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To predict the fatigue life for oblique hyperbola- and bilinear-mode S–N curves of metallic materials with various strengths, a machine-learning approach for direct analysis was employed. Additionally, to determine the fatigue limit of the utilized materials (AISI 316, AISI 4140 and CA6NM series) with different S–N curve modes using finite-fatigue life data, a Bayesian optimization-based inverse analysis was performed. The results indicated that predictions of the fatigue life for the utilized datasets via the random forest (RF) algorithm for AISI 4140 and CA6NM, and artificial neural network (ANN) for AISI 316, distribute within 2 factor error lines for most data. In the Bayesian optimization-based inverse analysis, the specific explanatory variables corresponding to the optimized maximum fatigue life were treated as the fatigue limits. The predicted fatigue limits either approximated to or slightly underestimated the experimental results, except for several cases with large errors. Using the inverse analysis to predict the fatigue limit for both S–N curve modes is applicable for current employed data-set. However, the explored maximum fatigue lives via BO corresponding to the predicted fatigue limit were underestimated for AISI 4140 and CA6NM, and was overestimated for AISI 316 because of effect of shape of S–N curves. By combining the ANN or RF direct and BO inverse algorithms, whole S–N curves (including the fatigue limit) were evaluated for the S–N curve shapes of the oblique hyperbola and bilinear modes.

To investigate the cumulative fatigue damage below the fatigue limit of multipass weldment martensitic stainless steel, and to clarify the effect of cycle ratios and high‐stress level in the statement, fatigue tests were conducted under constant and combined high‐ and low‐stress amplitude relative to stress above and below the fatigue limit. The outcomes indicate that neither modified Miner's nor Haibach's approach provided accurate evaluation under repeated two‐step amplitude loading. Moreover, effect of cycle ratios has been determined. Additionally, the cumulative fatigue damage saturated model is established and validated. Cumulative fatigue damage contributed by low‐stress below the fatigue limit in high stress of 700 MPa is higher than that with 650 MPa at identical conditions (fatigue limit 575 MPa). Thus, high stress affects fatigue damage behaviour below the fatigue limit. A new predicted approach has been proposed based on Corten‐Dolan law, whose accuracy and applicability have been proven.

Anterior cruciate ligament (ACL) injury is the most common traumatic injury to the knee joint. Suspensory fixation has become popular in ACL reconstruction because of its high primary stability, less invasiveness, and surgical convenience. There are two common types of suspensory fixation devices: those with fixed-length and those with adjustable-length loops. Owing to structural differences and differences in initial tensioning techniques, it is expected that mechanical property and damage to the tendons will vary from device to device; however, no literature has examined this so far. The main purpose of this study was to evaluate the damage caused to the tendon by three different suspensory fixation devices. An effective mechanical test was carried out as a prerequisite.First, the mechanical properties of simple loop device (SLD) as fixed-length loop device, first-generation, and second-generation adjustable devices (AD1 and AD2) as adjustable-length loop devices were tested (isolated device testing). Second, each device was tested using bovine extensor tendons (specimen testing). Cyclic testing included 2000 cycles; the devices were subsequently displaced until failure, and the ultimate tensile strength was determined using isolated device testing. Six samples of 3 devices were used in each testing experiment. After specimen testing, the surface structure of the tendon was evaluated quantitatively using optical coherence tomography (OCT) and our original histological scoring system.During isolated device testing, SLD demonstrated the least cyclic displacement, followed by AD1 and AD2. The highest ultimate tensile strength was observed in AD2, followed by SLD and AD1. In specimen testing, the least cyclic displacement was observed in SLD, followed by AD1 and AD2. Histologically, AD1 demonstrated a significantly lower score, with damaged surface morphology, than SLD and AD2. OCT values were significantly higher, with a more disturbing tendon surface structure, in AD1 than in SLD and AD2.The first-generation adjustable loop device exhibited greatest graft tissue damage at the suspensory site in a clinically relevant setting. The thinner adjustable loop mechanism may have elevated graft damage by frictional stresses during loop adjustment or by repetitive tensioning stresses.

With the rapid development of computer-aided design/computer-aided manufacturing (CAD/CAM) systems, the application of zirconia in removable partial dentures is expected to expand. Clasps composed of zirconia should improve esthetics without inducing the risk of metal allergy. The aim of this study was to examine the fatigue resistance of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) clasps for removable partial dentures. Yttria-stabilized tetragonal zirconia polycrystal and cobalt-chromium (Co-Cr) alloy were prepared using CAD/CAM systems. Specimens were either of the semicircular type or of the flat type, with cross-sectional areas of taper ratios of 0.50, 0.75, and 1.00. All specimens were tested using the cantilever test and the constant displacement fatigue test, and data were analyzed using ANOVA. During the cantilever test, the maximum displacement prior to fracture was greater than the required undercut, and the semicircular-type specimen exhibited a higher fracture load than the flat type. None of the specimens displayed permanent deformation and showed almost the same degree of deformation after fatigue testing. A lower taper ratio was associated with lower average load values and greater displacement. Within the limitations of this study, it was possible to conclude that Y-TZP provides the required undercut and adequate retentive force for removable partial denture clasps. Additionally, Y-TZP and Co-Cr alloy had almost the same degree of deformation even after the simulated lifespan of removable partial dentures.

In order to develop a rapid nitriding process for titanium alloy at a low temperature, fine particle peening (FPP) was performed prior to gas blow induction heating (GBIH) nitriding. The surface microstructures of a Ti-6Al-4V alloy treated by FPP and GBIH nitriding were characterized using X-ray diffraction, optical microscopy, scanning electron microscopy, laser microscopy and micro-Vickers hardness testing. The results indicate that nitrogen diffusion into titanium during GBIH nitriding was accelerated by the pre-treatment with FPP, and a nitrided layer was formed on the surface of the Ti-6Al-4V alloy at a relatively low temperature (923 K), which grain coarsening and phase transformation did not occur and a nitrided layer was not formed only by GBIH nitriding. This is because a fine-grained surface layer was generated by the pre-treatment with FPP. Reciprocating ball-on-disk wear tests were carried out to examine the wear resistance of the prepared specimens. GBIH nitriding at a low temperature improved the wear resistance of the Ti-6Al-4V alloy following the pre-treatment with FPP, due to the formation of a hard nitrogen compound layer at the surface. The results show that the proposed surface treatment process was effective at modifying the surface properties of a titanium alloy at a low temperature and within a short span of time while avoiding grain coarsening and phase transformation.

In general, the platinum alloy is used in glass production lines, due to an excellent corrosion resistance to melted glass at high temperature. On the other hand, the development of high quality glass is needed, because of wide use of glass application in recent years. So, Oxide-Dispersion-Strengthened platinum alloy is developed which had better fatigue properties than the conventional one. However, there are few researches about the fatigue properties in a practical environment with axial stress and bending stress. Therefore, in order to clarify fatigue properties and fracture mechanism of Oxide-Dispersion-Strengthened platinum-10% rhodium with dispersed zirconium oxide particles, bending fatigue test at 1400°C, fracture surface observation and internal cross-section observation were performed. As a result of the fatigue test, it was clarified that the tendency of fatigue life with axial stress depends on the times to failure rather than number of cycles to failure. Also, it was clarified that the intergranular fracture and void generation due to creep occurred under the condition of axial stress of 23.4MPa.

The influence of microstructure on crack initiation behavior of Ti-6Al-4V was investigated by using atomic force microscope (AFM) and electron backscattered diffraction (EBSD). This research considers the effects of both the Schmid factor (SF) value and the slip direction of the grain on fatigue crack initiation sites. The result shows that fatigue cracks tend to form basal slips in primary α grains. In addition, these cracks are generated from primary α grains with relatively high basal SF values. However, it was found that fatigue cracks do not necessarily originate from basal planes of primary α grain with the maximum SF value. Finally, a new parameter that combines SF and the slip angle Ω (slip angle Ω is the angle between the specimen surface and the slip direction) was suggested and that parameter enables to predict fatigue crack initiation sites, since it was revealed that fatigue cracks initiated from primary α grains with high SFsinΩ values.

Fatigue tests were conducted under constant amplitude loading with a stress ratio of R = −1 to evaluate the effect of defect/inclusion on fatigue life of welding martensitic stainless steel (13Cr-5Ni) and KSFA90 steel (manufactured for crankshaft). An analysis based on the combined area eff of defect/inclusion and linear elastic fracture mechanics (LEFM), was performed. The results indicate that defect/inclusion dominated the fracture mode for both materials utilized. Moreover, the combined area eff and LEFM methods lose their accuracy for predicting fatigue life. Final, random forest machine-learning approach provided acceptable precision for unified predicting the fatigue of materials utilized in the current study.

To investigate whether high-amplitude stress and cycle ratios affect cumulative fatigue damage below the fatigue limit in 316 stainless steel, fatigue tests were carried out under incorporating high- (fixed at 277 MPa) and low-amplitude stress in which high stress level was set higher than previous applied (fixed at 260 MPa) and low stresses were below the fatigue limit with varying cycle ratios. Cumulative fatigue damage values for various cycle ratios calculated via previously proposed approach are inaccurate, it indicates that both high-amplitude stress and cycle ratios affect cumulative fatigue damage below the fatigue limit. In additional, saturation cycles of low-amplitude stress in one test block which can contribute to fatigue damage effectively is less than previous value. Thus, a rational evaluative approach for predicting cumulative fatigue damage below the fatigue limit has been developed on the basis of incorporating high- and low-amplitude stress tests outcomes, whose accuracy has been proved by repeated four-step and random-amplitude stress tests.

Atmospheric-controlled induction-heating fine particle peening (AIH-FPP) using Cr and Mo shot particles was introduced to improve the electrochemical characteristics of AISI 1045 medium carbon steel in NaCl solution. AIH-FPP can form transferred and diffused layers of shot particles on the surface of carbon steel. The corrosion potential of the AIH-FPP-treated steel was higher than that of the untreated steel in a NaCl environment. Furthermore, a passivation region was observed in the carbon steel treated with AIH-FPP using Cr shot particles after peening with Mo shot particles through the formation of a surface-modified layer with high Cr and Mo concentrations in 20% NaCl solution.

One way of addressing environmental problems is to increase the use of light-weight materials in automobiles, such as the multi-material structure, which improves fuel economy and reduces pollution. However, it is necessary to develop a welding technique to join carbon fibre-reinforced plastic to metals to achieve a multi-material structure. So, this paper aims to shorten the welding time and to clarify the fatigue fracture mechanism of shear type friction stir spot welding joint between aluminium alloy and CFRP experimentally and analytically. As a result, the static and fatigue strength of the joint improved as the welding time increased due to the increase of total joint area to increased resin melting.

CP titanium with a bimodal microstructure consisting of a substrate surrounded by a network structure of nitrogen diffusion phase was fabricated by sintering nitrided powders, as a means of improving the mechanical and tribological properties. A nitrogen diffusion layer can be formed on CP titanium powder at temperatures above 873 K. The areal fraction of the nitrogen diffusion phase increased along with the sintering temperature. As results of ball-on-disk dry friction tests, CP titanium fabricated from powder nitrided at 873 K had a lower friction coefficient than compacts fabricated from as-received CP titanium powder. In contrast, adhesion of the counter material was observed over the worn surface of sintered compact fabricated from the powder nitrided at 973 K, which indicates a higher friction coefficient.

Atmospheric-controlled induction-heating fine particle peening (AIH-FPP) using Cr and Mo shot particles in a N 2 atmosphere was introduced to improve the electrochemical characteristics of AISI 316 austenitic stainless steel. The surface microstructure of the AIH-FPP-treated specimen was characterized using scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). AIH-FPP can be used to form transferred and diffused layers of shot particles on the surface of austenitic stainless steel. The thickness of the diffusion layers of Cr shot particles tended to increase with the heating time in the AIH-FPP process, whereas the Cr concentration at the surface tended to decrease. Electrochemical polarization tests were performed in 3 wt% NaCl + H 2 SO 4 and 20 wt% NaCl environments at 343 K using a three-electrode electrochemical cell connected to a computer driven potentiostat to examine the corrosion resistance of austenitic stainless steel treated with AIH-FPP. The pitting potential of the AIH-FPP-treated specimen was higher than that of the untreated specimen. In particular, there was clear improvement in the pitting potential of austenitic stainless steel by AIH-FPP with Cr shot particles following peening with Mo shot particles. AIH-FPP using Cr and Mo shot particles in a N 2 atmosphere is an effective method of improving the electrochemical characteristics of austenitic stainless steel.

The purpose of this paper is to establish the welding technology for dissimilar materials of carbon fibre-reinforced plastic. Therefore, this study focused on friction stir spot welding, which can be simply substituted for spot welding which is widely used for welding of automobile body. In this study, friction stir spot welding was used to weld joints of carbon fibre-reinforced plastic and aluminium alloy, and the effect of aluminium alloy surface treatments on the fatigue properties and the fracture mechanism of dissimilar material joints were investigated experimentally and statistically. As a result, it is possible to create welding joints with high fatigue durability by using the surface treatments on the aluminium alloy.

Fe-based alloys, such as ferritic stainless steels, developed for planar solid oxide fuel cell (pSOFC) interconnect commonly contain Cr and can form a chromia (Cr2O3) scale on the surface. At the high operating temperature of pSOFC, Cr can be oxidized to volatile Cr+6 species which can deposit in the cathode and lead to degradation of cathode performance and limit the lifetime of a pSOFC system. Coating a suitable material, such as lanthanum strontium manganite (LSM), has been practically conducted on the metallic interconnect to prevent such Cr poisoning in the cathode side of pSOFC. In this study, the joint strength between an SOFC glass-ceramic sealant (GC-9) and an interconnect steel (Crofer 22 APU) coated with La0.67Sr0.33MnO3 is investigated at room temperature (RT) and 800 °C in air under both shear and tensile loading modes. In particular, the effect of a long-term thermal aging at 800 °C on the joint strength is characterized. Results indicate that an LSM coating on the metallic interconnect degrades the joint strength between the given GC-9 glass-ceramic sealant and Crofer 22 APU interconnect steel. The shear strength at RT and 800 °C is significantly degraded by 36% and 65%, respectively, and the tensile strength is significantly reduced by 39% and 80% at RT and 800 °C, respectively. It is attributable to the existence of pores around the interface between GC-9 sealant and LSM coating. However, the shear strength of LSM-coated joint specimen is enhanced by 52% at RT and by 200% at 800 °C after 1000-h thermal aging in air. The given thermal aging treatment also improves the tensile strength of LSM-coated joint specimen by 50% at 800 °C. This may be attributed to a self-healing effect of the GC-9 glass-ceramic during thermal aging to reduce the pore size. Fractography analyses reveal that fracture path involving the LSM layer and its adjoining interfaces accompanies a lower joint strength.

To evaluate the accuracy of joint fatigue life estimations obtained using conventional theories, the fatigue properties of shear- and peel-type single spot welded joints were investigated experimentally and analytically. The observed crack initiation angles differed from the predictions obtained using conventional theories, indicating that the theories cannot be used to evaluate the fatigue properties of the joints. In contrast, the present analytical crack initiation angles were in good agreement with the experimental results. Therefore, the effect of the loading mode on the fatigue properties of the single spot welded joints was adequately determined from the range ΔKI,θmax of initial stress intensity factors thorough an analytical evaluation.

We performed in-plane bending fatigue tests under controlled load conditions on ASTM 309 stainless steel specimens with surface compressive residual stress. The results provide a fatigue limit of 415 MPa, which agrees with the value of 404 MPa calculated based on a modified Goodman line considering shakedown. Therefore, the surface layer was clearly restricted by the internal bulk and was relieved under controlled displacement, after which shakedown occurred. Then, the fatigue limit of the metal material with surface compressive residual stress should be estimated by using a modified Goodman line considering shakedown to avoid unexpected fractures that could occur by following a modified Goodman line that does not consider shakedown.