We have developed a new nut named 'super slit nut (SSN) '. which realizes anti loosening performance without complicated tightening procedures. In this study. tightening behavior and loosening behavior caused by shear load are analyzed by mean of three dimensional finite element method. It is found that SSN has a prevailing torque of 15 to 19 Nm. which closely agrees with experimental data. The load distribution of thread depends on the rotation angle of nut. At the angle of 24.6 degree, the distribution of 1st pitch turns to be 10% larger than that of conventional nut, reflecting the decrease in the thread at slit region. It is also found that the and loosening performance cas he realized by the thread contact force at the slit region. Since its contact force does not depend on the tightening force, the effect of and loosening performance drastically increases as the tightening force is decreased. Shear fracture would initiate not at slit region but at the bottom of 1st thread, whose stress is about 10% larger, as compared with conventional nut. Moreover, by mean of tensile and fatigue experiments, it is concluded that SSN involves sufficient strength in practical use.

View full abstract

Specimen and fracture test method for the strength analysis of MEMS micromirror have been proposed. Specimen with dimensions that closely resemble that of the actual product in order to mimic the actual working stress environment has been designed. Pure bending and combined loading tests have been performed and torsion strength (fracture criterion) has been estimated based on those results. Two-parameters Weibull distribution was used to evaluate the fractured stresses (nominal maximum principal stress) estimated from FEM model. It is found that there exists the difference in strength between pure bending and combined loading. From the SEM observations, it is found the flaw population depends on the structural geometry and is nonuniformly distributed. Thus, specimen strength will depend on flaw and stress distribution. Consequently, both geometry and stress distribution have to be considered simultaneously to effectively estimate the strength of MEMS. From FEM and load factor analysis, it is found torsional strength of the MEMS micromirror can be estimated on the safe side by using the result of combined loading test. Finally, MEMS design stress based on the confidence interval values for each Weibull parameter was shown

View full abstract

The Natural Strain is obtained by integrating infinitesimal strain increment on an identical line element over the whole process of the deformation path. Consequently, the shear strain becomes pure angular strain which is obtained by removing the rigid body rotation from the rotating angle of a line element. Since the expression of the Natural Strain is different from strain expression of ordinary rate type, the additive law of strain on an identical line element can be satisfied. In this paper, rate type expressions of the Natural Strain theory are formulated in a general deformation field. And, the method of decomposition of rigid body rotation from shearing strain component and the geometrical relation of strain rate is described.

View full abstract

Stress singularity at a vertex in three-dimensional joints is closely related to the strength of joints. It is very important to perform an analysis for evaluating the reliability of a real three-dimensional joint. However, the stress singularity fields near the vertex and along stress singularity lines are still unclear. In the present study, we investigated the characteristics of stress singularity field at a vertex and a point located on the stress singularity line in three-dimensional joints using a three-dimensional BEM and an eigen analysis based on FEM. It was shown that the order of stress singularity at the vertex is larger than that at the point on the stress singularity line, and the order of logarithmic singularity along the singularity line is larger than that at vertex. In the present analysis, a triple root and a quintple root of eigen value, p=1, occur at the vertex and a point on the singularity line, respectively. The order of stress singularity determined from the eigen analysis was agreed with that from BEM. The value of coefficient in a power-law singularity increased as approaching to the vertex along the singularity line. The stress field along the singularity line is more influenced on the logarithmic singularity than that at the vertex. In particular, coefficients of terms in logarithmic singularity vary in the same way with the angle from an interface.

View full abstract

Molecular dynamic simulation and anisotropic elastic theory are employed to determine the elastic fields of surface steps and vicinal surfaces. The displacement field near a step of Fe is determined using atomistic simulation and FS potentials. We derive an anisotropic form for elastic field associated with a surface line force dipole using a two-dimensional surface Green function for a cubic elastic half-space considering surface stresses. The displacements considering surface stresses are less than those no considering near the step. When surface stress varies in a step manner, the displacement in the normal direction of the surface occurs. We considered that surface stress would vary between the surface beneath the step and the surface. The displacement produced by adding the displacement due to the surface dipole force to the displacement due to the variation of surface stress is shown to be in excellent agreement with the simulation.

View full abstract

It is well known that nuclear pressure vessel steel shows embrittlement under thermal aging and strong neutron irradiation. We focus on nanoscale copper-rich precipitates and try to clarify the effect of the nanoscale copper-rich precipitates on embrittlement of reactor pressure vessel steels. Our final goal is to evaluate such embrittlement from microscopic viewpoint based on atomistic simulation. In this study, we simulate interaction between motion of an edge dislocation and copper precipitates using Molecular Dynamics method with a periodic boundary condition, where uniform shear strain is applied to the boundaries parallel to the slip plane (1 1 2) in the system. As the results, we clarify the effects of size, distance and pinning of the copper precipitates on dislocation motion.

View full abstract

The numerical analysis was performed to estimate the effect of material inhomogeneity induced by a temperature gradient on fracture toughness for SM 490 A steel. The temperature gradient in the specimen creates change in plastic properties at a position to the position to bring about inhomogeneity in the specimen. The experimental result shows the material inhomogeneity tends to change the fracture toughness from the expected one for the crack tip material property. In the numerical analysis, void volume fraction was used for a dimple fracture criterion, and a set of critical values of plastic strain, stress triaxiality and principal stress was taken as a cleavage fracture criterion. The stress and strain distributions at the same J-integral are different between the homogeneous and the inhomogeneous materials. The numerical results agreed with the experimental result that the material inhomogeneity induced by the temperature gradient has a significant effect on the fracture toughness.

View full abstract

This paper presents a temperature dependent static constitutive equation for carbon steels, which can be applied for wide temperature range involving the range where blue brittleness occurs. Generally, a stress induced in steel at a certain strain decrees with the temperature. However, the occurrence of blue brittleness of steels increases the values of work hardening. As a result, the stresses increase with the temperature due to the blue brittleness. Thus, the stress-strain relation-ships of steels seemingly have negative dependence to the temperature within the range involving the blue brittleness. Since this phenomenon arises remarkably at static strain-rate, the present paper has proposed a temperature dependent static constitutive equation. Concretely, the paper decomposes the stress-strain relation of steels into an unaffected part and affected part by the blue brittleness, and derives equations revealing those parts respectively. The proposed constitutive equation is expressed by the sum of them. The paper actually obtains unknown material constants involved in the proposed equations by a nonlinear least squares from measured results and confirms the appropriateness of the proposed constitutive equation over the wide temperature range.

View full abstract

In order to clarify the effects of hydrogen on the fatigue characteristics of an austenitic stainless steel, bending fatigue tests on plain specimens were conducted in air and in a hydrogen gas. Main results obtained are as follows. Effects of hydrogen are not clearly seen on the fatigue strain-life diagram, because the hydrogen gas environment has opposite effects to crack propagation and to crack initiation ; accelerates crack propagation, but retards crack initiation. Striation spacing or in-situobservations confirm the acceleration. The cause of retardation seems to be the lack of oxygen or water vapor in the hydrogen. Several cracks propagate in air, but only one crack occurred in hydrogen. The difference in the number of cracks is supposed to depend on the ratio of the crack initiation life to fatigue life.

View full abstract

The continuum damage mechanics is extended to cover the self-repair process as well as the damage process. The repair variable and its evolution equation are newly introduced to consider the repair process. In the constitutive modeling, the equation of creep based on kinematic/isotropic hardening theory is extended to take into account the effect of damage and the evolution equation of a repair variable is proposed, based on Dyson's equation of creep cavity growth. The validity of the proposed modeling is illustrated through the simulations for the self-repair process of two kinds of steels damaged by creep.

View full abstract

A constitutive equation incorporating stress rate dependence which has been used widely is shown to have a limit for its application, especially, in the case that strain rate changes abruptly its direction. Therefore, the constitutive equation does not have the potential for representing such plastic behaviour that stress vector largely delays relative to strain rate vector. Before proposing our constitutive equation, the basic correlation in a five dimensional stress space is dealt with between local geometries of associated paths of stress and strain under plastic deformations obeying a general constitutive equation incorporating stress rate dependence. Using the basic correlation, we proposed a constitutive equation with flexibility applicable for stress delay angle observed experimentally between stress and strain rate directions in many strain trajectories.

View full abstract

Low-carbon TRIP steel has high strength and excellent formability and is one of the key materials to meet the demand for weight reduction of automobile body parts. However, in order to disseminate the materials, the clarification of a complex plastic deformation mechanism depending on the strain rate and temperature and formulation of a proper constitutive equation is essential. The present investigation experimentally clarifies the quantitative effects of the strain rate and temperature on the material characteristics by means of tensile tests under strain rates from 1.7×10^-4 to 1.7 x 10^-1 and temperatures ranging from -50 to 250°C. The deformation and transformation behaviors substantially change in the range of 100 to 150°C. With regard to the relatively the low temperatures up to 100°C, retained austenite transforms into martensite. The increase in strain rate causes a rise in the flow stress of the ferrite phase and an increase in temperature, which suppresses the martensitic transformation. As a balancing effect, the stress-strain relationship expresses a high degree of strain rate independency. In the later stage of uniform deformation, the effective TRIP effect declines under the high strain rate and the uniform elongation decreases. However, the tensile strength is almost unchanged due to the very small amount of work hardening. Meanwhile, for the high temperature range above 150°C, the retained austenite transforms into bainite which requires a longer transformation time, which yields the strong strain rate dependency of the deformation behavior and the tensile strength and uniform elongation increase as the strain rate decreases.

View full abstract

This paper is concerned with a biaxial bending compression experiment for the case of eccentric at the upper and axial at the lower ends on carbon steel square pipes in the short column range, supported with spherical seat. An empirical formula for calculating the eccentric bending compressive buckling stress σ_cre* of the carbon steel square pipes is presented as follows ; σ_cre*/σ_cr =1/ (1+ ao), where σ_cc, is equal to axial compressive buckling stress, ao is equal to factor of the eccentricity and biaxial ratio. The measurement reveals that the results calculated by this formula are in good agreement with those obtained experimentally for the short column range.

View full abstract

In the present study, rotating bending fatigue tests were performed on an extruded aluminum alloy 2024-T3 to study a crack initiation and growth behavior on the smooth un-notched specimen. Effect of microstructure of the material on the crack initiation and growth behavior was also studied using an atomic force microscope, AFM. Small crack with a length of 1-2 μm initiates at grain boundary in the very early stage of fatigue life, N/N_f=6-10%. So the fatigue life is almost considered as a crack propagation life. The initiated crack propagated very slowly along the grain boundary especially at the lower stress amplitude region. The S-N curve can be estimated from an integration of the relation da/dN vs. M, the parameter proposed by authors.

View full abstract

Although research and development of biomaterials, such as an artificial bone, are energetically done recently, researches on bones are not enough. There is, in particular, still very little knowledge about fracture toughness and fatigue properties of bones, and the effect of microstructure on fracture characteristics of bones. Therefore fracture toughness of various parts of bovine and swine compact bones were investigated with relating microstructures in this study. Microstructures of bovine and swine's humeral and femoral compact bones are able to be divided into plexiform bone with cores of nonlamellar bone and lamellar bones between nonlamellar bones and haversian bone with osteons. The fracture toughness value is greater in the plexiform bone with cores of nonlamellar bone and lamellar bones between nonlamellar bones than in the haversian bone with osteons.

View full abstract

In the treatment of lumbar spinal diseases, the degree of lumbar spinal instability strongly affects the selection of treatment strategy and surgical method. However, a measuring instrument for intraoperative lumbar spinal instability has not been put to practical use yet. Therefore, the present evaluation of lumbar spinal instability depends on surgeon's experience and feeling. From above-mentioned point of view, we tried to develop the practical and simple measuring instrument for the objective and quantitative evaluation of intraoperative lumbar spinal instability. This instrument was consisted of Kocher hemostatic forceps with a strain gauge and a push spring, and could evaluate the displacement of spinous process to the cephalocaudal direction when the load was subjected between spinous processes. From the results of preproduction tests and clinical application, it was considered that the developed instrument was quite useful for the evaluation of lumbar spinal instability.

View full abstract

As congenital hip dislocation residual subluxation is the aftereffect of congenital hip dislocation, it is characteristic that the ailment remains. Hip joint disease is typically said to be difficult to treat within the medical orthopedic field. Although on exact cure is desired, when taking into consideration factors such as the operation method used and the age of the patient at the time of the operation, there is still no conclusive method at present because of the differences in medical treatments and other varying dynamics. In this research, the Salter method for pelvis osteotomy, including the operation method specific to this disease, was adopted. It operation was performed in order to fully understand the stress states. A Comparative examination of the states immediately after the operation and 6 weeks after the operation using the Salter method and comparison with a normal joint, was carried out using the 3-dimensional stress freezing method for analysis. It was found that, the states of stress on the hip joint immediately after the operation and 6 weeks after of the operation, were almost the same as for a normal joint. This finding corresponds to the treatment policy of the medical field for the results of a dynamic examination, and it has therefore been understood that this is a steady dynamically operation method.

View full abstract

Muscle fatigue has been studied in various fields. As it accompanied the change of its mechanical characteristics, we had studied the relation between muscle fatigue and its biomechanical characteristics (visco-elasticities) by using biomechanical impedances in case of the isometric contraction with continuous load. It was confirmed, as a result, that the condition of muscle fatigue was estimated from its visco-elasticities. In this study, we adopted the isometric contraction with intermittent load to examine how the rest time affected muscle fatigue. Three sets of 5 minutes 15% MVC (Maximum Voluntary Contraction) load were applied with 1 or 4 minutes interval on an antebrachial flexor muscle. The advancement and the recovery of muscle fatigue were observed in both loaded and unloaded situation. Longer rest decreased the fatiguing speed and caused an obvious recovery. Visco-elasticities were less sensitive to muscle fatigue at its early stage than MFs, which were calculated from surface EMGs.

View full abstract

A simplified equation, designed to obtain inter-layer residual stress arising when thermal load was provided to a viscoelastic laminate beam consisting of various materials, was proposed, and reasonableness of the equation was examined through comparison with exact solution based on thermal viscoelastic analysis. The proposed simplified equation is composed of the glass transition temperature, the rubber transition temperature, the elastic coefficient, and the linear expansion coefficient of the component material. Based on this composition, it has been clarified that the equation allows calculation of inter-layer residual stress in laminated beams. Because the simplified solution of the inter-layer residual stress that is generated in viscoelastic laminate beams is well consistent with the precise solution derived from the basic thermal viscoelastic formula, the rationality and efficiency of the simplified solution have been revealed.

View full abstract

Fatigue life prediction of a symmetric cross-ply carbon/epoxy laminate subjected to cyclic loading in the 0° fiber direction is attempted on a ply-by-ply basis. First, tension-tension fatigue tests on the cross-ply laminate under constant amplitude cycling at room and high temperatures are performed. The normalized S-N relationship for the cross-ply laminate using the fatigue strength ratio agrees well with that for the unidirectional laminate made of the same prepreg tape. This indicates that the fatigue behavior of the cross-ply laminate in the fiber direction is substantially governed by that of the constituent 0° plies in the laminate. Second, under the assumption that the final failure of the laminate is determined by the failure of the 0° plies, a simple fatigue failure model for the cross-ply laminate is developed on the basis of the classical lamination theory and the ply fatigue model considering the in-situ static strengths. Finally, validity of the proposed fatigue model for multidirectional laminates is evaluated by comparing with experimental results. It is demonstrated that the proposed fatigue model with a consideration of the in-situ strength of ply succeeds in adequately predicting the fatigue strength of the symmetric cross-ply laminate for the fiber direction.

View full abstract

For a rotating composite component such as a helicopter blade, delamination of composite laminates causes low reliability. Since it is difficult to detect the delamination of rotating component in-service with a wired system, wireless detecting system is demanded to improve the reliability. In the present study, the wireless system for detecting the delamination is proposed. This method adopts an electrical resistance change method and an oscillating circuit to transmit the information of the delamination. The electrical resistance change in the composite component due to the delamination creation causes the oscillating frequency change. This frequency change can be measured wirelessly. Since this system uses the composite structure itself as a sensor and the oscillating circuit is very small, it is applicable to a rotating component. The electrical resistance change and oscillating frequency change due to the delamination creation is experimentally measured by using carbon/epoxy specimen. Also the effect of temperature change is measured. As a result, the method can successfully detect the embedded delamination and estimates the size of delamination wirelessly, and the effect of the temperature change is minimized by using temperature compensation.

View full abstract

The free-edge stress singularity usually develops near the intersection of the free-surface and the interface for the bonded dissimilar materials. When two materials are bonded by using an adhesive, an adhesive layer may develop between two bonded materials. To defuse the residual stress which develops because of the difference of the coefficient of thermal expansion, an interlayer may be inserted between two materials. On the other hands, the free-edge stress singularity disappears for certain pair of materials. In this study, the disappearance of free-edge stress singularity by inserting the interlayer to the bonded dissimilar materials for which free-edge stress singularity develops were investigated theoretically and numerically. It was found that the free-edge stress singularity disappeared by inserting a proper material to the bonded dissimilar materials. It was theoretically shown that there existed combination of material parameters of such an interlayer. Stress distributions on the interface of bonded dissimilar materials with an interlayer were calculated by using the boundary element method, and disappearance of free-edge stress singularity was confirmed numerically. When the interlayer was very thin, stress distribution near the intersection of the interface and free-surface was controlled by the free-edge stress singularity of the bonded dissimilar materials without the interlayer.

View full abstract

This paper presents a shear lag analysis which enables us to calculate stress distribution in short fiber reinforced composites with soft resin coating at the end of fibers or fiber bundles. Stress distributions are obtained for the following two cases ; the fiber is bonded (Case A) and debonded (Case B) with matrix resin at the fiber ends. Finite element analysis is employed to verify the validity of the present analysis. It is confirmed that shear stress at the fiber/matrix interface is relaxed by the soft coating resin while the axial stress in the fiber decreases in both cases. Width and shear modulus of coating resin have larger influence on relaxation of stress concentration than its length. Shear stress distribution predicted using the shear lag analysis is in fairly good agreement with the finite element calculation.

View full abstract

In previous report it was revealed that sizing didn't spread in resin and much sizing was around strands. In this study effect of sizing around strands on tensile strength and fatigue strength of SMC was investigated. Six types of SMC differing in amount and properties of sizing were prepared. The results of tensile test for the specimens showed that specimens with much sizing had best tensile properties. The reason was suggested that sizing around strands prevented cracks on interphases between fibers and resin from growing and increased tensile strength. The results of fatigue test showed that the more amount of sizing had the higher fatigue strength and properties of sizing made effect on fatigue strength. According to degradation of stiffness ratio during fatigue test, the reason was suggested that sizing around strands made effect on fatigue mechanisms. In addition, it was likely that distribution of fibers relied on properties of sizing and had effects on transverse crack propagation. In result, the lower stress on fatigue test was, the larger effect of distribution of fibers was.

View full abstract

The flexural impact properties of a PAN-based carbon fiber/epoxy unidirectional composite are improved by applying an outer reinforcing layer of pitch-based, low modulus carbon fibers. This increase in the impact performance is due to a larger compressive failure strain of the outer layer, which delays the initiation of the fiber microbuckling failure of the PAN-based fiber layers on the compression side. This paper examined the failure mechanisms of interply hybrid laminates in order to determine the influence of suppressed fiber microbuckling on the flexural impact properties. PAN-based carbon fiber with fiber modulus of 230 GPa was used as the core, and an outer reinforcing layer of low modulus carbon fiber with fiber modulus of 55 GPa was applied on the compression side of the core. A drop-weight, flexural impact test suggested that the low modulus fiber layer increased the compressive failure strength of the PAN-based fiber core in the hybrid laminates. A damage mechanics analysis using a finite element (FE) method was performed to simulate the flexural failure. When the compressive strength of the PAN-based fiber core was increased to reflect the influence of hybridization, the FE analysis showed good agreement with the experimental results. It was indicated that the compressive strength of the PAN-based fiber core was increased from 1 470 MPa in a monolithic PAN-based carbon fiber unidirectional laminate to a maximum of 2 355 MPa in the hybrid laminates. The FE results then suggested that the compressive stress in the thickness direction around the loading point had an effect similar to that of a hydrostatic stress state, which restrains fiber microbuckling failure. The improvement in the flexural impact properties of the hybrid laminates was thus demonstrated by the FE analysis from the increased compressive failure strength of the PAN-based fiber core.

View full abstract

Recently, many optical grass fibers are used as the submarine cables because of excellent corrosion resistance, no electromagnetic noise and low transmission loss. The fiber has to be spliced to fabricate a long distance transmission line by the arc fusion method. However, there is a serious problem that the spliced part occasionally break after it is laid as the submarine cable, because the tensile strength of the spliced fiber reduces to about 1/2 than that of the virgin fiber. Therefore, the advance research for regeneration method of tensile strength of the fiber which is spliced by arc fusion is desired. For the above purpose, the position of fiber which was broken by a tensile testing device was measured, and the hardness of fiber's surface was examined throughout to the nonfusion region from the spliced center. And also, the shape and crack of indentation formed by hardness test were investigated. Form the correlation between the Vickers hardness for the distribution of fiber broken position and the growth of lateral crack of indentation, it was found that the main case of tensile strength was brought from a progress of brittleness of glass in the arc fusion.

View full abstract

In order to obtain some useful information on rapid process for functional film deposition, TiO ₂ film deposition by thermal plasma chemical vapor deposition (TPCVD) method under an atmospheric environment was carried out. The experiment was conducted under the condition where working gas was Ar, working gas flow rate was 201/min, spraying distance was varied from 10 to 60 mm and spraying time was 5 min. Titanium tetra buthoxide was used for the starting material. According to the XRD profiles, the TiO ₂ films formed by TPCVD contained peaks of rutile-type and anatase-type. The results of wettability and methylene blue decoloration tests suggest that the TiO ₂ films have good photocatalytic properties as the spraying distance is short. It is concluded that the proposed highly promising for rapid functional thin film formation.

View full abstract

Diamond films were synthesized on a Mo substrate using combustion flame. During cooling process, the most diamond films delaminated between the diamond film and the Mo substrate. It was caused by the thermal stress due to a mismatch of the thermal expansion between the diamond film and the Mo substrate. In this study, a three-step synthesis method was proposed and prevented the film from the delamination. In the first step, the Mo ₂ C and the diamond phases were synthesized on the Mo substrate, but the diamond phase was synthesized in the second and the third steps. The interfacial stress between the film and substrate was calculated by a finite element method. According to the results, the interfacial stress in the film made by the three-step synthesis method was smaller than that by the one-step synthesis method. The three-step method is useful for synthesizing the diamond film.

View full abstract