Search

This study aims at experimentally revealing the effect of accumulated damages in supporting porous components on loosening behaviour using Infrared thermography(IR) and Acoustic emission(AE). Aseptic loosening is occurred due to degradation of fixing force of acetabular cups by biological effects or mechanical loading. However, effects of mechanical loading on loosening behaviors have not been observed yet. An integrated assembly of hip joint components, which is composed of stems and acetabular cups was set in distilled water in order to apply cyclic load in vitro. We developed the simulation system of loosening behaviour of acetabular cups by cyclic loading using cantilever. Damage evaluations on interface between the acetabular cup, HAp coating and supporting porous components (we call it " simulated bone ", which has similar Young ’ s modulus and density for those of cancellous bone) using AE. Additionally inelastic damage behaviour in simulated bone was simultaneously observed using IR. IR could successfully observed dissipation energy by inelastic damage accumulated during cyclic loading, which indicate its fatigue strength within shorter cyclic loading. Cyclic loading test for 1 million revealed that both lateral and angular displacement of the acetabular cup can be associated with the progress of damages in delamination of Hap coating or inelastic compression of simulated bone Loosening mechanism of the acetabular cup by cyclic loading can be considered by the contribution of both damages at the interface and in the simulated bone.

The cost of solar cell production can be reduced by wafer thinning. A thinner wafer provides flexibility, and crystalline silicon solar cells are promising as flexible solar cells due to their flexibility. However, as wafers become thinner, production yield decreases due to wafer breakage caused by sawing damage; thus, to further reduce wafer thickness, it is necessary to suppress sawing damage. We investigated the flexibility of wafers under various slice conditions by conducting biaxial bending tests and clarified the dominant factor causing sawing damage to further reduce the wafer thickness for crystalline silicon solar cells. The results of damage observation by scanning electron microscopy and evaluation of the crystal structure by Raman spectroscopy confirm that the damage structure changes significantly depending on wire specifications. The results from the biaxial bending tests indicate that the three-dimensional flexibility of a wafer is determined by wire specifications.

While several metallic implants with bioactive coatings have been developed thus far for treating bone deformations or deterioration, a multifunctional coating with the desired mechanical and antibacterial properties has not been demonstrated. This study aimed to reveal the effect of the composition of hydroxyapatite (HAp)/gray titania coatings on the mechanical and antibacterial properties for biomedical applications. Suspension plasma spray (SPS) aided successful deposition of HAp/gray titania coatings on the surface of titanium substrates. The microstructure of coatings with different compositions was then characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy to identify the crystal structure. All results consistently demonstrated that SPS could transform Ti2O3 into TiO2 with mixed Magneli phases, such as Ti4O7 and Ti3O5, which could typically demonstrate photocatalytic activity. Hardness, Young's modulus, and interfacial strength of composite coatings commonly increased with an increase in the weight percentage of TiO2. A multi-modal damage assessment combining acoustic emission (AE), infrared ray camera (IR), and digital-image-correlation (DIC) was performed to monitor the damage process of HAp composite coating, which successfully revealed initiations of microcracks and nonlinear deformation at interface until fracture. Antibacterial test performed for examining the cytotoxic effects against E. coli under LED light irradiation conditions revealed that SPS HAp/gray titania coating could significantly enhance the antibacterial properties. Enhanced antibacterial properties can be attributed to an increase in the number of Magneli phases and better bacterial adhesion was attributed to hydrophilic properties conferred by submicron-sized particles. Hence, SPS can help fabricate visible light-responsive antibacterial coating, which can be used for medical devices.

Joining Mg to Al is challenging because of the deterioration of mechanical properties caused by the formation of intermetallic compounds (IMCs) at the Mg/Al interface. This study aims to improve the mechanical properties of welded samples by preventing the fracture location at the Mg/Al interface. Friction stir welding was performed to join Mg to Al at different rotational and travel speeds. The micro structure of the welded samples showed the IMCs layers containing Al12Mg17 (γ) and Al3Mg2 (β) at the welding zone with a thickness (> 3.5

In order to achieve recent weight reduction for transport equipment, it is necessary to replace steel with nonferrous materials not only for structural parts but also for joining elements such as bolts and nuts. Fatigue strength of high strength steel bolts has rarely been influenced by clamp force which acts as mean stress to the bolts because of shakedown caused by local plastic deformation at the first thread root. However the effects of clamp force on fatigue strengths for aluminum alloy bolts have not been sufficiently revealed yet. In this study, fatigue tests and elasto-plastic analysis for aluminum alloy A5056 and A6056 bolts have been conducted to reveal the influence of clamp force on fatigue strength. Hexagon head bolts made of aluminum alloy A5056 and A6056 were used. For the internal thread parts for the A5056 bolts, A5056 nuts were used. For the internal screw parts for the A6056 bolts, machined nuts made of die cast material ADC12 considering actual usage were used. Results showed that the fatigue strength for A5056 bolts decreased with an increase in the mean load. Although the fatigue strength for A6056 bolts decreased with an increase in the mean load if the mean load was lower than 6 kN, the fatigue strength for A6056 bolts did not decrease if the mean load was greater than 6 kN. Results of elasto-plastic analyses showed that the causes, that the behaviors of these fatigue strengths were different, were reduction of mean stress due to local plastic deformation at the root of the first thread so-called shakedown. This result indicates that we can tighten A6056 bolts with high clamp force although cannot tighten A5056 bolts with high clamp force.

Fatigue design of weld part in non-combustible magnesium alloy has been studied. Specimens for fatigue test were produced by TIG welding with different welding conditions. According to result of fatigue strength tests, all weld specimens tested in the present study were broken at the weld prat, and a weld defect was found as a fatigue fracture origin. Fatigue life was well arranged by effective stress intensity factor calculated with a size of weld defect played as a fracture origin and applied stress. Therefore, it is speculated that fatigue strength of weld part is depending on a size of weld defect and threshold stress intensity factor at the weld part. Size of weld defect and value of threshold stress intensity factor possibly changed by welding condition. Therefore, relationship between heat input during welding process and threshold stress intensity factor was studied by conducting fatigue crack growth test at the weld part. The value of threshold stress intensity factor range increased with increase in heat input of welding process. However, values for threshold stress intensity factor range almost coincided when the crack growth curves were arranged by effective stress intensity factor range. Difference in threshold stress intensity factor range due to difference in heat input of welding process was mainly induced by change in crack closure effect. It is proposed that effect of crack closure depending on mechanical property of weld part should be taken into account on fatigue design of weld part in non-combustible magnesium alloy.

Annealed 1050-aluminum sheets were severely deformed at the strain magnitude of 2.32 through constrained groove pressing (CGP) process. Texture variations and mechanical properties were investigated during CGP and subsequent friction stir processing (FSP) with different volume fractions of SiC nanoparticles. The results revealed that the predominant texture component in the annealed aluminum was { 001 } 〈 100 〉 cube texture. After CGP, deformed and shear texture components developed while the cube texture was partially remained. In the specimen undergone FSP without nanoparticles, { 001 } 〈 110 〉 rotated cube and nearly { 001 } 〈 110 〉 shear texture component C were mainly pronounced, which was indicative of shear deformation of material in the stir zone. Orientation distribution function analysis from the stir zone demonstrated variations in the texture development with the incorporation of SiC nanoparticles. An increase in the fraction of nanoparticles changed the grain orientation in such a way that the { 001 } 〈 110 〉 shear texture component C gradually developed from the rotated cube texture. However, the overall texture intensity became weaker by increasing the fraction of SiC nanoparticles due to the activation of particle stimulated nucleation mechanism forming randomly oriented grains. The incorporation of SiC nanoparticles in the stir zone also enhanced the yield strength, Young's modulus, and hardness of the stir zone without considerable reduction in the elongation. In such situation, Orowan strengthening was suggested as a dominant mechanism involved.

Resistance spot welding (RSW) was applied to non-combustible magnesium alloy, AX41 (Mg-4%Al-1%Ca) to investigate its weldability. The similar material joint of AX41 and dissimilar materials joint between AX41 and aluminum alloy, AA6061 were welded. Tensile shear test was carried out to evaluate joining strength in the similar and dissimilar materials RSW joints. In case of similar material joints, the maximum load obtained with tensile shear test in AX41 similar material joint was higher than that obtained in AA6061 similar material joint. Moreover, higher maximum load was obtained in a similar material joint without surface polishing compared to joint welded with surface polishing in AX41. In case of the dissimilar materials joint, the maximum load obtained was almost comparable with AX41 similar material joint, however scatter in joint strength was large. Weldability of the dissimilar materials joint became poor by applying surface polishing.

Fatigue strength tests were carried out under plane banding loading with different stress ratio in Mg-Al-Ca-Mn alloy and its TIG and MIG welds. The welds showed lower fatigue strength compared to the base material. Weld defects were observed as fatigue crack origins in both TIG and MIG welds. It was speculated that difference in size of weld defect and multiple cracking occurred in MIG weld might affect fatigue strength characteristics in the welds. Effect of stress ratio on fatigue strength at 107 cycles was not significantly observed in fatigue test results obtained with different stress ratio in the base material and the welds. Scatter in size and distribution of weld defect could influence fatigue fracture behavior in the welds.

In this study, we evaluated sawing damage of thin silicon wafers. Ultra-thin silicon wafers with great advantages of bendability and lightweight are suitable for needs such as to realize PV-powered vehicles. For thin wafers, it is important to realize high precision slicing to prevent breakage. We evaluated the distribution of sawing damage and crystallinity in order to clarify the cause of wafer breakage and establish low damage slice conditions. We confirmed phase transformation of silicon and crystalline defects on wire exit side on the conventional slicing surface, while the advanced slicing surface shows almost only single-crystalline Si phase.

This study aims to reveal the effects of pressure during cold isostatic pressing (CIP) on the microstructure and optical properties of fluorescent HAp complexes. Although the microsturucture-dependent properties of fluorescent HAp complexes have been reported to improve the antibacterial properties of photocatalyst coating layers, the mechanism behind the changes in the fluorescence properties of highly compressed HAp complexes has not yet been unveiled. CIP was successfully used to fabricate fluorescent HAp – amino acid complexes, and their fluorescence intensities increased with increasing fabrication pressure. Peak wavelength of fluorescence emitted by the HAp – amino acid complexes exhibited yellow to red shift. Although the thickness of the amino acid layer was saturated in higher pressure cases, the concentration of amino acids increased proportionally with pressure, which suggests changes in the packing structures of the ligands in the HAp– amino acid complexes. Polarized Raman spectroscopy measurements clearly detected ligands normally arranged to the HAp layer under high pressure fabrication conditions, which can provide the tightly packed ligand structure in the HAp– amino acid complexes. These tightly packed ligand structure in the HAp– amino acid complexes could emit stronger fluorescence owing to the increased density of complexations. This newly found pressure dependency in the optical properties of HAp–amino acid complexes is beneficial for developing biocompatible fluorescence materials or enhancement agents for antibacterial coating layers.

This study aims at experimentally revealing the effects of damages/fractures in HAp coating layer of acetabular cups on loosening behavior of the acetabular cups. Aseptic loosening is occurred due to degradation of fixing force of acetabular cups by biological effects or mechanical loading. However, effects of mechanical loading on loosening behaviour have not been observed yet. In order to simulate cyclic loading conditions of gaits, a testing system which can load entire components of joint including acetabular cups and stem parts was designed. Moreover, by applying two positions of AE sensors during fatigue testing, it was possible to observe the damage behavior of HAp coating. AE measurement detected different failure modes of HAp coating, which were locally occurred at an edge part of the acetabular cup due to stress singularity at that region. In the cases of changing fixation angles, even though damages in simulated cancellous bone surrounding acetabular cups were less occurred, extents of rotational displacements were compatible with the one in an original fixation angle.

Plates of AL6XN super-austenitic stainless steel with a single-V groove preparation were gas metal arc welded (GMAW) with and without electromagnetic interaction of low intensity (EMILI) during welding using an ER-NiCrMo3 filler wire and 97% Ar + 3% N2 as shielding gas. The fatigue behavior of the welded joints was evaluated under constant stress amplitude (Δσ/2) between 135 and 170 MPa (R = 0.1) and uniaxial load. The Wohler diagram indicated that for stress amplitude of 170 MPa, 4.19 × 105 and 2.96 × 105 cycles were required for failure without and with EMILI, respectively, whereas for 135, 140, and 145 MPa, 1 × 107 cycles were reached without failure. Welding with EMILI was found to have a positive effect nearby fatigue limit. Observation of the fractures indicates that failures started on the surface of the specimens in the weld metal (WM) due to the stress concentration induced by the abundant presence of precipitates located along the interdendritic spaces in this zone of the welded joint. These particles acted as crack-nucleating agents and then the crack propagated throughout the WM. Fractography revealed brittle fracture associated to cleavage.

A thick glass plate was cut by using hot wire. Crack growing was stopped when wire temperature was low. Ligament length decreased with increase in temperature of hot wire and full-cutting was achieved at the temperature of 650°C. The center region in the thickness direction seemed to propagate earlier compared to surfaces regions when the crack propagation was stopped. Finite element thermal stress analysis was carried out. According to distribution of thermal stress inside a glass plate, higher stress was generated in the bottom region at the beginning of the process but occurred in the center region in the later stage as matching with the experimental result.

The aim of this study is to observe visible light-induced antibacterial effects of the luminescent complex of hydroxyapatite and 8-hydroxyquinoline with gray titania coating. Plasma-sprayed Hydroxyapatite (HAp) coating has been widely used as bonding between alveolar bones with dental implants. However, bacterial infection on the surfaces of dental implants has recently been reported and conventional antibacterial technologies cannot last long-term use. Therefore a novel technology using the complex of hydroxyapatite and 8-hydroxyquinoline (8-Hq) with gray titania was proposed, which can be activated by visible light. Ti2O3 powder was used in a plasma-spraying process to fabricate visible-light-sensitive titania coating. The plasma-sprayed HAp/Ti2O3 was characterized by Raman Spectroscopy, FTIR and XRD. Its photo catalytic activity was evaluated using chemiluminescence observation and antibacterial property was evaluated by optical density measurement (OD), colony forming unit (CFUs) and fluorescent microscope observation. The plasma-sprayed Ti2O3 powder revealed that its phase changed to TiO2(Rutile) though the color of the plasma-sprayed Ti2O3 powder kept dark gray, which possessed its absorbency in visible-light region. The plasma-sprayed Ti2O3 powder was then called gray titania and 1 O 2 was generated from the gray titania by irradiating three types of laser (blue, green and red). Antibacterial evaluation revealed that both the existence of the complex and the irradiation of LEDs could significantly decrease the numbers of colony forming unit (CFUs). Furthermore, HAp-8Hq complex decreased adhesion of E. coli even without light irradiation. An enhancement in the antibacterial property of HAp complexes with gray titania coating can be attributed to an increased power density of light on the surface of gray titania by fluorescence.

This study aims at observing the effect of Mg concentration on the interfacial strength and corrosion fatigue behavior of Al-Mg coating layers on structural steel (SS400) substrates. Al-Mg coating has been applied to components of bridges as sacrifice coating layers. Although Al or Al-Mg coating layers are typically applied to the components located in severely corrosive environment, a mechanism behind the effective protection provided by increasing the concentration of Mg has not yet been clarified. The interfacial strength test using four-point bending revealed that a Al-Mg coating layer of higher Mg concentration showed a higher interfacial strength only before immersion in 3.5-wt% NaCl aq.. After immersion in 3.5-wt% NaCl aq. for 30 days, such the difference in interfacial strength was lost due to rapid dissolution of Mg in the coating layers. As regards the fatigue crack growth behavior, the Al-Mg coating with higher Mg concentration exhibited a lower resistance to vertical crack propagation and interfacial delamination. A fracture mechanics model, which includes both effects of corrosion and delamination/cracking was proposed. Numerical simulation based on the fracture mechanics model successfully predicted exposure lives of substrates due to fatigue failure of the Al-Mg coating layers. These results could provide a selection policy for Al-Mg coating layers in which a loading level and the severity of corrosive environment were considered.

In this study, austenitic stainless steel 316L and titanium alloy (ASTM grade 5) were welded together by micro-resistance spot welding at different combinations of welding parameters and by using specifically designed electrode geometry. The welded joints were subjected to tensile shear strength test in order to determine the strength of the welded zones. In addition, micro-hardness and microstructural examinations of the fracture mode (failure analysis) were carried out in order to examine the influence of welding parameters on the welded joints. The results showed that using a combination of 2.0 kN welding current, 100 ms welding time, and 241 N welding force yield the highest load value, 378.25 N by using full factorial design of experiment (DOE). Welding current is the most significant parameter which is obtained through analysis of variance (ANOVA). However, the increase in welding current should be controlled to avoid weld metal expulsion. The microstructure of these resistance-welded metals are detailed and investigated by using SEM and EDS mapping analysis. Based on the SEM observations, columnar dendritic structures can be seen at the fusion zone (FZ) of the welded nugget.

The fatigue strengths at 1000 °C of layered W-Re/TZM, bulk W-Re and bulk TZM for x-ray target materials were successfully evaluated under load-controlled four-point bending by introducing a fatigue failure criterion as two-times increase of initial compliance. The obtained fatigue strengths at 1000 °C for layered W-Re/TZM and bulk W-Re were similar and 280 MPa and 290 MPa at 106 cycles, respectively, while that of bulk TZM was 200 MPa. During fatigue loading at 1000 °C, dominant fatigue damage would be multiple intergranular crack nucleation and propagation, which would induce the increase of compliance. The reasonability of the fatigue failure criterion was confirmed by the fatigue process observations and the results of room temperature fatigue tests of the specimens tested at 1000 °C up to the cycles corresponding to the fatigue failure criterion. Keywords: Fatigue strength, High temperature, Fatigue damage, Microstructure-property relationship, Refractory materials

An observation system of loosening behavior of an acetabular cup by interfacial dam ages induced by cyclic loading was successfully developed. The purpose of this study was to investigate the effects of inplane cup angles, which changed the distance between position of screw holes and loading points, to the loosening behavior of the acetabular cup. Recently artificial hip joint is widely used to replace in human in order to reduce the pain in patients Revision cases of acetabular cups have been increased due to loosening. Loosening was considered to be caused by infection or osteolysis . However, in the long-term use of total hip joints, loosening without infections, called “aseptic loosening,” is a major cause of revisions. However, the mechanism of progression of aseptic loosening is still unclear. One of the unrevealed factor is interfacial damages by loading, and then it should be investigated an experimental system which can exclude the effects of infections. A cyclic loading system using a fatigue testing machine to an assembly of a stem, a femoral head, a liner and a acetabular cup was designed. The acetabular cup coated by plasma-sprayed hydroxyaptite (HAp) to simulate practical fixation condition of cementless bonding of the acetabular cup to surrounding acetabulum. AE (Acoustic Emission) sensor system was subsequently attached on the bottom of the acetabular cup to observe damages at the interface between the embedded acetabular cup with simulated bone during the cyclic loading. Interfacial damages were intermittently observed at the edge of the acetabular cup during cyclic loading tests and those frequency were varied by changing an inplane cup angles. SEM(Scanning Electron Microscope) observed significant delamination of HAp coating after the cyclic loading, which attributed to the rotational displacement of the acetabular cup. Furthermore, observed values of the rotational displacement of the acetabular cup were compatible with those observed in normal patient of THA(Total Hip Arthroplasty). The result demonstrated that loosening behavior of the acetabular cup can be occurred only by mechanical damages such as delamination of HAp coating , wear or damages in simulated bone, which enlightened the importance of mechanical factors in practical loosening behavior of aceptic loosening.

In situ SEM observation of fatigue crack growth behavior of low carbon steel under mechanically large grain condition, and EBSD analysis were carried out to investigate mechanisms of crack deflection and branching and effects of crystal orientation on them. It is found that the crack propagates along the activated slip bands in the present material and the crack deflection can be formed when a new activated slip band is created in a different direction from the growing crack. The crack branching can be formed by the following process: (1) the slip band along the crack cannot be activated further due to the restraint by such as grain boundary or strain hardening, (2) the crack cannot propagate further in the same direction, and (3) the secondary slip plane is activated to form a new slip band behind the crack tip. Not the stress intensity factors Kdef for deflected crack and ΔKeff for crack closure but rather the ΔKeff,tip is the intrinsic fracture mechanics parameter for controlling fatigue crack growth behavior of the material with crack deflection and branching.

The texture, microstructure, and mechanical properties of severely deformed aluminum subjected to friction stir processing (FSP) with SiC nanoparticles under ambient and cryogenic temperatures are comprehensively investigated. Even one pass of FSP in the ambient temperature results in the formation of quite large grain structure with random texture in the heat affected zone (HAZ). It suggests the occurrence of static recrystallization and subsequent grain growth because of the appreciable strain stored within the base metal. One FSP pass under condition of cryogenic temperature causes to the development of bimodal grain size distribution in HAZ, including the elongated grains with interior subgrains and very large grains as a result of texture-induced abnormal grain growth. Large grains with random texture are formed throughout HAZ during further FSP passes. In the stir zone where SiC nanoparticles are dispersed during FSP in the ambient temperature, fine grain structure with the shear texture components of C and A 1 ∗ is obtained through the geometrically dynamic recrystallization mechanism. When FSP is performed in the cryogenic temperature, the grain size of stir zone is decreased because of the increased cooling rate. Although the shear texture components developed in the stir zone are the same at both mentioned processing conditions, the texture strength is less in the case of cryogenic temperature, suggesting the contribution of additional grain formation mechanism, namely discontinuous dynamic recrystallization. This mechanism gives rise to the formation of randomly oriented grains. The nano-indentation test results confirm that FSP under cryogenic temperature improves the mechanical properties not only in the stir zone, but also in HAZ.

Fatigue strength characteristic of laser welded joint between austenitic stainless steel and ferritic stainless steel was studied at room temperature and 300 °C.The results showed that fatigue strength at 300°C was higher than that at room temperature in lower applied stress amplitude region. Fatigue crack mainly initiated at stress concentration part at room temperature. However, fatigue crack origin changed toward to the base material and the heat affected zone with increasing testing temperature. Increase in ductility of the base material and the weld metal induced by increasing testing temperature reduces stress concentration effect and resulted in change in fatigue mechanism. Appropriate weld position in a component with temperature gradient can be considered by minimizing the effect of stress concentration and taking into account degradation of strength due to increase in temperature.

The elastic-plastic fracture toughness JIC of two titanium-zirconium-molybdenum (TZM) alloys with different kinds of grain boundary particles was estimated at elevated temperatures using the convenient JIC test method with a suitable depth of side-groove for determining the JIC at the maximum load point. It was found that the convenient JIC test method can be successfully applied to evaluate high temperature fracture toughness at least up to 1200 °C. The JIC values at temperatures ranged from 800 °C to 1200 °C were almost constant regardless of temperature, while the JIC values of the TZM with carbide particles were higher than those of the TZM with oxide particles. The TZM with different forging rates showed similar JIC values, which suggested the effect of forging rate would be not significant at high temperatures.

Severely deformed aluminum sheets were processed by friction stir processing (FSP) with SiC nanoparticles under different conditions to improve the mechanical properties of both the stir zone and the heat affected zone (HAZ). In the case of using a simple probe and the same rotational direction (RD) of the FSP tool between passes, at least three FSP passes were required to obtain the appropriate distribution of nanoparticles. However, after three FSP passes, fracture occurred outward from the stir zone during transverse tensile tests; thus, the strength of the specimen was significantly lower than that of the severely deformed base material because of the softening phenomenon in the HAZ. To improve the mechanical properties of the HAZ, we investigated the possibility of achieving an appropriate distribution of nanoparticles using fewer FSP passes. The results indicated that using the threaded probe and changing the RD of the FSP tool between the passes effectively shattered the clusters of nanoparticles and led to an acceptable distribution of SiC nanoparticles after two FSP passes. In these cases, fracture occurred at the HAZ with higher strength compared to the specimen processed using three FSP passes with the same RD between the passes and with the simple probe. The fracture behaviors of the processed specimens are discussed in detail.

Effect of mean stress on fretting fatigue behavior of 304 austenitic stainless steel has been investigated by conducting fretting fatigue tests at a constant contact pressure of 100 MPa under three different mean stresses i.e., 0, 350 and 450 MPa. For comparisons, plain fatigue tests were also carried out. The influence of tensile overload on fretting fatigue life was also investigated. The results showed that with an increase in mean stress, the reduction in fatigue strength due to fretting increased drastically from 51% at 0 MPa mean stress to 71% at 450 MPa mean stress. The application of tensile overload during fretting fatigue had significant influence on the fretting fatigue lives when the tensile overload was above yield strength. The fretting variables, i.e., tangential stress and relative slip amplitude were measured during fretting fatigue tests. Fracture surfaces were examined using scanning electron microscope. The results have been discussed based on the tangential stress measurement, relative slip amplitude evaluation during fretting fatigue and fracture surface examinations.

The load-controlled and displacement-controlled fatigue tests of Ti-6Al-4V alloy notched specimen under the remote stress ratio of 0.1 were carried out in order to investigate notch fatigue behavior in a wide range of fatigue life from low to high cycle fatigue. The elastic-plastic finite element analysis of notched specimen under cyclic loading was also conducted to investigate the variation of local stress ratio at notch root and its influence on fatigue life. It was found that the local stress ratio at notch root varies from the remote stress ratio of 0.1 in high cycle region to −1 in low cycle region, where the transition region is defined as the region of local stress ratio variation. Taking account of the local stress ratio variation at notch root, fatigue life was predicted based on the SWT parameter combined with the FEA was in good agreement with the experimental results. It is suggested based on these local stress variation and fatigue life prediction that the low cycle fatigue life predicted assuming the stress ratio of −1 would give an unsafe side prediction in the transition region.