Issue 29

R. Dimitri et alii, Frattura ed Integrità Strutturale, 29 (2014) 266-283; DOI: 10.3221/IGF-ESIS.29.23 266 Focussed on: Computational Mechanics and Mechanics of Materials in Italy A consistency assessment of coupled cohesive zone models for mixed-mode debonding problems R. Dimitri, M. Trullo, G. Zavarise Department of Innovation Engineering, University of Salento, Lecce, Italy rossana.dimitri@unisalento.it , marco.trullo @unisalento.it, giorgio.zavarise@unisalento.it L. De Lorenzis Institut für Angewandte Mechanik, Technische Universität Braunschweig, Germany l.delorenzis@tu-braunschweig.de A BSTRACT . Due to their simplicity, cohesive zone models (CZMs) are very attractive to describe mixed-mode failure and debonding processes of materials and interfaces. Although a large number of coupled CZMs have been proposed, and despite the extensive related literature, little attention has been devoted to ensuring the consistency of these models for mixed-mode conditions, primarily in a thermodynamical sense. A lack of consistency may affect the local or global response of a mechanical system. This contribution deals with the consistency check for some widely used exponential and bilinear mixed-mode CZMs. The coupling effect on stresses and energy dissipation is first investigated and the path-dependance of the mixed-mode debonding work of separation is analitically evaluated. Analytical predictions are also compared with results from numerical implementations, where the interface is described with zero-thickness contact elements. A node-to-segment strategy is here adopted, which incorporates decohesion and contact within a unified framework. A new thermodynamically consistent mixed-mode CZ model based on a reformulation of the Xu-Needleman model as modified by van den Bosch et al. is finally proposed and derived by applying the Coleman and Noll procedure in accordance with the second law of thermodynamics. The model holds monolithically for loading and unloading processes, as well as for decohesion and contact, and its performance is demonstrated through suitable examples. K EYWORDS . Cohesive zone modeling; Contact; Debonding; Thermodynamics. I NTRODUCTION ohesive zone models (CZMs) as proposed by Dugdale [1] and Barenblatt [2], have been widely used in the last decades as numerical tool to study mixed-mode delamination, debonding, and more generally, crack propagation and/or initiation at material interfaces or within quasi-brittle materials. This is due to the computational efficiency of these models and their versatility for numerical implementation in many areas of Computational Mechanics. Despite the large number of cohesive models proposed, little attention has been devoted to ensuring their consistency for mixed-mode conditions, primarily in a thermodynamical sense, whereas the relative performance of different models has rarely been the subject of a comparative assessment. For many of these models, traction-separation laws have been C