Effect of moisture and temperature on thermal and mechanical properties of structural polyurethane adhesive joints

Fiber metal laminates (FMLs) are a kind of hybrid composite material that consist of metal sheets and fiber-reinforced composite layers. The use of FMLs has been particularly increasing in the production of aircraft bodies. However, the springback behavior that occurs during the formation of FML parts has a negative impact on the form of the final product. In the present study, FMLs were manufactured by combining aluminum 5754-H22 sheets and carbon fiber-reinforced plastic sheets by using adhesive. A set of experiments were performed to determine the effect of bending angle, face sheet thickness and core thickness on the springback behavior of FMLs. The results showed that the amount of springback in the FML specimen increased as the bending angle increased. It was found that when the thickness of the face sheet increased, the amount of springback in FML specimens was higher in all bending angles. In addition, the amount of springback in FML specimens decreased as core thickness increased.

Springback Behavior of Fiber Metal Laminates with Carbon Fiber-Reinforced Core in V-Bending Process

Adhesively bonded aluminium single lap shear joints were tested to failure under fatigue loading to ascertain the effects of surface pretreatment and moisture in both durability and fracture path. The aluminium substrate used was AA5754 with and without a silicon based pretreatment. The adhesive used was a commercially available DGEBA based epoxy resin cured by a modified dicyandiamide. Fatigue tests were performed at 20Hz using an R-ratio of 0.1. To monitor the effects of moisture, tests were performed in a chamber that generated 96% relative humidity (r.h.). S-N curves were generated and several microscopic and surface analysis techniques were employed to characterise the failure mode of the joints. The techniques included simple visual observation, SEM, TEM and high magnification video recordings. The fatigue performance of pretreated and untreated joints were similar when tested in air, but the performance of the untreated joints was greatly reduced when tested in 96% r.h. The differences in fatigue performance between untreated and pretreated joints in 96% r.h. are thought to be due to differences in failure mode of the joints arising from the improved interfacial bonding between the pretreatment and the adhesive. Pretreated joints failed predominantly cohesively through the adhesive, while untreated joints failed mainly interfacially at the adhesive/aluminium interface. High magnification video recordings have also shown that the adhesive fillet is a significant factor in determining the life of a single lap joint.

The effect of surface pretreatment and moisture on the fatigue performance of adhesively bonded aluminium

Bu calismada, aluminyum-karbon elyaf sandvic levhalarin V bukme operasyonu neticesinde olusan geri esneme davranisi deneysel olarak incelenmistir. Bukme yonunun geri esneme davranisi uzerine olan etkisini incelemek amaciyla farkli bukme yonlerindeki sandvic kompozit levhalar 15°, 30°, 45°, 60°, 75° ve 90° bukme acilarinda sekillendirilmistir. Farkli bukme yonlerinde sekillendirilen sandvic kompozit levhalarda meydana gelen geri esneme degerlerinin birbirine cok yakin oldugu tespit edilmistir. Ayrica, T1 (saat yonunun tersinde) bukme yonundeki sandvic kompozit levhalarin 75° ve 90° bukme acilarindaki testlerinde aluminyum ve karbon elyaf plakalar arasinda acilmalar gorulurken, T2 (saat yonunde) bukme yonundeki sandvic kompozit levhalarin 75° ve 90° bukme acilarinda ise dis taraftaki aluminyum sac levhalarda yirtilmalar olusmustur.

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Alüminyum-karbon elyaf sandviç kompozit levhaların V-bükme işleminde bükme açılarının ve bükme yönlerinin geri esneme üzerindeki etkisi

This study mainly evaluates the thermal aging properties of a new room temperature cured structural adhesive. Multiple adhesive specimens were thermal aged at 80℃, 100℃, 120℃ and 140℃, respectively, and subjected to the dynamic mechanical analysis (DMA) at different temperatures and frequencies. According to the results of DMA and thermodynamic analysis, the performance of the adhesive changes little after aging at 80℃, 100℃ and 120℃ for 30 days. However, the adhesive performance became unstable at 140℃, and deteriorated rapidly with the extension of aging time. Hence, this structural adhesive is suitable for the environment below 120℃. In addition, the generalized curve of the structural adhesive aging for 20 days at 100℃ was obtained, following the principles of time-temperature equivalence superposition and time-aging time equivalence superposition. The test time was shortened significantly. This research provides an accelerated characterization strategy for the long-term mechanical properties of other polymers, making it possible to obtain the generalized curve of polymers aging for a specific time at a specific temperature.

Effect of Thermal Aging on Dynamic Mechanical Performance of a Novel Structural Adhesive

In this study, the shear strength behavior of adhesively bonded joints, made of aluminum composite foams subjected to high-temperature processes, has been investigated. Aluminum composite foam and solid aluminum blocks were used to form single lap joints and as the binder, a methacrylate-based structural adhesive has been selected. Foam-foam and solid-foam joints were formed and cured at room temperature for 24 hours. After curing process, aging at 200 oC was performed on the samples for 15, 30, 45, 60 minutes. The aged samples were subjected to lap shear testing for adhesively bonded metals and the influences of aging duration on joint strength and failure type were investigated.As a result, lower strengths were obtained in all samples that aged under high temperature compared to non-aged samples. After the application of short-term (15-30 min) aging processes on samples, it is observed that they have joint strength values about 50% of the joint strength of non-aged samples. However, strength val...

Anil Sahin

Papers

Effect of Aging Time at High Temperature on the Shear Strength of Adhesively Bonded Aluminum Composite Foam Joints