Rotating bending fatigue tests were carried out for Ni base super alloy Inconel 718 at room temperature and elevated temperatures of 300°C, 500°C and 600°C in order to investigate the effect of surface oxidation at the elevated temperatures on the fatigue crack initiation and its early growth process. The fatigue strength was higher at the elevated temperatures than at room temperature when stress levels were low. This phenomenon was caused from that the growth of a crack smaller than the size of a few grains was suppresed at the elevated temperatures, though the growth of a larger crack was accelerated. The main reason for the suppression of the early growth of a small crack was a formation of oxide films on the specimen surface at the elevated temperatures.

View full abstract

Creep-fatigue damage at high-temperature on SUS 304 austenitic stainless steel is characterized by nucleation and growth of creep cavities on grain boundaries. We had carried out the continuous observation of the cavity growth under creep-fatigue condition and clarified its mechanisms. In this study, in order to clarify distribution properties of cavity nucleation under the creep-fatigue condition, creep-fatigue tests with CP waveform were conducted on SUS 304 stainless steel and the failure specimens were examined by scanning electron microscope. As a result, it was found that the cavitated grain boundaries exsisted almost normal to a stress axis regardless of tensile strain-rate and the volumetric density of damaged grain boundary increased monotonously with the inelastic strain range. The volumetric density of damaged grain boundary, whchi is expressed as a function of time-dependent strain, was proposed based on test results of CP waveform condition and the volumetric density under strain-hold waveform condition could be predicted with good accuracy.

View full abstract

Fatigue tests have been conducted on a duplex stainless steel, SUS 329 J 4 L, and an austenitic stainless steel, SUS 304, in order to clarify the influence of microstructure on crack initiation and early growth. Crack initiation of SUS 329 J 4 L occurred principally at austenite phase in room air and in 3% NaCl solution. In SUS 304, cracks were generated within austenite phase and at austenite grain boundary in room air and in 3% NaCl solution, respectively. The early crack growth behavior in the microstructurally small crack region was influenced by the phase change at crack front for SUS 329 J 4 L, and the crack hesitated at the phase boundary. Also in SUS 304 the fluctuations in crack growth rate were found at austenite grain boundaries, which were less remarkable in 3%NaCl solution than in room air. Early crack growth immediately after the initiation was enhanced in 3% NaCl solution for both stainless steels.

View full abstract

Fatigue crack growth tests were carried out on an annealed, pre-strained or quenched-and-tempered 0.45% carbon steel under rotating bending or reversed torsion. Crack opening displacement ranges (ΔCOD's) along a crack were measured in the neighborhood of the crack tip from the SEM photographs of the plastic replicas taken under the maximum and minimum stresses. The ΔCOD distributions under the same crack growth rate are almost the same in bending fatigue and torsional fatigue. Therefore, the ΔCOD distribution near a crack tip can be considered as a fundamental factor controlling consistently the crack growth rate, independent of loading conditions. The ΔCOD distribution under the same crack growth rate is the smallest in quenched-and-tempered steel, the middle in pre-strained steel and the largest in annealed steel. This suggests that the higher yield stress results in the smaller crack opening displacement under the condition of the same crack growth rate.

View full abstract

In order to clarify the fatigue behavior of Ni-base superalloy Udimet 720Li, four point bending fatigue tests of plain specimens were carried out at room temperature. Initiation and propagation behavior of major cracks was observed by plastic replica technique. At extremely early stages of cycling, cracking of TiN particles was generated. Fatigue cracks were always initiated from cracked TiN particles. The growth rate of a small crack can be determined by a term σⁿ_al, not by ΔK. The n is a material constant and was 3.6. On the other hand, the statistical characteristics of fatigue behavior were investigated to quantify the scatter in fatigue damage. Namely, the distribution for crack length, microcrack growth life and crack growth rate were analyzed by assuming a Weibull distribution. Moreover, the cracking time and cracking orientation of all the TiN particles were measured. The measurements suggested that the TiN particle were fractured by the principal tensile stress which is related to the variation in local strain around a particle.

View full abstract

Fatigue tests on solder joints of surface-mounted type electronic package models were carried out at different temperatures, cycling frequencies and controlled displacement amplitudes in order to examine the crack initiation life Nc, crack extension path, crack extension rate da/dN and crack extension life. The crack initiation life (Nc)_cal of solder joints was estimated using maximum equivalent inelastic strain calculated by three-dimensional elasto-inelastic finite element method (3D-FEM). The ratios Nc/(Nc)_cal were found 2.4∼9.8. Further, 2D-FEM crack extension analyses were performed to examine crack extension behaviors. The FEM analyses showed that crack extension path and rate were controlled by maximum opening stress range at crack tip, Δσ_θmax, in plastic zone under rather complicated stress tensor fields. Experimentally obtained crack extension rate was found to be related to Δσ_θmax in FEM analysis as da/dN=β [Δσ<θmax>]^α, with α=2.0 and β=2.65×10^-10mm⁵/N² being determined independently of the test conditions. The calculated values of crack extension life by the FEM analysis using the above equation were in good agreement with the experimental ones.

View full abstract

In this paper, a singular integral equation method is applied to calculate the distribution of stress intensity factor along crack front of two interacting 3-D semi-elliptial coplanar surface cracks. The stress field induced by the body force doublet in a semi-infinite body is used as the fundamental solution. Then, the problem is formulated as a system of integral equations with singularities of the form γ^-3. In the numerical calculation, the unknown density of body force doublet is approximated by the product of fundamental density function and polynomial. The results show that the present method yields smooth variations of stress intensity factors along the crack front very accurately for various geometrical conditions.

View full abstract

Experiments have been made to study the influence of loading frequency on fatigue crack propagation rate (FCPR) in 6/4 Brass plate. The experiments have been carried out in air and at room temperature in accordance with ASTM E 647 91. Compact tension (CT) specimens with an orientation T-L and 2.8mm in thickness were tested under three frequencies (2.5, 5, 8 Hz) of sine waveform tension-tension load. It was found that the FCPR increases with the increase of frequency under the condition that stress intensity factor range, ΔK, is between 13 and 31 MPa·m^1/2 in the case of R=0.11. And in the case of R=0.02, the FCPR decreases with the increase of frequency under the condition that ΔK is between 15 and 38 MPa·m^1/2. The results were testified by scanning electron-microscope (SEM) fractographical studies.

View full abstract

The interference effects of stress intensity factor K₁ in the case of a block with three cracks being heat-loaded transiently from the crack side are quantitatively investigated, using the crack length and the distance between the cracks as parameters, by caustic method. The results obtained are as follows. (a) The value K₁ increases abruptly at the outset of the contact of the hot plate, reaching the maximum K_1max at a certain time, and then gradually decreases. (b) The value K_1max in case of three cracks becomes smaller than that of a single crack. (c) The value K_1max increases almost linearly as the distance between the cracks becomes larger when the crack length is constant.

View full abstract

Carbon/Carbon (C/C) composites have attractive mechanical properties such as superior specific strength and high elastic modulus at high temperature exceeding 2000°C in an inert atmosphere. However, mainly due to lack of knowledge of design criteria, C/C composites have not been used in primary heat resistant structures. For example, almost no unified explanation has been given about fracture behavior of C/C composites. The objective of this paper is to examine whether the linear elastic fracture mechanics (LEFM) is able to be applied to a C/C composite. The LEFM is tried to apply to fracture behavior in tensile tests of the double-edge-notched and compact tension specimens and in the four-point bending test of the single-edge-notched specimens. It was found that the results of three kinds of fracture tests can be consistently and rationally explained by the LEFM concept with the aid of R-curve behavior if the pre-crack length is long enough to be able to neglect the notch tip radius. From fractographic observation it was found that R-curve behavior of the C/C composite was mainly attributed to the fiber-bridging effect near the notch tip.

View full abstract

In order to evaluate the cryogenic fracture toughness and the adiabatic heating of thick section weldment in forged JN1 type austenitic stainless steel plate with nickel base filler metals for fusion reactor magnets of the next generation, elastic-plastic fracture toughness (J_IC) testing was performed with IT compact tension specimens at liquid helium temperature (4K). Testing was conducted in accordance with ASTM standard E813-89 for determining J_IC using the unloading compliance technique to monitor crack growth. Au/0.07% Fe-Chromel thermocouples were used to measure the temperature rise near the crack tip. The effects of specimen location and nitrogen content on J_IC are examined.

View full abstract

A simplified equation to directly calculate the stress intensity factor of an arbitrarily located circumferential crack in a cylinder under radial temperature distribution was theoretically derived, based on the theory of cylindrical shell and compliance. The effects of the cylinder length and the crack position on the stress intensity factor can be evaluated by the equation. From the numerical illustration, it was shown that the stress intensity factor of a short cylinder is smaller than that of a long one, if the temperature distribution and the cylinder configuration are the same. In addition, in case the crack is located near the cylinder edge, the stress intensity factor became smaller than that in case the crack is located at the middle point of the cylinder length.

View full abstract

Two conventional creep damage rules, the life fraction rule and the strain fraction rule, were compared with experiments of SUS 304 steel obtained from both the constant stress creep test and the constant load one. It is shown that the life fraction rule overestimates most of the experiments when the value of creep damage constant D_c is equal to the unity, and that the experiments are distributed with a scatter band around the strain fraction rule. It is also recognized that the cumulative creep life depends on loading order of the applied stress, i. e. creep tests including a decrease step of the stress during creep has longer creep lives than ones including an increase step of the stress.

View full abstract

High temperature creep damage is caused by voids generated at grain boundary at elevated temperatures. Creep void formation is greatly influenced by stress state as well as metallurgical factors. In this paper, the notched component of 2.25 Cr-1 Mo steel, of which microstructure was prepared to be characteristic of the heat-affected zone in the welded joint by heat treatments, were creep tested at 630°C, Then the creep void density and total length of creep voids to grain boundary length fraction were measured in the area of 1×1mm² settled around the notch root in association with the inclined angle of grain boundary against loading axis and the stress state around the root of notch, which was calculated using inelastic finite element method. Consequently, it was found that creep void tends to initiate much more at the grain boundary more perpendicular to loading axis and with the greater normal stress, and seems to originate and grow almost independent of the shear stress on the grain boundary, The much easier initiation and growth of creep voids at welded joint and/or notch roots are considered to be due to the much higher normal stress to the grain boundary developed under the greater stress triaxiality.

View full abstract

In the present study, the plastic stress singularity occurring in a V-notch is studied. A practical method is introduced to solve homogeneous differential equations obtained in the analysis. The results so obtained appear to be quite satisfactory. Based on the numerical results, the effects of the notch geometry and the hardening power on the singularity are discussed. In particular, an approximate expression is presented for the evaluation of the plastic stress singularity.

View full abstract

When an infinite elastic medium with a spherical inclusion is suddenly subjected to an instantaneous heat source, a stress weve occurs at the interface of spherical inclusion the moment thermal impact is applied. The stress wave in an inclusion proceeds radially inward to the center of the inclusion. The wave may accumulate at the center and give rise to very large stress magnitudes, even though the initial thermal stress is relatively small. This phenomenon is called the stress-focusing effect. The stress wave in an infinite medium proceeds radially to infinity. In this paper, we analyze this phenomenon theoretically. The results give a clear indieation of the mechanism of thermal shock in the infinite medium with a spherical inclusion.

View full abstract

Recently, surface mount technology (SMT) in an electronic packaging is playing a leading role compared to the plated-through-hole technology. SMT allows to place more electric components on a printed circuit board. Many investigations on mechanical and thermal properties of solder have been conducted numerically and experimentally, since the electric components are mounted by only soldering on the board. It is hard to examine the failure of electric components in experiment, since the size of solder joint is relatively small. In this case, a simulation technology is very useful for evaluating the reliability of SMT solder joint. In the present paper, before performing the stress analysis of SMT joints, the shape of solder joint was first determined numerically by solving a multiregion problem considering the surface tension of molten solder and the gravity. The joint profile changing from an initial profile to an equilibrium one was simulated by using a finite difference approximation for time and the boundary element method for domain. The scheme for remeshing technique which is combined a cubic spline and a base spline to interpolate nodes on the free surface is presented in this paper. After that, a nonlinear and thermo-elasto-plastic stress analysis using MARC was performed to study the deformation behavior of solder joints subjected to a cyclic thermal loading. Profile data of SMT solder joint employed for finite element analysis were used the equilibrium profile calculated by BEM. It was shown that a thermal stress concentration occurred in joints with a large quantity of solder and with a small gap between the chip and the base plate. Finally, it was shown that the shape of SMT solder for improving the reliability has equally a little quantity of solder at both sides, a little quantity of solder at upper fillets and a small height between the chip and the base plate.

View full abstract

In this paper, a method of evaluation of static strength by the application of mixed mode stress intensity factors of angular corner is considered. Recently, it has been found that the stress field near a corner of jointed dissimilar materials is expressed as a sum of the symmetric state with a singularity of 1/γ^1-λ₁ and the skew symmetric state with a stress singularity of 1/γ^1-λ₂. In this respect, the fracture tests are carried out on the plane specimens of acrylic resin having a single sharp notch. Different artificial notches are introduced into the specimens with varying the opening and inclination angles. The fracture criterion for different shaped notch is discussed on the basis of the stress distribution near the notch. The usefullness of K_{1, λ1} and K_{11, λ2} for the evaluation of static strength under mixed mode fracture is confirmed through the experiment.

View full abstract

In this paper, a FEM analysis is developed on the basis of Ambartsumyan's plate theory. This method is simple and useful for calculating interlaminar shear stress in thin laminated plates, because Ambartsumyan's theory can consider the effect of transverse shear stress and deformation. The displacement functions in this FEM are defined to satisfy these conditions and the Lagrange multiplier method can satisfy the continuity of interlaminar shear stress. However this theory assume that the plate thickness is thin, so the application limit of the plate thickness is proposed. Also the validity of numerical results with this method is discussed in comparison with previous results.

View full abstract

In considering the mechanical behabior of polycrystalline metal, it is very important to know the elastic incompatible stresses near the grain boundary, which occur by the difference of crystal directions between neighboring crystals. Especially, the stress analysis around the triple subgrain boundary is meaningfull, where the incompatible stress becomes large and the micro crack occurs and expands. In this paper, we analyze the stress distribution around the triple subgrain boundary by the use of dislocation model in FEM. This dislocation model is based on that the dislocation can be considered as a dislocation of a displacement. Also, each crystal is considered as an isotropic or anisotropic elastic solid.

View full abstract

In this paper, for the sake of prediction of caustic experiments, explanation and verification of experimental results, a new numerical method based on the finite element method, which can directly simulate the caustic patterns, is presented. Based on this new idea, the program for directly determining the gradient solution from the 2 dimensional displacement solution is presented. It is also proven to be necessary for only 8 or 12 node isoparametric element to apply this new method to the 2 dimensional problem. For verifying the accuracy of this method, the simulations of 4 point bending problem and concentrated load problem are performed. The simulated results have good agreement with the theoretical values. As the applied examples, the simulation is carried out for the plate specimen with a single edge crack, or double edge crack, or a short single edge crack under mode I condition. The changes of caustic image under the influence of the interferometry between cracks and the influence of the boundary are given.

View full abstract

Raman spectroscopy was used to study the stress relaxation in broken fibers in long fiber reinforced unidirectional composites. A single-fiber model composite consisting of a high modulus PAN carbon fiber and an epoxy resin matrix was subjected to constant overall strain, which was applied to induce a fiber break. The stress profile in the broken fiber was then monitored for 1000 hours by determining fiber stress through the stress dependence of the 2700cm^-1 Raman band peak position. Interfacial shear stress was also evaluated from the axial distribution of fiber stress. It was thus observed that the stress profile in the broken fiber changed a little after 1000 hours whereas the normal stress in the matrix relaxed to about a quarter of the initial value in about 200 hours. It is discussed that this result, which does not agree with the linear viscoelastic analysis reported, is attributable to the matrix plasticity and/or interfacial shear sliding near the fiber break.

View full abstract

The Martin's method, which is used to obtain the internal displacement of atomic systems and elastic constants, is applied to the Tersoff potential. The potential is modified to provide a good description of the high-temperature elastic properties of silicon. The elastic constants of crystalline silicon were investigated at both low and high temperatures. Results were verified by the statistical thermodynamic method'Fluctuation formula'. It was found that elastic constant values and the influence of the internal displacement are valid. However at high temperatures, the gap becomes larger owing to the thermal fluctuation. Since the convergence of the Martin's method is faster by about two orders, it is the more effective method. It was also found that the fluctuation term includes the effects of the internal displacement and thermal fluctuation.

View full abstract

The elastic properties of thin silicon films were investigated using the Martin's method, which is useful for obtaining the internal displacement and elastic constants. It was found that a 1.6 nm thin film becomes very soft compared with the bulk value. Newly defined atomic elastic constants showed that the internal displacement of the atoms within 2-3 surface layers reduces elastic constants near the surface and throughout the thin film. The films with a thickness of about 20 nm or less become soft due to the effect of the internal displacement of the surface atoms. Thin films with a thickness of 2 nm or less become soft due to the the change in the atomic bonding properties. The macro-micro boundary is about 10 nm in thickness if a 10% decrease in elastic constants is defined as the boundary.

View full abstract

In this paper, a new method is suggested for the nondestructive measurement of elastic moduli, density and thickness of film by the dispersion curves of the two kinds of surface waves. It is confirmed that the surface wave velocities (Sezawa mode and Rayleigh mode) for gold on fused quartz substrate are simultaneously determined from the reflectance function obtained by the measured complex V (z) curve. The dispersion curves of two surface waves for thin film with the thickness of approximately 0.2 μm are measured in the frequency from 240 to 400 MHz with 20 MHz incremest. The elastic moduli, density and thickness of film were simultaneously identified by computer fitting to two measured dispersion curves using the direct search method. The elastic moduli and density of film were about 10% and 7% less than those of bulk, respectively. The film thickness determined by this method is in good agreement with that observed by scanning electron microscope.

View full abstract

The authors propose a new method for simultaneous determination of both fringe order and principal direction of birefringence in practical photoviscoelastic analysis using a white incident light with a set of the three primary colors. When using this method, not only fringe order but principal birefringence direction are successfully and easily determined from a single color image through a plane polariscope. Utilizing this method together with photoviscoelastic constitutive equations, timedependent principal stress and strain difference, also their directions are obtained. In this paper, the fundamental of the tricolor photoviscoelastic technique is described briefly, then a successful application of the method to the analysis of an example of viscoelastic problem is shown.

View full abstract

A study on the deformation behavior and elastic constants for sintered high chromium steel with uniformly dispersed titanium nitride particles was carried out. The influence of the porosity and the second phase on overall Young's modulus, the phase stress and the X-ray elastic constants was investigated. The experimental results were compared to the theoretical model developed by Taya and Chou. As a result, the following conclusions were obtained ; The increase of the second phase decreases the phase stress and the X-ray elastic constants of each phases. The increase of the porosity increases the phase stress and the X-ray elastic constants. The theoretical model proposed by Taya and Chou agreed to the experimental results in case of the volume fraction of TiN less than about 14%. The limits where the theory and the experiment agree each other were different between diffraction lines such as 211 and 310 diffractions, as well as between overall Young's modulus and the X-ray data such as the phase stress and the X-ray elastic constants.

View full abstract

Elastic constants of carbon fiber reinforced plastic (CFRP) composites that absorbed moisture were measured quantitatively and non-destructively by ultrasonic waves. The waves were transmitted through a moisture-induced unidirectional CFRP laminate which was immersed in water. By measuring phase velocities of transmitted waves for various incident angles, a full set of stiffness matrix components could be obtained. The moisture absorption was carried out in 60°C hot water before specimens were saturated with water. As the moisture content increased, all the elastic moduli decreased and Poisson's ratio increased. Particularly in-plane shear modulus decreased most. These changes show that the matrix resin was softened by moisture absorption. Furthermore, these changes were confirmed to be reversible through the measurement after moisture desorption.

View full abstract

Dynamic elastic-plastic deformation of pin-ended circular arches has been numerically analyzed with a discrete model composed of rigid bars connected with nonlinear springs. Equations of motion of the discretized arch are solved by the updated Lagrange method. The calculation has been performed for arches impacted by a flyer at the crown and the results are compared with the experimental ones. The temporal change in the deflection at the crown, the deformed shape, strain histories are well estimated by the calculation.

View full abstract

The prior theories about elastoplastic constitutive law for particle dispersed composite develop the relation between the average stress and the average strain in multiple phases. In our study, it is found that the local stress distribution in the mesoscale has a great effect on the global property of a composite that undergoes the plastic deformation. The present model considers the distributed stress in standard distribution function in each phase of the composite, where the distribution span is segmented. The macro-stress is linked with the distributed meso-stress by means of the proposed self-consistent compliance mixing law. On the other hand, a meso-mechanics analysis by FEM was conducted to investigate the interaction phenomena occurring in the composite. Also the result was used to provide a reference to the present constitutive model developed in this paper. The developed constitutive model shows an excellent correlation with the reference, thus demonstrates the effectiveness of the present model in both the elastic stage and the plastic stage.

View full abstract

Changes in surface roughness and the relation between the roughening and microscopic inhomogeneity of polycrystalline iron during cyclic plastic deformation were experimentally investigated. Cyclic four-point bending tests were performed under the alternating strain and the pulsating strain conditions, and the three-dimensional shape of the roughened surface were measured by a stylus instrument. The characteristics of respective grains, that is, the crystallographic orientation and the hardening ratio were also investigated, and the relationship between those characteristics and the deformation behavior of each grain was discussed. It is found that the surface roughness changes with the absolute value of the applied strain on the free surface at the early stage of cyclic bending, because the roughening on the surface grows with straining, and then decreases with reversal of the strain. The roughness is cumulated during cyclic deformation, and the cumulative ratio under the alternating strain condition is larger than that under the pulsating strain condition. The hardness numbers of respective grains become large after cyclic bending, and their deviations also increase. It is also found that some grains having larger Schmid factor tend to locate on the slope of the surface roughening. Such grains are considered to deform preferencially during cyclic deformation, and locate on the slope of the roughened surface.

View full abstract

The microcracking behaviors of two-phase materials with microinclusions exhibiting transformation plasticity are analyzed by using the two-dimensional meso-analysis method. Numerical studies have been conducted for some aspects of transformation-induced plasticity which is observed in Zirconia toughened ceramics. Irreversible strains and macro, stress-strain relationship due to dilatational transformation have been simulated under tensile loading condition. R-curve behaviors and microcracking patterns considering the mismatch between matrix and inclusions and the transformation plasticity of second-phase particles have been discussed under model-I loading condition. Influences of the total area fraction and the size of second-phase particles have also been studied through the calculated results.

View full abstract

This paper describes the effect of density of Diamond-Like Carbon (DLC) thin film on tribological property. DLC thin films having the density of 1.9-2.5 g/cm³ were prepared on (111) of Silicon surface by the hot cathode PIG Discharge Type Plasma-Enhanced CVD method. Ball on disk friction experiments were carried out using diamond ball. The friction coefficients increased from 0.05 to 0.20 with increasing film density in the density range below 2.185 g/cm³, but those did not change above 2.185 g/cm³. The specific wear value also increased with increasing film density. The effect of film density on tribological property between DLC thin film and diamond pin was examined by molecular dynamics simulation. The diamond pin slides to uniaxial direction on DLC thin film having the density 1.5-3.0 g/cm³. Atoms of DLC thin film having the density of 1.5 g/cm³ were moved most actively. Atomic movement being like to shear deformation was observed during frictional processes. The effect of film density on friction coefficients in MD simulations was similar to that in experiments qualitatively.

View full abstract

Circular tubes are known for their excellent energy absorption capabilities. When they are used in actual structures, some detailed design parameters must be considered. In this study, FEM analysis and compressive axial collapse tests of aluminum alloy tubes were carried out and experimental data from published papers were reviewed. Three main design parameters of circular tubes for the energy absorbing components were derived, i.e., (1)σ_m (mean crushing stress) and the effect of the elastic modulus and strain hardening on it ; (2)η_G (geometric efficiency) : crushing distance-to-tube length ratio ; and (3)η_L (load efficiency) : mean crushing stress-to-peak stress ratio.

View full abstract

The crushing behavior of cylindrical shells subjected to an axial impact force is studied by FEM, and a comparison between numerical results and theoretical predictions as well as a qualitative comparison between numerical estimates and experimental results are made and discussed. Moreover, a crashworthiness maximization technique for shell structures is developed and applied to the axial crushing problem of cylindrical shell. In the program system presented in this study, an explicit finite element code, DYNA3D is adopted for simulating complicate crushing behavior of shell structures. The response surface approximation technique is applied to construct an approximated design sub-problem in the preassigned design space by using the technique of design-of-experiment. The approximated sub-problem is solved by the usual mathematical programming technique. These optimization processes is repeated until the given convergence conditions will be satisfied.

View full abstract

In this paper, oxidation behavior of bare and SiC coated C/C composites and its effect on mechanical properties have been studied experimentaly. It was found in oxidation tests that oxidation of an SiC-coated C/C composite occurred by oxygen diffusion through the cracks of SiC coating and thus the weight loss was concentrated just underneath of the coating cracks. Due to this behavior, bending strength degradation of the SiC-coated C/C composite was found to be more serious than that of the bare C/C composite when the comparison was made under the same weight loss level. In particular, it is noted that the bending strength degradation of the SiC-coated C/C composite is more rapid at higher oxidation temperature even in low weight loss condition. On the other hand, interlaminar shear strength, ILSS, degradation was shown to be higher in case of low oxidation temperature than in high oxidation temperature. This tendency suggests that main source of the bending strength degradation of the SiC-coated C/C composite should not be the matrix damages but fiber damages at least under low weight loss level.

View full abstract

This paper describes the mechanical properties of plain woven carbon-carbon composites under pin loading. Bearing strength tests without lateral constraint were performed using specimens with different geometrical parameters : width, edge distance, and thickness. The minimum ratios of both width-to-pin diameter and edge distance-to-pin diameter to induce the bearing failure were estimated. The bearing strength depended on the specimen thickness. Delaminated layers that have no load-carrying capacity proved to affect the bearing strength. The thickness of no load-carrying layers was independent of the specimen thickness and was estimated to be 1.3mm for the materials studied.

View full abstract

Hysteretic behavior of unidirectional TiNi SMA/Epoxy composites subjected to a single isothemal loading and unloading cycle has been analyzed using a three-dimensional micromechanical unitcell model. The multiaxial constitutive equations developed in the previous study were applied to the description of the stress-induced rhombohedral and martensitic transformations of the SMA fibers embedded in the epoxy matrix. It was clearly observed that the global behavior of the SMA composites was governed by the pseudoelastic property of the SMA fibers. The hysteretic responses of SMA composites were significantly influenced by the SMA fiber volume fraction. For a high volume fraction of the SMA fibers, the rhombohedral transformation of the embedded SMA fibers characterized a pseudoelasticity-like behavior of SMA composites. This predication indicates a feature unique to the multiaxial SMA constitutive model developed in the previous report.

View full abstract

Roughness of a mechanically finished surface of any machine component is expected to depend on both finishing methods and evaluation procedures. It is supposed that the surface finished by buffpolishing is flat and smooth comparing with the surface finished by a shaper. Even if a surface is finished by a definite procedure, the roughness depends on the technical procedure of the measurement. If one observes a surface finished by a certain method with the naked eye, it looks flat and smooth. But the surface looks rough, if one observes it by means of a high-resolution microscope. The roughness tends to be distinct with an increase of the resolution of the microscope. This aspect can be attributed to a fractal nature of the mechanically finished metal surface. From this point of view, the fractal analysis is applied to evaluate the geometrical irregularity of the surface finished by typically different methods of shaper finishing, milling, grinding and buff-polishing. It is finally found that the geometrical irregularity of the surface is well evaluated by combining the fractal dimension and additional indices peculiar to the machining methods.

View full abstract

Laser ultrasound measuring experiments were conducted to investigate mechanical parameters of ultrasound generation by ruby-laser deposition. Mechanical parameters (pulse duration, pulse pressure, acting area, etc) are important for quantitative and precise understanding of laser ultrasound behavior in solid materials. Laser ultrasound was generated on a front specimen surface by q-sw ruby-laser deposition (2 joule/pulse), and was detected on the back surface using an optical heterodyne probe which reads surface displacement directly. We used thin steel specimens to avoid propagation loss of laser ultrasound and recorded laser ultrasonic waveforms as a function of ultrasonic generating position and specimen thickness. We examined these waveform data to make clear the ultrasonic behavior and the mechanical parameters of ultrasonic generation by laser deposition. Another experiment was carried out to measure impulse by ruby-laser deposition with a pendulum to which impulse by laser deposition was given.

View full abstract

The state of texture in polycrystalline materials can be understood through a pole figure, which is measured by the X-ray diffraction technique. In this study, a method to measure the pole figure with imaging plate (IP) was proposed. IP as a two dimensional detector can measure the entire Debye-Scherrer ring, and pole density distribution of multi direction can be recorded on the Debye-Scherrer ring at the same time. Moreover, if two or more Debye-Scherrer rings are recorded on an IP, two or more pole figures can be obtained at one measurement. The measurement of the pole figure using IP has the possibility to become more efficient than the measurement by conventional method. In conventional method, X-ray device which equipped with Schulz's goniometer and a pulse-counter is used. The measurement device which adopted this method was made, and the pole figure of a textured rolled aluminum sheet was measured. Finally, the measurement accuracy of this method was proven by comparing pole figures which had been obtained by this method and a conventional method.

View full abstract