Mixed Mode Loaded Adhesive Layers - from measurement of material data to analysis of structural behaviour

Doctoral thesis, 2007

ABSTRACT In manufacturing of multi-material products, a joining method that is able to cost-effectively assemble components made of dissimilar and similar material, with irregular geometries, is optimal. As an alternative, adhesive bonding is in-creasingly adapted by the industry, which is also used in manufacturing of multi-phase materials. In practice, adhesives are constrained to thin layers. An adhesive as a constrained layer behaves differently compared to the adhesive as a bulk material. In general, adhesive layers are loaded in peel (mode I), or in shear (mode II or III), or in a combination of peel and shear (mixed mode). This thesis deals with mixed mode loaded adhesive layers, from measurement of ma-terial data to analysis of structural behaviour. For studying of structural behaviour of adhesive joints, an integrated approach is developed. Arbitrarily end-loaded single-layer adhesive joints with arbitrary ad-herends of arbitrary length are analysed with the Beam/Adhesive layer (B/A) model. Closed-form solutions are obtained for the adhesive layer as well as for the adherends. For joints with a semi-infinite symmetric geometry, i.e. relative long joints with identical adherends loaded at one end, basic loading cases are obtained. Solutions to these basic loading cases are easy to use in designing of joints with this type of geometry. For nonlinear or general adhesive layers, a mode-dependent cohesive law is de-veloped. The normalized formulation is easy to implement in numerical simula-tions, yet, it captures the characteristics of adhesive layers. For experimental studies, this cohesive law is used to obtain the constitutive behaviour of an adhe-sive layer. The results confirm the ability and suitability of this cohesive law in modelling of adhesive layers. To obtain material data of adhesive layers, experimental methods are developed based on the J-integral. Two specimens, the Mixed mode double Cantilever Beams (MCB) specimen and the Unbalanced Double Cantilever Beams (UDCB) specimen, are designed to allow adhesive layers to be loaded in mixed mode. The MCB-specimen is implemented experimentally and the constitutive behav-iour of the tested adhesive layer is obtained.