A mechanics based study of crack closure measurement techniques under constant amplitude loading

An elastic–plastic finite element model was used to simulate a growing fatigue crack in a middle-crack tension specimen made of an aluminum alloy. The finite element analysis provided the load–displacement curve at various locations as is commonly done in experimental work, and the crack opening stress intensity factor (Kop) was determined with ASTM standard methods, Elber’s method, and the Adjusted Compliance Ratio (ACR) method. The performance of ACR was compared against the established standard methods. Measurement location effects on Kop and ACR were investigated. ASTM (2% offset) and ACR methods gave values that were dependent upon measurement location. Whereas, Elber’s method (0% offset) gave values that were independent of measurement location.