Key Engineering Materials Vols. 535-536

Abstract: We present an analytical solution for elastic and elastoplastic bending problem of a curved beam composed of inhomogeneous materials. Suppose the material is isotropic, ideally elastoplastic and it obeys Tresca’s yield criterion and the corresponding associated flow rule. And the elastic modulus and yield limit of the material vary radially according to general power functions. The expressions of stresses and displacements of a curved beam in both purely elastic stress state and partially plastic stress state are derived. The influence of material inhomogeneity on the elastoplastic behavior of a curved beam is demonstrated in numerical examples. Analytical solutions presented here can serve as benchmark results for evaluating numerical solutions.

Abstract: In this study, the elastic-viscoplastic properties of aluminum honeycomb sandwich panels are investigated using a homogenization theory for free edge analysis. For this, the mathematical homogenization theory is reconstructed for elastic-viscoplastic analysis of honeycomb sandwich panels by introducing a traction free boundary condition. Moreover, the domain of analysis is reduced to a quarter using point-symmetry of internal structures of honeycomb sandwich panels. The present method is then applied to the analysis of macroscopic elastic-viscoplastic behavior and microscopic stress distribution of an aluminum honeycomb sandwich panel subjected to in-plane uniaxial compression. It is shown that the stress concentration arises at face/core interfaces, especially at intersections of core walls.

Abstract: Vehicle structure must be lightweight in order to improve fuel-efficiency and reducing exhaust fumes. The most important goals in designing automobile are safety and environment-friendliness. There are lots of studies on the crushing absorption energy of a structural members in automobile. The crashworthy behavior of circular composite material tubes subjected to axial compression under same conditions is reported in this paper. Energy absorption of CFRP circular member is affected by lamination conditions. Test was executed in order to compare the results to the energy absorption and collapse shape.

Abstract: A railway buffer stopper is a crash energy absorbing device which is installed at the end of rail lines in order to prevent derailment. To stop a train which cannot otherwise stop at the rail end due to some kind of trouble, this device should be installed in a railway station or depot where the rail line finishes. Friction type buffer stoppers have been installed at railway stations in most European countries. These devices can absorb the crash energy of the train by using the friction between a friction element and the rail when the train crashes into the buffer stopper. This paper proposes a new concept for the buffer stopper which can replace the friction type buffer stopper. More economical and effective buffer stopper can be suggested by using a progressive compression process. When the train crashes into the new type buffer stopper, a metal strip installed at the rail is progressively compressed and absorbs the kinetic energy of the train through its own plastic deformation. The feasibility of the buffer stopper using the progressive compression process is first investigated using numerical analysis and then the design and concept for the new system are suggested by a parametric study. The design of the progressive compression type has been verified by a series of experiments.

Abstract: Line heating-induced deformation behavior of an SS400 thick plate was investigated through both numerical analysis and experimental counterpart by applying induction heating (IH) as a heat source. The drastic increase of temperature gradient upon increasing input power could mainly be predicted by numerical analysis, which attributes to the amount of permanent bending deformation of the thick plate. After plotting the amount of vertical deformation as a function of various positions from top surface of the plate, we found that the higher input power, the more thermomechanical deformation can be generated, regardless of the purposed doubly curved shapes such as concave and saddle-type plates. Also there is good agreement between the numerical analysis and experimental measurement in terms of the transverse curvature.

Abstract: This research presents a topology optimization approach based on Bi-directional Evolutionary Structural Optimization (BESO) for optimal design of compliant mechanisms. Due to the complexity of the design for various compliant mechanisms, a new multi-objective optimization model is established by considering the mechanism flexibility and structural stiffness simultaneously. The sensitivity analysis is performed by applying the adjoint sensitivity approach to both the kinematical function and the structural function. The sensitivity numbers are derived according to the variation of the objective function with respect to the design variables. Some numerical examples are given to demonstrate the effectiveness of the proposed method for the design of various compliant mechanisms.

Abstract: The y-directional mechanical properties of hexagonal honeycombs with various cell-wall angles are explored. The results of both the quasi-static experiments and the dynamic simulations show that the cell-wall angle has a significant influence on the honeycombs’ mechanical properties, although the latter is dominated by the honeycombs’ relative density. This influence is weakened by the increase of the impact velocity. With retaining the honeycombs’ relative density as constant, the honeycomb with the cell-wall angle of about 45^o exhibits the optimal crushing strength and energy absorption capacity.

Abstract: In this paper, the effects of the thicknesses of sheet and adhesive layer on plastic forming of adhesively bonded sheet metals were investigated by experiments and the corresponding numerical simulation. The main conclusions obtained are as follows: (1) When the thickness of the adherends increases, the gull-wing bend of the bent sheet and the transverse shear deformation in the adhesive layer become larger, which in some cases the delamination occurs in the adhesive layer. (2) The gull-wing bend of the bent sheet becomes larger with increasing adhesive layer thickness, but conversely the shear strain in the adhesive layer becomes smaller.

Abstract: Stress-strain responses of a high strength steel sheet of 980MPa grade under uniaxial tension and its springback in V- and U-bending were investigated at elevated temperatures ranging from 573-973K. The flow stress decreased drastically with the increase of temperature, from which it was expected that springback is reduced by warm forming. In V-bending test, however, the temperature effect on springback was not so clear, while in U-bending springback decreased with temperature rise. It was found that such difference in temperature dependent springback behavior between V- and U-bending was caused by stress relaxation which took place during unloading process.

Abstract: Transport is the safety and comfortableness during the transportation of passenger to desired location. Therefore, goals in transport design can be summarized as environment-friendliness and safety. Demand for weight reduction of transport has been growing in order to solve the environmental problems. In many countries, environment conservation forces the enhanced regulation on gas mileage and emission gas due to exhaustion of energy resource, adding an extra weight of environment pollution. CFRP(Carbon Fiber Reinforced Plastic) which the advanced composite materials has a widely used in lightweight structural materials of aircraft, ship and vehicle because of high strength and stiffness. In this study, collapse mode and energy absorption capability double CFRP hat-shaped section members were analyzed. The stacking condition were selected to investigate the effect of the fiber orientation angle (±15°, ±45°, 90°, 90°/0°and 0°/90° where 0°direction coincides with axis of the member)on the energy absorption of the CFRP double hat-shaped section members. The collapse mode and energy absorption capability of CFRP double hat-shaped section members was analyzed according to the change of the fiber stacking condition of CFRP.