Papers by Author: T.X. Yu

Abstract: Saturated impulse refers to the critical value beyond which the deflection of the beam or plate under pulse loading will no longer increase with further applied load. Previous effort has been made to study the saturate impulse for structures under rectangular pressure pulse loading. Through theoretical analysis, the present paper investigates the saturated impulse for fully clamped square plates subjected to linear-decay pressure pulse, which is closer to explosive loading pulse. The results indicate that the saturated impulse does exist if the decay duration is greater than a certain value (i.e. the minimum decay duration). The saturated impulse, saturated deflection and saturated duration all have nonlinearly relations with the dimensionless applied pressure, and grow with the increase of the decay duration.

Abstract: A numerical model of the aluminium foam with voronoi cells is built and uni-directionally crushed with various velocities from 1m/s to 110m/s. It is shown that the foam deforms homogeneously within the whole specimen and the stress in the foam increases gradually with the strain without an obvious plateau stage under the low-velocity compression, while the deformation is concentrated within a zone near the impact end and an obvious plateau stage can be found in the stress-strain curves of the foams under the high-velocity crushing. By analyzing the distribution of the density within the foams using the digital image processing technology, the densification strain of the foams under dynamic crushing can be determined. Then combining the foam’s stress-strain curve under the low-velocity compression, the dynamic plateau stress of the foams can be predicted. It is shown that both the densification strain and the plateau stress of the foams under the high-velocity crushing predicted by employing the digital image process technology are in good agreement with the numerical simulations. The results show that both the plateau stress and the densification strain of the foams increase with the impact velocity, which is essentially caused by the localization of the foam’s deformation under dynamic crushing.

Abstract: To examine the effect of elasticity in dynamic response of imperfect structures, by densely setting meshes in the vicinity of the imperfections, pre-cracked beams impinged by a striker are modeled and numerically investigated. The dynamic response patterns and failure history for two specific configurations are obtained. It is found that complex alternations of the elastic-plastic stress distribution exhibit, and the striker is rebounded and then separated from the beam, which well reflects the effect of material elasticity. The high stress and large deformation zones, corresponding to the plastic hinges in the rigid-plastic model, appear at the impinging position and the supporting ends, and the locations coincide with those in the modal pattern in rigid-plastic response. From comparison, it is concluded that when the impinging is intense, despite the effect of elasticity displaying in the early stage, the widely employed rigid-plastic analysis is still capable of providing favorable prediction on the final response parameters.

Abstract: The dynamic behavior of a thin-walled hollow sphere colliding onto a rigid wall has been studied by experiments, numerical simulation and analytical modeling, as reported in our previous papers. In the present paper, the impact crushing of metallic thin-walled hollow spheres onto rigid plates and the subsequent rebound are analyzed using finite element method. The effects of hollow sphere’s thickness-to-radius ratio, the material properties and the impact velocity on the dynamic responses are systematically investigated. The transition from axisymmetric dimpling to non-axisymmetric lobing is found to depend on the relative thickness of spheres and impact velocity; while the coefficient of restitution almost merely depends on impact velocity.

Abstract: This paper is concerned with the geometrical similarity of heat conduction-elastioplastic structural problems. When the dimensions of a structure are geometrically scaled down/up, the similarity relations for both isolated heat conduction and elastoplastic structural problems are derived. For cases of thermo-structural coupled, it is concluded that heat conduction-static elastoplastic problems can be geometrically similarly scaled down/up and a set of similarity relations are drawn accordingly. As examples, a full-, half- and quarter-scale unilaterally-tensioned plate and internally-pressured cylindrical shell irradiated by a laser pulse are numerically analysed and the numerical results have confirmed this conclusion. However, heat conduction-dynamic elastoplastic problems are found not to comply compatibly with the geometrically similar scaling.

Abstract: Experimental, numerical and theoretical analyses are carried out to obtain the relationship between the stress and relative density of metal hollow sphere (MHS) materials during their large plastic deformation in order to estimate the energy absorbing capacity of these materials under uniaxial compression. Based on a numerical parametric analysis empirical functions of the relative material density are proposed for the elastic modulus, yield strength and ‘plateau’ stress for FCC packing arrangement. Analytical stress-strain dependences are suggested for the yield strength and material strain hardening properties as functions of the relative density of MHS materials under uniaxial compression.

Abstract: Large shear deformation of plain woven composite sheets and corresponding failure mechanism are investigated by bias extension test. Digital image correlation analysis was conducted on a series of photos taken during the test. Four typical phases were identified, and a theoretical model of the large deformation is proposed from energy point of view. Numerical simulations have also been carried out, but it will be reported in a subsequent paper.