A new versatile stiff adherend test specimen is proposed. This specimen induces a uniform pure shear stress state practically free of tension and compression in the adhesive layer. The versatility of the specimen consists in the fact that, by loading the specimen in a rotated position, a mixed mode (MI + MII) or (MI + MIII) may be induced, but the present paper deals only with the pure shear case. Comparative finite element calculations of stress distributions, especially at the free adhesive edge, and strain-energy-release rates of cracked specimens, were performed. Experimental determinations provided accurate stress-strain curves of the adhesive systems tested as well as direct verifications of the strain-energy-release rate concept in adhesive joints.

A numerical study of the influence of adherend stiffness on adhesive bonded joints provided an insight into some of their fundamental properties. The stress yield in the vicinity of singular locations, in stiff and flexible adherend joints, was investigated. Linear elastic finite element analysis was used to compare the different systems. A special gradual refinement technique in the vicinity of stress singularities was used and proved to be very efficient. Parametric finite element analysis allowed for development of closed form expressions for the stress distribution in the vicinity of the singular points The singular stress distribution zone is limited by the adhesive strip thickness. Thus the stress intensity factors are attenuated in comparison with homogeneous bodies. The stress field in the singular region normalized to the developed stress concentration factor, appears to be invariant, and independent of joint configuration. The subsequent invariability leads to a general relationship between the Stress Concentration Factor SCF, unique for adhesively bonded joints.

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