Key Engineering Materials Vols. 488-489

Abstract: The aluminum mesh/plate bumper was designed by improving on AL-Whipple shield, and a series of hypervelocity impact tests were practiced with a two-stage light gas gun facility at Harbin Institute of Technology. Impact velocities of Al-spheres were varied between 3.5km/s and 5km/s. The diameters of projectiles were 3.97mm and 6.35mm respectively. The hypervelocity impact characteristics of 5052 aluminum alloy mesh bumper were studied through hypervelocity impact on aluminum mesh/plate bumpers. The fragmentation and dispersal of hypervelocity particle against mesh bumpers varying with material and specification were analyzed. It was found that the mesh wall position, diameter of wire and separation distance arrangement and mesh opening had high influence on the hypervelocity impact characteristic of aluminum mesh/plate shields. At similar impact velocity, hypervelocity impact characteristics comparison with aluminum sheet bumpers of equal areal mass was thrust. The optimized design idea of aluminum mesh/plate bumpers was suggested.

Abstract: Dynamic antiplane behaviors are investigated theoretically in this paper for a quarter infinite piezoelectric medium with a subsurface circular inclusion. Based on complex variable and mirror image method, the expressions are obtained on dynamic stress concentration factor (DSCF) and electric field intensity concentration factor (EFICF) at the inclusion’s edge caused by the interaction between the inclusion and the right angle edge under time-harmonic anti-plane shearing. While some calculating cases are plotted, so as to show how the frequencies of incident wave, the piezoelectric material’s parameters and the structure’s geometry influence on DSCF and EFICF. The calculating results indicate that dynamic analyses are important to a quarter-infinite piezoelectric medium with defects at the surface vicinity.

Abstract: The truck that is used as running equipment for freight car support is a core structural part that supports the load of the car body and that greatly influences the safety of freights and vehicles, as well as their running performance. The running equipment is composed of truck frames, wheels and wheel axles, independent suspensions, and brakes. Among these components, the truck frame supporting the load of the vehicles and freights may be the most important one. This study was carried out to analyze the structure of truck frames and to determine whether they are safe when the maximum vertical load, breaking load, and front and rear loads are applied to them. This was done by subjecting the truck frames to stress tests and then measuring the stress on each of their parts. Before the load test, a structural-analysis program was used for the stress distribution analysis of the truck frame. To measure the stresses based on the results of the structural analysis, strain gages were attached to the surfaces of truck frames. The results of the stress tests showed that truck frames have a safe vehicle load design.

Abstract: Fiber reinforced concrete is superior to plain concrete in toughness, which is the energy absorption at fracture. This study is intended to use fibers extracted from bamboo for tensile reinforcement of concrete. Some experiments were carried out to explore the possibility of bamboo fiber reinforced concrete. As a result, the compressive strength of concrete with 1-2% bamboo fiber is little different from the case without reinforcement. On the other, the splitting tensile and the flexural strength significantly increased with an increased volume fraction of fibers. The strength of bamboo fiber reinforced concrete increased with increasing fiber content as a result of fiber bridging.

Abstract: Residual plastic strains of the shipboard are the product of nonlinear behaviors during welding. Deformations of a welded shipboard injure the beauty of appearance of the ship, cause errors during the assembly of the shipboard and reduce the strength of the ship. Residual welding deformations of shipboard of a container vessel are studied in this paper. Nonlinear three dimensional transient temperature fields are analyzed by FEM first. The heat source is modeled as a moving heat flux following a Gaussian distribution. Then, applying the equivalent loads induced by the inherent strain on the shipboard, the final in-plane shrinkage and out-of-plane deformations are calculated. Being compared with the experimental results of deformations, the simulated results show mostly conformity.

Abstract: In this paper, the variational principle for the simply supported FGM plate is presented by the variational integral method. Then, the stationary value conditions are obtained with the derivation of the varitional principle. At last, the vibration governing equation is illustrated, which will be benefit for the numerical simulation with finite element method in further investigations. From the stationary value conditions deduced by the variational principle, it can be observed that the buckling characteristics of the simply supported FGM plate can be influenced by the temperature changes.

Abstract: The scattering of SH-wave caused by the subsurface circular cavities in an elastic half-space covered with an elastic layer was discussed, which was based on the complex function method ,wave functions expansion method and big circular arc postulation method in which the circular boundary of large radius was used to approximate straight boundary of surface elastic layer. By the theory of Helmholtz, the general solution of the Biot’s wave function was achieved. Utilizing the complex series expansion technology and the boundary conditions, we could transform the present problem into the problem in which we needed to solve the infinite linear algebraic equations with unknown coefficients in wave functions. Finally, the dynamic stress concentration factors around the circular cavities were discussed in numerical examples.

Abstract: In this study the tensile static and fatigue behaviour of a woven-fabric laminate is investigated in both the on-axis and off-axis material directions. Emphasis is placed on the development of damage and its influence on the stress-strain behaviour of the laminate. The test results illustrate that there is a high degree of anisotropic behaviour due to anisotropic damage development, which is evident by the variation of the material behaviour between the on-axis and off-axis test specimens. The fatigue tests also suggest that the on-axis specimens exhibit noticeable stiffness degradation, while the off-axis specimens do not. The qualitative results provide significant insight into the type of damage mechanism responsible for the observed behaviour.

Abstract: It is known that type 310S stainless steel is insensitive to hydrogen embrittlement. Then, the effect of hydrogen on the mechanical properties has not been studied in detail. In the present work, SSRT was carried out under hydrogen cathodic charging condition. Elongation increased by hydrogen charging, while reduction of area decreased. A lot of micro-cracks were observed on the side surface of fractured specimens into which hydrogen was charged, while no cracks were observed on the side surface of fractured specimens without hydrogen charging. Micro-cracks were also observed on the surface of unloaded specimens that were annealed after hydrogen charging. Therefore, it is considered that cracks occur from the defects induced by hydrogen charging.

Abstract: In order to investigate the effect of radical nitriding on fatigue strength of spheroidal graphite cast iron FCD400, rotating bending fatigue tests were carried out at room temperature. Fatigue strength was increased by nitriding. Fracture started from microshrinkages or abnormal graphites in the same manner as that of as cast iron. However, fracture mode was different according to the stress level. That is, fracture occurred from specimen surface at high stress levels and it occurred from defects in subsurface at low stress levels. The cause of these results was the hardened layer and the compressive residual stress, which suppressed the initiation of the surface crack.