Study of crack closure in laminated composite shells

Abstract

Fibrous composite shells containing through-wall-thickness cracks and subjected to bending loads have crack closure at the crack faces under compression. A study was undertaken to determine the effect of crack closure on the displacement and stress fields of a composite shell using the finite element method. Open cylindrical composite shells containing longitudinal center cracks were studied. The shells had unidirectional layers or cross-ply layers. Numerical analyses showed that crack closure could increase or decrease the crack opening displacement and bending stress around the crack tip at the tensile surface of a composite shell compared to those obtained without considering crack closure. Whether crack closure at the compression side increased or decreased the displacement and stress fields at the tension side depended on material properties of composite shells and crack orientation. A large transverse shear flexibility of the crack face caused an increase of crack opening displacement and bending stress at the tensile surface. The effect of crack closure was more significant for a unidirectional composite shell than for a cross-ply composite shell.