Crack closure in friction stir weldment using non‐linear model for fatigue crack propagation

Abstract

The fatigue crack propagation in a friction stir‐welded sample has been simulated herein by means of two 3‐dimensional finite element method (FEM)‐based analyses. Numerical simulations of the fatigue crack propagation have been carried out by assuming a residual stress field as a starting condition. Two initial cracks, observed in the real specimen, have been assessed experimentally by performing fatigue tests on the welded sample. Hence, the same cracks have been placed in the corresponding FE model, and then a remote load with boundary conditions has been applied on the welded specimen. The material behaviour of the welded joint has been modelled by means of the Ramberg‐Osgood equation, while the non‐linear Kujawski‐Ellyin (KE) model has been adopted for the fatigue crack propagation under small‐scale yielding (SSY) conditions. Owing to the compressive nature of the residual stress field that acts on a part of the cracked regions, the crack closure phenomenon has also been considered. Then, the original version of the KE law has been modified to fully include the closure effect in the analysis. Later, the crack closure effect has also been assessed in the simulation of fatigue propagation of three cracks. Finally, an investigation of the fracture process zone (FPZ) extension as well as the cyclic plastic zone (CPZ) and monotonic plastic zone (MPZ) extensions have been assessed.

Ductile fracture locus identification using mesoscale critical equivalent plastic strain

“…The results showed that the maximum MCEPS contributes to a better prediction compared to the homogenized MCEPS. Noted that further validation with different values of stress triaxiality and Lode parameter is recommended. Further research is needed: (i) comparing the identified fracture strain exposed to multiaxial stress status with different uncoupled damage models, (ii) investigating the void number and positions effects on the identified fracture strain and (iii) using the proposed failure index to predict the ductile fracture of additively manufactured materials 42,43 and welded joints 44,45 …”

Non‐linear fatigue propagation of multiple cracks in an aluminium metal matrix composite (AlMMC) with silicon‐carbide fibre reinforcement

“…In doing so, three cracks have been introduced into the MMC sample simulating the fatigue cracks propagation by means of both linear, ie, the Paris law, and non‐linear, namely, the modified Kujawski‐Ellyin (KE) or UniGrow laws. Non‐linear models for fracture mechanics can also assess the fatigue damage both at microstructural and macrostructural levels, which are based on the estimate of the energy release rate (ERR) for the prediction of fatigue crack propagation …”

“…Non-linear models for fracture mechanics can also assess the fatigue damage both at microstructural and macrostructural levels, which are based on the estimate of the energy release rate (ERR) for the prediction of fatigue crack propagation. [5][6][7][8]…”

Fatigue assessment of high strength welded joints through the strain energy density method

“…On the other hand, the so‐called local approaches allow a more realistic evaluation of the expected fatigue life 10–16 . In particular, among them, the authors consider in the present work the strain energy density (SED) method that, unlike other local approaches, like the notch stress intensity factor (NSIF) method, that allows to estimate the failure modes like, for example, weld root failure or weld toe failure 17 .…”