The connection between two different approaches for analyzing the fracture of an adhesively-bonded, tensile-loaded butt joint is examined. This type of joint is commonly used to evaluate adhesives and also presents a convenient geometry to analyze. Here an idealized butt joint with rigid adherends and a thin, essentially semi-infinite, bond is analyzed. This idealization is applicable when the adherends are much stiffer than the adhesive (e.g. steel adherends and epoxy adhesive), and when the bond thickness is much smaller than any other joint dimension. One approach for analyzing the fracture of an adhesively-bonded butt joint is to use a linear elastic fracture mechanics-based method. For example, Anderson 'And DeVries (1987, 1989) assume that the joint behaves as if a characteristic, inherent flaw is present. Their approach requires the determination of a critical toughness value, Gc, and also an inherent flaw size, ao. This is done by first measuring Gc using joints with intentionally inserted interfacial disbonds of known size. Joints without inserted disbonds are also tested. The energy release rate calibration (i.e., G value for a given crack length, load and specimen geometry) for the butt joint test geometry is then used to determine the ao value that is consistent with both the strength of the joints without inserted disbonds and G = Gc. Employing these Gc and ao values, the authors were then able to successfully predict the dependence of butt joint strength on bond thickness.
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