  The effects of shear on energy release rate and mode mixity in a symmetric
sandwich beam with isotropic layers and a debond crack at the face sheet/core
interface are investigated through a semi-analytic approach based on
two-dimensional elasticity and linear elastic fracture mechanics. Semi-analytic
expressions are derived for the shear components of energy release rate and
mode mixity phase angle which depend on four numerical coefficients derived
through accurate finite element analyses. The expressions are combined with
earlier results for three-layer configurations subjected to bending-moments and
axial forces to obtain solutions for sandwich beams under general loading
conditions and for an extensive range of geometrical and material properties.
The results are applicable to laboratory specimens used for the
characterization of the fracture properties of sandwich composites for civil,
marine, energy and aeronautical applications, provided the lengths of the crack
and the ligament ahead of the crack tip are above minimum lengths. The physical
and mechanical significance of the terms of the energy release rate which
depend on the shear forces are explained using structural mechanics concepts
and introducing crack tip root rotations to account for the main effects of the
near tip deformations.
