Impact response of laminated composite skewed hypar shell roof by finite element approach

Abstract

Man has related himself with shell structures through natural examples from the very first dawn of civilization. Enhanced load carrying capacity of curve surfaces have facilitated mankind and the earliest balloons, tyres, pressure cookers and domes were conceptualized imitating the natural examples of human skull, egg shell etc. The application, fabrication, construction and research on shell structures have sailed a long way and researchers are now engaged in analyzing and designing shell structures with laminated composites. Successful implementation of laminated composites in fabrication of shell surfaces requires understanding of its behavioral characteristics comprehensively. To attain this, understanding the current status of shell research and indentifying the areas which has not been explored are mandatory requirements. With this aim, the literature on laminated composites is reviewed thoroughly to identify the broad scope which needs to be addressed. The actual scope of the present study is defined subsequently from the broad scope and the skewed hypar graphite-epoxy shell is picked up for present study. A finite element formulation is developed using an eight noded curved quadrilateral element. The modified Harzian contact law is used to model the contact mechanics and the dynamic equation of equilibrium is solved using Newmark’s time integration scheme. The present code is validated through solution of a number of benchmark problems. A number of other problems with a number of practical parametric variations like stacking sequences and boundary conditions are solved. Both normal and oblique low velocity impact are considered. The results are presented systematically in form of tables and figures. The results are meticulously examined to extract meaningful conclusion of engineering significance. The conclusions are presented systematically at the end of the chapters. Scope of future research is indicated at the end of the thesis. The thesis is divided into nine chapters and one appendix. Chapter 1 contains the general introduction, course of development of shell structure and research importance of present study. In Chapter 2, the review of the existing literature is reported meticulously. The available literature is thoroughly analyzed and critically discussed to identify the lacunae present therein. Based on the elaborate review exercise, the actual scope of the present work is outlined and presented in Chapter 3. Having defined the scope, Chapter 4 contains the mathematical formulation employed in the present analysis. A wide spectrum of author’s own problems are taken up and solved with different practical parametric variations and are discussed in details in Chapters 5, 6, 7 and 8. Results are also obtained for some specific benchmark problems solved by earlier investigators to establish the validity of the present formulation in relevant chapters. Chapter 5 deals with impact response of simply supported laminated composite skewed hypar shells. Chapter 6 reports impact response of laminated composite skewed hypar shells with clamped boundary condition. Chapter 7 proposes some design guidelines for point supported laminated composite skewed hypar shells considering the dynamic behavior due to impact load. Response of simply supported laminated skewed hypar shell due to oblique impact is presented in Chapter 8 considering dry friction between the impactor and shell surface. Chapter 9 discusses about the future scope of the present study. The references are presented in the Appendix.