Application of the coupled stress-energy criterion to predict the fracture behaviour of layered ceramics designed with internal compressive stresses

Abstract

International audienceOne novel approach to improve the apparent toughness of ceramics is to design a multilayer architecture with embedded layers having compressive residual stresses. Surface cracks propagating during mechanical loading can be deflected within the compressive layers, in order to delay the final fracture of the whole structure. The design of high toughness laminates requires understanding the effect of residual stresses on the initiation and propagation of cracks in the material. In this work, a coupled stress-energy criterion is used to predict the initiation and propagation of surface cracks in ceramic laminates upon thermo-mechanical loading. Experiments were conducted on V-notched alumina-based laminates to show the effect of residual stresses and mechanical loading on their fracture behavior. The conditions for crack initiation as predicted for notched specimens agreed with the experimental observations. It is shown that the onset of cracks from V-notches is associated with (i) the tensile residual stresses in the first surface layer and (ii) the depth of the notch. The further propagation of the crack into the first embedded compressive layer was also studied. Based upon the coupled criterion, a short penetration of the propagating crack into the first compressive is foreseen. If the mechanical load is increased, the crack finally deflects within the compressive layer propagating with a certain angle which is also predicted with a good accuracy

Crack nucleation in hyperelastic adhesive bonds

“…Finite fracture mechanics has proved to be a qualified model for brittle structural failure. The coupled criterion was shown to accurately describe fracture events at a variety of singular (adhesive lap joints [10], composite laminates [11], layered ceramics [12]) and nonsingular (rounded notches [13], circular and elliptical [14] open-holes, crack patterns [15]) stress concentrations. A comprehensive review of the method and its applications is given by Weißgraeber et al [16].…”

Prediction of the surface cracking pattern of an oxidized polymer induced by residual and bending stresses

“…Predicting the nucleation of the first crack, leading to an abrupt failure or not, can also be done by performing an exact simulation of the 4-point bending test (Figure 3) and applying the CC to the entire structure as done for instance in (Leguillon et al, 2015b). A summary of the results is proposed in the following Table 5.…”

High temperature mechanical behavior of porous ceria and ceria‐based solid‐oxide fuel cells

“…Additionally, SEM analysis of the fractured half‐cells showed very good adhesion between layers (Figure ). Delamination is a common failure mode in layered ceramics and one that would be particularly damaging to SOFCs due to resulting ionic conductivity loss between layers . In the half‐cell coupons, it was clear that the fracture plane contained mixed transgranular and intergranular fracture.…”

“…conductivity loss between layers. 22,23 In the half-cell coupons, it was clear that the fracture plane contained mixed transgranular and intergranular fracture. Some grains were sheared through while others remained whole.…”