O'Brien (1985) suggested a simple closed-form expression for the strain-energy release rate for local delaminations growing uniformly from transverse crack tips. The expression is based on simple load shearing rules and the classical laminated plate theory. It gives the strain energy release rate that depends only on the laminate lay-up and thickness, the location of the cracked ply and subsequent delaminations, the applied load and the laminate width, and is independent of delamination size and matrix crack density. In the nomenclature of this paper it is given by

$\frac{{G}^{ld}}{{\overline{\epsilon}}_{xx}^{2}}=\frac{N{\stackrel{\u02c6}{E}}_{x}^{2}h}{2m}\left(\frac{1}{(N-n){\stackrel{\u02c6}{E}}_{ld}}-\frac{1}{N{\stackrel{\u02c6}{E}}_{x}}\right)$

(19.19a)

where h is the laminate ...

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