Design of adhesive joints based on peak elastic stresses (original) (raw)
Related papers
Stress intensity factor in bonded joints: Influence of the geometry
International Journal of Adhesion and Adhesives, 2010
This paper explores the effects of the main geometrical features of an adhesive single lap joint (subjected to tensile stress) on the singular stress field near to the interface end. First, an analysis on a bi-material block is carried out, to evaluate the accuracy obtainable from finite element modelling by comparison with the analytical solution for the singularity given by the Bogy determinant. Then, the study on the lap joint is carried out, by varying both macroscopic (bond length, thickness) and local (edge shape and angle) parameters, for a total of 30 cases. The great importance of the angle to reduce the singular stresses is confirmed, whilst the edge shape plays a lesser role. The bond length has the effect of increasing or decreasing the stress values and the stress intensity factor, and the adhesive thickness has a relevant effect only in case of square edge. Finally, the problem of the significance of the stress intensity factor, representative of the stress distribution only for a given edge angle, is recalled.
Strength assessment of adhesive-bonded joints
Computational Materials Science, 2008
This paper deals with non-linear analyses of adhesively bonded joints under tensile lap shear loading. 3D FEM models are taken into account. The effect of the number of elements through the adhesive layer thickness is considered. Tensile true stress-true strain curves are used as models of the adherend and adhesive materials. The single lap joints are tested to validated the numerical analyses.
Numerical and Analytical Investigations on The Stress Distributions in Single-Lap Joints
2016
The objective of this paper is to compare the shear and peel stress distributions in the single lap joints obtained using analytical model with those obtained using numerical analysis. The Zhao’s closed form solution that includes the bending moment effect was used as an analytical model. In the numerical analysis, two dimensional finite element model with plane strain assumption was used. Analyses were performed for brittle and ductile adhesive types both analytically and numerically. In addition, a comparison of peak shear and peak peel stress values was carried out on the basis of percentage error. The results show that both analytical and numerical analyses were in very close agreement.
IOP Conference Series: Materials Science and Engineering
Adhesive joints are widely used although different materials properties cause the singular stress field whose intensity is controlled by the adhesive joint geometry. Our previous studies showed that debonding strength can be expressed as a constant value of the critical intensity of singular stress field (ISSF) by applying two-dimensional modelling. By considering the real adhesive geometry, in this study, the ISSFs along the interface edge of three-dimensional prismatic butt joints are considered by varying the adhesive thicknesses. It is found that the critical ISSF in 3D modelling is almost constant independent of the adhesive thickness. The magnitude and position of the maximum ISSF are discussed by varying the corner fillet radius in comparison with two-dimensional modelling.
Convenient Adhesive Strength Evaluation Method in Terms of the Intensity of Singular Stress Field
International Journal of Computational Methods, 2018
A convenient evaluation method is proposed for the debonding adhesive strength in terms of the intensity of singular stress field (ISSF) appearing at the end of interface. The same FEM mesh pattern is applied to unknown problems and reference problems. It is found that the ISSF is obtained accurately by focussing on the FEM stress at the adhesive corner. Then, the debonding condition can be expressed as a constant value of critical ISSF. The usefulness of the present solution is verified by comparing with the results of the conventional method.
Adhesively bonded joints are becoming widespread in the composites industry and therefore there is a need for quantitative information on the mechanical strength of the material used. The great strength and stiffness of a composites structure may be strongly undermined by their weakest part, the bonded joint. Unfortunately, the testing of adhesives in bulk form may not be representative of their behaviour in a layered state, typically quite thin, because of differences in the polymerization process and lack of adhesive-adherend interfaces. The drawback of the test in thin layer is the stress concentration at the edges, typical in the single lap or t-peel joints, and also the chance of having the adhesive subjected both to a shear and predominant peel stress. This work deals with the characterization of adhesives in thin film under uniform distributions of multi-axial stresses, which is the typical application condition. The test exploits a tubular butt-bonded specimen, previously investigated by the authors, which guarantees a non-singular stress field over the adhesive layer both in shear and normal directions. According to the analytical prediction, in addition to the direct normal stress, both radial and circumferential secondary stresses arise in the adhesive, due to the constrained lateral contraction imposed by the adherends (Poisson's effect). The test campaign investigates two chemically different, commercial adhesives, an acrylic and an epoxy resin. By means of a biaxial testing machine, we applied to the specimens eight different combinations of normal and shear loads ranging from pure tensile to a shear-compressive stress state. As expected , both the pure shear stress and the compressive stresses lead to better performances of the adhesive layer with respect to tensile loading. The authors compare a variety of failure criteria from the literature and propose a simple multiaxial criterion to obtain a failure envelop of the experimental data. The applicability of the criterion is also assessed on experimental tests found in literature on different configurations and gives fairly good results. The outcome of study is a simple stress based, failure criterion, which can be used to predict the failure of several adhesive bonded joints, relying only on monoaxial experimental data.
Prediction of Failure Strength of Adhesive Joints Using Peel Stress and CTOA
52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 2011
The failure strength of adhesively bonded joints depends on many factors such as material properties (both adhesive and adherend), specimen geometries, test environments, surface preparation procedures, etc. Among them, adhesive properties can be regarded as the most dominating factor affecting the failure strength. In this study, the failure strengths of single lap joints and double strap joints were tested for different combinations of adhesives and adherends. Both adhesive failure mode and cohesive failure mode were generated by controlling the fabrication procedure together with different material combinations. For producing a pure adhesive failure, stainless steel adherends and an epoxy-based paste adhesive (Hysol EA9394) were used. It was observed that for consistent surface treatments, peel stress distributions along the interface near the crack initiation point show similar trend at failure loads for single lap joints with different geometrical combinations for which peel stress distributions were calculated using the finite element analysis. Cohesive failures were generated using two different joints, single lap joints consisting of aluminum adherends bonded with the Hysol adhesive and double strap joints with graphite/epoxy composite adherends bonded with film adhesive FM-94. It was observed that for double strap joints with different overlap lengths, peel stress distributions at the failure initiation point show a similar magnitude. Thus, the peel stress within a critical distance can be used as a parameter capable for predicting the joint strength for above cases. However, when boundary constraint effect (specifically adhesive thickness) changes significantly peel stress distribution near the failure initiation point is not capable of predicting failure strength for cohesive failure mode. In that situation, fracture mechanics based approaches or some other approach needed to be adopted. Fracture mechanics based approach assumed that there is pre existing crack within the structure and failure initiates when the crack starts propagating. One of the suitable approach to predict failure strength (crack propagation loads) for non-linear fracture mechanics is crack tip opening angle (CTOA) based approach. Cracks with a certain length along crack initiation points can be introduce in FEA model and CTOA values at failure load can be evaluated. This type of method is shown in this paper and the length of the pre existing crack is justified. It is observed from FEA that at failure load CTOAs follows a certain trend that can be obtained using other tests method such as double cantilever beam (DCB) tests. As CTOAs follows same trend as test data it can be adopted as parameter to predict joint failure strength. Nomenclature SLJ = Single Lap joint DSJ = Double Strap joint
Effect of Adhesive Thickness on the Intensity of Singular Stress at the Adhesive Dissimilar Joint
Journal of Solid Mechanics and Materials Engineering, 2010
This paper deals with the singular stress field at the adhesive dissimilar joint, and discusses the effect of material combination and adhesive thickness on the intensity of the singular stress when bonded strip is subjected to tension. A useful method to calculate the intensity of singular stress at the adhesive dissimilar joint is presented with focusing on the stresses at the edge calculated by finite element method. The intensities of singular stress are indicated in charts with varying adhesive thickness t under arbitrary material combinations for adhesive and adherents, and it is found that the intensity of singular stress increases with increasing the adhesive thickness t until t W = , when W is the width of adhesive. The intensity of singular stresses are also charted under arbitrary material combinations which are presented by Dunders' parameters α , β when / 0.001 t W = and / 0.1 t W = , and it is found that for a fixed value β the intensity of singular stress increases with increasing α when α is small while it decreases with increasing α when α is large.
IOP Conference Series: Materials Science and Engineering, 2018
Adhesive joints are extensively used in various manufacturing processes in different industrial sectors because of its high fatigue resistance. Different materials properties cause the singular stress field, whose intensity is depending on the adhesive joint geometry. Our previous studies show that debonding strength can be expressed as a constant value of the critical intensity of singular stress field (ISSF) by using two-dimensional butt joint models. By considering real specimen geometry, in this paper, the ISSFs on the interface outer edges of three-dimensional butt joints are analysed by varying the adhesive thicknesses. A meshindependent technique combined with three-dimensional finite element method (FEM) is shown to evaluate the ISSF. The ISSF distributions on the interface outer edges are analysed in comparison with the previous two-dimensional results. It is found that the critical ISSF considered 3D geometry is almost constant independent of the adhesive thickness.