Enhancing Fatigue Life and Strength of Adhesively Bonded Composite Joints: A Comprehensive Review (original) (raw)
Related papers
Society of the Advancement of Material and Process Engineering, 2017
Cohesive failure is preferred over adhesive failure in bonded joints. Cohesive failure can be defined in terms of mechanical properties of adhesive, while adhesive failure is a property of adhesion strength between two bonding surfaces. Although the benefits of bonding apply to both metallic and non-metallic materials, the use of bonding has proven particularly attractive for fiber-reinforced composites due to the complications involved with bolted attachment of composites. Bonding of composite parts is challenging since the interface (adhesive) failure or adherend failure should be avoided. The present work considers cohesive, adhesive and adherend failure in shear, so that the effect of bond quality on mode II crack growth can be better understood. Failure modes for weak bonds were observed to be adhesive failure in static and fatigue loading. Strong bonds showed cohesive failure for fatigue loading. However, in static loading, strong bonds with a tough adhesive had a cohesive-adherend mixed failure mode and strong bonds with the standard adhesive had a cohesive-adhesive mixed failure. The fracture toughness for strong bonds in comparison to weak bonds, increased by 100 % for a tough adhesive and 50 % for a standard adhesive. The fatigue crack growth rate for weak bonds increased with a decrease in adhesive toughness.
Damage mechanisms in composite bonded joints under fatigue loading
Composites Part B: Engineering, 2012
In the present paper, the fatigue damage mechanisms in composite bonded joints are analysed and discussed, with particular emphasis on the influence of layer orientation at the adhesive-adherend interface, corner geometry at the end of the overlap area and the stacking sequence. Results indicate that the corner geometry at the end of the bonded area as well as the length of the overlap have a significant influence on the fatigue strength of the joints, while the layer orientation at the adhesive/adherend interface was seen to have a lesser influence on the fatigue performance. The evolution of fatigue damage, consisting in its essential features of crack initiation followed by propagation up to a critical length, is investigated by means of optical and scanning electron microscopy and by monitoring the stiffness of the tested joints. As a result, it is seen that a 45°oriented layer at the adhesive-interface makes crack paths much more complicated with respect to 0°oriented interface joints, with an increase in the crack propagation resistance. Moreover, measurements of the evolution of axial stiffness are promising in order to develop a simplified technique to assess the crack propagation during fatigue life.
IOP conference series, 2018
Fiber-reinforced polymer composites are being used in an increasingly wide range of products. They are particularly popular in automotive and aerospace sectors because they offer an attractive combination of stiffness, strength and low mass. Adhesively-bonded joints of such materials are preferred by many designers due to their assembling advantages over other traditional mechanical joining systems, such as bolted and riveted joints. In this study, some experimental works have been carried out on adhesively-bonded adherends manufactured from a woven carbon fiber-reinforced polymer matrix composite (Hexply 8552S/A280-5H, produced by Hexcel), by using a film adhesive (AF163-2K produced by 3 M). The bonded specimens were prepared in the Single Lap Joint (SLJ) configuration, and tested in tensile and also in four-point bending loading. In order to assess the joint performance, three different overlap lengths, 15 mm, 25 mm and 40 mm, and two different thicknesses of the composite adherends, 2 mm and 3 mm, were used. The results shown that the parameters are controlled by the loading modes; while the overlap length increases the joint performance significantly in tensile loading, the opposite was the case for those in bending loading, which was affected mainly by the adherend thicknesses. The results were related to the mechanisms of joint failures; while the joints in the tensile failed in the adhesive layer with some exceptions, those in the bending mainly failed in the plies adjacent to the layer. The current study indicates that one of the important factors affecting the joint strength of the adherends manufactured from the laminated composites is the local failure of the plies. It is thought more focused-studies would be needed to lessen such problems, which would be possible via in-depth numerical analysis.
Adhesively bonded joints in composite materials: An overview
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, 2009
A review of the investigations that have been made on adhesively bonded joints of fibre-reinforced plastic (FRP) composite structures (single skin and sandwich construction) is presented. The effects of surface preparation, joint configuration, adhesive properties, and environmental factors on the joint behaviour are described briefly for adhesively bonded FRP composite structures. The analytical and numerical methods of stress analysis required before failure prediction are discussed. The numerical approaches cover both linear and non-linear models. Several methods that have been used to predict failure in bonded joints are described. There is no general agreement about the method that should be used to predict failure since the failure strength and modes are different according to the various bonding methods and parameters, but progressive damage models are quite promising since important aspects of the joint behaviour can be modelled by using this approach. However, a lack of rel...
Composite adhesive joints under cyclic loading
Materials & Design, 1999
With the increasing use of adhesive bonding in structural joints in many applications, the interest in the behaviour of adhesive joints under cyclic loading has increased as well. Much work has already been performed on the analysis of adhesively bonded joints under static loading. Also the damage growth and failure mechanisms of adhesive joints under cyclic loading has been investigated, to a less extent for joints in composite structures. A major difficulty is the large amount of parameters that can be of influence on crack initiation and growth in adhesive joints. This makes it hard to characterise the debond behaviour of a joint. This article is intended to give an overview of studies performed on adhesive composite joints under cyclic loading on and to serve as a starting point for designers who need information on experimental and analytical methods of composite adhesive joints.
In the present work, the mode I and II fatigue fracture performance of titanium-CFRP adhesive joints is investigated. The adhesive joint under study is composed from two thin adherents, one titanium sheet and one CFRP laminate, and is reinforced from both sides with two thick aluminum beams to increase its flexural stiffness and ensure the non-yielding of the metallic parts. The manufacturing process as well as the intended aerospace application of the joint are presented in our previous works. Here, the dynamic interfacial fracture resistance is in the focus and aspects such as the loading that defines the crack propagation threshold as well as the determination of an appropriate Paris law are under investigation. The fatigue crack growth rate (FCG) í µí±í µí±/í µí±í µí± is determined with two methods; i) through visual inspections with a special camera in mode I, and ii) through an effective crack length which utilizes the changes in experimental compliance in mode II. The equation of compliance over crack length is predetermined by a procedure known as the compliance calibration method (CCM). Detailed results are given, and useful conclusions are obtained for the fatigue crack propagation rates in such complex metal-composite adhesive joints.
Fatigue Strength Investigation of Bonded Joints
Journal of KONES, 2007
Numerous advantages of the bonded joints result in wide application in the aircraft, motor industry or powertrain components. These types of joints enable joining materials with different mechanical properties (e.g. stiffness) and dimensions without structure change. Proper joint design limits the field of local stress concentrations or even eliminates them. The structural integrity of complete structure depends on the fatigue estimation of the bonded joint. Application of the finite element method to life prediction of the double lap bonded joint metal-composite-metal is presented. Three dimensional numerical models are generated by professional engineering software tools. The contact problem is modelled between the epoxy resin and metal and composite surfaces. A laminated composite consists of the epoxy woven carbon prepreg. Elasto-plastic materials models of the adhesion and metal and orthotropy composite model allowed determining the contact normal stress in the interfaces in ea...
Fracture toughness and shear behavior of composite bonded joints based on a novel aerospace adhesive
Composites Part B: Engineering, 2012
In this paper, the mechanical performance of the newly developed LMB aerospace structural adhesive has been characterized experimentally. To this end, a comparison has been performed with the Epibond 1590 A/B adhesive on the basis of the effects of thermal aging, wet aging and adhesive thickness on the fracture toughness and shear behavior (static and fatigue) of bonded joints between CFRP laminates. Mode-I and -II fracture toughness was measured through tensile and 3-point bending tests on doublecantilever beam specimen, respectively, while the shear behavior of the joints was assessed through static and fatigue double-lap shear tests. A fractographic analysis of the fracture surfaces was performed in order to detect the failure mode of the bonded joint. The experimental results show a higher fracture toughness and improved fatigue behavior for the LMB adhesive.
Materials Today: Proceedings, 2020
The efficient and economic structures are high in demand in various firms due to the requirement of lightweight, a feasible joining of similar/dissimilar materials, safety and high durability. Adhesively bonded multi-material joints are coming into use in various structural applications due to the potential utilization of the merits of individual constituents. This research work provides the importance of adhesively bonded joints with different material combinations, which in turn were investigated experimentally. The present paper involves joining of tin as metal and glass fiber reinforced polymer (GFRP) as composite resulting in combinations as GFRP-GFRP, GFRP-Metal, and Metal-Metal Single lap joints (SLJs). The lap joint efficiency test results revealed that the highest lap shear strength was exhibited by GFRP-GFRP SLJ, amounting to a value of 6.84 ± 0.08 MPa. A decrement of 10.98% and 33.17% was recorded for Metal to GFRP and Metal-Metal SLJs, respectively. Similar trend was observed in maximum load underwent by different SLJs, where in GFRP-GFRP SLJ exhibited the highest load bearing capacity of 4280 ± 25 N. The Metal-Metal SLJs indicated the highest shear stiffness value of 4.48 MPa/mm, whereas the GFRP-Metal yielded into the highest toughness value of 21.56 ± 0.44 MPa*mm. Further, the fracture surfaces of SLJs revealed that there was a combination of cohesive and adhesive failures.
Evaluation of Fatigue Damage in Adhesive Bonding: Part 2: Single Lap Joint
2008
The damage parameters for crack initiation in a single lap joint (SLJ) are determined by combining continuous damage mechanics, finite element analysis (FEA) and experimental fatigue data. Even though a SLJ has a simple configuration, the stresses in the adhesive region are quite complex and exhibit multi-axial states. Such a condition leads to the need to introduce a general value for the triaxiality function in the damage evolution law rather than using a triaxiality function which equals unity, as in the case of a uni-axial stress state, e.g., the bulk adhesive test specimen presented in Part 1 of this paper. The effect of stress singularity, due to the presence of corners at edges, also contributes to the complex state of stress and to the variability of the triaxiality function along the adhesive layer in a SLJ. The damage parameters A and β determined in Part 1 for bulk adhesive are now extended to take into account the multi-axial stress state in the adhesive layer, as calculated from FEA.