A method for evaluating the fatigue crack growth in spiral notch torsion fracture toughness test
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The spiral notch torsion test (SNTT) has been a recent breakthrough in measuring fracture toughness for different materials, including metals, ceramics, concrete, and polymers composites. Due to its high geometry constraint and unique loading condition, SNTT can be used to measure the fracture toughness with smaller specimens without concern of size effects. The application of SNTT to brittle materials has been proved to be successful. The micro-cracks induced by original notches in brittle materials could ensure crack growth in SNTT samples. Therefore, no fatigue pre-cracks are needed. The application of SNTT to the ductile material to generate valid toughness data will require a test sample with sufficient crack length. Fatigue pre-crack growth techniques are employed to introduce sharp crack front into the sample. Previously, only rough calculations were applied to estimate the compliance evolution in the SNTT crack growth process, while accurate quantitative descriptions have never been attempted. This generates an urgent need to understand the crack evolution during the SNTT fracture testing process of ductile materials. The newly developed governing equations for SNTT crack growth estimate are discussed in the paper.
KeywordsSpiral notch torsion test Fracture toughness Fatigue pre-crack
This project is sponsored by US Department of Energy (DOE) and Oak Ridge National Laboratory Seed Money Program, and US Department of Transportation Pipeline and Hazardous Materials Safety Administration (PHMSA) Program. Oak Ridge National Laboratory is managed by UT-Battelle, LLC for the US Department of Energy under Contract DE-AC05-00OR22725.
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