The Natural Strain is obtained by integrating an infinitesimal strain increment on identical line element. Hence, this theory has merits that can remove the rigid body rotation from the rotating angle of a line element and it can satisfy the addition rule of strain on an identical line element. In our previous report, using the Natural Strain theory, the configuration of the yield surface has been examined by performing the proportional loading tests for tension and torsion after giving the pre-deformation of uni-axial tension to the test pieces. In this paper, the configuration of the yield surface, which is obtained after giving the pre-deformation of large simple shear, is estimated by investigating the modulus of strain hardening h for various directions in the stress space.

View full abstract

This paper is concerned with the estimation of the failure probability for structures with multiple failure modes through a directional importance sampling simulation where directional samples are generated so as to be weighted in the fi points directions on the respective limit state surfaces. The effect of importance sampling is proposed to compensate by concurrently evaluating the probability density of directional importance sampling at the sampled point of every simulation cycle, instead of constructing the directional importance sampling p.d.f. beforehand. Numerical example shows that the proposed method gives accurate estimations of the failure probability for structures with multiple failure modes efficiently.

View full abstract

Graphene has attracted much attention because of its extraordinary electronic and mechanical properties. It is expected graphene will become a new electronic material replacing silicon. The methods of making graphene on substrates will be prospective ways to fabricate graphene for commercial uses. In the present study, the morphology of graphene made on a 6H-SiC substrate is investigated using the molecular-dynamics method. The substrate is assumed to be either Si-faced or C-faced. The sizes of the substrate and graphene are varied retaining the similarity in their plane. The orientation of graphene with respect to an uppermost atomic layer of a SiC substrate is rotationally changed. The morphological variation of graphene with the increase of the angle of rotation is tracked. The wave length of the out-of-plane deformation of graphene changes with the increase of the angle of rotation. The roughness and potential energy of graphene are also obtained as a function of the angle of rotation, whereas the height of graphene from the uppermost surface of the substrate is obtained as a function of the size of graphene. These results will be useful for searching the condition that graphene of high quality may be obtained.

View full abstract

The effect of annealing in nitrogen gas on fatigue behavior was studied using austenitic stainless steel, type304. Annealing in nitrogen gas was performed at 1100°C and 1200°C, and chromium nitrides precipitated under both temperatures. The amounts of nitrides were much larger at 1100°C than at 1200°C. Hardness and tensile tests revealed that the surface hardness and static strength were highly improved by the annealing. Especially, the hardness increase of the specimen annealed at 1200°C was due to not only the nitride precipitation but also the nitrogen absorption into the matrix. Rotary bending fatigue tests were performed in laboratory air, and the fatigue strengths of the annealed specimens increased significantly compared with that of untreated one, where annealing at 1100°C resulted in higher fatigue strength than at 1200°C.

View full abstract

The effects of overloading condition on the fatigue threshold stress intensity factor range (AKth) in type 316 austenitic stainless steel (SUS316) were studied. Overloading was applied to a compact tension specimen of SUS316, then fatigue tests were carried out to determine the resultant zIKth. In the previous study, it was found that the apparent value of the AKth increased with increasing stress intensity factor by single tensile overloading. In this study, it was found that if a compressive overloading was applied after tensile overloading, the apparent z1Kth showed no increase. However, if a tensile overloading was further applied after compressive overloading, the apparent z11(th increased as high as the results obtained by a single tensile overloading.

View full abstract

For the use of structural components, most of the surface of austenitic stainless steel, JIS SUS316L, was ground to make a flat surface. When the grinding is conducted, tensile residual stress is induced at the surface. Introduction of the tensile residual stress is one of cause of stress corrosion cracking. To prevent the stress corrosion cracking, peening is conducted to introduce compressive residual stress. However, the surface roughness of the ground stainless steel treated after peening is seldom varied. Thus, the peening intensity treated after peening should be evaluated in case of the ground stainless steel. In the present report, to establish the non-destructive and relatively short-time evaluating method of the peening intensity, ground austenitic stainless steel using a disk grinder peened by cavitation peening is evaluated using an eddy current method with coil scanning. In results, the proper coil for the evaluation of ground stainless steel is existed, and the peened material can be evaluated by the eddy current method.

View full abstract

Fretting fatigue is one of the most important issues in design of mechanical components due to significant reduction in fatigue strength. In this study, the effect of hydrogen on the fretting fatigue strength of SUS316 was evaluated. The test specimen was received a thermal hydrogen pre-charging. The fretting fatigue strength of the hydrogen pre-charged specimen was lower than that of the uncharged specimen. The reduction of the fretting fatigue limit was less in SUS316 than in SUS304. The authors have reported that local adhesion between the contacting surfaces is one of the causes of the reduced fretting fatigue strength found in hydrogen gas. In this study, EBSD observation of the adhered part was done to promote understanding of the mechanisms. Refinement of crystal grain and strain-induced martensite structure were observed at the adhered part. The results indicated that the stress state in the vicinity of the adhered part was severer due to adhesion.

View full abstract

Specific numerical analyses have been required at designing modern high temperature machines and structures. Since analytical results usually depend on a constitutive equation of creep, it is necessary to derive a high-precision equation. Creep properties on deformation can be normally obtained using constant load creep machines, but constant stress creep tests are more suitable to acquire high-precision creep data. In order to keep the true stress constant, an applied load or the lever ratio should be changed during the test duration. Conventional uniaxial creep specimens have ridges attached on both sides of gauge length to measure deformation outside an electric furnace. For ductile materials, however, even if the constant stress creep testing machine are used, these ridges constrain area reduction around them, and unequal-uniform deformation breaks the constant volume condition in the gauge portion during deformation. Authors have proposed introducing slits into the ridge to release the circumferential constraint by the extensometer ridges. In this study, taking into account a realistic analytic condition, the authors carried out elastic creep Finite Element (FE) analyses to investigate an optimum depth of the slit. Subsequently, a series of constant stress creep tests using SUS304 steel are conducted to examine the effect of introducing slits on the performance of uniform deformation. The analytical and the experimental results show that the introduction of these slits into the ridges would improve uniform deformation effectively.

View full abstract

In high strength steels, it is indicated that hydrogen concentrates at the site of maximum hydrostatic stress. In this study, the hydrogen embrittlement test using hydrogen charged specimen was conducted. In this experiment, the different hydrogen embrittlement behaviors dependent on the applied stress wave form were observed. To investigate the effect of stress wave form on hydrogen embrittlement behavior, the analyses of hydrogen diffusion were conducted under cyclic loading conditions by using FEM and FDM coupled method. The relationship between fracture behavior by hydrogen embrittlement and hydrogen concentration was obtained.

View full abstract

Fatigue strength diagrams, applied to the estimation of fatigue strength under mean stress or residual stress, are not so common with regards to aluminum alloys because they do not have endurance limits, especially at high temperatures. Therefore, we created the generalized fatigue strength diagram at N cycles of aluminum alloy at high temperature, using the strength at N cycles, rather than at the endurance limit, and divided the single line into the multiple ones by fracture feature. The feature divisions are typical fatigue failure, failure with plastic deformation, and failure with creep deformation. Then, we formulated the constitutive equations for this set of the fatigue strength curves at N cycles. In this study, we estimate creep stress component n on the constitutive equation for creep mode. The results are summarized as follows: (1) n=7, the maximum value for general dislocation creep, is passable for some aluminum alloys on the safe side, (2) it becomes obvious that the constitutive equation for creep mode on the fatigue strength diagram involves both a time-depend fracture model and a cycle-depend one for more proper estimation.

View full abstract

There are several methods to make a membrane of a shape memory alloy. The sputtering method is one of them. The purpose of this study is to detach thin film from basal plate by using of the hertz contact stress in sputtering, and its analysis is performed by simulation. First, we create a finite element model of basal plate, ball and thin film. As the first step, we compare theoretical value and analytical value, and examine whether the contact stress expression of hertz can be used at simulation. Also we examine the optimal boundary conditions for thin film delamination from stress and strain distribution. The analysis showed that the analytical value is almost identical with the theoretical one.

View full abstract

In this study, we have suggested the new joint configuration, which has a curved surface at a bonded part, and we have named it an "adhesively waved butt joint". Mechanical properties in some present joints subjected to static tensile load were analyzed, using finite element method. FEM analyses to clarify the stress field at the bonded part were carried out. We have investigated specially in focus joint named "double-waved butt joint". To confirm the reliability of the analytical results, experiments about strain distribution by using strain gauges were performed. As a result, it was found that stress concentrations occur at both edges of adhesive interfaces. Furthermore, the value of maximum stress decreased as wave number at bonded part increased. It was proved that the strain distribution by analytical result is consistent with that measured with strain gauges.

View full abstract

Particle reinforced plastics (PRP) have highly stiffness and flexible workability. Therefore, they were widely used as efficient repair material for damages including cracks and erosions. However, delamination behavior and strength of lining-applied PRP have not been clarified. In this study, we examined tensile test using particle-reinforced resin material bonded on 2 types of tensile test pieces; one is made by polycarbonate as transparent material to observe delamination behavior, and the other is made by SUS304 to evaluate delamination strength for practical use. Each test was carried out with tension rate of 1.0 mm/min and strains of PRP, PC and SUS304 were measured by strain Gages. As the result of PRP bonded on PC tensile test piece, relationship between delamination behavior and strain was clarified. At first, delamination of PRP started and gradually propagated with increasing strain of PRP. After that, steep delamination occurred and strain of PRP steeply decreased. The result indicated that steep delamination of PRP can be determined by its strain. In the result of PRP bonded on SUS304 tensile test piece, steep delamination could be also observed as steep decrease of PRP strain. Strains of tensile test pieces at steep delamination for PC and SUS304 were different; strain of PC tensile test piece at steep delamination was higher than strain at 0.2 proof stress of PRP. Strain of SUS304 tensile test piece was smaller than that at 0.2 proof stress of PRP.

View full abstract

A method of strength evaluation based on fracture mechanics is important to analyze the fracture strength of material with crack. The heterogeneity of mechanical property in dissimilar materials causes change of fracture behavior. Analysis of mechanical property and fracture strength in dissimilar materials is important to evaluate fracture toughness with accuracy. The purpose of this paper is experimentally to analyze correlation between Young's modulus ratio and fracture toughness in dissimilar materials with a single edge crack. 4 kinds of specimen were used in this experiment. One was homogeneous material, the others were 3 kinds of dissimilar materials. The fracture behavior of dissimilar materials was analyzed by high-speed video camera and digital image correlation method. Then, specimens were bended and displacement near the crack was measured. Fracture toughness was experimentally calculated based on fracture mechanics. The experimental results showed that fracture energy and strain distribution around a crack tip were same values at all specimens. We conclude that relationship between Young's modulus ratio and fracture toughness in dissimilar materials is uncorrelated. Then, the heterogeneity of Young's modulus causes the change of crack opening displacement.

View full abstract

The adhesive joint is often used for a lot of structure, and is requested to have safety and reliability. Therefore, it is necessary to know the influence of different adhesive joints on strength. In the previous tensile testing on the SUS304 scarf joints the influence of the shear stress was observed. Then, we conducted the tensile testing by using V-shaped epoxy adhesive joint with a small difference by shear stress because of symmetrical configuration. The experimental result obtained is suitable for the evaluation of interfacial strength characteristics by the normal and shear stresses. Then, the condition of fracture of V-shaped adhesive joint is derived from these two stresses. Namely, the strength of the joint can be roughly predicted by this condition.

View full abstract

In this research, we investigate both analytically and experimentally the electrical properties of carbon nanotube (CNT)-based polymer composites. An analytical model was developed to predict the electrical conductivity of CNT-based composites. The micro/nanoscale structures of the nanocomposites and the electrical tunneling effect due to the matrix material between CNTs were incorporated within the model. Electrical conductivity measurements were also performed on CNT/polycarbonate composites to identify the dependence of their electrical transport characteristics on the nanotube content. The analytical predictions were compared with the experimental data, and a good correlation was obtained between the predicted and measured results.

View full abstract

Recently, regenerative medicine has been focused with stem cells that can regenerate the lost human tissues and organs. To measure healthiness of cells non-invasively, microwave atomic force microscope (M-AFM) which can measure electrical properties and topography of cells has been developed. M-AFM probe was fabricated by forming a microwave transmission line on the probe cantilever. We succeeded in measuring both the microwave response and the surface topography of dried mesenchymal stem cells after ethanol dehydration by M-AFM with the probe. As a result, the change of microwave signals depending on the cell tissues was detected.

View full abstract

The field of local conductivity measurement has produced many kinds of scanning probes to measure the electricalcharacteristics at the nanoscale. However, due to the design limitations, no appropriate probe has been developed to measureand simultaneously image the electrical characteristics at 100 nm order. This research aims to fabricate a four-pOint AFMprobe in order to image electrical characteristics at 100 nm ord Four-point atomic force microscope probe for imaging the electrical characteristics of materials Lin ZHANG", Yang JU*2 and Atsushi HOSOI*2 *1Nagoya Univ. Dept. of Mechanical science and Engineering Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan The field of local conductivity measurement has produced many kinds of scanning probes to measure the electrical characteristics at the nanoscale. However, due to the design limitations, no appropriate probe has been developed to measure and simultaneously image the electrical characteristics at 100 nm order. This research aims to fabricate a four-point AFM probe in order to image electrical characteristics at 100 nm order. Specifically, a certain tape of AFM probe for cell measurement e.g . Biolever, can be etched into four independent electrodes with an in-between space of 200 nm. The four electrodes are basically used to measure the electrical potential drop by allowing the electric current to pass through. The four-point probe is then integrated into a multimode AFM to realize the scanning and imaging simultaneously. The present experimental results show that the four-point probe fabricated can be used to image the surface topography of the Au nanowire, thereby permitting the simultaneous measurements of surface profiles and electrical characteristics of the samples at the next stage.

View full abstract

Characteristic of nanowire is gradually attracting many researchers with potential applications of nano devices, nano sensors, solar sells and so on. This paper describes fabrication and evaluation of high density Cu nanowire array grown in porous aluminum. To fabricate high density nanowire array, at first Ta and Cu films were evaporated on one side of Si wafer as a conductive working electrode. Nanowire array was formed via electrical deposition in copper sulfate aqueous solution. After etching in 2 M NaOH aqueous solution to remove porous aluminum, we obtained high density nanowire array on Si wafer perpendicular to its surface. High density Cu nanowires with average diameter of 200 nm, approximately, were observed by scanning electron microscope. In order to understand performances of Cu nanowire array, electrical and mechanical properties of them were studied in details.

View full abstract

In order to investigate effects of a texture and loading frequency on fatigue properties of an extruded and a drawn alloys of 2017-T4, fatigue tests were carried out under ultrasonic loading frequency (20kHz) in relative humidity of 25% and 85% and rotating bending (50Hz) in nitrogen gas. The extruded alloy had a marked texture of a (111) plane, but a specified orientation was not observed in the drawn alloy. Most of fatigue life was occupied by the growth life of a small crack in both alloys regardless of humidity. In low humidity, the growth of a crack retarded at about 0.3- 0.5mm in length in both alloys. Although the crack growth was accelerated by high humidity in the early growth process, there was no or little influence of humidity on the growth rate of a crack after the retardation in both alloys. After the retardation of the crack growth, fracture surfaces were covered with many slip planes in the extruded alloy and many facets in the drawn one.

View full abstract

Effects of a texture and a slip characteristic on fatigue properties of Al alloys in high humidity were investigated using plain specimens of an extruded bar and a drawn one of age-hardened Al alloy 2017-T4 and an Al alloy which annealed the extruded one in relative humidity of 25% and 85%. The extruded alloy and the annealed one had a marked texture of (111) plane, but there was no specified orientation in the drawn one. Fatigue strength was decreased by high humidity in all of the alloys, especially in the extruded alloy. The decrease in fatigue strength in the extruded alloy was mainly caused by the acceleration of a crack growth due to the change in growth mechanism of a crack from a tensile mode in low humidity to a shear one in high humidity, though the effect of humidity on the growth mechanism was very small in the drawn and the annealed alloys. The shear mode crack in the extruded alloy was related to the marked texture and the planner slip property and caused by high humidity.

View full abstract

The fatigue behavior of friction stir processed (FSPed) cast aluminum alloy, AC4CH-T6 was investigated. FSP conditions were set to be the tool rotational speed of 500rpm and traveling speed of 200mm/min, in which strain late was relatively low. Plane bending fatigue tests have been performed using as-cast and FSPed specimens. Fatigue strengths of the FSPed specimens were highly improved compared with the as-cast ones. Casting defects were eliminated by FSP, resulting in higher fatigue limit. However, the crack growth rates of the FSPed specimens were faster than those of the as-cast ones due to softening of the material by heat input during FSP. The improvement of fatigue limit by FSP with low strain late was higher than that by FSP with high strain late. The effects of FSP with low stain rate were discussed based on the microstructural consideration.

View full abstract

Cantilever type rotating bending fatigue tests were performed using A5052 aluminum alloy with hybrid coating of tungsten carbide including 12% cobalt (WC-12Co) interlayer and diamond-like carbon (DLC) film in order to investigate the effect of hybrid coating on the fatigue behavior. The WC-12Co layer was thermally sprayed by a high velocity oxygen fuel (HVOF) method on A5052 with the thickness of 70, 120 and 17011m. After that the DLC film was deposited with the thickness of 15[im. The fatigue strength of A5052 with WC-12Co single layer coating was improved compared with that of A5052 without coating and with the increase of thickness of WC-l2Co single layer, the fatigue strength was more improved. The fatigue strength of A5052 with the hybrid coating of 70tim WC-12Co and 15pm DLC film was more improved than that of A5052 with 70[tm WC-l2Co single layer coating and the hybrid coating was effective to improve the fatigue strength. However the effect of hybrid coating was not apparent in A5052 with thicker WC-l2Co layer of 120 and 170tim. Whether the hybrid coating is effective or not depends on that the DLC film could suppress the cracking of WC-12Co layer.

View full abstract

The technique to heal a fatigue crack in a stainless steel by controlling the high-density electric current field was studied. The high-density electric current field was applied at the crack tip using closely spaced electrodes. The crack on the specimen surface was observed by scanning electron microscope (SEM) before and after applying the high-density pulse current to examine the effect of the high-density electric current field on the fatigue crack. In addition, the displacement distribution was obtained by a digital image correlation method. With those data, the change of the crack shape was evaluated quantitatively. The experimental results showed that the fatigue crack was closed by the electrical stimulation.

View full abstract

Fatigue crack propagation behavior in polycrystalline aluminum under cyclic tensile load is observed, and the controlling of crack growth by plastic treatment method is studied in detail. Destruction of structural components is almost always correlated with metal fatigue. Stop-hole and shot peening are well-known methods to control or to increase durableness for the improvement of its fatigue strength. Stop-hole method is required for repairing places where it is hard to change the base metal immediately and it has dual nature. However, some results of the observation show that the crack propagates faster than untreated one despite the impact of work-hardening. It's suggesting the importance of the location of indentation from the crack tip and it enable us to grasp the concept of cracking control by observing unexpected rapid propagations. As a concrete method, we tried to make indentation at 2 to 3mm horizontal length from the crack tip and analyze the experiment from the view point of effects on strain-hardening and residual stress.

View full abstract

Effects of cavitation peening (CP) on the bending fatigue strength of aluminum alloy (A7075-T6) containing an artificial semi-circular slit were investigated. The bending fatigue test specimens with a small semi-circular slit with depth of 0.05" 0.3mm were subjected to CP. Then, bending fatigue tests were carried out with the specimens to determine the fatigue strength and the acceptable surface defect size by CP. It was found that the fatigue strengths were increased by CP. And the depth of the acceptable surface defect size was between 0.2mm and 0.3mm.

View full abstract

The constitutive equation based on continuum damage mechanics is formulated for concrete, assuming it as an elasto-viscoplastic damage solid. Lots of material parameters in the constitutive equation are determined by using the uniaxial compressive test results with the effect of hydration. Some parameters are time-dependent. The local approach to fracture analysis (the fully-coupled analysis) for the three-point bending tests of notched beams is conducted by using the finite element program with the identified constitutive equation model. The validity of the proposed model is illustrated by comparing the calculated results with the experimental results.

View full abstract

In our previous report, the combined loading tests for bending and torsion are carried out, and the visco-elastic response is investigated by performing experiments that changes the relative angle between the principal axis of stress and the braid. Moreover, the numerical model is proposed and the validity of the model is verified by comparing it with these experimental results. On the other hand, the buckling tests are carried out by applying the axial force and the twisting moment simultaneously, and the buckling region under combined loading of axial force and torsion is verified. In this report, changing the speed of axial displacement and twisting angle, the buckling region, which is obtained by applying the axial load and the twisting moment at the same time, is examined and the relation between the buckling region and the stress relaxation is revealed.

View full abstract

The purpose of this study is to investigate the physical property of catheter, which made of soft nylon resin and is reinforced with thin stainless wires. The buckling behavior under initial torsion has been examined by using short specimens, and the effect of stress relaxation on the buckling behavior has been revealed in our previous report. However, the snap-through phenomenon occurs when using relatively long specimens. So, in this report, buckling tests under initial torsion are carried out by changing the initial twisting angles and the length of specimens variously. Especially, performing the experiments with different axial displacement speed, the relation between the snap-through phenomenon and the visco-elastic behavior are investigated.

View full abstract

Motor vehicles on the market have been required to undergo the pedestrian head protection test since 2004 and engine-hoods need to meet the required standards for pedestrian head protection performance in addition to primary performance. The quality of engine-hood is evaluated by Head injury criteria (HIC) derived from 3-dimensional acceleration generated against the head. Based on HIC measurements, the authors tried to improve it is performance by using the hood with two panel structure. In this study, we examined impact response characteristics of the pedestrian head by numerical analysis. We focus on the brain concussion and the skull fracture as a severe injury to be injured at the time of an engine-hood collision. As a result, we revealed about mechanism of the head injury occur by dynamic deformation behavior of the engine-hood.

View full abstract

Pole side impact is one of the most common collision types of vehicles. The pole side impact with high vehicle speed induces not only local collapse but also bending of the vehicle. First, deformation and absorbed energy of the vehicle in pole side impact experiment at impact speed of 80 km/h was investigated. Next, lateral compression and three-point bending tests of rectangular steel tube specimens were performed, as a simple modeling of vehicle deformation at the pole side impact. It was found that the former induced mainly local collapse, while the latter induced bending of the tube specimen. Based on these facts, the test of lateral compression followed by three-point bending of the tube specimen was performed. In this test, the bending deformation occurred after the local collapse, similar to the deformation behavior of vehicles at the pole side impact experiment. The variation of the absorbed energy in the test was similar to that of the vehicle experiment. From this result, it can be summarized that the deformation and absorbed energy of the vehicle in pole side impact is possible to be modeled by the lateral compression and three-point bending tests of the rectangular steel tube.

View full abstract

Single-axis load cell is widely used in various fields. However, in order to manufacture high precision products, requires accurate measurement of load in three dimensions. In the study, we was developed a three-dimensional load cell as one body. This load cell can measure the load and load direction. At the same time, X, Y and Z direction force component forces can be measured.

View full abstract

An effect of rigid body rotation for the speckle image correction for electronic speckle pattern interferometry using DIC is investigated. The relationship between rigid body rotation and the change of static speckle pattern by single beam illumination is compared with the relation of rigid body translation and the change of static pattern. Additionally, the elimination of the interference fringe caused by rotation is examined by the position and the phase correction of the speckle image. Results show that the intensity error of the static speckle pattern by rotation is larger than the intensity error by translation, and the fringe pattern by rotation can be eliminated by the correction in the rotation range less than 10-3 rad.

View full abstract

In order to propose the fast nondestructive inspection, it is examined by experiments and numerical simulations how to detect wave radiating from a crack by using simple hold method. Simple hold method is necessary in order to check the mass of machine parts. In this study simple hold method is method for clamping the test piece by upper and lower clamps with acrylic plate. The acceleration sensor was fixed on the acrylic plate. Experiments and numerical simulations were performed to check if vibration of the crack is detected under the condition that test piece is held by simple hold method. Real crack in the machine parts was treated as two-dimensional crack model. Vibration of the crack was detected by acceleration sensor near the clamp area. And, the strain gauges were pasted near the crack, in order to detect vibration of crack. Numerical simulations were carried out by finite element method. The results of impact test were compared with the results of numerical simulation in the case of natural frequency and strain. Vibration of the crack was detected under the condition that a part of crack dose not exists in the clamp area. But, under the condition that a part of crack exists in the clamp area, vibration can not be detected.

View full abstract

In recent study, active thermography has reached a high status as an easy and speedy defects inspection method in a NDT field. This paper newly proposes a non-disassembly and non-contact NDT method using a Vibro-Thermography for detecting and evaluating of fatigue cracks at neck parts of the conveyance roll in the steel making plant. In this method, fatigue cracks are detected as localized high temperature areas caused by friction and collision at crack surfaces with an infrared camera, applying a high-amplitude ultrasonic vibration. In this paper, the most suitable nose-shape of horn type transducer, which is contacted with the curved roll surface, is developed for an effective propagation of ultrasonic vibration. In the case of the roll surface is covered with lubricating grease or dust, the crack detectability is shown. Self reference lock-in data processing technique is applied for improvement of signal noise ratio in the crack detection process. This technique makes it possible to perform correlating process without an external reference signal. Time and cost saving inspection method in the neck part of conveyance roll is carried out using this NDT technique.

View full abstract

In order to visualize fatigue cracks inside a specimen, computed tomography (CT) was carried out using synchrotron radiation at SPring-8 and industrial X-ray CT scanner. The images of the crack were reconstructed by both CTs under conditions as similar as possible. Refraction contrast effect is the major difference between reconstructed slice images by Synchrotron Radiation CT and industrial X-ray CT. The refraction contrast effect was prominent in the slice images of the Synchrotron Radiation CT, however it could not be observed in the image of the industrial X-ray CT. It is easier to evaluate the whole image of fatigue cracks by including the refraction contrast effect.

View full abstract

Rotating bending fatigue tests were carried out on specimens of ultrafine grained copper produced by equal channel angular pressing. The growth behavior of a small surface-crack was monitored. A major crack, which led to the final fracture of the specimen, initiated from shear bands (SBs). After initiation, the crack grew linearly in the shear direction of the final pressing. A decrease in growth rate with a change in growth path morphology occurred when the crack length reached 1- 0.1 mm. This decrease occurred because of a change in the crack growth mechanism and is explained by considering the interrelation between grain size and the reversible plastic zone size at the crack tip.

View full abstract

Effects of aging structure and humidity on fatigue properties of 350 grade 18% Ni maraging steel were investigated under rotating bending in relative humidity of 25% and 85%. Aging conditions tested were a conventional single aging and a double one which was aged at low temperature after the conventional aging. In each aging, the under and the peak aged steels were prepared. Both of tensile and fatigue strengths were increased and the decrease in the fatigue strength by high humidity was suppressed by the double aging. These improvements of tensile strength and fatigue properties by the double aging were discussed from a point of the precipitated particles.

View full abstract

In this paper, compressive strength properties of PBO fibers were investigated in direct compression test. Two types of PBO fibers were used in the experiment. One is conventional type of fiber. Another is high modulus type of fiber, and its crystal orientation is higher than conventional type of the fiber. Weibull analysis was performed to describe distribution of compressive strength. It was found that the compressive strength of both PBO fibers were well fitted the Weibull distribution function with 2 parameters. Shape and scale parameters of high modulus type PBO fiber were 8.85 and 238 MPa, respectively. Compressive strength of the high modulus type of PBO fiber showed a slight size effects for both length and diameter direction. Compressive strength of the high modulus type of PBO fiber was higher than that of conventional type of PBO fiber.

View full abstract

Variation of elastic modulus caused by plastic deformation is investigated in this study. The aluminum specimen which is used in this study has plastic region and elastic region. The elastic modulus is measured by the tensile test using strain gage and electronic speckle pattern interferometry (ESPI). The values of elastic modulus in elastic and plastic region are then determined by supposing the uniformity of stress distribution in the specimen. By comparing the result of elastic modulus measured by strain gage and ESPI, it is observed that the elastic modulus of aluminum sheet decreased by plastic deformation.

View full abstract

The magnesium alloy with many mechanical advantages is expected as structural material. However, the magnesium alloy does not have enough plastic deformability, because it has hexagonal close-packed structure. Therefore, the superplastic deformation with the grain boundary sliding is paid to attention. Huge plastic deformation can be realized by the superplastic deformation. On the other hand, a dynamic recrystallization is brought to the microstructure of the magnesium alloy by the superplastic deformation. It supposes that the change of this grain structure influences the mechanical properties. In this study, we investigated the influence of the superplastic deformation on the mechanical properties of the material, performing the tensile test at room temperature of AZ3 lmagnesium alloy after superplastic deformation. In addition, to investigate the correlation between the grain size and the mechanical properties at room temperature, the texture observation. As a result, the yield stress rose in the material after superplastic deformation.

View full abstract

This paper is described an indentation method to measure the Young's modulus of the early part and late part of wood material (Japanese cedar). I order to clarify the validity of the present method, the fluoro rubber and the soft vinyl, is indented. The obtained Young's modulus of fluoro rubber of the elastomer is in good accuracy. On the other hand, the Young's modulus of the soft vinyl and wood were considerably smaller than the value obtained by the other methods because of the plastic deformation. Therefore, in order to measure the Young's modulus of wood, the plastic deformation should be considered.

View full abstract

The constitutive equation based on the concept of continuum damage mechanics is formulated for the gray cast iron, assuming it as an elastic damage viscoplastic solid. The microscopic stress and strain evaluation is simplified in the two-scale model for the damage evolution. Lots of material parameters in the constitutive equation are determined by using the uniaxial tensile/compressive and the fatigue test results. The local approach to fracture analysis (the uncoupled analysis) for the fatigue tests of notched circular bars is conducted by using the identified constitutive equation model and the commercial three-dimensional finite element program. The validity of the proposed model is illustrated by comparing the calculated results with the experimental results.

View full abstract

A carbon/silica composite (composite) fabricated from agricultural waste of rice husk (RH) without using any binders. In the present study, the effect of heating temperature on the mechanical and material properties of the composite was investigated. The slab-shaped composites heated to 300, 500, 800, 1000, and 1200°C were prepared and their mechanical properties such as bulk density and compressive strength were evaluated. The composites heated to 1000°C displayed the highest bulk density and compressive strength, which were respectively 1.25 g/cm3 and 203.4 MPa. It was revealed that the composites were subjected to thermal shrinkage of the matrix material derived from RH. The thermal shrinkage led to a densification of the composite, improving the mechanical properties.

View full abstract

For ultra light MAV (micro air vehicle), low-density expanded polypropylene (EPP) has been noticed with keen interest. In this study, mechanical properties and optimal structure of low-density EPP are investigate by bending test. Bending stiffness is evaluated on the rib,truss,honeycomb internal structures. The deformation of the structures are analyzed using a finite element method and the maximum displacements are compared with experimental data. The results indicate that the honeycomb structure dose exhibit higher stiffness and the weight of structures are reduced by 50%, comparing with the bulk specimen. Bending stiffness is improved by making structures by cutting, compared with bonding structure.

View full abstract

One of the design methods for closing the end of a pressure cylinder is screw down a screw plug on the threaded end of the cylinder. In this case, these is the problem of stress concentration in the threaded end of the pressure cylinder. To solve the problem, it is necessary to know accurately the load distribution on the threaded end of the cylinder. To find the load distribution on the threaded end of the pressure cylinder engaged with the screw plug, the following experiments are carried out. Applying the Compressive load between the plug and the pressure cylinder and regarding the situation above as equivalent to the situation in which the internal pressure is applied, the load distribution is measured with the strain gauge. The influence of length of engaged thread on the load distribution of taper threaded end of pressure cylinder is presented and an expansion of design manual is discussed.

View full abstract

An important issue is how to determine a bolt preload of a bolted joint taking an external axial load into account. One method for determining the bolt preload is such that the stress at the bearing surfaces is less than the yield stress of the clamped parts taking account of the load factor. Another method is such that the stress at the bearing surfaces is higher than the yield stress of clamped parts. Firstly the load factor to obtain the increment F, in the axial bolt force is investigated using axi-symmetrical theory of elasticity, FEM analyses and experiments. Then, the contact stress distributions and the plastic displacement distributions at the bearing surfaces under external loads are examined using elasto-plastic FEM analyses. The prediction for the reduction in axial bolt force of the joint under external load is fairly consistent with the experimental result. It is noticed that a higher bolt preload according to the second method shows a small reduction in axial bolt force. Discussion is made on the critical stress at the bearing surfaces.

View full abstract

Honeycomb panels with diamond-cut patterned core were analyzed by the finite element method applying thestatic bend load. The structure analysis were done when core size and joint shape were changed. The thickness of coreplates was decreased to keep light weight. The displacement and the stress distribution of panels were compared, andthe effect of the core size on the rigidity ofpanels was examined.

View full abstract

In order to elucidate the hydrogen embrittlement of the aluminum alloys, it would be worthwhile to detect hydrogen evolution during tensile deformation and fracture. In this study, the hydrogen evolution behavior during tensile deformation and fracture in T6-tempered 6061 and 7075 aluminum alloys was detected by means of a testing machine equipped with a quadrupole mass spectrometer installed in an ultra-high vacuum chamber. Furthermore, local hydrogen evolution behavior of the both alloys was visualized with a hydrogen microprint technique. It is clarified that the hydrogen evolution started at the stage of elastic deformation in the both alloys. However, the amount of hydrogen evolved at the elastic deformation in 7075 alloys was much higher than that in 6061 alloys. This suggested that the hydrogen diffusion was promoted due to the existence of the stress field caused by second phase inclusions (A17Cu2Fe), since the 7075 alloy has higher proof stress than the 6061 alloy. In addition, the higher amount of hydrogen was evolved at the beginning of plastic deformation particularly in the 7075 alloy. This indicates that primarily dissolved hydrogen was transported to the surface of specimen with the aid of mobile dislocations.

View full abstract

The objective of the present study was to analyze the shearing characteristics of a resin sheet by a straight punch and dies. In this paper, in order to reveal the die clearance effect and the feed velocity effect on the sheared end-profile of deflection resin sheet which was attached with protection films, a precision shear testing device was developed. Shearing of the deflection resin sheet was experimentally carried out by varying the die clearance and the feed velocity of punch. The surface layers of deflection resin sheet were observed with a de-laminated state of protection films. Furthermore, the shear strength was discussed with the properties of the resin sheet.

View full abstract