The cross-section of an injection-molded plate of foamed long glass fiber reinforced polypropylene was analyzed using scanning electron microscopy. The distribution of the glass fiber orientations and the microcellular structure in the thickness direction were also studied. A multilayer representative volume element was constructed based on the fiber orientation tensors and the cell distribution. Nested and two-step homogenization methods based on the Mori–Tanaka and Voigt models were used to homogenize each layer of the representative volume element. Finally, classic laminate theory was used to obtain the effective elastic modulus of the material. The computed elastic moduli of the single-layer and multilayer representative volume element models with different loading directions predicted by the homogenization and finite element methods were compared with the experimental results. We found that the constructed multilayer representative volume element model can predict the elastic moduli of the foamed glass fiber reinforced polypropylene effectively and that the predicted results were accurate and stable.

In this study, the integral micro-sized composite wings are designed and manufactured by using carbon fiber reinforced plastics and low-density foam. The analytical expressions of bending stiffness of a multilayer sandwich structures for variable cross-section panel are determined. The obtained analytical bending stiffness is numerically verified using results of compressive buckling modes on wing panels from a numerical FE program and experimental tests by a series of stiffened structures which are empirically designed. Contrastive results demonstrate that the stiffener configuration tremendously affects the global buckling of the wing panels and the shapes, locations and intervals of the stiffeners which should be adjusted to construct a structure with maximum bending stiffness. Finally, with the use of the bi-directional evolutionary structural optimization method, the optimum design of the wing cross-section was determined by topology optimization method to pursue the best weight/stiffness. Compared with the initial structure, the optimum material layout of the topology structure performs better at reducing stress concentration and improving load carrying capacity of wing panels.

This paper investigates on a computational simulation of Twaron® fabric against ballistic impact. It proposed a hybrid shell element model considering the strain-rate-sensitive failure criterion. This model innovatively provided a resolution of the yarn level to better capture the unique properties of the woven fabric, such as yarn crimp, sliding contact between yarns, stress transmission on yarns and yarn broken. The fabric is modeled using a hybrid shell element analysis approach aim of reducing the complexity and computational expense while ensuring accuracy. The response characteristics of fabric under high velocity ballistic impact are studied by applying a 3D finite element program DYNA3D in this paper and the experimental investigation had been taken by Shim et al. According to the computational and experimental results, transverse deflection distribution and stress transmission of fabrics are presented. The ballistic limit, energy absorption, remaining velocity are calculated by simulation models and compared with the experimental results. This approach is also validated by comparing it against a 2D uniform shell model and a 3D interlacing shell model. The results show that the hybrid model can accurately reflect the buckling and fluctuation behavior of fabrics and has a relatively few computational consumption at the same time.