An improved 2D model for bonded composite joints

Abstract

A growing number of structural applications and repairs require strong adhesively bonded joints between composite parts. The viability of the finite elements method (FEM) for the design and analysis of such joints has been shown by several researchers (Composites 13(1982) 29, mechanics and mechanisms of damage in composites and multi-materials, ESIS11, Mechanical Engineering Publications, London, 1991, Structural adhesive joints in engineering, Elsevier Applied science Publishers, Amsterdam, 1984). Most of the proposed plane stress models for adhesively bonded joints have traditionally relied on effective lamina properties for the composite adherends because one of the primary goals was the study of adhesive stresses and failure criteria (J. Adhes. 42 (1993)). Such work has also been usually carried out on mainframe computers. However, with the rapid developments in computing, commercial FE codes now exists for PC applications. These present new possibilities, namely the construction of models which are closer in their approximation to the structures they represent. Within this context, a new 2D plane stress approach has been developed which allows ply-by-ply modelling of composite adherends in a joint. It is a development of the traditional 2D plane stress model used by several authors such as Siener (Compos. Mater.: Testing Des. 10 (1992) 444) in investigating of composite repair joints. This paper reports the application of this new approach to the modelling of scarf joints between composite adherends under tensile loading. Various scarf angles were investigated and ultimate joint failure predicted. The results of the analysis were compared to the experimental results published by Adkins and Pipes (Proceedings of the Fourth Japan–US Conference on Composite Materials, 1988, pp. 845–854). The main aim of work was to develop a model which could provided more information than conventional models. The new approach offers the prospect of accurately modelling more realistic joints because, through the retention of the laminated nature of the composite adherends, scope now exists for the application of more physically based failure criteria. This work has shown that it is possible to model adhesively bonded composite joints using an improved 2D plane stress model which retains the laminated nature of the composite adherends. There was good agreement between the predicted failure loads and the experimental results for 3.0°, 6.2° and 9.2° scarf joints. These predictions are dependent on the type of failure criteria used. For the composite adherends, the maximum stress criterion faired better in predicting the 3.0° scarf joint strength.