We investigated about a perforation behavior of a 0.8mm thin steel plate by a fired 38 caliber bullet. The two bullets, Full Metal Jacket (FMJ) and Lead Round Nose (LRN), were fired by a 38 caliber revolver. The perforation behavior was taken by a high speed camera with 105 frames per second. A collision side of the fired bullet and a thin steel plug punched out by the fired bullet were observed. A compressive stress area was occurred at the center of the collision side. On the thin steel plug, an area adhered of the bullet material was observed in the circumference of the compressive stress area. It was thought that the adherent of the bullet material occurred by the friction between the fired bullet and the thin steel plate. Because the collision side of the fired bullet was flat, it was thought that the bullet deformed before the thin steel plate started to deformation. The thin steel plate was indented by the fired bullet. Then, a circular crack occurred on the thin steel plate. The edge of the crack on the thin steel plate corresponded to the edge of the flat area on the fired bullet. The fired bullet passed the circular crack, and a hole opened.

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Erosion is a phenomenon that damage the surface of material is removed by the particles impact. Erosive wear becomes a problem in pulverized coal injection system and rotating chute. In order to reach an aim of high safety and low cost, it's important to develop wear resistant material and to estimate of life service during erosion. According to research pertaining to erosion, three types of conditions are known to affect. Particle's condition is hardness and particle shape. Impact condition is angle and velocity. Target material's condition is mechanical properties and structure. This study investigated that impact angle dependently on erosive wear by Finite-element-method (FEM). LS-DYNA suitable for contact problems was used in this study. Analysis conditions are shown below of specimens. Impact velocity of the particles was 20m/s. The contact time of the collision is 0.01ms. The dimensions of the impact material are 10 x 10 x 10mm. Test specimen was SUS630 stainless steel. The erodent particle used in this study was a 1mm alumina ball. Impact angle was analyzed from lOdeg. to 90deg. The particle was assumed to be rigid. The elastic constants of SUS stainless steel were used to define the particle material. For verification of the analysis result, a single impact experiments were conducted. The Correlation was obtained in result of experiment and analysis. As a result of focused on equivalent plastic strain and Mises stress. It's possible to test the efficacy of FEM analysis of impact angle dependency for high temperature erosive wear.

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Shot peening is the method that hard particles are shot on material surface. With this method, compressive residual stress and work hardening are induced and hard layer is fabricated on the material surface. Finally, the treated material has greater fatigue strength and abrasion resistance property. In shot peening, shot particles hit on the material surface and rebound, and its coefficient of restitution depends on material properties such as yield stress. Therefore, we carried out some experiments in order to investigate the relationship between the coefficient of restitution and yield stress. The results showed that the yield stress is proportional to e1'6. The proposed method to measure the yield stress is valid under high temperature condition. From the numerical analysis, the strain rate is about 7400 s^<-1>. Therefore, it is concluded that measuring yield stress at local area under high temperature and high strain rate is possible by using shot peening.

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In this study, the effects of washers for fatigue strength of bolted joints were investigated. In order to investigate the effects, single-shear specimen with/without washer were employed and fatigue load tests were performed. The fatigue limits of the two types of specimens were compared by fatigue strength at 50% probability of failure. The test results showed that the fatigue limit of the test specimen with washer is higher than the one without washer because the washers were thought to reduce bending stress around bolt head.

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Stress concentration occurs in the root of threads in the threaded cover structure of the pressure vessel. The internal pressure causes unequal load distribution of threads and stress concentration in the root of threads. Then, it is necessary to consider the fatigue fracture because of the stress concentration. In previous study, the improvement of the load distribution and unequal stress distribution in the threaded portion of the pressure vessel is considered by using a FEA. In this study, it was carried out hydraulic test to the threaded cover structure of the pressure vessel. Then, it was put strain gauges on the outer surface of the pressure vessel in order to measure axial strain. On the other hand, making a model of the pressure vessel of hydraulic test using Abaqus. Results of the FEA shows that setting of the tolerance of thread and the coefficient of friction affect the analysis results. Therefore, it shows the effect on the analysis result by the setting of tolerance of thread and the coefficient of friction. And, it shows a comparison with the strain obtained from the strain measurement results of the hydraulic test and analysis results.

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In this study, fatigue tests and life assessment method for welded structures are proposed. Specimens were sampled from welded structures containing embedded flaws inspected by ultrasonic testing. The loading conditions of the fatigue tests were set to be identified as the operating conditions of the structures considering the crack closure effect due to welding residual stress distribution measured by strain gauges. The assessment results represent good agreement with the experimental results within the factor of 2 scatter bands. Hence the fatigue life of the welded structures can be estimated within ±50 % accuracy in life.

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This paper deals with the effect of adhesion layer on the stress intensity factor for small edge interface crack in bonded plates under uniaxial tension or bending. In this study, the stress intensity factors of the small edge interface crack are analyzed by the crack tip stress method with varying the crack length, adhesive thickness and material combination. The stress intensity factor of the edge interface crack is controlled by the singular stress field at the interface free edge in adhesively-bonded joint without the crack when the crack is very small. The calculation shows that the normalized stress intensity factors of the small edge interface crack under uniaxial tension or bending are related to the ratio between the crack length and the adhesive thickness (a/h) and the singularity at the interface edge without the crack λ Then, it is found that the normalized stress intensity factors can be expressed as F_<1,2>=C_<1,2(h/a)^<1-λ> and the parameters C_1 and C_2 are constant values when a/h<10^<-3>.

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Although resistance spot welded joints are widely applied for fabrication of the monocoque body of cars, fatigue strength of the joints are less than the base materials in general. It is very important for satisfying the structural integrities of car bodies to evaluate the fatigue performance of spot welded joints. On the other hand, the S-N curves approach for the fatigue life prediction, which is commonly applied in the structural design stages, cannot give the fatigue crack growth history. Therefore, the fracture mechanics approach for estimating the fatigue crack growth history is expected. Improved effective stress intensity factor range based on the RPG load criterion and the numerical simulation method of fatigue crack growth which consider the fatigue crack opening and closing behaviour of the crack proposed by authors' group can be powerful method to estimate fatigue crack growth history under arbitrary loading sequences. This procedure could be applied not only a through thickness crack but also surface cracks from a sound stress concentration part. However, the changing manner of aspect ratio of a surface crack, which corresponds to the relationship between the aspect ratio and the dimensionless crack depth, must be given in advance. The aspect ratios of a fatigue surface crack occurred at the spot welded toe in SPCC270, SPCD270 and SPC440 steels, which are commonly applied for car bodies, during the growth were measured and confirmed the characteristics of behaviour of the aspect ratio for spot welded joints.

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Many kinds of joining methods are proposed for thin plate structures such as an automotive body. It is important to investigate the fatigue behavior of these joints. However, a large amount of fatigue tests are necessary to recognize the fatigue lives of these joints. Therefore, it is efficient to predict the fatigue life by numerical simulations to reduce the tests. In this paper, a fatigue life prediction method considering the transition from surface crack to through crack is reported. Numerical results of spot-welding specimens for SPC270 and SCGA590 are compared with the S-N curves obtained from fatigue tests, and proposed methodology is considered to be efficient for predicting S-N curves.

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In this paper, the possibility of fatigue life prediction of spot-welded joint under two steps variable amplitude load was investigated. The constant amplitude fatigue tests for the spot-welded tensile shear and peel, bend specimens were carried out and the results were arranged by using the nominal structural stress. As a result of prediction using Miner's rule, the fatigue life of spot-welded joint under two steps variable amplitude load could be estimated by Miner's rule considering mean load. Further, it was suggested to be able to estimate the fatigue life without depending on the kind of joint. Therefore, the nominal structural stress parameter showed the possibility of evaluating the fatigue life of spot-welded joint under variable amplitude load.

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In this paper, the influence of simultaneous variation of nugget diameter and spot welding location on fatigue life of the spot-welded joints was investigated under two kinds of loading, tensile shear and bending. The relationship between spot welding position and the nugget diameter and the nominal structural stress, which is used as fatigue life evaluation parameters, were examined. The variation of fatigue life due to varying the influence factors was quantitatively assessed by the sensitivity analysis. The fatigue test was conducted to verify the results of the sensitivity analysis. As a result, it was shown that the influence of the factors of the variation to the fatigue life was able to be accurately evaluated using the sensitivity.

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For the establishment of the spot welded structure fatigue life prediction method by CAE, there is a method of using the nominal structural stress of the spot welding as the evaluation parameter. The nominal structural stress calculation method can obtain the nominal structural stress accuracy by using the general loads and the displacements in the vicinity of nugget. In this study, the effect caused by moving the spot welding position was researched using the LL structure under the share load. As a result, it was found that the stress solution can be accurately obtained by using the general loads of when the spot welding position was moved and the value of a part of boundary displacement. And it was shown that the place where the nominal structural stress occurs was different according to the spot weld position.

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In one of the spot welded structure fatigue life prediction method, there is a method of using the nominal structural stress of the spot welding as the evaluation parameter. The nominal structural stress calculation method can obtain the nominal structural stress accuracy by using the general loads and the displacements in the vicinity of nugget. The FE model of spot weld is made as the octagon model that consists of the beam element and 8 rigid bar elements. However, it is not easy to apply this octagon model to the entire structure. In this study, the spot weld FE models other than an evaluation point were made as a simple model, and the accuracy of stress solution that was obtained from nominal structural stress calculation method was studied. As a result, it was shown that the nominal structural stress was accurately obtained by using the cross model that consists of the beam element and 4 rigid bar elements.

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In the present paper, the distribution of stress intensity factor along a small three-dimensional crack front locating at a vertex in an elastic block is investigated precisely. A tensile load is applied to the block with a small crack. Boundary element method is used for analyzing the stress distribution and eigenanalysis is conducted for determining the order of stress singularity at the intersection point of crack front and the free surface. The stress distribution near the intersection point is formulated using the distance from the intersection point and the angular functions derived from the eigenanalysis. The relationship between the stress intensity factor and the distance from the intersection point is confirmed by the comparison of the result obtained from the stress singularity analysis.

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Most piezoelectric materials are brittle. And determination of stress intensity factor is important because piezoelectric material often has defect such as crack or notch. There has been considerable research on the stress concentration and singularity for piezoelectric materials by using theoretical and numerically analysis method. But determination methods of the stress intensity factor for piezoelectric materials have not been fully-established because of difficulty of mechanical handing of piezoelectric material. In this study, we focused on similarity of analytical theory between piezoelectric materials and anisotropic materials. Based on that similarity, this analysis derived the similar general solutions for piezoelectric materials and anisotropic materials subjected to arbitrary loads at the crack or elliptical boundary. And it was shown that theory of anisotropic material was applicable to piezoelectric material by adequately replacing material constants. Furthermore, the extrapolating method on strain of piezoelectric material from experiment of anisotropic materials was discussed.

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Recently composite material has being applied in a wide range of engineering fields such as parts for automobile and aerospace equipments, because it has both heat resistance and toughness. Functionally graded hollow cylinder in which the material changes in the radial direction can be considered as a reasonable material for cylindrical components, such as piston cylinders. In this paper, the stress analysis of graded hollow cylinder having a radial crack based on Body Force Method(BFM) is carried out.

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Based on the linear notch mechanics, it is expected that the size and shape of the resulted plastic zone at notch root due to the excessive loading, is almost identical when the maximum elastic stress at the notch root and the notch root radii are identical. In the present study, the influence of the notch root radius on the plastic zone size is discussed when the maximum elastic stress at notch root is identical. It was found from numerical analysis that, the size and shape of the plastic zone is strongly influenced by the notch root radius. The more the notch root radius becomes small, the larger plastic zone spreading in the direction perpendicular to the external load can be found.

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In this study, the effect of surface condition on small fatigue crack initiation and growth of austenitic stainless steel was investigated. In constant strain range tests, surface roughness depended on strain range. Two step variable amplitude straining tests were performed to reveal the effect of surface roughness on fatigue crack behavior. Surface roughness was affected from experimental condition. Typically, when lower strain range was applied after higher strain range, surface roughness was larger than that of constant strain range tests. The relationship between crack growth rate and J integral range of two step variable amplitude straining tests was similar to that of constant strain range tests. Fatigue tests were conducted for specimen with machined surface, there are many scratches developed by turning. Fatigue crack was initiated from the scratch. Microstructure of turned specimen was observed by electron back scatter diffraction method. Surface roughness was approximately constant during fatigue life for as-machined and grinded specimen while it increased gradually for electro-polished specimens. Crack growth characteristics were coincided regardless of machined condition, and thus fracture mechanics approach was available to predict the fatigue lives.

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This paper describes a J-integral evaluation procedure applicable to unstable failure analysis for a circumferential through wall crack in a pipe. Japan Sodium cooled Fast Reactor (JSFR) pipes are made of Mod.9Cr-1Mo steel. The fracture toughness of the material is inferior to that of conventional austenitic stainless steels. In addition, JSFR pipe has small thickness and large diameter and displacement controlled load is predominant. Therefore, the load balance in such piping system changes by crack extension and 2 parameter method using J-integral is applicable to unstable failure analysis for the pipes under such conditions. As a J-integral evaluation method for circumferential through wall crack in a cylinder, EPRI has proposed a fully plastic solution method. However, the geometry of JSFR pipe and material characteristics of Mod.9Cr-1Mo steel exceed the applicable range of EPRI's method. Therefore, a series of elastic, elastoplastic and plastic finite element analyses (FEA) were performed for a pipe with a circumferential through-wall crack to establish a J-integral evaluation method applicable to such conditions. J-integrals obtained from the FEA were resolved into elastic, local plastic and fully plastic components. Each component was expressed as a function of analytical parameter, such as pipe geometries, crack size, material characteristics and so on. As a result, a simplified J-integral evaluation method was proposed.

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A ductile damage progress of an aluminum single crystal under tensile loading was verified by a profile analysis using white X-ray obtained in BL28B2 beam line of SPring-8. In this study, the aluminum single crystal of the purity 6N was used as a specimen prepared in I-type geometry for tensile test. Notches were introduced into both sides of the center of a parallel part of the specimen by the wire electric discharge machining. White X-ray beam, which has 0.05 mm in both height and width, was incident into the specimen on the Bragg angle θ of 3 degrees using energy dispersive X-ray diffraction technique. The specimen was deformed by elongation in the direction of 45° to [111] and [1-10] crystal orientations, respectively, and a diffraction profile of the white X-ray from A1220 and A1222 planes were analyzed. The Gauss component of integral breadth related to non-uniform strain was deter-mined by eliminating the broadening by the instrumental function from the diffraction profile of white X-ray. As a result, the characteristics of ductile damage progress near the notch of the aluminum single crystal were inspected from the distribution of both dislocation density and rotation of dislocation cell.

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We proposed new evaluation method for crack tip fracture toughness in ceramic materials by a combination of Vickers indentation and finite element method. We paid attention to the smallest applied load of the radial crack which occurs to material surface by a Vickers indentation. The crack tip fracture toughness was decided based on the stress distribution by FEM analysis. Work hardening coefficient was measured by a Vickers indent observed using 3-D optical microscope. Pre-existing defect sizes were presumed from a material surface which was treated with a thermal etching. The validity of this evaluation method was compared with other evaluation method. It found out that this evaluation method is better than other ones.

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It's well known High Strength Steel shows internal origin type fatigue failure called Fish eye failure in low stress and high cycle region. In this failure, ODA(Optically Dark Area) is formed and this ODA occupies the great portion of fatigue life of Fish eye failure. Although the explication of the mechanism of ODA formation is needed for the explication of the Fish eye failure mechanism, the explication is not yet accomplished. It's reported that internal fatigue crack in high strength steel is propagating extremely slowly by recent investigations. However, it is not clear the relationship between the extremely slow fatigue crack growth behavior and the mechanism of ODA formation, and whether it is a peculiar phenomenon of high strength steel. In study, fatigue test was done in vacuum environment. As a result, fractography suggest that more obvious ODA is formed by smaller stress ratio when internal crack is extremely slowly propagating.

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Sonic-IR, which is based on the thermographic detection of the temperature rise due to frictional heating at the defect faces under ultrasonic excitation, has an advantage in the detection of closed and small defects. However, this method has a lot of unclear factors relating to heat generation. In this study, effects of rust in the crack faces on the crack detection based on the sonic-IR method is experimentally investigated by using crack specimens. The heat generation by ultrasonic excitation was observed regularly during rust accelerated test using original device. The distribution of temperature change around the crack was changed with the progress of rust. This change in heat generation, it believed to be due to change in the contact state of the crack surface due to rust. As a result, it was found that heat generation by ultrasonic excitation is affected by rust in the crack faces. And it was also found that crack detection can be conducted by sonic-IR even if rust was generated in the crack faces.

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Welded structures are widely used for construction machines, automobiles, railway vehicles, etc. In these structures, the welded parts are generally the weakest points. In particular, the toes of welded and the tops of non-welded and welded cracks become causes of welding fractures because these are stress concentration points. Thus, a method for fatigue life evaluation that can evaluate these stress concentration points in a lump is required. In this study, a new evaluation method for welded parts using strain singularity parameters was developed. The conclusions are as follows: (a) Comparing strain approximation equation Δε = H_εr^<-λε> (Δε: Amplitude of elastic strain, r: Distance from stress concentration part, H_ε: Magnitude of strain singularity, λ_ε: Broadening of strain singularity) to the strain distribution of test specimens calculated using elastro-plastic analysis, the strain singularity parameters H_ε and λ_ε were derived. Using the parameters and fatigue life data that was obtained from the fatigue testing of V-groove specimens (Simulated crack length: 3-8 mm, non-offsetted), a fatigue-life surface was derived. The equation of the surface was logN=-5.3146logH_ε-4.3048λ_ε+21.6888. (b)After comparing the fatigue life calculated by the fatigue-life surface equation and the fatigue life derived by all types of specimens fatigue testing, the calculated fatigue life had approximately good agreement with the fatigue life derived in the test.

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Slip deformation in tri-crystal models subjected to cyclic deformation is investigated by a finite element crystal plasticity analysis code. Accumulation of geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs) are studied in detail. Results of the analysis shown that non-uniform deformation and the high density of GNDs and SSDs accumulated in the form of band around the grain boundary triple junction, these dislocation pattern formation shown that develop during increase of number of cyclic deformation and extend of development of dislocation pattern depend on the strain amplitude. Mechanism of dislocation pattern formation and extend of development of dislocation pattern are discussed from the viewpoint of influence of strain amplitude on dislocation interaction of primary and secondary slip systems.

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Mechanical properties of the spheroidal graphite cast iron are dependent on the spheroidized graphite. In the field of casting, rare earth (RE) is used in a spherical shape of the graphite. However, domestic production of RE is small, I rely on imports. Therefore, reduction of the RE elements is an issue. In this experiment, as compared to the previous studies were produced spheroidal graphite cast iron by using a sphering agent unified element other than RE, we were subjected to fatigue tests. From the results, RE in spherical agents is I have investigated the effect on the test specimen. Test specimen the RE content of 0%, 0.3%, 0.5%, using a 1.0% four types of smooth test specimen were subjected to fatigue tests by a plane bending fatigue tester. Decreased fatigue strength is about 20-33% in the RE0% test specimens were compared with RE-containing test specimens. Result of cross-sectional observation of the fractured test specimen by the test, a large casting defects were observed inside the RE0% specimens. Thus the fatigue strength it is believed to have significantly reduced.

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The study has clarified the relationship of fatigue strength reduction factors K_f of engineering plastics PBT, PEEK, PC between strain concentration factor K_ε in the region of high- and low-cycle fatigue. In this study, we proposed new method of calculation on the basis of the size-effect defined on the ratio of notch to smooth fatigue damaged area. In order to verify the new Kf calculation method to consider the size-effect, elastic-plastic simulation FEM analysis and elastic-plastic fatigue tests fatigue area of carried out on specimens with four kinds of elliptical hole which are made of PBT, PEEK and PC. As results of experiments and calculation, it is clarified that there is the proper relationship between K_f and K_ε in PBT and PEEK, on the other hand, there is not good relation in PC.

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Role of grain boundaries in crack nucleation and crack propagation path in SUS430 stainless steels during high-cycle fatigue was investigated based on the observation results of grain boundary microstructure evaluated by scanning electron microcopy (SEM)/ electron back scattered diffraction (EBSD) analyses, to obtain a clue to grain boundary engineering for improvement of the fatigue property. Fatigue cracks preferentially nucleated along high-energy random boundaries, while the low-angle and low-Σ coincidence site lattice (CSL) boundaries showed the higher resistant to fatigue cracking. Fatigue crack path was affected by local grain boundary character distribution (GBCD). The fatigue crack deflected and branched where the crack tip reached to the low-Σ CSL boundaries.

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To investigate the effects of change in loading amplitude on surface topography, two-step loaded low-cycle fatigue tests of SUS316NG austenitic stainless steel were conducted. During the tests, the specimen's surface topography was regularly measured using a laser scanning microscope. The surface topographies obtained were analyzed by frequency analysis to separate the surface relief due to persistent slip bands from that due to crystal grain deformation. The persistent-slip-bands-induced surface relief evolution and the grain-deformation-induced one were quantitatively evaluated by using arithmetic mean roughness R_a and arithmetic mean waviness W_a, respectively. As a result, the rates of increase in R_a and W_a changed obviously after changing loading amplitude. The results for R_a and W_a agree with the results of surface observation, the increases in the numbers of slip bands and deformed crystal grains changed after changing loading amplitude.

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Society of Automotive Engineers of Japan (JSAE) tested fatigue strength by shear fatigue test for mild steel, JSC270C, and high tension steel, JSC590Y, joined by rivets. As the result of the tests, fatigue strength was independent of the strength of base materials. JSAE reported pre-strain of the rivet affect the fatigue strength.This study investigates fatigue test method of cold rolled steel sheet and estimates material dependence of pre-strain on fatigue strength. We conducted fatigue test for virgin and pre-strained materials. Pre-strain was given to specimen by bending. Pre-strain levels were evaluated by hardness test. Cracks from both sides of the specimen have developed. Many cracks were initiated on the specimen surface and grown with coalescences. It was unlikely to have storong effect of pre-strain on the fatigue strength.

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Fatigue Strength properties of three types of press forming die steels for high tensile strength steel sheets were investigated. Cold work die steel, JIS SKD11 and high speed tool steel, JIS SKH51 were employed as the test material. In addition, newly developed cold work die steel, was less primary carbide than SKD11 was employed as the test material. Four point bending static and fatigue tests were conducted in air. From the experimental results of static bending test, it was found that the flexural strength was higher with increasing carbon content. From the results of fatigue test, Fatigue strength of newly developed cold work die steel was the highest value in three die steels. Fatigue limit of it showed 220 MPa higher than the comparative material steel, JIS SKD11 and 70 MPa higher than the high speed tool steel, JIS SKH51. From the results of fracture surface observation by SEM and EDX, fatigue strength of SKD11 and SKH51 were governed by stress intensity factor range ΔK_I. It was concluded that fatigue strength of newly developed cold work die steel was governed by intrusion and extrusion of the surface caused by surface roughness.

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SKD11 contains many coarse carbides to improve wear resistance and hardness. However fatigue strength of SKD11 decreased due to coarse carbides. Therefore new SKD11 was developed for improving adhesion to surface coating and less primary carbide than SKD11. Rotary bending fatigue test in air at room temperature using hourglass shaped specimen is conducted to clarify S-N property and effect of the carbide on fatigue strength of cold work tool steels. From the experimental results of fatigue test, it was found that the fatigue strength of improved showed high values in the range from 10^4 to 10^7 cycles than that of JIS SKD11. Fatigue strength was increased 220〜240 MPa in low cycle and 250〜260 MPa in high cycle, significant difference in fatigue strength was observed in high cycle. From the results of fracture surface observation by SEM and EDX, it was found that fracture origin of JIS SKD11 was internal coarse carbide. Fracture origin of new SKD11 was surface.

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WC-Co cemented carbides have been widely used for cutting tools, die tools, and machine parts because of their high compressive strength and excellent wear resistance, which are superior to those of tool steels. To use them safely and effectively without failure, it is critical to understand their fatigue crack growth behavior. In this study, the fatigue crack growth tests under a stress ratio R of -1 were carried out on several grades of cemented carbide with different microstructures, in terms of both Co content and WC grain size. Experimental results show that the crack growth resistance increases with increase in both Co content and WC grain size particularly in the low-K_<max> region. Effect of microstructure is discussed in terms of the crack growth path.

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In order to investigate very high cycle fatigue property of AC4CH-T6 casting aluminum alloy, axial loading fatigue tests were performed. Because it was known that the fatigue property of casting aluminum alloy was affected by the influence of casting defects inside the material, the defect inspection of the specimen was conducted by computed tomography with the industrial X-ray CT scanner after making them. As a result, it was expected that this material showed an excellent fatigue property, because there was no large defect in all of the specimens. However, this material had poor fatigue property contrary to expectation. And then, some large size facet of α-dendrite structure weres observed in the crack initiation site.

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For further miniaturization and lightweight of industrial products and electronic devices are required, the necessity for investigating the mechanical properties of micro-materials such as thin films or fine wires increases. Many researchers have been investigated the mechanical properties of micro-materials. Because researchers use different devices and methods in experiments of mechanical properties, there is little data with high reliability of the micro material. In this study, tensile test and fatigue test were carried out using magnesium alloy AZ31 and AZ61 fine wires with the diameter of 200μm for the establishment of new test method and the accumulation of the mechanical propertied data. As results of tensile tests, the tensile strengths and elongations at break from stress- strain diagram of AZ31 and AZ61. As results of fatigue test, S-N diagrams of AZ31 and AZ61 were obtained. The fracture surfaces of tensile and fatigue test specimens were observed using SEM. Finally, the maximum stress intensity factors were calculated from the size of fatigue crack propagation.

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In this study, the fatigue tests were carried out for the cast aluminum alloy. The fatigue property and fatigue crack initiation life of cast aluminum alloy were investigated. As the results of fatigue tests of rotary bending type, the test specimens were fractured over 10^8 cycles in very high cycle area. The fatigue limit did not appear. The crack initiation origins were cast detects at the specimen surface or the specimen sub surface. As the results of the fatigue tests under two-step load variation, in the high stress amplitude area, the fatigue cracks were initiated at the initial stage of the fatigue life of D_1=0.0625〜0.125 in the primary stress damage value. It is found that the cast detect size √<area> on the cross section of the specimen follow Weibull distribution. When the maximum cast detect size is estimated using Gumbel distribution, the estimated maximum cast detect size √<area> agreed well with that measured from the experiment.

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Titanium alloy (Ti-6Al-4V) having bimodal "harmonic structure", which consists of a coarse-grained structure surrounded by a network structure of fine-grains, was produced by mechanical milling (MM) and spark plasma sintering (SPS) to achieve high strength and good plasticity. The microstructure of the MM-processed powder and the sintered compacts were characterized using a micro-Vickers hardness tester, an optical microscope, scanning electron microscope (SEM) and an electron backscatter diffraction technique (EBSD). Harmonic structure was created in the sintered Ti-6Al-4V compacts prepared from the MM-processed powders having fine grains at its surface. The effects of the harmonic structure on the 4-points bending fatigue properties of Ti-6Al-4V alloy was investigated under the stress ratio R = 0.1 in ambient air without any controls of the temperature. The compacts with harmonic structure exhibited higher fatigue strength compared to the conventional coarse-grained material prepared from as-received powders. This was because the harmonic structure increased the tensile strength of Ti-6Al-4V alloy. Moreover, fatigue fracture mechanism of Ti-6Al-4V alloy with harmonic structure was discussed from viewpoints of fractography and microstructural orientations. As results of observing the fracture surfaces, the Ti-6Al-4V alloy with harmonic structure failed from the coarse grained structure with almost the same crystal orientation in the surface fracture mode.

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The purpose of this study is to evaluate fatigue crack growth characteristics of cast Ni based super alloy, Alloy 246. Fatigue crack growth tests are conducted under stress intensity factor range, ΔK, increasing and ΔK decreasing tests to investigate difference of fracture surfaces. It is revealed that fracture surfaces are strongly affected by ΔK. Results of electron back scatter diffraction patterns (EBSD) show that fatigue crack propagates along slip direction. When AAT is increased gradually, fracture surfaces tend to remain mixed mode. When AAT is increased rapidly, fracture surfaces change from mixed mode to mode I. Fatigue crack growth rate of mode I fracture surface is faster than that of mixed mode fracture surface. Based on the evaluation of effective stress intensity factor range, ΔK_<eff>, obtained by displacement field around crack tip using digital image correlation (DIC), crack growth resistance of mixed mode fracture surface is higher than that of mode I fracture surface.

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Zr_<55>Cu_<30>Ni_<30>Al_<10> bulk metallic glass (BMG) is known to show high strength and high corrosion resistance. In the present study, 4-point bending fatigue tests environment have been conducted in air and in water to investigate the effect of corrosion on fatigue properties of the BMG Fracture surface and tensile-loaded surface were observed by scanning electron microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). Experimental results give a significant decrease of fatigue limit in water compared with air environment. In addition, fatigue test in water environment shows a significant corrosion of the tensile-loaded surface. A detailed SEM and EDS analysis has emphasized an increase area subjected to corrosion for specimens in water compared with in air. Finally, corrosion leads to the formation of local stress concentration, resulting in decrease of the fatigue limit of Zr_<55>Cu_<30>Ni_<30>Al_<10>.

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Aiming to enhance corrosion resistance of steel cup, the formability of pure titanium clad sheet by multistage deep drawing was investigated. Since pure titanium has excellent corrosion resistance, the use of the pure titanium sheet is very effective as the anticorrosion coating for steel. The blank was constituted by interposing steel between two sheets of pure titanium sheets. In the experiment, the materials were pure titanium sheets TP270, ultralow-carbon steel SPCC, and stainless steel SUS316L. The initial thickness of the sheet was 0.2 to 0.5 mm in thickness. A total plate thickness of the blank was 1.0 mm. In the deep drawing process, the blank was employed and a flat sheet blank was formed into a circle by a punch. Various cups were drawn by exchanging the punch and die. The die was a conical shape without a blankholder in the subsequent stages. For the prevention, pure titanium blank was treated by oxide coating. By this method, the fresh and clean titanium is not in direct contact with the die during the forming due to the existence of the oxide layer. By oxide coating, the titanium sheet has sufficient ability in preventing the seizure in multistage deep drawing. It was found that the titanium clad cups were successfully drawn.

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Environment problems are calling more and more attentions, so magnesium is a candidate due to its advantages such as light weight and high strength. However, it is difficult to deal with magnesium at a room temperature because of its poor ductility and heating device is need. So friction stir incremental forming process was developed in our laboratory to use the friction heat to form magnesium alloy sheets. Furthermore, incremental forming process was used at that situation which can change the shape of products only changing the NC code. In this study, to solve the problem that magnesium alloys have poor corrosion resistance, it is tired that magnesium alloy sheets and aluminum sheets are jointed during forming into a designed shape. Because of the thickness of sheets, the processing conditions for joining is restricted. Experiments were carried out to find the narrow range of working conditions for joining two sheets. Then the working conditions that sheets were formed and joined simultaneously were found. The joined products were observed under a scanning electron microscope and it has been confirmed that surface alloying was happened at the boundary area between two sheets.

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The effect of the inner diameter of the tools on the mechanical properties of studs formed by friction protrusion forming was investigated. The outer diameter of the tool was fixed at 8 mm, whereas the inner diameter was varied among 3,4 and 5 mm. Studs of 5052 aluminum alloy was formed on 5052 aluminum alloy plates by friction protrusion forming using a friction welding machine. Microstructures and Knoop hardness distribution of the formed studs were analyzed. On the surface of the studs, traces of contact with the tool were observed. The backsides of the base plates show discoloration. The weld interfaces were unclear. The use of tools with inner diameter of 3 or 4 mm resulted in the formation of hollow root. The top of the studs had coarser grained structures than the base metal.

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To improve efficiency of fuel consumption in automotive industry, high tensile strength steels become to be used for automotive body parts. High strength sheets, however, induce large springback in press working, and a variation in bending angle becomes also large as the bending angle and springback increase. To reduce the variation in bending high strength sheets, a servo press was employed and carried out two-stage V bending. SUS304 stainless steel sheets with a thickness of 1 mm was used for specimen. The objective bending angle was set to 90 degrees. From the experimental results, the bending angle in the first stage bending for obtaining minimum variation was 80 degrees. The bending angle in the second stage bending could be predicted from the results of the bending angle in the first stage bending and the stroke was adjusted to get the objective angle. This feedback control enabled to reduce the variation of the bending angle.

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A5052 aluminum alloy sheets were formed into concavo-convex shape by friction stir incremental forming. By the conventional friction stir incremental forming, sheet metals were formed from one side and formed into only concave or convex shape without supporting die. But in this study, an equipment for forming from both sides simultaneously was developed and it was tried to form the sheet metals into concavo-convex shape. To evaluate the forming accuracy by simultaneous forming, formed shapes by double side forming and single side forming with reversing the sheet for forming from both sides were compared. A5052 aluminum alloy sheets with the size of 100 mm x 100 mm x 0.5 mm were used for specimen. From the experimental results, it was conformed that since both sides simultaneous forming is possible to make the two products in one processing, it is possible to shorten the forming time to be half. Forming accuracy of the center part of the sheet can be improved when the forming of the sheet to close the working distance.

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Bending processed the pipes of AZ31 and AZ91 alloy that it is lightest and control on vibration characteristic are superior. It bent the press with the press machine and performed turn pull bending with CNC pipe Benda of KEIYO BEND CO., Ltd. grasp temperature and speed in the bending and checked the influence that a bending condition give to a sample. Performed press bending and rotary pull bending to grasp bending condition to bend the AZ31 and AZ91 alloy that difficulty on bending to welding and bend it. Bend from bending condition, but crack and wrinkle accepted by appearance observation, and becoming wall decreasing thickness and flatness in healthy specimen. Temperature management to important, and decreasing thickness and flatness have to pursue a relationship with becoming it in each bending than this, but examine a method to let burden compression stress axially, and to prevent wall decreasing thickness because it impossible that the rotary pull bending prevents wall decreasing thickness only by temperature management.

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A newly developed Ni base dual two-phase intermetallic alloy that has greater high-temperature strength and hardness than many conventional super alloys has been applied to FSW tools used to join mild steel plates with 1.0mm thickness. Appropriate welding conditions are evaluated by appearance of welded lines and tensile properties. The results show that the higher the tool revolution, the wider the appropriate ranges of welding speed. Furthermore, within the range of the experimental conditions, the slower the welding speed, the higher the tensile strength of the joints.

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Intermetallic alloys and compounds have attractive properties as high temperature structural materials. A dual two-phase Ni_3Al-Ni_3V intermetallic alloy with a nominal composition of Ni 75.0 Al 7.5 Vl 5.0 Nb 2.5(at%) doped with 50 mass ppm boron was formed by low pressure plasma spray process using atomized powder. The dual two-phase and intermetallic alloy whose microstructure exhibits the cuboidal primary Ni_3Al phase and the surrounding channel region composed of Ni_3Al and Ni_3V phases, and contains neither voids nor intermediate products were obtained by heat treatment after spraying. Relationships between the microstructures of the coatings and conditions of spray were discussed.

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The effect of natural aging on the mechanical and damping property of friction welded small rod of 2024 aluminum alloy joint using micro fiction welding machine was investigated The damping property were direction of torsional on vibration testing system. Microstructure of the weld interlace showed fine grain structure than that of the base metal. The hardness of weld interlace shows higher value than the base metal. Softened zone was observed in welded joint, and joint of 4 days after welding showed higher value than that of the joint of 1 day after welding.The maximum tensile strength of welded joint showed 482 MPa became joint efficiency was approximately 97 % of base metal. Elongation of joints were increased by increasing friction time. Damping capacity of welded joint had increased as the hardness of softened zone with decrease than the base metal.

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Critical for the use of aluminum alloys for engine pistons are strength and durability behind customers demand high power and low fuel consumption to protect environment. In general, there are many case of generating cracks in a top part of the piston by thermal load of combustion during car driving. As a countermeasure, AC8A casting aluminum on a top part of the piston partially substitutes with A6061 wrought aluminum which is more strengthen than the ACS A. This paper deals with the joint characteristics of friction welded joint between the A6061 solid cylinder and the AC8A casting pipe. If the joint was made by a conventional friction welding machine, it was clarified that the friction welding of A6061 solid cylinder and ACS A casting pipe was difficult because the travelling phenomenon of the weld interface was cause by the combination of the shapes of the friction welding specimens. To prevent braking deformation until rotation stop, the joint was made by a continuous drive friction welding machine that has an electromagnetic clutch. In addition, the joining strength improved through the joining cross section of both specimens are the same shape of pipe by digging out the surface of the A6061 cylinder. As a result, the joining could be successfully achieved and that had the joint efficiency of 80 - 97% when the joint was made with a friction pressure of 25MPa, a friction time of 0.7s, and a forge pressure of 75MPa and post-weld heat treatment with the T6 of AC8A.

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In the punching rivet method, it is possible to fasten the sheets without drilling. The joint has high strength and out-of-plane deformation of the joint is also small because of the rivet and the rivet holder that are peculiar to this method, hi this study, the punching rivet method was applied to joining of an acrylic resin sheet and an aluminum alloy sheet. The fastening condition and the strength of the joints made by the method were examined. From obtained results, it was possible to fasten an acrylic resin sheet and an aluminum alloy sheet by an aluminum alloy rivet. The acrylic resin sheet of the joint after joining had no crack and joint strength was high. It was certified that the punching rivet method became new joining method for a resin sheet and a metal sheet.

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