Static uniaxial compressive experiments were conducted to study the mechanical behaviors of polyvinyl alcohol (PVA) hydrogels in ambient conditions. It was found that water is expelled during the compression of hydrogels that have high water contents. It means hydrogels may be a mass variable under the compression. In order to depict the mechanical properties intrinsically, a variable mass model with meso-scale cells was proposed to simulate PVA hydrogels. In the model, there are uniform cells with frames of polymer fibers and water, and a virtue membrane designed to wrap up the boundary of the model. The model not only depicts the behaviors of the compressive mechanics and the expelled water, but also explains the nonlinear stress–strain relation of PVA hydrogels and why the hydrogels with high water content demonstrate a modulus considerably lower than the bulk modulus of water.

In the design of a thermoelectric generator, both the heat transfer area and the number of thermoelectric modules (TEMs) should be increased accordingly as the generator power increases; crucially, both aspects need to be coordinated. A kilowatt thermoelectric generator with a fin heat exchanger is proposed for use in a constant-speed diesel generator unit. Interior fins enhance convective heat transfer, whereas an exterior fin segment increases the heat transfer area. The heat transfer surface is double that of a plane heat exchanger, and the temperature field over the exterior fins is constrained to a one-dimensional distribution. Between adjoining exterior fins, there is a cooling water channel with trapezoid cross-section, enabling compact TEMs and cooling them. Hence, more TEMs are built as a series-parallel array of TEMs with lower resistance and more stable output current. Under nonuniform conditions, to prevent circulation and energy loss, bypass diodes and antidiodes are added. Experiments and numerical calculations show that, with matching and optimization of the heat exchanger and TEM array, a stable maximum output power is obtainable from the interior of the thermoelectric generator system, which can be connected to an external maximum power point tracking system.

With the demand of lightweight structure, more and more metal foams were employed as impact protection and efficient energy absorption materials in engineering fields. But, results from different impact experiments showed that the strain rate sensitivity of metal foams were different or even controversial. In order to explore the true hiding behind the controversial experimental data about the strain rate sensitivity of metal foams, numerical simulations of split Hopkinson pressure bar (SHPB) tests of the metal foams were carried out by finite element methods. In the analysis, cell structures of metal foams were constructed by means of 3D Voronoi, and the matrix metal was assumed to be no strain rate sensitivity, which helps to learn the strain rate effects quantitatively by the foam structures. Numerical simulations showed that the deformation of the metal foam specimen is not uniform during the SHPB tests along the specimen, and the strain-stress relations of the metal foams at two ends of the specimen are different; there exists strain rate sensitivity of the metal foams even the matrix metal has no strain rate sensitivity, when the strain of the metal foams is defined by the displacement difference between the ends of the specimen; localized deformation of the metal foams and the inertia effect of matrix metal are the two main contributions to the strain rate sensitivity of the metal foams.

In order to study the penetration ability of fragment simulation projectile(FSP) to armored steel target, and to detect the protection ability of target plates with different thicknesses. Combined with numerical simulation and experiment, the penetration process of FSP on armored steel target plates with different thickness ratios is studied. The design and implementation preparations were made for the damage of the steel target plate by the fragments, and the relevant data were obtained and analyzed. The analysis results show that the finite element analysis and the experimental study are in good agreement, and the ballistic limit of armored steel targets with different thicknesses and the calculation formula of the residual velocity of the FSP are obtained. The research results provide the basis and support for the evaluation, design and improvement of armored vehicle protection capability.

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