Crystal plasticity FE study of the effect of thermo-mechanical loading on fatigue crack nucleation in titanium alloys D. OZTURK, A. SHAHBA and S. GHOSH Department of Civil Engineering, Johns Hopkins University, Baltimore, MD , USA Received Date: 29 October 2015; Accepted Date: 13 January 2016; Published Online: 19 February 2016 ABSTRACT In this paper, crystal plasticity simulations are conducted with a stabilized finite deformation finite element model to study the effects of microstructure as well as thermal and mechan- ical loading conditions on fatigue crack nucleation of Ti alloys. The crystal plasticity model includes a non-local crack nucleation model. Results of simulations are used to understand the effects of dwell loading periods and microtexture on fatigue nucleation life in polycrys- talline microstructures in comparison with experiments. From the thermo-mechanical studies of these alloys, it is found that anisotropic thermal expansion under thermal loading can induce stresses normal to the basal plane, which can help opening up microcracks. Moreover, in agreement with experimental results, the simulations show diminished load shedding at elevated temperature because of weakening of plastic anisotropy. Keywords crack nucleation; crystal plasticity model; dwell fatigue loading; load shedding; microtexture; thermal stress. NOMENCLATURE A i Surface area of grain i A ij Common surface area between grains i and j B, B Crack opening displacement vector and magnitude b α Burgers vector B CF Closure failure of Burgers circuit c Equilibrium crack length C,[C ij ] Fourth-order and Voigt representation of elasticity tensor E e Elastic Green–Lagrange strain tensor F Total deformation gradient F e , F θ , F p Elastic, thermal and inelastic components of deformation gradient g α Slip system resistance G α Shear modulus K c , K mix , K n , K t Critical, mixed, normal and shear intensity factors m Material rate sensitivity MI < c > axis misorientation index m α 0 Slip direction N nucl Number of cycles to crack nucleation n slip Total number of slip systems n b Normal to crack surface n α 0 Slip plane normal Q α Activation energy R Crack nucleation parameter S Second Piola–Kirchhoff stress tensor α Tensor containing thermal expansion coefficients β Ratio of shear to normal fracture toughness :γ α Plastic slip rate on slip system α γ s Surface energy θ Temperature Correspondence: S. Ghosh. E-mail: [email protected] © 2016 Wiley Publishing Ltd. Fatigue Fract Engng Mater Struct, 2016, 39, 752–769 752 SPECIAL ISSUE CONTRIBUTION doi: 10.1111/ffe.12410
Crystal plasticity FE study of the effect of thermo-mechanical loading on fatigue crack nucleation in titanium alloys
Jun 14, 2023
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