Numerical determination of plastic CTOD

Abstract

In previous works, a da/dN versus plastic crack tip opening displacement model was proposed to study fatigue crack growth. The plastic crack tip opening displacement, δp, which quantifies the crack tip plastic deformation, is determined numerically using the finite element method. The predictions are affected by different numerical parameters which must be identified and studied. The main parameters are the crack propagation distance, the distance of measurement points relatively to the crack tip, the size of crack tip elements, and the number of load cycles between crack increments. Some crack propagation is required for the stabilization of δp, which occurs when δp reaches its minimum value. The measurement point behind crack tip has a major effect on δp. The peak value occurs at the first node behind crack tip and a progressive decrease of sensitivity is observed with the increase of distance to crack tip. A mesh refinement study showed a coincidence of the predictions obtained with different meshes, which is a good indication for the robustness of the procedure. Finally, there is a significant effect of the number of load cycles between crack increments, NLC, in the presence of crack closure. The increase of NLC reduces the crack opening level and so increases δp.

A Literature Review of Incorporating Crack Tip Plasticity into Fatigue Crack Growth Models

“…To talk about numerical models of crack growth and their relation to plastic phenomena in the crack tip environment is to talk about Fernando Antunes. Building on the discrete approach by Pokluda [66], Antunes [67] presents an elasto-plastic numerical model, which provides a different perspective by excluding the contact between the crack flanks, thereby focusing on the relationship between CTOD, plastic phenomena at the crack tip, and crack growth rate. The work [67] presents an elasto-plastic numerical model where On a similar note, Zhang [63] developed a fatigue crack propagation model emphasising the effect of compressive stress, thereby adding another dimension to the understanding of fatigue crack growth under tension-compression loading.…”

“…Building on the discrete approach by Pokluda [66], Antunes [67] presents an elasto-plastic numerical model, which provides a different perspective by excluding the contact between the crack flanks, thereby focusing on the relationship between CTOD, plastic phenomena at the crack tip, and crack growth rate. The work [67] presents an elasto-plastic numerical model where On a similar note, Zhang [63] developed a fatigue crack propagation model emphasising the effect of compressive stress, thereby adding another dimension to the understanding of fatigue crack growth under tension-compression loading. The stress near the crack tip, the displacement, and the size of the plastic zone were obtained from a kinematically hardened material.…”

“…Building on the discrete approach by Pokluda [66], Antunes [67] presents an elasto-plastic numerical model, which provides a different perspective by excluding the contact between the crack flanks, thereby focusing on the relationship between CTOD, plastic phenomena at the crack tip, and crack growth rate. The work [67] presents an elasto-plastic numerical model where the contact between the crack flanks is obviated. In all simulations, the CTOD and CTOD P were measured.…”

“…In plane strain, the higher the number of cycles, the lower the CTOD P , unlike in plane deformation. In [67], the methodology for the calculation of the CTOD P in numerical tests is established in detail, as well as the parameters that will affect this calculation, such as the crack propagation distance, the size of the crack, the distance of the points with respect to the edge, the size of the elements, and the number of previous cycles. The mesh size and the software used are those mentioned earlier in Antunes' work.…”

Analysis of biaxial proportional low-cycle fatigue crack propagation for hull inclined-crack plate based on accumulative plasticity

“…It was observed that the plastic-induced crack closure has a substantial influence on the delay effect of fatigue load. Antunes [7] used the finite element method to determine the plastic CTOD values under the action of different crack increments, including different crack tip mesh sizes and different loading cycles in the numerical method. In recent years, the research based on 3D-DIC of CTOD has advanced rapidly with the development of digital image correlation technology.…”