New experimental technique (Disk-on-Rod Test) for the evaluation of thermal shock fracture behavior of ceramics was developed. The disk specimen with 20mm radius was heated to high temperature and quenched by means of contacting with the cool metal rod. The transient temperature on the disk specimen was measured by IR camera and thermal stress was calculated by finite element method. AE signals during thermal shock fracture were detected using an AE sensor attached on the bottom of the metal rod. It was understood that the maincrack was initiated at the center of the disc specimen and it was propagated with the deflection, arrested and re-propagated after several seconds. This behavior showed good agreement with the result of the thermal stress field and AE analysis. The critical stress for maincrack formation was determined by AE analysis. Consequently, the microfracture process during thermal shock fracture was well understood.

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The purpose of this investigation is to examine the quantitative evaluation of adhesion strength of the porcelain enamel with the steel boll indentation test and AE method. The fracture toughness test and the body force method analysis of the steel boll indentation test were carried out the investigation of relations of crack propagation and boundary fracture. In result, (1) the characteristic of ring crack and contact impression were found by AE method, (2) using fracture toughness test and body force method analysis, the occurrence load of boundary fracture was about 400N.

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This report describes the study on joining phenomena in 1st phase of friction welding. Observation of the joining phenomena showed that during the weld faying surfaces rubbed each other, the friction torque was maintained nearly constant. The seizure and the joining occurred at the center portion of them. Then, as they extended from the joint center axis toward the periphery (outer surface), the friction torque increased rapidly. The friction torque reached to the initial peak torque after the welded interface was joined completely, and upsetting of both substrates occurred. It was clarified that the friction time from the friction start (surface contacting) to the initial torque, hereafter called as "elapsed time for initial torque", were variant with the pre-heat at the weld faying surface. The initial torque and the elapsed time for initial torque decreased with increasing the weld faying surface temperature. As a conclusion, the 1st phase can be divided the initial friction part and the seizure part, and the mechanism in the 1st phase of friction welding will be clarify by them.

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This report describes the simulation of friction torque and temperature at welded interface in 1st phase of friction welding. The simulation models at the initial friction part and the seizure part were made from the observed joining phenomena at the 1st phase. In actual simulation, the real contact area and the thermal stress at welded interface in initial friction part, and the seizure temperature and the relative speed of welded interface in seizure part were considered. The calculation of the friction torque and the temperature at welded interface were carry out in compound of the friction pressure, the relative speed and the flow stress at base metal. The calculated values about friction torque, initial torque and elapsed time for initial torque were approximately consistent the experimental values. The calculated values about temperature at welded interface of center portion were higher than that of periphery (outer surface) portion at the time that the friction torque reached to the initial torque. As a conclusion, the friction torque and the temperature at welded interface could be simulated by the made simulation model in 1st phase of friction welding.

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An investigation has been carried out concerning the influence of wet environment on the fracture behavior of γ-alumina single fiber (Altex). Tension-tension fatigue tests were conducted under sinusoidal waveform in dry air, laboratory air and wet air. Sustained load tests (SCC tests) were conducted in dry air and wet air. For fatigue tests in dry air, two types of failure mode were detected; fracture during the first cycle and no failure after 1.0×10^6 cycles. In contrast with this, for fatigue tests in laboratory air and wet air, fiber fractured depending on the cyclic stress. The fatigue strength in laboratory air and wet air was lower than that in dry air, indicating that the strength decreased with the increase of amount of moisture. The same tendency was observed for SCC tests. In dry air, some specimens fracture at the beginning of SCC tests and the others did not fracture after 2.0×10^5s: the strength of SCC tests in wet air was smaller than that in dry air. Time to fracture of fatigue and SCC tests were almost the same. The fracture surfaces were observed with a high-resolution field emission type scanning electron microscope and were quantitatively analyzed to correlate the fracture behavior of the fiber.

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An experimental investigation was made on the effect of fatigue on the change of interface shear sliding stress in SiC fiber-reinforced Ti-15-3 composite. Push-out and push-back test was carried out for both pristine and fatigued composites to examine the change of the interface shear sliding stress by using in-situ SEM push-out equipment. The interface shear sliding stress of pristine composite decreases with increasing test temperature. After the fatigue test, the interface sliding stress was strong dependence on the interface wear behavior during fatigue.

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To clarify the effect of hardness on fatigue characteristics of structural steel in an Extremely High Cycle Fatigue(EHCF) regime, rotational bending fatigue tests were carried out for two types of specimen with different hardness of microstructure. Fracture surfaces were observed using a Scanning Electron Microscope to examine the fracture mechanisms. Two types of fracture modes, surface fracture and internal fracture, were observed for high-strength steel. In middle strength steel, however, surface fracture mode alone was observed instead of fatigue crack started at nonmetallic inclusion. Computer simulation was also performed to discuss the fatigue properties in EHCF regime. The proposed model was possible to predict fatigue properties of both high-and middle-strength steel and showed that the possibility of internal failure (fish-eye failure) in EHCF of middle-strength steel.

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Uniaxial tension fatigue tests of high strength steel, SNCM439, were carried out in air and high vacuum environment. As a result, the following were obtained : (1) Compared with surface fractures in air, the fatigue life of surface fractures in high vacuum tended to be longer. (2) High vacuum environment strongly influenced the fatigue fracture surface in the initial stage of crack propagation. (3) High vacuum environment was similar to inner environment of materials. (4) The formation of Optically Dark Area (ODA) closely related to mean stress.

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Gigacycle fatigue characteristics of high speel steel, JIS SKH51 was investigated under cantilever-type rotary bending fatigue tests in an open environment at room temperature. As a result of fatigue tests, S-N curve was clearly classified into two types of fracture modes by the different crack origins. One fracture mode occurred at the surface inclusion in the region of short fatigue life and high stress amplitude level. The other was at the subsurface inclusion in the region of long fatigue life and low stress amplitude level. The transition of crack initiation site from surface to subsurface appeared at about the stress amplitude of 1050MPa and 2x10^4 cycles, which was not affected by the tempering temperature of the specimen. Fatigue fracture mechanisms were discussed through the detailed observation of subsurface crack initiation site.

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To investigate the interrelation between high-cycle fatigue behavior and stress ratio (R=σ_<min>/σ_<max>), uniaxial fatigue tests were carried out under two different stress ratios, R=-1 and -0.5. The results are as follows: (1)The difference of stress ratios had a great influence on mechanism of interior fracture. (2)When stress ratios were negative, softening type fracture sometimes occurred. (3)Stress ratios had significant effect on aspects of fracture surface. (4)It is inappropriate and risky to apply modified Goodman diagram to the evaluation of a long fatigue life where interior fractures occur.

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In order to apply the ultra-sonic fatigue test as an accelerated method for the practical use, fatigue test have been performed on ferrite-base spherical graphite cast iron. Materials used have various graphite diameters and the tensile strengths. The testing method includes the axis-direction fatigue, rotating-bending and ultra-sonic fatigue tests. In the present study, after various parameters have been considered, a equation is proposed for prediction the rotating-bending or axis-direction fatigue limits from the ultra-sonic fatigue testing results.

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Rotating bending fatigue tests were carried out on austempered ductile cast iron (ADI) with shot-peening (SP) treatment, and influences of the SP treatment on fatigue property and fracture morphology were investigated. As results, the improvement of fatigue strength of shot-peened ADI specimens was identified before the region of the 10^7cycles. Therefore, the S-N diagram of shot peened ADI and fatigue strength of non shot-peened ADI cross at near 10^8cycles. It is expected that the SP treatment results not only the high level work hardening and the high level compressive residual stress on the surface layer of the specimens, but also the decrease in casting defeats in near surface. Generally they lead a considerable improvement of fatigue strength. So the hardness distribution in the surface layer of the SP treated specimens was measured. Furthermore, the fatigue fracture mechanism was discussed in detail from fracture morphology that obtained by observation of crack initiation site with a scanning electron microscopy.

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The object of this study is to investigate the effect of coating of ceramic film on the fatigue characteristic of the ultra thin sheet material. Smooth specimens of austenite stainless steel SUS304 (0.05mm thick) were fatigue tested under constant tension-tension loading condition after the surface of the specimen was coated with sputtered TiN film of thickness from 0.5 to 2.5 μm. The influences of coating on the S-N curves were examined. The micro hardness of TiN film and the residual stress of the surface of SUS304 were also measured. The following results were obtained, (1) the fatigue strength of coated specimens increased at about 30 % in the high cycle region and were little influenced in the low cycle region, (2) the fatigue strength in the high cycle region somewhat depended on the film thickness, (3) the increase in fatigue strength is explained by the hardness rather than the residual stress.

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This paper reports the endurance of cobalt-cemented tungsten carbide (WC-Co) cutting tools with CVD diamond coatings, which were deposited with various methane concentration. We examined the adhesive toughness of coatings deposited on WC-Co substrates with various methane concentration. Discussion would be focused on the correlation between the adhesive toughness of diamond coatings and the performance as wear-resistant coatings.

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The influence of environment on fatigue crack growth behaviour was investigated in nearly lamella and duplex titanium aluminides. The hydrogen evolution kinetics was analized by thermal desorption spectroscopy. When the cathodic charging is applied, the fatigue crack growth rate becomes higher than in dry air, in particular at higher stress intensity factor range. The hydrogen evolution rate is increased by cathodic charging, with lower temperature peaks and higher ones. The peaks at lower temperature are correlated with hydrides decomposition and detrapping of hydrogen from microstructual imperfections such as microvoides. As received materials also show an evolution peak at a higher temperature, and the evolution rate is independent of cathodic charging. In addition, the evolution rate at a higher temperature above 800℃ is increased by cathodic charging. These hydrogens are considered to have an important role on fatigue crack growth acceleration.

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The experimental study on the optimum thickness of coating film for the fatigue strength of surface modified TiAl intermetallic alloy was carried out. The main results were obtained as follows. (1) The fatigue strength of TiAl intermetallic alloy could be improved through the optimum thickness of TiAlN hard coating film, that is 3 μm. (2) From micro-fractography, two different types of fatigue fracture mechanisms were found. For the thinner coating film, the shear mode of fatigue initiation crack was occurred. On the other hand, the thicker coating film, the TiAlN film cracking triggered off the tensile mode of the fatigue initiation crack. (3) Therefore, it could be comprehended that the optimum thickness of coating film for the fatigue strength of surface modified TiAl intermetallic alloy had been controlled through the two types of roles in the hard film. Then, the one effect is the constraint of slip deformation and the other is the Griffith crack of film cracking.

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In the past efforts were focused on pursuing the formulation of chemical composition rather than the heat treatment conditions of aluminum alloys which become strong as being aged. Studies on optimizing the heat treatment conditions are few, and reports dealing with heat treatment conditions and test conditions based on actual use are quite rare. In this study, two aluminum alloys, AC4C and AC2B, as representative alloys being used for vehicle engines, were T6 tempered and additional annealed before measuring the mechanical properties and thermal fatigue of the materials. Especially temperature dependency was evaluated to compare the two materials. Thermal fatigue life was evaluated only on AC4C, and the effects of aging on fatigue life were clarified by studying relation between plastic strain energy density and fatigue life, as well as by observing the microstructure of aged samples by TEM.

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Heat cycle test of ceramics-sprayed type 304 stainless steel was carried out. Surface strain was measured using the laser speckle strain/displacement gauge (SSDG) during the heat cycle test. Fatigue processes were discussed with result of both surface strain measurement and microscopic observation in the longitudinal section of the specimen. It was found that heat cycle fatigue life of LPPS-bond-coated specimen was longer than that of APPS-bond-coated specimen.

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Statistical characteristics of relaxation behavior of compressive residual stresses with time, about in 1500 days after quenching, was investigated for two kind of induction hardened carbon steel S45C quenched into city water (W specimen) or the water containing 3 % polyvinil-alcohol (S specimen). The longitudinal and circumferential stresses at two points on the surface of specimen were measured by X ray sin^2 ψ method again after some intervals. A little relaxation of compressive residual stresses with time in room temperature (mean temperature 21℃) was recognized for S specimen and W specimen. Relaxation behavior of median value with time may be expressed by an equation which was almost equivalent with the relaxation behavior during creep process.

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This study was performed to demonstrate the feasibility of performing liquid helium temperature (4 K) small punch (SP) tests on austenitic stainless steel weld for Large Helical Device(LHD) superconducting magnets. The SP specimens (10×10×0.5 mm) were prepared from the different locations of electron-beam weld in type 316 stainless steel to examine the variation of the fracture properties in the weld and its heat affected zone. Previously proposed correlations for SP and elastic-plastic fracture toughness test methods were applied to predict a SP test-based fracture toughness from equivalent fracture strain. A finite element analysis was also performed to convert the experimentally measured load-displacement data into useful engineering information. The maximum strain energy density was calculated and correlated with equivalent fracture strain. The heat affected zone with high Vickers hardness at room temperature shows lower fracture toughness, compared to other regions.

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