The two-dimensional mesoscopic simulation method previously proposed by one of the authors for brittle microcracking solids is applied to the analysis of two-phase materials containing short fibers. Numerical results are presented to demonstrate validity of the proposed method. The effect of elastic property, slenderness, volume fraction, fiber-end cracks and orientation-distribution function of short fibers on overall elastic properties of two-phase materials has been studied. The microcracking behavior under tensile, shear and bending stress conditions accompanied by crack deflection, crack bridging and fiber pull-out has also been analyzed by the proposed mesoscopic simulation method.

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This paper describes the reliability-based optimization of a clamped laminated composite plate subject to buckling. A buckling failure is modeled as a series system consisting of eigen modes. Mode reliability is evaluated by FORM, where material constants and orientation angles of individual layers are treated as random variables as well as applied loads. The system reliability approximated by Ditlevsen's upper bound is maximized in terms of the ply orientation angles. Through numerical calculations, the reliability-based design is demonstrated to be important for the structural safety of the laminated plate in comparison with the deterministic buckling load maximization design.

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This paper deals with a critical condition of a buckling deformation caused by welding. The buckling of welded plate is affected by welding conditions, sizes of plate and material properties. The experiments for making clear the critical condition of buckling were done under changing welding conditions, such as sizes and welding processes. The heat input parameter is useful for arranging the critical condition of buckling from the many data which were given under changing plate thickness and heat input. The difference between GTAW and laser welding (LW) is dealt by using the net heat input given in the plate. New parameters derived from both a numerical analysis are useful in engineering sence.

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In this paper, we present the Green's functions of closed form for a steady state heat source in a semi-infinite transversely isotropic thermoelastic solid when the functions are expressed as the Cartesian coordinates. For thermal boundary conditions, both cases of the adiabatic condition and/or the zero temperature prescribed on the boundary plane are treated, and for the stress and the displacement boundary conditions the following three cases are treated : (1) the stress free condition on the boundary plane, (2) the fixed displacement condition on the boundary plane and (3) only the displacement u_z in the direction z vanishes on the boundary plane. To obtain the solutions of the problem the mirror reflection method is developed by using the solution of the infinite transversely isotropic thermoelastic solid reported in the previous paper. Furthermore, the closed form solutions in a semi-infinite isotropic thermoelastic solid are also shown. Finally, the numerical results for titanium in both cases of isotropy and transverse isotropy are given.

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In this work, stress concentration factors (SCFs) of a round bar with a circular-arc or V-shaped notch K_t are considered on the basis of exact solutions for special cases and accurate numerical results. First, for the limitting cases of deep and shallow notches, the body force method is used to calculate the SCFs ; then the formulas are obtained as K_td and K_ts. On the one hand, upon comparison of K_t and K_td, it is found that K_t is nearly equal to K_td if the notch is deep or blunt. On the other hand, if the notch is sharp or shallow, K_t is mainly controlled by K_ts and the notch depth. The notch shape is classified into several groups according to the notch radius and depth ; then, the least squares method is applied for calculation of K_t/K_td and K_t/K_ts. Finally, a set of convenient formulas useful for any shape of notch in a round test specimen are proposed. The formulas yield SCFs with less than 1% error for any shape of notch.

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This paper is concerned with the one-dimensional problem of thermal and thermal stress waves resulting from a suddenly applied laser-pulse heating in a finite plate, initially unstressed and at a constant temperature. The laser-pulse absorption is assumed to have Gaussian temporal profile with time, and to decay exponentially with depth. In this investigation, based on the generalized thermoelasticity, a coupling between thermal and mechanical fields is taken into account and the classical Fourie's law is also modified by adding a thermal relaxation term to the heat conduction equation to eliminate the paradox of the infinite thermal speed of the classical thermoelasticity. The numerical procedure employs the method of characteristics. The numerical calculations are carried out for two types of temperature-change input ; one is ramp-type heating on the boundary surface and the other is internal heat generation by laser-pulses. The influence of relaxation time τ₀ on thermal and thermal stress waves are found for two values of τ₀ and the results are shown in figures.

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This paper describes the effect of tool materials on the mechanism of atomic-scale indentation and cutting process of thin films in an atomic force microscope (AFM) by molecular dynamics simulation. The interatomic force between tool and thin film is assumed to be derived from the two-body interatomic potential using parameters based on the ab-initio molecular orbital calculation for a (Cr, Ni)-(C, Si)₆H₉ atom cluster. Molecular dynamics simulated the atomic-scale indentation and cutting process of chromium and nickel thin films using diamond, silicon and diamond-like carbon (DLC) pin tools. The indentation was formed by diamond and DLC pin tools, but was not formed by a silicon pin tool. Load-penetration depth curves showed the yield behavior in the indentation using diamond and DLC pin tools, but did not show that using a silicon pin tool. Elastic moduli of chromium and nickel thin films calculated from load-penetration depth curves were larger than experimental values. These are resulted from the effect of the surface energy of thin films on the elastic modulus. The machinability of the cutting process of thin films using a diamond pin tool was better than that using a silicon pin tool. The surface of thin films in nano-scale cutting experiments with AFM was similar to that in atomic-scale cutting by molecular dynamics simulation.

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The shape irregularities of graphite particles and ceramic aggregates are separatedly analysed by the different procedures in the last papers. In order to establish the common analytical procedure, the concept of fractal analysis was combined with Kaye's method and Fourier analysis in the present study. Three kinds of graphite particles in cast iron and two kinds of ceramic aggregates processed by different methods were here employed as samples. The shape irregularity of each object was actually analysed by the present method, and the excellent applicability was successfully confirmed. It is finally found that the shape irregularity of the actual aggregates is effectively evaluated by the combination of the microscopic and macroscopic aspects of the shape irregularity.

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The purpose of the present research is to analyze how the introduction of a fracture criterion affects the truncation strength as well as truncation characteristics in proof testing of ceramic materials. When a fracture criterion, e.g., K_I=K_IC (K_I ; the stress intensity, K_IC ; the fracture toughness), is introduced to the analysis, a corresponding truncated strength necessarily exists and it is only the function of unloading velocity. On the other hand, when the truncation problem is analyzed being based on surviving conditions, no clear truncation can be found. As a consequence, the introduction of a fracture criterion, in itself, brings analytical truncation in proof tests ; the truncation strength and its characteristics depend upon adopted fracture criteria.

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The failure process of the Si-Ti-C-O fiber bonded ceramic material was investigated under tensile and flexural loading conditions. Tensile and three-point bending tests showed the significant difference between the failure modes caused under the two types of loading. The tensile failure process was calculated using a Monte-Carlo simulation method based on a shear-lag model. The calculation successfully predicted the distribution of the tensile strength of the Si-Ti-C-O fiber bonded ceramic material. The finite element method was employed for calculating the failure process of the Si-Ti-C-O fiber bonded ceramic material under three-point bend loading, where the statistic properties of the tensile strength obtained from the above Monte-Carlo simulation was taken into account. The calculated load-deflection response and failure process were in quite good agreement with the experimental data. Furthermore, the discrepancy in the distribution of the strength was calculated under tensile and three-point bend loading conditions ; the larger Weibull shape parameter and the smaller average value in the tensile strength than in the flexural strength were successfully assessed through the calculations. Finally, the effect of the interlaminar shear strength on the strength and its distribution was discussed under bend loading.

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Dynamic stress intensity factor K_ID and crack velocity a were determined using single-edgecracked tensile specimens of PMMA and Homalite-100. To study unloading behavior of the material, load P applied to the specimen was also evaluated as a function of time t. Unloading rate P, the time derivative of P, was determined to correlate with K_ID and a. The findings showed that the change in P was qualitatively in accord with the change in K_ID or a. However, there existed slight differences among the values of t giving peak values of P, K_ID and a, so that their order was a, P and K_ID.

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An investigation has been carried out concerning the influence of electron radiation on tensile and impact fracture as well as compression after impact (CAI) behavior of carbon fiber reinforced thermoplastic matrix composite (AS-4/PEEK), having a quasi-isotropic stacking sequence of [0°/±45°/90°]_2s. Specimens were irradiated in air with electron energy of 1.5 MeV, resulting in total absorbed dose of 1000 Mrad. The tensile strength was higher in irradiated specimens than nonirradiated ones. The impact tests were carried out by a falling weight tester. Impact induced delamination was observed with a scanning acoustic microscope (SAM). The delamination area was evaluated by the subtraction method. Impact-load-induced delamination area was increased by electron radiation. However, no influence of electron radiation on CAI strength was observed. The fracture surface was closely examined using a scanning electron microscope, and the fracture mechanisms were discussed.

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Numerical simulations are effective approach for the safety design of machines and structures subjected to impact loading and the investigation of impact phenomena. Dynamic mechanical properties which accurately model the response of materials to impact loading are necessary for such numerical simulations. In this research, the equation of state and failure criteria are measured by plate impact testing, and then the accuracy of these measured dynamic mechanical properties is evaluated based on numerical simulation results. Followings are useful information obtained. (1) The equation of state and failure criteria measured by plate impact testing are sufficiently accurate for numerical simulations. (2) Pure W which is the brittle metal, follows stress-dependent failure criterion. (3) W-Ni-Fe alloys which are the ductile metals, follow time-dependent failure criterion. (4) W-Ni-Fe alloy has the lower critical value for spall failure than its matrix phase. (5) The failure strains of W-Ni-Fe alloys depend on the state of stress.

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A method of measuring mass density and elastic moduli near surface has been developed. In this method, the velocities of the leaky creeping, surface SV and leaky Rayleigh waves were measured as well as the attenuation of the last wave due to the energy leak into liquid with a focused PVDF ultrasonic transducer and digital measurement system. The density of a solid was determined analytically with the Victorov equation on longitudinal and transverse wave velocities of the solid, the velocity and the attenuation of leaky Rayleigh wave, and the properties of the liquid. The accuracy of measured densities of fused quartz and aluminum alloy is within 10%.

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In this paper, the effect of average graphite diameter on low cycle fatigue life was investigated in spheroidal graphite cast irons involving the same volume of graphite. Three kinds of average graphite diameter D_m were used (D_m=16.5μm ; SGD, D_m=31.1μm ; MGD, D_m=42.7μm ; LGD). Low cycle fatigue tests were carried out using cylindrical specimens. As a result, it was clear that the difference of fatigue life was small as comparison with the difference of average graphite diameter. That is, the fatigue life in SGD is 1.5 times as long as that in other cast irons, though average graphite diameter in SGD is about one third smaller than that in LGD. These results can be explained by three factors controlling fatigue life that we proposed. The cause of increase of fatigue life in SGD is that the crack initiation length in SGD is shorter than that in other cast irons. The crack initiation length depends on the microshrinkage size or dross size, not depending on average graphite diameter.

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The diamond film by CVD method offers outstanding impact, fatigue and wear resistance relative to conventional coating film, ex., TiC, TiN film. For that reason, the diamond film on substrate attracts a large expectation in mechanical industry. In proceeding paper, we reported relationship between fatigue strength and microstructure of diamond coated WC-Co alloys with various CVD conditions. However, we have not investigated at the effect of film thickness on fatigue strength and another mechanical properties of this material. In this study, the mechanical properties of diamond film coated WC-Co alloys having a few thickness was discussed on the basis of bending fatigue test. The main results obtained in this work are as follows : (1) The fatigue property of diamond coated WC-Co alloy was essentially depended on the thickness of film. However, the influence of microstructures, i.e., phase transformation of Co phases near substrate surface and process of film growth appeared for the fatigue strength of this materials at film got thin. (2) In the finite element method, FEM, analysis, the stress concentration part differed by Young's modulus of thin film. In case of high Young's modulus, the stress concentration was occuring at surface in material, it had be moving into a interface with decreasing Young's modulus of the film.

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With a gas carburizing treatment processed to pearlitic ductile cast iron (CPDI), the investigations were carried out about its high cycle fatigue strength and abrasive wear resistance. The high cycle fatigue strength were evaluated by rotating bending fatigue tests, and the fatigue strength was improved about 20 MPa greater than virgin test pieces not-carburized (PDI). The crack initiating point and fracture is from irregular graphites of surface or from microdefects in casting, which PDI and CPDI specimens were not in an inner type fracture. Furthermore, a good result was obtained in the abrasive wear resistance test than in that of austempered ductile cast iron (ADI). Those were expressed by the difference of matrix structures. Its matrix structure of CPDI is transformed a martensite structure from SEM observation.

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The complex deterioration of stress and heat on fatigue reliability was investigated on carbonfiber-reinforced PEEK and PA 66. In particular, this study was focused on the estimation of fatigue life by Miner's law under two-step loading above glass transition temperature. The main results were as follows. (1) Under two-step loading, the damage of PEEK materials could not accumulate, that is, the estimation of fatigue life by Miner's law was not applied to PEEK materials. On the other side, the damage of PA 66 materials could accumulate and the estimation of fatigue life by Miner's law was applied to PA 66 materials. (2) From fractography using SEM (Scanning Electron Microscope) and temperature rising, it was recognized that PEEK materials were more remarkably influenced of stress history of first-stress than PA 66 materials. (3) The mesocrack on surface of specimen of PEEK materials was small compared with that of PA 66 materials. Therefore it could be understood that the estimation of fatigue life by Miner's law was not applied to PEEK materials because of existence of stress relaxation by initiation of minute mesocrack during the fatigue process.

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Thin-walled cylindrical low alloy steel specimens were thermally fatigued in a pressurized autoclave. Since high and low temperature water was alternately supplied into the autoclave, the specimens were subjected to homogeneous thermal stress through the wall thickness. The thermal fatigue life was defined as the number of cycles to crack penetration to the inside of the cylindrical specimen. The thermal fatigue strength was compared with the mechanical fatigue strength performed in air and in high temperature water. If taking account of the Higuchi-Iida formula, which considers the effects of strain rate, dissolved oxygen concentration and water temperature on the fatigue life, the thermal fatigue lives of low alloy steel were found to coincide with the mechanical fatigue lives.

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Dynamic thermal stresses and crack growth behavior produced by single and repeated thermal shocks were studied on cermets containing a different quantity of TiN. Thermal shock was applied to specimens using a quenching method. Using the precracked specimen, crack growth behavior was investigated under the repeated thermal shock tests. It was clarified that the crack growth resistance of cermets containing a smaller quantity of TiN was lower than that of cermets containing a larger quantity of TiN in the high stress intensity factor region. This difference was discussed from the viewpoint of their microstructures.

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A set of simplified equations to directly calculate the stress intensity factor of an arbitrarily located circumferential crack in a finite length cylinder, under axisymmetric bending loads, were presented. They were derived based on the simplified method previously reported by the authors. The effects that the cylinder length and the crack location have on the value were illustrated by using the equations. The results indicated the necessity to pay attention on the effects of the cylinder length and the crack location, in evaluating the stress intensity factor of a circumferentially cracked cylinder, under symmetrical bending.

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The effect of the specimen thickness and the crack length on the fracture toughness are investigated for three point bend (3PB) specimen and CCT specimen. In 3PB specimen the J_IC^ap value increases with decreasing the crack length and the clear thickness effect dose not exist for fracture toughness value. The three dimensional finite element analysis are conducted for these specimens. The Q factor decreases with decreasing the crack length or the specimen thickness in 3PB specimen. The Q factor of CCT specimen is lower than that of 3PB specimen. The relation between the Q factor and J_IC^ap value is examined. The J_IC^ap value increases with decreasing the Q factor when the crack length decreases in 3PB specimen. The dimple fracture surfaces of 3PB, CCT and CCB (center cracked bend) specimens are observed by SEM. The dimple diameter of CCB specimen is the smallest and the diameter of CCT specimen is smaller than that of 3PB specimen.

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The central burst defect, also called chevron crack, in the extruded product worked under plane strain is analyzed. To the prediction of central bursting the criterion based on plastic instability is used. It satisfies the sufficient condition s_iε_i=0 for multiplicity of solution, which is derived from the consideration based on its necessary condition Δs_iΔε_i=0, where s_i denotes the nominal stress rate, and Δ shows the difference of any two multiple solutions. The criterion gives the limit strain identical to the one derived from Swift's criterion under plane stress condition, but its concept is quite different with Swift's. Stress and strain in the specimen are evaluated using FEM. The measure y_M to present the occurrence of central bursting is proposed and it is calculated using the stress and strain on the central line of the product. When y_M<0, the bursting occurs. The value of y_M is shown in the range of combination of cone angle and reduction. It is found that the zone denoting the central burst is very similar to the one obtained by slip line method.

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The dynamic strength of an adhesively bonded single lap joint was investigated analytically and experimentally. Stress distributions and the variation of stress with time in the joint were analyzed by FEM. The dynamic strength of the joint under impact loading was calculated by applying failure criteria to the stress distribution. The strength of the joint was measured experimentally using a drop-weight testing machine. The analytical prediction of the strength agreed to the experimental result. The dynamic strength of the joints increases with increasing lap length. The effects of increasing lap length on strength decrease when the lap length is large.

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The friction welding for copper and aluminum is useful to minimize the diffusion thickness at the interface between copper and aluminium. The minimization of diffusion thickness is required for maintaining the joint strength. However, it is generally difficult to maintain the joint strength. Because brittle intermetallic compounds are necessarily formed at the friction weld interface between copper and aluminium. The improvement techniques on joint strength characteristics have not fully been clarified. In this study, stress singularities at the intersection of free surfaces and the interface between copper and aluminium were investigated using finite element analysis. It was informed that the no free-edge stress singularities existed below an apex angle of 59° and between angles of 98° and 126°. In this experiment, copper and aluminium friction welded joints were fabricated as to minimize (>1μm) the welding condition of the diffusion thickness at the interface between copper and aluminium. It was confirmed that the good tensile strength could be observed in all cases tested. However, the Charpy impact energy became comparatively low in case of an apex angle of 90°, and showed a remarkable high impact energy can be obtained in case of no free edge stress singulalities.

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A hydraulic machine is usually composed of many components. Oil seal plugs, which are used for preventing oil leakage, are one of the most important machine elements among them. Currently, it is sometimes reported that with increase of operating oil pressure, leakage occurs from the regions where oil seal plugs are attached. The configuration of oil seal plug is quite similar to that of ordinary hexagon bolt, except that the grip length and the height of head are particularly small. It is, therefore, anticipated that the specific shape of oil seal plug may yield characteristics significantly different from those of hexagon bolts. Despite its importance, however, it seems likely that mechanical behaviors of oil seal plug have not been investigated so far. In this paper, such fundamental characteristics of oil seal plug as the amounts of tightening torque required for desired clamping force and distributions of contact pressure relating to seal performance are analyzed using finite element method which deals with multi-body elastic contact problem. It is also examined how the rapid rising of oil pressure applied affects the variations of contact pressure with time and whether it might cause the oil leakage, using one-dimensional spring element together with the integration scheme proposed by Newmark.

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Geometry of pipe flange is standardized by JIS in detail and it almost follows ISO. However, the dimensions thus specified are not necessarily determined on the basis of estimating the mechanical behaviors of pipe flanges. It is, therefore, extremely important to systematically examine the mechanical properties for making more rational standards. In this study, as a first stage of this purpose, a numerical approach, which can efficiently analyze fundamental mechanical characteristics of pipe flange using FEM as a three-dimensional elastic contact problem, is proposed, and the effects of such important factors as flange interface geometry, numbers of bolts, thickness of flange and nominal diameter of clamping bolts are discussed. The analytical objects are pipe flanges specified in JIS B 2238. The validity of the numerical method proposed here is ascertained by experiment, where pipe flanges are subjected to axial tension and internal pressure, and experimental results of variations in tensile stress of clamping bolts are compared with those by FEM.

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With the use of a special contact element by which the frictional contact behavior between leaves is systematically expressed in combination with beam finite elements, the load-deflection hysteresis has been analyzed by a finite element method for two kinds of multi-leaf springs i.e., conventional and progressive types. The load-deflection curve obtained by FEM is neally linear for the conventional type, whereas the curve is highly nonlinear for the progressive one. The numerical results are very close to the experiments in both types of leaf springs. In particular, the proposed method can predict well the hysteresis behavior of the spring. Thus, the proposed FEM analysis using beam elements can be used for designing various types of multi-leaf springs.

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In this paper, Genetic Algorithm (GA) to solve the problem which determines the optimum postures of an adaptive truss structure is proposed. It is difficult to obtain a global solution of posture determination problem on adaptive truss containing many adjustable elements using traditional methods. It is said that the global solution can be found with higher probability by GA. The validity of GA is shown numerically through the application to the configuration control of a variable geometry truss containing ten adjustable elements. This paper particularly discusses the problem about the case that the position of the load is constrained.

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External fixation technique is a convenient treatment for wide clinical use such as bone fracture. In this treatment, it is important to make decision when the external fixation device is detached and the patient start rehabilitation, in order to achieve early healing. Evaluation techniques for bone healing level can offer useful suggestions to the doctor making decision. Thus, we develop an evaluation method of mechanical properties of callus on bone fracture fixed by external fixator. In the method, strains are measured using strain gauges which are attached to some parts of the fixator fixing bone fracture with a certain loading. The strains are inputted to a mathematical or computational model of the fixator and bone, then the callus properties are evaluated inversely. We consider a case of transverse plane fracture of human tibia with external fixator, and apply the evaluation method using an experimental model, a finite element model and a model based on beam theory. Efficiency of the proposed method is discussed from the results.

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Epidemiological studies have suggested that because of their frequent exposure to mechanical vibration, bus and truck drivers are especially susceptible to disc disorders. It has been reported that drivers of such vehicles are subjected to low-frequency vibration up to 6 Hz. The intervertebral disc regulates the viscoelastic properties of spinal segments. It is thought that the intradiscal pressure plays an important role in the mechanical response of a spinal segment to vibrations. While previous studies have made direct in vivo measurements of intradiscal pressure under static conditions, no data has been reported on intradiscal pressure response to vibration loading under either in vivo or ex vivo conditions. The present study was undertaken to measure the intradiscal pressure response to cyclic loading in a physiological saline solution simulating in vivo conditions. The effects of mean load, amplitude and frequency of cyclic loading on the intradiscal pressure response were investigated using calf lumbar spinal segments. The experiment employed mean loads of 20, 60, and 100 N with amplitudes of 10, 15, and 20 N and compared the low-frequency effects of 0.05, 0.5 and 5 Hz. The mean load was applied for 1 hour prior to the cyclic loading test in order to take the equilibrium intradiscal pressure into account. The relationships between load versus displacement. and load versus intradiscal pressure were found to be affected by the mean load and the frequency of cyclic loading.

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