Closed-form crack mouth opening displacement (CMOD) for a surface flaw in a plate under remote tension was obtained first, based on the analogy of the displacement around an elliptical crack in an infinite elastic solid and that of a surface crack. This closed form CMOD showed good agreement with the experiments by Torii et al. and with results by our boundary element analysis (BEA) for a wide range of flaw configuration. Next, a closed-form local stress intensity factor (SIF) was obtained primarily by assuming that this CMOD is applied to a single edge cracked strip (general compliance method) with the same crack depth, and secondarily by modifying SIF based on the near crack tip displacement by BEA results. Finally, our closed form SIF was compared with Newman-Raju's empirical solution at the deepest point for reference. Our closed form SIF is expected to give a straightforward perspective of the solution for the crack.

View full abstract

The edge dislocation void interaction was solved by G.Z.Ganeyev-T.E.Turkebaev in 1988. And in 1990 M.W.Charles studied the edge dislocation inclusion interaction by using Love's solution. However, those solutions are not easy to apply to more complex problems. In this paper, the interaction between an edge dislocation and a spherical inhomogeneity is solved analytically in terms of isotropic elasticity theory. The inhomogeneity is assumed to be perfectly bonded with the surrounding matrix. The problem is formulated in terms of Papkovich-Neuber displacement potentials. The effects of the stiffness ratio, inclusion size and aspect ratio on stresses near the inclusion and dislocation force are shown.

View full abstract

Three-dimensional analysis is attempted to simulate delamination growth around a circular hole in laminated composites. First, stress analysis for a laminated composite is made using conventional finite element method where stress singularity of crack tip is ignored. Next, stress intensity factor at the edge of delamination is evaluated by using singular elements that is comparable to conventional elements. The singular element is generated on the basis of asymptotic solution near the tip of interface crack.

View full abstract

The effects of moisture and heat on the residual stresses in organic composites are theoretically investigated. From the experimental results, the tensile strength of CFRP cross-ply laminates ([0゜/90゜]_45) at 298k in the high vacuum condition is larger than that in the atmosphere. It is considered that the degas and/or moisture desorption from the matrix of epoxy resin and from the interface occur in the high vacuum condition, and then the mechanical properties of CFRP are changed. On the basis of the theory of diffusion, and coupling of the moisture and the heat with temperature varying the diffusivity, we derived the diffusion equations of the moisture and solved them by the use of the finite deference method. Some numerical calculations for the stresses in the composites are carried out by the use of the finite element method. The stress distribution and the hygrothermal residual stresses in organic composites are shown graphically.

View full abstract

It is known that crystal structures near the surface are different from those in bulk. In the present paper, the boundary condition taking into consideration of surface density and surface stresses is used for examining the velocity of the surface wave against wave number. The dispersion of the surface wave in an isotropic material is first investigated, and it is shown that the wave velocity decreases with decreasing the wavelength in the case where the surface density and the surface stresses are taken into account. The dispersion properties of surface wave in anisotropic materials, in particular, Ni(001) and W(110) are next investigated, and the dispersion relationship obtained by a continuum approach is compared to the experimental results of surface phonon. The theoretical results considering the surface density and the surface stresses are almost agreed with the experimental ones. In this analysis, the surface density plays an important role for the explanation of behavior of surface phonon against the wave number.

View full abstract

This paper is concerned with the two-dimensional thermal and thermal stress waves in finite elastic plates subjected to the impulsive heating. The formulation of the problem is based on the generalized theory of thermoelasticity, and the solutions are obtained by using the method of bicharacteristics and the explicit finite difference methods. Numerical calculations are carried out for finite elastic plates subjected to the local ramp-type heating on the surface of the plate.

View full abstract

This paper describes axisymmetric three-dimensional generalized thermoelasticity based on the Lord-Shulman's theory and the Green-Lindsay's theory by use of the state space approach. The fundamental equations of generalized thermoelasticity, which include both generalized theories, are used. The generalized thermoelastic problem for a layered medium, which consists of homogeneous and isotropic layers and whose surface is traction free and subjected to axisymmetric heating, is analyzed by means of Laplace and Hankel transforms. The inversions are carried out numerically. The numerical calculations for temperature and stresses based on the Lord-Shulman's theory are carried out.

View full abstract

A theoretical model was formulated by the authors for ultrasonic attenuation coefficient based on the evaluation of energy loss of ultrasonic wave for unidirectional composite material consisting of elastic fibers and viscoelastic matrix. In the present study, the theoretical model is applied to transverse waves which propagate perpendicularly to the fibers in fiber reinforced material (unidirectional CFRP). From the numerical analysis, it is shown that there are the case in which the attenuation coefficient of composite material fall below that of matrix and the case with reversed. And attenuation coefficients for two polarization directions of the transverse wave, parallel to the fibers and normal to the fibers, are compared.

View full abstract

The characteristic partial non-linear differential equation for wave front shape is solved by the method of characteristic strips. The solution which gives wave front is expressed in a parametric form. As numerical examples, two type of anisotropy are considered : rectilinearly and cylindricaly anisotropic solids.

View full abstract

The present paper addresses a numerical modeling of ultrasonic attenuation in particle-reinforced composites based on wave scattering theory. In particular, the viscoelastic nature of the matrix is explicitly taken into account. It is assumed that the ultrasonic attenuation loss in composites consists of the absorption loss in the matrix as well as the particles, and the scattering loss due to the inhomogeneity. An energy estimate for these loss mechanisms is illustrated, and a simple formula is given for the overall attenuation coefficient of the composite. A numerical example is obtained for longitudinal waves propagating in a glass-particle reinforced epoxy-matrix composite. The results show that the attenuation coefficient of the composite may or may not exceed the matrix attenuation coefficient depending on the relative magnitude of certain measures of scattering versus absorption losses.

View full abstract

Transient SH wave from a point source in an inhomogeneous elastic solid is considered for two types of inhomogeneity, exponential and linear variations of SH-wave velocity. An exact solution for a transient SH-wave, i.e. Green functions is obtained for each type in a simple form of integrals. In the case of the exponential velocity variation, a finite jump is found on a front of a evanescent wave which is coming back from the infinity.

View full abstract

Phase transformation of PSZ in PSZ/SUS304 FGM plate is used for the purpose of the reduction of thermal stress during cooling process after high temperature synthesis. The optimization of cooling process of the FGM plate is necessary for the effective use of the phase transformation together with the volume change. In this research, an analytical solution is derived for the transient heat conduction problem during an arbitrary cooling process in the FGM plate with arbitrary thermal nonhomogeneities by the Piecewise-Linear Nonhomogeneous Approximation Method developed by Sugano et al. and the convolution theorem of Laplace transformation. An expression of the thermal stress taken into account the phase transformation is obtained from an extension of thermal stress expression in the FGM plate with arbitrary mechanical nonhomogeneities through the thickness derived by Sugano.

View full abstract

In the present paper, the equations governing plane-stress behavior of a piezoelectric solid of crystal class 6mm are presented. A solution technique based upon displacement and electric potential functions is developed, and application is made to a problem of a circular disk exposed to axisymmetric surface heating. Numerical results obtained for the radial stress and electric potential are shown to be in good agreement with those found using the previously derived three-dimensional solution.

View full abstract

1500-MPa-plus class high strength steels with high resistance to delayed fracture and giga-cycle fatigue have been developed in the ultra steel project. Giga-cycle fatigue of high strength steels is dominated by internal fracture, initiated at inclusions and matrix cracks and its fatigue strength is lower than the estimated one for surface fracture from the empirical eqation σ_W=0.5σ_B, where σ_W and σ_B are fatigue and tensile strengths. Modified ausforming and controlling the size and hardeness of inclusions cleared the spring steel SUP12 withσ_B=1800 MPa of internal fracture. The fatigue strength was higher thanσ_W=0.5σ_B, even through internal fracture occurred from controlled inclusions.

View full abstract

Fatigue tests were carried out for two spring steels (heat A and D1) and one valve spring steel (heat F) with Vickers hardness HV=518∿528. Heat A, F and D1 were produced in 1986,1997 and 1998. The sizes and compositions of inclusions were controlled in heat F and D1. The internal fracture occurred for all three steel. The fatigue strength σ_w=640,and 720 MPa at (10)^8 cycles for heat A, D1 and F was lower than the estimated on. σ_w=874 MPa from the empirical equation σ_w=1.6HV for the surface fracture. The Al_2O_3 inclusion, and TiN inclusion and matrix crack were observed at the internal crack initiation sites for heat A and F, whereas only the matrix crack was observed for heat D1 where the inclusions were controlled. These results suggest that the fatigue strength σ_w could be improved for heat D1,if the matrix crack is prevented.

View full abstract

The effect of hydrogen embrittlement on internal fracture of giga-cycle fatigue was investigated for the spring steel SUP12 of heats A and D1 with Vickers hardness HV=520 and 518,where Al_2O_3 inclusions and matrix cracks were observed at the fracture sites, respectively. Fatigue tests were conducted after specimens were heated up to 300℃ in the high vacuum of 2x(10)^2 pa. The treatment did not give the intemal fracture originated at Al_2O_3 inclusions, whereas matrix cracks were eliminated and fatigue strength σ_w=874 MPa from the empirical equationσ_w=1.6HV for the surface fracture. It is suggested from these results that the hydrogen embrittlement influences the matrix crack-originated internal fracture and that the creation of tempered martensite with high resistance to hydrogen emnbrittlement in heat D1 makes the fatigue strengthσ_w estimated for the surface fracture possible.

View full abstract

Fatigue crack propagation properties for SUP12 spring steel with tensile strength of σ_B=1720MPa were investigated in air and Vacuum. Fatigue crack propagation rate was higher for the high strength steel of SUP12 than for the low strength steels of 1Cr-1Mo-0.25V, SUS304 and SUS403 in air, while it was independent of the steel in vacuum. Fatigue threshold was independent of the steel in air and vacuum. The SEM fractograpy suggested that the acceleration of fatigue crack propagation for SUP12 steel in air was caused by hydrogen embrittlement.

View full abstract

Giga-cycle fatigue properties were investigated for an ausformed spring steel SUP12 with Vickers hardness Hv=534. The fatigue limit σ_w=900 MPa at (10)^8 cycles was higher than σ_w=854 MPa estimated from σ_w=1.6Hv, which is the empirical equation for the surface fracture of ordinary quenched and tempered low alloy steels. This is because the matrix crack at the internal fracture origin and hydrogen crack area (optically dark area) around inclusions were not formed for the ausformed spring steel with controlled inclusions.

View full abstract

Microstructural examination for seven tempered martensitic steels by an optical and atomic force microscopes show that prior-austenitic grain size and block width were about 18 and 0.7μm, respectively. An Ultra-micro and Vickers hardness tests show that there are three empirical equations of HV=2Hv*, σ_w=1.68HV and σ_w=3.36Hv*, where HV and Hv* are macro-and nano-hardness and σ_w is fatigue limit. It is apparent from these results that σ_w=3.36Hv* is the fundamental equation for the analysis of high-cycle fatigue mechanisms.

View full abstract

Hardness and microstructures of high strength tempered martensitic steels SUP12 were investigated using the nanoindentation tester and atomic force microscope. The ausformed steel, which has improved fatigue properties, has almost the same hardness as the conventional QT steel in both nanoscopic and macroscopic tests. Microstructural observation reveals the QT steel has 10μm-large lower bainites as defects that are not observed in the ausformed steel. The uniform microstructure is a possible reason for improvement in fatigue properties of the ausformed steel, in addition to absence of ODA (optically dark area) around inclusions.

View full abstract

In this study, long life fatigue behavior of SUJ2 steel were examined and fish-eye nucleation process were analyzed by using the FRASTA technique. The major results of this study are summarized as follows : (1) The existence of grinding layer on the specimen surface does not influence the long life fatigue behavior of SUJ2 steel. (2) The FRASTA technique is promising for studying a fish-eye nucleation process during long life fatigue tests.

View full abstract

In order to clarify the fatigue behavior in long life region together with fracture surface characteristics, gigacycle fatigue tests were performed by means of same type of many testing machines and same type of specimens of high strength steel, SUJ2. As a result of this study, we found that the complicated S-N property of high strength steel, SuJ2,was successfully explained as duplex S-N characteristics corresponding to the respective two different fracture modes of surface slip governed fracture and inclusion governed fisheye fracture. In this report, relationships between interior defect and fatigue life were especially discussed from a viewpoint of the fracture mechanics.

View full abstract

In order to investigate the properties of interior originating fractures, uniaxial tension fatigue tests were carried out in air and vacuum environments using pieces high strength steel (SNCM439) with various finishing conditions. As result, the following were obtained : (1) All of the fractures occurred from small inclusions located in the interior of the test pieces. (2) The interior originating fractures were not affected by surface conditions and environment. (3) △ K values at the inclusions of fracture origins were mach smaller than △ Kth of surface originating fractures. (4) Rough and strongly structure sensitive fracture surface were observed around the origins and almost all of the fatigue lives were estimated to be spent in these regions.

View full abstract

In order to clarify investigate influence factors on the high-cycle fatigue of high strength steel SUJ2,the fatigue tests have been carried out up to (10)^8 cycles under rotating bending at room temperature. The higher stress amplitude damage to specimen surface under the condition of two step stress amplitude, Surface failure is observed even in the specimen broken in high cycle region. It considered that fretting corrogion of specimen's handle has an effect on fatigue life in high cycle region.

View full abstract

To investigate the effect of surface conditions on fatigue strength in gigacycle range of high carbon-chromium bearing steel, JIS SUJ2,cantilever-type rotating-bending fatigue tests were conducted using specimens with mechanical-polishing, electro-polishing and two kinds of shot-peening. Duplex S-N curve having surface fracture mode and internal one was obtained for the mechanical-and electro-polished specimen. Fatigue limit of surface fracture mode for the electro-polished specimens decreased as compared with the mechanical-polished one. On the other hand, single S-N curve due to the internal fracture mode appeared for the shot-peeing specimens and was not affected by the any surface conditions.

View full abstract

In order to investigate the fatigue properties of high strength steels and surface hardened steels in the super-long life range (N&ge1×(10)^7), cantilever type rotating bending fatigue tests were carried out for the SUJ2 high carbon chromium bearing steel which was finished by the electro-polishing. The surface of notch bottom was removed up to 30μm deep by electro-polishing because the depth of residual stress in the notch bottom of grinding specimen has been 20μm. As a result of fatigue tests, in the case of "surface crack origin type fracture", it was found that the fatigue life of eletctro-polishing specimen were shorter than that of grinding specimen. In the case of "interior crack origin type fracture", it was found that the fatigue life of electro-polishing specimen were almost equal to that of grinding specimen. The causes for this are discussed.

View full abstract

Recently, ultra high cycle fatigue researches of high strength steel and surface modified steel are studied actively. Because fatigue strength in these materials had decreased again at about (10)^7 cycles in each S-N curves. So, we used SNCM439 steel by radical nitriding and studied about its fatigue strength. As a result, Fracture of radical nitrided one started from surface in short life region and inside in long life region. Fracture pattern on fisheye failure in radical nitrided one was different from quenched and tempered one.

View full abstract

Rotary bending tests for notched pearlite matrix ductile cast iron were conducted to evaluate the effect of ion carburization on fatigue strength. The carburization increased more than 30MPa the fatigue strength of the unnotched specimens and made the fatigue strength of notched specimens comparable to that of not-carburized unnotched specimens. The fact that the carburized notched specimens showed no decrease in fatigue strength deserves attention. Practically, shallownotched element members were improved by ion carburization better in fatigue strength than not-carburized notched ones. In the ion carburization process, carburization depth can be controlled by adjusting glow discharge time. Ion carburization process is friendly to enviroment in terms of no pollution and energy saving.

View full abstract

The purpose of stress/strain measurements, in other word, experimental mechanics is to check whether designed structures have enough strength for expected loads or not and whether we can, for aging structures, continue to use them or not. For the latter purpose other technologies, like NDI and maintenance inspection, have already been using today. But, here, the author suggests that we will open up new technolgy for the latter purpose, which will overcome their defections, as a new field of experimental mechanics, and offers several study topics related with this new field.

View full abstract

It is known that patient of osteoporosis is increasing with greater age. As the bone becomes less dense, its mechanical properties alter and it is more likely to fracture during the body motion. It is one of the important problems which quantification of the relationship between in vivo bone stiffness and damage. We examined mechanical reliability of heel bone using ultrasonics, that is young's modulus of heel bone was calculated. Waking cycle was measured using force plate, then stress subjected of heel bone was analyzed by finite element method with bone area ratio (B.A.R) of heel bone. The results show that mechanical reliability of heel bone (B.A.R33%) is sufficient during normal walking (1.4m/s) because the calculated Mises stress was under the fracture damage stress of a wet bone.

View full abstract

The temperatures of the surfaces of intact Epipremunum Aureum and Ficus Elastica leaves partially subjected to different intensities of ultraviolet (UV-B) irradiation as a function of time were investigated using a thermal video system and compared with those for the cases of in the dark and plant-upbringing irradiation. The results showed that the variations in the leaf temperature for UV-B irradiation were different from those for cases of in the dark and plant-upbringing irradiation, and were depended on the kind of plant studied and UV-B radiant intensity, as well as those previously obtained for case of leaves of intact Epipremumum Aureum and Ficus Elastica wholly subjected to UV-B irradiation.

View full abstract

This study is concerned with bending properties of spiderwort. Young's modulus and a change of deflection of stalk with time were examined for different stalk diameters. Young's modulus was decreased with increasing diameter of stalk. The change in the deflection with time was represented by an exponential function, and the creep rate increased with the stalk diameter, but the convergent value was decreased with the diameter. To investigate a biological reaction, action potential was also measured before and after bending.

View full abstract

In recent years, flexible materials with very high performance are widely used. In the present paper, a new measuring method to investigate the longitudinal modulus (Young's modulus) for flexible materials in considering large deformation behaviors is proposed. a new test method is based on the large deformation theory. Various kinds of flexible materials were tested by using this new idea. It is made clear that the new method is suitable for flexible materials. By the way, a measured modulus is the Secant modulus.

View full abstract

Recently, polymeric composite materials are widely used in engineering. We have to study on fracture mechanism of composite materials. This paper is concerned with the strength of Short Carbon Fibre Reinforced Polyimide (SCFR-PI) in room condition and high vacuum condition. The materials prepared for tests have three kinds of weight percent of carbon fibre 0wt%, 20wt% and 30wt%. Tension tests were performed by using dumbbell-type specimens of the composites. The relationship between the load P and loading point displacement δ is recorded in X-Y recorder. The tensile strength increase as increasing short carbon fibre weight percent in high vacuum condition as well as in room condition.

View full abstract

It was not permited "It coexists G54∿G59 with G92 in a numerical control program". But, it is permited by this study, just now. This method necessitates not user-macro, and it is least memory. And this study discovers relations between coolant system and cutting chips. It a avoids traps of coolant. Maximum coolant system bear in this paper at the moment.

View full abstract

We investigated a method to evaluate fatigue damage of steels without contact using laser speckle. In the earlier stage of fatigue, slipbands appear on a metal surface. Using this method, we are able to detect fatigue damage based on speckle pattern change due to surface property change caused by the slipbands. In this study, we investigate the relation between change of surface properties and speckle pattern during fatigue loading under constant stress amplitude. Surface roughness, frequency distribution and fractal dimension in surface profile diagrams were observed as fatigue damage increases. Parameter to evaluate fatigue damage was investigated.

View full abstract

As a fundamental study of a smart structure having the functions of crack prevention and crack closure, the temperature distributions on the surface of shape memory alloy (SMA) wires embedded in epoxy resin plates and heated by supplying electric current were investigated using an infrared camera and finite element method (FEM). The temperature distributions of SMA in the air and of specimen surface obtained using FEM were in good agreement with those obtained using the camera. The analytical results showed that the temperatures of the SMA surface embedded in the plates were less than half of those in the air.

View full abstract

Jones Matrix Image Fourier Polarimeter based on photoelasticity, is newly constructed to measure three optical parameters, i.e., phase differenceδ, azimuth angleθ and ellipticity angleε simultaneously. These three parameters are essential to analyze three dimensional stress field. Since the system and algorithm is still in developing stage, the author measures only two optical parameters, i.e., phase difference and azimuth angle in a two dimensional case. As the results, stress concentration near contact point is measured in high accuracy.

View full abstract

The impact perforation characteristics of CFRP and GFRP laminated composite plates are studied using a punch shear version of the split Hopkinson bar. Cross-ply and plain-weave CFRP and plain-weave GFRP plates are tested. The results for the perforation energy (or absorbed energy) and perforation resistance at low and high rates of loading are presented. It is shown that the perforation energy and the maximum shear load decrease with increasing displacement rate.

View full abstract

As the spline shafts have been used for various machines to transmit big power for the power-driven machine. Recently, data on the strength and the fracture is necessary. In the past, some studies on the spline shafts has been reported, but there is a few study torsional loading spline shafts having three-dimensional crack. In this study, we produce the spline shafts for epoxy resin and make various cracks. We used stress frozen method for the spline shafts under the state of torsional load. Photoelasticity and method of caustics are used to determine the deformation pattern of the tip of a cracks and to calculate stress intensity factor for fracture mechanics.

View full abstract

The phenomenon in that occurred temperature change when the object adiabatically receives elastic deformation is known from since a long time as a thermoelastic effect. Recently, the speedup of the temperature distribution measurement also advances by using the high-performance sensor and speedup of output signal processing of the sensor with improvement of thermometry measurement accuracy of the infrared thermography. Furthermore, in this study, to investigate the reliability of the data got by infrared ray stress image system, specimens of which the crack shape differed were made, and a stress concentration factor was obtained and was clarified using the infrared ray stress measurement system.

View full abstract

Several methods in displacement measurement using color images are discussed. In application of color images to fine search of digital image correlation using Newton-Raphson method, resolution and accuracy is improved slightly. However, it is shown that the use of color images is effective in coarse search. In another method, a new concept for fine search using color image and small subset, shows that the speed of data processing is greatly improved.

View full abstract

We previously developed a shape measurement method by a grating projection method using two reference planes. Because this method does not use lens center positions to obtain a point position on an object, the resultant shape has no distortion caused by the lens distortion. But the method has a problem that the accuracy is worse at intermediate positions between the two reference planes than near positions with the reference planes. In this paper, we propose a method using multiple reference planes to improve the accuracy. The accuracy of this method is good at all positions between the measurement range.

View full abstract

The tensile stress-strain response and cyclic stress-strain response were investigated for sintered silicon nitride ceramics at elevated temperatures, using the Ultra-High Temperature-Use extensometer which was developed in the authors' laboratory. The large inelastic strain, which is greatly dependent on stress rate, was produced under tensile and cyclic push-pull triangular wave loadings in this material at 1300℃. Furthermore, the creep strain was measured during stress hold period under the cyclic trapezoidal wave loading at 1300℃, which is larger on the tensile stress side than on the compressive side. It was found from these tests that inelastic strain is easier to generate under tensile loading than under compressive one in cyclic loading test ; the stress-inelastic strain hysteresis loop was characterized by the fatter shape on the tensile stress side than on the compressive stress side.

View full abstract

This report try to measure the dynamic strain applied cyclic load by using the piezo polymer film. Piezo polymer film has a property, which is no use amplifier to measure output voltage. So this research uses this to measure dynamic strain measurement. The experiments were carried out as follow ; piezo polymer film and strain gages are put on a test specimen and are applied dynamic cyclic load. The output voltage of a piezo polymer film are measured and compared to strain gage datas. An Experimental results are as follow. It is possible to measure the dynamic strain (applied cyclic load) by using piezo polymer film as well as strain gages.

View full abstract