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The deformation mechanism of unit cell wall is investigated by use of FEM, and the numerical simulation results show that the predominant deformations consist of shear deformation and compressive deformation. One new model based the shear deformation and the compressive deformation is put forward to investigate the longitudinal shear modulus of honeycomb cores. Owing to taking skin effect into consideration in our model, it is found that the equivalent shear modulus depends on not only the material properties and configuration parameters of cores, but also the material properties and configuration parameters of facesheets.

In this paper, in order to enhance the equivalent shear strength of the corrugated ribbon sandwich structures, one new optimal design concept is brought forward to design the corrugated ribbon sandwich structures subjected to biaxial shear loads. Based on the performance harmony concept, the equivalent shear properties have been investigated and given. Analytical results show that the equivalent shear properties of the corrugated ribbon sandwich structure depend on not only the lattice truss cores, but also the facesheets, the interface and the shear loads imposed on the facesheets.

The deformation behavior and damage mechanism of 3-D carbon/epoxy braided composites with different braiding angles under the monotonic compressive loading are investigated by the acoustic emission (AE) technique. The damage process is divided into several different regions based on the change of the accumulative AE event counts. Correlations between the damage mechanisms and the AE results are established in terms of the events energy and amplitude. These correlations can be used to monitor the fracture growth process in the braided composites. Experimental results reveal that the AE technique is an effective tool for identifying damage mechanisms.

A new model is put forward to bound the effective elastic moduli of composites with ellipsoidal inclusions. In the present paper, transition layer for each ellipsoidal inclusion is introduced to make the trial displacement field for the upper bound and the trial stress field for the lower bound satisfy the continuous interface conditions which are absolutely necessary for the application of variational principles. According to the principles of minimum potential energy and minimum complementary energy, the upper and lower bounds on the effective elastic moduli of composites with ellipsoidal inclusions are rigorously derived. The effects of the distribution and geometric parameters of ellipsoidal inclusions on the bounds of the effective elastic moduli are analyzed in details. The present upper and lower bounds are still finite when the bulk and shear moduli of ellipsoidal inclusions tend to infinity and zero, respectively. It should be mentioned that the present method is simple and needs not calculate the complex integrals of multi-point correlation functions. Meanwhile, the present paper provides an entirely different way to bound the effective elastic moduli of composites with ellipsoidal inclusions, which can be developed to obtain a series of bounds by taking different trial displacement and stress fields.