Abstract: During the fabric preform and/or mold closure processes of the resin transfer molded composites (RTMCs), the discontinuous fabric patterns such as wrinkling and overlapping can be occurred and influenced the failure strength. It is found that the composites with discontinuous fabric preform had two failure mechanisms as functions of fabric ply number and discontinuous fabric length under the three-point bending. First, the failure modes can be related to the bend strengths that were controlled by the interfacial bonding strength depending on the discontinuous fabric length. Second, the failures were controlled by the potential strength of fabric when the discontinuous length reached the critical value. Moreover, the experimentally measured results of the normal and discontinuous preform models under bending were compared to examine the safety conditions as functions of fiber content and other factors.
Abstract: Powder compaction at elevated temperature or known as warm compaction is a process of producing green compacts from metal powder, which is generally conducted between the ambient and the recrystalization temperature of the main powder constituent. Even though, warm compaction was initiated at around 1998, not a lot of information can be found in the literature especially on the numerical simulation of the process. Therefore, this paper presents the simulation of warm metal powder forming process by using the developed computer code. The Elliptical Cap yield model has been used to represent the deformation behaviour of the powder mass during the forming process at above ambient temperature. The material properties of powder mass, i. e., friction coefficient, elastic index, and plastic index, at different forming temperature, are established through warm compaction experiment. The simulation was conducted to generate a green compact of a plain bush component. Some numerical simulation results were validated through experimentation, where a good agreement was found between the numerical simulation and the experimental results.
Abstract: By employing a dipole defect model, two-dimensional phase field simulations of domain switching in the crack tip vicinity of a crack embedded in a relaxor ferroelectric single crystal, which was subjected to mechanical loading and electric field, have been carried out. The interaction between the dipole defects and crack, the influence of the dipole defect concentration density on the switching process, and the coupling effect of mechanical stress and electric field on domain switching in the vicinity of the crack tip have been studied. Comparing the results obtained from relaxor ferroelectrics with those of normal ferroelectrics, the former showed that, due to the interaction between the dipole defects and crack, polarization switching in the vicinity of the crack tip was suppressed. Moreover, the coupling between applied mechanical stress and electric field can either promote or suppress domain switching in the vicinity of a crack.
Abstract: This study has investigated the cracking of Ti-51.45at.%Ni thin films deposited on Cu substrate. An analysis is presented that relates the crack spacing and the Vickers microhardness values to the strain in the film. Tensile tests are carried out on CSS-44100 electron universal testing machine. The strain rate is 1.1 × 10-4 s-1. The average crack spacing is obtained using scanning electron microscopy (SEM). The Vickers microhardness values are determined by Everone MH-6 microhardness tests. The results have showed that a series of parallel cracks grew in the film and the cracks are equally spaced. The minimum crack spacing is about 87 μm. The mean crack spacing is dependent on the tensile strain in the film. The crack spacing decreases as the film elongation increases. The Vickers microhardness values increase as the film elongation increases.
Abstract: Metallic sandwich plates have been widely used in blast-resistance structures due to the excellent capacity of energy absorption. In this work, dynamic response of square honeycomb sandwich plates is investigated using LS-DYNA. The effect of mass of TNT charge on the deformation and on internal energy of square honeycomb sandwich plate is numerically analyzed. The relationship of deflection, as well as internal energy and the mass of TNT charge is obtained. The performance of square honeycomb sandwich plate is compared with monolithic solid plate with the same mass and blast loading. During the response of sandwich plate, the deformation includes local dent of upper face sheet, overall bending and stretching of both face sheets and buckling of square honeycomb core while the deformation of monolithic solid plate is involved in overall bending and stretching. It denotes that square honeycomb sandwich plate has better capacity of resistance-deformation and energy absorption than that of monolithic solid plate with the same mass and the same blast loading.
Abstract: The mechanics of interface delamination in CFRP composite laminates is examined using finite element method. For this purpose a 12-ply CFRP composite, with a total thickness of 2.4 mm and anti-symmetric ply sequence of [45/-45/45/0/-45/0/0/45/0/-45/45/-45] is simulated under three-point bend test setup. Each unidirectional composite lamina is treated as an equivalent elastic and orthotropic panel. Interface behavior is defined using damage, linear elastic constitutive model and employed to describe the initiation and progression of delamination during flexural loading. Complementary three-point bend test on CFRP composite specimen is performed at crosshead speed of 2 mm/min. The measured load-deflection response at mid-span location compares well with predicted values. Interface delamination accounts for up to 46.7 % reduction in flexural stiffness from the undamaged state. Delamination initiated at the center mid-span region for interfaces in the compressive laminates while edge delamination started in interfaces with tensile flexural stress in the laminates. Anti-symmetric distribution of the delaminated region is derived from the corresponding anti-symmetric ply sequence in the CFRP composite. The dissipation energy for edge delamination is greater than that for internal center delamination. In addition, delamination failure process in CFRP composite can be described by an exponential rate of fracture energy dissipation under monotonic three-point bend loading.
Abstract: With the rapid development of our economy, the urban traffic becomes increasingly busy. To ease traffic congestion, underground rail transportation is becoming one of the main modes of transportation in city. At present in order to relieve the traffic congestion most major cities in China are accelerating the construction of subway tunnels. The relative position change of metro double tunnels and construction of the sequence will affect the surface subsidence deformation and the interaction of the tunnel lining. It is more concerned about these issues in tunnel design. It is the main purposes, in this paper, to analyze the metro double tunnels surface deformation, which affect by the position changes of new construction double and the sequence of construction. From the numerical simulating results, in order to reduce surface subsidence and ensure the structural safety over the subway tunnel, it should try to make double-tunnels at the same horizontal plane in design. If the double tunnels could not be located at the same horizontal plane, the double-hole tunnel construction sequence of the deformation of the surface subsidence effects are obvious it is obvious that the double tunnels construction sequence differently make the deformation of the surface subsidence. To reduce the deformation of the surface subsidence, it should be first excavated the shallow tunnels and then excavated the tunnel buried deeply. The ideal distance of the double tunnels center is greater than 4 times the tunnel diameter. It can make the surface subsidence reduce to the minimum during the metro tunnel construction.
Abstract: Surface roughness and wettability determines the stability of bone-implant integration. Stable implants can be found in those with a rough and hydrophilic surface. Sandblasting and surface mechanical attrition treatment (SMAT) are among the current techniques to obtain surface with such typical properties. In addition, both treatments increase mechanical strength of metal through surface grains refinement. In this paper, the effect of sandblasting and SMAT on surface roughness, wettability, and microhardness distribution of AISI 316L is discussed. All treatments were conducted for 0-20 minutes. The result shows a rougher and a more hydrophilic surface on the sandblasted samples rather than on those with SMAT. A harder surface is yielded by both treatments, but the SMAT produces a thicker hardened layer.
Abstract: Bamboo is a typical natural fiber reinforced composite material with superior mechanical strength and toughness. As a typical hierarchical material, the macroscopic properties of bamboo are determined by its microscopic structure. The vascular bundles are the reinforce phase in bamboo composite. There was little research on the variation of mechanical properties of bamboo vascular bundles. In this work, the mechanical properties of Moso vascular bundles along the axial direction were investigated by tensile test. It is shown that the longitudinal Young’s modulus and strength of the Moso vascular bundles are linearly increased from inner zone to outer surface.
Abstract: The implantation of nitrogen ion is one of the important techniques for modifying the surface characteristics to improve wear and corrosion resistance of commercially pure (cp) Titanium. Although nitrogen ions implanted titanium in various dose demonstrated significant changes of the wear and corrosion resistance, the variable energy implanted is still not yet fully studied. Nitrogen ions were implanted in cp Titanium surface with varies of both dose of 0.5; 1.0 and 2.0 x1017 ions cm-2 and energy of 80, 100 and 115 keV. The nitrogen ion implanted cp Titanium demonstrated an increase in the surface hardness and improvement in corrosion behavior. The maximum surface hardness was delivered by the specimens implanted with the dose of 2.0x1017 ions cm-2 at energy of 80 keV. Grazing incidence x-ray diffraction studies indicated that TiN phase was formed on near surface substrate. Electrochemical tests in 3.5%-wt NaCl solution depicted significant improvements in corrosion resistance for specimens implanted with dose of 0.5x1017 and 1.0x1017 ions cm-2 at energy of 80 keV, dose of 1.0x1017 and 2.0x1017 ions cm-2 at energy of 100 keV. The dose of 2.0x1017 ions cm-2 and energy of 100 were the best implantation parameter in this study.