Finite element bending behaviour of discretely delaminated composite conoidal shell roofs under concentrated load

Abstract

Laminated composites are increasingly getting used in civil engineering structural components including shell structural units due to their light weight, high specific strength and stiffness properties. One of the major causes of failure in these laminated composites is delamination resulting from the interlaminar debonding between the laminae forming the laminate. A review of literature that exists on composite shells reveals that the research reports on delaminated shells are very few in numbers. Among the shell forms used popularly in the industry, the conoidal ones are aesthetically pleasing and also easy to fabricate being singly ruled surfaces. To use these conoids widely with confidence, behaviour of these forms with possible delamination damage has to be studied in depth. Hence, in this paper, a study on bending behaviour of delaminated composite conoidal shells is done. An eight noded isoparametric element with five degrees of freedom per node is used together with Sanders’ strain displacement relationships. To satisfy the compatibility of displacements and rotations along the crack edges a multipoint constraint algorithm is incorporated. Benchmark problems are solved to validate the present approach and a wide variety of composite conoidal shell problems with midplane delaminations are solved by varying the stacking sequence, extents of delamination and boundary conditions under central point load. The results are critically discussed to arrive at conclusions of engineering significance highlighting particularly the differences in behaviour between undamaged and damaged shells.

Keywords: Laminated composite, conoidal shells, delamination, finite element method, roofs, concentrated load.