High Cycle Fatigue Life Regions Research Articles

Statistical estimation of fatigue design curves from datasets involving failures from defects

In the present paper, two methodologies for the estimation of the design curves of datasets with failures originating from defects are proposed. With the first methodology, the Likelihood Ratio Confidence Bound of a specific quantile P-S-N curve is considered. The second method is based on the bootstrap approach, with a large number of datasets simulated starting from the stress life and the defect size distributions estimated from the experimental data. The two approaches have been validated on literature datasets covering also the Very High Cycle Fatigue (VHCF) life region, proving their effectiveness.

Biocompatible mechanical surface modification processing and mechanical properties of beta-type titanium alloys

Biocompatible mechanical surface modification processing and mechanical properties of beta-type titanium alloys

Mechanical Performance and Biocompatibility of Biomedical Beta-Type Titanium Alloy Subjected to Micro-Shot Peening

Beta-type Ti-29Nb-13Ta-4.6Zr (TNTZ) was recently developed as a representative biomedical Ti alloy. As-solutionized TNTZ has a low Young’s modulus less than 60 GPa close to that of cortical bone along with very low cytotoxicity and good bone biocompatibility. Solution treatment and aging (STA) is a typical heat treatment for improving the mechanical properties of beta-type titanium alloys. However, STA also drastically increases the Young’s modulus. Therefore, this study investigated the effects of surface modification, micro-shot peening, on the mechanical properties of TNTZ subjected to severe thermomechanical treatment in order to maintain a relatively low Young’s modulus. The bone contact characteristics of TNTZ samples subjected to surface modification and cancellous bone were also compared. The Vickers hardness of cold-swaged TNTZ (TNTZSW) subjected to micro-shot peening was significantly increased within 20 mm from the very edge of the specimen surface. The fatigue strength of TNTZSW subjected to micro-shot peening increased especially in the high cycle fatigue life region. The fatigue limit was around 400 MPa. The bone formations on TNTZSW subjected to micro-shot peening and TNTZSW with the mirror surface as comparison material were almost identical to each other. However, the relative bone contact ratio of TNTZSW subjected to micro-shot peening was better than that of TNTZSW with the mirror surface.

微粒子衝突処理を施した生体用低ヤング率型チタン合金の機械的強度と骨接触性の変化

Beta-type Ti-29Nb-13Ta-4.6Zr (TNTZ), which is a recently developed biomedical titanium alloys, shows a relatively low Young’s modulus of around 60GPa when subjected to a solution treatment. However, our focus in this study was on the practical applications of TNTZ in vivo because its mechanical strength decreases with solution treatment progress. Therefore, we investigated the effect of fine particle bombarding (FPB) on the mechanical properties of TNTZ subjected to a cold-swaging treatment in order to maintain its relatively low Young’s modulus and to improve its mechanical properties. The relative bone contact ratios between the cancellous bones of Japanese white rabbits and column-shaped TNTZ samples subjected to FPB were also evaluated. The microstructure of cold-swaged TNTZ showed a single beta-phase with a marble-like structure. Moreover, its Vickers hardness did not increase remarkably with changes in its diameter, although the average diameter of the beta-grains of solutionized TNTZ ranged from 5.0 to 20 μm, depending on the increase in the holding time of the solution treatment. The Vickers hardness and Young’s modulus of TNTZ subjected to FPB increased at the edge of the specimen surface to be around 70% and 15%, respectively, more than those of cold-swaged TNTZ. Further, the fatigue strength of TNTZ subjected to FPB became significantly higher than that of cold-swaged TNTZ in the high-cycle fatigue life region. Lastly, TNTZ with a rough surface texture (Ra: 0.65μm) showed a relative bone contact ratio of more than 80% after undergoing FPB; this value was significantly higher than that of cold-swaged TNTZ with a very smooth surface texture (Ra: 0.07 μm). [doi:10.2320/matertrans.M2014349]

High-frequency corrosion fatigue behavior of AZ31 magnesium alloy in different environments

The high-frequency corrosion fatigue behavior of extruded AZ31 magnesium alloy was investigated in different environments: air, gear oil and 3.5% NaCl solution. Compared with that in air, the corrosion fatigue limits were degraded by approximately 3.52% and 58.91%, respectively, and the corrosion fatigue lives were shortened by about 13.43% and 89.36%, respectively. In the same environment, the high-frequency fatigue limits are all higher than those tested at low frequency. The specimen geometrical shape plays a certain factor on stage characteristics of S–N curves. Compared with that of arc transition specimens, the stress sensitivity of line transition specimens is only reflected in a relatively high cycle fatigue life region. Different environments influence the corrosion failure kinetics processes (the crack initiation mechanism), but do not change the fatigue fracture mechanism of the alloy, and the higher loading frequency only accelerate the crack nucleation processes.

Mechanical Properties of a β-Type Titanium Alloy Cast Using a Calcia Mold for Biomedical Applications

A calcia mold, which is stable at high temperatures for dental precision casting of � -type titanium alloys such as Ti-29Nb-13Ta-4.6Zr (TNTZ) with high melting point, has been developed. The applicability of the calcia mold to casting TNTZ was evaluated with focusing on the mechanical properties of the casting in this study. The molten TNTZ was cast into the calcia mold of which dimensional accuracy was controlled by adding pure zirconium particles. The tensile and fatigue properties of TNTZ cast into the calcia mold were examined with comparing those of TNTZ cast into the magnesia mold, which is the conventional one for casting titanium alloys. The tensile properties of TNTZ cast into the calcia and the magnesia molds are not markedly different. The fatigue strength of TNTZ cast into the calcia mold in the low- and high-cycle fatigue life regions is slightly higher than that of TNTZ cast into the magnesia mold. Therefore, the calcia mold is expected to be applicable to the dental precision casting of TNTZ. [doi:10.2320/matertrans.L-M2009828]

Change in Fatigue Strength of Biomedical β-Type Titanium Alloy through Heat Treatment Processes

Relationships between fatigue properties and microstructures of hot-forged Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) in under aged, peak aged, and over aged conditions at aging temperatures of 673K and 723K are investigated. The changes in the fatigue properties of TNTZ subjected to thermomechanical treatments, which includes an aging treatment at 673K or 723K for 259.2ks after a severe deformation process by cold rolling, are also investigated.At an aging temperature of 673K, ω phase precipitates at the early stage of aging, but α phase precipitates at relatively longer aging time. The precipitation site of α phase changes from intra-grain to grain boundary at around peak aging time when TNTZ is aged at 673K and 723K. The elastic modulus of TNTZ increases simply with increasing aging time at both 673K and 723K. The fatigue strength of TNTZ increases considerably when α phase precipitates compared with when ω + α phases co-exist. The fatigue strength of TNTZ decreases slightly due to the coarsening of α phase precipitated in β grain and its grain boundary. TNTZ aged at 723K for 259.2ks after cold rolling exhibits the highest fatigue strength in both the low- and high-cycle fatigue life regions. Furthermore, the fatigue limitof about 770MPa (fatigue raito : 0.71) is nearly equal to that of hot-forged Ti-6Al-4V ELI alloy subjected to aging after solution treatment with equiaxed α structure.

Change in Tensile and Fatigue Properties of Biomedical Ti-29Nb-13Ta-4.6Zr Alloy Fabricated by Various Processings

The tensile and plain fatigue properties of the β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ), which was subjected to various thermomechanical treatments, and cast TNTZ were investigated in order to judge its potential for biomedical and dental applications. The tensile strengths of TNTZ aged after solution treatment and that aged after cold rolling decrease with an increase in the aging temperature; however, their elongation exhibits an opposite trend. TNTZ composed of the ω phase or the ω and α phases in the β phase exhibits a tensile strength of about 1000 MPa or more. The tensile properties of the cast TNTZ with and without a surface reaction layer is are not significantly different, and are almost identcal to those of as-solutionized TNTZ. The plain fatigue strengths of TNTZ aged after solution treatment and those of TNTZ aged after cold rolling increase with the aging temperature. In particular, TNTZ aged at 723 K after cold rolling exhibits the highest fatigue strength in both the low- and high-cycle fatigue life regions. Further, the plain fatigue limit, which is about 770 MPa, is nearly equal to that of hot-rolled Ti-6Al-4V ELI alloy subjected to aging after solution treatment; Ti-6Al-4V ELI alloy is a representative α+β-type titanium alloy for biomedical applications. The plain fatigue strength of cast TNTZ with a surface reaction layer is considerably less than that of the as-cold-rolled and as-solutionized TNTZ. Consequently, in the low-fatigue life region, the fatigue crack easily occurs at the surface reaction layer, which is brittle, and in the high-fatigue life region, the fatigue crack occurs at the sites of casting defects (shrinkage). The fatigue limits range from 180 MPa to 200 MPa.

Experimental and numerical investigation of the effect of clamping force on the fatigue behaviour of bolted plates

In this research, both experimental and numerical methods were used to investigate the fatigue behaviour of bolted plates. In the experimental part of the research, a holed plate was clamped using a bolt and a nut, and then tested under axial cyclic load in a fatigue testing machine. In order to obtain S– N curves and investigate the direct effect of the isolated clamping force on the fatigue behaviour of the bolted plates, three batches of specimens each subjected to different clamping forces were fatigue tested. The clamping forces were obtained experimentally from the compressive axial strain of a steel bush which was placed between the nut and the plate. In the numerical method, to determine the stress and strain distributions due to combined clamping force and axial load in plate, 3D finite element models were generated using a numerical package. Numerical simulation and experimental results showed that the fatigue life of bolted plates improve because of the compressive stresses created around the plate hole due to clamping force. The life improvement was greatest at the high cycle fatigue life region of the S– N curves.

OS7-1-3 Fretting Fatigue Characteristics and Microstructures of Dental Low-noble Ag-Pd-Cu-Au-Zn Alloy

Plain and fretting fatigue characteristics of dental low-noble Ag-Pd-Au-Cu-Zn (S-12) alloys with different microstructures obtained by solution treatment and aging after solution treatment were investigated. In addition, the fracture surface and the surfaces of the specimen and pad after the fretting tests were also examined. The fretting fatigue strength of the S-12 alloy subjected to both heat treatments is lesser than its plain fatigue strength especially in the high cycle fatigue life region. The fretting fatigue strength of the S-12 alloy aged after the solution treatment is less than that of the one subjected only to solution treatment. Small fretting fatigue cracks initiate at the wear scars; these cracks link with each other, thereby leading to the main crack.

Improvement in fatigue characteristics of newly developed beta type titanium alloy for biomedical applications by thermo-mechanical treatments

Tensile and plain fatigue properties of β type titanium alloy, Ti–29Nb–13Ta–4.6Zr, which underwent various thermo-mechanical treatments, were investigated in order to judge its potential for biomedical applications. Microstructures of Ti–29Nb–13Ta–4.6Zr (TNTZ) aged directly at 723 K for 259.2 ks after cold rolling and TNTZ aged at 723 K for 259.2 ks after solution treatment are composed of precipitated α phase in β phase. While, microstructures of TNTZ aged directly at 598 K and 673 K for 259.2 ks after cold rolling and aged at 598 K and 673 K for 259.2 ks after solution treatment are composed of precipitated ω phase, and precipitated α and ω phases in β phase, respectively. Tensile strength of aged TNTZ after solution treatment and aged TNTZ after cold rolling decreases with increasing aging temperature although the elongation shows the reverse trend. TNTZ composed of ω phase or ω and α phases in β phase shows the tensile strength of around 1000 MPa or more. Young's moduli of aged TNTZ after solution treatment and aged TNTZ after cold rolling decrease with increasing aging temperature. TNTZ conducted with solution treatment has the lowest Young's modulus of around 60 GPa. Fatigue strengths of aged TNTZ after solution treatment and aged TNTZ after cold rolling increase with increasing aging temperature. In particular, TNTZ aged directly at 723 K after cold rolling shows the greatest fatigue strength in both low cycle fatigue life and high cycle fatigue life regions, and the fatigue limit, which is around 770 MPa, is nearly equal to that of hot-rolled Ti–6Al–4V ELI conducted with aging, which is one of representative α + β type titanium alloys for biomedical applications.

Effects of Contact Pressure on Fretting Fatigue Characteristics of Ti-4.5Al-3V-2Mo-2Fe with Acicular Alpha Structure

The effects of microstructure and contact pressure on fretting fatigue characteristics of Ti-4.5Al-3V-2Mo-2Fe conducted with annealing at 1123 K and 1223 K were investigated in this study. Fretting fatigue tests in low and high cycle fatigue life regions of the alloys with equiaxed α and acicular α structures were carried out at each contact pressure of 10, 15, 30, 45, 75, 105 and 153 MPa. In the alloy with equiaxed α structure, fretting fatigue strength tends to be very low at contact pressures of 10 MPa and 15 MPa in low and high cycle fatigue life regions, respectively. Furthermore, fretting fatigue strength tends to be nearly constant at the contact pressure over 45 MPa in each fatigue life region. On the other hand, in the alloy with acicular α structure, fretting fatigue strength tends to be very low at contact pressures of 15 MPa and 30 MPa in low and high cycle fatigue life regions, respectively. Furthermore, fretting fatigue strength tends to be nearly constant at contact pressures of 45 MPa and over 30 MPa in low and high fatigue life regions, respectively.

Influence of Bone Structure on Mechanical Properties of Bovine and Swine Compact Bones

Recently, more attention has been focused on the research and development of biomaterials such as an artificial bone because of the rapid-increasing demand for biomaterials from the aging society in the world. However, the study on the bone itself is not enough. In particular, there is little information about the fracture toughness, and fatigue property of bones, and effect of the microstructure on the fracture characteristic. In this study, the fracture toughness of the bovine and swine humerus and femur as well as the fatigue property of the bovine humerus and femur was investigated with relating microstructures. The fracture toughness of plexiform bone is greater than that of haversian bone, and the fatigue strength of the plexiform bone taken from the humerus and femur is a little greater than that of the haversian bone taken from the humerus and femur in particular in high cycle fatigue life regions.

Fatigue Characteristics of Low Cost β Titanium Alloys for Healthcare and Medical Applications

Two new low cost β titanium alloys, Ti–4.3Fe–7.1Cr (TFC alloy) and Ti–4.3Fe–7.1Cr–3.0Al (TFCA alloy) for healthcare and medical applications have been recently developed. As for such applications, the alloys are necessary to have high fatigue performance. The aim of this study is, therefore, to investigate fatigue characteristics of the alloys subjected to solution treatment above β transus. Fatigue tests were carried out at a stress ratio, R, of 0.1 and a frequency of 10 Hz.Fatigue limit of the solution treated TFC alloy is higher than that of the solution treated TFCA alloy, but both are higher than that of the existing biometallic materials. Fatigue strength of the TFC alloy is almost independent of solution treatment temperature, while, fatigue strength of the TFCA alloy strongly depends on solution treatment temperature, especially, in the low cycle fatigue life (LCF) region. The fatigue ratio and biofunctionality of these new alloys are much higher than those of the existing biometallic materials. In general, a crack initiates from the surface in the LCF region and from subsurface (internal) in the high cycle fatigue life (HCF) region for the TFC alloy, while, in the case of the TFCA alloy, a crack tends to initiate from the subsurface in both LCF and HCF regions. The internal crack initiation sites are found to be the area with low β phase stability in the LCF region and at the area with high stability of β phase in the HCF region. The relatively low fatigue strength of TFCA alloy is associated with the addition of Al that leads to precipitate α phase in which both crack initiation and facet formation are easier to occur.

等軸および針状組織を有する高加工性チタン合金のミクロ組織とフレッティング疲労特性

The effects of microstructure and contact pressure on fretting fatigue characteristics of a Ti-4.5Al-3V-2Mo-2Fe alloy with a Widmanstatten a structure were investigated in comparison with that with an equiaxed a structure in this study. In fretting fatigue of the Ti-4.5Al-3V-2Mo-2Fe alloy with a Widmanstatten a structure in a high cycle fatigue life region, and that with an equiaxed a structure in low and high cycle fatigue life regions, the fretting fatigue life does not change linearly with contact pressure, and the fretting fatigue life shows the minimum at a certain contact pressure. In a low cycle fretting fatigue region of the alloy with Widmanstatten a structure, the fretting fatigue life changes linearly with changing in contact pressure. At contact pressures over a certain value, fretting fatigue life of the alloy tends to become nearly constant in each fatigue life region. At relatively lower contact pressures, the main small crack in the alloy with equiaxed a structure tends to be formed at uneven wear damaged parts by fretting wear in the slip region in each fatigue life region. At relatively higher contact pressures, the main small crack in the alloy with equiaxed a structure tends to be formed at the boundary between slip and stick regions in each fatigue life region. The main small crack in the alloy with Widmanstatten a structure tends to be formed in the slip region in each fatigue life region.

生体用Ｔｉ‐２９Ｎｂ‐１３Ｔａ‐４．６Ｚｒ合金の切欠き疲労特性

The effects of microstructures on notch fatigue propertes of a Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) subjected to various thermo-mechanical treatments were investigated in this study. The notch fatigue strengths of TNTZ subjected to aging at 673 K and 723 K after solution treatment or cold rolling at stress concentration factors of 1 (without the notch), 2 and 6 in both low and high cycle fatigue life regions are greater than those of as-cold rolled and as-solutionized TNTZ, and TNTZ subjected to aging at 598 K after solution treatment or cold rolling. A single fatigue crack initiates on a specimen surface and at the tip of the notch at stress concentration factors of 1 and 2. While, a few cracks initiate the tip of the notch having a stress concentration factor of 6. Notch sensitivity factor of TNTZ is almost equal to or smaller than those of other materials such as Ti-6Al-4V, CP-Ti, S35C, S45C and SUS304. It is considered that the notch sensitivity factor decreases with decreasing the width of lath like α phase and its volume fraction.

Fatigue Performance of Low Rigidity Titanium Alloy for Biomedical Applications

Microstructures of Ti-29Nb-13Ta-4.6Zr (TNTZ) aged at temperatures between 573 and 723 K after solution treatment at 1063 K have super fine omega phase, or both super fine alpha and omega phases, respectively in beta phase with an average grain diameter of 20 µm. Plain fatigue strength of TNTZ aged after solution treatment is much greater than that of as-solutionized TNTZ in both low cycle fatigue and high cycle fatigue life regions. This is due to the improvement of the balance of strength and ductility by the precipitation of alpha phase. Fretting fatigue strength of TNTZ conducted with various heat treatments decreases dramatically as compared with their plain fatigue strength in both low cycle fatigue and high cycle fatigue life regions. In this case, the decreasing ratio of fretting fatigue life increases with increasing the small crack propagation area where both the tangential force and frictional force at the contact plane of pad exist. In fretting fatigue in air, the ratio of fretting damage (Pf/Ff), where Pf and Ff stand for plain fatigue limit and fretting fatigue limit, respectively, increases with increasing elastic modulus. In fretting fatigue in Ringer’s solution, the passive film on specimen surface is broken by fretting action in TNTZ, which have excellent corrosion resistance, and, as a result, corrosion pits that lead to decreasing fretting fatigue strength especially in high cycle fatigue life region, are formed on its surface.

Fretting Fatigue Characteristics with Relating Contact Pressure and Surface Roughness of Highly Workable Titanium Alloy, Ti-4.5Al-3V-2Mo-2Fe

The effects of contact pressure and surface roughness on fretting fatigue strength of Ti-4.5Al-3V-2Mo-2Fe conducted with annealing at 1123 K were investigated in this study. Fretting fatigue tests in low and high cycle fatigue life regions of the alloy were carried out at each contact pressure of 10, 15, 30, 45, 75, 105 and 153 MPa using relatively rough surface specimens with roughness number around 120∼140 nm. Furthermore, the fretting fatigue tests were also performed on the relatively smooth surface specimens with roughness number around 13.2∼32.2 nm at a selected contact pressure of 153 MPa. The fretting fatigue crack initiation mechanism is changed by contact pressure. At a contact pressure of 15 MPa, fretting fatigue life tends to be very low in each fatigue life region. The tangential force tends to increase with increasing contact pressure in each fatigue life region. Contrary to this trend, the tangential force coefficient tends to decrease with increasing contact pressure in each fatigue life region. The fretting fatigue life of the alloy with smooth surface is greater about 20% and 10% in low and high cycle fatigue life regions, respectively, than that of the alloy with relatively rough surface.

Fatigue, Fretting Fatigue and Corrosion Characteristics of Biocompatible Beta Type Titanium Alloy Conducted with Various Thermo-Mechanical Treatments

Plain and fretting fatigue properties of β type titanium alloy, Ti-29Nb-13Ta-4.6Zr, underwent various thermo-mechanical treatments were investigated in order to judge its potential for biomedical applications. Ti-29Nb-13Ta-4.6Zr aged directly at 723 K for 259.2 ks after cold rolling shows the greatest fatigue strength in both low cycle fatigue life and high cycle fatigue life regions, and the fatigue limit, which is around 770 MPa, is nearly equal to that of hot-rolled Ti-6Al-4V ELI conducted with aging, which is one of representative α + β type titanium alloys for biomedical applications. Fretting fatigue strength tends in proportion to Young's modulus. Fretting fatigue limits of the forged bar of Ti-29Nb-13Ta-4.6Zr conducted with solution treatment, and aging at 723 K after solution treatment are around two thirds and a half of plain fatigue limits, respectively, and those are around 180 MPa and 285 MPa, respectively. Passive current densities of the plate of Ti-29Nb-13Ta-4.6Zr conducted with a multi-step-thermo-mechanical treatment, where the cold rolling and solution treatment are repeated 4 times, in 0.5%HCl and Ringer's solutions are much smaller than that of Ti-29Nb-13Ta-4.6Zr conducted with general thermo-mechanical treatment, and the values are a little smaller than those of forged Ti-15Mo-5Zr-3Al conducted with annealing and hot rolled Ti-6Al-4V ELI conducted with aging.

OS07W0142 Fatigue characteristics of low rigidity titanium alloy, Ti-29Nb-13Ta-4.6Zr, for biomedical applications

Plain fatigue strength of cold-rolled and forged Ti-29Nb-13Ta-4.6Zr(TNTZ) aged after solution treatment is much greater than that of TNTZ conducted with solution treatmet in both low cycle fatigue and high cycle fatigue life regions. The plain fatigue strength of TNTZ is not degraded in Ringer's solution. Fretting fatigue strength of forged TNTZ and Ti-15Mo-5Zr-3Al conducted with various heat treatments decreases dramatically as compared with their plain fatigue strength in both low cycle fatigue and high cycle fatigue life regions. In this case, the decreasing ratio of fretting fatigue life increases with increasing the small crack propagation area where both the tangential force and frictional force exist at the contact plane of pad. In fretting fatigue in air, the ratio of fretted damage (P_f/F_f), where P_f and F_f stand for plain fatigue limit and fretting fatigue limit, respectively, increases with increasing elastic modulus. In fretting fatigue in Ringer's solution, the passive film on specimen surface is broken by fretting action in TNTZ, which has excellent corrosion resistance, and, as a result, corrosion pits that lead to decreasing fretting fatigue strength especially in high cycle fatigue life region, are formed on its surface.