Influence of the cohesive law shape on the composite adhesively-bonded patch repair behaviour (original) (raw)
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Frattura ed Integrità Strutturale
The aim of this work is to analyze the failure behavior of a simple lap joint of type metal / metal consisting of 2024-T3 Aluminum plate bonded with an Araldite adhesive using the finite element method to predict damage of the metal in tensile and compressive load under the effect of geometric parameters such as the length of the overlap and the geometric shape of the two plates according to the overlap length. The numerical analysis is performed by the ABAQUS calculation code. The adhesive was modeled by an element of the CZM cohesive zone. the adhesive will be submitted in mixed mode given the non-linearity of the two applied load. the calculation of the failure load will be determined according to the different parameters mentioned above. It is well demonstrated that the type of loading and the parameters taken into consideration condition the strength of the structure. The effect of these different parameters on the strength of the adhesive joint is presented as results by failure load curves.
Journal of Adhesion Science and Technology, 2016
The paper presents a comparison of the cohesive zone model (CZM) and the continuum damage mechanics approach in predicting the static failure of a single lap joint (SLJ). The effect of mesh size and viscosity were studied to give more understanding on the failure load and computational time. Both the load-displacement response and the backface strain technique were utilised to compare the validity of predictions. Peel and shear stress and damage distributions along with the damage progression are compared to understand the behaviour of the models in predicting the static failure response. In general, both approaches show good accuracy in predicting the failure load; however, the cohesive zone approach requires shorter computation time than the continuum damage approach. The continuum damage approach shows some mesh-dependency particularly for elements with high aspect ratios, whereas the cohesive zone approach is not. The continuum damage approach is less sensitive than the cohesive zone approach to the artificial damping required to achieve convergence. Another interesting finding is using the same ultimate stress level of damage in the continuum damage approach at the peak load is much lower than that in the cohesive approach; but the failure process in this approach is faster.
Critical assessment of failure criteria for adhesively bonded composite repair design
2012
Due to the high stress concentration and nonlinear deformation in bonded joints, accurate strength prediction remains challenge. The aim of this paper is to evaluate the accuracies of different failure criteria and computational methodologies for bonded composite joints and their suitability as an engineering design tool. A total of four analytical and four numerical predictive models were evaluated against experimental results obtained from single lap and skin-doubler joints. Experimental observations reveal two main failure modes: cohesive and first-ply fracture. Strain-based models based on cohesive properties were found to be applicable only to joints exhibiting cohesive failure. Fracture mechanics-based models, on the other hand, can predict both cohesive and composite ply failure.
Non-linear three dimensional (3-D) finite element analyses (FEA) of the single lap joints (SLJs) having pre-existing rectangular adhesion failure in the interface of the strap adherend and the adhesive have been carried out. The effect of the size, the shape and the aspect ratio of the pre-existing rectangular adhesion failure on (i) the strength, (ii) the interfacial stresses and (iii) the strain energy release rates (SERRs) in the vicinity of the adhesion failure front have been presented in this research work. The SLJ is subjected to uniformly applied tensile load. The adherends are made with very high strength steels and the adhesive is a commercially available AV119. The analyses of the adhesion failure propagation have been carried out by sequentially releasing the constraints of the nodes ahead of the pre-existing adhesion failure front in finite element model. The SERR values in the vicinity of the adhesion failure fronts are computed using the virtual crack closure technique (VCCT) for assessment of the structural integrity of the SLJ. The strength of the SLJ, the interfacial stresses, and the three modes of strain energy release rates (SERRs) have been found to be significantly affected by the shape and size of adhesion failures. The SERRs and interfacial stresses along the rectangular adhesion failure front are compared with the corresponding values around the circular adhesion failure front of same area, pre-existing in the SLJ. It is observed that the circular and rectangular adhesion failures of the same area will have dissimilar growth rate and the mode II is the dominant failure mode. The total strain energy release rate and the failure strength, computed from the 3-D FEA of the SLJ is in good agreement with the experimental fracture toughness of the AV119 adhesive and the experimentally obtained failure loads, respectively.
Failure Analysis in Adhesively Bonded Composite Joints
2019
In this paper, the mechanical performance and failure behavior of adhesively bonded single lap joints are investigated. A mechanical test program is conducted on single lap shear specimens. Without changing composite and adhesive base materials, parameters including the stacking sequence and adherend thickness are considered. Additionally, an analytical finite element analysis program, to perform failure analysis and to determine the load carrying capacity of the selected composite part in an airplane wing structure. For modelling the bond line, the cohesive zone approach is used. Both damage initiation and propagation are performed with the same approach. The effect of geometry on the mechanical performance of the adhesively bonded joints are analyzed. Analytical results are used to determine the stress concentrations within the joint to understand the failure mechanisms. INTRODUCTION Adhesive bonding is a joining process in which two neighboring surfaces are connected with the app...
Structures built from several components require some means of joining. In this context, bonding with adhesives has several advantages compared to traditional joining methods, e.g. reduction of stress concentrations, reduced weight penalty and easy manufacturing. Adhesives can be strong and brittle (e.g., Araldite ® AV138) or less strong and ductile (e.g., Araldite ® 2015). A new family of polyurethane adhesives combines high strength and ductility (e.g., Sikaforce ® 7888). In this work, the performance of the three above mentioned adhesives was tested in single-lap joints with varying values of overlap length (L O). The experimental work carried out is accompanied by a detailed numerical analysis by Finite Elements, based on Cohesive Zone Models (CZM). This procedure enabled detailing the performance of this predictive technique applied to bonded joints. Moreover, it was possible to evaluate which family of adhesives is more suited for each joint geometry. CZM revealed to be highly accurate, except for largely ductile adhesives, although this could be circumvented with a different cohesive law.
Local evaluation of adhesive failure in similar and dissimilar single-lap joints
Engineering Fracture Mechanics, 2017
Single-lap joints made of aluminium and carbon fibre adherends are tested to understand better the behaviour of such dissimilar joints. Local deformation fields are monitored by using the digital image correlation method (DIC). Over the overlap length strain gauges are emulated as to measure properly the strains in the adhesive. Peeling and shearing strains are investigated, emphasizing that peeling is important in the region where failure is initiated, towards the extremity of the overlap region. Cohesive Zone Modelling (CZM) available in Abaqus Ò was used to simulate the behaviour and strength of dissimilar single-lap adhesively bonded joints. A linear elastic FEM was used. A distinct CZM model is used to show the variation of normalized stresses and damage in the process zone of the single-lap joint. Experiments show that the use of dissimilar aluminium-carbon and carbon-carbon adherends is reducing the strength and stiffness of the joints as the delamination and pull-out of the carbon fibres compromises their integrity. Numerical simulations overestimate the experimental strength and stiffness of the joints. FEM model has to be improved as to consider a refined laminate modelling.
Procedia Engineering, 2015
Structures built from several components require some means of joining. In this context, bonding with adhesives has several advantages compared to traditional joining methods, e.g. reduction of stress concentrations, reduced weight penalty and easy manufacturing. Adhesives can be strong and brittle (e.g., Araldite ® AV138) or less strong and ductile (e.g., Araldite ® 2015). A new family of polyurethane adhesives combines high strength and ductility (e.g., Sikaforce ® 7888). In this work, the performance of the three above mentioned adhesives was tested in single-lap joints with varying values of overlap length (L O). The experimental work carried out is accompanied by a detailed numerical analysis by Finite Elements, based on Cohesive Zone Models (CZM). This procedure enabled detailing the performance of this predictive technique applied to bonded joints. Moreover, it was possible to evaluate which family of adhesives is more suited for each joint geometry. CZM revealed to be highly accurate, except for largely ductile adhesives, although this could be circumvented with a different cohesive law.
Mathematical and Computational Applications, 2011
This paper examines the failures and strengths of joints bonded by a Neoxil CE92 N8 adhesive at different overlap lengths and different taper angles. The study was carried out both as experimental and numerical. In the experimental stage, lap-shear tests on Single-Lap Joints (SLJs) with different taper angles and overlap lengths were conducted. The stress analyses in the SLJs were obtained using a linear Finite Element Analysis (FEA) in numerical stage. It is assumed that adhesive and adherend have both geometrical nonlinearity and linear material behaviour. Scrutinising carefully the surfaces of the SLJs, two different failure types, cohesive failures (CF) and special cohesive failures (SCF) were observed. The obtained numerical results were compared with experimental ones. Results indicate that the increasing of both overlap length and taper angle increase the joint strength and, in particular, the highest strength values in all joint geometries are attained by specimens having a taper angle of 15°.