Numerical modelling of crack shielding and deflection in a multi-layered material system

Fatigue crack shielding and deflection in plain bearings under large-scale yielding

“…The shielding and amplification trends observed are consistent with those reported in similar previous investigations based on J-integral estimates of systems with principally plastic [7] but also elastic [10] mismatch. The amplification effect is noted when the crack approaches the more compliant interlayer, and shielding when the crack approaches the stiffer backing within the interlayer.…”

“…In a scenario where crack bifurcation and deflection is not present, it is clear that bi-layer architectures and the associated shielding effect would retard crack growth to a great extent. However, it has been shown experimentally and numerically [10,21] that as the crack approaches a stiffer interface, the tendency to deflect or bifurcate grows despite the absence of mixed-mode loading. In the context of bearing design, it should be noted that mixed-mode and variable amplitude loading is present in such components promoting crack deflection and bifurcation.…”

“…Although the J integral can be estimated so that it also represents local conditions [5,7,8,10], it is generally adopted as a global measure and as such, it requires a more intricate implementation in the case of bi-materials under large scale yielding. The CTOD is also theoretically better suited for characterizing cyclic loading in the context of a fatigue crack propagation law and was here obtained as the relative displacement of two nodes placed at the two ends of the blunted tip semi-circle.…”

“…As the crack length a is extended, this angle increases up to a value of 55º. According to Joyce et al [10], the kink angle corresponding to the maximum CDF, represented by the J-integral, reached the value of 90º. Using CTOD as an initial deflection indicator did not lead to path deflections of such a magnitude.…”

“…Crack shielding has been shown to cause deflection and bifurcation in such specimens despite the absence of far-field mixed-mode loading [10,11], as shown in Figure 2(a). J integral estimations based on finite element modeling of the three-point bending tests [10] reported a strong tendency for highly deflected bifurcated crack paths, corresponding to a sharply increasing J integral, representing the crack driving force as the crack tip approaches a stiffer layer. This was in accordance with experimental results and explained in terms of the crack following the path that offers the least resistance or maximizes the CDF.…”