Yield Behavior Of Aluminum Alloy Foams And NOMEX Honeycombs

Cellular material are widely used in many important fields, such as ship, aircraft, automotive and aerospace industries, mainly on account of lightweight, high strength and favorable cushioning properties. In this paper, theoretical analysis, computer simulation and experiment verification are combined to carry out this research for the mechanical behavior of NOMEX honeycombs and aluminum alloy foams. The main contents can be stated as follows:This paper presents an experimental investigation on the yield behavior of Nomex honeycombs under combined shear-compression with regard to out-of-plane direction. Four different types of specimens were designed in order to investigate the influence of in-plane orientation angle on the yield behavior of honeycombs under combined loads. Two different failure modes of honeycomb specimens, i.e. the plastic buckling and the extension fracture of cell walls, are observed under combined shear-compression. Base on this experimental results, the upper and lower limits of shear strength and shear modulus have been determined. The experimental results validate that the in-plane orientation angle has a significant influence on the developments of the experimental yield surface. The experimental yield surfaces are compared with a phenomenological yield criterion capable of accounting for anisotropic behavior. The comparative analytical results indicate the experimental yield surfaces are approximately consistent with the theoretical yield surfaces in the normal-shear stress space. These experimental results are useful to develop constitutive models of Nomex honeycombs under combined shear-compression.Combined shear-compression tests and combined shear-tensile test have performed on closed-cell aluminium alloy foams with three relative densities over a wide range of loading rates in order to probe their failure behaviors under different loading conditions. Quasi-static uniaxial compressive and tensile tests have also been conducted to investigate uniaxial failure behaviors of the aluminum alloy foams. The materials exhibit uniaxial failure stress asymmetry due to different failure mechanism in the uniaxial tensile and compression. Comparison is made between three phenomenological failure criteria and the measured failure stresses under different loading conditions to verify these criteria. The experimental failure surfaces of the aluminum alloy foams provide support for the three phenomenological failure criteria when suitable Poisson’s ratio is employed. The shape of the experimental failure surface in principal stress plane was not significantly influenced by variation in the relative density. The slight expansion of the failure surfaces with loading rate happened to be isotropic for this investigated closed-cell aluminum alloy foams in combined shear-tensile. A Hopkinson Pressure Bar system (SHPB) with beveled ends of different angles is employed to apply the desired shear-compression combinations. The data processing methods are investigated and validated by using.numerical simulation. A series of experiments on closed-cell aluminium alloy foams with three relative densities were performed at the impact velocity of about10m/s with the loading angles ranging from0(corresponding to the pure compression) to60. The experimental failure surface in normalized principal stress plane was obtained on the basis of the above testes. The experimental failure surfaces for three relative densities all exhibit an almost isotropic expansion over the range of loading rates studied. Based on the experimental results, a phenomenological failure criterion as a function of the strain rate is proposed. The capability of the phenomenological failure criterion was examined by simulating high strain rate yield behavior of the closed-cell aluminium alloy foams with three relative densities in tension and in combined shear-compression tests. The simulation results revealed very good predictions between the experimental results and the responses obtained from this failure criterion.