Tapered-double cantilever-beam joints were manufactured from aluminium-alloy substrates bonded together using a single-part, rubber-toughened, epoxy adhesive. The mode I fracture behaviour of the joints was investigated as a function of loading rate by conducting a series of tests at crosshead speeds ranging from 3.33 x10 -6 m/s to 13.5 m/s. Unstable, (i.e. stick-slip crack) growth behaviour was observed at test rates between 0.1 m/s and 6 m/s, whilst stable crack growth occurred at both lower and higher rates of loading. The adhesive fracture energy, G Ic , was estimated analytically, and the experiments were simulated numerically employing an implicit finite-volume method together with a cohesive-zone model. Good agreement was achieved between the numerical predictions, analytical results and the experimental observations over the entire range of loading rates investigated. The numerical simulations were able very readily to predict the stable crack growth which was observed, at both the slowest and highest rates of loading. However, the unstable crack propagation that was observed could only be predicted accurately when a particular rate-dependent cohesive zone model was used. This crack-velocity dependency of G Ic was also supported by the predictions of an adiabatic thermal-heating model (ATM).
Publication information Polymer, 53 (24): 5540-5553Publisher Elsevier Item record/more information http://hdl.handle.net/10197/5950 Publisher's statementThis is the author's version of a work that was accepted for publication in Polymer. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Polymer (53, 24, (2012)) DOI: http://dx.doi/org/10.1016/j.polymer.2012.09.049Publisher's version (DOI) http://dx.doi.org/10.1016/j.polymer.2012.09.049 NotesOther RMSIDs: 316516744Some rights reserved. For more information, please see the item record link above. Bosnia and Herzegovina AbstractThe current work is a combined experimental--numerical study of the fracture behaviour of a nano--toughened, structural epoxy adhesive. The mode I fracture toughness of the adhesive is measured using tapered double--cantilever beam ( IntroductionThe accurate and efficient determination of the fracture toughness and the associated fracture mechanisms of a structural adhesive are of fundamental importance to adhesive manufacturers and end users alike. The ability to predict the behaviour of such joints can lead to better designs, increased performance, reduced costs and enhanced safety. Better understanding of the structure--property relationship will ultimately lead towards improved adhesives with tailored properties. However, the behaviour of joints in real structures is difficult to predict since their behaviour, including the failure mechanisms, are complex to measure and model. The testing of prototypes and trial structures is costly and time--consuming. Consequently, there has been a growing motivation for the development of theoretical models for predicting the damage and failure of adhesive joints. These models require geometry independent material parameters, which are usually obtained from tests with simpler geometries and subsequently applied in the analysis of more complexgeometries.An important parameter in adhesive joint design is the bond gap thickness (BGT) which needs to be accurately controlled in order to obtain a consistent and reliable joint strength. In the current work, the mode I fracture behaviour of a nano--toughened, structural epoxy adhesive was examined using low--rate TDCB tests with various bond gap thicknesses. The Application of the CZM to adhesive jointsCohesive zone models are widely used to model the fracture of adhesive joints. In general, the substrates are modelled as elastic--plastic continua while two main approaches are adopted for the modelling of the adhesive layer: i) CZM is used to represent the entire adhesive layer, ii) the adhesive layer is modelled as a continuum while CZM is used to describe the local fracture process. A number of authors have used a single row of cohesive zone elements to represent the adhesive layer, e.g. ...
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