Rotating bending fatigue tests on plain specimens were carried out for ultrafine grained copper. The specimens were produced by equal channel angular pressing with 4 passes (UFG4) and 12 passes (UFG12). The growth behavior of a small surface-crack was monitored. A major crack, which led to the final fracture of the specimen, initiated from slip bands and shear bands. After initiation, the crack grew linearly in the shear direction of the final pressing. There were different morphological features in fracture surfaces between UFG4 and UFG12. This difference could be explained by a quantitative model with the reversible plastic zone size and grain size.

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Recently, polymer materials have increasingly used in many industries due to their unique properties, such as chemical corrosion resistance and its lightness. Despite the investigations which are being carried out on the fatigue phenomena of epoxy resin with various kinds of fibre, the epoxy does not seem to have been fully studied. Moreover, there is lack of understanding about the fatigue behavior and its mechanism. In cyclic bending fatigue tests, on the other hand, the resin are easily fractured even though the stresses are below the critical values. The objective of this study is to analyze the fatigue crack growth behavior of epoxy resin (bisphenol-A-epichlorohydrin type epoxy resin) during mechanical repeated loads. The rotating bending fatigue test was carried out in order to analyze the fatigue crack propagation. A notch was introduced on the specimen, therefore a crack propagates and cause the final fracture of the specimen. In this paper we tried to find the fatigue crack behavior.

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In the design of structures made of engineering plastics by analysis, the most important mechanical property is fatigue strength. In this paper, in order to obtain fatigue strength of engineering plastics namely PC, PBT and PEEK, the fatigue test applied cyclic out-of-plane bending is performed on three kinds of specimen which is hour glass shape, a center circled hour glass shape and a strip with a center circle hole. The fatigue tests were performed in the wide range of failure life from 5000 to 10^7 cycles. It is cleared by the test that (a) low cycle fatigue life of PC, PBT and PEEK is almost equal each other and (b) fatigue endurance limits of PBT and PEEK is equal each other, but their values is 2.8 times that of PC. These fatigue strength behaviors of engineering plastics is different from that of general metal materials

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The fatigue crack propagation behaviors were measured using compact tension and center cracked tension specimens made of polycarbonate, polybutylene terephthalate and polyetheretherketone. Crack propagation rates of these materials were successfully correlated with cyclic stress intensity factor. In addition, we measured and simulated semi-elliptical surface fatigue crack propagation in polycarbonate. The simulation results were in good agreement with experimental, indicating that the fatigue crack propagation behaviors of polycarbonate can predict using the same prediction method for metals.

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In order to study the effect of the interaction and coalescence of multiple surface cracks by slit type surface crack on static fatigue behavior of brittle materials such as glass and ceramics, the various slit length were introduced on the surfaces of plate specimens of glass ceramics by scriber. Where, glass ceramic material with crystal grain size of about 0.05μm was used. It was found that the time-to-failure for a given applied stress significantly decreased with a increase in the distance of the slit length. Furthermore, the fatigue crack propagation was examined by ultrasonic testing. As the result, the ultrasonic velocity of transversal wave decreased with the progress of loading time.

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R-curve and crack propagation behabior were studied for partially stabilized zirconia. R-curve obtained by the indentation strength in bending method, where beam strength measurements were made using the specimens with indented loads in the range of48-294 N, indicated that there was no increasing crack extension resistance, i.e. flat R-curve behavior. On the other hand, .KI-V curve obtained by constant stress rate tests using indented beam specimens indicated that there was a large effect on fatigue fracture of slow crack growth, i.e. the small crack propagation parameter of n=7.3. As a result, it is considered that the high fracture toughness value in partially stabilized zirconia is not caused by process zone wake, but is done by only frontal process zone produced in the crack tip.

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This article verifies a method of predicting the fatigue life of materials under random vibration containing nonlinear loading. We approximated stress frequency distribution in nonlinear range by exponential function. Next, fatigue lives were predicted with stress frequency distribution calculated by Dirlik's method and mathematically-formulated frequency in nonlinear range. As the result of the comparison, the error in the predicted fatigue lives calculated by Dirlik's method to those calculated by proven Rainflow method was within 50 percents. In addition, the predicted fatigue lives calculated by Dirlik's method were 1.79 times as much as those resulted from random fatigue tests with sheet welding test pieces in average (Rainflow method was 1.93 times). We indicated this improved method could predicted the fatigue live with same precision with Rainflow's method.

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A small artificial hole is regarded as a pre-crack and square root area parameter is considered as one of the most important parameter for the fatigue limit of materials which contain small defects. In this study, introducing a sharp notch by using focused ion beam (FIB) or a small artificial hole which have the same area on the quenched and tempered 0.45% carbon steel specimen, we carried out these specimens fatigue tests and we investigated the difference of the two defect shape in the hard material. From the fatigue tests, we obtained two important results. First, the fatigue limit of the specimen with the small artificial hole was higher than the specimen with the FIBed notch. Second, fatigue crack initiation and propagation behavior was different between the two types of the specimens. Usually, there are no differences for annealed steel in the two defect shapes. Therefore, the hardness may affect the fatigue crack behavior of the two defect shapes.

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In the present sturdy, fatigue test ware different specimen taking directions and load ratios using extruded Mg alloy to take a particular texture with respect to the extrusion direction, investigated effect of fatigue crack propagation behavior due to the difference in the loading directions on crystal. Fatigue crack propagation behavior ware investigated to crack propagation experiment, surface observation, fracture surface observation and pole figure measurement.

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Stress strain behavior at the notch root under cyclic loading was investigated with finite element analysis for 2024-T4 aluminum alloy. Results of the analysis indicated that plastic deformation occurred at the notch root and stress ratio at the notch root decreased with increase in applied stress amplitude level. Fatigue tests were carried out with smooth and notched specimens. The experiment results showed transition behavior of S-N curve in notched specimen. According to result of finite element analysis, decrease in stress ratio induced by local plastic deformation at the notch root might affect the transition behavior of S-N curve in notched specimen.

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In the present paper, fatigue strength of a notched specimen subject to multi-axial cyclic stress is formulated as a function of an equivalent cyclic stress ratio (named as R_<EQ> -ratio). R_<EQ> -ratio is derived from a hypothesis of plastic adaptation that reflects micro-mechanical behavior of a persistent slip band, and it is proposed as a corresponding parameter between cyclic stress conditions of notched and un-notched specimens subject to multi-axial cyclic stress. R_<EQ> -ratio is given as function of a theoretical stress concentration factor K_t and a nominal cyclic stress ratio RN. A notch-root stress range Δσ_<NR> of the multi-axial stress condition is defined based on Kawamoto's Fatigue Criterion. Fatigue strength is plotted on R_<EQ> -Δσ_<NR> diagram. As a result, the fatigue strength σ_<w1> and σ_<w2> are clearly distinguished. A notch size effect is considered on the basis of the notch behavior map and a size effect factor is introduced for each of σ_<w1> and σ_<w2> . Consequently, both fatigue strength diagrams of σw1 and σw2 are formulated.

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In the present study, rotating bending fatigue test were performed on cold tool steel SKD11 to investigate characteristics of fatigue strength, internal crack propagation and surface crack propagation. In addition, fracture surfaces of the failed specimens were analyzed with a scanning electron microscopy (SEM).

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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 and fatigue properties is limited. In the present study, a rotating bending fatigue test was carried out on a fine-grained WC-Co cemented carbide to evaluate its fatigue life and crack-growth behavior. From successive observations of the specimen surface during the fatigue process, it was revealed that most of the fatigue life of the tested WC-Co cemented carbide was occupied with crack-growth cycles. Using the basic equation of fracture mechanics, the relation between the rate of fatigue crack-growth da/dN and the maximum stress intensity factor K_<max> of the WC-Co cemented carbide was derived. From this relation, both the value of the threshold intensity factor K_<th> and the fatigue fracture toughness K_<fc> of the material were determined. Fatigue lives of the WC-Co cemented carbide were estimated based on the fatigue crack-growth law. Furthermore, relationship between its crack-growth rate and crack-growth path was studied on the basis of the detailed observations of the crack-growth path.

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A TWIP (Twinning Induced Plasticity) steel is an austenitic steel which contains about 30% Mn , 3% Si and 3% Al, and have attracted much attention for their excellent mechanical properties such as its strength and strain hardening. Fatigue life is an important property of the material. In the study, to find the relationship between the strain hardening and the fatigue life for the Fe-30Mn-3Si-3Al TWIP alloy, analyses of the strain hardening under different applied strain were performed. For this, tension and compression strain controlled low-cycle fatigue tests were carried out in order to obtain the relationship between the strain hardening and the fatigue life. From the test, the stress-strain curve and the stress which changes as increasing the number of cycles were obseved. Briefly, the results indicated the state of hardening rate under Δε = 2.0% was higher than Δε = 1.0% conditions. In this paper we tried to find the work-hardening effect under the low cycle fatigue loading.

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Fatigue crack growth behavior of metallic materials before and after high pressure torsion (HPT) treatment was investigated using RCT-specimen under tension-tension loading. In order to clarify the influence of crystal lattice on fatigue crack propagation process, specimens made of pure Fe (bcc) and 99.9%Ni (fee) were examined. The growth of fatigue crack was observed by optical microscope during fatigue process and the fracture surfaces were observed using scanning electron microscope. From the results, it is found that the relationships between crack growth rates, da / dN, and stress intensity factor range, ΔK, in HPT-processed specimen of the both materials are almost the same at low ΔK region, but in ΔK values is above 30MPam_<1/2>, da / dN of 99.9% Ni increased in comparison with that of Fe-11ppmC. Stripe like pattern was observed in the fracture surface of the both HPT-processed specimens, but not observed in untreated specimen.

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A model for crack initiation, growth and coalescence of low cycle fatigue for steels was proposed based on experimental observations. In the present model, crack initiation resistance, R, was given for grain boundary by weibull random number. Grain boundary accumulated strain, ε, in each cycle and cracks initiated from the grain boundary when R < Σε. Parameters of weibull random number and ε was determined so that the number of cracks and sum of crack length agreed with the experimental results. Crack growth was calculated by elasto-plastic fracture mechanics. Crack coalescence was considered based on FEM simulations, while the effect of low aspect ratio caused by crack coalescence was considered. Fatigue simulations were performed for three steels, whose fatigue lives and crack growth behaviors of simulations exhibited fairly good agreement with those of experimental result including many coalescences.

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When crack analyses are performed for the structural integrity evaluations, the hexahedral elements are adopted in generally. It is very time consuming to build the finite element mesh using the hexahedral elements. Therefore, automated mesh generation by using the tetrahedral elements is adopted in present software system. Automated parametric analysis system from the meshing to the stress intensity factor computation can eliminate the manual operations completely. In this paper, automated parametric system is briefly described and a numerical example is presented.

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Creep damage and creep -fatigue damage were imposed to the austenite stainless steel SUS304HTB for boiler tube use. EBSD (Electron BackScatter Diffraction pattern) observations were conducted on the creep and the creep-fatigue damaged samples using GROD (Grain Reference Orientation Deviation) maps and Phase maps. Area averaged GROD: GRODave and area fraction of alpha phase f_a(%) were used as the evaluation parameter to creep strain and accumulated creep strainrange. GRODave showed linear relationship with those strains except at final rupture stage. fa showed similar linear relationship with those strains except at the final rupture stage and the initial stage. Proportional relationship was also observed between the equivalent diameter d_v obtained from the creep void area and the estimated creep strain value ε_<cg> obtained from GRODave as well as f_a. These results indicated the EBSD observation could be effective for quantitative evaluation of permanent strain and phase transformation during creep and creep-fatigue damage process.

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The change in fatigue strength due to the mean stress and root causes of the change were investigated for Type 316 stainless steel. 20% cold worked specimens were subjected to stress controlled fatigue tests under the mean stress in air at room temperature. Although the mean stress tended to show a beneficial effect on the fatigue life under the same stress amplitude, it had a detrimental effect under the same effective strain range. It was shown that the reduction in fatigue life was brought about by ratcheting deformation during the fatigue tests.

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To clarify the effect of surface conditions for fatigue strength of super duplex stainless steel, plane bending fatigue tests were conducted with four types of surface conditions; emery polished, machined, shot blasted and grinded surface. Furthermore, surface residual stress, hardness and roughness were measured. As the result, fatigue limits were varied by surface conditions and it was considered to be affected by not only surface roughness but also residual stress and work hardening. In this study, √<area> parameter model with a-phase stress gave a good prediction for fatigue limit of super duplex stainless steel.

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Acoustic emission (AE) testing is one of the major nondestructive testing (NDT) techniques, and it can be used as the real-time monitoring method for the purpose of detecting fatigue damages. However, AE testing data for steels during the low-cycle fatigue test is rarely reported. In this study, AE monitoring was conducted during low-cycle fatigue test for austenitic stainless steel with the aim of detecting fatigue damages and identifying the source of AE. Those AE occurred in the process of increscent phase which is loading under tensile and unloading under compression and the contact of the crack surfaces were observed at the increscent phase. This means that friction of the crack surfaces induced AE. Therefore, the potential for monitoring low-cycle fatigue crack was demonstrated by focusing on the friction-induced AE (secondary AE).

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The fatigue and fracture behavior of C/C composites fabricated using fine-woven carbon fiber laminates with α=0/90° direction were investigated. The effect of the slit configuration on crack initiation and growth behavior was observed. Specimens with blunt-notches and center-holes were also used to compare the fatigue strength and crack growth behavior. Non- propagating cracks were observed and fatigue limit was defined as the maximum stress at which specimen did not break for N=10^7 cycles stress application. The longest fatigue life was obtained in the case of specimens with shorter slits. The relationships between fatigue strengths and specimen shapes were analyzed by stress concentration, K_t and stress intensity factor, K_I. The effect of slit configuration on fatigue strength was then discussed regarding both the experimental and calculated consequences.

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Fatigue fracture behavior in two types of laminate specimen ([0_4/90_8/0_4] and [90_4/0_8/90_4]) with a hole in the middle was investigated under cyclic tensile loading. Two parameters were examined and evaluated: an equivalent stiffness and a dissipated energy calculated from hysteresis loop area in one cycle loading. Fatigue damages of specimen surface and around a hole were observed using replicated method and a scanning acoustic microscope (SAM) respectively. Four stages of fatigue damage process were recognized; (I) matrix cracks appeared around a hole and propagated in longitudinal and transverse directions, which led to steep reduction of the equivalent stiffness. (II) inter laminar delamination at 0/90 inter-ply occurred at the initiation sites of matrix cracks, and grew to the edge of the specimen. This brought on increasing area of hysteresis loop and reduction of stiffiiess. (III) inter laminar delamination took place fully in the transverse direction followed by further extension in the longitudinal direction. (IV) when the propagation of inter laminar delamination grew to the gage points of the displacement meter, fatigue loading was sustained by 0 degree layer, i.e.,0 degree fiber.

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The following conclusions were obtained as a result of examining the fatigue strength characteristic from observation of fatigue testing and a fracture paying attention to damage to the resin / fiber interface in GFRP based modified PC. 1) The damage mechanism was the same although Young's modulus fell PDMS-PC compared with PC-EP. 2) In fatigue testing, the life difference in a high stress region is based on the difference in a damage mechanism.

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The influences of fiber orientation and stress ratio on the crack propagation behavior were studied with single edge-notched specimens which were cut from an injection-molded plate of short fiber reinforced plastics (SFRP), at five fiber angles relative to the loading axis, i.e. θ=0° (MD), 22.5°, 45°, 67.5°, 90°(TD). Macroscopic crack propagation path was nearly perpendicular to the loading axis for case of MD and TD. For the other fiber angles, the crack path angle increased with decreasing fiber angle. In the relation between crack propagation rate and the stress intensity factor range, ΔK, the propagation rate of fatigue cracks was slowest for MD, and increased with increasing fiber angle. When the crack propagation rate was correlated to ΔK/E (Young's modulus), the relations for different orientations merged together. The crack propagation rate was mainly controlled by the maximum stress intensity factor K_<max> at high rates and by stress intensity factor range ΔK at low rates.

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The stress induced martensitic transformation stress and the yield stress of the Fe-28Mn-6Si-5Cr shape memory alloy under various temperature conditions were studied. From the result, the martensitic transformation stress increased by 1.0MPa/℃ with the increase of temperature. On the other hand, the yield stress decreased by -0.7MPa/°C for the temperature conditions from 80℃ to 280℃. While the stress induced martensitic transformation occurs in low stress rather than the slip in the region room temperature to 135℃, those critical stresses reverse at about 135℃.

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The effect of a thermomechanical pre-treatment on the shape memory property of Fe-28Mn-6Si-5Cr shape memory alloy was studied. The thermomechanical pre-treatment is the plastic deformation of a strain of 10.0% and then annealing performed at 700℃ for 15 minutes. From the results, it was found that the transformation strain of this material increases with increasing maximum stress applied on deformation, and reaches an upper limit at a certain stress. In the case of the original material without any thermomechanical pre-treatment, the upper limit of the transformation strain is about 2%. On the other hand, the transformation strain of the material with the thermomechanical pre-treatment rises to about 3%.

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Shape memory alloys (SMAs) have been widely used many applications because of its unique characteristic. Among various kinds of SMAs, an Fe-based alloy indicates the excellent formability, machinability and weldability. Furthermore, its production cost is lower than other alloys. Therefore, the alloy attempts to be applied to structural members such as the joint. When the Fe-based alloy is used as structural members, it is conceivable to deform at higher deformation rate because of earthquake. Thus, it is important to investigate the rate sensitivity of the alloy. In this study, three-point bending test is conducted at various deformation rate by using thin plate of Fe-Mn-Si system. The rate sensitivity of its bending deformation during loading and shape memory effect by heating after unloading are investigated. The experimental result shows that the positive rate sensitivity, which means the stress level increases with increasing in the deflection rate, can be observed in the alloy. However, it is hard to conclude that shape recovery deflection depends on rate deflection rate clearly.

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Ni-Mn-In films containing cobalt were deposited on a poly-vinyl alcohol (PVA) substrate or an alumina substrate using a dual magnetron sputtering apparatus using Ni45Mn4oInisand Co targets. The RF power for Ni-Mn-In target was kept at 200 W, and the DC power for the cobalt target was changed from 0 to 15 W. The thickness of the deposited films was kept at about 1 μm. After deposition, the films were annealed at 1123 K for 3.6 ks. The cobalt concentration of the films depended on the DC sputtered power and the martensitic transformation temperature decreased with cobalt concentration of films. After heat treatment, the films showed the good crystalline order. The mechanical properties of the films were measured by a nanoindentation method. Hardness and elastic modulus of the heat-treated films were lower than those of as-deposited films. These values of the films were affected by the Co concentration and microstructure.

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In order to develop a brain spatula or a brain retractor made of a shape memory alloy (SMA), the bending deformation characteristics of the brain spatula of TiNi SMA made by the precision casting were discussed. The results obtained can be summarized as follows. (1) The maximum force obtained from the cyclic three-point bending test increases from first cycle to tenth cycle and a rate of increase is low after tenth cycle. (2) In the cyclic three-point pulsating-plane bending, recovery strain and maximum force change slightly except for initial cycle. Residual strain disappears after heating. (3) The fatigue life in pulsating-plane bending both with heating and cooling and at room temperature is longer than that in alternating-plane bending. (4) If bending direction of brain spatula is decided as pulsating, the change of bending deformation property is small during cyclic use, and long-life is achieved.

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The nitrogen ion was implanted to TiNi shape memory alloy wires, and the influence of implantation treatment on the phase transformation temperature, tensile deformation and bending fatigue properties was investigated. The results obtained are summarized as follows. (1) If the dose of ion implantation increases, the reverse transformation temperature increases. (2) The larger the bending strain amplitude, the shorter the fatigue life is. If the strain amplitude is 4 %, the fatigue lives of all wires are almost the same. If the bending strain amplitude is small, the fatigue life becomes longer in the case of higher dose of ion implantation. (3) The fatigue crack nucleates at a certain point on the surface of the wire. In the case of higher ion implantation in the region of small strain amplitude, the fatigue crack initiation point differs from the maximum bending strain point, resulting in longer fatigue life.

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The creep and creep recovery behaviors under the stress-controlled subloop loading in TiNi shape memory alloy tape were investigated. The results obtained can be summarized as follows. (1) If stress is kept constant at the upper stress plateau after loading up to the stress-holding start strain under a constant stress rate, creep deformation occurs due to the spread of the stress-induced martensitic transformation (SIMT) process. (2) If stress is kept constant at the lower stress plateau after unloading down to the stress-holding start strain from the maximum strain under a constant stress rate, creep recovery deformation occurs due to the reverse transformation. (3) If the stress-holding start strain is large, the creep strain rate under constant stress is high and the maximum strain is large. The creep strain rate increases based on temperature increase due to the exothermic SIMT up to the stress-holding start strain.

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In this research, the influences of applied strain during repeated heat-treatment under constrained strain on fatigue characteristics of Ti-Ni shape memory alloy (SMA) for stent was investigated. The chemical composition of the alloy is Ti-50.4at%Ni. The condition of repeated heat-treatment under constrained strain was in the following; the heat-treatment condition is 773K for 18ks, the applied strain in each heat-treatment is varied from 8 to 13.3%, and the total applied strain is 40%. The fatigue test for the specimens is rotary bending test and carried out at the 310K (bodily temperature). The bending strain range during fatigue test is varied from 1.0 to 5.0%. The fatigue life of the specimen heat-treatment under constrained strain is slightly lower than that of initial state. In addition, the differential of the fatigue limit between the specimen heat-treatment under constrained strain and the specimen of initial state is little. Meanwhile, the fatigue limit of each specimen is improved by the surface preparation, and the differential of fatigue curve between the specimen heat-treatment under constrained strain and the specimen of initial state is disappeared by the surface preparation. However, the effect of the surface preparation decreases with increasing of bending strain. This tendency is caused by the differential of crack initiation, which is caused by the variation of bending strain.

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To give the two-way shape memory effect to shape memory alloy (SMA), shot peening treatment is locally applied to SMA. Plastic deformation occurs on the shot region, and the region behaves like a bias-spring. To design the two-way SMA actuator optimally, we need a constitutive model of SMA which can capture the plastic deformation as well as elastic deformation and phase transformation. The authors proposed a simple constitutive model which could express the feature of plastic deformation. However, this model could not express temperature dependence of the plastic deformation. In this paper, a new constitutive model of SMA, which can express temperature dependence of plastic deformation, is developed by considering plastic deformation of austenite phase. Stress-strain curves of SMA wire including plastic deformation and fracture are measured and simulated by using the developed model. Comparison between them shows this model can express the feature of the stress-strain curves well.

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The purpose of this study is to development weight transfer type heat engine using shape memory alloy. The shape memory springs were made from Ti-50.0 at% Ni wires of 0.8 mm in diameter. The outside diameter of coil is 12 mm and the total coils are 7. The heat treatment condition is 400 ℃ -1h. The reverse transformation start temperature is 55 ℃. The weight of 11.3 g, 30 g, 45 g and 112.5g were used for the heat engine. The results are summarized as follows. (1) The engine was rotate stably in the hot water above 60℃.. (2) As the weight increase up to 40g, the output of engine was increased. (3)The maximum output power is 40mW at 90℃.

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Basic deployment behavior of a functional component of a satellite in micro G and on the ground is discussed. We propose the deployable object using shape recovery behavior of a TiNi-shape memory alloy wire and fabricate that. The wire is placed in a circular arrangement of a round-cut film and then folded up. When the wire is heated above reverse transformation temperature, the object is deployed due to shape recovery force of the wire. In this paper, we present the detailed configuration of the object and the difference in the deployment behavior between in the micro G and on the ground.

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The heating and cooling system of offset crank type shape memory alloy heat engine was improved. In the proposed method, both warmed and cold waters were used for heating and cooling of individual SMA coil springs. The offset crank type shape memory alloy heat engine can be driven by simple supply of both warmed and cold waters. By using this system, the output power characteristics of offset crank type shape memory alloy heat engine were investigated. As a result, it was found that the rotating speed of the engine increases with increase of the difference temperature of warmed and cold waters.

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Shape-memory polymer (SMP) composites are increasingly investigated for various uses owing to their good shape-fixity and shape-recovery performance. Though fiber-reinforcement compensates for SMP's weakness, it decreases its deformability. In order to fully utilize the advantages of SMP composites, it is necessary to give careful consideration to material's deformability and stiffness in designing SMP composite applications. In this research we attempted to discuss the optimal distribution of material properties in morphing skins using SMP composites. We investigated the effect of material properties distribution on deformation performances of morphing skin by simulating shape-recovery processes of SMP morphing skins. The results showed that large camber change is allowed by using SMP composites with high shape recover ratio in outer ply of morphing skins, and it is effective to use stiffer materials in outer ply in order to decrease strain concentration. In addition, even stiffness distribution in thickness direction makes less out-of plane deflection caused by aerodynamic forces.

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Shape memory polymer (SMP) composites are increasingly investigated for many uses, especially deployment mechanism because of their good shape fixity and shape recovery properties. In order to deploy SMP composites, it is needed to heat SMP composites. However, there is little knowledge of nonuniform heating condition for activating SMP composites, and usually, heat conditions are only determined by its glass transition temperature T_g. For the further understanding of heating condition in relation to the characteristic of SMP composites, we made SMP composites from SMP sheets and glass fiber fabrics, attached heating wire to SMP composites, and conducted deployment experiment and measuring temperature by using thermography. Also we conducted these experiments by using the specimens which differed in heating temperature and heating intervals. The experimental results showed that the temperature which is needed for deployment is under T_g, and the longer distance of heating lines of SMP composites is, the longer time it takes to deploy SMP composites.

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Recently, the bonding technology is used to construct a lot of structures. A bonded joint makes reduction of the stress concentration and the vibration, etc. and products compact compared with other joint methods. In this study, we have obtained the following findings by static tests and the corresponding FEM analysis for elastic bonding double lap joint. (1)Adhesive strength decreases with increasing temperature. (2)Adhesive strength increases linearly with increasing adhesive layer thickness in logarithm scale. (3)Adhesive strength increases with increasing loading speed. (4) Almost no stress concentration can be observed in shearing stress distributions in a lap part. Average principal stress is effective as the fracture criterion of an elastic adhesive joint.

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Stress distributions and deformation states were analyzed by using Three-dimensional Finite Element Method so as to predict the strength properties of three adhesively bonded lap joints "single-lap, reverse-bent and wavy-lap", subjected to four-points bending moments. Flexural strength tests and experiments concerning strain distributions were conducted for measurement of joint bending strengths, for verification of numerical results, respectively. In addition, the effects on stress distributions at adhesive layers according to the difference between tensile shearing loads and bending moments were investigated. From the numerical results, it is inferred that peel stresses at the edges of the adhesive layer for the wavy-lap joint are the lowest of the three joint types. As a result of the flexural strength test, it is also found that both averaged values of bending strength and maximum displacement for the wavy-lap joint are maximal in all of the joints.

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A tack is important physical property for pressure-sensitive adhesive that shows instantaneous adhesiveness. Recently, thinner adhesive has been developed and often applied in industry while the occurrence and the mechanism of the tack have not been clarified yet. It is known that as adhesive is thinner than 5μm, the tack becomes much weaker. To improve and develop the thin but strong adhesive it is necessary to observe the peeling phenomena of the adhesive. In this study, the aim is to investigate the effect of the adhesive's thickness on peeling behaviors and tack strengths with probe tack tests. We confirmed that as adhesive is thicker, peel force becomes larger but the rate of increase of peel force becomes lower and the amount of adhesive deformation becomes larger. We observed the displacement of fine particles mixed in adhesive. As result, as the particles reaches deeply from the surface of the adhesive to its inside, the displacement of the particles becomes smaller and the movement of the particles isn't seen at 25 μm from the surface.

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Dissimilar materials spot joining between polyethylene terephthalate (PET) and type 304 stainless steel (SUS304) was carried out by using fiber laser. Bubbles were formed in PET side near the interface by heating due to laser irradiation. Contact force was applied at bottom of joining part to control the formation behavior of bubbles. Bubble area ratio and density of bubbles increased with increase the contact force. Tensile shear strength of the joint decreased with increase the bubble area ratio. Bubbles formed at the interface were assumed as multiple cracks to evaluate stress intensity factor. It is speculated that higher density of bubbles formed by applying higher contact force induces connecting of cracks easily. Strength of the joint could be controlled by applied contact force as a result of change in formation behavior of the bubbles.

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Fretting fatigue process have many features such as early stage crack initiation at contact edge, very slow crack propagation and fatigue failure after very long life operation. In previous paper we present fretting fatigue model which was considering the wear process, and this model can explain these fretting fatigue features reasonably. But, the estimation of fretting wear process require a large amount of labor, so this precise wear estimation method is not suitable for actual design site. In this paper we try to present simple fretting fatigue limit estimation method considering wear. In the final stage of wear process the stress distributions near contact edges converge to a nominal contact pressures. So, we estimate the ultra high cycle fretting fatigue limit as the crack propagation threshold on this uniform contact pressure conditions. This crack propagation threshold is analyzed using fracture mechanics analysis. Finally these estimated results are of ultra high cycle fretting fatigue limit compared with the experimental results, and can confirmed the availability of this simple fretting fatigue limit estimation method.

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Fretting fatigue is composite phenomenon of metal fatigue and friction. Fretting fatigue is one of the major factors in the design of mechanical components because the fatigue strength at cantact part is significantly reduced by fretting. Since hydrogen can influence on both fatigue and friction properties, it is conceivable that hydrogen also influences fretting fatigue properties. A significant reduction in the fretting fatigue strength due to hydrogen is found. The reduction of fretting fatigue strength due to hydrogen was influenced by other factors such as hydrogen charge, work hardening and addition of oxygen. Gaseous hydrogen and internal hydrogen work in decreasing the fretting fatigue strength independently and also synergistically. The fretting fatigue strength decreased with increase hydrogen content. The fretting fatigue strength was improved by work-hardening. However, the reduction in the fretting fatigue strength of the work-hardening material due to hydrogen was more significant. The addition of oxygen to the hydrogen had a beneficial effect by improving fretting fatigue strength.

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We present fatigue life estimation method in low cycle fatigue region using critical distance stress theory. Generally this critical distance theory was applied to the fatigue limit estimation using fatigue limit of smooth specimen σw0, and threshold stress intensity factor range ΔK_<th>. In this paper, we estimated the low cycle fretting fatigue life based on new critical distance theory, which is modified for high stress region using ultimate tensile strength σ_B, and fracture toughness K_<IC>. The critical distance for estimating low cycle fretting fatigue strength was calculated by interpolation of critical distance on fretting fatigue limit (estimated from σ_<w0> and ΔK_<th> ) with critical distance on static strength (estimated from σ_B and K_<IC> ). By unifying these low cycle fretting fatigue life estimation method with high cycle fretting fatigue life estimation method we can estimate the total fretting life easily.

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Fatigue strength evaluation for small crack using fracture mechanics has a disadvantage that the value of stress intensity factor is low than long crack. We apply the critical distance theory to that. Critical distance theory is fatigue strength evaluation that the stress is fatigue limit when stress distribution of crack specimen matches a point of a stress distribution of smooth specimen and threshold stress intensity factor. Pulsating fatigue test conditions are 20Hz of frequency and 0 of stress ratio. Based on the critical distance theory, we applied analysis of stress distribution using FEM to evaluate the fatigue strength evaluation. As the crack lengths approach small crack, stress distribution of crack tips tend to reduce. As the result of critical distance theory using stress distributions, fatigue strength evaluations for long cracks using fracture mechanics were consistent to critical distance theory. On the other hand, fatigue strength evaluation for small cracks using critical distance theory and fatigue test results were convergent to a point of fatigue limit of smooth specimen. As the result, fatigue strength evaluation based on the critical distance theory is effective in all crack lengths. However, because the results depend on the fatigue limit of smooth specimen and the threshold stress intensity factor, we need to find the accurate value based on the experiment.

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Most studies of bolted joint fatigue have been conducted for a bolted joint subjected to only axial vibration or only transverse vibration. However it is considered that the actual bolted joints are subjected to multi-axial vibration. Bolted joint fatigue under multi-axial vibration, axial vibration and transverse vibration, has been investigated in this study. The results said that even if the bolted joint was subjected to multi-axial vibration, the fatigue strength was the same as the uni-axial fatigue strength. However the apparent fatigue limits were different according to the vibration conditions.

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Recently in many industrial machinery or machine tools vibration is increasing as the duty of these machinery become hard, such as high speed and high cycle duty. These vibration come the fatigue failure or leakage in piping joint parts. So, recently the request of fatigue reliability and shockproof improvement become increased. In this paper we clarify the loosening behavior under cycling internal pressure loading conditions. As the specimens we use the bite type tube fitting. When extreme tightening force is higher than the appropriate value, plastic deformation will occur, but when tightening force is lower than the appropriate value, the elastic holding portion will reduce. They both cause loosening.

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