Fatigue Strength Of Adhesive Joints Research Articles

Experimental study of the impact of notches and holes made in the front edge of adherends on the properties of static and fatigue strength of adhesive joints

The paper presents the results of experimental studies aimed at determining the effect of holes and notches at the front edge of adherends on the strength of adhesive joints. Single-lap joints made of S235JR steel sheets joined with Araldite 2014-2 epoxy adhesive were tested. Comparative tests of static strength in the shear test as well as high-cycle fatigue strength tests were carried out. Joints with three holes with a diameter of 3 mm filled with adhesive and notches 3 mm wide and 4 mm long also filled with adhesive were tested and compared with reference joints, i.e. without modification. The assumption was that the structural changes applied were to contribute to the reduction of the peak of peel and shear stresses that typically occur in this type of joint. Based on the static strength tests, no significant effect of the applied modifications on the strength of the connections was demonstrated. However, in the case of fatigue strength, a significant improvement in fatigue lifetime was demonstrated, which in the area of low cycle fatigue increased by 328.6 % for the joint with notches and by 640.8 % for the variant with holes. For the fatigue fracture surfaces, a topography analysis was carried out by determining the roughness parameters. Significant differences were exposed since at the leading edge, the selected parameters were significantly lower for the reference variant than for variants with notches and holes.

Experimental Study of the Impact of Notches Made in the Front Edge of Adherends on the Properties of Static and Fatigue Strength of Adhesive Joints

This paper presents the effect of simple structural changes consisting in making notches on the edge of adherends on the static and fatigue properties of adhesive joints. The study is based on the set of experimental static strength tests of the single lap shear adhesive joints. It has been shown that a slight increase in load capacity is possible by using adhesive-filled notches. However, this structural modification leads to an increase in the standard deviation of test results. Based on the fatigue strength tests done at the limit number of cycles equal to 2×106, it was shown that the use of notches on the front edge of adherends, which are filled with adhesive, can significantly increase the fatigue lifetime of the joint. The effect is shown in the area of low-cycle fatigue, where for fatigue stress with a maximum value of 11.5 MPa, an increase in the average value of fatigue lifetime by 481.5% was shown for joints with notches. On the basis of fractography analyses using SEM microscopy, it was shown that the positive effect of the notches is caused by the absorption of some energy by the adhesive filling the notches, due to the increased susceptibility of the adhesive in this area to elastic deformations.

Study on the impact of Nano-reinforcements on the fatigue strength of adhesive joints

Single overlap joints had been created by combining two AISI 302 stainless steel sheets with the help of 3 M DP270 grade epoxy and their fatigue characteristics were examined under shear stress condition. Further, the effect of adding three distinct proportions of nano-titania with epoxy, on the mechanical characteristics of the joint was analyzed. The overlap lengths was selected as 20 mm and nano-titania proportions were elected as 1.0%, 2.0% and 4.0%, respectively during shear load condition. When the experimental findings were analyzed, it was shown that the mean damaging load associated with the usage of nano-dispersed adhesives rose significantly in general. As a consequence of the trials, it was discovered that the most effective nanoparticles proportion for boosting the fracture strength of adhesive joints is 4.0 percent, and the enhancement in rate of failure strength increase was noted as 85.52 percent. Additionally, it was shown that strain of nanoparticle had a noteworthy role in the shear characteristics of the adhesive junctions. Additionally, it has been shown that incorporating nanoparticles into the glue enhances junction extension. When the adhesive interfaces of the specimens were inspected, impairment was detected as adhesion dissociation, but nanoparticle replenishment had been detected as a combination of cohesive as well as adhesive characteristics.

Impact of multiwall carbon nanotubes on the fatigue strength of adhesive joints

This paper presents the results of research undertaken to determine the possibility of improving the fatigue properties of peel-loaded adhesive joints by dispersing multiwall carbon nanotubes (MWCNTs) into epoxy-based adhesives. The fatigue strength tests were carried out on an electromagnetic inductor with the resonance frequency of the adhesively bonded joint specimen. The tests were conducted for three types of epoxy adhesives whose properties were modified through the introduction of multiwalled carbon nanotubes, into their structure. Carbon nanotubes were synthesized by means of the Chemical Vapour Deposition (CVD) method with Fe-Co catalysts. A quantity of 1wt.% of the dried material was dispersed into the epoxy adhesives. The results of the fatigue strength tests revealed a significant improvement of the fatigue lifetime of adhesive joints due to MWCNT introduction as filler for epoxy adhesives. In the case of the Epidian 57/PAC adhesive composition, a more than twofold increase in the fatigue lifetime was obtained (an increase of 106.8%). For the Bison Epoxy adhesive composition, the fatigue lifetime increased by 69.3%. The fatigue strength for the best result increased by about 13%.

Investigating the influence of the chamfer and fillet on the high-cyclic fatigue strength of adhesive joints of steel parts

This paper presents the results of research undertaken to determine the possibility of improving the fatigue properties of peel-loaded adhesive-bonded joints by the constructional modification of the adherend. Fatigue strength tests were carried out on the electromagnetic inductor at the resonance frequency of the adhesive-bonded joint specimens. The tests were carried out on the specimens bonded by means of Bison Epoxy and Epidian 57 epoxy compositions with poly-aluminium chloride hardener. The joined elements were modified by making the chamfer or fillet to enlarge the thickness of the adhesive layer with the aim of reducing the stress concentration in the frontal part of the joint. This modification is the result of a research that confirms the existence of a stress concentration on the short section of the frontal part of an adhesive joint. This phenomenon can lead to the rapid initiation of adhesive joint destruction. The fatigue strength tests revealed a significant improvement in fatigue endurance.

Study on the fatigue strength of AA 6082-T6 adhesive lap joints

A research study on the fatigue behaviour of aluminium alloy adhesive lap joints was carried out to understand the effect of surface pre-treatment and adherends thickness on the fatigue strength of adhesive joints. The adherend material used for the experimental tests was an aluminium alloy 6082-T6 in the form of thin sheets, and the adhesive used was a high strength epoxy (Araldite 420 A/B). The surface preparation included an abrasive preparation (AP joints) and sodium dichromate–sulphuric acid etch (CSA joints). A maximum fatigue strength was obtained for the CSA surface treatment with a 1.0 mm adherends’ thickness. The fastest fatigue damage was related with a high surface roughness and a high stress perpendicular to adhesive surface, which helps to promote the adhesive failure. A numerical analysis was also performed to understand the effect of the adherends thickness on the stress level. Results showed an increase of the out-of-plane peak stresses with the increase of adherends thickness.

Evaluation Method for Fatigue Strength of FRP/Metal Adhesive Joints Considering Mean Stress

The fatigue strength of two types of FRP/metal adhesive joints at low temperature, a double lap joint and an embedded joint, was evaluated analytically and experimentally. First, the stress singularity parameters of the delamination edges under mechanical and thermal loadings were analyzed by FEM for various delamination lengths. The delamination propagation rate of the double lap joint under mechanical cyclic loadings at room temperature was measured. Using the relationship between the measured propagation rates and the analyzed ranges of stress singularity intensity, we estimated the fatigue strength of the embedded joint, which coincided well with the measured one. Second, we developed an evaluation method that separates the effects of temperature on fatigue strength into two effects: thermal residual stress and low temperature. Third, the fatigue strengths of the double lap joints were measured for various mean stresses. Fatigue limit of adhesive joints was experimentally measured and compared with analytical intensity of stress singularity. A method for evaluating the fatigue strength of adhesive joints by taking mean stress into account was developed.

Fatigue Strength of Adhesive/Rivet Combined Lap Joints

Abstract Adbesive/rivet combined bonding has attracted special interest recently as a joining technique of highstrength steel because of its high joint efficiency. In the present study, the strength characteristics of adhesive/rivet combined lap joints were investigated. To darify bonding conditions capable of improving the fatigue strength of combined joints, fatigue tests were conducted on the rivet, adhesive and adhesive/rivet combined joints with different lap widths, adhesive and rivet strengths. Furthermore, to compare fatigue crack initiation and propagation behavior of the adhesive joint with that of the combined joint, the strain changes were measured by strain gauges bonded onto the adherend plate near the lap end. The results indicate that the fatigue strength of adhesive joints can be improved through combination with rivets of nearly equal or slightly higher fatigue strength than the adhesive joint. Furthermore, we also confirmed that fatigue cracks propagate more gradually in combined joints than in adhesive joints after crack initiation.

The Effect of Ageing and Environment on the Static and Fatigue Strength of Adhesive Joints

Abstract This paper describes the results of a durability programme designed to test the effects of ageing and environment on the performance of adhesive joints. Specimens were kept under a variety of loading and environmental conditions and the paper reports results of static and fatigue tests after 8–9 years storage. Some adhesive joints showed excellent durability performance, while others were adversely affected by the environment, particularly high humidity and natural exposure. It was found that the effect of ageing on static and fatigue performance is not necessarily the same.

接着継手の疲労強度の界面破壊力学による評価

Fatigue tests of the single lap adhesive joints of thin mild steel plates were carried out and the effect of the thickness of the adhesive and plate on the fatigue strength was investigated. The boundary element two-dimensional elastostatic analysis was also carried out and the effect of the adhesive and plate thickness on the stress distribution at the interface was investigated. Moreover, to evaluate the fatigue strength of adhesive joints quantitatively, the stress intensity factors for interface cracks in the adhesive joints were analyzed by using the BEM. The extrapolation method proposed by the authors was used to determine the stress intensity factors. It was found that the stress intensity factor range ΔKi=√ΔK21+ΔK22 can well characterize the fatigue strengthes of SLJ type adhesive joints with different adhesive and plate thicknesses. It is expected that the interfacial fracture mechanics is very useful for evaluating the fatigue strength of the adhesive joints.

Improvement of Fatigue Strength of Adhesive Joints through Filler Addition

The effect of filler addition on the fatigue strength of adhesive joints was in vestigated. Both epoxy resin (Epikote 828) and polyamide (Versamid 125 or 115) were adopted as the adhesive components; the filler added in the adhesive was chrysotile- asbestos. The experimental results showed that the fatigue strength is improved by add ing the filler and depends on adhesive layer thickness as well as adhesive composition. Furthermore, the variation trends in strain range of the adhesive layer during the fatigue process were examined for the specimens with/without filler. For the specimen with the filler the strain range rapidly increases just before the fracture, and a fatigue hardening phenomenon is revealed in the fatigue life over 106 cycles.