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Predicting Failure Initiation in Structural Adhesive Joints
Final rept. May 2009-May 2012
CENTRO DE INVESTIGACION EN MATERIALES AVANZADOS S C CHIH (MEXICO)
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The aim of this project is to bring a better knowledge of the phenomena involved in the failure of structural adhesive joints and to develop new tools to predict the initiation of this failure. First, a constitutive model of the adhesive was developed by carrying out several experiments on three types of adhesives. For two of these adhesives, a rigorous proof of important viscoplastic phenomena is shown. This is a first important contribution of this project. Arcan tests, tensional and torsional tests on butt joints and double lap joints were performed with the three adhesives and two metallic substrates in order to obtain a set of data for testing the accuracy of the predictions of a failure criterion. Linear and non-linear solid finite element calculations were carried out to analyze the stress state in the tested specimens. A layer-wise model was developed to ease the calculation and analysis of stresses in plate-like adhesive joints. For these joints, a solid finite element analysis may become unaffordable owing to the computational cost. The layer-wise model is able to take into account non-linear phenomena in the adhesive layer and its calculations were validated theoretically and experimentally. This is a second important contribution of this project. In order to predict failure initiation, the solid finite element calculations and a twofold failure criterion involving simultaneously stress and energy conditions were applied. Accurate predictions were obtained for the adhesive joint specimens tested in this project. This is a third significant impact of this work. The layer-wise model was applied to the prediction of failure in tests with plate-like adhesive joints published by other researchers. A criterion on the cumulative plastic strain in the adhesive provides accurate predictions of cohesive failure for the considered joints. This is another noteworthy contribution of this project.
APPROVED FOR PUBLIC RELEASE