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A shear deformation theory including residual thermal and moisture effects is developed for the analysis of either symmetric or asymmetric laminates with midplane edge delamination under torsional loading. The theory is based on an assumed displacement field that includes shear deformation. The governing equations and boundary conditions are obtained from the principle of virtual work. The analysis of the [90/(±45)n/(∓45)n/90]s edge crack torsion (ECT) Mode III test layup indicates that there are no hygrothermal effects on the Mode III strain energy release rate because the laminate, and both sublaminates above and below the delamination, are symmetric layups. A further parametric study reveals that some other layups can have negligible hygrothermal effects even when the sublaminates above and below the delamination are not symmetric about their own midplanes. However, these layups may suffer from distortion after the curing process. Another interesting set of layups investigated is a class of antisymmetric laminates with [±(θ/(θ–90)2/θ)]n layups. It is observed that when n takes on even numbers (2 and 4), both hygrothermal and Mode I effects can be neglected. From this point of view, these layups provide a way to determine the Mode III toughness between two dissimilar layers. However, when n takes on odd numbers (1 and 3), both hygrothermal and Mode I effects may be strong in these layups. In particular, when θ equals 45°, the layups are free from both hygrothermal and Mode I effects irrespective of n.
fatigue (materials), fracture (materials), composite materials, laminated composites, fracture toughness, delamination, strain energy release rate, Mode III fracture toughness tests, torsion
National Research Council resident research associate, NASA Langley Research Center, Hampton, VA
Senior research scientist, U.S. Army Research Laboratory, Vehicle Structures Directorate, NASA Langley Research Center, Hampton, VA