The effect of repair using thermal fusion bonding (TFB) on residual compressive strength was investigated in carbon fiber reinforced polyamide 6 (CF/PA6) cross-ply laminate with several impact damage. Cross-ply laminates with different ply-thickness (0.04 mm and 0.12 mm) were prepared in order to investigate the influence of the different impact damage due to ply thickness. The experimental results indicated that TFB was shown as one of the effective methods to repair the impact damage caused by matrix failure and to recover the compressive strength. On the other hand, TFB was not effective to decrease in compressive strength caused by fiber breakage due to buckling before reaching compressive strength of intact specimen.

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Protection of critical facilities against an accidental impact loading is becoming an important consideration to ensure safeguard of the facility. Recently considered accidental impact conditions involving critical facilities are aircraft impact, impact of tornado generated large objects, and impact of tsunami generated large objects on nuclear facilities. Most of protective structures in such critical facilities are reinforced concrete walls, and the prediction of impact performance of these walls is challenging even with sophisticated commercial software as there are variety of concrete material models. Selection of an appropriate concrete material model and corresponding model parameters is not always straight forward. In the present study, performance of two concrete material models available in LS-DYNA is compared using experimental results of aircraft engine impact on reinforced concrete walls. The study is useful for engineers and researchers who have limited experience on the selection of appropriate model for concrete and corresponding model parameters.

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In this study, the impact deformation behavior at the interface of a bi-material having different elastic wave velocities difference of each material is investigated. A split Hopkinson pressure bar method is used for the impact test. The deformation behavior of each material are observed using high-speed digital camera at the speed of 1 million frames per second and the strains distributions at the interface are measured using digital image correlation. The results are compared with the strains in a specimen without interface. The results show that the strain distribution in one material near the interface is affected by the strain in another material. The complicated deformation behavior is observed at the bi-material interface as the results of the interaction of elastic weaves in both materials.

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C/C composites plate was brazed to Ni-based alloy, Inconel-600 plate using Fe-Cr-Ni-(Si,P) brazing filler metal with various thickness of Nb foil inserted. Niobium foil was solved into the brazing filler layer and precipitated along the C/C composites' surface. Although, Nb layer remained in the brazed interface was thinner than the original Nb foil thickness, it acted as the stress relief layer. The shear strength of brazed joint varied with the remained Nb layer's thickness. The shear strength increased for the brazed joint with 100μm of Nb layer, but once dropped for the joint with 200μm. The FEM analysis revealed that the shear strength of brazed joint monotonously increase with Nb layer's thickness. The microstructure in the brazing filler layer was considered to contribute to the tendency of the shear strength with Nb layer thickness.

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Epoxy resins are utilized in many industrial areas as matrix of composite materials and adhesives because of high strength and stiffness. Fatigue properties are important in terms of the long time reliability. To enhance the fatigue life of the epoxy adhesives, the fracture mechanism of the resin between rigid substrates under cyclic loading should be clarified. In this study, the fatigue crack propagation behavior of toughened epoxy adhesive was investigated and was compared with that of bulk resin. The fatigue crack propagation behaviors of adhesives are similar to those of the bulk resins. As the results of fractographic observation, the fracture surface for the adhesive layer are very flat and was different from that of bulk resin where the plastic deformation was popular. The deformation around the crack tip was restrained by the rigid metal substrates and the tri-axial stress was kept in spite of the rubber particle cavitation.

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According to the method based on the Taylor impact test, stress can be calculated by theoretical formulae derived from momentum balance. Various kinds of formulae have already proposed and the optimum theoretical formula depends on material of specimen. In this study, to determine an optimum theoretical formula for annealed and unarmealed pure aluminum, stress-strain curve obtained by an impact compressive test based on the SHPB technique and the Taylor impact test are compared at a similar level of strain rate.

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Armored fighting vehicles with Mine Resistant Ambush Protected (MRAP) designed to counter Improvised Explosive Device (IED) have attracted special interest recently. This paper describes dynamics response of the shock absorption seat to blast load. Mathematical models have been developed to predict the effects of the blast load on the seat-passenger systems. We propose hook-spring mechanism which consists of two springs (hook-spring and cushion spring). Hook spring (harder spring) supports seat and human under normal operation. When they receive the blast force, they tear loose from its spring. After then cushion spring (softer spring) support them. The effect of the hook-spring mechanism seat to blast load is confirmed by numerical simulations and experiments.

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Carbon Fiber Reinforced Plastic (CFRP) is high strength and high elastic modulus composite material. Currently, machining method weaves dry with wet. Sufficient consideration is not accomplished about influence on machining properties of CFRP caused by the immersion. On another front, machining of CFRP is difficult because of excessive extreme tool wear and delamination. The authors investigated face milling performance of CFRP using a newly developed Poly Crystalline Diamond (PCD) tool, water absorption test of CFRP and built up chip collector system which is better suited for PCD tool. We reached the following conclusions. Surface roughness meets precision prescribed. CFRP has water absorptivity. Chip collector system has satisfactory performance.

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The ultimate tensile strength of carbon/epoxy laminated composites in the through-thickness direction at deformation rates up to nearly 1 m/s is determined using the split Hopkinson bar. Two carbon/epoxy laminated composites (i.e., unidirectional and cross-ply) with almost the same thickness are tested at room temperature. Waisted cylindrical specimens are machined such that the direction of the tension loading is perpendicular to the fiber direction of the laminates. The effects of deformation rate and reinforcement geometry on the ultimate tensile strength are examined. It is shown that the ultimate tensile strength increases significantly with increasing deformation rate. The ultimate tensile strength of the unidirectional carbon/epoxy laminated composite is slightly higher than that of the cross-ply one at low and high rates of deformation.

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We examined ejecta size distribution when aluminum alloy 2017-T4 spheres with a diameter of 3.2 mm impacted aluminum alloy 6061-T6 targets with a plane surface and a curved surface at velocities of 4 km/s. We used a two-stage light-gas gun at the Institute of Space and Astronautical Science (ISAS)/Japan Aerospace Exploration Agency (JAXA). To examine the scattering angles of the ejecta, the following was placed 50 mm in front of the target: a witness plate (150 mm × 150 mm, 2 mm in thickness) made of copper with a hole of 30 mm. The ejection behaviors of fragments were observed using a high-speed video camera. The number of ejecta when impacting on the curved surface target was more than that when impacting on the flat surface target.

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When In this study, uniaxial compression tests for synthetic quartz were carried out at quasi-static and dynamic rates to clarify the relationship between the luminous phenomena and the stress-strain curves. The intensity of light generated in the fracture of quartz was measured by a photodiode with photo-sensor amplifier. The fracture manners of quartz such as the number of fragments, the area of fracture surface and the volume of fragments were also examined. Even in the static test, dynamic response of load associated with fracture was precisely evaluated by the load cell apart from the specimen with taking account of unloading stress wave propagation. It was clearly found that the peaks in the signal record of light generated during the fracture of quartz correspond to the changing points of the slope on load-time curves. Especially, the largest peak was measured at the dramatic drop of the load due to the fracture of quartz. The total quantity of light from fracture surface generated in dynamic compression tests was greater than that observed in static tests because the finer fracture fragments collected after dynamic tests provides the wider area of the fracture surface than those in static tests.

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Polyhydroxyalkanoate (PHA) is a microbial origin (inedible origin) plastic, which expected to deal effectively with the food security issue. In this study, in order to use PHA for industrial and machinery parts and products, a polycaprolactone (PCL) pellet was blended with a PHA-based pellet to improve ductility and tensile strength because PCL is a bioabsorbable and biodegradable polymer having high ductility. When the mixing ratio of PCL was 50%, the elongation at break of polymer blend was large and the gauge area of tensile test specimens whitened in the case of static tensile tests, whereas the elongation at break of polymer blend was very small in the case of dynamic tensile tests.

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The effects of bonding configurations on the strength of T adhesive joints have been investigated experimentally. T-joint specimens consisting of glass fiber reinforced plastics (GFRP) and GFRP sandwich panel with structural foam were prepared. An end surface of the GFRP sandwich panel, i.e. a bonding member (web), was bonded to a surface of the GFRP, i.e. a bonding member (flange). Two types of acrylic adhesives, which are different Young's modulus and ductility were used. Three types of joint geometries were proposed and experimentally discussed in terms of the joint strength.

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In the previous study, the effect of strain rate on the micro-indentation (load-displacement relation) has clarified. Therefore, we develop the method for evaluation of the strain rate dependence of materials using the load-displacement relation. First, the relationship between the material constants for Cowper-Symonds constitutive equation (dynamic constants) and the loading curvature was constructed by the response surface, and then the dynamic constants were determined using the inverse analysis. It was confirmed that the dynamic constants could be obtained by substituting the result of the micro-indentation for unknown material into the response surface. By using this method, it is possible to evaluate the strain rate dependence of materials.

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Dynamic numerical simulations for penetration into a target of granular medium were performed and the time and spacial distributions of ejectors were clarified for two kinds of projectiles. Trajectories of particles were also identified and were discussed in connection with the densified wave propagation in the target.

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A novel experimental method for characterizing properties of carbon fiber-reinforced plastics under impact loading was proposed in this study. The dynamic compressive test was carried out by using a Split Hopkinson Pressure Bar (SHPB) system. A zinc buffer was used to reduce the oscillation of the specimen, and consequently the relation of stress-strain could be estimated precisely. The longitudinal strain of gage area could be estimated from the nominal deformation of gage area, and consequently the failure process could be grasped in detail from the relation of stress-strain. The dynamic compressive strength of the material was slightly higher than the static compressive strength.

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The purpose of the present study is to develop a novel implant material which has a superior biocompatibilities and high strength by means of a coating technology. In this study, the cold spray technique was selected and used to surface modification method of a titanium alloy for the development of implant material; the porous titanium coating was sprayed on a titanium alloy, Ti-6Al-4V, by means of the cold spray technique. The cold sprayed biomedical titanium coatings had a low elastic modulus, high adhesion and enough tensile strength after the post-sprayed heat treatment. In this study, the TEM observations of the porous titanium coating sprayed cold spray were carried out.

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Mg coatings prepared at different powder injection position and powder size by cold spraying were investigated as well as their microstructure, micro-hardness and adhesion strength between a magnesium coating and substrate. It is necessary to lengthen the heating section of the nozzle to raise the particle temperature at the time of the collision for coating formation of the Mg by the cold spray. In addition, it was not supposed a remarkable difference of adhesion strength and coating section hardness by the powder size.

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Cold spraying is a promising process to fabricate functional coatings. Because of the solid state particle deposition, the electrical and chemical properties of the cold-sprayed coatings are almost similar to the bulk materials. The most important factor to deposit a particle through cold spraying is known as the critical velocity. When the particle velocity is beyond the critical velocity, the plastic deformation of both sprayed metallic particle and metallic substrate cause the removal of surface oxide layers and newly-formed surfaces are explored. The newly-formed surface yields the metallic bond, and then the cold spray deposition can be obtained. Therefore, the substrate conditions also must be considered to understand the cold spray process. In this study, the influence of substrate roughness on adhesion strength of coatings was investigated by grit blasting. The adhesion strength was examined by a shear adhesion test. The shear adhesion test showed that the grit blasting enhances the adhesion strength. As the causes of these, an anchor effect was suggested.

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Intermetallic alloys and compounds have attractive properties as high temperature structural materials. A dual two-phase Ni3Al-Ni3V intermetallic alloy with a nominal composition of Ni 75.0 Al 7.5 V 15.0 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 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 properties of the coatings and the conditions of spray and heat-treatment were discussed.

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Agglomerated and clushed TiO_2 powders were sprayed by cold spray equipment on an Aluminum (JIS A-1100) substrate. DYMET 412k manufactured by OSPC was used as cold spray equipment and the process gas was compressed air. Sprayed specimen were observed and analyzed by FE-EPMA. Gas decomposition test was carried out using acetaldehyde gas under ultra-violet (365nm) and visible (405nm) LED irradiation. Their impacted particle morphology on substrate was different. Clushed TiO_2 powder could not form coating and their particles were put into substrate. Agglomerated TiO_2 particle powder could form very thin coating and the sprayed plate could decompose acetaldehyde gas under both LED irradiations. It was indicate that cold spraying was useful method to deposit photocatalytic powder.

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In a cold spray technique, which used for making dense and thick metallic coatings without oxidation, a lot of fine solid particles are impinged at supersonic velocity and deposited on a substrate materials. The deposition behavior is affected by many factors, such as particle velocity, size, shape, material, temperature, surface condition, and so on. However, these influences are not completely understood, because accurate measurements of these factors are complicated. Therefore, we developed a large-scaled single particle shot system. Using this system, a pure Al particle with approx. 1 mm diameter was impinged and deposited on a pure Al substrate. The particle velocity was accurately measured and the critical velocity which deposition begins was evaluated. And the microstructure of deposited particles was investigated by SEM and EBSD. From the results, the plastic deformation in a particle increased with increasing particle velocity, and the crystal grains with large plastic deformation adjacent to the particle/substrate interface tended to contribute to adhesion between a particle and a substrate.

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In recent years, we have a problem that the depletion of natural resources caused by large consumption of energy, and global warming caused by greenhouse gases. Therefore, effective utilization of biomass resources friendly to natural environment is attracting wide attention. We have prepared the C/C composite using bacterial cellulose and the third ingredient of Bamboo in this study. The C/C composite developed is a kind of glassy carbon material having excellent sliding properties. This can be used as the sliding parts of robots and soon. So, sliding experiments this material, to clarity the friction and wear characteristics. From the results, it data was possible to obtain a better than diamond-like carbon (DLC). At the same time we have also observed effects on materials to be sliding. As a result, we have found that the influence of the materials to be sliding is changes with sintering temperatures of C/C composite and the third ingredient.

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We conducted on numerical analysis on hydrodynamic and material solutions of a small type wind turbine with about 1.5-2 m diameter of wind receiving area having maple seed type blades made from CFRP. We have proposed a new type of wind turbine blade having the possibility of easy producing the blades which are imitated the rotation of falling maple seed in the nature world. Since the wind power as renewable energy has been come into the limelight by global warming and energy problems, small type wind turbine has been settled in general home and company. However, the widely used wind turbine blades are ordinary propeller type, and there is more complicated technique at the field of producing the blades. We used maple seed type blades made from CFRP because we kept the blades strength by becoming larger diameter of wind receiving area. We obtained the numerical results of Von Misses stress and displacement in the blade on the basis of the results from CFD around the blades. Finally, we investigated the power of the wind turbine in a large wind tunnel.

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In this study, micro-glass balloon reinforced composites which improve by interface reinforcement. The matrix resin of composites is epoxy resin and their filler is the micro glassy hollow particle materials of "Sirasu Balloon". Bending tests was performed by using coupon type specimens of composites. The mechanical properties of the composites were examined from the experimental results. By using scanning electron microscope, the observations for the interfaced bond of particle dispersion and for fracture surfaces were performed from the viewpoint of micro-mechanical study.

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This research treats with high precision shearing process for the plastic sheet. By performing the tensile test, the material characteristics of plastics were evaluated. Furthermore the Finite Element Method (FEM) analysis was performed for the shearing process of the plastic sheet. In addition, the optimum clearance between the punch and the die was examined for the machining condition affecting the cut end shape. The various stress distributions near the crack tip, the punch force strength and the appearance of shear plane were shown in the figures for the evaluation of the process. The optimum processing condition were discussed from those result.

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NTC thermistor is used as temperature sensor which would be hold in severe temperature environment. We must needto know not only electrical properties but also mechanical properties in the sever conditions. In this paper, we study mechanical properties and resistance to thermal shock of poly-crystal semiconductor. After doing tensile tests for 4 types of materials with different compounding ratio, we clarified the difference of mechanical properties for these material. Choosing a type of thermistor specimens, we have done thermal shock test and evaluated the Young's Modulus and flexural strength of NTC thermistor after thermal shock tests from the view point of composite materials.

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Bacterial Cellulose is the natural cellulose, characterized by a three-dimensional structure network of micro fibril. BC possesses an array of unique properties, including high crystallinity, high tensile strength, therefore BC have been an interesting topic in the field of research and development. In this paper, the fabrication condition of Carbon/Carbon composites with BC and phenolic resin, especially temperatures was described and the effects of temperature condition on mechanical properties were investigated. The testing specimens were prepared by burning various carbonizing temperature with different heating rates.

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In order to examine the fatigue limit in interior induced fracture mode for bearing steel, rotating bending fatigue tests were carried out at the stress amplitude 1100MPa below the fatigue limit in surface induced fracture mode. The tests were interrupted at arbitrary number of cycles to charge hydrogen. And then the fatigue tests were continuously carried out. Based on SEM observations of the fracture surfaces, FGA was not formed in all specimens. Fracture mechanics study was performed for FGA formed fracture surfaces. As a result, the relation between the stress intensity factor range of FGA, AKFGA, and number of cycles before hydrogen-charging did not show good correlation. However, AKFGA tended to increase with an increase in the ratio of prediction FGA size to real FGA size. From this relation, AKFGA in which FGA is not formed in very high cycle fatigue regime was estimated.

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It has been clarified that fracture accompanying a fish-eye on its fracture surface occurred under long fatigue life regions in the stepwise S-N curve of an austenitic stainless steel obtained at 700℃. After a large fish-eye, which origin was located at the interior of the specimen, had reached the specimen surface, the fish-eye became a large surface crack and propagated as a Stage II crack. After a small fish-eye, which origin was located at the subsurface of the specimen, had reached the specimen surface, two types of fracture processes occurred. One type was that the fish-eye became a small surface crack and propagated as a Stage II crack. The other type was that fracture surface of the fish-eye was covered with oxides and the fish-eye became a non-propagating occluded crack. In the latter case, initiation of a new crack at the specimen surface was induced by the occluded crack and then fracture occurred. The depth of fish-eye origin from the specimen surface and stress intensity factor at the tip of fish-eye when it reached the specimen surface were pointed out as factors controlling which type of fracture processes occurred.

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It is known that high strength steel will cause the characteristic internal fracture called Fish eye fracture in very high cycle region. From this, in order to use high strength steel more efficiently and more safely, the elucidation of the mechanism of the Fish eye fracture produced in low stress and long-life and construction of the lifetime evaluation method of Fish eye fracture are desired. In this study, we did ΔK decrease fatigue test under vacuum environment, and examined the relation between internal fracture in very high cycle region and extremely slow fatigue crack growth behavior under vacuum environment. As a result, the influence of material strength was not seen under vacuum environment. Moreover, opening stress increases with increases of maximum stress.

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The effects of vacuum environment on fatigue fracture surfaces of high strength steel were investigated quantitatively. Uni-axial fatigue tests were carried out on SNCM439 in vacuum and air environments. 3D-fractography was then performed using 3D-SEM to determine the fracture surface roughness and to clarify the effects of environments on fracture surface. These analyses targeted on three typical fracture surfaces as follows: (a)surface fracture in air environment, (b)surface fracture in vacuum environment and (c)subsurface fracture. As a result, fracture surface roughness of surface fracture in air environment was large compared to that in vacuum environment. On the other hand, fracture surface roughness of subsurface fracture agreed quite well with that of surface fracture in vacuum environment. These results show that the effects of vacuum environment and environment inside subsurface crack on fatigue crack propagation are exactly similar. Therefore the behavior of subsurface crack propagation can probably be estimated from surface crack propagation in vacuum environment.

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Sub-surface fatigue fractures in titanium alloys are frequently observed in very high cycle region. However, the mechanism of sub-surface fractures has many unclear points. This study focused on an idea that the environment around sub-surface cracks resembles vacuum environment. To reveal the effects of vacuum environment on small fatigue crack propagation, uni-axial fatigue tests were conducted in air and vacuum environments using specimens with an artificial small defect. Crack propagation rates were measured by observation of crack propagation behaviors. As a result, fatigue crack propagation rates in vacuum were much lower than those in air. And the distinctive characteristics of small fatigue crack growth behaviors were more remarkable in vacuum than in air.

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Solid solution nitriding (SSN) treatment at 1200℃ was applied to type 304, and the effect of sensitization on fatigue behavior was studied. Furnace-cooled and water-quenched specimens were used for fatigue tests in 3%NaCl condition. In addition, thrnace-cooled specimen was re-solution treated to dissolve CrN. The fatigue strengths of SSN specimens were lower that of untreated one due to sensitization, while water quenching could reduce the effect of sensitization.

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Axial loading fatigue tests had been conducted using friction stir welded Al-Mg-Sc alloy and the effect of welding conditions on the fatigue behavior was investigated. The fatigue strengths were insensitive to the welding conditions due to the high heat stability of Al_3Sc hardening precipitates. Fatigue crack initiation locations were dependent on the stress levels irrelevant to the welding conditions. The dependence on the stress levels could be attributed to the transition of fatigue crack initiation mechanism.

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Orientation changes during fatigue crack initiation process in Si-added ferrite steels were evaluated by the electron backscatter diffraction (EBSD). To discuss the mechanism of the orientation changes, height measurement by leaser scanning microscope and transmission electron microscope (TEM) observation are conducted. The area of large orientation rotations and that of large slope had good correlation with fatigue damaged area. Moreover, the upper 2.3% value of orientation rotation was almost equal to that of large slope. TEM observation showed that steel with lower Si content tends to form clear sub-grain. However, there was little difference in dislocation structure between large and small orientation region in each steels, regardless of Si content. These results suggest that orientation change is mainly brought about by the transformation of surface slope.

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A metal thin film doesn't necessarily appear general fatigue behavior like a bulk material. By a balk and film material, there is difference of restricted state because of differing in the number of grains to the direction of film thickness. In this research the diagram of ratio of slipped grains and number of cycle was sorted by film thickness/grain size ratio in carbon steel thin film under cyclic shear loading. Then slip ratio under film thickness/grain size ratio 0.80 saturated. The influence of grain size was considered to slip band formation by examining grain's existence frequency to direction of film thickness. It was bringing close to actual grains by extending two dimensions grain size to three dimensions. As a result, there was the relation between the slip ratio and the grain's cumulate existence frequency in the value whose film thickness/grain size ratio are near 0.9.

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The following conclusions were obtained as a result of examining the fatigue strength characteristic and the relation of a damage process paying attention to damage to the resin/fiber interface in GFRP based modified PC. 1) Fatigue crack growth rate of the difference in the fatigue characteristics of PDMS-PC and PC-EP is the cause. 2) The damage process of PDMS-PC is a type of crack distribution destroyed while two or more GF end cracks connect.

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Stage I fatigue crack propagation in thin-wall superalloys were experimentally investigated at room temperature, employing miniature compact tension (CT) specimens directly extracted from as-cast Ni-base superalloys. At first, the effect of crystallographic orientation on the fatigue crack propagation was investigated, using a single crystal (SC) Ni-base superalloy, NKH-304, with different primary orientations. Based on the test result of the SC specimens, some significant interactions between the crack and grain boundaries were discussed, using a directionally solidified (DS) superalloy, Mar-M247. It was found from a series of experiments that the Stage I fatigue crack propagation rate in both SC and DS superalloys were significantly affected by the primary crystallographic orientation and the vicinity of the grain boundaries.

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R-curve and fatigue crack growth behavior of partially stabilized zirconia were studied using indentation-strength-in-bending (ISB) method and static and cyclic fatigue tests. The indentation-strength measurements in ISB method indicated that there is no increasing crack extension resistance, that is, a flat R-curve behavior. On the other hand, the relation between crack growth rate and stress intensity factor in subcritical crack growth obtained from lifetime measurements in the static and cyclic fatigue tests indicated that the cyclic loading accelerated the subcritical crack growth rate. X-ray diffraction patterns of fracture surfaces showed that stress induced phase transformation from tetragonal to monoclinic occurred by the loading. As the results, it is considered that the R-curve appeared to be rising fast but saturated at high toughness value, and the micro cracks induced by cyclic loading facilitated the subcritical crack growth.

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The maximum crack size rendered harmless on the weld toe of type 316 stainless steel welded joint by conducting Portable Pneumatic needle-Peening (PPP) was estimated focusing on stress intensity factor of crack tip. Stress intensity factor of external force and that of residual stress introduced by conducting PPP were calculated by FEM analysis. Then, it was found that the maximum crack size rendered harmless is 1.44 mm by comparing the stress intensity factor of semi-circular slit and the threshold stress intensity factor. The estimate value coincided with the result of bending fatigue test.

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The effect of long term thermal aging (900℃, 30,000h) on fatigue crack growth behavior of a directionally solidified superalloy has been studied at both room temperature and high temperature (850℃). At room temperature, the threshold level of the stress intensity factor range, Δk_<th>, decreased for the aged specimen compared to the non-aged specimen. The results were discussed with relation to the microstructure.

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Crack propagation tests of lead-free solder were conducted using center-notched plates under load-controlled conditions. The loading waveform was triangular with fast loading and fast unloading (pp waveform), and trapezoidal with hold time under tension and compression (cc-h waveform). Creep J-integral, ΔJ_c, and fatigue J-integral, ΔJ_f, estimated from load-displacement relations were used to correlate the crack propagation rate. The crack propagation rate, da/dN, was cycle-dependent at high frequency and gradually became time-dependent with decreasing frequency. The transition of da/dN from cycle to time dependence is the region of creep-fatigue interaction. This creep-fatigue interaction was mainly caused by creep deformation was enhanced by cyclic plastic deformation. The relation between da/dN and ΔJ_f for fatigue growth and that between da/dN and ΔJ_c, for creep growth are rather independent without interaction. The striation spacing found on fracture surfaces was nearly equal to the crack propagation rate. A model of the formation of striation formation under creep-fatigue interaction was proposed.

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It is well known that WC-Co cemented carbides have an excellent wear resistance. However, information about their fatigue crack growth behavior is limited. In the present study, the fatigue crack growth behavior of the fine grained WC-Co cemented carbide was investigated as a function of the stress ratio, R. The crack growth rate, da/dN, depends upon the stress intensity range, ΔK, and R. This feature is similar to that of ceramics than that of metallic materials.

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The influence of plate thickness on the crack propagation behavior was studied with single edge-notched specimens which were cut from injection-molded plates (IMP) of short-fiber reinforced plastics at three angles of the loading axis relative to the molding flow direction (MFD), i. e. θ=0° (MD), 45°, 90° (TD). Injection molded plates had the thickness of 1 and 4mm, and were called IMP1 and IMP4, respectively. IMP have three layer laminated structure where the core layer was sandwiched by two shell layers. The fiber orientation in the shell layer was parallel to MFD and that of the core layer was nearly perpendicular to MFD. The fraction of the shell layer to the plate thickness was 0.845 for IMP1 and 0.185 for IMP4. In the relation between the crack propagation rate and the stress intensity factor range, ΔK, MD has slower rates than TD and 45° in IMP1, while in IMP4 MD has faster rates. When the crack propagation rate was correlated to ΔK/E, the relations for different orientations merged together in the case of IMP1. On the other hand, in the case of IMP4, the relations didn't merge. Macroscopic crack path was nearly perpendicular to the loading axis for MD and TD with both thicknesses. The crack growth direction of 45° plates of IMP1 was inclined against the loading axis, while that of IMP4 was nearly perpendicular with repeated up-and-down.

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Cast aluminum alloy, AC4CH-T6, was microstructurally-modified by friction stir process (FSP) with two different conditions of strain rates and plane bending fatigue tests were performed to investigate the effect of process condition on the fatigue behavior. The tool traveling speed was set to be constant, 150 mm/min and the tool rotational speeds were set to be 500 and 1000 rpm. Casting defects were eliminated and the fine grains were obtained by the FSP. Grains became finer in specimen FSPed in lower strain rate compared with that FSPed in higher strain rate. The fatigue strengths of FSPed specimens were highly improved compared with the as-cast material, which is attributed to the elimination of casting defects and the grain refinement. The fatigue strength of the specimen FSPed in lower strain rate was higher than that FSPed in higher strain rate. EBSD analyses revealed that the strong texture was formed in the FSPed specimen along which fatigue crack grew.

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The general method is not always effective for the measurement of fatigue small crack growth properties by relation of accuracy and a device characteristic. Non-contact and the highly precise measurement are expected by the use of a magnetostriction effect to apply in this study. The small crack growth properties measurement by a magnetic field change with the magnetostriction effect that was one of a characteristic of magnetism of ferromagnetic substance was studied. Using a coil, a magnetic field change with magnetostriction effect was detected, and the waveform change of the output was inspected. The experiment result was revealed that the small crack affects a magnetic field change by a magnetostriction effect.

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In rolling contact fatigue (RCF), cracks are usually initiated from inclusions under the surface and propagated to the contact surface. In the present study, RCF cracks was observed using synchrotron radiation computed laminography (SRCL) in SPring-8. For observation of crack propagation, ex situ rolling fatigue test and SRCL were applied to same sample. Laminography is suitable for the observation of sheeted material and sheeted sample is useful for operation of rolling fatigue tests. The specimen with flaking damage was measured by SRCL. It was found that two types of cracks, vertical crack and horizontal crack under the contact surface, which is typically rolling fatigue crack, can be measured by SRCL. For observation of RCF crack propagation, vertical crack which initiate from inclusion and propagated in the direction perpendicular to the contact surface, could be detected. SRCL and fatigue tests were conducted three times. As results, crack propagation could be observed between first and third measurements, while the different part of crack was detected in second measurement. Residual compression stress is considered to affect the observation of RCF crack. SRCL is concluded to be effective for evaluation of initiation and propagation behavior of crack in the rolling fatigue.

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This study has applied the potential difference method using small four-point probe to the non-destructive evaluation of multiple-site small cracks in the low cycle fatigue of SUS316L at 823K in air. The variation of the potential difference detected by the small probe monotonically increased with the number of load cycles and showed sudden increase in the last stage of fatigue. The laser microscopy determined the morphology of small cracks, revealing the random nature of crack initiation sites and increase in the standard deviation of surface crack length with the progress of fatigue. These results revealed that the present fatigue process can be divided into four stages and that the beginning of the last stage can be detected by the four-point probe.

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