Cleavage behavior of bonds made with adherends capable of plastic yield

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Abstract
The failure behavior of adhesive joints under cleavage stresses depends upon the thickness of the adherend. With thick, rigid adherends failure occurs by rapidly propagated adhesive rupture. Thinner adherends can exhibit plastic flexural yield, the subsequent adhesive failure then being progressive and strain‐limited, and occurring only in the region of bond directly adjacent to the yielding adherend. A fairly sharp discontinuity between these two types of behavior occurs over a small range of adherend thicknessT. Work to rupture can differ by more than an order of magnitude, for otherwise identical joints havingTabove or below the transitional range (aroundTc). ForT>Tcthe applied loadPcausing rupture is proportional toT1.5while the moment arm remains constant, as predicted by Yurenka. ForT < Tcthe turning moment during failure is proportional toT2and is substantially independent of the nature of the adhesive. Empirically, the radius of the yielded adherend after failure is proportional toT. The manner of interaction of various adhesive mechanical properties in definingPin the two ranges and, thereby,Tc, are related to this and other empirical correlations. The initial free moment arm in the joint,L, determines the stability of peel at initiation of adhesive rupture. ReducingLleads ultimately to instability. The change of controlling factors asL→ 0 is discussed.

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