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.
Design development tests for composite crashworthy helicopter fuselage
Design development tests were conducted to investigate the crashworthy characteristics of composite helicopter fuselage subcomponents, and to design helicopter center beam/bulkhead specimens lighter than structural elements of honeycomb sandwich construction. Skinstringer designs of center beams - made of carbon, and hybrids of carbon and Kevlar - were fabricated and tested in axial compression. Crashworthy design parameters of specific energy, operating load and stroke efficiency were investigated. 8 references, 15 figures, 2 tables.
Volume fraction determination of Kevlar 49/epoxy composites
A knowledge of filament, matrix, and void content is generally required in order to characterize and study composite materials. It is difficult to obtain such data for Kevlar 49/epoxy composites due to chemical attack of the Kevlar filaments when techniques developed for other composite systems are used. This paper presents a chemical dissolution technique for Kevlar 49/epoxy composites by which less than one percent loss of the filament weight occurs. The procedure involves swelling the epoxide matrix in hot dimethylsulfoxide and then rapidly dissolving the degraded epoxide in a nitric aciddimethylsulfoxide solution. This technique allows the determination of filament, matrix, and void volume fractions of Kevlar 49/epoxy composites with a single procedure and has been successfully applied to fabric and filament-wound composites and to a variety of epoxides. Results obtained with this dissolution technique show excellent agreement with those from optical and weight-difference methods.