Modelling the nucleation and propagation of cracks at twin boundaries

Abstract

Fracture arising from cracks nucleating and propagating along twin boundaries is commonly observed in metals that exhibit twinning as a plastic deformation mechanism. This phenomenon affects the failure of macroscopic mechanical components, but it is not fully understood. We present simulations in which a continuum model for discrete twins and a cohesive zone model are coupled to aid the understanding of fracture at twin boundaries. The interaction between different twin systems is modelled using a local term that depends on the continuum twin variables. Simulations reveal that the resolved shear stress necessary for an incident twin to propagate through a barrier twin can be up to eight times the resolved shear stress for twin nucleation. Interface elements are used at the interfaces between all bulk elements to simulate arbitrary intragranular cracks. An algorithm to detect twin interfaces is developed and their strength has been calibrated to give good agreement with the experimentally observed fracture path. The elasto-plastic deformation induced by discrete twins is modelled using the crystal plasticity finite element method and the stress induced by twin tips is captured. The tensile stress caused by the tip of an incident twin on a barrier twin is sufficient to nucleate a crack. A typical staircase fracture path, with cracks propagating along the twin interfaces, is reproduced only if the strength of the twin interfaces is decreased to about one-third of the strength of the bulk material. This model can be used to help understand fracture caused by the activation of multiple twin systems in different materials.

Direct Imaging of the Structural and Morphological Evolution of Epitaxial LiCoO2 Films during Charge and Overcharge

“…We also examined an over-delithiated LCO/SRO/STO(001) sample by STEM (Figure S7a). Cracks along the Li-containing planes are observed which appear to preferentially nucleate along the twin-boundary defects, agreeing with previous studies. , As shown in Figure S7b, more thorough phase transition is observed in LCO/SRO/STO(001) which is consistent with the relatively high degree of delithiation (Figure a).…”

Cold dwell behaviour of Ti6Al alloy: Understanding load shedding using digital image correlation and dislocation based crystal plasticity simulations

“…At each time increment ∆t, the increment of the Cauchy stress in the sample reference frame is calculated as [34,35,36,37]:…”

An FFT-based crystal plasticity phase-field model for micromechanical fatigue cracking based on the stored energy density

“…However, these analyses have been so far limited to the use of finite element methods, which are limited in their ability to handle large RVEs [13], and discrete fracture methods such as X-FEM that cannot capture complex cracking conditions (3D, crack branching and coalescence, etc.) [14][15][16]. A step-change in short fatigue crack growth modelling can be achieved by exploiting recent advances in the development of computationally efficient techniques, such as Fast Fourier Transform (FFT)-based methods, and of robust diffuse (phase-field) fracture mechanics models.…”