Partition of mixed modes in layered isotropic double cantilever beams with non-rigid cohesive interfaces

• Analytical partition theories for non-rigid cohesive interfaces are developed.
• Double cantilever beams modelled with beam theories and 2D elasticity.
• Mixed-mode fractures are partitioned using the orthogonal pure modes.
• Finite element simulations validate the analytical theories.

The authors’ existing mixed-mode partition theories for rigid interfaces are extended to non-rigid cohesive interfaces for layered isotropic double cantilever beams. Within the context of Euler beam theory, it is shown that the two sets of orthogonal pure modes coincide at the first set of pure modes due to the absence of any crack tip stress singularity for a non-rigid interface. The total energy release rate in a mixed mode is then partitioned using this first set of pure modes without considering any ‘stealthy interaction’. Within the context of Timoshenko beam theory, it is shown that the mode II component of energy release rate is the same as that in Euler beam theory while the mode I component is different due to the through-thickness shear effect. Within the context of 2D elasticity, a mixed-mode partition theory is developed using the two sets of orthogonal pure modes from Euler beam theory with rigid interfaces and a powerful orthogonal pure mode methodology. Numerical simulations are conducted to verify the theories.