High Fatigue Limit Research Articles

High-precision control of microstructure and mechanical properties of Ti–6Al–4V thin-walled titanium alloy components by laser peening without coating

In this paper, the stress distribution and evolution of LPwC and LSP in thin-walled model are compared by simulation. The mechanical properties and microstructure changes of LPwCed TC4 titanium alloy thin-walled components were further analyzed by experiments, and the mechanism of LPwC induced grain refinement was analyzed in detail. The results show that compared with LSP, the stress field introduced by LPwC is more uniform, the depth of the influence layer is shallower, and the shock wave energy decays faster. At the same time, LPwC can control the deformation of the specimen more accurately. At 30 mJ energy, the high cycle fatigue limit of the LPwCed TC4 titanium alloy thin-walled sample is 467.1 MPa, which is 14.3 % higher than that of the untreated sample. The maximum hardness can reach 367.2 HV0.1, which is 12.0 % higher than that of the untreated sample, and the depth of the influence layer is 0.3 mm. The surface residual stress is −61.43 MPa, and the depth of the influence layer can reach 250 μm. At the same time, the formation of dynamic recrystallized grains under the action of LPwC promotes the texture orientation of the sample to change from [ 10−10 ] to [-12-10 ].

Estimating the fatigue limits for quenched and tempered steel rods treated with multifunction cavitation considering residual stress, hardness, and surface pits

AbstractIn this study, multifunction cavitation (MFC) was performed on low‐alloy steel (AISI 4140 steel) rods with different hardnesses to increase their fatigue limit. It was found that a high compressive residual stress was generated on the surface of steel rods by MFC and that the magnitude of the compressive residual stress tended to increase with increasing specimen hardness, which resulted in a higher fatigue limit. However, fatigue cracks are known to be initiated from the pits and red rust that form on the surface during MFC treatment in water. Furthermore, relaxation of the compressive residual stress was also investigated during the fatigue test to elucidate the mechanism for improving the fatigue properties. The results showed that the fatigue limit for MFC‐treated steel rods was accurately estimated by considering residual stress relaxation, hardness, and pit formation. Validation of the fatigue limit estimation was also conducted through comparison with Murakami's equation.

Effect of atmospheric-pressure nitrogen plasma treatment at low temperature on fatigue properties of low-alloy steels

A device for parallel-plate-type atmospheric-pressure nitrogen plasma (APNP) treatment, which can generate plasma in a sealed environment with high-purity nitrogen gas, was developed. The objective of the present study was to use microstructural analyses to investigate the effect of APNP treatment at low temperatures on the fatigue properties of low-alloy steels. The APNP treatment was conducted at 473 K, which is lower than the common gas nitriding temperature. X-ray analyses revealed that a nitrogen–oxygen diffusion layer with high fatigue limit was formed on the steel by the APNP treatment at 473 K. Thus, the APNP treatment is an effective approach for increasing the fatigue limit of steels by increasing their surface hardness.

Improving tension fatigue performance of gray cast iron by LSPwC-induced gradient structure and carbon diffusion

HT250 Gray cast iron (GCI) commonly utilized in diesel engine cylinders, is susceptible to fatigue failure under alternating stress conditions. To address this issue, the investigation involved the application of laser shock peening without coating (LSPwC) on HT250 GCI to assess its impact on the high cycle tension fatigue properties of the material. Both experimental and simulation methodologies were employed to analyze the effects of LSPwC on residual stress, microhardness, and microstructure in HT250 GCI. The LSPwC resulted in a substantial 29% enhancement in the high cycle tension fatigue limit of the HT250 GCI, which is attributed to a synergistic combination of factors induced by LSPwC, including high-amplitude compressive residual stresses, elevated microhardness, grain refinement, and carbon diffusion. This study contributes valuable insights into the reinforcement of complex cast components.

Characterization and Fabrication of Ankle Foot Orthoses using Composite with Titanium Nanoparticles

Orthoses and prostheses were Chosen and laminated based on their high Yield, ultimate stresses, bending stresses, and fatigue limit. Response Surface Methodology (RSM) was utilized to find the best values for two parameters reinforcement perlon fiber and percent of Titanium Nanoparticle coupled with the matrix resin during optimization. The response surface methodology combined the expertise of mathematicians and statisticians to construct and analyze experimental models. Using this method, we identified 13 different lamination samples comprising a wide range of perlon number and Ti nano Wt% in their Perlon layer composition. All lamination materials defined by RSM methods and produced by a vacuum system were subjected to a battery of tests, with fatigue tests performed on the ideal laminating material in contrast to laminations created in the first study (Tensile test, Bending test, and Fatigue tests according to the ASTM D638 and D790 respectively). In comparison to the other 12 laminations tested using Design Expert version 10.0.2, the lamination with ten perlon layers and 0.75 percent Ti nano proved to be the strongest overall in terms of Yield, ultimate, and bending loads. This study used composite materials and titanium nanoparticles to characterize and fabricate ankle foot orthoses. Strength in bending should amount to about 70 MPa, around 85 MPa in tensile tension. Two empirical quadratic equations for the models of peak bending strength and maximum tensile stress with 95% confidence were created using the response surface approach and analysis of variance within the design of experiments software.

High fatigue resistance in a titanium alloy via near-void-free 3D printing.

The advantage of 3D printing-that is, additive manufacturing (AM) of structural materials-has been severely compromised by their disappointing fatigue properties1,2. Commonly, poor fatigue properties appear to result from the presence of microvoids induced by current printing process procedures3,4. Accordingly, the question that we pose is whether the elimination of such microvoids can provide a feasible solution for marked enhancement of the fatigue resistance of void-free AM (Net-AM) alloys. Here we successfully rebuild an approximate void-free AM microstructure in Ti-6Al-4V titanium alloy by development of a Net-AM processing technique through an understanding of the asynchronism of phase transformation and grain growth. We identify the fatigue resistance of such AM microstructures and show that they lead to a high fatigue limit of around 1 GPa, exceeding the fatigue resistance of all AM and forged titanium alloys as well as that of other metallic materials. We confirm the high fatigue resistance of Net-AM microstructures and the potential advantages of AM processing in the production of structural components with maximum fatigue strength, which is beneficial for further application of AM technologies in engineering fields.

Test Data Evaluation of Very High Cycle Fatigue Based on Maximum Likelihood Method

The very high cycle fatigue tests of TC4 alloy were accomplished through ultrasonic fatigue experiment which were conducted on the ultrasonic fatigue testing system at frequency range of 20000 ±1000 Hz. In contrast to the commonly used Basquin model, a Maximum Likelihood Method to fit the three-parameter nonlinear model was used to verify the adaptability in very high cycle fatigue regime. These two methods were used to estimate S-N curves of three types of materials which were TC4 alloy, GH4169 alloy and TC17 alloy in the very high cycle fatigue regime and the results were compared with test data. The evaluation result of the MLM model based on the three-parameter nonlinear model shows a good agreement with test data. The mean and variance of relative error of the MLM model are less than those of the Basquin model, providing a suitable evaluation method for predicting very high cycle fatigue limit which often has higher scatter.

High cycle fatigue properties of high-nitrogen steel hot-rolled with the yield strength level of 1000 MPa

The fatigue properties of an Fe-19Cr-20Mn-0.6N high-nitrogen steel (HNS), which was hot-rolled with the yield strength level of 1000 MPa, were investigated by means of tension–tension fatigue tests. The results showed that the fatigue life increased in a power law manner with the decrease of the maximum stress from 1040 MPa to 880 MPa. The fatigue limit at the 107 cycles was about 840 MPa, with the ratios of the fatigue limit to yield strength and tensile strength being 0.79 and 0.69, respectively. The high fatigue limit could be attributed to its high yield strength level, which was resulted from the mixed microstructure consisting of ultrafine grains and elongated grains with some slip bands.

Effect of Pore Defects on Very High Cycle Fatigue Behavior of TC21 Titanium Alloy Additively Manufactured by Electron Beam Melting

Titanium alloys additively manufactured by electron beam melting (EBM) inevitably obtained some pore defects, which significantly reduced the very high cycle fatigue performance. An ultrasonic fatigue test was carried out on an EBM TC21 titanium alloy with hot isostatic pressing (HIP) and non-HIP treatment, and the effect of pore defects on the very high cycle fatigue (VHCF) behavior were investigated for the EBM TC21 titanium alloy. The results showed that the S-N curve of non-HIP specimens clearly had a tendency to decrease in very high cycle regimes, and HIP treatment significantly improved fatigue properties. Fatigue limits increased from 250 MPa for non-HIP specimens to 430 MPa for HIP ones. Very high cycle fatigue crack mainly initiated from the internal pore for EBM specimens, and a fine granular area (FGA) was observed at the crack initiation site in a very high cycle regime for both non-HIP and HIP specimens. ΔKFGA had a constant trend in the range from 2.7 MPam to 3.5 MPam, corresponding to the threshold stress intensity factor range for stable crack propagation. The effect of pore defects on the very high cycle fatigue limit was investigated based on the Murakami model. Furthermore, a fatigue indicator parameter (FIP) model based on pore defects was established to predict fatigue life for non-HIP and HIP specimens, which agreed with the experimental data.

Study of the Effect of L-PBF Technique Temporal Evolution on Microstructure, Surface Texture, and Fatigue Performance of Ti gr. 23 Alloy

Titanium alloys are widely used in various technological fields due to their excellent performance. Since the early stages of the 3D printing concept, these alloys have been intensively used as materials for these processes. In this work, the evolution of the performance of the 3D printing process has been studied by analysing the microstructure and the mechanical properties, fatigue and tensile, of the Ti gr. 23 alloy produced by two different models of Concept Laser M2 Cusing machines (an old model and a more recent one). The process parameters recommended by the manufacturer were adopted for each machine. Both microstructural and surface texture characterisations were carried out to better correlate the differences with the production process technique. For the same purpose, tensile tests and microhardness profiles were obtained, while the dynamic mechanical properties were evaluated by means of fatigue tests aimed at determining the fatigue limit of the material using a staircase approach. The mechanical tests were carried out on specimens with three different orientations with respect to the building platform, using two different SLM techniques. The fatigue behaviour was then analysed by evaluating the fracture surfaces and, in particular, the crack nucleation sites. By comparing the calculated fatigue values with the results of local fatigue calculations, an estimate of the residual stresses near the crack nucleation site was obtained. The results showed that the specimens produced on a newer machine had lower roughness (about 10%), slightly higher ductility, and a higher fatigue limit (10–20 MPa) compared to the specimens produced with the same material but on older equipment.

Effects of Heat Treatment and Diamond Burnishing on Fatigue Behaviour and Corrosion Resistance of AISI 304 Austenitic Stainless Steel

The surface cold working (SCW) of austenitic stainless steel (SS) causes martensitic transformation in the surface layers, and the percentage fraction of the strain-induced martensite depends on the degree of SCW. Higher content of α′−martensite increases the surface micro-hardness and fatigue strength, but deterioration of the corrosion resistance is possible. Therefore, the desired operational behaviour of austenitic SS can be ensured by the corresponding degree of SCW and heat treatment. This article evaluates the effects of SCW performed by diamond burnishing (DB) and heat treatment on the surface integrity (SI), rotating fatigue strength, and corrosion resistance of AISI 304 austenitic SS for two initial states: as-received hot-rolled bar and initially heat-treated at 1100 °C for one hour followed by quenching in water. Then, DB was implemented as a smoothing and hardening process, both alone and in combination with heat treatment at 350 °C for three hours after DB. The electrochemical performance was examined by open circuit potential measurements, followed by potentiodynamic tests. For both initial states, smoothing DB provided the lowest roughness, whereas an improvement in the maximum surface micro-hardness was obtained after hardening DB and subsequent heat treatment. The maximum fatigue strength was obtained by hardening multi-pass DB without subsequent heat treatment for the as-received initial state. Smoothing DB and subsequent heat treatment maximised the surface corrosion resistance for the two initial states, whereas a minimum corrosion rate was obtained for the initially heat-treated state. For the as-received state, smoothing DB and subsequent heat treatment simultaneously lead to a high fatigue limit (equal to that obtained by hardening single-pass DB) and a low corrosion rate.

Influence of Pre-Milling of Cr3C2-25 NiCr Spray Powder on the Fatigue Life of HVOF-Sprayed Coating on ASTM A516 Steel Substrate

The aim of the present investigation is to evaluate the influence of the powder size of Cr3C2-25NiCr spraying powder on the fatigue behavior of HVOF-sprayed coating on the ASTM A516 steel substrate. Conventional commercial Cr3C2-25NiCr spraying powder was previously treated through high-energy milling. The crystallite sizes of milled powders were measured by X-ray diffraction and transmission electronic microscopy. Three different powder formats of the same Cr3C2-25NiCr composite were subjected to HVOF spraying to produce (i) a Milled-Coating (from high-energy milled spray powder), (ii) an Original-Coating (from conventional commercial spray powder), and (iii) a 50%-50% mixture of both (Milled + Original-Coating). The same spraying conditions were adopted for all the assessed cases. The sprayed coatings were investigated through the Knoop hardness test and SEM-EDS analysis. In addition, 3-point bending fatigue tests were conducted at different stress levels up to 107 cycles. The coating morphology and roughness effects on fatigue behavior were analyzed. The Cr3C2-25NiCr milled coating presented a lower fatigue life above the fatigue limit and a higher fatigue limit than other coatings; this outcome could be attributed to its lower surface roughness and finer grain size microstructure.

Fatigue Behaviour of Concrete Using Siderurgical Aggregates

The use of concrete with aggregates with reduced environmental impact, as is the case of concrete with siderurgical aggregates (recovered slags), will inevitably increase in the future, as a result of policies promoting development of more sustainable construction materials. These concretes offer an excellent response to static loads, but their behaviour under dynamic loads has not yet been studied. The aim of this study is to characterize the fatigue behaviour, in terms of fatigue limit, of a concrete with siderurgical aggregates by comparing it with an analogous conventional limestone concrete. This characterization was carried out using the Locati method, which stands out for its convenience, speed and low cost, with the feature of being carried out at a high frequency corresponding to the resonance frequency. Performing high-frequency tests has drastically reduced test times and thus costs. Likewise, the results obtained show that, using various criteria found in the literature, concrete with siderurgical aggregates has a higher fatigue limit in absolute terms (MPa), but a lower one in relative terms (% fc).

High cycle fatigue behaviors and deformation mechanisms in Ti47Al2Cr2Nb alloy at room temperature and 700 °C

This study systematically investigated the high cycle fatigue behaviors and deformation mechanisms in Ti47Al2Cr2Nb alloy at room temperature and 700 °C through scanning electron microscope and transmission electron microscope. The results showed that high temperature deteriorated the fatigue performances, especially under the higher stress levels. Large scatter in fatigue lifetimes under the lower stress levels was observed at high temperature. After 107 cycles, the high cycle fatigue limit at 700 °C was about 20 MPa lower than that at room temperature. Fracture morphologies showed that brittle fracture presented at both temperatures and fatigue cracks initiated from the surfaces. Fracture modes at room temperature included trans-lamellar and trans-γ grain fractures, while those at 700 °C included trans-lamellar, interlamellar and inter-γ gain fractures. Fatigue deformation at both temperatures mainly occurred in the γ phase, dislocation multiplication and slip bands were found in the deformation microstructures. Dislocation slip was the main deformation mechanism at both temperatures. A few mechanical twins were observed in the deformation microstructures of room temperature. Slip bands and mechanical twins transferred through γ/γ true-twin interfaces with a deflection while they transferred through γ/γ rotational boundaries straightly. Mechanical twins had a blocking effect on slip bands, resulting in the dislocation arrays in slip bands piling up at the intersections.

Fatigue behavior and damage analysis of PIP C/SiC composite

In this work, we study the fatigue behavior of a C/SiC composite produced by several cycles of polymer infiltration and pyrolysis (PIP). Fatigue tests were performed with maximum stresses corresponding to 60–90% of the tensile strength of the composite. During the fatigue tests, acoustic emission (AE) monitoring was performed and the measured AE energy was utilized to quantify the damage and distinguish possible damage mechanisms. Most of the fatigue damage in the form of matrix cracking, interface damage and fiber breakage occurs in the first cycle. As loading cycles proceeded, damage in form of matrix crack re-opening and interfacial friction constantly accumulates. Nevertheless, all samples survived the run-out of 1,000,000 cycles. After the fatigue tests, an increase of the tensile strength is observed. This phenomenon is associated with the relief of process-induced internal thermal stresses and the weakening of the fiber-matrix interface. In general, the studied material shows very high relative fatigue limit of 90% of its tensile strength.

High cycle fatigue limit prediction of foreign object damaged aerofoil samples by the theory of critical distance

The fatigue limit at 3 × 107 cycles predicted by the theory of critical distance (TCD) on Ti–6Al–4V aerofoil samples subjected to foreign object damage (FOD) was studied. First-order bending vibration fatigue experiments were carried out with 18 FOD samples after FOD tests. First-order bending vibration mode analysis of each notched sample with various semi-elliptical notch dimensions were carried out by finite element method and the critical distance is deduced by test results and numerical simulation. FOD and HCF tests were carried out on another 9 aerofoil samples, and fatigue limit predictions were carried out using the Peterson formula and the TCD model. The results showed that the TCD model has higher prediction accuracy.

Comparison of the fatigue behavior of wrought and additively manufactured AISI 316L

Additive manufacturing (AM) is becoming increasingly important in engineering applications due to the possibility of producing components with a high geometrical complexity allowing for optimized forms with respect to the in-service functionality. Despite the promising potential, AM components are still far from being used in safety-relevant applications, mainly due to a lack of understanding of the feedstock-process-properties-performance relationship. This work aims at providing a full characterization of the fatigue behavior of the additively manufactured AISI 316L austenitic stainless steel and a direct comparison with the fatigue performance of the wrought steel. To this purpose, a set of specimens has been produced by laser powder bed fusion (L-PBF) and subsequently heat treated at 900 °C for 1 hour for complete stress relief, whereas a second set of specimens has been machined out of hot-rolled plates. Low cycle fatigue (LCF) and high cycle fatigue (HCF) tests have been conducted for characterizing the fatigue behavior. The L-PBF material had a higher fatigue limit and better finite life performance compared to wrought material. Both, LCF and HCF-testing revealed an extensive cyclic softening.

The effect of epoxy coating on the fatigue strength of grade-A mild steel

In this study, tension fatigue tests of grade-A marine mild steel with epoxy type of coating were carried out and the corresponding S–N curves with a survival probability of 97.5% are derived. Compared to the uncoated specimens studied previously, Epoxy coating has increased fatigue life of Mild steels by about 50% in the case of high cycle fatigue and fatigue limit by 6%. This improvement on fatigue strength is mainly due to crack-tip bridging phenomenon of coating which fills micro surface cracks and delayed surface crack propagation. The effect of surface finishing method on adhesion strength of Epoxy coating is investigated by pull-off tests. The DIC method is used to determine the in-plane strain distribution in the necking region of tensile test of uncoated specimens. The final image before fracture shows that the vertical and horizontal local strain in the necking position is 155 and 32%, respectively.

Mechanical performance of a hybrid zirconia developed through hydrothermal treatment and Room-Temperature Atomic Layer Deposition (RT-ALD)

ObjectiveA silica-based nanofilm has been successfully deposited via Room-Temperature Atomic Layer Deposition (RT-ALD) on the surface of a glass. The purpose of this study was to evaluate the mechanical performance of a hybrid interface created between yttria-stabilized zirconia (Y-PSZ) transformed layer and silica-based nanofilm via RT-ALD. Material and methodsFully-sintered Y-PSZ (14 × 4.0 × 1.5 mm) specimens in different translucencies (MO, MT, LT; IPS e.max Zircad, Ivoclar Vivadent) were distributed in 5 groups: control (C - no treatment); hydrothermal treatment (HT- 15h, 134°C, 2 bar); alumina blasting (B - 50 μm Al2O3); RT-ALD silica deposition (S); HT followed by silica deposition (HTS). RT-ALD cycles consisted of the sequential exposure of specimens to tetramethoxysilane orthosilicate (TMOS - 60s) and ammonium hydroxide (NH4OH - 10 min) vapors in 40 cycles. Mechanical performance was analyzed by flexural strength (FS) (n = 10) and fatigue failure load (staircase method; n = 20) tests. Surface hardness (H) and Young's modulus (YM) were analyzed by nanoindentation. For surface chemical and topographical characterization, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were performed. Data from surface H, YM, FS, and fatigue limit (FL) were analyzed by two-way analysis of variance (ANOVA). ResultsThe interaction between material and treatment had a significant effect on FS (p < 0.001). The FS values ranged from 436.23 MPa to 856.65 MPa. HT resulted in the highest FS (856.65 MPa) for LT and the lowest FS (436.23 MPa) for MO zirconia. For all materials, S and B treatments resulted in similar FS values (p > 0.410). S did not affect FL when compared to the C group (p > 0.277) for any material investigated. HTS resulted in higher FL than S for LT and MO materials (p < 0.001). Surface hardness and modulus were similar between control and S-treated specimens for all materials analyzed. XPS analysis showed homogeneous silica content after 20 and 40 RT-ALD cycles, and SEM did not show significant changes in surface morphology between C and S-treated specimens. ConclusionRT-ALD resulted in effective silica deposition without any deleterious effect on zirconia-based materials mechanical properties. Alumina blasting promoted higher alteration on surface topography. HT prior to S resulted in superior FL (for MO and MT) and flexural strength (MO) for some of the materials investigated.

High cycle fatigue behavior and microstructure of a high-speed rail material

We describe here the high cycle fatigue (HCF) behavior of a rail steel comprised of multiphase structure of bainite, martensite and film-like retained austenite, which was processed by the quenching and tempering (Q&T) heat treatment process. Conventional mechanical properties of experimental materials were determined, and the high cycle fatigue S–N curve of rail steel was obtained through ultrasonic fatigue test. The fatigue fracture details under cyclic stress were observed and analyzed in detail by scanning electron microscope (SEM). It was observed that the bainite/martensite (B/M) composite structure exhibited good performance, and its fatigue limit was as high as ~790 MPa, meanwhile the ratio of the fatigue limit to the tensile strength of rail steel was up to ~0.53. Finally, a comparison of the mechanical properties with other high-strength steels was made, which suggested that the rail steel with multiphase structure has both good strength and high fatigue limit. Thus, multiphase structure of steel has broad prospects in engineering applications.