Effect Of Adhesive Thickness Research Articles

A simplified hardening cohesive zone model for bondline thickness dependence on adhesive joints

In this paper, a tri-material adhesive system with nonlinear cohesive springs embedded between two elasto-plastic adhesive layers is proposed to predict the adhesive thickness effects on the fracture energy of bonded joints. The localized plastic and damage behaviours along the interface are described by the hardening cohesive zone models. The thickness dependent interfacial energy release rate is divided into the essential separation energy rate and the energy dissipation rate of the plasticization. The adhesive thickness dependent hardening cohesive zone model is implemented into the proposed numerical method to predict the failure of the adhesive joints. The validation of the model is performed by comparison with the experimental data.

Effect of adhesive thickness on the stringiness of crosslinked polyacrylic pressure‐sensitive adhesives

ABSTRACTThe effect of adhesive thickness on stringiness behavior during 90° peel testing was investigated for crosslinked poly(n‐butyl acrylate‐acrylic acid) (A) and poly(2‐ethylhexyl acrylate‐acrylic acid) (B) with a constant crosslinker content. The adhesive thickness was varied over the range from 15 to 60 μm. All adhesive thicknesses exhibited sawtooth‐type peeling with a front frame for B, but only the 30‐μm thickness generated a front frame‐type for A. The peel rate decreased from 15 to 45 μm and plateaued above 45 μm under a constant load test. These results indicate that the adhesion strength increases with adhesive thickness, but reaches a constant value at high thicknesses. The stringiness was also analysed for B and the sawtooth interval observed to increase with increasing thickness. This means the sawtooth number decreased. As a result, the concentrated stress per sawtooth induces easier peeling and so this factor tend to increase the peel rate. Conversely, the stringiness width increased with increasing thickness. The stress load over the stringiness region decreased with an increase in thickness, meaning that a decrease in the concentrated stress decreases the peel rate. The actual peel rate is influenced by the contributions of these two factors. The strain rates during constant peel rate tests decreased slightly with increasing thickness, due to a reduction in the apparent modulus. The molecular mobilities near the adherend and the backing surfaces were evidently restrained by these surfaces, and the relative rates of motion of such restrained molecules decrease with increased thickness. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42210.

界面縁き裂の応力拡大係数に及ぼす接着層厚さの影響

界面縁き裂の応力拡大係数に及ぼす接着層厚さの影響

OS0501-122 接着層厚さが小さい場合における接着接合板の応力特異性強さ

Adhesive joints are widely used in wide industrial fields, supplementing or replacing traditional joining technologies. However, a mismatch due to different materials properties may cause stress singularity at the edge of an interface between the materials, which causes debonding of structures. Since few studies are available for evaluating the bonded strength, this study focuses on the solutions for the intensity of the singular stress for the semi-infinite butt joint. In this research, an effective numerical method combined with FEM results is used to obtain the SIFs at corner of adhesive joints in arbitrary material combinations. Here, the solution of bonded plate, which has already been solved accurately in the previous study, is used as the reference problem. In this paper, the effect of adhesive thickness on the intensity of singular stress will be analyzed, also the effects of material combination on the intensity of singular stress at the end of the adhesive with thin layer in a semi-infinite plate will be discussed.

Adhesive thickness effects of a ductile adhesive by optical measurement techniques

Adhesive bonding is an excellent alternative to traditional joining techniques such as welding, mechanical fastening or riveting. However, there are many factors that have to be accounted for during joint design to accurately predict the joint strength. One of these is the adhesive layer thickness (tA). Most of the results are for epoxy structural adhesives, tailored to perform best with small values of tA, and these show that the lap joint strength decreases with increase of tA (the optimum joint strength is usually obtained with tA values between 0.1 and 0.2mm). Recently, polyurethane adhesives were made available in the market, designed to perform with larger tA values, and whose fracture behaviour is still not studied. In this work, the effect of tA on the tensile fracture toughness (Gnc) of a bonded joint is studied, considering a novel high strength and ductile polyurethane adhesive for the automotive industry. This work consists on the fracture characterization of the bond by a conventional and the J-integral techniques, which accurately account for root rotation effects. An optical measurement method is used for the evaluation of crack tip opening (δn) and adherends rotation at the crack tip (θo) during the test, supported by a Matlab® sub-routine for the automated extraction of these parameters. As output of this work, fracture data is provided in traction for the selected adhesive, enabling the subsequent strength prediction of bonded joints.

The Effect of Adhesive Thickness on the Mechanical Behavior of a Structural Polyurethane Adhesive

One parameter that influences the adhesively bonded joints performance is the adhesive layer thickness. Hence, its effect has to be investigated experimentally and should be taken into consideration in the design of adhesive joints. Most of the results from literature are for typical structural epoxy adhesives which are generally formulated to perform in thin sections. However, polyurethane adhesives are designed to perform in thicker sections and might have a different behavior as a function of adhesive thickness. In this study, the effect of adhesive thickness on the mechanical behavior of a structural polyurethane adhesive was investigated. The mode I fracture toughness of the adhesive was measured using double-cantilever beam (DCB) tests with various thicknesses of the adhesive layer ranging from 0.2 to 2 mm. In addition, single lap joints (SLJs) were fabricated and tested to assess the influence of adhesive thickness on the lap-shear strength of the adhesive. An increasing fracture toughness with increasing adhesive thickness was found. The lap-shear strength decreases as the adhesive layer gets thicker, but in contrast to joints with brittle adhesives the decrease trend was less pronounced.

Stress Distribution in Single Lap Joints with a Cracked Composite Adherend—Part II: Laminated Adherends

The effect of a crack in the overlap region of an adhesive single lap joint is studied on the shear stress distribution in adhesive layer. Each adherend is considered to be a laminated composite material with unidirectional fibers aligned in the direction of the applied load. Crack location is selected to be in the top adherend laminate, in the form of cut fibers and matrix bays. The crack can occur in any layer. The shear-lag model is used to derive the equilibrium equations which are then solved by means of eigenvector expansion. The effects of adhesive thickness, crack size, and location in the adherend, total number of layers in each adherends, volume fraction of fibers, and type of fibers are investigated on the shear distribution in the adhesive as well as load distribution in the intact fiber at the crack tip located in the top adherend. The effect of dissimilar laminated adherends is also investigated on the adhesive shear stress distribution. According to the results, in the presence of a crack, the peak shear stress in the adhesive layer and load concentration in the fibers are very susceptible to the adhesive thickness and number of layers in laminated adherends.

Static Tensile and Transient Dynamic Response of Cracked Aluminum Plate Repaired with Composite Patch – Numerical Study

In this study, the central cracked aluminum plates repaired with two sided composite patches are investigated numerically for their response to static tensile and transient dynamic loadings. Contour integral method is used to define and evaluate the stress intensity factors at the crack tips. The reinforcement for the composite patches is carbon fibers. The effect of adhesive thickness and patch thickness and configuration in tensile loading case and pre-tension, pre-compression and crack length effect on the evolution of the mode I stress intensity factor (SIF) (KI) of the repaired structure under transient dynamic loading case are examined. The results indicated that KI of the central cracked plate is reduced by 1/10 to 1/2 as a result of the bonded composite patch repair in tensile loading case. The crack length and the pre-loads are more effective in repaired structure in transient dynamic loading case in which, the 100 N pre-compression reduces the maximum KI for about 40 %, and the 100 N pre-tension reduces the maximum KI after loading period, by about 196 %.

Analytical Solution of Stress Field in Adhesively Bonded Composite Single-Lap Joints Under Mechanical Loadings

In this paper, considering an adhesively bonded composite single-lap joint, a novel approach is presented to predict the peel and shear stress distributions of the adhesive layer for an ASTM standard test sample. In current method, the equilibrium equations are derived using the energy method and based on the Timoshenko’s beam theory. Two solution procedures then are discussed, one of which represents a solution approach based on the direct variational method allied with use of the Ritz approximation; while the second one is based on a linear estimating function. Unlike previous methods, in which the variation of stress through the thickness of adhesive is neglected or is assumed to be linear and they cannot be used to analyze the joints with thick adhesive layers; considering the effects of adhesive thickness makes it possible to employ present method to analyze the joints with thick adhesive layers as well as thin ones.

Effect of adhesive thickness on adhesively bonded T-joint

The aim of this work is to analyze the effect of adhesive thickness on tensile strength of adhesively bonded stainless steel T-joint. Specimens were made from SUS 304 Stainless Steel plate and SUS 304 Stainless Steel perforated plate. Four T-joint specimens with different adhesive thicknesses (0.5, 1.0, 1.5 and 2.0 mm) were made. Experiment result shows T-joint specimen with adhesive thickness of 1.0 mm yield highest maximum load. Identical T-joint specimen jointed by spot welding was also tested. Tensile test shows welded T-Joint had eight times higher tensile load than adhesively bonded T-joint. However, in low pressure application such as urea granulator chamber, high tensile strength is not mandatory. This work is useful for designer in fertilizer industry and others who are searching for alternative to spot welding.

Three-Dimensional Finite Element Analysis of Single-Lap Joints: Effect of Adhesive Thickness and Poisson's Ratio

Three-dimensional (3D) elastic stress distributions in the vicinity of overlap corners of single-lap joints are investigated. A detailed 3D finite element (FE) model is carried out to study the intensity of the in-plane and out-of-plane stress distributions along the plate width direction. The effects of adhesive thickness and Poisson's ratio are also studied. The FE results show the presence of coupled modes at the overlap corners of the joint. In particular, sharp increment of out-of-plane fracture mode very near the lateral free surface of the joint is worth noting.

Effect of adhesive thickness, adhesive type and scarf angle on the mechanical properties of scarf adhesive joints

The effects of adhesive thickness, adhesive type and scarf angle, which are determined as the main control parameters by the dimensional analysis, on the mechanical properties of a scarf adhesive joint (SJ) subjected to uniaxial tensile loading are examined using a mixed-mode cohesive zone model (CZM) with a bilinear shape to govern the interface separation. Particularly, the adhesive-dependence of the vital cohesive parameters of CZM, which mainly include initial stiffness, total fracture energy and separation strength, is introduced emphatically. The numerical results demonstrate that the ultimate tensile loading increases as the adhesive thickness decreases. Cross the ultimate tension, the joint loses the load-bearing capacity when adopting the brittle adhesive but sustains partial load-bearing capacity while selecting the ductile adhesive. In addition, for the joint with the ductile adhesive, the maximum applied displacement until the complete failure of it is directly proportional to the adhesive thickness, which is different from the case using the brittle adhesive. Taking the combination of the ultimate loading and applied displacement into account, failure energy is employed to evaluate the joint performances. The results show that the failure energy of the joint with the brittle adhesive increases as the adhesive thickness decreases. Conversely, the situation of the joint using the ductile adhesive is vice versa. Moreover, the effect of the adhesive thickness becomes more noticeable with decreasing the scarf angle owing to the variation of the proportion of each component of the mixed-mode. Furthermore, all the characteristic parameters (the ultimate tensile loading, the maximum applied displacement and the failure energy) that adopted to describe the performances of SJ increase as the scarf angle decreases. Finally, the numerical method employed in this study is validated by comparing with existing experimental results.

Static and fatigue failure analysis of adhesively bonded thick composite single lap joints

Static and fatigue behavior of thick composite laminate single lap joints with thick adhesive bondline is experimentally and numerically investigated. Stress based analysis is used to understand the uniaxial tensile behavior of thick glass fiber reinforced epoxy laminates bonded with relatively thick epoxy adhesive. The effect of adhesive thickness on relatively thick adherend on the fatigue initiation life was modeled with generalized stress singularity approach. It was observed that the failure onset always occurred at adherend–adhesive interface. Subsequent crack propagation mostly resulted in interlaminar failure of adjacent first angle ply near to this interface. Both static and fatigue strength values decrease with increase of bondline thickness. Evaluation of generalized stress intensity factors of the corner geometry (square edge joint) provided a good correlation between predictions and experimental measurements.

Orthogonal Microcutting of Thin Workpieces

With a broader intention of producing thin sheet embossing molds, orthogonal cutting experiments of thin workpieces are conducted. Challenges in machining thin workpieces are many: machining induced stress and deformation, fixturing challenges, and substrate effects. A setup involving continuous orthogonal cutting with a single crystal diamond toolof an aluminum alloy (Al6061-T6) workpiece fixtured using an adhesive to reduce its thickness is used to study trends in forces, chip thickness, and to understand to what level of thickness we can machine the workpiece down to and in what form the adhesive fails. There are no significant changes observed in the forces and chip thickness between thick and thin workpieces during the experiments, meaning that the cutting energy required is the same in cutting thick or thin workpieces. The limitation to achieve thinner workpiece is attributed mainly due to the detachment of the thin workpiece by peel-off induced by adhesive failure mode, which occurs during initial chip formation as the tool initially engages with the workpiece. We use a finite element model to understand the stresses in the workpiece during this initial tool engagement when it is thick and when it is thin, as well as the effect of the adhesive itself and the effect of adhesive thickness. Simulation results show that the tensile stress induced by the tool at the workpiece-adhesive interface is higher for a thinner workpiece (45 μm) than a thicker workpiece (150 μm) and higher at the entrance. As such, a thinner workpiece is more susceptible to peel-off. The peeling of thin workpiece is induced when the high tensile stress at the interface exceeds the tensile-at-break value of the adhesive.

English

  The aim of this study is to research the effects of adhesive thickness, which is one of the factors that affect the stress distribution in the prismatic plug-in joints. The effect of adhesive thickness was theoretically researched in the study. Epoxy-based and acrylic-based adhesives, which are widely used in combining metal joints, were applied. After testing the mechanical characteristics of the adhesives, the models of the prismatic plug-in joints combined with adhesive were designed in the Pro-engineer program. The mechanical analysis of the models was performed in Ansys Workbench and the results are presented as a comparison.       Key words: Adhesive, mechanic properties, bulk specimens, acrylic, epoxy

Analytical solutions for adhesively bonded composite single-lap joints under mechanical loadings using full layerwise theory

In this paper, analytical solutions for adhesively bonded composite single-lap joints (SLJs) are presented within the framework of the full layerwise theory (FLWT). The adhesively bonded composite SLJ is divided into a large number of mathematical plies through the thickness and three regions along its length. The equilibrium equations of each region are obtained using the principle of minimum total potential energy. The three sets of fully-coupled governing equations then are simultaneously solved by introducing the state space variables. The effects of adhesive thickness and loading conditions including uniaxial tension and bending moment on the interfacial peel and shear stress as well as the von Mises stress distributions along the length and through the thickness of the adhesive layer are studied. The present results, which are verified via analytical, experimental, and numerical investigations available in the literature, can be introduced as scaling solutions to verify the authenticity of other methods.

Study on the effect of adhesive thickness of single lap joints using acoustic emission and FEA

Study on the effect of adhesive thickness of single lap joints using acoustic emission and FEA

Influence of Adhesive Layer on Actuation of Lamb Wave Signals

In this work, Lamb wave generation and propagation have been modelled in composite plates. Actuation and acquisition of signals when the PZT transducers are tied to the structure or bonded with an adhesive layer are investigated. The effect of adhesive thickness and actuation frequency of Lamb wave have been examined.

Performance improvement by glass fiber of adhesively bonded metal joints at the cryogenic temperature

The performance of adhesively bonded joints composed of aluminum sheet and stainless steel foils was investigated at the cryogenic temperature for the secondary barrier LNG (Liquefied Natural Gas) containment system. Since the huge adhesive bonding area such as LNG carriers or floaters cannot be surface-treated economically by chemical treatment, new flame surface treatment method for the metal foils was evaluated and compared with other conventional surface treatments such as mechanical or chemical surface treatments at the cryogenic temperature. The surface wettability by contact angle measurement of the metal foil was investigated with respect to surface treatments and environmental aging conditions. The effects of adhesive thickness on the adhesive bond strength and fracture toughness have been also investigated at the cryogenic temperature.The experimental results showed that the bonding performances depended strongly on the surface treatment method, adhesive thickness and fiber reinforcement for the adhesive, such. It was also found that the thick adhesive joint had a reduced bonding strength at the cryogenic temperature, but the glass fiber reinforcement improved much the bonding strength and fracture toughness for thicker adhesive at the cryogenic temperature.

Load transfer in adhesive double-sided patch joints

In this work, the application of adhesively bonded joints to connect two structural elements with a double-sided patch is studied. On the basis of the shear lag model, a simple closed-form solution was obtained. The analytical solutions can be used to predict the shear stress in the adhesive and the load transfer between the structural elements and the external patches. The load and shear stress distributions in the adhesively bonded region are presented. For verification of the analytical model, finite element analyses were employed to calculate the load transfer and shear stress for the double-sided patch joint under static tensile loadings. Good agreement was found between the theoretical predictions and numerical results. To obtain a better understanding of the joints, the effects of adhesive thickness, adhesive shear modulus and patch Young's modulus on the load transfer and shear stress distributions were investigated. The results show that the maximum shear stress occurs at the edge of the adhesive. The maximum value of the shear stress increases as the adhesive shear modulus and patch Young's modulus increase and as the adhesive thickness decreases. A more gradual load transfer can be achieved by increasing the adhesive thickness and decreasing the adhesive shear modulus. The simple analytical solution presented in this paper has the advantages of avoiding the numerical difficulties and giving explicit relationship between the stress state and joint parameters. Moreover, from the designer's point of view a closed-form and easy-to-use solution is preferred.