Effect Of Bondline Thickness Research Articles

Effect of bondline thickness on the mechanical performance of CFRP laminate with asymmetric damage repaired by double-sided adhesive patch

As a common CFRP repair method, double-sided adhesive patch has been widely used in the automotive and aeronautic industry. More specific research is thus needed to help better understanding the effect of repairing parameters on the mechanical performance of CFRP structures after patch bonding. In this paper, experimental and Finite Element Modelling (FEM) efforts were made on the adhesive repaired CFRP laminate with different bondline thicknesses. Artificial damage was prefabricated in the centre of the CFRP laminate, which was then repaired through double-sided adhesive patch. Quasi-static tensile tests were conducted on the repaired specimen up to failure, to obtain the load-displacement curves. With a bondline thickness of 0.5 mm, the repaired CFRP structure reached its maximum peak load, increased by 25.3% and 26.4% compared to 0.2 mm and 1.0 mm bondline thicknesses, respectively. SEM observations were used to analyse the influence of adhesive thickness on the fracture modes. Combined with Cohesive Zone Model (CZM) for the adhesive layer and Hashin damage criterion for the CFRP, the FE model of the CFRP laminate repaired with double-sided adhesive patch subjected to tensile loading was established. Finally, the damage evolution as well as the failure modes in the parent laminate and adhesive layer with different bondline thicknesses were compared and analysed. It was revealed that bondline thickness can effectively affect the mechanical performance of CFRP laminate after adhesive patch repair.

A novel cohesive zone modelling approach to represent mixed mode loading and bond line thickness effects

ABSTRACT Accurate representation of the traction–separation response for mixed mode loading in a cohesive zone model (CZM) is critical to predicting the response of adhesive joints in a number of applications, including transportation and vehicle crashworthiness. Traditionally, the Mode I and Mode II responses are treated independently, with mixed mode response determined by relationships between the degree of mode mixity and separation, potentially leading to overprediction of the plateau traction and underprediction of the plateau length in mixed mode loading. This poor fit is due to the indirect relationship between mixity and traction and having minimal fitting options for separation-to-plateau and softening. To address this limitation, a mixed mode CZM approach is proposed, based on measured mixed-mode traction–separation results for a toughened epoxy adhesive. The effects of bond-line thickness were considered, to examine the ability of the proposed approach to include additional effects (beyond mode mixity) that are known to affect the traction–separation response. The CZM implementation was assessed using the original test data and was shown to capture the measured experimental traction–separation response across a range of mixed mode loading and bond line thickness more accurately compared to traditional CZM treatments.

Adhesive properties of thiol-acrylate-epoxy composites obtained by dual-curing procedures

Composite materials were prepared using a thiol-acrylate-epoxy dual-curing system filled with Boron Nitride (BN) agglomerates. The adhesive properties obtained with two different acrylate ratios (r a ) were tested to characterize differences and applicability of final thermosets. The effect of bondline thickness, BN wt% and curing procedure on the adhesive strength was evaluated for both acrylate ratios r a by means of lap-shear tests. Materials with viscous intermediate (r a = 0.2) results were observed to have the best performance reaching a maximum of almost 5 kN with 20 wt% of BN. On the other hand, materials with an intermediate gelled network (r a = 0.5) showed a high accuracy in dimension control but lower values of adhesive strength were obtained. A decrease of adhesive strength with the increase of thickness was found for both r a , while the increase of BN wt% lead to higher adhesive strength. The beneficial effect of dual-curing processing on the adhesive properties of liquid intermediate materials was also experimentally demonstrated.

Effect of bond-line thickness and mode-mixity on the fracture behavior and traction separation law of Sn-0.7Cu solder joints

In this research, cohesive parameters were extracted for Sn-0.7Cu/Cu solder joint failure. Double cantilever beam (DCB) specimens were used to study the fracture of the joint under both mode-I and mixed-mode conditions. A bilinear traction separation law (TSL) was used to capture the failure of the joint. Increasing the bond-line thickness from 110 to 880 µm increased the critical energy release rate for crack initiation (Gci) and maximum traction of the bilinear TSL. This increase in the Gci was attributed to an increase in plastic zone area (PZA) ahead of the pre-crack tip. Varying the mode-mixity with phase angle (ψ) in the range of 00–330 showed an insignificant change in Gci and maximum traction of the bilinear TSL.

Effect of Ag Sintered Bondline Thickness on High-Temperature Reliability of SiC Power Devices

Nano-Ag sintering is a promising die-attach technology for the wide bandgap semiconductive power devices, while the high cost of nanosilver limits industrial application. Reducing bondline thickness (BLT) is effective for cost-saving but its effects on reliability have been rarely studied, especially at high-temperature operation. In this work, an organic-free nanostructured silver film was prepared by pulsed laser deposition (PLD) for various BLT joints. The effect of BLT (3.5– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$60~\mu \text{m}$ </tex-math></inline-formula> ) on the high-temperature reliability of die-attached modules was systematically investigated. The results indicated that with the increase of BLT, the shear strength and power cycling number of joints both increased. The optimal BLT ranged in 25– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50~\mu \text{m}$ </tex-math></inline-formula> considering both reliability and cost. It was very interesting to find that the connection ratio along the BLT direction existed two valleys at the die- and DBC-bondline interfaces, which clearly corresponded to the crack propagating in the power cycling test.

Viscoelastic model to capture residual stresses in heat cured dissimilar adhesive bonded joints

The thermal loading during the curing process of an adhesive-bonded joint induces residual stresses in the joint, thereby affecting its performance. The problem becomes worse in the case of a multi-material joint involving varying coefficients of thermal expansion (CTE) for different parts. A novel approach was developed to model the properties of automotive grade structural adhesives during the heat curing process. The material model was divided into two components: curing kinetics model and viscoelastic mechanical model. The models were calibrated using experimental data from Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) tests performed on an epoxy-based single-component adhesive. The calibrated material model parameters were fed into a finite element simulation and the prediction results were compared to a unique set of experiments utilizing two substrate combinations of adhesive-bonded single lap shear joints. An excellent agreement between the simulated and experimental results (displacement across the bond, force applied by the adhesive) was achieved. The modeling results give a better understanding of the residual stresses and agree with the experimental trend on the effect of bondline thickness on the joint.

The effect of bond-line thickness on fatigue crack growth rate in adhesively bonded joints

The effect of adhesive thickness on fatigue crack growth in an epoxy film adhesive (FM94) was investigated, using a combination of experiments and numerical modelling. For the range of thicknesses investigated an increased thickness led to an increased crack growth rate. It was found that the energy required per unit of crack growth did not depend on the adhesive thickness. In contrast, the energy available for crack growth does depend on the adhesive thickness.The numerical analysis confirms that the energy required per unit crack growth is not sensitive to the adhesive thickness, but that the plastic energy dissipation increases with the thickness. The experimental results imply that this increase of plasticity has an anti-shielding effect, as the crack growth rate is increased.

Strength prediction of adhesively bonded single lap joints with different bondline thicknesses: A critical longitudinal strain approach

The effect of bondline thickness on the strength of adhesively bonded single lap joints (SLJs) is still an open issue. According to the analytical methods and also finite element (FE) results, increasing the adhesive thickness causes a more uniform stress and strain distribution along the adhesive layer and consequently leads to higher strength of the SLJs, while the experimental data has shown lower strength for joints with thicker bondlines. This paper deals with the effect of the adhesive thickness on the strength of SLJs from the perspective of the longitudinal strain along the adhesive mid-plane. The longitudinal strain is a recently proposed failure parameter which should be measured along the adhesive mid-plane, at a specific distance away from the joint bonding end. The FE results showed that under a constant tensile load, the values of longitudinal strain along the adhesive mid-plane, increase with adhesive thickness. It could be concluded that the introduced failure parameter could take into account the decrease in joint strength due to an increase in bondline thickness. Some experiments on SLJs with different adhesive thicknesses and bonding lengths were conducted to validate the method. Good correlation between the experimental results and the predictions were seen. The method was also applied on experimental results published by other researchers. The results again showed that the new strain based method could well consider the strength reduction of SLJs due to increasing adhesive thickness.

Superior dissimilar adhesive joint of mild steel and aluminium using UDM processed epoxy based TiO2 nano-filler composite adhesive

Abstract Characteristics of the lap joints of mechanically and chemically treated faying surface of dissimilar metals (Mild Steel and Aluminium) prepared by using UDM processed TiO 2 -epoxy nano composite adhesive was investigated. Influence of the extent of TiO 2 nano (25–35 nm) particle reinforcement (5, 10 and 15 wt%) in the composite adhesive on the improvement of tensile lap shear strength of the adhesive joints has been studied. Effect of bond line thickness of the adhesive in lap joints of the differently treated faying surfaces of the dissimilar metals on lap shear strength of the joints has also been studied. The joints of 10 wt% TiO 2 nano-filler content epoxy adhesive shows maximum lap shear strength of the joints. Its lap shear strength was also studied at elevated temperatures in the range of 100–250 °C. In order to establish the potentials of nano composite adhesive to relatively improve the properties of the joint, the lap shear strength of the adhesive joint of neat epoxy adhesive was also studied and compared.

Evaluation of mechanical and laser surface pre-treatments on the strength of adhesive bonded steel joints for the automotive industry

Recent research efforts in the automotive industry have been focused on the integration of high-strength steels within lightweight vehicles by using improved joining techniques. The present work falls in this subject area and is focused on the analysis of adhesive bonded dual-phase steel/epoxy joints for the automotive industry. Two quasi-static loadcases were considered, i.e. single-lap and T-peel tests, and various surface preparation strategies were evaluated. In particular, the mating surfaces were pre-treated by using pulsed laser irradiation with a fiber laser (1064 nm) and comparisons were made with degreasing and sand blasting. Moreover, the effects of bondline thickness and adhesive type were also assessed. To this aim, two epoxy adhesives with fairly different mechanical behavior (i.e. strain hardening versus elasto-plastic) were deployed for joints fabrication. Finally, T-peel tests were also carried out after sample cycling under controlled high humidity and temperature (i.e. accelerated aging). The obtained results highlighted the beneficial effect of laser irradiation on the joints’ mechanical behavior under both static and hydrothermal loadings.

A tapered bondline thickness double cantilever beam (DCB) specimen geometry for combinatorial fracture studies of adhesive bonds

The characterization of fracture energy (GIc) of an adhesive joint as a function of bondline thickness requires multiple specimens covering a range of bondline thicknesses. In this work, DCB specimens with linearly increasing or decreasing bondline thickness were studied for their feasibility to determine fracture energy as a function of bondline thickness. In a combinatorial characterization sense, this approach explores the possibility to characterize the effect of bondline thickness on fracture energy through fewer tests than those required for a “one at a time” characterization approach, thus offering a significant reduction in characterization times. Fracture energies were characterized under mode I loading conditions using corrected beam theory. The results obtained from linearly increasing or decreasing bondline thickness specimens showed good agreement with those obtained from specimens with a range of constant bondline thicknesses.

Interfacial Bond Strength of Resin-Impregnated Fibre-Reinforced Polymer Laminates Bonded to Concrete Using Vacuum and Heat: Experimental Study

Two processing techniques commonly used in the repair of concrete structures via bond of fibre-reinforced polymer (FRP) onto the substrate are known as the pultruded plate and wet lay-up systems. The pultruded FRP plate and wet lay-up systems both involve the curing of resins of up to several days under ambient conditions to achieve full load capacity and rely on workmanship to achieve good bond. Hence, new techniques for the application of FRP that adopt a vacuum consolidation process and heat to impregnate FRP fibres with resin to improve the curing process, bond strength and speed of application are being developed. In this article, the interfacial bond behaviour of pre-impregnated FRP laminates attached to concrete in the presence of vacuum and heat is studied and compared to more conventional methods of FRP strengthening systems. Further the effects of bondline thickness on the bond performance of pre-preg FRP laminates are also studied whereby three different bondline thicknesses are examined. The interfacial bond thickness was changed by application of resin films between FRP plates and concrete surface.

Application of Heat/Resin Injection in the Presence of Vacuum for FRP Attachments on the Concrete Substrate

Advanced processing techniques for the application of Fibre Reinforced Polymer (FRP) materials to repair concrete structures include the adoption of a vacuum consolidation process coupled with heat and/or resin injection to improve the curing process, bond strength and speed of application. The vacuum can contribute to the penetration of the resin into the surface around the exposed aggregates in order to achieve higher bond in strengthened elements. Since, debonding of FRP materials from the substrate is a brittle failure, it is essential to study this phenomenon and propose significant ways to improve the behaviour of the bondline. In this article, the interfacial bond behaviour of FRP laminates attached to concrete in the presence of vacuum and heat/resin injection is studied. The results of single lap shear tests have been utilized to investigate the capability of this system in strengthening of concrete elements. In this regard, several FRP-bonded concrete prisms will be examined in a single lap shear test set-up. Further, the effects of bondline thickness on the bond performance of adhesively bonded joints are studied.

Effects of bondline thickness on Mode-I nonlinear interfacial fracture of laminated composites: An experimental study

Delamination or interfacial fracture is one of the most important issues for laminated composite structures. For the recent two decades, cohesive zone models (CZMs) have been receiving intensive attentions for modeling interfacial fracture of composite structures. Numerous global fracture tests have been conducted to measure the interfacial toughness of laminated composite plates. Some local tests have also been conducted to determine the interfacial traction–separation laws in adhesively bonded joints. However, most of these local studies focused on the interfacial fracture between metal adherends. Limited studies have addressed the local test of interfacial fracture between laminated composite plates. While it was well known that the bondline thickness has an important effect on interfacial fracture, very few studies investigated its effects on the local interfacial traction–separation laws of laminated composite plates in the literatures. In this work, both global and local tests are employed to investigate the effect of bondline thickness on the interfacial energy release rate, interfacial strength, and shape of the local interfacial traction–separation laws. Basically, the measured laws in the present work reflect the equivalent and lumped interfacial fracture behaviors which include the cohesive fracture, damage and plasticity. The experimentally determined traction–separation laws provide valuable baseline data for parameter calibrations in numerical models. The experimental results may also facilitate the understanding of bondline thickness dependent delamination of composite structures.

Effect of Bondline Thickness on Mixed-Mode Fracture of Adhesively Bonded Joints

The effect of bondline thickness on the critical strain energy release rate (CSERR) was investigated using aluminum adherends and an epoxy adhesive. Complete mixed Mode I/II fracture envelopes for adhesive thicknesses ranging from 0.203 to 1.52 mm were developed using double cantilever beam (DCB), mixed-mode bending (MMB), and end notch flexure (ENF) tests methods. Bondline thickness strongly affects the CSERR for different amounts of Mode II component. Pure Mode II had the largest CSERR and showed monotonic increase with bondline thickness, whereas pure Mode I had the lowest CSERR and exhibited non monotonic relationship with bondline thickness. The shape and size of the plastic zone that develops prior to crack propagation was predicted by finite element analysis. Variation of CSERR as a function of adhesive layer thickness was shown to be related to the size of the plastic zone for Mode I and MMB 50% fracture. No correlation was observed for the MMB 75% and Mode II, however.

Effect of Bondline Thickness on the Static Strength of Structural Adhesives Under Nearly-Homogeneous Shear Stresses

An usual experimental observation retrieved in the technical literature is that the strength of an adhesive joint decreases by increasing the adhesive layer thickness. This well-known behaviour is still not completely understood. All works found in the literature consider a complex stress state in the adhesive with mode mixing, stress concentrations on the midplane, and stress singularities at the interface occurring at the same time. This paper aims at estimating the effect of the adhesive thickness on its intrinsic static shear strength and evaluate whether this strength can explain the behaviour of a real bonded joint. A nearly uniform shear stress distribution is obtained through an ad-hoc tubular butt joint subject to pure torsion. A standard single lap joint is considered as a benchmark, due to its complex and singular stress field into the adhesive. The experimental campaign is focused on two brittle adhesives: a modified methacrylate and high-strength epoxy. Four levels and three levels of the adhesive thickness were considered in the tubular butt joint and in the single lap joint, respectively, all in the range between 0.05 and 0.4 mm. The effect of the adhesive thickness on the static strength of the adhesive is investigated by considering the type of failure and by comparing the structural stresses in the tubular butt joint with the ones on the midplane of the adhesive layer in the single lap joint. Moreover, the stress intensity factor in the single lap joint is calculated.

Effects of bondline thickness on Mode-II interfacial laws of bonded laminated composite plate

For a variety of modern industries, interfacial delamination is a critical issue for the design and application of laminated composite structures. Numerous global experimental studies have been conducted to characterize the toughness of adhesively bonded composite structures. In the recent two decades, cohesive zone models (CZMs) have been receiving intensive attentions. The local interfacial traction–separation laws as the fundamental input are crucial for the successful applications of CZMs. Several local tests have also been conducted to determine the interfacial traction–separation laws in adhesively bonded joints. However, very few tests have been employed to investigate the dependency of the local interfacial traction–separation laws on the bondline thickness, particularly, for the laminated composite joints under Mode-II loading conditions. In this work, the effects of bondline thickness on the interfacial behavior have been systematically investigated at various typical bondline thicknesses (from 0.1 to 0.8 mm). The effects of adhesive thickness on the interfacial toughness, interfacial strength, and shapes of the local interfacial traction–separation laws have also been evaluated. The test results indicated that the measured Mode-II (shear test) interfacial shear strength of the composite joints increases as the adhesive layer becomes thicker. It was found a significant dependency of the measured shapes of the Mode-II interfacial laws on the bondline thickness. Several other interesting issues were also reported in this work. This work may provide valuable baseline test data for analytical and numerical modeling of fracture and failure of laminated composite structures.

Effect of adhesive thickness on fatigue and fracture of toughened epoxy joints – Part II: Analysis and finite element modeling

The effect of bondline thickness on the fatigue and fracture of aluminum adhesive joints bonded using a rubber-toughened epoxy adhesive was studied using finite element analysis. The fatigue data of Part I examined the dependence of the fatigue threshold and cyclic crack growth rate on the adhesive thickness under both mode-I and mixed-mode loading. The fracture data of Part I illustrated the relation between the adhesive thickness and the quasi-static crack initiation and steady-state critical strain energy release rates. These experimental trends are explained in terms of the effects of the adhesive thickness and the applied strain energy release rate on the stress distribution in the bondline, the stress triaxiality at the crack tip, and the plastic zone size in the adhesive layer.

Effect of adhesive thickness on fatigue and fracture of toughened epoxy joints – Part I: Experiments

The effect of bondline thickness, from 130 μm to 790 μm, on the fatigue and quasi-static fracture behavior of aluminum joints bonded using a toughened epoxy adhesive was studied experimentally under mode-I (DCB) and mixed-mode (ADCB) loading. Under mode-I loading, it was found that the fatigue threshold energy release rate, G th , decreased for very thin bondlines, while under mixed-mode loading, the G th changed very little with bondline thickness. In both cases, the effect of bondline thickness was more pronounced at higher crack growth rates. For quasi-static fracture, the effect of adhesive thickness on the energy release rate for the onset of fracture from the fatigue threshold, G c 0 , was similar to that found for the fatigue threshold; however, the steady-state energy release rate, G c s , increased linearly with increasing bondline thickness.

Static and fatigue behaviour of room temperature vulcanising silicone adhesives for high temperature aerospace applications

AbstractThis paper focuses on the mechanical properties of room temperature vulcanising (RTV) silicone adhesives for aerospace applications. In view of the very limited amount of published data on this subject, we analyzed the performances of two RTV silicone rubber adhesives through adhesive joint tests. The standard Thick Adherend Shear Test (TAST) was performed in order to measure the shear properties of the adhesives. Single lap joints (SLJs) were fabricated and tested to assess the adhesive performance in a joint. The influence of temperature on the lap‐shear strength of the adhesives was investigated. It is shown that the lap‐shear strength of both adhesives decreased with increasing of temperature. The effect of bondline thickness and overlap length on the lap‐shear strength of the adhesives was also studied. The reduction of failure load with an increase of the bondline thickness is a very common situation when dealing with structural adhesives. However, for the tested RTV silicone adhesives the failure loads increased as the bondline was made thicker. Also, the failure loads of RTV silicone adhesive joints increased almost proportionally with increasing the overlap length. Fatigue tests were also performed and show a low dispersion of the results.