PSI - Issue 26

S.M.J. Razavi et al. / Procedia Structural Integrity 26 (2020) 225–228 Razavi et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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has been studied recently by some researchers. In a research by Khoramishad and Razavi (2014), the effect of reinforcement Aluminum fiber spacing on the overall shear strength of SLJs was investigated both numerically and experimentally. According to their results the reinforced joints not only experienced an increase in strength, but also an increase in the displacement to failure. It was found that by decreasing the fiber spacing, a joint could experience a shear strength enhancement of up to 133.9% compared to a non-reinforced single lap joint. The effect of fiber orientation (Nemati Giv et al., 2018), flexural behavior (Esmaeili et al., 2018) and fracture behavior (Razavi et al., 2017) were then studied in other published researches. It was reported that incorporation of metallic fibers improves the stress distribution in adhesive layer beside the fact that relatively higher thermal conductivity of the reinforcing fibers compared to the adhesive, can result in better heat transfer during curing thus resulting in lower residual stresses in the adhesive layer. The current research aims to evaluate the effect of reinforcing fibers on the fatigue strength of the single lap adhesively bonded joints by use of fatigue experiments on both non-reinforced and reinforced adhesive joints. 2. Experimental procedure A two- component epoxy namely Araldite® 2015 was used in this study. Araldite® 2015 is an a dhesive with high shear and peel strength and has a low shrinkage under curing. The adherends were machined from steel alloy to the final dimensions shown in Fig. 1. In addition, a hole of 6 mm diameter was drilled in the endtab of the adherends to accommodate accurate mounting in the tensile testing machine. Reinforcement fibers of Forta 304/4301 austenitic stainless steel with a diameter of 0.5mm were used for reinforcing the adhesive. It is an alloy consisting of 18% chromium and 8% nickel, with an ultimate tensile strength of 650 MPa normally used for locking wire for bolts. The fiber spacing parameter a is a dimensionless parameter based on distance between the fibers divided by the adhesive layer thickness. The reinforced adhesive joints with fiber spacing of a = 0.9 and 1.9 were fabricated. In addition to the reinforced specimens, control adhesive joints without reinforcement fibers in the adhesive layer were used to evaluate the reinforcing effect. The adhesive was oven cured at 60⁰C for 30 minutes followed by cooling in room temperature (20⁰C and relative humidity of 26%) and post-curing for three additional days. When the specimens were fully cured, excess glue and reinforcement fiber removed, and the specimens were clean-up. The fatigue tests were conducted at room temperature (20⁰C) and at a relative humidity of 26% using an Instron (model E10000) linear motor testing machine. The specimens were tested under a frequency of 30 Hz and stress ratio of R = 0.1 (tension-tension loading). Prior to fatigue tests, a set of static tests was conducted on the non-reinforced and reinforced adhesive joints and the ultimate shear strength was obtained. In order to obtain fatigue data, at least 12 specimens were tested for each case. Different percentages of the ultimate tensile strength were applied to the adhesive joints to obtain the stress-life diagram both for reinforced and non-reinforced joints. The applied fatigue loads were selected in a range between 40% to 65 % of static failure load.

Fig. 1. Schematic view of the adhesively bonded joints (dimensions in mm).