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Time-variant assessment for adhesively bonded assemblies with non-linear behaviour in naval applications

Adhesive bonding is becoming a widely used assembling process in the naval field; it can allow great productivity, simplify design constraints and can lead, in general, to a significant weight reduction. Unfortunately, this technology is not completely mastered; parameters like the cure process, size of defects, joint adhesive thickness variations, size of parts to be assembled and non-linear behaviour of the adhesive joint, have to be considered to assess the risks and predict the service life. Moreover, for naval applications adapted state functions have to be proposed in order to take into account this variability of material properties, the time dependency of parameters like damage, solicitations or loads. Under these assumptions, time-independent reliability is insufficient to allow a pertinent-related failure probability calculation. The solution of such a problem can be given by the use of time-dependent reliability tools. This passes through coupling structural reliability software evaluation with a non-linear finite element code. This choice requires robust mechanical models able to describe the behaviour of naval structure with an acceptable numerical cost in order to perform the reliability study. This paper presents a time variant reliability approach based on the PHI2 method. Cohesive-zone models are used to model the adhesive. This choice allows limiting the numerical cost of simulations and permits us to model the non-linear behaviour of adhesive. It also presents a good compromise between numerical costs and quality of results. The damage at the interface can be modelled and it has been proven that using cohesive zone models is well suited for bonded joints as the possible degradation zone is well defined. In order to determine the cohesive zone model parameters, tests were performed. The most relevant results are presented. Different numerical results showing the feasibility of this approach for adhesively bonded assemblies are discussed and the case of a representative part of a naval structure has been studied in this paper.