Fatigue hot spot simulation for two Widmanstätten titanium microstructures

Abstract

A simulated microstructure-sensitive fatigue study has been performed for two titanium alloy microstructures. The investigated materials exhibit a Widmanstätten structure and include the α–β alloy Ti–6Al–4V and the near β alloy Ti-18 in a β-annealed, slow-cooled, and aged condition (BASCA). In other work [1], crystal plasticity models implemented into ABAQUS (2011) [2] UserMATerial subroutines have been calibrated to experimental cyclic deformation data for both materials. The current study utilizes calibrated crystal plasticity models to simulate fatigue loading of varying microstructures for each material to study the influence of key morphological and crystallographic aspects on the fatigue performance, e.g., the mean colony size, phase volume fraction, and crystallographic texture. Localized stress and plastic strain are studied via computation of fatigue indicator parameters (FIPs), which represent the driving force for fatigue crack formation and early propagation in the microstructure. The maximum FIP values are sampled over several stochastic simulations and are utilized to determine extreme value statistical distributions which demonstrate the trends in the microstructural influence on fatigue performance. Marked radial correlation functions developed by Przybyla and McDowell [3] have also been employed to study the correlation between favorably oriented slip systems and the extreme value FIP locations within the instantiated microstructures. The simulation results suggest that reduced lamellar colony sizes, reduced α-phase, and a transverse texture within a reference plane normal to the applied uniaxial loading direction can enhance resistance to formation and early growth of fatigue cracks.