Abstract
The use of adhesive bonding for designing lightweight load-bearing components has increased in recent decades. In this paper the influence of plasticity on the lifetime prediction of bonded joints using the stress-life approach was investigated. The adhesive was a toughened epoxy for structural applications. Stress calculations were performed using finite element analysis. Three material models were employed, a linear-elastic model and two elastoplastic models: Von Mises (pressure independent) and Drucker–Prager (pressure dependent). Effective stress was calculated using the theory of critical distances. Lifetime predictions were based on SN curves from literature for scarf and single-lap joints at four different temperatures (−35, −10 °C, RT, +50 °C). The material properties were acquired from uniaxial tensile quasi-static experiments on bulk adhesive specimens. These experiments showed a reduction in the values of Young’s modulus and yield stress with increasing temperature. A model was proposed based on an Arrhenius-type equation in order to fit the yield stress as a function of temperature. The model showed good agreement to the experimental findings. Regarding lifetime predictions (a) the influence of critical distance was higher for single-lap joints than scarf joints and (b) the prediction errors were lower for elastoplastic modelling than linear-elastic modelling, especially for single-lap joints.
Highlights
The use of adhesive bonding in the design of load-bearing components has increased in recent decades due to the advantages of this joining technique
Regarding lifetime predictions (a) the influence of critical distance was higher for single-lap joints than scarf joints and (b) the prediction errors were lower for elastoplastic modelling than linear-elastic modelling, especially for single-lap joints
Beber et al [7] studied the effect of temperature on the fatigue behaviour of a toughened epoxy adhesive at five different temperatures ranging from −35 to +80 °C and found that with increasing temperature the fatigue strength is reduced
Summary
The use of adhesive bonding in the design of load-bearing components has increased in recent decades due to the advantages of this joining technique. These advantages include uniform load distribution, enhanced fatigue properties and the ability to join dissimilar materials [1] These characteristics make adhesives very attractive for lightweight applications in a wide range of industries such as the automotive, aerospace and rail sectors [2, 3]. In this context, fatigue is one of the main issues to address when designing bonded joints because cyclic loads occur in almost all engineering structures and may cause failure under loads that are considerably smaller than the quasi-static strength of the materials [4]. Several authors employed the TCD with success for analysis of specimens under quasi-static and/or cyclic loads and involving a wide variety of materials [10,11,12]
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