Low-cycle Region Research Articles

Fatigue Resistance of the Sheets of Heat-Resistant Titanium Alloys

The results of a study of the resistance to fatigue fracture of sheets made of heat-resistant titanium alloys VT18U (Ti–6.5Al–4.3Zr–2.4Sn–0.8Nb–0.7Mo–0.1Si, wt.%), VT8 (Ti–6.4Al–3.4Mo–0.3Si, wt.%), and VT25U (Ti–6.51Al–3.76Zr–1.71Sn–3.94Mo–0.5W–0.13Si, wt.%) has been presented. Fatigue curves have been obtained in the initial state and in the oxidized one after isothermal annealing at a temperature of 560 °C for 1000 h in air. It has been established that after annealing, the fatigue resistance of all oxidized alloys in the low-cycle region decreases by an order of magnitude. The fatigue limit of the oxidized alloys VT18U and VT25U does not change and is about 320 MPa. The high-cycle fatigue limit of the VT8 alloy decreases from 300 MPa in the initial state to 230 MPa in the oxidized state. It has been established that after annealing, the phase composition of an oxide of 250 nm in thickness on the surface of the alloys is different and contains the phases of anatase and rutile for the VT18U and VT25U alloys and contains predominantly rutile for the VT8 alloys, which is why the fatigue limit of the oxidized alloys differs.

The Effect of Prior Surface Roughness on Fatigue Life of Nitrided Specimens

The effect of surface roughness of virgin specimens (prior roughness) made of low-alloyed high strength steel on their fatigue life after the case-hardening treatment was studied by rotating bending tests of virgin and nitrided samples. In a whole range of S-N curves, the fatigue strength of virgin samples after lathe-turning machining (high roughness) was naturally much higher than that of samples after grinding (low roughness). As expected, the fatigue strength of nitrided specimens was higher than that of virgin samples when averaged through the whole fatigue life range. When distinguishing the rough and smooth nitrided samples, the low-cycle fatigue strength of rough samples revealed to be lower than that of the smooth ones and vice a versa in the high-cycle region. This could be explained by the fact that, in the low cycle region, the cracks in the rough samples nucleated from deep surface defects while, in the smooth specimens, they nucleated from shallow defects (or as fish eyes) which prolonged their initiation stage. Almost all cracks in the high cycle region initiated as fish-eyes but the extent of nitrided layers in the rough specimens was slightly higher than that in the smooth specimens. Therefore, the fish-eye centers were shifted further to the interior of the rough specimens which increased their fatigue life.

Effects of planting distance and depth on PTO load spectrum of a small riding-type transplanter

The aim of this study was to analyze the effects of the planting distance and depth on the power take-off (PTO) load spectrum of a small riding-type transplanter for the optimal design of the transplanter. To measure load data during actual planting operation, a load measurement system was developed using a torque sensor, a data acquisition system, and an inverter. Field experiments were conducted at four planting distances (26 cm, 35 cm, 43 cm, and 80 cm) and three planting depths (85 mm, 105 mm, and 136 mm) in a field with similar soil conditions. The measured load data were inverted into a load spectrum using rain-flow counting and Smith-Watson-Topper (SWT) methods. The safety factor of a transplanter according to the planting conditions was analyzed using the converted load spectrum and commercial software. The load spectrum for all planting conditions showed torque ratios similar within a high cycle region of 108 to 109. The torque ratio increased when the planting depth increased and planting distance decreased in the low cycle region under less than 108 cycles. The safety factors of the PTO driving gear and the driven gear increased as the planting distance increased at all planting depths. When the planting depth decreased at the same planting distance, the safety factor of the PTO gears increased. The results of this study might provide useful information for a transplanter PTO design considering the working load according to the various planting conditions. Keywords: transplanter, planting distance, planting depth, power take-off, load spectrum, safety factor DOI: 10.25165/j.ijabe.20201302.4187 Citation: Kim W-S, Kim Y-S, Kim T-J, Nam K-C, Kim T-B, Han T-H, et al. Effects of planting distance and depth on PTO load spectrum of a small riding-type transplanter. Int J Agric & Biol Eng, 2020; 13(2): 57–63.

The effect of iron content on fatigue lifetime of AlZn10Si8Mg cast alloy

The problem with utilization of the Al-scrap as a material for casting the Al-Si alloys lies in the fact that the scrap, unfortunately as a rule, is contaminated with iron. The current study presents an investigation of the effect of different iron contents (0.150 and 0.559 wt%) on microstructure, porosity and bending fatigue properties in the secondary (recycled) self-hardening AlZn10Si8Mg cast alloy. Rotating bending fatigue tests were realized for a defined number of cycles 3 × 106 with a stress asymmetry ratio R = −1 at room temperature. Observation by the optical and SEM microscopy using deep etching and image analysis highlight the role of the plate/needle-like Fe-rich intermetallic (Al5FeSi phase), formed during the solidification process. The quantitative metallography and CT scan was used to quantify the amount of pores.The results show that Al5FeSi phases play an important role in the low cycle region. The higher amounts of needle/plate like Fe-rich particles (Al5FeSi) with increased porosity degraded fatigue lifetime in the short and medium life-time regime (<106 cycles) and there was no effect or slight increases the fatigue lifetime for long life-time regime (≫106 cycles). In the high cycle’s region are the pores more detrimental than Fe-rich phases to the fatigue strength. Fracture surface of the fatigue specimens were analysed by SEM to characterize the micromechanism and the initiation fracture local.

Fatigue characteristics of welded high strength steel in the low cycle region of loading

Automotive industry is the one of the most rapidly developing sector of engineering. Using of new, progressive materials can make significant benefits because of growing durability and reducing weight of structural parts, which can lead to the materials and fuel savings. The authors of this paper discuss fatigue characteristics on arc metal welding process of high strength steels STRENX 700MC obtained in low cycle region (N approximate to 1.10(3) divided byN= 1.10(7) cycles) at low-frequency loading (frequency approximate to 35 Hz, T = 20 +/5 degrees C,R= -1). Authors compares results of their own experimental works and subsequently discus these result and their possible effect on the fatigue lifetime of these steels.

A Whole-Range S–N Curve for Fatigue Assessment of Steel Orthotropic Bridge Decks

The fatigue assessment of orthotropic bridge decks under routine traffic loading is a significant task to ensure the serviceability and safety of steel bridges. The sequential law computes fatigue damages using whole-range [Formula: see text]–[Formula: see text] curves and sequential stress histories and has been proven to provide more realistic results than Miner’s rule under variable amplitude loading. In this paper, a whole-range [Formula: see text]–[Formula: see text] curve covering the very low-cycle region, the low-cycle region, the finite life region, the high-cycle region, and the very high-cycle region is proposed for the sequential law to evaluate the fatigue performance of steel orthotropic bridge decks. The mathematical model of the whole-range [Formula: see text]–[Formula: see text] curve is first deduced based on the partially known [Formula: see text]–[Formula: see text] curve recommended in steel bridge design codes. The properties of the whole-range [Formula: see text]–[Formula: see text] curve are then explained from the geometrical point of view in the double logarithm coordinates system. Finally, rib-to-deck joints in steel orthotropic bridge decks are used as a case study. Fatigue test data are used to validate the proposed model. The whole-range [Formula: see text]–[Formula: see text] curve, with a 97.5% survival limit, is established for fatigue assessment of rib-to-deck joints in real bridges. The results show that the proposed whole-range [Formula: see text]–[Formula: see text] curve allows a good fit of experimental data and excellent agreement with code [Formula: see text]–[Formula: see text] curves in the finite life region and provides an effective extrapolation from the finite life region to the whole range of cycle numbers.

Mixed-mode fatigue crack growth and life prediction of an automotive adhesive bonding system

Mixed-mode fatigue crack growth behavior of an automotive adhesive bonding system (AA5754O-A951-BM4601) has been investigated using a compound compact mixed-mode specimen. The test was performed under load control with 0.1 R ratio and 3 Hz frequency. A long-distance moving microscope was employed to record the real-time length of the fatigue crack in the adhesive layer during testing. The strain energy release rate components of the crack were analyzed by finite element method. The pure-mode fatigue crack growth test results show that a given value of GI results in a fatigue crack growth rate over an order of magnitude higher than for an equal value of GII. The mixed-mode tests results indicate that under a given loading angle, the fatigue crack growth behavior is also influenced by the test load due to the changing shear mode ratio when the crack grows. The fatigue crack growth data were then processed by a generalized Paris relation formula and employed in the direct fatigue life prediction of single lap shear joints with the same bonding system. The life prediction shows good results in the low-cycle region but slightly conservative results in the high-cycle region when compared to coupon fatigue tests.

Low-Cycle Fatigue Behavior of Al1070 Severely Deformed by Equal Channel Angular Pressing Process

In this paper, the low-cycle fatigue behavior of commercially pure aluminum severely deformed through equal channel angular pressing was studied by the use of data gathered from rotating-bending tests. After designing and manufacturing a suitable die, four passes of severe plastic deformation through strain path B c were successfully performed on aluminum samples. The annealed and processed samples were then subjected to simple tensile test, Vickers hardness test and rotating-bending fatigue test. The results showed a significant increase in the hardness and yield strength of processed samples but also a significant decrease in their ductility. A simple mathematical analysis was used to calculate the plastic strain applied in the fatigue test, and then the strain–life curves were plotted for the low-cycle region. The plotted strain–life curves showed that, as compared with annealing, the equal channel angular pressing process greatly reduces the transition fatigue life (N t) of commercially pure aluminum. Examination of Coffin–Manson curves obtained for samples subjected to annealing and severe plastic deformation revealed that equal channel angular pressing has an undesirable effect on the low-cycle fatigue of commercially pure aluminum and decreases the fatigue life in this region.

Notch fatigue behavior of Ti-6Al-4V alloy in transition region between low and high cycle fatigue

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.

Comparability of structured and flat reference specimens made of thin sheet metal

Abstract The literature review reveals that the honeycomb-structured thin sheet metals are not adequately investigated with regard to their fatigue strength. A question that remains almost completely ignored in the process is the direct comparability of structured thin sheet metals with flat reference specimens. A thin sheet is not a classic specimen to determine the fatigue strength because of the known problem of the fracture mechanics. Structured thin sheet metals of deep-drawing steel DC04 with a thickness of 0.5 mm were examined. Flat specimens were used as reference material. The frequency analysis was used for comparison. Fundamental differences in the mechanical behavior between flat and structured sheets under cyclic load were observed. Whereas an extremely flat S-N curve in the low-cycle region with a high slope coefficient was observed for the smooth thin sheets, the structured specimens show a curve typical for notched specimens. Moreover, the smooth sheets have a specific cyclic hardening and/or softening behavior. The state of plane stress of a fine sheet in contrast to a multi-axial one for the structured sheet complicates the direct comparison. For this reason, such a comparison with respect to their fatigue strength in the Wohler diagram should only be considered with caution. This contribution is the second of a series of articles on this subject.

G0301305 高強度鋼の極低速き裂進展下におけるODA形成に及ぼす応力比の影響

It's well known High Strength Steel shows internal origin type fatigue failure called Fish eye failure in low stress and high cycle region. In this failure, ODA(Optically Dark Area) is formed and this ODA occupies the great portion of fatigue life of Fish eye failure. Although the explication of the mechanism of ODA formation is needed for the explication of the Fish eye failure mechanism, the explication is not yet accomplished. It's reported that internal fatigue crack in high strength steel is propagating extremely slowly by recent investigations. However, it is not clear the relationship between the extremely slow fatigue crack growth behavior and the mechanism of ODA formation, and whether it is a peculiar phenomenon of high strength steel. In study, fatigue test was done in vacuum environment. As a result, fractography suggest that more obvious ODA is formed by smaller stress ratio when internal crack is extremely slowly propagating.

Mechanical behaviour of cp-magnesium with duplex hydroxyapatite and PEO coatings.

Hydroxyapatite-magnesia coatings were formed on cp-magnesium by plasma electrolytic oxidation (PEO) followed by cathodic electrodeposition (CED). The static tensile and cyclic fatigue performance of the coated samples were investigated. The cracking behaviour of the coatings during the tensile tests was studied by fracture analysis. The effects of the surface treatment on the fatigue performance of the magnesium substrate were addressed. Tensile strength of cp-Mg was not significantly affected, whereas the fatigue performance was improved by the PEO+CED coatings in the low-cycle region, possibly due to compressive residual stress induced to the metal substrate by the surface treatment. However, reduced fatigue strength was observed in the high-cycle region, which might be attributed to the defects at the coating/substrate interface produced during the surface modification. The in vitro corrosion reduced the fatigue strength in both the low- and high-cycle regions. Finally, the applicability of surface engineered magnesium for biomedical applications was demonstrated from the mechanical standpoint.

Cyclic deformation and fatigue of extruded Mg–Gd–Y magnesium alloy

Cyclic deformation and fatigue of extruded rare-earth Mg–8.0Gd–3.0Y–0.5%Zr (GW83) magnesium (Mg) alloy were experimentally investigated by carrying out fully reversed strain-controlled tension–compression experiments along the extrusion direction with the strain amplitudes varying from 0.275% to 5.0%. Monotonic tension and compression stress–strain curves display a smooth transition from elastic to elastic–plastic deformation and exhibit a fairly yielding symmetry. Different from conventional Mg alloys, the material shows near-symmetric stress–strain hysteresis loops and marginal cyclic hardening with almost zero mean stress in the fully reversed strain-controlled experiments conducted. With increasing number of loading cycles, a transition of stress–strain response from concave-down shape to sigmoidal shape occurs in both tension and compression reversals when the strain amplitudes are larger than 2.0%. The strain-life fatigue curve displays a similar feature to that of conventional Mg alloys: A detectable transition from low-cycle region to high-cycle region occurs at a kink point in the vicinity of a strain amplitude of 0.75%. The cyclic deformation and fatigue properties of GW83 Mg alloy and the associated cyclic deformation mechanism are discussed and compared with those of a typical conventional Mg alloy.

Low-Cycle to Ultrahigh-Cycle Fatigue Lifetime Measurement of Single-Crystal-Silicon Specimens Using a Microresonator Test Device

The authors used a ramping-amplitude fatigue-test method to perform low-cycle fatigue tests in micrometer-sized single-crystal-silicon specimens using a resonant-type fatigue-test device. Very short delayed fractures from 4 ms to 29 s were observed by controlling the amplitude ramping rates with two self-oscillation electric circuits and different parameters. These lifetimes were converted to corresponding constant-amplitude lifetimes from 101 to 105 cycles using the relationship derived from a crack-growth analysis. S-N plots of measured lifetimes exhibited the transition of fatigue lives at the high-cycle region with a crack-growth exponent of 18.0, to the static fracture strength of 6.50 GPa at the low-cycle region corresponding to the original crack length of 7.9 nm. The existence of a very rapid fatigue fracture within 1 s was confirmed. From the obtained crack-growth parameters, the evolution of crack length and the effects of humidity were discussed.

Low Cycle Tension-Tension Fatigue Properties of 316L Stainless Steel Thin Sheets

In this paper, tensile fatigue properties of 316L stainless steel thin sheets with a thickness of 0.1 mm are studied. The tests are implemented by using micro mechanical fatigue testing sysytem (MMT-250N) at room temperature under tension-tension cyclic loading. The S-N curve of the thin sheets descends continuously at low cycle region. Cyclic σ-N curve and ε-N curve are obtained according to the classical macroscopical fatigue theory. The results agree well with the experimental fatigue data, showing that the traditional fatigue research methods are also suitable for description of MEMS fatigue in a certain extent. The effect factor of frequency was considered in this study and the results show that the fatiuge life and the fatigue strength are increased as loading frequency increasing.

Fretting Fatigue Life Estimations Based on the Critical Distance Stress Theory

Generally fretting fatigue S-N curve have two stages, one is high cycle (low stress) region and second is low cycle (high stress) region. In previous paper we introduced the fretting fatigue life estimation methods in high cycle region by considering the wear process. And in this estimation method the fretting fatigue limit can be estimated as the crack initiation limit at contact edge. In this paper we estimated the low cycle fretting fatigue life based on new critical distance theory, which is modified for high stress region using ultimate tensile strength σB, and fracture toughness KIC. Firstly the critical distance for estimating low cycle fatigue strength was calculated by interpolation of critical distance on fatigue limit (estimated from σw0 and ΔKth) with critical distance on static strength (estimated from σB and KIC). The validity of this method is confirmed by the V notch specimens. And then we applied this method on estimation of low cycle fretting fatigue strength and life. By unifying these low cycle fretting fatigue life estimation method with high cycle fretting fatigue life estimation method which was presented previous paper we can estimate the total fretting life easily. And to confirm the availability of this estimation method we perform the fretting fatigue test using Ni-Mo-V steel.

OS14-3-3 Fretting Fatigue Life Estimations Based on Critical Distance Theory

Generally fretting fatigue S-N curve have two regions, one is high cycle (low stress) region and second is low cycle (high stress) region. In previous paper we introduced the fretting fatigue life estimation methods in high cycle region by considering the wear process. And in this estimation method the fretting fatigue limit can be estimated as the crack initiation limit at contact edge. In this paper we introduce the low cycle fretting fatigue life estimation method using the critical distance theory. Generally this critical distance theory was applied for the fatigue limit estimation using fatigue limit of smooth specimen σw0, and threshold stress intensity factor range ΔKth. In this paper we estimated the low cycle fretting fatigue life based on new critical distance theory, which is modified for high stress region using ultimate tensile strength σB, and fracture toughness KIC. The critical distance for estimating low cycle fretting fatigue strength was calculated by interpolation of critical distance on fretting fatigue limit (estimated from σw0 and ΔKth ) with critical distance on static strength (estimated from σB and KIC ). By unifying these low cycle fretting fatigue life estimation method with high cycle fretting fatigue life estimation method which was presented previous paper we can estimate the total fretting life easily. And to confirm the availability of this estimation method we perform the fretting fatigue test using Ni-Mo-V steel.

Fretting fatigue life estimations based on fretting mechanisms

Generally the fretting fatigue S– N curve has two regions: one is the high cycle (low stress) region and the second is the low cycle (high stress) region. In a previous paper we introduced the fretting fatigue life estimation methods in high cycle region by considering the wear process; with this estimation method the fretting fatigue limit can be estimated to be the crack initiation limit at the contact edge. In this paper we estimate the low cycle fretting fatigue life based on a new critical distance theory, modified for a high stress region using ultimate tensile strength σ B and fracture toughness K IC. The critical distance for estimating low cycle fretting fatigue strength was calculated by interpolation of the critical distance on the fretting fatigue limit (estimated from σ w0 and Δ K th) with critical distance on static strength (estimated from σ B and K IC). By unifying this low cycle fretting fatigue life estimation method with the high cycle fretting fatigue life estimation method, which was presented in the previous paper, we can estimate the total fretting life easily. And to confirm the availability of this estimation method we perform the fretting fatigue test using Ni–Mo–V steel.

Bending Fatigue Strength of Austenitic Stainless Steel SUS316 in Mercury

Liquid mercury target system for spallation neutron source is installed at Materials and Life Science Experimental Facility in Japan Proton Accelerator Research Complex (J-PARC), which will promote innovative science. Austenitic stainless steel SUS316 for a structural material of the target vessel is contact with mercury, and imposed by cyclic pressure that is induced by pulsed proton beam injection at 25Hz. Therefore, it is important from the viewpoint of the structural integrity to investigate the effect of mercury on fatigue behavior of the structural material. Bending fatigue tests in mercury and air were performed to evaluate the effect of mercury on fatigue behavior. FRActure Surface Topography Analyses (FRASTA) were carried out to evaluate the change in fracture morphology with mercury. It was confirmed that the fatigue strength was decreased by mercury immersion in low cycle region less than 105 cycles and intergranular fracture surface was observed, while in high cycle region the mercury immersion effect was hardly recognized.

Effect of fabrication on high cycle fatigue properties of copper thin films

The influence of fabrication on the tensile and fatigue behavior of copper films manufactured by 3 kinds of fabrication methods was investigated. The tensile and high cycle fatigue tests were performed using the test machine developed by authors. Young's moduli (72, 71 and 69 GPa, respectively) are lower than the literature values (108–145 GPa), while the yield strengths were as high as 358, 350 and 346 MPa, respectively and the ultimate strengths as 462, 456 and 446 MPa, respectively. There is not much difference in the tensile properties of the 3 kinds of films. There is little difference in the fatigue properties of the 3 kinds of films but one of them has shorter fatigue life than others in high cycle region and longer fatigue life than others in low cycle region.