Fracture Characteristics of Shear Adhesive Dissimilar Joint (original) (raw)
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Fracture toughness of adhesively bonded joints
Engineering Fracture Mechanics, 1985
The fracture toughness of an epoxy-based film adhesive has been investigated using Mode I and combined Mode 1 + Mode II loadings. The opening Mode, Mode I, was realized by employing the Tapered Double Cantilever Beam (TDCB) specimen, while the mixed opening and shear modes, Mode I + Mode II, resulted from utilizing the Cracked Lap Shear (CLS) specimen. Fracture toughness was studied under conditions of constant elongation rate as well as sustained load. Furthermore, the environmental effects of both temperature (up to 70°C) and water were investigated in the sustained load case. Experimental results showed that the resistance to crack growth decreased in both the uniaxial and biaxial loading cases when sustained loads were applied, compared to the case of constant elongation rate. Higher temperatures (up to 70°C) in air did not cause any significant decrease in fracture toughness. However, the combination of water and temperature resulted in a significant decrease in the resistance to crack growth. Finally, mixed mode loading showed the most pronounced effect on the critical energy release rate parameter, GI,, as compared to a uniaxial, opening mode loading. The combined effect of biaxial load, temperature (up to 70°C) and water resulted in a drastic decrease in fracture toughness of the studied film adhesive in comparison to uniaxial loading ambient conditions. This result is of practical importance when fracture characteristics are entered in the design considerations for an adhesively bonded structure.
Systematic Evaluation of Bonding Strengths and Fracture Toughnesses of Adhesive Joints
Journal of Adhesion, 2011
A systematic experimental investigation to determine the shear, tensile, and fracture properties of adhesive joints with bonded same-materials (polymer-polymer) and bi-materials (metal-polymer) is reported. Full-field optical techniques including photoelasticity and coherent gradient sensing (CGS) are employed to record the stress development and failure in these adhesive joints. Five types of strong and weak adhesives are used in conjunction with five different types of materials [aluminum, steel, polymethylmethacrylate (PMMA), polycarbonate, and Homalite®-100] to produce a variety of bonded material systems. Weld-on®-10 and a polyester bonding consistently show higher tensile and shear bonding strengths. Bi-material systems in shear and fracture report lower properties than the same-material systems due to a higher property mismatch in the former. The resulting complete experimental data are expected to be immensely helpful to computational mechanists in simulating failure mechanics of adhesive joints.
Role of adherend material on the fracture of bi-material composite bonded joints
Composite Structures, 2020
The aim of this study is to investigate the effect of the adherend material on the mode I fracture behaviour of bimaterial composite bonded joints. Both single-material (steel-steel and composite-composite) and bi-material (steel-composite) joints bonded with a structural epoxy adhesive are studied. Additionally, two adhesive bondline thicknesses are considered: 0.4 mm (thin bondline) and 10.1 mm (thick bondline). The Penado-Kanninen reduction scheme is applied to evaluate the mode I strain energy release rate. The results show that the mode I fracture energy, G Ic , is independent of the adherend type and joint configuration (single or bi-material). G Ic shows average values between 0.60 and 0.72 N/mm for thin bondlines and 0.90-1.10 N/mm for thick bondlines. For thin bondlines, the failure is cohesive and the similar degree of constraint that is imposed to the adhesive by the high-modulus (i.e., steel) and/or relatively thick (i.e., composite) adherends results in similar values of G Ic for both single-and bi-material joint types. For thick bondlines, the crack grows closer to one of the adhesiveadherend interfaces, but still within the adhesive. The results show that the adhesive could deform similarly, although the crack has been constrained on one side by different types of adherends, either a steel or composite.
The evolution of damage at the tip of cracks in adhesive bonds deforming in shear was monitored in real time using a high-magnification video camera. Brittle and a ductile epoxy resins were evaluated, with the bond thickness t being an experimental variable. An extensive zone of plastic deformation developed ahead of the crack tip prior to fracture. In the case of the brittle adhesive, for relatively thick bonds tensile microcracks formed within that zone. Increased loading caused the microcracks to grow from the interlayer to the interface, which led to a complete bond separation after interface cracks emanating from adjacent microcracks linked. In contrast, for the ductile adhesive the crack always grew from the tip. Strain gradients tended to develop there when the bond thickness was large. The adhesive shear strain was determined from fine lines scratched on the specimen edge. For both adhesives, the average crack tip shear strain at crack propagation rapidly decreased with increasing t. This effect was attributed to the changing sensitivity of the bond to the presence of flaws; thicker bonds can accommodate larger microcracks or microvoids which cause greater stress concentration. For a given bond thickness, the critical crack tip shear strain agreed well with the ultimate shear strain of the unflawed adhesive ?s previously determined using the napkin ring shear test 1-12]. This suggests that the ultimate shear strain is a key material property controlling crack growth. The critical distortional strain energy/unit area of the unflawed adhesive W~ was determined from the area under the stress-strain curve in the napkin ring test. Good agreement between W, and the adhesive mode II fracture energy was found for all joints tested except for relatively thick bonds. For the particular case of an elastic-perfectly plastic adhesive, the agreement above implies Gnc = W s =-tzy)~f.
FRACTURE STUDIES OF AN ADHESIVE JOINT INVOLVING COMPOSITION ALTERATION
Journal of Chemical and Pharmaceutical Sciences, 2015
Adhesive joints are widely used in industries because they have several advantages when compared to welded and riveted joints. One of the important factors is that they distribute the load and stresses uniformly over the entire bonded area providing good vibration resistance. Adhesive joints can readily bond dissimilar materials. The prediction of crack propagation validating the adhesive joint durability and toughness is a significant point that is addressed through various experimental methodologies based on the type of loading conditions. The analysis is hindered by the unpredictable adherend and adhesive behavior due to the loading conditions, the nature of crack propagation, and the geometry. The impact of hardener resin ratio alteration is a parameter that needs to be explored invalidating the joint toughness. The Double Cantilever Beam tests which are used for analyzing the fracture toughness for mode-1 loading in adhesive joints focus on adhesive thickness variation extensively. The alteration of composition and its role in influencing the crack propagation is explored from a limited perspective. An attempt is made in this work to analyze the adhesive composition variation and its impact on the joint toughness with the help of a DCB test involving three specimens incorporating variations in the hardener resin composition. The analytical and experimental results provided significant insights into the adhesive joint toughness validation.
Israel Society of Aeronautics and Astronautics 34th Israel Annual Conference on Aerospace Sciences, 1994
The evolution of damage at the tip of cracks in adhesive bonds deforming in shear was monitored in real time using a high-magnification video camera. Brittle and a ductile epoxy resins were evaluated, with the bond thickness t being an experimental variable. An extensive zone of plastic deformation developed ahead of the crack tip prior to fracture. In the case of the brittle adhesive, for relatively thick bonds tensile microcracks formed within that zone. Increased loading caused the microcracks to grow from the interlayer to the interface, which led to a complete bond separation after interface cracks emanating from adjacent microcracks linked. In contrast, for the ductile adhesive the crack always grew from the tip. Strain gradients tended to develop there when the bond thickness was large. The adhesive shear strain was determined from fine lines scratched on the specimen edge. For both adhesives, the average crack tip shear strain at crack propagation rapidly decreased with increasing t. This effect was attributed to the changing sensitivity of the bond to the presence of flaws; thicker bonds can accommodate larger microcracks or microvoids which cause greater stress concentration. For a given bond thickness, the critical crack tip shear strain agreed well with the ultimate shear strain of the unflawed adhesive ?s previously determined using the napkin ring shear test 1-12]. This suggests that the ultimate shear strain is a key material property controlling crack growth. The critical distortional strain energy/unit area of the unflawed adhesive W~ was determined from the area under the stress-strain curve in the napkin ring test. Good agreement between W, and the adhesive mode II fracture energy was found for all joints tested except for relatively thick bonds. For the particular case of an elastic-perfectly plastic adhesive, the agreement above implies Gnc = W s =-tzy)~f.
Fracture Analysis of Adhesively Bonded Joints as a Function of Temperature
International Conference on Mechanical, Manufacturing and Process Engineering (ICMMPE – 2022), 2022
In this study, adhesively bonded joints' fracture parameters have been investigated. Double Cantilever Beam (DCB) and End Notch Flexure (ENF) tests have been simulated using ABAQUS ® simulation software to analyze the effect of low temperature on the epoxy adhesive Mode I and Mode II fracture toughness respectively. Varying material properties for different low temperatures have been used to simulate the tests at low-temperature conditions. The fracture load has been determined from the P-δ curve at various low temperatures. The stress intensity factor has been evaluated to get the strain energy release rate which has been used to describe the fracture toughness of the adhesive. The result showed that the fracture load and fracture toughness for Mode I slightly increases by the reduction in temperature. Whereas with the reduction of temperature fracture load and toughness for Mode II increases greatly. The fracture load has increased by 12.6% and 65.1% and the fracture toughness has increased by 36.5% and 84.3% with temperature reduced to-80°C from room temperature for Mode I and Mode II respectively.
Multi-material adhesive joints with thick bond-lines: Crack onset and crack deflection
Composite Structures, 2021
This study investigates the fracture onset and crack deflection in multi-material adhesive joints with thick bond-lines (≈10 mm) under global mode I loading. The role of adherend-adhesive modulus-mismatch and pre-crack length are scrutinized. The parameters controlling the crack path directional stability are also discussed. Single-material (i.e. steel-steel and GFRP-GFRP) and bi-material (i.e. steel-GFRP) double-cantilever beam joints bonded with a structural epoxy adhesive are tested. The joints are modelled analytically, considering a beam on elastic-plastic foundation, to include characteristic length scales of the problem (e.g. adhesive thickness, plastic zone) and numerically using Finite Element Model. An empirical relation, in terms of geometrical and material properties of the joints, that defines the transition between non-cohesive and cohesive fracture onset is found. Above a specific pre-crack length the stress singularity at pre-crack tip rules over the stress singularity near bi-material corners, resulting in mid-adhesive thickness cohesive fracture onset. However, the cracking direction rapidly deflects out from the adhesive layer centre-line. Positive T-stress along the crack tip is found to be one of the factors for the unstable crack path.
Frattura ed Integrità Strutturale, 2020
Development in material science imposes to use different materials in production. This causes a problem for joining different materials because traditional joining techniques such as welding could not overcome this problem in industries such as automotive. Hence, adhesive bonding overcomes this problem by its superiorities to join different materials. The joint strength of epoxy-based adhesives is affected by adhesive thickness, adherent's surface quality, and curing conditions. In this study, two different materials (SAE 304 and AL7075) were bonded by epoxy adhesive (3M DP460NS) as single lap joint (SLJ) of Aluminum-Aluminum, Steel-Steel, and Aluminum-Steel. The effects of adhesive thickness (0.05, 0.13, 0.25 mm) and surface roughness (281, 193, 81 nm) to strength were compared. SLJs were tested for 1, 10, 25 and 50 mm/min displacement rates. Adhesive surface structures were imaged by Scanning Electron Microscopy (SEM) to investigate adhesive fractures. Surface roughnesses were examined by using Atomic Force Microscopy (AFM) to compare its influence on failure load. Finite Element Analysis (FEA) was conducted by using Cohesive Zone Model with ANSYS 18.0 software to obtain stress distribution of adhesive. Optimum values according to the present conditions of the thickness (0.13mm) and roughness (<200nm) were determined. Experimental results were demonstrated that while displacement rates rose, failure loads increased as well. FEA analysis was fit to experimental results. It has been observed that along with material type, peel stresses become an important factor for joint strength.