Prediction of Progressive Failure Behaviour of Composite Skewed Hypar Shells Using Finite Element Method

Progressive failure behaviour of laminated composite skewed hypar shells is investigated in this paper through finite element approach. For composite materials which are weak in transverse shear, failure may initiate at any inner lamina or interface and may remain undetected and unattended to. Such latent damages may progress gradually and lead to a sudden total ply failure. An iterative method is adopted using the various failure theories to predict the first ply failure load. After the first ply failure, the stiffness of the failed element is totally discarded from the laminate and the remaining laminate is considered for further analysis. The developed finite element code is validated through solution of a benchmark problem. Numerical experiments are carried out to obtain the first ply and progressive failure of simply supported hypar shells under transverse distributed load. While obtaining the failure loads, the shell is considered to be under plane stress condition and in linear elastic range. Results are studied meticulously to extract a set of conclusions of practical significance regarding the failure characteristics of composite hypar shells. 1. Introduction In modern engineering and technology, a composite is defined as a material composed of stacked layers with fiber reinforcement held in proper location with the rigid binder. A number of laminae are bonded together to obtain a “laminate” which stands for a structural unit of a beam, plate, or shell. Nowadays researchers are emphasizing more on laminated composite shells realizing the strength and stiffness potentials of this advanced material. Shell structures are preferred in the industry to cover large column free open spaces as are found in airports, shopping malls, auditoriums, and car parking lots. A skewed hypar shell is aesthetically appealing and being doubly ruled is easy to cast. Moreover, this configuration can allow entry of north light and due to this advantage it finds use as roofing units in practical civil engineering applications. Researchers like Sahoo and Chakravorty [1, 2] and Nayak and Bandyopadhyay [3] studied bending and vibration characteristics of graphite-epoxy hypar shells. It is important to note that failure study of the laminated hypar shell is needed for their confident application in the industry. First and ultimate ply failure of composite plates have received attention from researchers like Singh and Kumar [4], Akhras and Li [5], and Ganesan and Liu [6] who reported that failure of the laminated composites is progressive in nature and the load at which