Toshio Sugibayashi

A study and evaluation of the shear strength of adhesive layers subjected to impact loads

Experimental equipment was developed in order to measure easily the shear strength of adhesive layers subjected to impact loads. The stress state of an adhesive joint was calculated with the finite element method (FEM). The results calculated from the FEM were compared with those from experiments conducted with the equipment. It was shown that the fracture behaviour of the joint depended on the level of the incident stress wave. When loading a comparatively high incident stress, the adhesive layer fractures mainly with the shear stress. It is considered that the maximum shear stress measured is the shear strength under impact loads. In order to confirm the validity of this evaluation method, the maximum shear stress was compared with the impact shear strength, which was measured using a cylindrical butt joint subjected to impact torsional loads. Both values accorded well. From this we were able to conclude that the shear strength of the adhesive layer subjected to impact loads could be evaluated with this equipment.

Benchmark tests on adhesive strengths in butt, single and double lap joints and double-cantilever beams

The RC99 committee of the Japan Society for Mechanical Engineers conducted the benchmark tests on strengths of adhesive joints using different testing methods. The effects of joint configuration, loading mode, adherend yield strength and so on, on the strength and data scatter were investigated using two typical epoxy adhesives. The strengths obtained by various tests were compared with each other. The relationships among strengths of butt, single lap and double lap joints and fracture toughness were given. Thirteen member institutes of the committee participated in this project. The benchmark results allow us to recognize that the joint strengths are strongly affected by the curing process. The key to obtaining the appropriate joint strength, is precise temperature control inside the adhesive layer for curing. Toughened adhesives do not always give higher joint strengths than untoughened adhesives. The yield strength of adherends much affects the observed lap joint strength of adhesives.

Application of three-dimensionally reinforced carbon-carbon composites to dovetail joint structures

Abstract In development of an air-turbo-ramjet engine with an expander cycle (ATREX) for a space plane, application of carbon–carbon (C/C) composites plays an important role to achieve high performance. Above all, dovetail joints are one of the key structures to realize the turbine system made of C/C composites. In this study, the feasibility of dovetail joints made of three-dimensionally reinforced C/C composites was investigated. Tensile tests were carried out on simplified dovetail joint models. The shoulder angles of the dovetail joint and fiber volume fractions of the C/C composites were taken as parameters to optimize the shape of the dovetail joint. Finite element analyses were also carried out for various cases. Comparison between the experimental and the calculated results suggests that fracturing of the dovetail joint was controlled by the average shear stress, which implies that the shear stress concentration on the shoulder was relaxed during the fracture process. It was also shown that the dovetail joint made of C/C composites is feasible for use in the ATREX engine.

Features of bolted joints with tap bolts (The case where a clamped part with a metallic gasket is the cover of a pressure vessel)

Abstract This paper deals with the distribution of contact stress and the load factor (the ratio of an increment of bolt axial force to an external load) of bolted joints fastened with tap bolts, when a clamped part with a raised face metallic gasket is the cover of a pressure vessel. The distribution of contact stress is analyzed as a three-body contact problem, using the axisymmetrical theory of elasticity. The effects of the stiffness and the position of the gasket are shown on the distribution of contact stress by numerical computations. The contact stress has been measured by means of an ultrasonic technique. The load factor and the maximum stress produced in the bolts are analyzed. For verification, experiments have been performed. The analytical results are in fairly good agreement with the experimental results. In addition, the analytical results of the effective gasket seating width and the moment arm are compared with those obtained from JIS (Japanese Industrial Standard).

Strength Evaluation of Scarf and Stepped Lap Joints Bonded with Adhesive Resin

The deformation and strength of adhesively bonded scarf and stepped lap joints were investigated both analytically and experimentally. The joint consisted of adherends of carbon steel and adhesive of epoxy resin. The strain distributions of both joints under tensile loadings were found out by the finite element method, and their validity were confirmed by the experiments. The strength of both joints was predicted by applying the strength criterion corresponding to the adherends, adhesive layer and adhering interfaces on the stress distributions in the both joints. The difference in the initial failure strength and the final fracture strength between scarf and stepped lap joints was examined by the obtained analytical and experimental results. It was found that the initial failure strength of scarf joints was better than that of stepped lap joints because of the difference in stress distribution of both joints.