Comparison between cohesive zone models and a coupled criterion for prediction of edge debonding

International audienceThe onset of edge debonding within a bonded specimen submitted to bending is modeled with two numerical approaches: the coupled criterion and the cohesive zone model. The comparison of the results obtained with the both approaches evidences that (i) the prediction of edge debonding strongly depends on the shape of the cohesive law and (ii) the trapezoidal cohesive law is the most relevant model to predict the edge debonding as compared with the coupled criterion

Mode II loading in sharp V-notched components: a comparison among some recent criteria for brittle fracture assessment

Abstract Different criteria are available in the literature to assess the fracture behaviour of sharp V-notches. A typical and well-known criterion is based on the application of the notch stress intensity factors (NSIFs), which are able to quantify the intensity of the stress fields ahead of the notch tip. This work considers two recent energy-based criteria applied here to sharp V-notches. The first criterion is based on the averaged value of the strain energy density (SED), while the second one called Finite Fracture Mechanics (FFM) criterion is available under two different formulations: that by Leguillon et al. and that by Carpinteri et al. Considering the averaged SED criterion, a new expression for estimating the control radius R c under pure Mode II loading is proposed and compared with the sound expression valid under pure Mode I loading. With reference to pure Mode II loading the critical NSIF at failure can be expressed as a function of the V-notch opening angle. By adopting the three criteria considered here the expressions for the NSIFs are derived and compared. After all, the approaches are employed considering sharp V-notched brittle components under in-plane shear loading, in order to investigate the capability of each approach for the fracture assessment. With this aim a bulk of experimental data taken from the literature is used for the comparison

Prise en compte des contraintes résiduelles dans un critère de rupture fragile

On étudie la fissuration, sous chargement mécanique et thermique, d'un joint de colle reliant deux substrats d'aluminium. Les extrémités des interfaces entre le joint et les substrats constituent des points de concentration de contraintes pour la structure, caractérisés par des champs élastiques singuliers. Sous certaines hypothèses sur le comportement des substrats d'aluminium, l'analyse est menée sur la couche d'adhésif. Un critère d'amorçage déjà existant est étendu aux chargements thermo-mécaniques et permet de prédire la contrainte à rupture. Les résultats théoriques sont comparés à des mesures expérimentales disponibles dans la littérature. Nos prédictions sont en accord satisfaisant avec l'expérience mais il est clair qu'une meilleure connaissance des conditions d'élaboration, donc des contraintes résiduelles, permettrait de mieux rendre compte des résultats expérimentaux

Numerical implementation of the coupled criterion: Matched asymptotic and full finite element approaches

An implementation of the coupled criterion (CC) for crack initiation simulation in the commercial finite element (FE) code Abaqus/Standard is proposed. This finite fracture mechanics approach allows crack initiation to be modeled by fulfilling simultaneously a stress and an energy conditions, which results in the determination of the loading level and crack length at initiation. Two procedures are considered and compared: the first one relies on matched asymptotic expansions while the second one is based on full FE calculations. The asymptotic approach is computationally more efficient than the second one since it requires less calculations to be performed. However, it is restricted to cases for which the crack initiation length remains small compared to the smallest characteristic dimensions of the studied structure. For such cases, both methods leads to similar results as illustrated by crack initiation modeling of notched specimen under three point bending. The provided source codes and the tutorials help understanding and applying the CC for crack initiation modeling

Understanding the tensile strength of ceramics in the presence of small critical flaws

The objective of this paper is to analyze the effect of small critical flaws on the strength of polycrystalline ceramic materials. For this purpose, a finite fracture approach based on the coupled criterion (CC) is used to describe the initiation of a crack near a stress concentrator. The initiation criterion combines both a stress and an energy condition. The required input fracture-mechanics parameters are the tensile strength and the fracture toughness. Both a blunt and a sharp geometry are studied. The size of the starter crack developing near the stress concentrator can be easily estimated in each case when the CC is fulfilled. Based on the calculations, if the size of the defect is smaller than the characteristic material length, numerical predictions reveal that the defect (either sharp or blunt) has no effect on the strength, reaching the intrinsic tensile strength of the material. This result is in a good agreement with experimental results obtained from the strength measurements of ceramic materials with controlled flaws. It is also shown that combining two fracture tests after introducing flaws with controlled sizes enables to identify the fracture parameters of the ceramic material