High Cycle Fatigue Properties Research Articles

Effects of the specimen form on high cycle fatigue properties of 7050-T7451 and 2524-T3 aluminum alloys

High cycle fatigue properties of 7050-T7451 and 2524-T3 aluminum alloys at three stress ratios R=-1, 0.06, and 0.5 were experimentally studied, in which the axial stress control method was used to measure the funnel-shaped and iso-section specimens, with a MTS electro-hydraulic test system. Stress-life data were obtained and equivalant stress-life curves were plotted based on the equivalent stress model. Results showed that as for 7050-T7451 and 2524-T3 aluminum alloys, stress-life curves obtained with two kinds of specimens basically agreed, and effects of the specimen form on high cycle fatigue properties of these two aluminum alloys can be neglected.

Characterization of High-Cycle Bending Fatigue Behaviors for Piston Aluminum Matrix SiO2 Nano-composites in Comparison with Aluminum–Silicon Alloys

In automotive industries, one failure mechanism in engine pistons is due to the fatigue phenomenon. Therefore, to enhance fatigue properties of piston aluminum alloys is a major concern for designers. One reinforcement method could be the addition of nano-particles in the aluminum matrix. In this article, high-cycle fatigue properties of the aluminum matrix nano-composite were characterized under bending loadings and then compared to those of the aluminum–silicon alloy. For this objective, fully reversed bending fatigue tests were performed on standard specimens, based on the ISO-1143:2010 standard. Before testing, nano-composite samples were stir-casted by the addition of 1 wt% SiO2 nano-particles, and aluminum specimens were gravity-casted in a cast-iron mold. The microstructure of materials and the distribution of nano-particles in the aluminum matrix were evaluated by the optical microscopy and the field emission scanning electron microscopy. Experimental data indicated that nano-particles had a significant effect on the high-cycle fatigue lifetime. The reason for this improvement in high-cycle fatigue properties could be finer grains, higher hardness, the proper distribution of nano-particles in the aluminum matrix and stronger bonding strength at the Al/Si interface. However, based on fracture surfaces, all samples had the brittle behavior due to cleavage and quasi-cleavage marks.

Tensile and high-cycle fatigue performance of HRB500 high-strength steel rebars joined by flash butt welding

In this research, extensive testing results of the specimens of HRB500 high-strength steel rebars joined by flash butt welding were demonstrated, including metallographic and micro-hardness tests, monotonic tensile tests, high-cycle fatigue tests, and fracture surface analysis. The chief aim of the present research is to investigate the applicability of flash butt welding for HRB500 high-strength steel rebars. Thus, these tests were executed on the welded specimens, which were previously manufactured to evaluate the tensile and high-cycle fatigue properties. Meanwhile, a series of experimental technical details were proposed in the test process. Some conclusions can be obtained as follows: welding heat can change the metallographic structures of HRB500 high-strength steel rebars, and the welding heat-affected zone on the steel rebars with diameter of 16 mm is totally about 10 cm in length. Besides, the deformability and tensile strength of the welded specimens decline with their diameter degrees increasing, and brittle fractures occur in those welded specimens with diameter of 32 mm. Furthermore, three-parameter S-N curves of the welded specimens and the steel rebars base materials are obtained based on the fatigue test results. Fatigue strengths of welded specimens decrease with their diameters increasing, and reduction of high-cycle fatigue strength is more apparent for large-diameter welded specimens. Welded specimens are more prone to pre-mature fatigue failure than base materials of HRB500 high-strength steel rebars, and the rate of change in fatigue strength of welded specimen decreases with the increase of loading cycles. At last, mechanism of crack propagation in fatigue process is analyzed and further evaluated by fracture surface analysis with the aim of wider application.

High-cycle fatigue and fracture behavior of double-side friction stir welded 6082Al ultra-thick plates

For welded structures of precipitation-strengthened aluminum alloys, achieving sound joint with good fatigue property is not an easy task, especially for thick plates. In the present work, ultra-thick 6082Al-T4 alloy plates with 80 mm in thickness were double-side friction stir welded and heat-treated. The high cycle fatigue (HCF) property and fracture behavior of the joint were investigated using trisection specimens in thickness, and the key factors that affect the fracture behavior were addressed. High quality joint was achieved with the three-layered specimens fractured along the lowest hardness zone (LHZ) in the static tensile testing. Further, the fatigue life curves exhibited almost the same distribution tendency, and the same fatigue limit (110 MPa) and fatigue ratio (0.49) were achieved in the three-layered specimens. During fatigue testing, the middle and lower layers fractured along the LHZ, which was similar to those during the static tensile tests, while abnormal fracture occurred in the nugget zone (NZ) of the upper specimen. Further examination revealed that the residual stress in the NZ of the upper layer was tensile stress (+9 MPa) whereas it was compressive stress in the lower layer (–31 MPa). The tensile residual stress together with the external loaded cyclic tensile stress resulted in more serious fatigue damage in the upper layer and led to the abnormal fracture in the NZ.

Fatigue Performance of the Novel Titanium Alloy TIMETAL®407

TIMETAL®407 (Ti-407) is a novel titanium alloy formulated as a medium strength, highly ductile alloy offering a range of manufacturing cost reduction opportunities. It can be used as a direct replacement for Ti-6Al-4V or Ti-3Al-2.5V alloys, particularly in applications where energy absorption during fracture or HCF endurance are the key design criteria. The effect of thermo-mechanical processing on microstructure has been characterised and the room temperature high cycle, low cycle and dwell cycle fatigue properties of Ti-407 containing 30-40% primary alpha volume fraction are presented and discussed. These results are compared with data generated from Ti-6Al-4V processed to provide a similar but non-standard microstructure and demonstrate that Ti-407 shows superior HCF endurance strength, despite having a significantly lower tensile and yield strength.

Effect of Heat Treatments on Fatigue Properties of Ti-6Al-4V Alloy Fabricated by EBM Additive Manufacturing

The powder bed fusion method using a heat source for 3D printing can be applied to fabricate the geometrical shapes of some parts, and enables rapid melting and cooling. 3D EBM additive manufacturing can supply a near-net-shape or net-shape and precise parts better than micro scale casting and precision casting. Casting parts have residual stress in the matrix and their microstructure, which can affect the dynamic properties, but if they are heat-treated under the optimal conditions, the residual stress can be reduced to enhance the dynamic-mechanical properties of 3D printed parts. In this study, Ti-6Al-4V bulk bars were fabricated by EBM additive manufacturing, and the microstructures, residual stress, and various interior defects of the specimens were analyzed. The residual stress and surface tension were measured and calculated in different specimens heat-treated at 850~950 ℃ . The relationship between the residual stress and surface tension was explained using the related equations and the influence on the high cycle fatigue properties was evaluated.

Thermomechanical process route to achieve high fracture toughness in Ti-17 forgings for high temperature applications

Mechanical properties of Ti-17 are typically strongly influenced by different thermomechanical process parameters such as applied strain, cooling rates and heat treatment temperatures and times. A variation of theses parameters allows the optimization of material properties. Today Ti-17 is mainly used for aero engine applications, where a high strength and good low cycle fatigue properties are needed up to 450°C. For structural parts damage tolerance properties are the main focus and therefore fracture toughness and fatigue crack propagation are the main driving factors for the design. In large forgings such as aero structural parts, the tempering cross section generally varies significantly, which makes it extremely challenging to achieve uniform properties in each area of the forging especially in case of low buy-to-fly ratio. The aim of this work is to develop a robust thermomechanical processing route for large Ti-17 die forgings with complex geometry and high fracture toughness requirements. Hand forging trials with four different thermomechanical processing routes resulting in a lamellar microstructure have been performed and their strength and fracture toughness properties were studied. In addition, one die forging using a promising process route was manufactured and strength and fracture toughness were compared with values typically achieved for Ti6-4.

High cycle fatigue behavior of a dissimilar metal welded joint in ultra-supercritical steam turbine rotor

The high cycle fatigue (HCF) property and microstructure of a dissimilar metal welded joint (DMWJ) for ultra-supercritical steam turbine rotor were systematically investigated in this paper. The DMWJ was fabricated using narrow gap submerged arc welding (NG-SAW) technique with buttering layer. Conditional fatigue strength of 30Cr1Mo1V (BM-1), buttering layer (BL), weld metal (WM) and 30Cr2Ni4MoV (BM-2) based on S-N curve was obtained by HCF tests at room temperature. The microstructure and second-phase carbide as well as fracture appearance of BM-1, BL, WM and BM-2 were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The results show that the BL has lower fatigue strength, which are related to more content of the soft ferrite and less content of the hard carbide. The acicular ferrite represents better fatigue properties than massive ferrite due to barrier effect. Additionally, dislocation density sharply increases near the carbides, grain boundaries, and lath structures resulting in dislocation tangle after HCF test, which helps to improve the fatigue strength of the welded joint. The carbide precipitated, aggregated, and grown in the grain boundaries promoted crack nucleation, reduced the crack propagation rate and affected the crack propagation path.

Very High Cycle Fatigue Properties of Ferritic-Pearlitic Steel after Micro-Shot Peening

An alloyed ferritic-pearlitic steel is studied after micro-shot peening with balls from a high-speed steel. The morphology and the roughness of the surface of the specimens are determined. Specimens with smooth and notched surfaces are subjected to multi-cycle fatigue tests. The fatigue resistance of the specimens with a smooth surface and with a notched surface increases by 22 and 27%, respectively, after the shot-peening. Observation of crack growth in specimens with small holes shows that micro-shot peening hinders crack propagation.

Effect of Mg addition on high-cycle fatigue properties of 7000 series aluminum alloy

Effect of Mg addition on high-cycle fatigue properties of 7000 series aluminum alloy

Effect of Dry-Electropolishing on the High Cycle Fatigue Properties of Ti-6Al-4V Alloy Manufactured by Selective Laser Melting

Effect of Dry-Electropolishing on the High Cycle Fatigue Properties of Ti-6Al-4V Alloy Manufactured by Selective Laser Melting

Effect of Rare Earth Element Content on High Cycle Fatigue Property of Titanium Alloys

High cycle fatigue (HCF) properties for high temperature titanium alloys without and with different content of rare earth element Y have been tested at ambient temperature at a frequency of 100Hz or so and a load ratio R of 0.1, and the effect of Y on fatigue fracture behavior was also analyzed. The results indicated that the HCF strength for the alloys increases with the increment of rare earth element content, and the strength of the two alloys with Y are lower than that of the alloy without Y. Compared with the alloy without Y, the strength for the two alloys with Y decreases 11.2% and 17.4%, respectively. The particle size for rare earth oxide dispersely precipitated from the matrix alloy varies from several hundred nanometer to several micrometer. The crack initiations for the alloys are related to the fracture of rare earth oxide particles.

Influence of surface conditions and specimen orientation on high cycle fatigue properties of Inconel 718 prepared by laser powder bed fusion

High-cycle fatigue testing of nickel-based superalloy Inconel 718 made by laser powder-bed fusion was performed on round uniform-gauge or hourglass specimens for various specimen orientations, stress ratios and surface conditions (as-built and machined). Only surface conditions, specifically near-surface process defects, influenced fatigue properties. There was a systematic bias of the azimuthal position of crack initiation sites. Crack initiation in specimens with as-built surfaces occurred at 50 µm diameter near-surface features. These dimensions were used in conjunction with fatigue limits derived from tests suspended at 107 cycles to calculate threshold ΔK values of 2–6 MPa √m due to as-built surface conditions.

Faceted crack induced failure behavior and micro-crack growth based strength evaluation of titanium alloys under very high cycle fatigue

Very high cycle fatigue properties of titanium alloys under symmetrical and asymmetrical loads were experimentally examined to clarify the failure behavior. An inhomogeneous microstructure zone (IMZ) containing facets is observable. By focused ion beam testing, the interior micro-crack extends along the maximum shear stress plane and the facet plane is about 45°. By the modeling of growth rate and the definition of controlling line, a strength evaluation approach with the failure behavior was well proposed. This reflects that the micro-crack growth rate in IMZ stage is below one Burger’s vector.

Very High-Cycle Fatigue Properties and Residual Stress Relaxation of Micro-shot-Peened EA4T Axle Steel

In this paper, EA4T alloy railway axle steel was shot peened with steel balls and ceramic balls with a diameter of 50 μm, and 109-cycle fatigue tests of unpeened and peened specimens were carried out. The fatigue properties and the surface compression residual stress relaxation processes were investigated. The results of surface fracture observation indicated that all the cracks initiated from the surface, and both peened and unpeened specimens have conventional fatigue limits in the very high-cycle fatigue regime. Moreover, compared with unpeened (UP) specimens, the fatigue limits were improved by 31 and 28% for ceramic shot-peened (CSP) and steel shot-peened (SSP) specimens, respectively. The improvement of fatigue limit is related to the surface compressive residual stresses (SCRS) and the surface-hardened layer. The SCRS and full-width half-maximum (FWHM) values during the relaxation processes have been analyzed. At stress amplitudes lower than the cyclic yield strength, the residual stress of SSP specimens relaxed quickly in the first loading cycle and then remained stable, while the residual stress of CSP specimens relaxed quickly in the first loading cycle and relaxed slowly afterward, then remained stable. For all SSP and CSP specimens with applied stress amplitudes larger than the cyclic yield strength, the residual stress relaxed quickly in the initial cycles, and then remained stable after the first loading cycle.

High cycle fatigue property of electron beam welded thick section of Ti–6Al–4V plates

High cycle fatigue property of electron beam welded thick section of Ti–6Al–4V plates

Effect of Microstructure on the High-Cycle Fatigue Behavior of Ti(43-44)Al4Nb1Mo (TNM) Alloys

To investigate the high-cycle fatigue (HCF) behavior of TNM alloys, three different microstructures were designed and obtained by different heat treatments. Staircase tests and fatigue tests in a finite life-region were performed to evaluate the fatigue properties. Then, the fracture surfaces were analyzed to study the fracture behavior of TNM alloys with different microstructures. Results showed that the TNM alloys with duplex microstructure possesses the highest fatigue strength and fatigue life, followed by near lamellar TiAl alloys. HCF failure exhibited cleavage fracture morphologies, and multiple facets were generated in the crack initiation region of different TNM alloys. Two different crack initiation modes, subsurface crack nucleation and surface origin, were observed. Both crack initiation modes appeared in near lamellar alloys, while only subsurface crack initiation were obtained in the duplex (DP) alloy. It contributes to the high scatter of S-N data. The HCF failure of TNM alloys was dominated by crack nucleation rather than crack propagation. These findings could provide guidance for optimizing the microstructure and improving the HCF properties of TiAl alloys.

Effect of Nanoscale Mesoscopic Structural States Associated with Lattice Curvature on the Mechanical Behavior of Fe-Cr-Mn Austenitic Steel

The paper explores the effect of high-temperature cross rolling followed by cold rolling on the internal structure of metastable Fe-Cr-Mn austenitic stainless steel, formation of nonequilibrium martensite e and α′ phases in it, dynamic rotations on fracture surfaces, fatigue life under alternating bending, and wear resistance. Scratch testing revealed a strong increase in the damping effect in the formed hierarchical mesoscopic substructure that promotes the formation of a nanocrystalline grain structure, formation of hcp e martensite and bcc α′ martensite in grains, formation of a vortical filamentary substructure on the fracture surface, and an increase in the high-cycle fatigue properties and wear resistance. These processes are associated with a high density of nanoscale mesoscopic structural states that arise in lattice curvature zones during high-temperature cross rolling followed by cold rolling with smooth rolls. The described effects are explained by the self-consistent mechanical behavior of hcp e martensite laths in fcc austenite grains and bcc α′ martensite laths formed in cold rolling of the steel after high-temperature cross rolling.

Effect of Zr on the high cycle fatigue and mechanical properties of Al–Si–Cu–Mg alloys at elevated temperatures

The Zr-modified Al–Si–Cu–Mg alloy with 0.14 wt%Zr addition was studied against the counterparts of commercially used EN-AC-42000 (Al7Si0.5Cu) baseline alloy for the effect of Zr on the high cycle fatigue (HCF) and mechanical properties at elevated temperatures of 150, 200, 250 °C. It was found that the fatigue life was significantly improved by 8–10 times at the high stress amplitude of 140 MPa in the Zr-modified alloy at all different temperatures. The fatigue strength coefficient, σf', of the baseline alloy was 574.9, 589.8, and 514.8 MPa at 150, 200, and 250 °C, respectively, which was greatly increased to 1412.3, 620.1, and 821.6 MPa for the Zr-modified alloy. The tensile strength was considerably improved by 34%–50%, dependant on the testing temperatures. The improved fatigue and tensile properties in the Zr-modified alloy could be mainly ascribed to: (1) the refined microstructure, with α-Al grain size decreasing from 335 to 253 μm and the secondary dendrite arm spacing (SDAS) dropping from 39 to 28 μm; (2) the reduced porosity; and (3) the additional precipitates strengthening effect by the nano-sized Al–Si–Zr–Ti dispersoids.

Tensile and fatigue properties of the Bridgman directionally solidified Fe-Al-Ta eutectic

Fe-Al-Ta eutectic composites were obtained by a modified Bridgman directional solidification technique at different solidification rates. High-oriented lamellar (or rod-like) Fe2Ta(Al) phase is uniformly distributed into Fe(Al,Ta) matrix. Micro-hardness, tensile and high cycle fatigue properties of the Fe-Al-Ta eutectic at different solidification rates were systematically studied. Moreover, the fracture morphologies were observed by SEM. It is found that the mechanical properties of the Fe-Al-Ta eutectic composites are better than that of the as-cast Fe-Al-Ta eutectic alloy because of the directional heat flow. Finally, the strengthening mechanism of Fe-Al-Ta eutectic was discussed.