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 characteristics of composite tubes with different fibers and matrix under axial quasi-static and impact crushing conditions
The collapse characteristics and energy absorption capability of composite tubes with different fibers and matrix were studied in present article under axial quasi-static and impact crushing conditions. The sensitivity to fibers, matrix and loading conditions were thoroughly discussed for the crushing modes and energy absorption capability. Experimental results showed specimens with different matrix and fibers exhibit three typical types of crushing modes. Specimens G803/3234 and G827/3234 had better energy absorption performance than the specimens with 5224 matrix. Impact loading condition led to lower energy absorption capability as compared to quasi-static loading condition. Moreover, impact loading condition also caused the crushing mode transition from splaying mode to fragmentation mode for G803/3234 and G827/3234.
The crush behavior of glass fiber reinforced plastic sections
Abstract The crush response of glass fiber reinforced plastic tubes, of cylindrical, square and rectangular section, made from unidirectional tape with various alternating 0° and 90° lay-ups, and also of small samples cut from these tubes, was studied with particular reference to the effects of the geometry of the crush trigger initiator. It was found that the propagation of delamination cracks contributed little to the energy absorption capacity, most of the crush resistance being derived from the development of kink bands in the fiber structure. The crush resistance of square tubes with thinner walls was largely provided by the corners. As the wall thickness increased, the planar portions contributed more to the crush resistance. Approximate estimates of the specific energy may be made from crush tests of simple flat sections. The trigger geometry alters the energy absorption capacity by the extent to which it generates deformation flaws which can then propagate within the wall structure. Softer crush anvils reduce the effectiveness of the trigger crush initiator and can lead to global failure of the section, rather than to stable, progressive crush.