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Crack Growth Resistance Curves and Measures of Fracture Toughness
Published in Ashok Saxena, Advanced Fracture Mechanics and Structural Integrity, 2019
The objective of the procedure is to apply load to a fatigue precracked, standard specimen of one of several geometries to obtain one or both of the following responses: (a) unstable crack extension, including significant “pop-in,” resulting in instability in the specimen; (b) stable crack extension or ductile tearing. As mentioned earlier, fracture instability without significant stable crack extension results in a single fracture toughness value determined at the point of instability. Stable tearing results in a crack growth resistance curve, also called the R-curve (or JR-curve) from which the fracture parameters can be determined. The load and load–point displacements are continuously measured during the test. For developing the R-curve, it is also necessary to obtain periodic measurements of crack length. The load, load–point displacement, and crack size data along with specimen geometry and size information are used to obtain the R-curve. Prior to discussing the details of data analysis, some additional experimental details about the methods are provided.
A new approach for evaluating crack growth resistance curve of mode II delamination by doubly end-notched tension tests
Published in Advanced Composite Materials, 2018
Shigeki Yashiro, Toshihide Agata, Akinori Yoshimura
This study proposed and demonstrated doubly end-notched tension (DENT) tests that realized growth of pure mode II delamination as observed in a double-lap joint. A corresponding shear-lag analysis was also presented to evaluate the mode II energy release rate. This theory indicated that the energy release rate in the DENT specimen is constant. Therefore, this test method achieved stable growth of the mode II delamination by a simple tensile test, and enabled us to measure the mode II interlaminar fracture toughness in the crack growing stage, i.e. the crack growth resistance curve. The conclusions are summarized below.Two mode II cracks grew stably in the doubly end-notched tension specimens under quasi-static tensile loading with displacement-controlled condition.The initial fracture toughness GIIC measured by the present method agreed with the result of the conventional ENF test. Almost identical GIIC was obtained by different initial crack lengths. These results confirmed the validity of the DENT test and the corresponding shear-lag analysis.The mode II fracture toughness in the crack growing stage, GIIR, was successfully obtained by unloading-reloading tests.