Strength prediction of epoxy adhesively bonded scarf joints of dissimilar adherends Mohd Afendi a,b,n , Tokuo Teramoto a , Hairul Bin Bakri c a Graduate School of Systems and Information Engineering, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8573, Japan b School of Mechatronic Engineering, Universiti Malaysia Perlis, Arau, Perlis 02600, Malaysia c Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka, Locked Bag No. 1752 Pejabat Pos Durian Tunggal, Durian Tunggal, Melaka 76109, Malaysia article info Article history: Accepted 25 January 2011 Available online 8 March 2011 Keywords: Bond thickness Scarf angle Singularity Dissimilar adherends Interface mechanics FEM abstract In this study, strength of epoxy adhesively bonded scarf joints of dissimilar adherends, namely SUS304 stainless steel and YH75 aluminum alloy is examined on several scarf angles and various bond thicknesses under uniaxial tensile loading. Scarf angle, y ¼451, 601 and 751 are employed. The bond thickness, t between the dissimilar adherends is controlled to be ranged between 0.1 and 1.2 mm. Finite element (FE) analysis is also executed to investigate the stress distributions in the adhesive layer of scarf joints by ANSYS 11 code. As a result, the apparent Young’s modulus of adhesive layer in scarf joints is found to be 1.5–5 times higher than those of bulk epoxy adhesive, which has been obtained from tensile tests. For scarf joint strength prediction, the existing failure criteria (i.e. maximum principal stress and Mises equivalent stress) cannot satisfactorily estimate the present experimental results. Though the measured stress multiaxiality of scarf joints proportionally increases as the scarf angle increases, the experimental results do not agree with the theoretical values. From analytical solutions, stress singularity exists most pronouncedly at the steel/adhesive interface corner of joint having 45–751 scarf angle. The failure surface observations confirm that the failure has always initiated at this apex. This is also in agreement with stress-y distribution obtained within FE analysis. Finally, the strength of scarf joints bonded with brittle adhesive can be best predicted by interface corner toughness, Hc parameter. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction Adhesive joint is definitely the ideal substitute for any conven- tional bonding methods (e.g. rivet, welding, diffusion bonding, etc.) in structural engineering and industrial applications. To extend the exploitation of adhesive joints the evaluation of strength and failure mechanisms becomes very crucial. However, strength and failure behavior of adhesive joints are not only complex but also depend extremely on the mechanical properties of the adhesive layer and the state of stresses inside it as imposed by the constraint effect of stiff adherends [1–3]. Therefore, in the literature, many works have been devoted on elucidating the critical factors affecting the reliability and integrity of sandwiched adhesive joints. These include investigations upon the effect of joint geometry (i.e. bond thickness, rigid or flexible substrate, scarf angle, spew fillet, etc.), loading rate and temperature. The effect of bond thickness upon the strength of adhesive joint has been investigated extensively by numerous researchers for many years. Zhu and Kedward [4] analyzed the effect of bond thickness and fillet upon the titanium single and double lap joints using finite element method and closed-form solutions. Their parametric studies revealed that the maximal strength of lap joints of ductile adhesive increased with decreasing bond thickness. Taib et al. [5] studied the effect of bond thickness on L-section joints of composite adherends using two components structural paste adhe- sive Hysol EA 9359.3. They attributed the decreased failure load to increasing bond thickness in terms of the stress state (i.e. plane stress or plane strain) prevailing inside the adhesive layer: the thin bond thickness favors plane stress while thick bond thickness favors plane strain state. More recently, Davies et al. [6] examined the physico-chemical and mechanical behavior of aluminum substrates bonded with commercial epoxy adhesive joints of several thick- nesses. They noted a small reduction in the mechanical properties of adhesive layer as the bond thickness was increased. They also explained this feature by a change in the stress state as the modified Arcan fixtures of thick adhesive layer were tested within their numerical analysis results. In general, the strength of adhesive joints increases as the bond thickness decreases [7]. However, this is not necessarily true. Park et al. [8] tested thick aluminum lap joint specimens Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ijadhadh International Journal of Adhesion & Adhesives 0143-7496/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijadhadh.2011.03.001 n Corresponding author at: Graduate School of Systems and Information Engineering, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8573, Japan. Tel.: þ81 298 53 5242; fax: þ81 298 53 5207. E-mail address: s0830194@u.tsukuba.ac.jp (M. Afendi). International Journal of Adhesion & Adhesives 31 (2011) 402–411