Advanced Materials Research Vols. 33-37

Abstract: The explicit numerical method is used to trace the impact procedure of the tube columns impacted by a rigid body. The bar and rectangle tube models are both used to simulate the tube column. The elastic and elas-plastic impact load with different mass ratio and impact speed are obtained. The calculation results show that: for elastic models, the bigger the mass ratio and the higher the rigid body speed, the bigger the peak value of elastic impact load; at the same time, the more obvious the reduction effect of local buckling of rectangle tube on the peak value of impact load and the longer the contact time of tube model; so the peak value of impact load of the rectangle tube is not proportional to the rigid body speed. The stress wave in the tube causes a little difference between the load curves of tube model and bar model. For elas-plastic models, the higher the rigid body speed and the smaller the mass ratio, the bigger the peak value of impact load and the longer the contact time. The higher the rigid body speed, the bigger the difference between elastic and elas-plastic impact load peak value due to the expanding of plasticity. Because of the effect of local buckling, the peak value of elas-plastic impact load of rectangle tube is always lower than that of bar.

Abstract: We demonstrate how algorithms to compute hierarchical triangular meshes. We can generate the hierarchical triangular meshes using level-of-detail for the mesh data structure. We perform hierarchical regional partitions using Ward's method with hierarchical data structure to achieve the level-of-detail. The meshes using this data structure can be hierarchically compressed and be unpacked at a faster pace. Additionally, we introduce the adaptive mesh generation algorithms for the parameters of computational mechanics by setting some kind of metrics in the level-of-detail.

Abstract: A group of geometrically similar elements is automatically generated layer by layer around the tip of crack. By taking advantage of the same stiffness and similar mass of similarly shaped elements, the combined stiffness matrix and combined inertia matrix in area
can be expressed by the displacement row matrix of outer polygon. The global stiffness matrix will be obtained if the combined stiffness matrix and combined inertia matrix of area
are assembled to those of another elements according to corresponding nodes. The small set of generalized coordinates can be obtained through solving the equation, and then the dynamic stress intensity factor of crack will be obtained. The three points bending with single crack and shearing model with double cracks in explosive loading were calculated with finite geometrically similar element method.

Abstract: Experimental works using a drop weight impact test method have been performed on a circular sheet specimen to evaluate and to characterize the impact resistance of the sheet-type plastic components designed for automotive wheel covers. Evaluation has been conducted for a set of engineering plastics: polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS) and their blend (PC/ABS). The testing results showed that the PC/ABS blend specimens failed in brittle manner under higher impact speeds with very few of whitening zones. Secondary cracks captured perpendicular to fracture surface were also found in the mid-plane of the scattered PC/ABS blend specimens. Investigation is then focused on this blend and the testing results describe that impact resistance of the specimen made of this alternative material is determined by ABS not by PC. Combination of structures between PC and ABS through the thickness in the core due to their immiscibility was observed by scanning electron microscope (SEM) on the etched PC/ABS specimen. This latter result well correlates the results obtained from the testing. It therefore reveals that immiscibility between PC and ABS in the blend plays an important role in determining the impact resistance of the components. This paper also presents simulative results of the test obtained from a FEA work by introducing a 3D- layered finite element (FE) model of the PC/ABS specimen to take into account effect of a layer in the core on the behavior of the blend.

Abstract: In this paper, the prediction and comparison of the behavior of thin-walled prismatic structures (square tube, top-hat and double-hat sections) in absorbing energy using theoretical and numerical analysis are presented. Equations to predict crushing length and dynamic mean crushing force of top-hat and double-hat sections were applied for material mild steel St37 and the effect of spot weld positions are also figured out. For comparison, an explicit non-linear commercial finite element code LS-DYNA was used to predict the response of the structures subjected to axial crushing. It was found that results of numerical methods and theoretical prediction have good agreement. Assuming that the failure of spot-weld is neglected, mean dynamic crushing force of double-hat section is 90% higher compared to that of square tube.

Abstract: The 3-D finite element analysis model of beam-edge structure with spaced multiple layers under bird impact is established. Numerical simulations are implemented by using the non-linear contact-impact code ANSYS/LS-DYNA when the birds collide at three locations of the structure respectively. The failure process of the structure and the equivalent plastic strain at supports are obtained. The residual strength of the structure after impact is predicted. The results show that the front spars are penetrated or cracked after the leading edge is perforated. The equivalent plastic strain at the support is much higher when the bird impacts the structure at the central location. Both the structure deformation and failure mode from the simulation are consistent with the results of full scale test, which proves the validity of the method proposed in this paper.

Abstract: This paper attempted to study the properties of Slapper detonator non-energetic elements through exerting impact on them by Hopkinson Pressure Bar and evaluating the acceleration that samples received in accordance with one-dimensional stress wave theory. The results showed that the velocity pulse width could be controlled and acceleration pulse width be improved by varying the pulse shaper material and strike bar length. And the critical acceleration causing the failure of the initiator was closely connected with acceleration pulse width as well as acceleration amplitude. When the strike bar length were 126 mm, 190 mm, 270 mm and 460 mm, the acceleration pulse width were 58 μs, 93 μs, 130 μs and 160 μs, respectively, and the critical acceleration causing the failure of the initiator were about 240 000 g, 130 000 g, 74 000 g and 72 000 g, respectively. The accurateness and reliability of acceleration value was accredited to the methods of changing sampling frequency, smoothing velocity and acceleration curve, and fitting curve. The FEM analog simulation was also conducted by using the LS-DYNA finite element program. Good agreements were achieved between the acceleration curve and the simulation results.

Abstract: Creep properties of polymer bonded explosives (PBXs), a particulate composite, was studied by using the method of moiré interferometry in this paper. The specimens fabricated by different heat pressing technology were used. Extensive creep deformation of PBXs material was indirectly measured by the aid of compressive circular disk test. The obtained results shown that creep properties are greatly influenced by pressing pressures and temperature of heat pressing technology. The results indicated that the higher the temperature and the pressing pressure are in the heat pressing technology to some degree, the better the PBXs material creep resistance is. The creep fracture surfaces of PBXs were also observed using Scanning Electronic Microscopy (SEM). It was shown that most of the fracture crack was initiated and propagated along the explosives crystal surface during creep.

Abstract: Considering the time effect of surrounding rock and the long time stability of the underground caverns after being excavated, a method on the finite element viscoelastic displacement based on Kelvin model. The recursion formula is obtained by the displacement analytic solution of Kelvin model. It can be used to predict the viscoelastic displacement development fast and accurately. Finally this method is employed into a project, and the calculated values by this method agree well with the measured values. Prove that the method is effective.

Abstract: The cast magnesium alloys as AM50 offer a good strength, ductility and surface finish for automotive industry. But the poor creep resistance limited its application to power components such as engine and transmission cases at temperatures in excess of 100°C. In order to investigate the cyclic creep behavior of Magnesium Alloy at high temperature, creep tests of plate specimens AM50 were conducted in this work. Based on the analysis about the microstructure and defects of AM50 under the condition of cyclic creep, a cyclic creep constitutive model with isotropic and scalar damage parameter was developed. Furthermore, the proposed model was experimentally verified by analyzing the cyclic creep and recovery response of Cast Magnesium alloy under cyclic loading with dwell time. Comparisons between calculated results and experimental data showed good agreement.