Experimental and Numerical Studies to Strengthen the Adhesive Bonded Single Lap Joint

Abstract

In this work, an attempt has been made to strengthen the adhesive bonding using various concepts like hybrid joints, dual and mixed adhesive bonded joints. One of the most commonly occurrence of defect in adhesive bonded joints are the weak bonds. Hence, weak bond effects in single and dual adhesive bonded joints also have been investigated. Initially, numerical studies have been carried out on adhesive bonded joints and hybrid joint between carbon fibre reinforced plastic (CFRP) and aluminium adherends. From this study it is found that the hybrid joints increases the interface strength there by reducing the peel and shear stress at the ends of the bonded joint. But still, the hybrid joints are not recommended for all applications because riveting requires initial drilling of the adherends that introduces localized damage and the damage area is strongly concentrated around the rivet. Additionally, drilling of CFRP laminate is not recommended because of delamination and fiber damage near the hole. Hence, in the following studies, dual adhesive concept has been considered to strengthen the adhesive bond between different similar and dissimilar adherends. Then, experimental and numerical studies have been carried-out on single and dual adhesive bonded lap joints between different adherends. AV138 brittle and Araldite-2015 ductile adhesives are used alone in the bonded region as single adhesive bonded joints. In dual adhesive bonded joints, AV138 brittle adhesive is used in the middle of the bonded region at different dimensions and Araldite-2015 ductile adhesive is used at the ends of the overlap because of high shear and peel strength. The numerical results are closely matching with the experimental results. From this studies it is found that, the use of dual adhesives helps in increasing the bond strength between CFRP and aluminium adherends.

Further in this direction, experimental and numerical studies of single and dual adhesive bonded joint concept have been continued using different adhesives between similar and dissimilar composite adherends. From these studies, it is found that the use of dual adhesives helps in increasing the bond strength between CFRP to GFRP and CFRP to CFRP joints. However, the same dual adhesive bonded joint concept reduces the bond strength between GFRP to GFRP joints but still better than single brittle adhesive bonded joint is observed. Numerical simulations have been carried out using ABAQUS software coupled with CZM for similar composite joints (CFRP to CFRP and GFRP to GFRP). The results obtained from numerical and experimental studies have been plotted and compared. In continuation, the mixed adhesive concept has been considered to strengthen the adhesive bond between dissimilar adherends. Mixtures of adhesives have been used in the bonded region in varied proportions to strengthen the adhesive bond. The X-ray radiography testing and ultrasonic inspection have been performed to check the quality of bonding. The failure patterns have been identified using optical and scanning electron microscope. This studies indicate that, the strengthening of adhesive bonding is achieved by mixing of two adhesives and highest bond strength obtained when the mixture of AV138 and Araldite-2015 adhesives are used in equal proportions. In addition to these studies, it is found that, the combinations of adhesives are required to increase the bond strength. However, constructing the perfect bond is very important because if there is any mismatch during the fabrication, which leads to weak bonding. Hence, an attempt has been made to characterize weak bond effects in adhesive bonded joints between the dissimilar adherends. Weak bond effects in adhesive bonded joints between CFRP and aluminium adherends have been investigated. Further, in this direction, experimental and numerical studies of weak bond effects in single and dual adhesive bonded single lap joints between CFRP and aluminium adherends have been carried-out. X-ray radiography testing and acoustic wave propagation technique have been performed. From the studies, it is found that the the weak bond effects in dual adhesive bonded joints are not significant when compared to single adhesive bonded joints.