Damage Tolerance Analysis of Adhesively Bonded Repairs to Composites Structures (original) (raw)
Related papers
Strength Prediction of Adhesively-Bonded Scarf Repairs in Composite Structures under Bending
Materials Science Forum, 2010
This work reports on the experimental and numerical study of the bending behaviour of two-dimensional adhesively-bonded scarf repairs of carbon-epoxy laminates, bonded with the ductile adhesive Araldite 2015 ® . Scarf angles varying from 2 to 45º were tested. The experimental work performed was used to validate a numerical Finite Element analysis using ABAQUS ® and a methodology developed by the authors to predict the strength of bonded assemblies. This methodology consists on replacing the adhesive layer by cohesive elements, including mixed-mode criteria to deal with the mixed-mode behaviour usually observed in structures. Trapezoidal laws in pure modes I and II were used to account for the ductility of the adhesive used. The cohesive laws in pure modes I and II were determined with Double Cantilever Beam and End-Notched Flexure tests, respectively, using an inverse method. Since in the experiments interlaminar and transverse intralaminar failures of the carbon-epoxy components also occurred in some regions, cohesive laws to simulate these failure modes were also obtained experimentally with a similar procedure. A good correlation with the experiments was found on the elastic stiffness, maximum load and failure mode of the repairs, showing that this methodology simulates accurately the mechanical behaviour of bonded assemblies.
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.
Influence of the cohesive law shape on the composite adhesively-bonded patch repair behaviour
Composites Part B: Engineering, 2016
In this study, the cohesive failure of the adhesive layer of an adhesively bonded joint under uniaxial tensile loads in static conditions is discussed as an approximation to the behaviour of adhesively bonded repairs. A three dimensional finite element model of a single lap joint was developed using the com mercial code Abaqus. Cohesive Zone Models (CZM) coupled to Finite Element Analysis, were used to study the failure strength of the joint. They allowed the prediction of the initiation of the crack and its growth. CZM are governed by a traction separation law, which can acquire different shapes. The nu merical model, considering a linear cohesive law, was validated with 2D numerical and experimental results available in the literature. The effect of different cohesive law shapes, such as exponential and trapezoidal, on the failure load of the joint was studied. In addition, a cohesive parametric analysis was performed, varying the adhesive toughness and cohesive strength. The most suitable cohesive law was the trapezoidal, since the failure load results were close to the experimental data taken from the liter ature. The cohesive strength is identified as the most influential parameter on the studied variable.
Buckling Behaviour of Carbon–Epoxy Adhesively-Bonded Scarf Repairs
Journal of Adhesion Science and Technology, 2009
The present work is dedicated to the experimental and numerical study of the buckling behaviour under pure compression of carbon-epoxy adhesively-bonded scarf repairs, with scarf angles varying from 2 to 45 • . The experimental results were used to validate a numerical methodology using the Finite Element Method and a mixed-mode cohesive damage model implemented in the ABAQUS ® software. The adhesive layer was simulated using cohesive elements with trapezoidal traction-separation laws in pure modes I and II to account for the ductility of the adhesive used. The cohesive laws in pure modes I and II were determined with Double Cantilever Beam and End-Notched Flexure tests, respectively, using an inverse method. Since in the experiments interlaminar and transverse intralaminar failures also occurred, cohesive laws to simulate these failure modes were also obtained experimentally following a similar procedure. Good correlations were found between the numerical predictions and experimental results for the elastic stiffness, maximum load and the corresponding displacement, plateau displacement and failure mode of the repairs. by an accident (e.g., tool impact during maintenance). Since this kind of damage significantly reduces the structures' strength, replacement or repair must be followed. Repair of these structures is more efficient from economical and ecological points of view, since composite materials are difficult to recycle. Repair by adhesive bonding is a valid option due to its numerous advantages over the conventional bolting or riveting methods, e.g., more uniform stress distributions, reduced weight penalty, minimal aerodynamic disturbance, and fluid sealing characteristics. If a full or significant strength recovery is required, or if a repair without aerodynamic perturbation is needed, a scarf repair should be used. The higher efficiency of this repair method, compared with the easy-execution strap repairs, is due to the larger bond areas and the reduction of stress concentrations at the bond edges due to the adherend tapering effect.
Composite Structures, 2019
The repair of composite materials has received much attention in recent decades because these materials are used in a wide range of industrial applications owing to their excellent mechanical properties. In this work, the failure of scarf patch-repaired composite laminates subjected to bending loads was experimentally and numerically investigated. Thirty repaired laminates with a scarf angle of 5.7° or 3.8° were prepared and tested under different bending loads. Three-dimensional finite element models implementing cohesive elements were created to examine crack initiation and propagation in the specimens during loading. Experimental results revealed that a combination of adhesive, intralaminar, and interlaminar failure occurred in the bonding surface area. Compared to the failure of repair under tensile loading, additional failure occurred in the patch. Simulations reproduced these failure modes well with cohesive elements. The failure loads were also accurately predicted with a maximum prediction error of 9.7%.
Materials & Design, 2013
Adhesives play important roles in bonded composite repair as it ensures the transfer of load between the composite patch and the cracked aluminum component. Also, it holds the two structures together. The damage of the adhesive can thus reduce significantly the efficiency and the durability of the bonded composite repair. The adhesive damage models using critical zone have proven their effectiveness due to simplicity and applicability of the damage criteria in these models. The scope of this study is the estimation of the adhesive damage and failure in bonded composite repair of aircraft structures using modified damage zone theory. The effect of this damage on the repair efficiency was analyzed. In order to achieve these objectives, non-linear finite element analyses of adhesive joints considering the material nonlinearity of the adhesive layer were performed. The obtained results show that adhesive damage is principally located at the free edges of the patch and over the crack region. The damage zone ratios depends on the applied load, it affects the repair efficiency when its value approaches the critical value of 0.22.
2014
In this study, the adhesive damage in bonded composite repair of aircraft structures is analyzed using a three dimensional finite element method. Four different patch shapes were chosen to analyze the adhesive damage: rectangular, trapezoidal, circular and elliptical. The modified damage zone theory was implemented in the FE code to evaluate the adhesive damage. The obtained results show that the rectangular shape is beneficial for the repair durability but it presents a disadvantage for the repair efficiency. The elliptical patch is found the optimal whereas the trapezoidal patch represents the worst shape among the four types analyzed in this paper.
Composites Part B: …, 2011
In this study, the three-dimensional finite element method is used to analyze the effects of the patch shape on the efficiency end the durability of bonded composite repairs of aircraft structures. The stress intensity factor at the crack tip is used as fracture criteria. The determination of this factor allows us to estimate the repair efficiency. The analysis of the stresses distribution in the adhesive layer allows us to estimate the durability of the adhesion between the damaged plate and the composite patch. The obtained results show that the repair performances are closely related to the patch shape. It was demonstrated that the rectangular shape of the patch could be improved using an ''H'' shape of the patch. This last shape could also be improved using an arrow shape.
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...
Tensile Failure Prediction and Measurement in Composite Scarf Repair (Preprint)
2007
: Oversized quasi-isotropic tensile specimens were manufactured from IM6/3501-6 graphite/epoxy prepreg. Seven specimens were scarfed in the center of the panel, and four of the panels were subsequently repaired. The repair patch consisted of a ply-by-ply replacement of the removed material with a FM-300M095 film adhesive placed between the repair patch and the scarfed specimen. The patch and adhesive were then co-cured. The repaired and unrepaired specimens were strain gaged and tested to failure. A three-dimensional failure analysis was performed. The strength prediction was based on the state of stress in the 0(exp 0) plies by taking into account the redistribution of stress due to adhesive failure. The performed analysis accurately predicted both the strength of the scarfed and repaired panels based solely on properties characterized by testing unnotched standard coupons.