A Computational Fatigue Indicator Parameter for Crack Incubation Prediction in A Nickel Titanium Alloy
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ABSTRACT Damage metrics (such as fatigue indicator parameters) can be computational tools for materials design against fatigue and fracture and are useful in ranking deleterious microstructural features when designing engineering alloys. However, several studies (notably [1]) show mixed accuracy in predicting crack locations. This study addresses such a parameter for a nickel titanium alloy (often used in biomedical devices). Through a combination of high energy diffraction microscopy and micro-tomography, the stress, strain, and grain morphology of a nickel titanium alloy under fatigue loading is demonstrated. Using these results, a grain-level calibration of a crystal plasticity model is performed. The role of super-elastic deformation is also addressed. This calibrated model is used to simulate cyclic loading and demonstrate a fatigue indicator parameter that properly correlates to the measured crack location. This approach uses non-local fatigue indicator parameter averaging [2] for increased accuracy and shows that grain morphology augments the mechanical state values traditionally considered to drive of crack nucleation. REFERENCES [1] H. Hallberg, S. K. As, B. Skallerud, Crystal plasticity modeling of microstructure influence on fatigue crack initiation in extruded Al6082-T6 with surface irregularities, International Journal of Fatigue 111 (2018) 16–32. [2] John A. Moore, Caitlin Martinez , Ayushi Chandel, A Nonconformal Nonlocal Approach to Calculating Statistical Spread in Fatigue Indicator Parameters for Polycrystals, Fatigue & Fracture of Engineering Materials & Structures 2023; 46:4801–4806, (http://doi.org/10.1111/ffe.14158).
