Strength comparison of ductile and brittle adhesives under single and repeated impacts
© Kemiklioglu et al. 2015
Received: 11 August 2015
Accepted: 19 October 2015
Published: 26 October 2015
In this study, the failure strengths of adhesively bonded joints were investigated. The glass fiber epoxy composites used as adherends were manufactured by using vacuum assisted resin infusion method (VARIM). The adhesively joint materials were Loctite-9466 and DP-460 as a brittle and ductile material, respectively. Since the strengths of these materials are close to each other under static loading, the applied axial energies were determined using different levels of 5, 10, 15 and 20 Joules. In order to determine the energy characteristics of the experiments, axial impact loadings were applied as both single and repeated three times under the same conditions. The results showed that the failure strengths of these two different adhesives of Loctite-9466 and DP460 changed depending on single and three times repeated axial impact loadings. This paper is intended to give an overview between ductile and brittle adhesives under both single and repeated impacts. In addition, it will help for designers who need information on mechanical properties of ductile and brittle adhesives under single and repeated impacts.
Composites are the materials with lower bulk and higher strength as compared to metals. Besides, composites materials are usually assembled in the forms of mechanical fastened or bonded. Owing to their mechanical, physical and chemical properties such as high strength, weight ratio, high stiffness and less chemical corrosive, composite materials have been greatly used in engineering applications such as aerospace, automotive industry, military, air vehicles, especially for use in aviation and aerospace engineering. Many researcher have been studied different methods to examine the mechanical properties of composite materials and their adhesives to improve the usability of these materials in applications.
Kihara et al.  found the shear strength of the adhesive layer under impact test by using experimental method for the case of double-lap joint. Vaidya et al.  determined the failure of adhesively bonded joints under effect of transverse impact loading. Yang et al.  proposed an analytical solution for obtaining to strain–stress distribution of adhesively composite joints under tension. Sayman et al.  investigated an elastic–plastic stress analysis using theoretical methods as well as numerical methods and they showed a good agreement between analytical and numerical methods. In addition to these studies, Kim et al.  performed experimental and numerical analysis to find damage modes occurring from out-of-plane impacts. Sayman et al.  carried out analytical and numerical elastic–plastic stresses in a ductile adhesively bonded single-lap composite joint. Her  studied stress analysis in single and double-lap joints using analytical and numerical methods. Keller and Vallee  proposed experimental and numerical research for investigating the effects of geometrical parameters on the joint strength. Avilla and Bueno  proposed an experimental study on a new design of adhesive bonded joints which is called wavy-lap joint. Aktas and Polat  proposed a method to improve the strength of single-lap composite joints by using a pin. As well as, the experiments performed using both numerical and experimental methods many researcher studied only experimental methods using commercial materials. Sayman et al.  investigated failure analysis of adhesively bonded composite joints under transverse impact and different temperatures. Loctite-9466 was used as an adhesive material. Temperatures were selected as −20, 23, 50 and 80 °C. The impact energies were applied as 5, 10, 15 and 20 J. Bouchikhi et al.  studied the reduction of interfacial stresses when using bonded laminates in strengthening existing structures. They used mixed adhesive joints (MAJs) between the adherents and obtained lower interfacial stresses. Goeij et al.  investigated composite adhesive joints under cyclic loading. They compared adhesive joints under static and fatigue failures.
In this study, we carried out a series of experiment on the failure strength at adhesively bonded joints subjected to single and repeated axial impact at different energies of 5, 10, 15 and 20 J. The three times axial impact energies were applied to joints as a repeated impact. Two different adhesives were used with ductile and brittle properties, respectively. These materials are commercially used in composite structures repairements in aerospace, marine and automotive industries.
In our study, fiber reinforced polymer (FRP) composite plates were manufactured by using the vacuum infusion method. FRP composite plates composes of glass fibers and resin. We fabricated epoxy glass fiber composites using E glass fibers and resin via the vacuum infusion method. In order to prepare FRP composite plates, six woven E glass fibers (0.90) with a density of 500 g/m2 were used with epoxy resin.
Results and discussion
The impact strengths were measured for the single and repeated (three times) axial loadings.
The single and repeated loadings were performed under 5, 10, 15 and 20 J. The strengths were obtained for 5, 10, 15 and 20 J for the single impact after measuring the tensile forces. But the failures occured under repeated 20 J loadings in all the joints without tensile loadings.
The strengths of the DP-460 joints are higher than the Loctite-9466 joints for the single impacts.
The strengths of the Loctite-9466 are higher than those of the DP-460 in the 5 and 10 J for repeated impacts.
The strength of the joints was found to be higher than that of other energy loadings fort he energy of 10 J impact loading for single and repeated cases.
The failure strengths of Loctite-9466 under single impact was obtained smaller than that of repeated impact of Loctite-9466.
UK prepared the specimens and performed the experimental measurements and also helped to OS for writing the paper. OS and TB designed the experiments. OS and IFS made data analysis. TA and EA helped for UK and IFS. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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