A strain-based criterion for failure load prediction of steel/CFRP double strap joints

Abstract

One of the most effective approaches to improve the strength of steel structures is using the carbon fiber reinforced polymer (CFRP) as externally-bonded sheets. In this paper, a strain-based failure criterion, namely the critical normal strain (CNS) is employed to predict the failure load of adhesively bonded double strap joints which are made of CFRP and steel plates. According to this approach, the adhesive joint fails when the normal strain along the adhesive mid-line attains a critical value at a critical distance. This work is based on a two-dimensional linear elastic finite element analysis. Failure load capacities are estimated theoretically for steel/CFRP double strap joints with different bonding lengths. The predicted values of failure loads are compared with the experimental data reported in literature. It is shown that a good consistency exists between the experimental failure loads and the theoretical predictions based on the new strain-based criterion. x distance from the bonding edge MHSM modified Hart smith model PCNS theoretical failure load predicted by CNS criterion PExp. experimental failure load SLJ single lap joint 1. Introduction Carbon fibre reinforced polymer (CFRP) sheets have many applications in industrial components, for instance they are used in order to increase the service life and load carrying capacities of damaged steel 3 structures. Nowadays, Due to the reduced weight and cost of CFRP laminates, they are often applied in retrofitting of steel structures instead of utilizing the conventional mechanical fastening procedures like welding or bolting. In huge industries like aerospace, wind energy, marine structures, etc., application of CFRP laminates is widely growing. One of the major applications of CFRP laminates is to reduce the overall weight of structures. For instance, it can be pointed to Boeing 787 aircraft, in which 43% of metal structures including fuselage, wing, etc. were replaced by CFRP laminates. Therefore, since CFRP have attracted considerable attention as a new retrofitting material to increase the LBC and the service life of structural components, proposing a suitable failure prediction model to estimate the load bearing capacities (LBCs) of the steel/CFRP bonded joints can be very necessary. Up to now, many approaches have been proposed to analyze the behavior of steel components strengthened with CFRP patches [1-5], including nonlinear theory [6], digital image correlation (DIC) [7-10], extended finite element method (XFEM) [11, 12] and cohesive zone model (CZM) [13-16].Determination of failure mechanisms in steel/CFRP adhesive bonded joints is an important issue due to its undeniable effect on the operational life of the components. Several failure criteria have been proposed by researchers to predict the failure load of adhesively bonded joints. The majority of the available failure criteria are based on stress, strain or energy condition in the bond layer [17][18][19][20][21][22][23][24]. Due to their importance shear stress and normal stress (also known ...

Fatigue performance of single lap joints with CFRP and aluminium substrates prior and after hygrothermal aging

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“…The size of the finite elements assigned for the steel plates was selected based on the results provided by the preliminary analysis, which had shown that no significant effects were produced at this level. A mesh refinement with the level set to 0.1 (0.1 mm maximum length of the mesh elements) was performed for the edges of the bond area since these regions are susceptible to stress concentrations [43,44]. The transition between the meshing areas with different elements and distinct refinement levels has been progressively achieved, with a reduced gradient, through specific zones, also called smooth transition regions.…”