Design of lamina orientation for biaxially loaded off-axis tunnelling cracks

The primary objective of this work is to demonstrate how the condition for biaxially loaded off-axis tunnelling crack growth can be reproduced in a modified laminate under uniaxial loading. More specifically, laminates with the stacking sequences [0/θ/0/-θ]_s and [0/α/0/-α]_s have been considered for the biaxial and uniaxial loadings, respectively. A steady-state crack growth condition is analysed for an isolated off-axis tunnelling crack. The crack tip stress state is expressed in terms of a through thickness averaged mode mixity and energy release rate. The presented framework uses an energy accounting method with the crack opening displacements extracted from a finite element analysis. Results shows that the tunnelling crack tip stress state of the modified laminate under uniaxial loading matches with the biaxially loaded laminate. With a modified off-axis lamina orientation and the additional load amplitude from the biaxially loaded laminate, a simplified uniaxial testing laminate can be designed that yields the same biaxial tunnelling crack tip conditions.