Almost all of the latest accidents of pipe flange connection are due to a leakage from gasket bearing surface. Important factors for the leakage problem are considered to be contact pressure distribution and the magnitude of contact area at the gasket bearing surface in service. The previous studies are not necessarily sufficient because of some restrictions involved in numerical analyses. In this study, therefore, the mechanical behaviors of pipe flange connection are evaluated in more detail using FEM as a three-dimensional elastic contact problem. The changes in contact pressure distribution at the gasket bearing surface and bolt axial stress are estimated with increasing inner pressure and bending moment. The analytical objects are pipe flanges specified in JIS B 2238 with solid-metal flat gaskets being inserted. The effects of material properties and thickness of the gasket are also studied. It has been clarified that the contact pressure distributions are different from those reported in the previous papers. The validity of the numerical method is ascertained by experiment.

View full abstract

Fundamental characteristics of the tightening process with a bolt heater have been evaluated in the previous report, where a numerical procedure for estimating the tightening process is proposed using FEM as an elastic contact problem in the transient temperature field. In this study, the effects of thermal resistance and radiation at interfaces are incorporated into the foregoing numerical approach for achieving better accuracy. It is clarified how the clamping force is generated in the cooling process of bolted joint. In addition, the tightening process of a bolted joint with larger grip length is also analyzed as an example of common engineering use. The effectiveness of the finite element approach proposed here is ascertained by comparing numerical results of temperature distribution and axial bolt force to experimental ones. An effective tightening procedure to control the axial bolt force with high accuracy is suggested by measuring the surface temperature of exposed threads and the elongation of bolt.

View full abstract

This paper describes the analysis of impact fracture of asymmetrically laminated glass, which consist of two different thickness glasses and polyvinyl butyral film, using the discrete element method (DEM). Asymmetrically laminated glass beams with both ends fixed are analyzed when a cylindrical rigid body impacts on the center of beams with a certain initial velocity. The DEM is applied to simulate the impact fracture behavior of several asymmetrically laminated glass beams. From the numerical analysis it is obvious that the first peak value of impact force of asymmetrically laminated glass having impact surface at the thinner glass side is less than one of laminated glass and penetration energy of asymmetrically laminated glass is larger than one of laminated glass. From above reasons, it is concluded that asymmetrically laminated glass is in safety than laminated glass as windshield glass.

View full abstract

Electric Heated Windshield (EHW) for Vehicles is laminated glass and metal oxide is coated on the laminated surface of inner glass. The heat performance of EHW is decided by electric resistance of metal oxide and its distribution. On the other hand the shape of windshield is usually not simple, therefore to obtain uniform temperature distribution of EHW is difficult. In this paper, optimum resistance distribution of metal oxide is obtained by using the genetic algorithm. 2 models of resistance distribution are analyzed. One is 2 levels distribution model and another is 6 levels distribution model. The former model reduces 37% differences of temperature and 29% thermal stress than the uniform resistance model. The latter model reduces 39% differences of temperature and 28% thermal stress too.

View full abstract

A high-performance domain decomposition method is proposed for the parallel finite element analysis using meshless virtual nodes along the domain interface. The domains, which are analyzed independently in parallel by the finite element method, are connected by the virtual nodes based on the moving least square method. The conjugate gradient method is applied to the virtual nodes to obtain the solution on the domain interface. To verify this method, various two-dimentional problems are solved. The accuracy of the solutions are good enough for parctical use, and the convergence of the conjugate gradient method and the parallel performance are improved with less number of virtual nodes. This method can be applied to the problem with non-conforming interface among domains. This method can also accelarate the convergence of the CG method.

View full abstract

The MAL(method of arbitrary lines) is a technique of reducing a partial differential equation to a system of ordinary differential equations. It is known that a relevant use of this procedure yields high accuracy in some problems of 2-dimensional elasticity and elasto-plasticity. Since the basic concept of MAL is simple and of generality, it is expected that many problems in other fields can be solved effectively by this method. In this paper we consider the application of MAL to 3-dimensional (3D) elasticity analysis. We first give a MAL formulation of 3D elastic problems, and demonstrate its effectiveness and accuracy on a typical problem. The reported numerical results compare with the exact solution or the finite element method (FEM).

View full abstract

Cracking mechanism in IC plastic packages during reflow soldering was analyzed considering both vapor pressure and thermal stress. The vapor pressure induced stress, which was considered as the dominant factor for the IC package cracking, strongly depends on the total amount of absorbed water. The IC package cracking was observed, even when the vapor pressure induced stress was much lower than the strength of the molding compound, which was almost constant at temperatures above 200°C. The cracking was found to occur when the total amount of the stress, which was caused not only by the vapor pressure but also by thermal stress, reached the strength of the moling compound. Therefore, thermal stress is also the important factor for IC package cracking during reflow soldering.

View full abstract

This paper describes the evaluation of adhesion strength between the amorphous Silicon carbide (a-SiC) thin film, Diamond-Like Carbon (DLC)/a-SiC laminated thin film and materials used for the cutting tool. The a-SiC and DLC/a-SiC thin films were deposited on the tungsten carbide steel substrate:K10 and on the high speed steel substrate;SKH51 by Plasma-Enhanced CVD method of the hot cathode PIG discharge type. Scratch tests were carried out for examining the critical fracture load of the films. Finite Element Method (FEM) analyses were also performed to clarify the stress distribution at the interface between the films and substrates. The stress intensity factors K_I and K_IIand the fracture toughness K_C were calculated from results of scratch tests and FEM analyses. The K_I, K_IIand K_C of a-SiC and DLC/a-SiC thin films deposited on the K10 substrate were larger than those of the thin films deposited on the SKH51 substrate. The K_I, K_II and K_C of both of the films were directly proportional to the density of a-SiC thin films. In turning experiments, the delamination area of DLC/a-SiC thin films deposited on the cutting tool of K10 is closely related to the K_C obtained from the scratch tests and FEM analyses.

View full abstract

This paper deals with the influence of debonding damage between particles and matrix on a crack-tip field in a glass-particle-reinforced nylon 66 composite. In order to explain the influence of debonding damage on the fracture toughness, numerical analysis of a crack-tip field was carried out on the interface-treated and nutreated composites by using a finite element method developed based on an incremental damage theory of particle-reinforced composites. At the crack-tip region, the damage zone due to the particle-matrix interfacial debonding develops in addition to the plastic zone due to matrix plasticity. The damage evolution around a crack-tip depends on the interfacial strength between particles and matrix and the particle volume fraction. It is found that the debonding damage reduces the stress level around a crack-tip and acts as the toughening mechanism. The mechanical performance of particle-reinforced composites is obtained as the results of the competitive effects of the intact hard particles and debonding damage.

View full abstract

Present study shows the mechanism of the fractal branches of the stacking sequence of laminated composites, and proposes a novel approach for stacking sequence optimizations named Fractal-branch and bound method. The method is limited to the stacking sequence optimizations that can be computed only by out-of-plane lamination parameters. First, values of the objective function are approximated by response surfaces as functions of the out-of-plane lamination parameters using the design of experiments and the least square method, and the optimal set of lamination parameters is obtained. After that, a set of candidates of optimal stacking sequences is collected using branch-and-bound method near the optimal point of the set of lamination parameters. All of the candidates examined and the real optimal stacking sequence is obtained. The fractal-branch and bound method is applied to the stacking sequence optimization problems for a maximization of buckling load of a simply supported rectangular plate, and the method obtained the exact optimal stacking sequence by very small computational cost.

View full abstract

This paper presents a method of structural damage detection. Specifically, we focus on the use of localized flexibility properties that can be deduced either from the experimentally determined global flexibility matrix or from a localized structural identification procedure. To this end, first we present the underlying theory that can be viewed a generalized flexibility formulation in three different generalized coordinates, viz., localized or substructural displacement, elemental deformation-basis, and elemental strain basis. It is shown that the three different-basis substructural flexibilities can be related to the measured global flexibility matrix via a nonliner equation. The changes in the substructural flexibilities of nominal and damaged cases are used as localized damage indicators. The present methods are then applied to a damage detection of CFRP laminates.

View full abstract

Analytical solutions are presented for a transient temperature field and the associated thermal stress field in a hollow hemisphere of functionally graded material (FGM) in the radial direction due to axisymmetric heatings on the inner and outer spherical surfaces. The temperature field in the FGM hollow hemisphere is obtained by solving the transient heat conduction problem in a multilayered hollow hemisphere by means of the introduction of Legendre transformation method and a new orthogonal relation of the eigenfunction with the discontinuous-weighting function for multilayer regions. The associated thermal stress problem is solved by the use of the thermoelastic displacement potential and Papkovich-Neuber's stress fuunctions.

View full abstract

This paper deals with generalized stress intensity factors at the end of an elastic cylindrical inclusion in an infinite body under asymmetric uniaxial tension. These stress intensity factors control singular stress fields at the end of inclusion. The problem is solved on the superposition of two auxiliary loads;(i)biaxial tension and (ii)plane state of pure shear. The problem is formulated as a system of integral equations with Caushy-type or logarithmic-type singularities, where un-knowns are densities of body force distributed in infinite bodies having the same elastic constants as those of the matrix and inclusion. In the numerical analysis, the unknown functions of the body force densities are expressed as fundamental density functions and weight functions. Fundamental density functions are chosen to express the symmetric stress singularity of the from 1/γ^1-λ11/γ^1-λ3 and the skew-symmetric stress singularity of the form 1/γ^1-λ21/γ^1-λ4. Then, the singular stress fields at the end of a cylindrical inclusion are discussed with varying the fiber length and elastic ratio. The results are compared with the ones of a cylindrical inclusion under longitudinal tension and the ones of a rectangular inclusion under transverse tension.

View full abstract

Analytical procedure to evaluate the surface irregularity of tensile fracture surfaces for several carbon steels was developed by applying a concept of fractal and a curve fitting technique. Main conclusions obtained in this study are summarized as follows;(1)Tensile fracture surfaces for pure iron and carbon steels such as S 25 C, S 35 C, S 45 C and S 55 C heat-treated under several conditions have the fractal nature. (2)It is found that the geometrical irregularity of the fracture surface is well evaluated by combining the fractal dimension and additional indices governed by several factors such as heat-treatment condition, carbon content and mechanical properties. (3)Fractal dimension D and additional indices for the fracture surface nature such as C^* and (B-E)/A have a definite relation to the carbon content and mechanical properties such as elongation, yield stress and tensile strength. Especially, index of (B-E)/A is significantly related to the fracture model and the strength level of the materials.

View full abstract

The shape memory alloy with the shape memory and superelastic functions has been used for many applications such as actuators, sensors, and so on. In order to undertake reliable engineering designs and optimum material selection, it is important to clarify the fatigue lives of shape memory alloy under thermal and mechanical cycles. In this paper, the fatigue lives of Ti-41.7 at% Ni-8.5 at% Cu alloy are investigated experimentally. Experiments are carried out by repeating the combination of the thermal cycle and the loading-unloading cycle. And the variations of the recovery stress, the irrecoverable strain and the recovery strain energy with cycles are investigated for various heating temperatures and strains. Furthermore, the fatigue lives for various heating temperatures and strains are investigated, and fractured surfaces are observed by SEM. Results show that the fatigue lives are divided into three regions according to the maximum strain and depend upon heating temperature. It is also noted that the fatigue lives can be estimated in relation to the dispersion strain energy obtained by the amount of decrease of recovery strain energy per cycle.

View full abstract

An experimental study was carried out with the aim of development of a fatigue reliability design method for surface modified materials using the smooth specimens SMn 435, with three kinds of surface treatment, ;that is, TiCN coating by PVD method, gas-nitriding and duplex treatment with the gas-nitriding followed by the TiCN coating. Fatigue strength of the surface modified specimens was improved as compared with untreated specimen. The highest fatigue strength was the duplex surface modified specimen, followed by the gas-nitriding one and the lowest was the TiCN coating one. This tendency was obvious at the region of high stress amplitude and disappeared at low stress amplitude region. The difference in fatigue strength between the duplex surface modified specimen and the TiCN coating one was discussed cracking in TiCN coating. It was found that cracking in TiCN coating film was attributable to cyclic plastic deformation in the subsurface region.

View full abstract

Fretting fatigue occurs at contact regions of structural components subjected to contact pressure, friction stress and cyclic fatigue stress. In fretting fatigue the early stage of crack growth is influenced by the magnitude of the above pressure and stresses and its main crack grows to oblique direction to the contact surface. A method for evaluating stress intensity facotrs K_I and K_II for not oblique but normal cracks in fretting fatigue has been proposed by Rooke & Jones. This paper expanded the method into oblique cracks by obtaining the Green's functions of stress intensity factors for oblique cracks by the boundary element analysis. The results were represented by formulae as functions of crack angle, crack length, and applied load conditions, such as bulk fatigue stress, contact pressure, friction stress, and their distribution. The stress intensity factors under arbitrary fretting fatigue conditions can be calculated easily by substituting those values.

View full abstract

Inherent damage zone model assumes that σ_γ0which is the stress at a small distance γ₀ from the crack initiation position, governs the fatigue characteristics regardless of the geometric configuration of the specimen. The distance γ₀ represents the size of effective Damage zone and it is an inherent length of the material. A special feature of the model is using the exact solution of σ_γ0. Neuber's analytical solution for notched specimen and Westergaard's stress function for cracked specimen are employed for this purpose. In this paper, the strength of small fatigue crack is investigated based on the inherent damage zone model. A new crack propagation equation which is applicable to both small and large cracks is proposed and the crack propagation property at lower stress intensity factor range is evaluated. Mechanism of non-propagating crack is explained by the comparison of magnitude of σ_γ0 between crack and notch with the same length. Occurrence condition of non-propagating crack is evaluated for elliptic notches and circular holes. Predicted strength properties of small cracks are in good agreement with the previous experimental data.

View full abstract

Fatigue crack propagation tests of silicon nitride were conducted under constant K_max and constant stress ratio R using double eccentric pulsating compressive loading at room temperature. The crack propagation rate da/dN could be expressed as a function of K^α_<max>·ΔK^(1-α).However, scatter due to bridging friction was observed in the diagram of da/dN versus K^α_<max>·ΔK^(1-α). The plotting of da/dN against ΔK_eff reduced the influence of bridging friction on the expression of crack propagation. Also, the plotting revealed that the crack propagtion under high K_max is caused by static fatigue and the propagation under lower K_max is by pure fatigue. From these observation, it is suggested that ΔK_eff defined as the range of stress intensity factor during crack opening is close to the range of stress intensity factor at crack tip K_tip/

View full abstract

The subsurface crack growth that led to a flaking failure of Si₃N₄ was investigated under spherical Hertzian rolling contact. The subsurface crack was observed to grow in the two stages:firstly, the crack grew in a concentric circle;secondly, the crack extended in the direction parallel to the ball movement keeping with a constant width. The crack growth model, in which the effect of crack face friction was taken into account, was provided on the basis of the observation. A calculation was described of the variation of stress intensity factors at the crack tip of the effective area both in the perpendicular direction and in the parallel direction to the motion of the ball. The maximum values and the minimum values of stress intensity factor K_II were found to remain constant during the crack growth in the parallel direction, which was consistent with the observation that the subsurface main crack continued to grow in the parallel direction. In the perpendicular direction, the crack grew in out-of-phased Mixed mode with Modes II and III. For the crack-face frictional coefficient less than the threshold value of 0.3, the behavior of the maximum value of |K_IIImin| was found to be consistent with the experimental observation.

View full abstract

The strength evaluation of ductile and brittle fracture characteristics of high pressure steel tubes have to be comfirmed for the hydraulic pressure tests. The elastic-plastic fracture tough-ness;J_in tests were carried out with the small size arc-shape specimens from 2 kinds of steel tubes of different materials. The new tubes were made in several years before, and used tubes were made in 30 years before. (STBA 12, the chemical compositions are different from each other and used tubes might have the creep damage under 480°C, 2×10⁵ hours in boiler super heater). And J_in characteristics were discussed on these rusults of elastic-plastic fracture toughness test.

View full abstract

Delamination of interface between dissimilar materials is one of the main causes of failure of composite materials, electronic packages and so on. The interface crack problems are primarily mixed mode and often include the residual stress. We developed a new method for the stress intensity factor analysis of an interface crack under thermal stress condition in the previous study. In this study, we focus on the mixed mode fracture toughness and the kink angle of an interface crack. We measure residual stress and perform mixed mode fracture tests for three types of interface crack. Two of them are cracks between aluminum and epoxy resin and another is an interface crack between two epoxy resins which have different stiffness. Each obtained mixed mode fracture toughness including residual stress is successfully described by stress intensity factors K_I and K_II for each interface crack. The kink angle of each interface crack also can be expected by the stress intensity factors using the modified maximum hoop stress criterion.

View full abstract

The uni-directional FRP have very complex stress fields because of their anisotropy. Many researchers have reported the methods to calculate stress intensity factors or stress concentration factors. But only these parameters are not sufficient to evaluate the strength of materials in structures. The mechanical parameter for the equivalence of elastic fields also is required. In this paper, the characterization of the elastic fields near a notch root in an anisotropic plate is discussed. To consider the problem, the versatile analysis based on Body Force Method is developed. And the evaluation method of the elastic field near a notch root is developed with Stress Intensity Factor under the normal strain criterion.

View full abstract

The fracture criterion for notched uni-directional composites is discussed in this paper. The tensile tests of specimens are carried out with various fiber angles and various shaped notches. The fracture origins are carefully observed and the elastic analysis shows that the initiation of the fracture is dependens on the transverse strain to the fiber direction. The maximum strain criterion should be applied to the fracture. Then the criterion is extended to consider the relation between the fracture strength of speciment with various fiber angles. The extended criterion is based on the local equivalent elastic fields with Stress Intensity Factor.It is confirmed from the experimental data of CFRP that the criterion can be applied to the strength evaluation of the real structure.

View full abstract

In this paper, dynamic stress intensity factors of bonded dissimilar materials were determined by using caustics methods. Bonding between epoxy resin and polycarbonate composed specimens by epoxy bond. Upper materials of specimens were epoxy resin and polycarbonate. Lower materials were polycarbonate with V notches for all. V notch length was 3mm. As the result of this experiment, dynamic stress intensity factor of bonded materials was larger than non-interface specimen. It is clear that crack tips influenced these interfaces and mechanical properties of upper meterials. In dynamic behavior, each specimens showed a similar tendency up to 300, 600 and 900 μs. Dynamic stress intensity factor increase became less at 300, 600 and 900 μs, and afterwards became moer. Cracks were propagated at t=950 μs for interface next reached interface and became interface crack. Dynamic fracture toughness of bonded materials was larger than non-interface specimen, but time of crack propagated were faster than this.

View full abstract

It was shown previously that a crack in a weld line between two different steels may cause mode II type fracture, even under so-called mode I type loading, due to the difference of material properties. In this study, the fracture experiments of the specimen in which a crack parallel to a weld line between high-tension steel and mild steel exists in its neighborhood are carried out. It is shown that mode II type fracture occurs when a crack is in the heat affected zone, the fracture mode changes to mode I type with the distance of crack position from the weld line and mode I type fracture occurs when a crack exists in each mother material. After that, finite element analyses corresponding to the experiments are carried out taking material properties in the weld line and heat affected zone into account, and the CED (crack energy density) in an arbitrary direction is evaluated through the results of finite element analyses. The applicability of fracture criterion based on the CED in an arbitray direction is demonstrated to the crack growth initiation behavior of a crack parallel to a weld line between two different steels. Moreover, the effect of inhomogeneity by welding on the fracture resistance with the crack position is investigated based on the CED in an arbitrary direction.

View full abstract

In this report the combined model of molecular dynamics with micromechanics was applied to a tungsten single crystal, and a crack propagation process was simulated till the material was fractured. In the simulation a pre-crack was introduced on a (110) plane and the direction was <001>. Cleavage, then, occurred along (121) plane which was in an inclined direction with respect to the pre-crack. The cleavage along (121) plane was also observed in an experiment. Three sizes of molecular dynamics regions were tested to investigate dependence of a simulation result on a size of a molecular dynamics region. It was found that the differences in the three simulation results were quite small. Fracture toughnesses in simulations, however, were about twice as large as that in an experiment.

View full abstract

In this paper, a new estimation method is proposed for a size distribution of particles in materials. Especially in this first paper, a configuration of particle is supposed as spheroidal and all observed informations are obtained from cutting planes. These apparent size distribution from the 2-D is corrected to the true size distribution of the 3-D and the expected size distribution can be estimated from a small size to an extreme size. This size distribution is the most versatile method involved with Saltycov's method and extreme statistics. This method can be useful in the whole region of particle size. The method is applied to artificial materials with a given particle in computer, the estimated results are compared with the given distributions, and the validity is confirmed.

View full abstract

The cyclic deformation of a torque converter (T/C) assembly for automatic transmission motor vehicles was studied to evaluate the endurance under constant-amplitude cyclic internal pressure. An electric-hydraulic servo controlled endurance test machine was developed to estimate the cyclic deformation by monitoring the volume of hydraulic fluid supplied to T/C assembly. The cyclic volume expansion of T/C assembly from 0 MPa to the test pressure in each cycle was obtained from the supplied hydraulic fluid. The volume expansion decreased first and increased with increasing cycle, followed by the oil leakage. The number of cycles at the minimum of the volume expansion corresponded with the cycles to the crack initiation inside the T/C assembly. Since the life of crack growth has a good relation with that of crack initiation, the total life could be evaluated in term of the life of the crack initiation. This suggested that the timesaving endurance test should be possible for T/C assembly.

View full abstract

Using FEM structural analysis, a load bearing frame for a light weight prosthesis made of carbon fiber reinforced plastic (CFRP) was developed, complying with both severe spatial restrictions and the ISO specification for strength. This paper focuses on the optimum design of the joint between the thin CFRP frame and a metal knee joint. A special bracket, which is implanted into the frame and prevents rotation of the knee, was developed for the joint, in order to reduce the stress concentration generated around the bracket hole of the frame. The orientation of the carbon fiber cloth ply was optimized taking the anisotropy of the CFRP into account. The static fracture strength of the CFRP frame predicted by the analyses agreed well with the results of fracture tests.

View full abstract