PSI - Issue 19

Hiroyuki Oguma et al. / Procedia Structural Integrity 19 (2019) 224–230 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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However, there are difficulties in productivity, process-ability, machinability [3] and heat resistance. Multi-material design is of current interest as one of means to solve the problems, and the joining technology is an important key for the design approach and manufacturing [4]. Meanwhile, in order to improve the productivity of FRPs, introduction of thermoplastic resin which enables high-speed or continuous molding by pressing machines has proceeded [2]. One of the joining technique for thermoplastic resins includes thermal fusion bonding or welding [5], however, the details of the effects of changes in fiber volume fraction in the fusion zone, strain and residual stress caused by heat input on strength properties are not clear at this time. Therefore, our research projects focus on adhesive bonding techniques [6]. By using adhesion, it becomes possible to join materials which are sensitive to heat and thin plates. In addition, the gap filling property of the adhesive makes it possible to improve the processing accuracy of parts and to achieve high-precision positioning compared to the case of fusion bonding. Applications of bonding technology have been expanded; however, the strength estimation and design methods for bonded structures have not been fully established. New design concepts and standards related to strength and reliability are required from industries. Loading conditions are complicated, and the effect of mean load on the fatigue properties should be understood for mechanical designs [7-10]. In this work, tensile-shear static and fatigue tests were carried out with single-lap joint specimens made of a glass-fibre-reinforced polypropylene composite plate and an acrylic adhesive to investigate the effects of stress ratio on fatigue properties of adhesively bonded structures. Tested material was a glass-fiber-reinforced polypropylene composite plate (TEPEX ® DYNALITE 104 RG600(6)/47% ， BOND LAMINATES), and adhesive was an acrylic adhesive (Scotch-Weld TM DP8005, 3M). Generally, it is extremely difficult to join polypropylene with adhesive. The adherends underwent chemical and physical surface treatment, such as cleaning with acetone (hereinafter called As-received) and sandblasting (Sandblasted) to control the surface conditions. Surfaces of the adherends are shown in Fig. 1. Organic solvent cleaning removes mold-releasing agent. Sandblasting is expected to increases the anchor effect in bonding due to the roughness. 2. Materials and test conditions

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Fig.1. Surface conditions (a) as-received; (b) sandblasted.

Strength tests were carried out with single-lap joint specimens. A specimen configuration and a magnified photograph of the bonded part are shown in Figs. 2 and 3. The overlap length was 12.5 mm, and the adhesive thickness was about 100  m. Testing facilities are shown in Fig. 4. Tensile tests were carried out in reference to ASTM standard under a crosshead speed of 1 mm/min [11]. 10 specimens were tested for each surface condition of