Many engineering structures, in applications such as automobiles, bridges, etc. are assembled by joining the different parts together. Therefore, joints in the mechanical applications play a critical role in durability, flexibility of the mechanical assemblies. Recent advances in adhesive technology have made adhesive joining one of the plausible options in many engineering applications that demand high impact resistance such as ground vehicle armor or civilian vehicles. However, because most of the polymer-based adhesives have non-linear mechanical behavior and loading rate sensitivity caused by their viscoelastic properties, characterization of the adhesives under different loading and environmental conditions become vital in the design of durable and reliable joints in any structure. This study investigated the mode I (bending) response of the adhesive joints to shock-wave loading generated in a large-scale shock tube. The critical failure pressure (P 5 ) of adhesive joints was determined experimentally. Determining the material properties of the adhesive were estimated by the FEM parametric study, and energy absorption capacity of the adhesive joints under different strain rate loadings were investigated.

Adhesive joint technology has been developed gradually, and the application fields of this type of joints have been expanded increasingly since they reduce the weight of the applications, provide uniform stress distribution across the joints, allow to bond similar, and dissimilar materials, and contribute to dampen the shock, and vibration. However, the performance of the adhesive joints under high loading rate such as blast or ballistic loading has been studied by few researchers. In this study, fully laminated plates consisting of 6061 aluminum plates (15” in diameter and 1/16” thick) and FM300K epoxy film adhesive were tested under shock wave loading. Full displacement field over the testing plates were obtained by TRC-SDIC technique, and the strain on the plates were computed by classical plate theory for large deflections. FEM model was analyzed and the results were compared with experimental results.

The growth of lightweight components and need for non-destructive fastening techniques leads to the use of adhesives in many industries. Modeling the behavior of adhesives in fastening joints can help in the design process to make an optimized joint, with minimal waste. However, in available material properties provided by manufactures of adhesives there is a gap in what is sufficient to accurately model and predict the behavior of real-world adhesive conditions. An adhesive joint may be loaded in mode I, mode II, mode III, or a combination of these in service. In components with outdoor application the ambient temperature outside in many regions can vary to below freezing to over 40 °C. The environmental conditions at these temperatures may influence the adhesive material properties. This body of research presents the results of adhesive properties subject to temperature testing. The needed material properties to compose an accurate model have been shown to be the mode I cohesive strength, mode I cohesive toughness, mode II cohesive strength, and mode II cohesive toughness. These properties can be measured with a test specimen designed to isolate that loading mode and condition. The specimens used are the Dog Bone Tensile Specimen (DBTS), the Double Cantilever Beam (DCB), Shear Loaded Dual Cantilever Beam (SLDCB), and Double Lap Shear (DLS). The effect of temperature will be tested by testing each specimen at −30°C, 20°C, and 45°C. Triplicates of each specimen at the respective temperature were tested. These results will be used in a cohesive zone model that will be validated with additional testing. The results from the two tested adhesives, Plexus MA832 and Pliogrip 7779/220, indicate these temperature conditions can change the cohesive strength in mode I by −60 to −40 % and mode II by −13 to 2% when at high temperatures (HT). The cohesive toughness in mode I by −40 to −20% and mode II by −40 to −2% when at high temperatures. The cohesive strength in mode I by −50 to 15% and mode II by 8% to 60% when at low temperatures (LT). The cohesive toughness in mode I by −70 to −20% and mode II by 30 to 60% when at low temperatures. As compared with those tested at room temperature (RT). The ranges here represent the response for both adhesives.

This research article presents the crashworthiness response of carbon fiber composite front bumper crush can (FBCC) assembly subjected to 40% offset frontal impact loading. Automobile manufacturers continue to strive for overall vehicle weight reduction while maintaining or enhancing safety performance. Therefore, the physical testing of lightweight materials becomes extremely important under a crash scenario in order to apply them to automotive structures to reduce the overall weight of the vehicle. In this study carbon fiber/epoxy lightweight composite material is chosen to develop frontal bumper beam crush can assemblies. Due to lack of available studies on carbon fiber composite FBCCs assemblies under frontal offset crash scenario, a new component-level experimental study is conducted in order to develop data that will provide assistance to CAE models for better correlation. A sled-on-sled testing method was utilized to perform tests in this study. 40 % offset frontal tests on FBCC structures were conducted by utilizing three high-speed cameras (HSCs), several accelerometers and load wall. Impact histories i.e. crash pulse, force-time history, force-displacement, impact characteristics and deformation patterns from all FBCC tests were consistent. The standard deviation and coefficient of variance for the energy absorbed were very low suggesting the repeatability of the 40% offset tests. Excellent correlation was achieved between video tracking and accelerometers results for time histories of displacement and velocity. Post-impact photographs showed the progressive crushing of composite crush cans, bumper beam/crush can adhesive joint failure located on unimpacted side and breakage of the bumper beam due to the production of shear stresses as it is stretched due to its curvature after hitting the sled.

Inspired by biological suture joints with wavy morphology, wavy adhesive joints were designed and the shear resistance of the designs were explored via finite element (FE) simulations. The influences of waviness and material properties of the layer on the mechanical behaviors of the adhesive joints were quantified. Both adhesive and cohesive failure mechanisms were explored: (1) delamination along the interface between the softer layer and the harder substrates, and (2) layer material failure. In the FE models, both cohesive interaction and ductile damage mechanics models were used to capture the two failure mechanisms. The effects of Young’s modulus and damage evolution parameters on the force-displacement relation were studied. Both failure mechanisms were observed by varying the material properties in the adhesive layer. It was found that, the stiffness, strength and the failure mechanisms of the wavy adhesive joints are largely dependent on the geometry and material properties of the layer.

Adhesive use in fastening is increasing in many industries. Modeling the behavior of adhesives allows joints to be optimized, decreasing costs from over-design and validation testing. Unfortunately, available adhesive material properties provided by manufactures are often insufficient to accurately model and predict behavior under real-world conditions. An adhesive joint in service is often subjected to a combination of mode I (tensile) and mode II (shear) loading. Also, when used in outdoor environments, ambient temperatures can vary from below freezing to over 40°C. This paper describes a project to measure the relevant adhesive material properties at the environmental conditions of interest for two specific adhesives and to use them in subsequent modeling. The needed material properties have been found to be mode I cohesive strength, mode I cohesive toughness, mode II cohesive strength, and mode II cohesive toughness. These properties are measured individually using four tests that isolate each of the material properties by using specimens with distinct geometries and loading conditions. These geometries allow the process zone of the adhesives to be controlled. A large process zone will relate to the cohesive strength, and a small process zone will relate to the cohesive toughness, in either mode I or mode II loading. Since the values of cohesive strength and toughness of the adhesives included in this study are unknown before testing, iterations of each specimen are varied by changing the process zone size to ensure valid properties are measured. Testing is conducted at −30°C, 20°C, and 45°C. In order to conduct this testing a temperature chamber was designed, fabricated, and validated. Commercially available temperature chambers were either too small or prohibitively expensive. The temperature chamber this project created was constructed of laser cut and bent stainless steel sheets with an insulated double-wall construction. Two seals were used at every entry point to maintain an air-tight chamber. A heating and cooling circulator and heat exchanger were used for temperature control. The chamber can heat to 45°C in approximately 15 minutes, and cool to −30°C in approximately 30 minutes.

The failure behavior of adhesive joints under shock-wave loadings was investigated in a large scale shock tube facility for the first time. An overlapping specimen consisting of two parts, one circular patch and one supporting ring were bonded together in a specially designed jig. Sub-miniature semi-conductor strain gauges were attached on the specimen to monitor the transient strain on specific locations. A high speed camera was used to record the detachment of the patch from the ring. Image processing tool was used to track the position of the patch as a function of time. This information yield estimates of velocity, acceleration and kinetic energy of the patch. A finite element model was also created and the computation results were compared to the experimental values obtained.

In the present study, the effects of cohesive parameters on the mixed-mode failure of double-scarf adhesive joint (DSAJ) subjected to uniaxial tensile loadings were examined and discussed numerically. For DSAJ with no perpendicular or parallel with the external loading direction, complex stress state (mixture of tensile and shear stresses) occurs at the adhesive interface. In addition, adhesive joint failure, which is a gradually process rather than a sudden transition, is accompanied by energy dissipates gradually at the crack tip. Correspondingly, cohesive zone model (CZM) coupled with finite element method (FEM) was implemented to verify the mechanism of crack from initiation to the complete failure. As the constitutive relation of the adhesive layer, the traction-separation (T-S) law determines the interface damage evolution. Additionally, the shape of T-S curves in mode I and mode II are crucially decided by the cohesive strengths and critical fracture energies in each mode, respectively. Firstly, the non-dimensional-normalized form of ultimate tensile loading of DSAJ was obtained using dimensional analysis. Then, three cases of cohesive parameters (case of constant anisotropy extent & case of constant critical fracture energy in each mode & case of constant cohesive strength in each mode) according to the non-dimensional-normalized form of adhesive properties were designed. Two types adhesives (brittle and ductile) were chosen to examine the effects of adhesive properties on the failure of DSAJ in this study. To avoid the influence of the geometries on DSAJ mechanical behaviors, the thickness of the adhesive layer and the scarf angle θ were held constantly, respectively. In numerical calculations, the change trends of the ultimate tensile loading ( F u ), the failure energy ( E f ) and the damage level ( D ) corresponding to F u with respect to the cohesive parameters were discussed. It can be observed the cohesive strengths in mode I and mode II codetermine F u of DSAJ with unequal rates. Moreover, E f of DSAJ, which is the necessary energy for the joint failure, is governed by the critical fracture energies in mode I and mode II with different contributions. Besides, it also obtained that the evolutions of D corresponding to F u of DSAJ with brittle and ductile adhesives are certain different. Generally, D of DSAJ with brittle adhesive is higher and more uneven than that of DSAJ with ductile adhesive. Accordingly, it can be concluded that DSAJ with brittle adhesive has lower ability to distribute the loading over a smaller cohesive zone with less uniform distribution. In addition, the numerical results revealed that with the increment of ratio in each case set in this paper, D of DSAJ does not rise obviously.

To create an energy efficient vehicle there are a number of aspects that need to be optimized, namely; the drive train of the vehicle and energy source, aerodynamics and weight. Focusing on weight reduction, while still maintaining the desired performance and structural strength, many manufacturers are turning to advanced composites due to their superior strength to weight characteristics. Solar car racing provides a research platform that drives this innovation through technology development and efficiency. A lightweight vehicle suspension system design is being presented, together with an introduction into future testing. A suspension system is made up of a number of critical components which are dynamically loaded during standard operation due to undulating forces imposed by the road surface. Unidirectional cross-wound carbon fiber tubing is used for suspension and steering arms. The tubing is interfaced with small steel inserts and pivoting arm tie rod ends. Concerns within the design are the adhesive bonding of the carbon tubing to the steel inserts, and what type of tensile loading the interface can withstand. Due to forces imposed on the system during cornering and shock loading the components are required to withstand a minimum of 1.2 times the weight of the overall vehicle, i.e. 258 kg. Tensile test results show that the mechanical properties of the adhesive joints rely somewhat on the surface characteristics and bond preparation. The target load of 258 kg was successfully obtained under static loading for two types of sample sets. The first based on the standard for describing the lap shear strength of adhesively bonded carbon fiber to aluminum, and the second based on the working component itself.

Adhesive bonded joints have been increasingly employed in aerospace, automotive, and other mechanical systems due to the advantages of uniform stress distribution, less stress concentration, light in weight, etc. However, the early damage stage of the adhesive bond joints, which are usually named as kissing bond, can significantly impact the structural integrity and safety. Kissing bond is difficult to detect and identify using current non-destructive evaluation (NDE) techniques since there is no clearly gap or interface between the bond area. Attempts using advanced ultrasonic methods have reached limited success, but more reliable methods need to be developed before adhesive joints can be more widely applied to the engineering field. This paper focuses on the development of detection method using digital image correlation (DIC) technique. Three types of adhesive kissing bond joint samples were fabricated using different contamination recipe to simulate the kissing bonds. The performance of the fabricated joint samples were tested using uniaxial hydraulic test frame and the detection capability of DIC system was investigated. The noncontact strain field measurement method using DIC can indicate the existence of kissing bonds with limited load. The results of DIC measurement is encouraging and can be further used for the NDE estimation of mechanical properties of the kissing bond.

The influence of interior and surface flaws in Z-shaped adhesive joints of carbon/epoxy wind turbine blades is examined using finite element method. Contour integral method is used for evaluating the stress intensity factors at the flaw tips, while the strength of the joint is assessed through the crack initiation and propagation simulation. The effect of adhesive shear modulus has also been investigated.

With the weight reduction requirements for vehicles and the cost reduction tendency for carbon fibers, carbon fiber reinforced plastics (CFRPs) will be applied more and more in automobile bodies in place of some steel materials. However, the structural design method using CFRPs is much different from that using steel. For example, the anisotropic material properties and the brittle plastics matrix need to be considered, and the connection between components is through adhesive joints, which is possibly weaker than the traditional spot welding. These features make CFRPs sensitive to impact loads, especially the repeated low-energy impact. This paper presents a damage-based residual modulus and strength prediction method, which may be utilized in the design of composites components subject to repeated impact loads. First, the CFRPs samples were impacted repeatedly by the pendulum hammer at a constant kinetic energy, 2J, and then, the residual bending modulus and strength were measured by static three-point bending machine. According to the test data, the relationship between impact number and residual stiffness and residual strength were established, and the damage factors after each impact were calculated. In subsequent numerical simulation, the damage accumulation effect was included in the one-step prediction model through replacing the initial modulus by the degradation modulus, and this method was verified numerically by comparison with N-step prediction results after N-times impact calculations. Finally, two kinds of composite joints were analyzed numerically, which provides theoretical guide for the design of composite joints in automobile body.

The objective of this work is to predict the fracture behavior of adhesive joints in the 4-ply carbon/epoxy wind turbine blades through finite element method. The influence of through-thickness flaw in the adhesive layer was examined. The contour integral method was used for evaluating the stress intensity factors (SIF) at the flaw tips, while the strength of the joint was assessed through the crack initiation and propagation simulation. The effect of adhesive shear modulus has also been investigated. Results suggested that the maximum stress occurred at the adhesive-shell interface and increased stress levels were observed in the case of adhesive layer with flaw. It also highlighted distinct edge effects along the thickness of the adhesive joint. Compared to the perfect adhesive, the static strength of the adhesive joint with flaw remained unchanged. Large shear modulus of the adhesive diminished the strength of the adhesive joint with the increased SIF.

The continued desire for an alternative to lead-based solder materials for electrical interconnections has led to significant research interest in Anisotropic Conductive Adhesives (ACAs). These create bonds using a combination of metal particles and epoxies to replace solder. The novel ACA discussed in this paper allows for bonds to be created through aligning columns of conductive particles along the Z-axis. These columns are formed by the application of a magnetic field, during the curing process. The benefit of this novel ACA is that it does not require precise printing of the adhesive on pads and also enables the mass curing without creating shorts in the circuitry. The novel ACA’s applicability for PCB-level assembly has been successfully demonstrated by RIT. The research at RIT has also characterized the base material properties, analyzed the effect of various process parameters, identified failures, and investigated the ACA’s long-term reliability for surface mount PCB assembly. Reliability testing included an investigation of the assembly performance in temperature and humidity aging, thermal aging, air-to-air thermal cycling, and drop testing conditions. For example, it has been shown that by modifying the filler particle size and coating, reliability of >1500 hours in high temperature, high humidity aging (HTHH), and 100 hours in highly accelerated stress testing (HAST) can be successfully achieved. This paper highlights research comparing the shear loading performance of the novel ACA to that of tin-lead and lead free solders. Samples assembled with the adhesive and the solders were subjected to multiple tin-lead and lead free reflow cycles. The primary objective was to understand the deterioration in shear loading as influenced by multiple reflow cycles. Published research materials have shown the influence of the change in solder joint performance with multiple reflows due to the increase in intermetallic thickness. The results of a DOE study show the influence of the various factors and levels. Shear stress calculations indicate higher stress experienced by the adhesive joints as compared to the solder joints due to the spreading of the solder during wetting. Empirical relationships will be derived from the experimental data to help determine the required contact area for a given level of shear loading. The experimental results also reveal the rapid decrease in Shear stress between the first and second reflow and the slow decline in strength up to five reflows. Findings from this work will be used to assess the use and reliability of this adhesive for attaching the top component of Package-on-Package (PoP) 3D stacked components, in thermal cycling, HAST and HTHH environments.

In a test-fixture that the authors were using, steel tabs adhesively bonded to an aluminum panel debonded before the design load on the real test panel was fully applied. Therefore, studying behavior of adhesive joints for joining dissimilar materials was deemed to be necessary. To determine the failure load responsible for debonding of adhesive joints of two dissimilar materials, stress distributions in adhesive joints as obtained by a nonlinear finite element model of the test-fixture were studied under a gradually increasing compression-shear load. It was observed that in-plane stresses were responsible for the debonding of the steel tabs. To achieve a better understanding of adhesive joints of dissimilar materials, finite element models of adhesive lap joints and Asymmetric Double Cantilever Beam (ADCB) were studied, under loadings similar to the loading faced by the test-fixture. The analysis was performed using ABAQUS, a commercially available software, and the cohesive zone modeling was used to study the debonding growth.

Growing usage of lightweight materials such as Al and Mg alloys in automotive body manufacture has come to a point that bonding of dissimilar materials is a realistic problem to address. A significant issue related to the bonding of dissimilar materials is that the differences in substrate surface conditions and substrate strengths often lead the bond to fail at strength far less than the bond strength established by adhesive manufacturer for a balanced joint. This research experimentally studied several factors potentially influencing initial strengths and debonding modes of adhesively-bonded Al-steel joints using single lap-shear coupons with comparison to like-substrate joints. Three commonly-used SLS coupon fabricating processes were investigated to determine which provided consistent bond strength and was efficient in making large quantities of coupons for the subsequent study. Next, the effect of prelube on the initial bond strength and debonding mode was investigated since the amount of prelube varies from sheet to sheet in automotive production. It was observed that even a very small change in the amount of prelube being applied on Al affected the initial bond strength. The more the prelube the weaker the bond became and the more adhesive failure occurred on the bonded Al surface. On the other hand, varying amount of the mill oil on the steel surface did not make much change to the bonding strength. Finally, various combinations of Al and steel substrates were studied to observe the effect of substrate materials on the initial bond strength and failure behavior. It revealed that the strength of joints between a relatively strong substrate and a relatively weak substrate fell below the strength of identical material joint made of the relatively strong substrate, and was closer to the strength of identical material joint made of the relatively weak substrate. For bonds having a high joint efficiency, adhesive failures were observed mostly on the surfaces of relatively weak substrates in the dissimilar material bonds due to large deformation in the weak substrate resulting in higher loading on that interface.

The bonding strength of metal-metal single-lap joints with different adhesives applied on steels and aluminum alloys were studied. The bonding strength is found to be related to the type of adhesives and the backing metal, the surface roughness, the surface scratch orientations, the adhesive layer thickness, and the loading conditions (static vs. cyclic and loading rate). SEM observation of fractured surfaces reveals some common feature of bonding strength enhancement, fracture paths and the mechanisms of fracture. The direction of the adhesive joint design is suggested.

This paper deals with an FEM stress analysis of stepped-lap adhesive joints of similar hollow cylinders under static tensile loadings. The effects of Young’s modulus ratio between the adherends and adhesive, the thickness of the adhesive, scarf angle, the number of steps, and singular stress on the interface stress distributions are calculated using FEM. The code of FEM employed is ANSYS. The singular stress is found to occur at the edge of the interfaces. The singular stress at the inside edge is larger than that at the outside edge. It is shown that the maximum principal stress at the edge of the interface decreases as Young’s modulus ratio between the adherend and the adhesive and the adhesive thickness decreases while it decreases as the number of steps increases. Using the obtained interface stress distribution, we can predict the joint strength. For verification of the strength prediction, experiments to measure the joint strength were carried out. The numerical results of the joint strength are in a fairly good agreement with the experimental results.

Under cathodic conditions, rubber/steel adhesive bonded joints have been documented to ‘weaken’ due to attack by the generated alkali. If this were to occur under the action of cleavage mechanical loads, the bonds are likely to completely ‘delaminate’ causing the bonded constituents to physically separate. These two modes of disbondment are referred to as ‘weakening’ and ‘delamination’, respectively. Previously, Hamade and coworkers have implemented empirical and semi-empirical approaches to modeling cathodic disbondment of adhesive joints. Here, a method is presented to simulate bond weakening progress via numerical solutions. Bond degradation is modeled as a liquid-solid chemical reactor due to the attack by the alkaline medium. Specifically, the diffusion and chemical reaction processes involved in weakening are mathematically represented via a simplified, 2 partial differential equations (p.d.e.) boundary value problem (BVP). This is a reduced version of the more complex electrochemical formulation needed to fully describe the chemistry at the bondline under cathodic conditions. The weakening model is capable of simulating weakened bond lengths vs. time as function of electrolyte type (artificial sweater, ASW, or 1N NaOH), cathodic potential, and temperature. Furthermore and to model bond delamination, a mechano-chemical failure criterion is incorporated into the weakening formulation effectively coupling fracture mechanics principles with those of cathodic degradation. A fracture mechanics parameter, applied strain energy release rate, G, is used to represent the effect of externally applied loads. The failure criterion stipulates that the bond will delaminate if the applied G exceeds that of the degraded bond’s residual resistance. Both, the weakening and delamination formulations are validated against experimental data of bond weakening and delamination under a variety of conditions. As such, the numerical simulations developed in this work may be used to provide first order estimates of the life of rubber/steel bonded joints (weakened or delaminated lengths vs. time) as function of cathodic parameters and applied G (if the joint is loaded in the case of delamination).

The effects of environmental degradations on the deformation behavior of an epoxy resin for structural adhesive are experimentally examined using an INSTRON-type material testing machine. The effects of environmental degradations on the shear strength of adhesive joints are also examined using an INSTRON-type material testing machine and a split Hopkinson pressure bar apparatus. The results of quasi-static tensile tests for an epoxy resin for structural adhesive shows that the effect of the resistant to heat degradations tests is small on the deformation behavior, while it seems that the yield stress decreases and the elongation after the rupture increases as the degradations day increases in the resistant to moisture degradation tests. The results of quasi-static and impact shear tests for the adhesive joints shows that the effect of the resistant to heat degradations tests is small on the joint strength, while the shear strength decreases as the degradations day increases at any strain rate in the resistant to moisture degradation tests. In addition, the stress distributions at the adhesive interface of adhesive joints are examined using finite element stress analysis. From the numerical results, it is assumed that the joint strength increases as Young’s modulus of the adhesive decreases and the adhesive thickness is 0.25 mm. For verification of the FEA, the loading responses between the experimental and the numerical results are compared. A fairly good agreement is found between the experimental and the numerical results.