Fatigue Life Of Adhesive Joints Research Articles

An experimental-cohesive zone model approach to predict fatigue life of adhesive joints with varying modes of loading and joint configurations for automotive applications

ABSTRACT Predictive fatigue life models of adhesive joints are necessary to enable the assessment of automotive-bonded structures while reducing costly experimental testing. However, contemporary models have typically been calibrated for specific joint configurations and modes of loading, limiting their applicability to large-scale structures. Additionally, available models are based on simulation of cumulative fatigue cycling, making them computationally prohibitive. In the current study, cross-tension (CT) (load angles of 0°, 45°, and 90°) and single-lap shear joint (SLJ) configurations were bonded using an epoxy adhesive (BetaGuard CI6125R; PPG, France) used in automotive production (one part) and tested under fatigue cyclic loading. A total of nine joint configurations, having symmetrical (same material and thickness) and asymmetrical (dissimilar material or unequal thickness) joints, were tested. Fatigue tests at load levels between 25% and 75% of the static peak load were performed until joint failure or to runout (two million load cycles). The static tests of the joints were simulated to failure using finite element (FE) models with the cohesive zone method (CZM). The maximum strain energy release rates ( G max ) were calculated within the adhesive bond line at static loads corresponding to the peak loads of the fatigue tests. The G max values, computed from single cycle, specimen-specific FE simulations, were correlated with the measured fatigue life ( N f ) of the adhesive joints with varying modes of loading and joint configurations. The fatigue life prediction model, based on G max − N f correlation and following a crack propagation approach, predicted the cycles to failure for 85% of the fatigue tests, and 81% of the independent validation tests. The proposed fatigue life prediction approach provides computational efficiency and large-scale compatibility.

Effects of singular and non‐singular stress fields on very high cycle fatigue life of adhesive joints

AbstractSingular stress fields represent a concern during the design of mechanical connections as they could trigger cracks within the joint, under low‐amplitude loads, generating failures and reducing its service life. Appropriate design plans should therefore be implemented to produce more reliable apparatus. This paper explores the effects induced by both the presence and the absence of stress singularities on the very high cycle fatigue (VHCF) performance of adhesively bonded butt joints through analytical, numerical, and experimental methods. Analytical models defined the conditions to design a stress singularity‐free joint, global–local finite element descriptions studied the stress distributions in detail, and then VHCF experiments extracted S–N outcomes. The suitability of this approach is confirmed numerically while a substantial increase of the joint life is experimentally observed if the singularity is removed. Nonetheless, a non‐singular configuration leads to higher scatter data compared to the original specimen configuration.

A progressive damage model to predict the shear and mixed-mode low-cycle impact fatigue life of adhesive joints using cohesive elements

A progressive damage model to predict the shear and mixed-mode low-cycle impact fatigue life of adhesive joints using cohesive elements

The influence of mode mixity and adhesive system on the fatigue life of adhesive joints

AbstractIn real applications, adhesive joints are commonly subjected to fatigue and mixed mode loading conditions. The aim of the current work is to experimentally analyse the influence of mode mixity on the fatigue strength of joints with an epoxy‐based adhesive. Different adhesive systems (acrylic and epoxies) were considered for pure mode I fatigue loading conditions. To achieve this, Arcan joints with an epoxy adhesive were manufactured and tested at different mode mixities. Based on stiffness degradation, monitored during the tests, damage evolution was calculated for different loading conditions and for all the tested adhesives. Finally, fatigue envelopes were constructed for different fatigue life regimes. Results show that a shear loading component reduces both the static strength and fatigue life of the joints. A small reduction rate of the stiffness was found throughout the most part of the life until a sudden drop was observed, indicating a smooth damage evolution.

Influence of microcork particles on the lap shear strength of an epoxy adhesive subjected to fatigue loading and different environmental conditions

The present study deals with the effects of temperature and cyclic loading on the strength of single lap adhesive joints enhanced with different amounts of microcork particles. To achieve this, different joints with various overlap lengths were manufactured and tested. The joints were tested at two different temperatures (−20 ℃ and 75 ℃) in quasi-static conditions. Results of high temperature (75 ℃) show that the joints tensile strength decreases with the amount of cork particles. For low temperature (−20 ℃), the strength of the joint with 1 vol.% of cork increased; however, higher amounts of cork led to a reduction of the joint strength. To investigate the influence of cork particles on the fatigue endurance, joints were tested at room temperature under sinusoidal cyclic loading. Based on the experimental data it was found that the cork particles can significantly improve the fatigue life of adhesive joints (up to 4.6 times). Microfailure analysis of the tested joints was also performed using the scanning electron microscope technique.

Numerical analysis of mixed-mode fatigue crack growth of adhesive joints using CZM

With the increased use of adhesive joints in industrial environments, the need for improvement of this bonding technology arises. Namely, a reliable fatigue life estimation is essential to prevent catastrophic failure in adhesively bonded structural components. The cohesive zone model (CZM) approach has been used in numerical models to assess degradation by fatigue under pure mode conditions. However, in real life, components are subjected to multiaxial loads, the aim of this paper is to perform a numerical estimation of the fatigue behavior of an epoxy-based adhesive subjected to mixed mode loading conditions. To achieve this, the mixed mode was split into the corresponding components of mode I and mode II. For each mode, the adhesive’s cohesive properties were degraded by fatigue, according to a relation previously published for pure mode I and which has also been validated for pure mode II. Fatigue tests were performed on DCB specimens to calibrate the degradation model which, along with a triangular shaped CZM, was included in an Abaqus user material subroutine (UMAT) to perform a simulation of the fatigue behavior. Results showed that such approach can be applied to estimate the fatigue life of adhesive joints under mixed mode loading conditions.

Mode II modeling of adhesive materials degraded by fatigue loading using cohesive zone elements

Because of maintenance issues, the concept of safe life is an important philosophy for designing adhesive joints where the service load is cyclic. However, this philosophy needs a tool to be able to estimate the total fatigue life. The objective of this study is to develop a numerical tool to predict the fatigue life of adhesive joints for pure mode II loading conditions. To achieve this, a previously published mode I data degradation approach was extended for pure mode II. Fatigue tests were performed on end notched flexure (ENF) specimens to calibrate the degradation model. A triangular shape cohesive zone model (CZM) in combination with a data degradation method were considered in an Abaqus user element (UEL) subroutine. Based on the results, it was found that the proposed method can be applied for fatigue life estimation of adhesive joints in pure mode II conditions as well as pure mode I.

Normalized strength reserve principle for variable amplitude fatigue life prediction of adhesively bonded aluminium joints/Normalisiertes Festigkeitsreserve-Prinzip für die Vorhersage der Lebensdauer von geklebten Aluminiumverbindungen bei variablen Lastamplituden

Abstract Over the last several decades, adhesive bonding has been validated as a good alternative to traditional joining methods in metallic construction. On the other hand, the main factor that limits the wider use of structural adhesives in civil engineering industry is scepticism about their long-term performance, especially when subjected to variable amplitude fatigue loading. Most of the research on predicting the fatigue life of adhesive joints subjected to this type of loading dealt with composite adherends. In this paper, straightforward method for prediction of strength degradation and fatigue failure under random spectrum loading is presented and validated for the case of adhesively bonded single lap joints made of aluminium adherends. It is based on the normalized strength reserve principle, proposed by the same authors in their previous research. The normalized strength reserve model is expanded to the case of variable amplitude fatigue, incorporating the cycle mix parameter in order to account for load interaction effects. Very good agreement was obtained between the fatigue life predictions of the presented method and experimental results from the literature.

Fatigue performance and life estimation of automotive adhesive joints using a fracture mechanics approach

Practical fatigue life prediction methods using computer aided engineering (CAE) for adhesively bonded joints are needed to reduce the risk of potential fatigue failures and unnecessary over-designs for automotive body structures. This paper presents an investigation on the tensile and fatigue behaviors of adhesively bonded lap shear and coach peel joints for A5754-O. From suspended tensile tests, macroscopic cracks were found in the adhesive layer of the lap shear joints before the joints reached the peak quasi-static strengths. A fatigue life estimation approach for automotive adhesive joints was developed based on coarsely meshed finite element models and the analytical J-integral solution. This approach also includes the influence of the macroscopic cracks in the adhesive layer on the fatigue life of lap shear joints. Finally, the fatigue life estimation approach was validated with fatigue test results of U-shape specimens, and it was found that the J-integral based parameter can effectively predict the fatigue life of adhesive joints with different substrate thicknesses and various joint types.

The relation between the adhesive application method and the fatigue lifetime for a photocatalytic adhesive joint

Joint design, surface preparation and adhesive selection are considered the most important factors that control fatigue life of adhesive joints. Early research by the authors showed that for adhesive glass-polycarbonate joints using the photobond 4455 adhesive the statistical spread in fatigue life was large. Follow up research showed that the adhesive application method was the main causal factor in determining the fatigue life. Some application methods yielded good shear strength but low fatigue life. The results suggest that polarity of the photobond 4455-monomer results in micro defects being introduced by certain application procedures. This can lead to differences in fatigue life of a factor 10 or more.

The dependence of the fatigue life of adhesive joints on surface preparation

The fatigue life of epoxy-bonded, single-lap shear joints was investigated as a function of surface preparation both with and without a silane pretreatment, under both dry and wet conditions. The effect of R-ratio was also investigated. The results showed that even in the dry condition, the fatigue life of unsilaned joints was reduced by about an order of magnitude from silaned joints. The fatigue life of the silaned joints was equivalent to that of joints that showed no apparent adhesive failure in the wedge test. Fatiguing the joints while immersed in water had very little effect on both the silaned and unsilaned joints except at low loads where there was an indication that the unsilaned joints performed more poorly than in the dry condition. The unsilaned joints showed very little R-ratio effect, while the silaned joints showed a substantial effect.

Diagnosis criterion for damage monitoring of adhesive joints by a piezoelectric method

Adhesive joints have been widely used for fastening thin adherends because they can distribute the load over a larger area than mechanical joints, require no holes, add very little weight to the structure and have superior fatigue resistance. Since the reliability of an adhesive joint is dependent on many parameters, such as the shape of joint, type of applied load and environment, an accurate prediction of the fatigue life of adhesive joints is seldom possible, which necessitates an in situ damage monitoring of the joints during their operation. Recently, a piezoelectric method using the piezoelectric characteristics of epoxy adhesives has been successfully developed for adhesive joints because it can continuously monitor the damage of adhesively bonded structures without producing any defects induced by inserting a sensor. Therefore, in this study, the damage of adhesive joints was monitored by the piezoelectric method during torsional fatigue tests in order to develop the diagnosis criterion for damage monitoring of adhesive joints by the piezoelectric method. The diagnosis criterion was developed by analyzing damage monitoring signals under various test conditions and adopting normalized parameters.

The effects of ageing and environment on the fatigue life of adhesive joints: Su, N., Mackie, R.I. and Harvey, W.J. Int. J. Adhesion and Adhesives Apr. 1992 12, (2), 85–92

Conventional Surface-Enhanced Raman Spectroscopy (SERS) for fast detection of drugs in urine on the portable Raman spectrometer remains challenges because of low sensitivity and unreliable Raman signal, and spectra process with manual intervention. Here, we develop a novel detection method of drugs in urine using chemometric methods and dynamic SERS (D-SERS) with mPEG-SH coated gold nanorods (GNRs). D-SERS combined with the uniform GNRs can obtain giant enhancement, and the signal is also of high reproducibility. On the basis of the above advantages, we obtained the spectra of urine, urine with methamphetamine (MAMP), urine with 3, 4-Methylenedioxy Methamphetamine (MDMA) using D-SERS. Simultaneously, some chemometric methods were introduced for the intelligent and automatic analysis of spectra. Firstly, the spectra at the critical state were selected through using K-means. Then, the spectra were proposed by random forest (RF) with feature selection and principal component analysis (PCA) to develop the recognition model. And the identification accuracy of model were 100%, 98.7% and 96.7%, respectively. To validate the effect in practical issue further, the drug abusers'urine samples with 0.4, 3, 30 ppm MAMP were detected using D-SERS and identified by the classification model. The high recognition accuracy of > 92.0% can meet the demand of practical application. Additionally, the parameter optimization of RF classification model was simple. Compared with the general laboratory method, the detection process of urine's spectra using D-SERS only need 2 mins and 2 μL samples volume, and the identification of spectra based on chemometric methods can be finish in seconds. It is verified that the proposed approach can provide the accurate, convenient and rapid detection of drugs in urine.

The effects of ageing and environment on the fatigue life of adhesive joints

This paper presents the results of a durability programme designed to study the effects of ageing and environment on the fatigue life of adhesive joints. The adhesives were typical of those which might be used in civil engineering applications. Specimens were kept under a variety of loading and environmental conditions for 8 years. It was observed that some adhesives showed excellent durability properties, and that the fatigue life of some specimens actually improved with age. Other adhesives were adversely affected by the environment, particularly high humidity or exposure to the natural environment. It was found that good performance in a laboratory high humidity environment does not guarantee good performance when exposed to the natural environment. The durability performance of the adhesive bore a close relation to the effects of moisture uptake in the adhesives.