Crack Characterization

Abstract

Although cracks in structural components are, in general, highly undesirable, not all of them are detrimental to the life of the structure. To determine precisely how detrimental the crack actually is, one must characterize several crack parameters, particularly the location, size, shape, and orientation with respect to the applied stress. With these parameters and the magnitude of the applied stress, the driving force on the crack can be calculated by determining the stress intensity factor K or the stress intensity range ΔK. Most inspections today are performed in a scanning mode. If indications of some anomaly appear, the inspection is concentrated on these locations; and, if the response verifies the presence of a flaw, the size, shape, orientation of the flaw and the potential for future growth of the flaws are determined. This process is now termed “quantitative nondestructive evaluation” (QNDE).This short review is devoted to recent advances in the characterization of cracks in various stages of development. The increase in sophistication in instrumentation and the use of computers for data analysis and interpretation has been dramatic and will certainly continue.In the laboratory, compliance gauges and electrical potential drop methods are now extensively used for crack length and shape measurements. Acoustic methods are being widely used in industry as nondestructive testing and evaluation tools because they are relatively easy to apply to real structures.