3D Grain-Based Mesoscale Modeling of Short Fatigue Crack Growth for Bridge Weldments Considering Crack-Front Evolution

Abstract

To evaluate short crack growth and fatigue damage accumulation in steel structures, efforts have been made based on a two-dimensional (2D) grain-based model for fatigue life assessment under variable amplitude loads. However, crack arrested in a 2D field could be problematic since the arrested 2D crack might propagate toward the out-of-plane direction. In addition, the pure plane stress/plain assumption in 2D simulation could not be applied to many complex stress states. In this paper, a three-dimensional (3D) fatigue damage estimation model is proposed based on a twofold nonlinear grain-based fatigue life assessment method. The persistent slip band based short fatigue crack growth model is implemented in this model combined with Miner’s rule for grain fatigue accumulation evaluations. Rain-flow counting method and the linear damage rule in grains are employed for fatigue damage growth within each grain. Meanwhile, in the grain and subgrain regime, the crack is assumed to nucleate and grow along with persistent slip bands. Also, an adjacent persistent slip band detection algorithm is developed to locate the potential crack propagation path. Therefore, fatigue damage is calculated grain by grain until the crack length reaches the characteristic length (such as over 0.1 mm), where linear elastic fracture mechanics (LEFM) thoery becomes more reliable. Sensitivity analysis is conducted for the number of grains and the element size in statistical volume element model under constant amplitude loads. Finally, a case study is performed to demonstrate the proposed method for variable amplitude loads, and the results are compared with the 2D model results in the literature.