, can be annoying and costly when they involve substantial financial loss and human lives. The post World War II period was an era when large size structures such as passenger air transports, ships, storage tanks, pipelines, etc, were fracturing unexpectedly for no obvious reasons at the time. Crashing of jet transports alerted the FAA to withdraw certification, pipelines failed by rapid crack propagation for kilometers and oil tankers splitted in two were certainly indicative of the lack of fundamental understanding of how to built fail-safe structures. In retrospect, it can be said that the traditional approach of material testing of the 18th century was inadequate for the design and fabrication of large size structures with high constraint and/or high strength metal alloys. New approaches were needed to determine the conditions when material, geometry and loading rate could combine into a state of “brittleness” where a structure can fail with explosion-like speed and no warning. The feeling was that crack-like defects had to be considered as a potential source of failure initiation.