How to predict the mechanical properties of a composite structure assembled with a metal structure

University essay from Uppsala universitet/Tillämpad mekanik

Author: Mubarak Ali; [2019]

Keywords: ;

Abstract: Adhesive joints are used extensively in the automotive industry. There are many ongoing studies on the area of application of joining composite to other material using adhesive joints. In this study, an analysis of mechanical behaviour of composite single lap-joint (SLJ) for carbon fibre reinforced polymer (CFRP) assembled with steel is presented and the analyses are divided into three phases. The first phase consists of a parametric study on a SLJ using Volkersen analytical model (AM), which is the effect of adhesive thickness and overlap length of the SLJ under tensile load. It was found that with increasing the adhesive thickness the final peak load (strength of the joint) increases. The peak load also increases with increasing the overlap joint, but the limit value for the overlap length varies for different adhesive thickness. For example for the case of adhesive thickness of 0.5 mm, the curve reaches to its plateau with overlap length of 40 mm. It was also observed the increase of adhesive thickness leads to decrease of maximum shear stress at the edges of the single lap joint, but it increases as it approaches the middle of the overlap length. Phase two of this study consist of a shear stress comparison with the Volkersen AM with the finite element model (FEM) using ANSYS Parametric Design Language(APDL) software. The purpose of this comparison was to validate the AM. It was found that the AM has a good agreement with the numerical-model (NM). However, the shear stress from the AM at the edge is a little higher than the NM, this is because the analytical method only takes into account the shear stress in one direction but the NM also takes into account the normal shear stress in the other direction. Phase three of this study consists of an experimental analysis of SLJ mechanical behaviour due to the change in temperature of 180 degrees and change in adhesive thickness and also a comparison with the NM. Three adhesive thickness 1, 0.5 and 1.5 mm were tested. Different boundary conditions (BC), namely as with frame and fixed BC are tested for NM. The one with frame BC is to compare with experimental setup and the fixed BC is the equivalent to Volkersen’s geometry. Both experimental and numerical results, show that the relative deformation of the SLJ decreases with the increase of the adhesive thickness. Although the experimental values were much lower than the numerical one, they agree well with the numerical result in term of trend of relative deformation. In experimental analysis, it was found that increasing the adhesive thickness from 0.5 mm to 1.5 mm decrease the relative deformation from 7.8% to 5.3%. It was concluded that increasing the adhesive thickness decreases the stiffness of the joint and allows more thermal movement in the joint.

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