Research On Mechanical Behavior Of X-COR Reinforced Foam Sandwich Composited Structure

X-cor reinforced foam sandwich structure is a novel material generated from the implementation of z-pin technology into foam core sandwich. It possesses strength- and stiffness-to-weight ratios such to compete with honeycomb constructions, while overcoming many disadvantages of foam sandwich, including low compression and shear properties, debonding between face sheets and cores, etc. The enhanced tailoring ability to specific design needs through using various foam cores, pin materials, pin diameters, pin layouts, pin densities and pin insertion angles, etc, makes the novel material an attractive alternative for aircraft structures. Researches abroad on the novel structure have been carried out and obtaining certain achievements while we just investigate its manufacturing procedures and mechanical properties primarily.After reviewing relevant reports on X-cor foam sandwich structure, the study carries out the analysis and evaluation of its out-of-plane properties (tension, compression and shear), using the approach of test, theory and FEM. Firstly, influence of core parameters (pin diameter, insertion angle, density, oblique angle, insertion depth and its layout) on tension, shear and compression response is investigated experimentally. And results demonstrate that the X-cor, consisted of pins in a truss pattern, improves the mechanical performances of foam core construction significantly. Among all parameters, pin insertion angle, pin diameter and pin density are primary for compression and shear properties, while the oblique angle and pin layout could be neglected except that pins on transverse plane about shearing load have little contribution to the shear behavior. The tension property is also enhanced as the increases of pin density, pin diameter and insertion depth. In addition, the adhesive film on core-face interface may improve the out-of-plane tension strength through foam core, while having little impacts on tension stiffness.Based on experimental phenomenon, the study investigated the deformation and failure mechanism of X-cor foam sandwich principally. 1) Compression. The behavior exhibited by the novel composite is indicative of a buckling failure mechanism in out-of-plane compression loading condition. This is followed by the building of a compression stiffness analytical model using the rule of mixture and the improving of compression strength model by employing pin-end restriction correction coefficient and considering the effects of transverse shearing force. 2) Shear. The shear failure results from the pulled out of most pins and rupture of foam core. Followly, a shear strength analytical model is established taking account the influence of adhesive film. Besides, the shear stiffness analytical model is improved through analyzing the local restriction mechanism between skin and pin. And the pin-end constraints are used in a FE model to compute the equivalent shear modulus.3) Tension. The tension failure mechanism consists of pulled out of most pins and rupture of foam core. Taking account the effects of adhesive film, a tension strength model was set up. Finally, results of the above models are compared with experimental values to verify their validities. Shortcomings are also pointed out for advanced investigation.The influence of all parameters on the integral out-of-plane mechanical property was analyzed as a whole in the end. 1) In condition, an excellent X-cor foam sandwich could be tailored by choosing the pin insertion angle and oblique angle as about 22°and 30°respectively, and improving the insertion depth properly at the same time. 2) Bond skin-core interface with adhesive film and preserve the foam core may improve both the toughness and efficiency of the novel structure. 3) The out-of-plane mechanical property dependents on whether the outstanding axial property of pin could be exerted adequately.