Miscellaneous joint geometries

As stated in Section 6.4.2, an annular butt joint, or napkin-ring, specimen tested in shear minimizes the variation of shear stress in the adhesive and has been used by many workers to assess the shear strength and shear stress versus strain behaviour of adhesives [14,17,111-115] and is also listed for this purpose as ASTM E 229 (see Table 6.1). The independence of the measured strength upon specimen geometry has been substantiated by Bryant and Dukes [112] and Foulkes et al. [110] and the shear stress distribution calculated using linear elasticity theory is  

However, if the failure of the adhesive involves significant plastic deformation then a more uniform stress results through the width of the annulus and the fracture stress, Xaf, is now given by [116]  

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MECHANICAL BEHAVIOUR OF ADHESIVE JOINTS 6.4.8 Miscellaneous joint geometries... 

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