In this paper, rotating fatigue tests of a low carbon steel were carried out. The change of specimen surface during each stress repetition was observed with an atomic force microscope, and the fracture surface was observed with a scanning electron microscope. Moreover the crystallographic orientation of the grain related to the crack nucleation was estimated with an etch pit method. Based on the above-mentioned three kinds of data, the fatigue crack nucleation mechanism under high-cycle was clarified microscopically in the case of an intergranular crack of bcc material.

抄録全体を表示

In this paper, the relation between low cycle fatigue life and fracture ductility was investigated in various aluminium alloys. Low cycle fatigue tests were carried out using cylindrical specimens, and the propagation of small cracks were measured and observed. As a result, it was clear that there was no consistent relation between low cycle fatigue life and fracture ductility. In materials with large fracture ductility, fracture ductility can be considered as low cycle fatigue which has fracture at N=1/4, and fatigue life can be estimated from fracture ductility. However, in materials with small fracture ductility, experimental fatigue life is larger than estimated one from fracture ductility. In materials with large fracture ductility, the cause of decrease of experimental fatigue life is that the crack growth rate is accelerated by the connection of each crack in the early stage of fatigue life.

抄録全体を表示

The rain flow method (RFM), widely used as one of the useful fatigue damage counting methods, was re-examined in conjunction with the actual fatigue process such as crack initiation and propagation. The low-cycle fatigue tests were conducted on a mild steel under variable strain amplitude. A special attention was paid to correlate the fatigue life controlling-volumetric parameter, plastic strain range Δεp, with a fracture mechanics parameter ΔCTOD. Then, a physical meaning of RFM was given on the basis of small crack growth law. The experimental results of the variable strain amplitude fatigue tests showed that the trend of the change of the value Δεp was similar to that of ΔCTOD. In addition, the small crack growth rate versus ΔCTOD showed a linear relationship.

抄録全体を表示

Effects of TiN thin films prepared by ion beam and vapor deposition method on fatigue behaviors were investigated on 13Cr martensitic stainless steel with high tensile strength of about 1900 MPa, under plane bending load condition. TiN thin films of 2μm thick were coated on the surface of plate specimen of 1 mm thick with titanium deposition rate of 2∼10 Å/s, nitrogen ion energy level of 10 keV and nitrogen ion current density of 10 mA/cm². Results of fatigue tests revealed that the coat of TiN thin film raised fatigue resistance of the materials by choosing appropriate coating conditions. Characteristics of the TiN thin films were evaluated from XPS (X-ray photoelectron spectroscopy), XRD (X-ray diffraction pattern), hardness and residual stress measurements. The chemical properties of TiN films were those of crystalline Ti, Ti₂N, TiN and amorphous TiN. High hardness and high compressive residual stress were measured at TiN thin films of specimens attained to high fatigue resistance. Some specimens had defects bigger than the size of film thickness distributed on the specimen surfaces. They revealed low fatigue resistance despite they were coated with TiN thin film under a coating condition of high fatigue resistance.

抄録全体を表示

In order to investigate the effect of surface roughness on the fatigue strength, push-pull type fatigue tests were performed using 0.25%C annealed steel and polycarbonate specimens. Specimens with four different surface roughness were examined for both materials. The larger surface roughness gave the lower fatigue strength and the tendency became more remarkable for longer life except near the fatigue limit of carbon steel. This was more remarkable on polycarbonate rather than carbon steel. Good correlation was observed btween the surface roughness R_max and the fatigue strength reduction factor RF, which was defined by ratio of the fatigue strength for the specimen with surface roughness to the fatigue strength of the smooth specimen with the smallest surface roughness. This relation was presented by the equations RF=C₁R^m_<max> and m=C₂+C₃ log N_f, where C₁, C₂ and C₃ were material constants and N_f was the fatigue life.

抄録全体を表示

Temperature fluctuations in power plants may cause thermal fatigue in structures. In order to maintain integrity of structures, the thermal fatigue life has to be evaluated. Although a Coffin type thermal fatigue testing apparatus induces a homogeneous thermal strain in a specimen, high cycle thermal fatigue with strain distribution under the specimen surface can not be performed by it. In this study, a facility for high cycle thermal fatigue testing in pure water was developed. High and low temperature water are continuously supplied into an autoclave with a rotating cylindrical fatigue specimen, so that the specimen surface is simultaneously surrounded by high and low temperature water. Since the specimen is driven by a motor outside of the autoclave, the specimen suffers from the rotation synchronized thermal fatigue. Using the developed facility, heat transfer coefficients on the specimen surface of type 304 stainless steel were measured at various revolution frequency. The heat transfer coefficients were found to increase with the revolution frequency and were greater than 50 kW/m²K at the frequency higher than 5 Hz. High cycle thermal fatigue cracks are expected to be initiated since higher stress than the fatigue limit of mechanical fatigue can be initiated with this facility.

抄録全体を表示

To improve the fatigue reliability for SMn 435 steel by an environmentally sound surface modification, the influence of the modification on fracture mechanism was studied experimentally. The fatigue properties of SMn 435 are found to be obviously improved by gas soft-nitriding, so that they can no longer be estimated by using a concept of "S-N Globe"which has successfully been applied to many surface-treated materials. The detailed observations have revealed that fatigue crack initiation in a gas soft-nitrided SMn 435 specimen occurs in a hardened region near surface not in a subsurface region with virgin microstructure. The crack initiation is attributable to cyclic plastic deformation in the subsurface region. Such a crack initiation mechanism is different from that previously observed in other surface treated materials, explaining the reason why the S-N Globe concept can not be applied to the present case.

抄録全体を表示

Fatigue reliability of compacted graphite cast iron CGI produced by Sinter Cast method was investigated with attention to relationship between fatigue crack behavior and graphite profile. The main results obtained are as follows. (1) For the fatigue strength ratio, that is the fatigue strength per the tensile strength, CGI is superior to spheroidal graphite cast iron SGI. (2) The compacted graphite profile was very complicated like coastline with higher fractal dimension. (3) The graphite of CGI can be bonded with pearlite matrix. Because it was observed on the fracture surface of CGI that the fatigue crack propagated through the graphite cracking. This suggests that the compacted graphite bears loading. (4) The meso crack growth was considerably influenced by the compacted graphite due to its irregular profile. Non-propagating crack observed in fatigue limit was meso cracking process. (5) Higher fatigue strength ratio of CGI resulted from outstanding resistance against crack propagating due to irregular profile of compacted graphite of CGI.

抄録全体を表示

In order to estimate fatigue reliability of super-rapid induction quenched spheroidal graphite cast iron, FCD500, FCD700, the influence of complex surface microstructure on the fatigue strength was examined through fractography. The main results obtained are as follows : (1) Fatigue strength of quenched FCD500 was superior to that of quenched FCD700 in the long-life region (N> 5.0×10⁵), in spite of tensile strength of FCD500 was lower than that of FCD700. (2) Fatigue property of super-rapid induction quenched spheroidal graphite cast iron could be estimated using a concept of "S-N globe". (3) Initial stress intensity factor at crack initiation under the surface of quenched FCD500 was comparable to that of quenched FCD700, therefore the improvement in fatigue strength of FCD500 depended on the crack propagation behavior through the complex surface microstructure, not the crack initiation behavior. (4) The prevention of crack propagation through the complex surface microstructure gave and appearance of high level fatigue reliability of FCD500.

抄録全体を表示

Matrix cracking evolution in composite laminates is formulated in the framework of the continuum damage mechanics. In this paper, the damage evolution of a cracking layer is exclusively focused on. We propose a new concept that a cracked lamina is replaced by an equivalent uniform worksoftening layer, and the analytical method of plasticity is introduced to describe the behavior of the work-softening layer. The most important element of this model is a definition of work-softening modulus which is concerned with the damage evolution law. The elastic analysis proposed by Hashin is shown to be available for formulation of the damage evolution law, and it is also shown that adoption of the cracking layer energy release rate as a cracking criterion leads to a reasonable damage evolution law. The model formulated in this paper can be used for general composite laminates.

抄録全体を表示

In Part I of this study, the constitutive equation of a cracking layer was formulated introducing the new concept that a cracked lamina was replaced by an equivalent uniform work-softening layer. Part II formulates laminate constitutive equation in damage process using the results obtained in Part I and the laminate theory. In this formulation, influence of lamina stacking sequence is discussed through the magnification of an initial damage surface. It is shown that the damage evolution law in Part I can be used for general laminates even if the initial damage surface is enlarged, as long as cracking layer energy release rate is adopted as a cracking criterion. Present model is shown to reproduce experimental results with good accuracy. Finally, discussions about laminate stiffness reduction and stress path in damage process are given.

抄録全体を表示

In the experiments of unidirectional CFRP subjected to tensile load in the fiber direction, the various fracture modes are observed depending on the thickness ratio, the fiber volume fraction and the testing temperature. In case that the values of these factors are low, tensile fracture mode occurs, while their values high, shear fracture mode occurs. In the previous experimental study, the mechanism of this fracture mode transition was discussed. In this study, in order to clarify the mechanism, numerical analyses are conducted using finite element method and the fracture mode transition is simulated. Especially, the attention is paid on the effects of the thickness ratio and the fiber volume fraction on the fracture mode transition. The analyses results well agree with the experimental results and show the validity of the proposed simulation method.

抄録全体を表示

A method for simulating three-dimensional deformation in rotary piercing of a seamless pipe from a round bar with skewed rolls is proposed on the basis of the rigid-plastic finite element method using generalized plane-strain modeling. In this method, the rotary piercing is approximated to be a roll forging process, and the elongation of the workpiece in the rolling direction is kept uniform in the cross-section. The effect of the shear deformation in the rolling direction is included in the generalized plane-strain modeling. In addition to the short computing time, the treatment of the contact boundary conditions for the rolls and plug becomes simple. The effects of working conditions on deformation behavior and the occurrence of a central crack in the rotary piercing are examined.

抄録全体を表示

When leaf springs are subjected to loads, the contact points between leaves as well as friction forces at those points change complicatedly during loading and unloading process. Accordingly, the load-deflection curve of the springs shows a nonlinear hysteresis. To predict the hysteresis behavior of leaf springs by FEM with beam elements, we propose a special contact element by which the states of the non-contact, sticking contact and slipping contact are handled in a unified manner. The frictional force between the leaves are replaced by the nodal force of the special element. The validity of the contact elememts has been confirmed for beams with a frictional constraint support under loading-unloading process of the axial force and the transverse force at frictional support. With the proposed special element for supported ends of a leaf spring, it has confirmed that FEM with beam elements express well the hysteresis of the load-deflection curve.

抄録全体を表示

This paper describes an algorithm to generate the triangular mesh within arbitrary planar domains. When applied finite element method to numerical simulation, the discretization of the domain is the essential part of the procedure. There are many reports of the automatic mesh generation methods, such as coordinate transfomation, blending function, quad-tree, delaunay, advancing front method etc. The characteristic of the proposed algorithm is that the position of nodes is generated in original polygonal region as possible as the form of an equilateral triangle and the triangulation of the inner nodes is carried out by bucket method in computational geometry prior to the global construction of the triangular mesh modelling. Then the triangulation of residual region is carried out utilizing advancing front method. The processing scheme is developed and applied to several examples. The numerical results are shown and the effectiveness is discussed.

抄録全体を表示

Recently, the super-micro hardness test has been developed to evaluate the material property of very thin surface layer material of meso scale thickness, such as μm. This test employs the very small indentation load, 2∼500 mN, and the indentation depth, sub-μm∼10μm. The material characterization of very thin surface layer, by differentiation from the matrix and binding layer, is very complicated. The computational simulation scheme by employing the elastic/crystalline viscoplastic finite element code and experimental verification is developed to provide the reliable material property determination in this paper.

抄録全体を表示

This paper presents work on a numerical simulation method for eddy current testing applied to the in-service inspection of steam generator tubes in nuclear power plants. When finite elements (FEs) are used to predict eddy current signals, test articles, coils, cracks and air must be modeled. Additionally, it is necessary to compute the eddy current signals with the coil motion. While an easy way might be to use boundary elements (BEs) or the FE-BE hybrid method, the matrices of algebraic equations arrived at by these methods become full populated. Realistic problems require the modelling of natural cracks with complex geometries such as stress corrosion cracks or intergranular attacks. In this paper governing equations for an eddy current field are introduced to represent the current sources without using finite elements to model the coils, and a meshless method is proposed for crack representation. Finally, the results of numerical simulation are compared with experimental measurements, followed by a numerical study to briefly consider the application of this approach to the natural cracks.

抄録全体を表示

There are many experiments of quasi-static strength in vehicle development, such as roof intrusion, seat belt anchor strength, etc. Recently, explicit dynamic codes are used for quasi-static large deformation analysis. In this paper three explicit dynamic methods are applied to (1) panel strength analysis with large deformation and (2) buckling analysis of shallow arch and (3) collapsed analysis of spot welded thin-walled hat shape columns subjected to axial crushing. The system damping method is the quasi-static analysis that in the dynamic FEM equation we use large damping vector, which is obtained by multiplying the first eiginvalue to mass matrix. and 2nd is dynamic relaxation method, and 3rd is mass-scaling method. First, we point out that the system damping method is superior to conventional static FEM from the viewpoint of accuracy and efficiency only with the eigenvalue in which the eigen mode is similar to the first generated static buckling mode. Second, we point out that the dynamic relaxation method is the best analytical method for the (1) problem and for the (2) problem, system damping method is the best one and mass-scaling method is the best one for the (3) problem.

抄録全体を表示

This paper describes a new mesh generation algorithm, namely Intelligent Local Approach, which controls well size and aspect ratio of quadrilateral and hexahedral element simultaneously. Here we define the following three fields, i. e. a distribution of element size, that of aspect ratio and that of priority of element creation. The ILA also ensures mesh quality. In ILA, elements are created sequentially considering local information on geometrical constraints and user's demand on quality of the element to be created. To efficiently deal with various complicated geometrical constraints in a local region, a fuzzy knowledge processing technique is effectively utilized. Fundamental performances of the ILA are examined in detail through generating several quadrilateral meshes.

抄録全体を表示

Computing point analysis is a new scheme of boundary element analysis for nonlinear problems without domain discretization. It was pointed out that the accuracy of solution is principally affected by the boundary element discretization employed. Adaptive boundary element is proposed here for nonlinear Poisson problem by using the scheme. Local reanalysis, which measures approximately the sensitivity of the boundary element solution to local mesh changes, is employed for error estimation. An h-version mesh refinement strategy is described and applied to some two-dimensional numerical examples.

抄録全体を表示

In this paper, effect of shape of inclusions on the elastic modulus of composite materials is considered when equally shaped 2D inclusions are arranged in matrix. The effective elastic modulus of the composite materials is numerically analyzed by the application of FEM. Accuracy of approximate formula based on law of mixture is examined. From the comparison between the results of rectangular and elliptical inclusions, it is found that the effective elastic modulus is determined by two major parameters, that is, (i) the area fraction of inclusions projected in tensile direction, and (ii) the volume fraction of inclusion, almost independent of shape of inclusion. A convenient method of calculation is newly proposed for the effective elastic modulus of composites by using the replacement of the equivalent rectangular inclusions.

抄録全体を表示

This paper deals with numerical solution of singular integral equations of the body force method in an interaction problem of two ellipsoidal inclusions under asymmetric uniaxial tension. The problem is solved on the superposition of two auxiliary loads ; (i) biaxial tension and (ii) plane state of pure shear. These problems are formulated as a system of singular integral equations with Cauchy-type or logarithmic-type singularities, where the densities of body forces distributed in the γ, θ, z directions are unknown functions. In order to satisfy the boundary conditions along the ellipsoidal boundaries, the unknown functions are approximated by a linear combination of fundamental density functions and polynominals. The present method is found to yield rapidly converging numerical results for stress distributions along the boundaries.

抄録全体を表示

In order to clarify the dynamic response of a fluid-filled crack in the earth's crust, dynamic elastic response of a two-dimensional fluid-filled crack is studied, emphasizing the effect of fluid viscosity, permeability of rock and the stiffness due to contact between the asperities on the upper and lower surfaces of the crack. It is revealed that the eigen angular frequencies normalized by C_γ/a (C_γ : S wave phase velocity, a : half crack length) are governed primarily by the crack interfacial stiffness. The aspect ratio, i.e., the ratio of the crack length to the initial aperture of the crack, has only weak effects on the normalized eigen angular frequencies except for the case of a crack that is completely open initially. For larger crack interfacial stiffness, attenuation is stronger. It is also revealed that, for larger crack interfacial stiffness, the normalized eigen angular frequencies become smaller with permeability and attenuation becomes stronger with permeability. When crack interfacial stiffness is absent, permeability has weak effect on the normalized eigen angular frequencies and intensity of attenuation.

抄録全体を表示

In this paper, we propose parallel computing of BEM analysis by domain decomposition with conjugate gradient method (CG method) which have been widely applied to parallel computing of finite element method. The CG method is introduced for renewal of unknowns on the fictitious boundary in place of Schwarz method, which makes possible for determination of a parameter required in the renewal iteration automatically. This results in decrease of the load for users in setting and tunning of a parameter. We apply the proposed scheme to the elastic and potential examples and examine the convergency of solutions, the parallel computing efficiency on workstation cluster system connected by LAN.

抄録全体を表示

In previous reports, an optimization method for a two-dimensional structure subjected to a plastic deformation was presented and some numerical examples were shown to demonstrate the validity of the algorithm. The algorithms is based on the generalized layout optimization method presented by Bends■e and Kikuchi, where an admissible design domain is assumed to be composed of microstructures with cavities and the cavity size and the rotational angle of the microstructures are design valuables. In this study, the method is applied to a thin shell based on the layered approach subjected to a plastic deformation, For the sensitivity analysis, two-dimensional data base of macroscopic elasto-plastic material tensor which was calculated by the homogenization method is adapted to the in-plane stiffness of each layer. Several numerical examples are shown to validate the present method. The algorithm is also adapted to finite deformation problems. The effectiveness of this method is shown by a numerical example.

抄録全体を表示

Recently, applications of the optical shadow method of caustics is a very powerful technique for measuring the value of the stress-intensity factor in a small scale yielding of the crack tip. However, the value of the elastic-plastic fracture parameter in a big scale yielding of the crack tip is J-Integral. In this study, the J-Integral value was determined by using the reflective caustics method and J-Integral method of an ASTM standard. The diameter of the caustics is measured experimentally by using the CT specimens. The specimen used here is a high tension steel of WEL-TEN 590 RE with different thicknesses and different initial crack lengths. J-Integral value of elastic-plastic fracture parameter is dependent to singular zone of a crack tip, characteristic of materials and optical parameters. It is concluded that hybrid method with J-Integral method of an ASTM standard is necesary to measure accurately the elastic-plastic fracture parameter J.

抄録全体を表示

Elaboration of a uniaxial constitutive model of superplasticity taking account of grain and cavity growth proposed by the present authors and its extension to a multiaxial form are discussed. First the expression of an inelastic strain-rate is improved by adopting the hyperbolic sine law proposed by Garofalo to represent the stress dependence of inelastic strain-rate. The evolution equation of cavity volume fraction is also improved by incorporating the strain-rare dependence of cavity growth induced by inelastic deformation. A multiaxial constitutive equation at finite deformation is established by using the flow theory of von Mises type. Comparison of the predictions with the corresponding monotonic tension experiments in literature shows that the proposed model can give much better predictions of the typical deformation behavior of superplasticity ; e.g. the S-curve in the stress versus strain-rate relation on a log scale, the strain-rate dependence of the slope of hardening curve, the strain-rate history dependence of flow stress in the presence of static grain growth, and the softening of flow stress due to cavity growth.

抄録全体を表示

The necessary condition for the multiplicity in deformation rate was given by Hill. The condition is Δε_uΔs_u=0, where s_u denotes the nominal stress rate, and Δ shows the difference between any two multiple solutions. However, many proposed criteria of plastic instability in published literature did not take into consideration this necessary condition. They were based on phenomenological aspects. The sufficient condition for the multiplicity is deduced from the requirement which makes the equivalent strain rate ε_s indefinite. This is given by ε_uε_u=0, which is called Z-plane in s_u space. Plastic instability or unloading from a stable state always occurs on Z-plane. With respect to the formability in metal forming, especially, the possibility of plastic instability, processes are examined in plane stress, plane strain and three dimensional conditions. In sheet forming alternative cniterion, s₁=0 is also proposed for positive γ which is defined by the ratio ε₂/ε₁. In bulk forming, the dependency of ductility upon mean normal stress is discussed, and the decrease of ductility is shown with increasing the mean stress. Furthermore, the occurrence of shear banding and its mode are studied. Since the shape of loading path is normally monotonic in s_u space, a loading path intersects Z-plane only once and then plastic instability also can occur only once. Therefore, localized necking, in general, is merely the plastic deformation confined into a very thin layer with a rigid region on its both sides.

抄録全体を表示

Mode I fracture behavior of modified epoxy (#133, Toho rayon) and carbon-fiber/modifiedepoxy composite (IM 600/133, Toho rayon) was examined over eight decades of loading rates from 0.01 mm/min to 15 m/sec to study the correlation of their rate dependence. Although the fracture toughness of both epoxy resin and composite laminates showed negative rate dependence, the epoxy resin was more rate-sensitive than the composite laminates especially at very low loading rates. Microscopic observation showed that the debonding of the interface between carbon fibers and matrix resin was dominant at low loading rates but that the fracture of matrix resin was dominant at high loading rates in composite laminates. This was considered to be the cause for the difference of the rate dependence between in the composite laminates and in the epoxy resin at very low loading rates. The crack growth behavior was unstable at low loading rates but stable at high loading rates in the epoxy resin. In the composite laminates, however, the crack growth behavior was almost stable over the range of loading rate tested in this study.

抄録全体を表示

A series of fatigue tests have been performed on CFRP angle-ply laminate specimens. Prior to fatigue tests, all specimens were given the impact of a free fall rod. The extension of surface cracks and of delaminations were observed using a replicated method and a scanning acoustic microscope (SAM), respectively. The crack growth process consisted of four stages, and crack growth rates gradually decreased over these stages. Although the area of delamination did not increase with the surface crack growth, once either of crack tip reached the edge of specimen, the delamination area began to extend with the internal matrix cracks. After surface cracks were generated on the upper surface given impact, fatigue damage propagated rapidly. Specimens were ruptured when the delamination area of the upper surface extended sufficiently.

抄録全体を表示

The effect of water environment on delamination fatigue crack propagation behavior was investigated using unidirectional CFRP laminates made from Toray prepregs T 800 H/3900-2. T 800 H/3900-2 has toughened interlayer which is composed of epoxy resin and thermoplastic polyamide particles. Tests were carried out under mode II loading using end notched flexure specimens which were moisture-conditioned up to the saturated level. In the static tests, the value of the fracture toughness for the moisture-saturated specimen was slightly smaller than that for the dry specimen in air. In the fatigue tests, the crack propagation rate, da/dN, was expressed as a power-law function of the maximum energy release rate, G_IImax, in the region where da/dN>5×10^-10m/cycle. Below this region, there exists the threshold value of G_IImax. The threshold value for the moisture-saturated specimen in water was smaller than that for the dry specimen in air. Glass transition temperatures were measured both in moisture-saturated state and in dry state using differential scanning calorimetry. The decrease in the glass transition temperature indicated the ductility increase of epoxy. Microscopic observation revealed that the ductility increase of the epoxy affected the morphology of the fracture surfaces under fatigue loading.

抄録全体を表示

The paper describes the constitutive model for a particle dispersed composite material in elastic regime. Two models, which are EMT model and SCC model, are proposed. The former is based on the Eshelby's equivalent inclusion concept and the Mori-Tanaka's mean field theory, as published other models often practice. EMT assumes that the compliance surrounding the particle is the same as that in the matrix, whereas the SCC does in the averaged composite. In SCC, the final formula of the constitutive law is obtained in a self-consistent form, where the solution is obtained in an iterative fashion. The accuracy of those were checked with a meso-mechanics analysis by FEM performed on a uniaxial tension of an infinite composite domain. The accuracy of the models by EMT and other existing models depends on the volume fraction of the inclusion and also on the rigidity ratio of the two phases, giving satisfactory results only up to about thirty percent of volume fraction. On the other hand, SCC model returns quite a good accurcy over the entire ranges of the volume fraction and the rigidity ratio that includes void inclusions and rigid inclusions as extremes. The paper also discusses the significance of microgeometric effects on the global material performance.

抄録全体を表示

Smart structures are one of the appropriate approaches to obtain high structural reliability of CFRP. Electrical potential method for detections of damages does not bring strength reduction of CFRP structures. However, Iaminates of CFRP have orthotropic electrical conductivity, and it is required to evaluate the effects of orthotropic electric resistance on detections of delamination. In the present study, orthotropic electrical resistance is shown to be a main factor of difference between experimental results of authors and of Moriya by FEM analyses. The analyses show the low electric conductivity in the thickness direction causes small inclination of the relation between delamination crack length and electric resistance. A new approach for measurement of the electric conductivity in the thickness direction also proposed.

抄録全体を表示

A computer program to analyze residual stress and deformation, which occur by cooling after the curing process of resin-molded products, is developed. Visco-elastic behavior of the resin is simulated in this program. This program enables simple analysis of the molded body of a complicated three-dimensional shape because (1) it uses approximation with exponential function of the relaxation modulus, (2) it applies this approximation to the creep finite-element method, (3) it uses the effective stress function method. Comparative experiments, using test pieces of molded metals to confirm the performance of this program, showed that the deformation of the test pieces during cooling after curing agreed well with the calculated results.

抄録全体を表示

A shape memory alloy (SMA) is intended to be used as structural elements at elevated temperatures. The static tensile and fatigue properties of Ni-Ti-Nb SMA were examined at room temperature and 561 K. The chemical composition of Ni-Ti-Nb SMA is 51 wt.% Ni, 38 wt.% Ti and 11 wt.% Nb. The shape recovery temperature is around 350 K. The 0.2% proof stress and tensile strength are slightly decreasing, but the elongation and the reduction of area are increasing with increasing temperature below 561 K. Young's modulus increases with increasing temperature. The fatigue strength at high temperature is slightly higher than that at room temperature in air. The fatigue limit in water almost agrees with that in air at 561 K. Fatigue limits at 561 K are about 290, 240 and 150 MPa for stress ratios of R=-1, 0 and 0.5 respectively. Since fatigue crack is found to initiate from the Ti-rich precipitates at the sub-surface, the fatigue strength is considered to be affected by mean stress. The SMA is found to have sufficient mechanical and fatigue strength for structural elements at elevated temperature in water.

抄録全体を表示

Elastic-Plastic analyses for tori-spherical head of strain hardening material, which is a typical gross structural discontinuity of pressure vessels, are carried out in the practially wide geometrical range of the component. Plastic behaviors, such as yield zone, deformation, stress and strain in plastic range are investigated in detail. As a result, plastic collapse point is mechanically defined as the turning point of the plastic strain increment ratio at the maximum stress point of the component, which is qualitatively characterized as the starting point to excessive plastic deformation.

抄録全体を表示

Previous investigation proposed the mechanical definition of plastic collapse for pressure vessel components as the turning point of the plastic strain increment ratio at the maximum stress point of the components. The applicability of the definition is confirmed for the small end and the large end of cone-cylinder junctions and for the practical tori-spherical head of SUS 304 material with actual geometrical change. Finally, collapse pressure determined practically by using pressure-deflection curve is proposed as the pressure at the 4 times the deflection of the first yield. The practical validity of the proposed determination method is verified by comparing with various proposed methods.

抄録全体を表示

Deformation around concavity created by indentation of a conical indenter in an ultramicrohardness tester is analyzed using FEM computer simulation. Effects of indenter tip radius on concavity shape and hardness from concavity depth both under loading and load-free conditions in soft material which has low yield stress and high work hardening rate are examined. The results obtained are as follows. (1) Concavity created by a conical indenter is sinking-in type including concavity rim. The larger tip radius and the deeper concavity depth make concavity rim more unclear. The maximum elastic recovery is at the bottom of concavity. (2) At the same depth the applied load increases linearly with tip radius. (3) An increase in tip radius makes the plastic zone broader and the maximum equivalent plastic strain at the bottom of concavity lower. The stress field around the concavity is compressive. (4) Correction of errors at the indenter tip is effective to a conical indenter with tip radius 0∼3μm.

抄録全体を表示

Spot welding is widely used in automotive and other manufacturing operations. Therefore, it requires a nondestructive testing which is quantitative and practical method. This study attempts to establish effective nondestructive testing using ultrasonic. As a results of the testing, it confirmed that nugget size and tensile shear strength of spot welding are evaluated by ultrasonic pulse-echo. The diameter of nugget is estimated by height of echoes from non-weld zone. The thickness of nugget is estimated by attenuation of echoes from weld zone. In addition, numerical analysis for ultrasonic wave in spot welded joint is performed in order to compared with results of ultrasonic testing. It denoted high consistency in the comparison.

抄録全体を表示

The semi-destructive hole drilling method for measurement of residual stresses using electrical resistance strain gages has been used for a wide range of engineering materials. In this paper, a new method with two holes (measurement hole and release hole) based on the elastic stress concentration by successive interactions of the neighboring holes is proposed for the case of anisotropic materials. This method is named as Double Holes Drilling Method. Several numerical results are shown as the variation of strains which detect with three gages around the measurement hole, the values of parameters such as distance of two holes, principal angle of anisotropy, radius of release hole and so on. Then, the back analysis by use of the measured strains is given for determining the residual biaxial stresses.

抄録全体を表示

Regarding mechanism of electrical conduction through anisotropically conductive adhesive films (ACF), one model was already proposed by the authors. It was that there were two kinds of electric current passing through ACF : one passing through electrically conductive particles and the other passing through direct contacts between circuits ; the current passing through conductive particles did not change so much even after high temperature and high humidity treatment but the current passing not through conductive particles significantly reduced after the treatment mentioned above. In this paper the expression of the relationship between electrical resistance and number of particles on a terminal is obtained by least square method. The above-mentioned two kinds of electrical resistance are figured out one by one with use of the expression. The proposed model is proved by it.

抄録全体を表示

This paper presents the structural design scheme by using the concept of cellular automata. A design domain is divided into small square cells and then, thickness of each cell is taken as the design variable. Considering the cells as the finite elements, the stress analysis is performed by the finite element method. The thickness of the cell is modified by the local rule with the states of the cell and the neighboring cells. The present scheme is applied to the two-dimensional elastic problem in order to confirm the validity.

抄録全体を表示

Methods are proposed for multiplying the original fringes obtained from a photoelastic experiment and extracting the fringes using the original-or multiplied-fringe image. The multiplication method is based on the trigonometric identity of the double and triple relations of the sine and cosine functions. The extraction method utilizes two image obtained in dark-and light-field circular polariscope. In order to investigate the accuracy of the measurement, a computer simulation is used for the theoretical fringes in a circular disk subjected to a concentrated. Continuous photoelastic fringes near the crack tip are accurately extracted. This method is applied to an epoxy resin plate with a crack at one side 3-point bending and the stress intensity factor is calculated. The stress intensity factor is obtained accurately using multiplied fringes.

抄録全体を表示

Experience has shown that a bolt-nut assembly system properly tightened can be loosened under vibrating load or impact. This paper experimentally investigates the loosening response of an assembly when a stress wave is transmitted from a gross area of a bolt, a face of a circular disk, or a screw thread of the thick circular disk assembly fastened by the bolt-nut unit. When a falling bar strikes the opposite side of a threaded rod fastened to the circular disk, or a falling circular pipe collides with the circular disk or with the anvil attached to the end of a screw, a stress wave propagating from the collision interface is transmitted into the assembly. The axial stress of a bolt tightened by a hexagonal nut in conjunction with a plain washer is measured, while a number of incident waves are impinged into the assembly. The shift of axial stress due to the stress wave transmitted from the portion of the screw thread is the largest. The cause of the loosening is investigated by observing the stress waves transmitted into the circular disk assembly system.

抄録全体を表示

Recent experiments have shown that the isolated outer hair cell (OHC) can elongate and contract in response to electrical stimulation. From the OHC's position relative to the basilar membrane, it is deduced that the OHC length change directly affects the basilar membrane motion. Thus, this electromotile property of the OHC may play a key role in cochlear tuning. In order to evaluate the OHC's ability to influence the basilar membrane motion and tuning, a few experiments and numerical analyses have already been reported. However, the OHC motility within the range of the human ear (20 Hz∼20 kHz) and the force generated by the OHC are unknown. In this study, an attempt is made to analyze the OHC motility by using the shell theory. The OHC is modelled as a cylindrical composite shell and the function of the motor protein is taken into consideration. Substituting the estimated mechanical properties of the plasma membrane and cortical lattice to the shell model, the force generated by the OHC is obtained numerically. Then these mechanical properties are determined by comparing the numerically obtained OHC force with the experimental data of the previous report. Also the dynamic equations of the shell model are derived, and the dynamic behavior of the OHC is examined. The results indicate that the axial and circumferential stiffnesses of the cortical lattice are 1.3×10^-2N/m and 2.0×10^-2N/m, respectively, and that the numerically obtained dynamic behavior of the OHC is consistent with the experimental data.

抄録全体を表示

The adaptive bone remodeling phenomenon was analyzed using the three dimensional finite element method on two important clinical problem ; a proximal femur after prosthetic total hip joint replacement (THR) and vertebral bodies fixed by the anterior spinal instrumentation (SI). On the THR simulation, a normal hip joint model which composed of the proximal femur and the pelvic bone including femoral head and acetabular was constructed three-dimensionally. On the simulation of spinal instrumentation, a normal lumbar spine model which composed three vertebral bodies and four intervertebral discs was constructed three-dimensionally. Each normal model was used to determine the bone density distribution in normal bone tissue using the adaptive bone remodeling theory proposed by Weinans et al. It was confirmed that the bone density distribution obtained from the simulation was almost similar to the physiological distribution. Subsequently, THR model was constructed by the insertion of a noncemented prosthesis of Harris Type into the normal hip joint model, and SI model was constructed by the insertion of Kaneda device into the normal lumbar spine model. As a result, the remodeling simulation showed that the bone density and the stress decreased significantly at cancellous bone around bone-inplant interface.

抄録全体を表示