Relationship between mechanical-property and energy-absorption trends for composite tubes
U.S. Army helicopters are designed to dissipate prescribed levels of crash impact kinetic energy without compromising the integrity of the fuselage. Because of the complexity of the energy-absorption process it is imperative for designers of energy-absorbing structures to develop an in-depth understanding of how and why composite structures absorb energy. A description of the crushing modes and mechanisms of energy absorption for composite tubes and beams is presented. Three primary crushing modes of composite structures including transverse shearing, lamina bending, and local buckling are described. The experimental data presented show that fiber and matrix mechanical properties and laminate stiffness and strength mechanical properties cannot reliably predict the energy-absorption response of composite tubes.
Energy-absorption capability of composite tubes and beams. Ph.D. Thesis
In this study the objective was to develop a method of predicting the energy-absorption capability of composite subfloor beam structures. Before it is possible to develop such an analysis capability, an in-depth understanding of the crushing process of composite materials must be achieved. Many variables affect the crushing process of composite structures, such as the constituent materials' mechanical properties, specimen geometry, and crushing speed. A comprehensive experimental evaluation of tube specimens was conducted to develop insight into how composite structural elements crush and what are the controlling mechanisms. In this study the four characteristic crushing modes, transverse shearing, brittle fracturing, lamina bending, and local buckling were identified and the mechanisms that control the crushing process defined. An in-depth understanding was developed of how material properties affect energy-absorption capability. For example, an increase in fiber and matrix stiffness and failure strain can, depending upon the configuration of the tube, increase energy-absorption capability. An analysis to predict the energy-absorption capability of composite tube specimens was developed and verified. Good agreement between experiment and prediction was obtained.
Design Considerations in Energy Absorption by Structural Collapse
A general treatment of the absorption of mechanical energy by the axial collapse of a variety of structural shapes, including tubes, honeycombs and foams is developed which encompasses both the geometry of the structure and also the material properties. The use of the method in the design of load bearing structures in which energy absorption is an additional design function is illustrated. High strength-to-weight ratio materials offer a significant weight saving for energy absorbing components, although such materials may have a reduced tensile ductility. The implications to situations in vehicle crashworthiness are discussed. /SAE/