Limited weld residual stress measurements in fatigue crack propagation: Part II. FEM‐based fatigue crack propagation with complete residual stress fields

Abstract

A B S T R A C T Using a limited set of residual stress measurements acquired by neutron diffraction and an equilibrium-based, weighted least square algorithm to reconstruct the complete residual stress tensor field from the measured residual stress data, the effect of weld residual stress on fatigue crack propagation is investigated for 2024-T351 aluminium alloy plate joined by friction stir welding. Through incorporation of the least squares, complete equilibrated residual stress field into a finite element model of the Friction Stir Weld (FSW) region, progressive crack growth along a direction perpendicular to the welding line is simulated as part of the analysis. Both the residual stress redistribution and the stress intensity factor due to the residual stress field, K res , are calculated during the crack extension process.Results show that (a) incorporation of the complete, self-equilibrated residual stress field into a finite element (FE) model of the specimen provides a robust, hybrid approach for assessing the importance of residual stress on fatigue crack propagation, (b) the calculated stress-intensity factor due to the residual stress field, K res , has the same trend as measured experimentally by the 'cut-compliance method' and (c) the da/dN results are readily explained with reference to the effect of the residual stress field on the applied stress intensity factor.

Influence of foreign object damage on fatigue crack growth of gas turbine aerofoils under complex loading conditions

“…The initial steady‐state residual stresses associated with FOD may not persist because of the potential relaxation or redistribution during subsequent fatigue loading and/or crack extension. The magnitude and rate of relaxation have been found to be dependent on the initial residual stress, applied loads and FOD‐induced stress concentration 6,33 . The stress relaxation is typically associated with the reordering of dislocations and the occurrence of cyclic softening, that is reduction in the flow stress during cyclic loading.…”

“…The magnitude and rate of relaxation have been found to be dependent on the initial residual stress, applied loads and FOD-induced stress concentration. 6,33 The stress relaxation is typically associated with the reordering of dislocations and the occurrence of cyclic softening, that is reduction in the flow stress during cyclic loading. In addition, upon the formation of a fatigue crack, the relaxation can further increase due to the stress-concentration effect and plasticity associated with the crack.…”

Recent advances in friction-stir welding – Process, weldment structure and properties

“…This is an important finding and can be used by welders as a guiding principle to produce high-quality welds. Not surprisingly, crack propagation rates are known to correlate strongly with the state of stress [141].…”

A modified loading method for separating the effect of residual stress on fatigue crack growth rate of welded joints

“…In these methods, FCGR data obtained by laboratory specimen tests are adopted for the life prediction of components based on the theory of linear elastic fracture mechanics (LEFM). Significant amount of research has been conducted in the past 20 years to understand the crack growth behaviours in welded joints . Some works indicate that changes in microstructure and hardness play a major role in the fusion zone or weld nugget and residual stress plays a major role outside these zones .…”

“…Significant amount of research has been conducted in the past 20 years to understand the crack growth behaviours in welded joints. [4][5][6][7][8][9][10][11][12][13] Some works indicate that changes in microstructure and hardness play a major role in the fusion zone or weld nugget and residual stress plays a major role outside these zones. 10,13 Therefore, it is a common practice that only the primary influential factor is considered in crack growth analysis of welds; e.g.…”