As regard to car frontal crash, previous researches have indicated that the front side member plays a major role in energy absorption. For protecting the passengers, the front side member is expected to absorb crash energy as much as possible. In this study, we investigated the crash characteristics of half cut type side member structure by optimal design method to improve energy absorption ability. We developed an automatic optimal design system, in which the analysis meshes are generated with a group of design parameters and shape optimization is carried out automatically, The design variables are side member cross section shape, spot welding pitch length, divisional section numbers and radius difference along the axial direction, and the number of subdivision levels. As the result, the optimal side member structure with half cut type is capable of absorbing 1.44 times (1.29 times per unit mass) more energy than the original rectangular cross sectional side member structure with half cut type which is generally used.

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The equivalent stress concentration of laminated composite plates reinforced by curvilinear fibers is minimized with respect to fiber geometries under uniaxial tensile load. Projection of contour lines in cubic-polynomial is used to represent curvilinear geometry of fibers, and this description makes it possible to tolerate multi-valued function without solving simultaneous equations, typically seen in the process of using the spline function. The finite element method is employed with the eight-node quadrilateral isoparametric element for stress concentration analysis. In this FEM procedure, curvilinear fibers are approximated by assuming straight short fibers in each element. The optimum curvilinear fiber shapes are searched for minimizing the equivalent stress concentration using a simple genetic algorithm, and the coefficients of terms in cubic polynomial are used as design variables. In numerical examples, single-layer and angle-ply laminated composite plates are considered for different aspect ratios of circular holes. The optimized results show that the present plates with optimally shaped curvilinear fibers can make the equivalent stress concentration lower than those of the conventional plates with optimally oriented parallel fibers.

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Simplified inelastic design procedures for elevated temperature components have been required to reduce simulation cost and to shorten a period of time for developing new projects. Stress redistribution locus (SRL) method has been proposed to provide a reasonable estimate employing both the elastic FEM analysis and a unique hyperbolic curve: ε^^〜={1/σ^^〜+(κ-1)σ^^〜}/κ, where ε^^〜 and σ^^〜 show dimensionless strain and stress normalized by corresponding elastic ones, respectively. This method is based on a fact that stress distribution in well deformed or high temperature components would change with deformation or time, and that the relation between the dimensionless stress and strain traces a kind of the elastic follow-up locus in spite of the constitutive equation of material and loading modes. In this paper, FEM analyses incorporating plasticity and creep in were performed for a tapered nozzle in reactor vessel under some thermal transient loads through the nozzle thickness. The normalized stress and strain was compared with the proposed SRL curve. Calculation results revealed that a critical point in the tapered nozzle due to the thermal transient load depended on a descending rate of temperature from the higher temperature in the operation cycle. Since the inelastic behavior in the nozzle resulted in a restricted area, the relationship between the normalized stress and strain was depicted inside the proposed SRL curve: Coefficient κ of the SRL in analyses is greater than the proposed one, and the present criterion guarantees robust structures for complicated components involving inelastic deformation.

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The contact gasket stress distribution in a box-shaped bolted flange connection with non-asbestos compressed sheet gasket subjected to internal pressure at elevated temperature is analyzed taking into account a hysteresis of the gasket behavior using finite element method (FEM) for estimating an amount of leakage from the gasket interfaces in the connection. Leakage tests were also conducted using an actual connection subjected to internal pressure at the elevated temperature to demonstrate the validity of estimated results. The effects of the test temperature, liner thermal expansion coefficients of the flanges and the gasket, and bolt preload are examined on the contact gasket stress distributions. In addition, a method for determining the bolt preload for satisfying the allowable leak rate at the elevated temperature is examined using the estimated results. The estimated leakage is in a fairly good agreement with the measured result. It is found that the estimated bolt preload using the allowable leak rate of inner fluid can be determined conservatively. In addition, the differences on the gasket characteristics on the asbestos and the non-asbestos sheet gasket are shown.

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This paper describes an adaptive elasto-plastic analysis using the view-dependent progressive meshes. As well known, adaptive method requires a frequent remeshing. With the conventional mesh generation methods such as the Delaunay triangulation, the calculation cost is not cost-effective. On the other hand, the view-dependent progressive meshes, having hierarchical data structure, are able to achieve high-speed remeshing. In this paper, we consider to apply this kind of meshes to adaptive elasto-plastic analysis with the h-approach as well as the posterior error estimation method proposed by Zienkiewicz and Zhu. The performances of the adaptive elasto-plastic analysis are demonstrated through the analysis of a square plate with a hole under tension.

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In this paper, the elasto-plastic collapse of thin-walled square tubes subjected to torsional loading is studied by using the finite element method (FEM). It is found that there are three collapse modes. The first mode is a collapse due to elastic buckling. The second mode is a collapse due to plastic buckling. The third mode is a collapse due to denting of the cross section. Based on these facts, approximate numerical methods to estimate the peak torsional moment are proposed, and their validity are verified by comparing with the numerical results by FEM under various conditions.

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In this paper, crushing behaviours of stepped circular tubes subjected to oblique load are studied by using finite element method. It is found that the deformation behaviour of stepped tubes can be classified into two modes (Stable mode and Unstable mode). For the case of the Stable mode, the tube keeps erection in comparison and absorbs compressive energies as much as axial load. However, in the Unstable mode, the tube does not keep erection in comparison and its compression loads are much lower than those in its axial crushing. Also, it is found that the compressive load of the stepped tube in the oblique crushing increases as the difference between the radius of large tube and small tube decreases and as the total length of the tube increases. When the geometric sizes which take values located near the boundary between two modes in the mode map, the stepped tubes show maximum energy absorption efficiency. Moreover, it is found that the absorption efficiency of stepped tubes is proportional to the thickness t in about 1.8th power.

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Recently, many analytical tools have been developed for the structural design and assessment of structural integrity. For welded structures, however, application of the welding simulation as a design tool is relatively limited due to its lack of verification characteristics. So, is necessary to develop a new analytical procedure for evaluation of the welding deformation and residual stresses. For this purpose authors have developed an inversed problem approach based on eigen-strain analysis, where further improvement of accuracy is desired. In this study, eigen-strain characteristics which reproduce both welding deformations and residual stresses are examined by utilizing welding simulations. Eigen-strain components that affect to a specific type of deformations are made clear. By using these results, welding deformations and residual stresses can be reproduced with selected eigen-strain components by image processing of welded plate surface before and after the weld.

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In this paper, the applicability of a technology with using infrared sensing was elucidated for mine exploration, where it is comparatively easy to specify the surface emissivity. It is very important to avoid the danger pertaining to mine exploration as much as possible by using an appropriate nondestructive testing method. From the viewpoints of empirical investigation and numerical simulation with an appropriate mathematical model, the exploration mechanism, the exploration limit, various factors which accompany the mine exploration are examined systematically. As a result, the following facts are found: It is clarified that the numerical simulation considered the effect of water content ratio on thermo-physical quantities has a great improvement in reproducibility of the experimental value, compared with the numerical simulation without considering water content ratio. We say that the water content has a great influence in infrared mine exploration except for the influence factors which were informed in previous report.

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Crack propagation of SCM440H low alloy steel under varying load is enhanced by absorbed hydrogen. Substantial acceleration of crack propagation rate up to 1000 times was observed compared with that of uncharged material. The role of factors affecting enhanced acceleration was investigated by changing hydrogen concentration absorbed in metal, specimen thickness, loading frequency and temperature. Results are as follows, (1) 0.2 mass ppm diffusible hydrogen in metal was enough to cause enhanced acceleration. The predominant fracture mode showing acceleration was quasi cleavage. (2) In the case of specimen as thin as 0.8mm, the constraint of the crack was weak, and the enhanced crack propagation did not appear. However, the introduction of side-groove to 0.8mm thick specimen resulted in enhanced acceleration. (3) The crack propagation rate in time domain was almost constant irrespective of loading frequency. Lower loading frequency resulted in higher crack propagation rate in cycle domain. (4) The crack propagation at different temperature was controlled by thermal activation process. The crack propagation rate in time domain is controlled by the diffusion of hydrogen. Enough concentration of hydrogen, enough constraint and low loading frequency resulted in enhanced acceleration of crack propagation.

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Fatigue crack growth tests were conducted to investigate the influence of irreversible hydrogen on the fatigue crack growth in a cold drawn high strength steel. The fatigue crack growth rate was accelerated by irreversible hydrogen in low ΔK or ΔK_<eff> region, and the acceleration increased with a decrease in ΔK or ΔK_<eff>. Moreover, the fatigue crack growth rate under irreversible hydrogen charging increased as the cyclic frequency decreased. To investigate the behavior of irreversible hydrogen near the crack tip under cyclic loading, a hydrogen microprint technique was applied to the fatigue crack growth tests. After the fatigue crack growth under irreversible hydrogen charging, silver particles precipitated along the fatigue crack: this proved that irreversible hydrogen desorbed out from its trap site under cyclic loading. The precipitation area of silver particles was larger than a monotonic plastic zone. Considering the dependency of stress cyclic frequency on the crack growth rate, it is concluded that the hydrogen desorbed from irreversible trap site due to cyclic loading diffuses to the fatigue crack tip and accelerates the fatigue crack growth rate under irreversible hydrogen charging condition. This is the reason why the fatigue crack growth rate was dependent on stress cyclic frequency.

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The effect of halogenation treatment by hydrofluoric acid on bond strength of pressure welded joint of tin have been investigated by SEM observations of the interfacial microstructures and fractured surfaces. The halogenation treatment was carried out by exposing a tin surface (finished by electrolytic polishing) in hydrofluoric acid vapor in a closed container for 30s. The pressure welding was carried out in a vacuum chamber at bonding temperatures T_j of 353〜443K and under a bonding pressure of 7MPa (bonding time=1.8ks). The bond strength of the joint was increased with a rise in bonding temperature. The halogenation treatment decreased bonding temperature by 40K at which bonded joints could be obtained and bond strength comparable to the base metal was achieved. SEM observations of the joint interface revealed that massive particles of a few μm in size were distributed at the interface. As the bonding temperature was increased, the particles coarsened and decreased in number densities, leaving the surrounding area with much smaller amounts of inclusions distributing in the tin substrate than those of the Sn-oxide observed at the joint interface bonded without the halogenation treatment at the same bonding temperature. The formation and enlargement of the areas with much smaller amounts of inclusions in the interfacial region probably contributed to the increase in the bond strength at lower bonding temperature by the halogenation treatment.

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