A Combined Experimental and Modelling Approach to Elastic–Plastic Crack Driving Force Calculation in the Presence of Residual Stresses

Abstract

Since all residual stress measurement methods have inherent limitations, it is normally impractical to completely characterise a three-dimensional residual stress field by experimental means. This lack of complete information makes it difficult to incorporate measured residual stress data into the analysis of elastic-plastic fracture without resorting to simplified methods such as the Failure Assessment Diagram (FAD) approach. We propose a technique in which the complete residual stress field is reconstructed from measurements and used in finite element analysis of the fracture process. Residual elastic strains and stresses in three-point bend fracture specimens were measured using neutron diffraction and an iterative method was used to generate a self-consistent estimate of the complete residual stress field. This enabled calculation of the J contour integral for a specimen acted on by both residual stress and an externally-applied load, allowing the interaction between residual and applied stress to be observed in detail.

Mixed‐mode brittle fracture test of polymethylmethacrylate with a new specimen

“…Five concentric contours around the crack tip were used to determine the fracture parameters, and then the values from middle three contours were used to obtain the mean parameters since no significant domain-dependence was observed in brittle model. 33 The calculated SIFs and T-stress were then substituted into Equations 1 and 2 to obtain the dimensionless parameters Y I , Y II and T * as a function of 2a/W, D/W and β. The model used plane stress conditions in this research because the fracture coefficients are independent of the plane stress or plane strain state.…”

“…The SIFs and T‐stress were obtained from the stress and strain fields calculated by Abaqus utilizing the contour integral method. Five concentric contours around the crack tip were used to determine the fracture parameters, and then the values from middle three contours were used to obtain the mean parameters since no significant domain‐dependence was observed in brittle model 33 . The calculated SIFs and T‐stress were then substituted into Equations 1 and 2 to obtain the dimensionless parameters Y I , Y II and T * as a function of 2 a / W , D / W and β .…”

Investigating the influence of residual stresses on fatigue crack growth for additively manufactured titanium alloy Ti6Al4V by using peridynamics

“…The current numerical model assumes that the material is linearly elastic, and the effects of the residual stresses due to the temperature distribution and the applied stresses due to the tension loading are superimposed. The following assumption is not an absolutely accurate criterion as the existence of the residual stresses effects on the crack tip stress field and when the sample is loaded, the distribution of plastic strain in the crack tip field occurs [30]. The non-uniform distribution of the residual stresses in the AM structures [6][7][8] and the internally self-equilibrating stresses due to the crack initiation complicates the prediction of FCGR.…”

The Effects of Residual Stress on Elastic-Plastic Fracture: Two Diffraction Studies

“…However, there has been little experimental work on this topic due to the difficulty involved in measuring the complex stress fields which occur close to a crack tip. We performed two experiments to observe these stress fields and, using this data in conjunction with finite element analysis, investigated the effect of residual stress on the mechanism of elastic-plastic fracture [5], [6].…”