Rotating Bending Fatigue Research Articles

Influence of specimen geometry and notch on fatigue lifetime and fracture behavior of aluminum-based nanocomposite under stress-controlled fully-reversed bending loads.

In the present article, the effect of the specimen geometry and the sample notch was studied on the high cycle fatigue lifetime and fracture behavior of the aluminum-based nanocomposite. For such an objective, rotary fully-reversed bending fatigue tests were performed on smooth and notched specimens, with the frequency of 100 Hz. Then, simulated results using the MSC Fatigue software were calculated and compared to the fatigue lifetime in the experiments for validation. Moreover, scanning electron microscopy was utilized to observe the fracture surface of failed samples after testing. Obtained results indicated that the fatigue lifetime increased by enhancing the sample diameter. However, the fatigue lifetime reduced when the stress concentration factor changed from 1.0 to 2.9. All samples with three geometries had a brittle fracture due to cleavage and quasi-cleavage marks on the fracture surface.

Effect of surface coating on fatigue life and fatigue crack growth behavior of AISI D2 tool steel

To study the effect of the specimen surface coating on the fatigue life and fatigue crack growth behavior, rotating bending fatigue tests were performed with a specimen coated with a TiCN thin film on AISI D2 tool steel (JIS SKD11) and a bare specimen without coating. Fatigue cracks developed inside the specimen because compressive residual stress was present on the surface of the coated and bare materials. The fatigue crack growth behavior of the internal cracks was investigated with the two-stage double-stress experimental method proposed by the authors. The fatigue life estimated from the fatigue crack growth (FCG) behavior of the internal cracks and the experimental results agreed. Furthermore, a method was proposed that can easily evaluate the effect of residual stress on fatigue life and FCG behavior. The evaluation and experimental results are in good agreement. In addition, the effects of atmospheric and vacuum conditions on FCG behavior are discussed.

Optimization of 3D printing parameters in polylactic acid bio-metamaterial under cyclic bending loading considering fracture features

3D printing has become a crucial additive manufacturing technique with the applications in various industries. Fused deposition modeling (FDM) is a common additive manufacturing process that offers considerable flexibility in the component fabrication through multiple parameters, which strongly influence the properties of the produced parts. This study focused on the impact of different printing parameters on the fatigue behavior of polylactic acid (PLA). The standard samples were 3D-printed with varying speed (5, 10, and 15 mm/s), print temperature (180, 210, and 240 °C), and nozzle diameter (0.2, 0.4, and 0.6 mm). The fatigue properties were evaluated through rotating bending fatigue tests, and a model was developed based on the results with a statistical analysis. The model accuracy was validated and the interactions between the parameters were analyzed. The optimization study found that a print speed of 5 mm/s, print temperature of 210 °C, and nozzle diameter of 0.2 mm were optimal. The fracture surfaces were also examined using a scanning electron microscopy, revealing the presence of crazing despite the brittle behavior of PLA.

Improved rotating bending fatigue performance of laser directed energy deposited Ti6Al4V alloys by laser shock peening

A major challenge for additive manufactured titanium blades is to improve an unfavorable fatigue life. In this work, the rotating bending fatigue test was carried out on the laser direct energy deposited (L-DED) titanium alloy to simulate the service condition of the rotating blade, and the laser shock peening (LSP) post-processing was adopted to enhance the fatigue performance. The results showed that LSP induced gradient layer and phase transformation in L-DED Ti6Al4V alloy, and increased the fatigue limit to 570 MPa. The compressive residual stress dominated the crack source transfer confirmed by the finite element method, and its retention capacity under fatigue cycles reduced the semi-elliptical crack growth rate. A fatigue limit prediction formula was established to quantify the contribution of microstructure, residual stress and roughness changes.

High-cycle rotating-bending fatigue performance of S690QL welded joints

In recent decades, high-strength steels have become increasingly popular in the construction industry. Materials like S690QL steel are mainly characterised by their enhanced mechanical properties, including high yield and tensile strength. As a result, this leads to improved performance, durability, and safety of steel components, making such materials commonly used in several offshore applications due to their exceptional strength and cost-efficiency. Within the offshore industry, the most critical connections are usually the welded joints, thus rising significant concerns regarding the characterisation of the material in the area close and affected by the welding process. Furthermore, this material is highly prone to the appearance of cold cracks. To address these issues, rotating-bending fatigue tests were successfully conducted on S690QL steel to evaluate and compare the fatigue life within different regions of the investigated welded joints, specifically the weld material, heat-affected zone and base material. Increasing thickness of the weld plates was found to have a negative impact on the fatigue resistance, which aligns with the lower static strength for the thicker case. Also, variations in fatigue strength across the thickness were observed. The heat-affected zone exhibited a heterogeneous microstructure, leading to increased fatigue variability during testing, but the fatigue resistance observed aligns with the findings in the literature for comparable steel grades. Detailed experimental results are presented, particularly regarding this heat-affected zone, where the majority of fatigue failures occur, which provide bases for the development of new normative material-scale SN curves.

Improving the fatigue resistance of plasma electrolytic oxidation coated titanium alloy by ultrasonic surface rolling pretreatment

Plasma electrolytic oxidation (PEO) damages fatigue strength of titanium alloy, ultrasonic surface rolling process (USRP) pretreatment is used to mitigate this adverse effect. The microstructure, stress distribution and fatigue performance of Ti6Al4V alloy with different treatment are tested by FESEM, TEM, X-ray stress tester and rotating-bending fatigue tests, and anti-fatigue mechanism of co-strengthened sample is discussed. USRP treatment refines surface grains and introduces a compressive stress field of above 560 μm, which helps to improve the compactness and reduce surface roughness of PEO coating, and significantly increase fatigue resistance of PEO coated samples. Under covering the coating of 20 μm, the fatigue life of co-strengthened sample is about 14 times higher than that of simple PEO sample at 600 MPa, and fatigue crack source also changes from multi-source to single-source and transfers to the subsurface. PEO consumes part of surface nanocrystalline layer and releases some compressive stress for ultrasonic-rolled sample, but the effective compressive stress field with a thickness of 180 μm is still present, and the grains at coating/substrate interface also remain at the nanoscale (∼81 nm), which are the key reasons for USRP to improve fatigue resistance of titanium alloy treated by PEO.

Effects of Loading Modes on Fatigue Limit Estimation in Terms of Rotating Bending Fatigue and Rate Process Theory

In this study, the influence of loading modes on the fatigue limit estimation of low-to-medium-carbon steels was modeled in terms of the rate process theory proposed by Guennec et al. The axial loading model established in terms of the rate process theory has been shown to be effective for axial loading fatigue, but its applicability to rotating bending fatigue is uncertain. Therefore, low- and medium-carbon steels were tested for rotating bending fatigue, and the fatigue limits obtained were compared with those estimated by the axial loading model established in terms of the rate process theory. However, since the model could not be applied, we propose a new model in which the material parameters of an estimation equation established in terms of the rate process theory are expressed based on Vickers hardness, which was introduced to improve the usability of the model. It was found that there was a discrepancy between the axial load fatigue limit and the rotating bending fatigue limit due to the effect of the loading mode. To solve this discrepancy, the stress index was introduced into the model. The proposed model provides a method for estimating the frequency-dependent fatigue limits for different loading modes.

Corrosion fatigue behavior and life prediction of railway axle EA4T alloy steel with artificial indentation

The combined effects of aggressive media and artificial surface indentation on the fatigue behaviours were investigated to evaluate the defect tolerance of high-speed hollow railway EA4T steel axles. Corrosive rotating-bending fatigue tests were performed on both smooth and notched specimens to assess their fatigue strengths and failure mechanisms. Based on the corrosion testing campaign, which mainly included examinations of the microstructure, residual stress, and fatigue crack resistance, material deformation underneath the bottom of indentations triggered corrosion fatigue cracks. The results also showed that the corrosive media was responsible for the decrease in fatigue strength, and notched specimens were more sensitive to 3.5 wt% NaCl solution than to air. The fracture surface indicated that cracks were mainly initiated from the notch of specimens in air, whereas cracks were formed from multiple sources in specimens in the corrosive medium. Finally, a three-parameter Kitagawa-Takahashi diagram was established to correlate the threshold stress range (Δσth) and critical defect size (a) with the corrosion fatigue life (N) in terms of the El-Haddad model, thus providing a scientific reference for the service safe region identification of high-speed railway axles subjected to corrosive environments.

Evaluation of stress-controlled high-cycle fatigue characteristics in PLA-wood fused deposition modeling 3D-printed parts under bending loads.

PLA (Poly-lactic acid)-wood provides more biodegradability through natural fibers, a significant advantage of pure PLA. Nevertheless, these bio-composites may have inferior mechanical properties compared to non-degradable polymer composites, considering the lower strength of natural particles compared to synthetic fibers. This research examines the fatigue behavior of additive-manufactured biopolymer PLA-wood and assesses its comparability with pure PLA. Therefore, solid fatigue test samples were printed using the FDM (fused deposition modeling) method. Afterward, fully reversed rotary bending fatigue experiments were performed at 4 different stress levels (7.5 to 15 MPa) to extract the S-N curve of PLA-wood. Moreover, the fatigue fracture surfaces of the PLA-wood were investigated and compared at the highest and lowest stress levels using an FE-SEM (Field Emission Scanning Electron Microscopy), indicating more ductile fracture marks at higher stress levels. The fatigue lifetime of the PLA-wood decreased by 87.48% at the highest stress level (15 MPa), rather than the result at the lowest stress level (7.5 MPa). Additionally, the results demonstrated that the fatigue characteristics of the printed pure PLA and PLA-wood were comparable, suggesting that the 3D-printed PLA-wood with the used printing parameters can be an alternative choice.

Surface Integrity induced by the Belt Finishing Process and Effects on the Fatigue Limit of a 27MnCr5 Carburized Steel

Among superfinishing processes, belt finishing is well known for its ability to induce compressive residual stresses and low surface roughness. Moreover, it is promoted by industry, as this process requires limited investments and is easy to handle. Combined with hard turning, precise dimensions and fine surface roughness of the parts can be ensured. Therefore, the combination of these processes could replace the grinding operation performed on automotive gear shafts for example. The article proposes to study the effects of the belt finishing operation on surface integrity of 27MnCr5 carburized steel shafts. Residual stresses and surface roughness are investigated for hard machined and belt finished samples. Afterwards, rotating bending fatigue tests are performed, and the fatigue limit of the belt-finished samples is compared with hard machined ones.

Kaji Eksperimental Karakteristik Fatik Komposit Berpenguat 2 Lapis Serat Nenas dan Orientasi Serat 45 Derajat atau 90 Derajat

The aim of this study is to experimentally investigate the effects of fiber orientations on the fatigue strength, fatigue life and surface fracture of 2 ply Pineapple Leaf Fiber Composite. Fatigue test specimens with 45o and 90o fiber orientation are loaded using rotary bending fatigue test machine at several load levels. Fatigue strength and fatigue life are measured during fatigue test and fracture surface of fatigue specimens are observed using microscope. The results show that 2 ply Pineapple Leaf Fiber Composite with 45o fiber orientation have highest fatigue strength than 2 ply Pineapple Leaf Fiber Composite with 90o fiber orientation. The shape of the surface fracture in the test specimen varies widely which is generally caused by Multiple Origins or several fault starting points at once which can erode or tear the surface of the specimen before the specimen finally fails or breaks.

Effect of ultrasonic rolled material layer on the corrosion fatigue resistance of railway axle EA4T alloy steel

Surface treatment has been validated to improve the fatigue crack resistance of engineering components, while the coupling effect of corrosive atmosphere and external loading is relatively less reported with detailed experimental studies. In this study, gradient structure (GS) axle EA4T alloy steel specimens were prefabricated by using the ultrasonic surface rolling process (USRP), and their corrosion fatigue resistances were investigated. First, the optimal USRP parameters were determined via orthogonal tests. After the USRP treatment, the microstructure, surface topography, surface roughness, residual stress, and electrochemical corrosion behavior were measured to characterize the surface under various conditions. The electrochemical tests results indicated that the compressive residual stress (CRS) is an important factor in improving the corrosion resistance of axle steel. Rotating bending fatigue tests in both air atmosphere and corrosion liquid showed that the fatigue and corrosion fatigue performances could be significantly improved with the strengthened layer obtained via the USRP. Factor separation analyses substantiated that the remarkable enhancement of fatigue and corrosion fatigue strengths can be mainly attributed to the CRS introduced by the surface strengthening treatment. Simultaneously, the GS layer and hardened layer exhibited a synergistic effect.

A Study on a Novel Process Combines Cutting and Joining by an Automatic Lathe

The Swiss-type automatic lathe is designed for continuous mass production of the same product. In the research, the authors propose a combined turning process in which a joining process using the frictional welding method is introduced into the automatic lathe. If the joining process is performed with a Swiss-type automatic lathe, it is expected that the problem of a large amount of residual material due to the mechanical structure can be solved. Generally, the friction welding method is performed by a dedicated machine and is pressure controlled by a hydraulic power source, however in the case of an automatic lathe, friction welding is controlled by the feed length and feed rate. The low rigidity of automatic lathes is also concerned. In the study, the authors investigated the tensile strength and rotational bending fatigue strength of the A6061 bonding material to investigate and quantitatively evaluate the optimum friction welding conditions that can obtain good bonding results in the friction welding method using a multi-axis automatic lathe. Upset speed was the most influential factor for tensile strength and friction rotation speed was good at about 4000 rpm. This fact suggests that excessive heat input leads to a decrease in tensile strength. The tensile strength was equivalent to that of the annealed material. It also seems that the air-cooled annealing phenomenon occurs during the friction welding process. The results of rotational bending fatigue strength were similar to those of the annealed material. It is clarified that friction welding with an automatic lathe is feasible, however, the strength of the bonded material is reduced to the same level as that of the annealed material.

Fatigue strength evaluation of case‐hardened components combining heat‐treatment simulation and probabilistic approaches

AbstractIn order to raise the hardness and strength of the surface layer of mechanical components and induce favorable residual compressive stresses, case‐hardening procedures have become established in the heat treatment of steel. In this work, a calculation concept for the fatigue strength of components that have been case‐hardened through carburizing heat treatment is being developed. The residual stress and the load stresses in complex‐shaped, carburized materials are determined using a finite element (FE) model. The fatigue limit of the components is derived using probabilistic methods and taking into account hardness gradients, residual stresses, and non‐metallic inclusions. The model is validated with available axial bending fatigue test data and then used to predict the rotating bending fatigue limit of samples with various geometries and heat‐treatment conditions. This work demonstrates the capability of combining probabilistic and FE‐based modeling to represent complex interactions between variables that affect the fatigue of heat‐treated components, such as steel cleanliness, notch shape, case‐hardening depth, or loading conditions.

Effect of Repeated Processing Passes during Ultrasonic Rolling on Fatigue Performance and Corrosion Resistance of Ti6Al4V Alloy

Ultrasonic surface rolling processing (USRP) is a new method to improve the fatigue performance of titanium alloy, and repeated processing pass is an important factor that affects its strengthening effect. The effect of USRP passes on the surface microstructure, residual stress, fatigue performance and corrosion resistance of titanium alloy is researched via SEM, X-ray diffractometer, rotating–bending fatigue test and electrochemical impedance spectroscopy. The results show that Ti6Al4V alloy undergoes cumulative plastic deformation during USRP process, the surface grains are refined and a residual compressive stress field with a thickness of 500 μm is introduced, which together improve the fatigue performance of the Ti6Al4V alloy. Increasing the repeated processing passes will deepen the grain refinement layer and increase the surface hardening effect, but the fatigue life of the Ti6Al4V alloy does not increase with an increase in processing passes. A five-passes processing under a static force of 550 N can result in a greater gain for the fatigue resistance of the Ti6Al4V alloy; the fatigue life of a five-passes-processed sample under 600 MPa is 8 times higher than that of an untreated sample, and its fatigue crack source initiates at the subsurface away from the surface of 180 μm. Furthermore, Ti6Al4V alloys treated by USRP show a better corrosion resistance in both neutral and acidic solutions, especially for the five-passes-processed sample.

Influence of post weld aging treatment on microstructural features and fatigue behaviour of unnotched and notched specimens of friction stir welded AA6061-T651 aluminium alloy joints under completely reversed stress cycle

A comparative investigation on rotating bending fatigue behaviour between unnotched and notched specimens of friction stir-welded (FSW) AA6061-T651aluminium alloy joints has been conducted under completely reversed cyclic loading (R = −1). Post-weld aging treatment was done for 8 h at 200°C on the welded joints. After post-weld aging treatment, the fatigue strength was significantly improved, while the grain size remained unchanged. Microstructural evolution before and after post-weld aging treatment was studied using orientation imaging microscopy (OIM) and transmission electron microscopy (TEM). It was found that post-weld aging treatment decreased dislocation density and facilitated precipitation hardening through the reprecipitation of fine β″(Mg2Si) particles. Fine particles of post-weld aged specimens of FSW joints were sheared by dislocations generated during cyclic loading, resulting in difficult crack initiation and tortuous crack propagation. Fractographic results confirmed that Post-weld aged specimens of FSW joints have better fatigue resistance than as-welded specimens, owing to the presence of significant precipitates along the grain boundary.

The Effect of Electroplated Ni Nanocoating on Fatigue Life of 1020 AISI Low Carbon Steel

Low carbon steel 1020 AISI has been selected in this study to show the influence of Ni Nano coating on fatigue life of this metal under fatigue loading at room temperature with a stress ratio R= -1. The prepared specimens are exposed to electroplated process using Nano nickel with 40 nm at diverse situations to improve the fatigue limit of metal. (SCHENCK PUNN) rotating bending fatigue test, hardness, tensile strength, microstructure, surface roughness and SEM, XRD diffraction tests have been completed for base metal and electroplating treated metal. The experimental results indicate that Ni nano coating by electroplating improve the fatigue life at due to steel substrates are typically polished mechanically and chemically before deposition to enhance the fatigue properties and nano nickel have fair distribution on steel surface.

Effect of brittle TiN coating on fatigue performance of TC11 titanium alloy under rotating bending and tension-tension

In this paper, the effect of brittle TiN coating on fatigue performance of TC11 titanium alloy (Ti-6.5Al-3.1Mo-1.05Zr0.35Si) under rotating bending and tension-tension were investigated. TiN coating causes a reduction in high and low cycle fatigue performance of TC11 under both conditions. The median fatigue strength at 1 × 107 cycles of TC11 decreases from 582.5 MPa and 896.0–547.5 MPa and 531.0 MPa under rotating bending and tension-tension fatigue loading, respectively. In scenarios involving rotating bending fatigue, fatigue failure initiation for both TiN coated and uncoated TC11 specimens reside on the droplet in coating surface, irrespective of high or low stress conditions. As for tension-tension fatigue loading, both TiN coated and uncoated TC11 specimens experience surface-based fatigue initiation points under high fatigue stress. However, during low-stress tension-tension loading, the incorporation of a TiN coating prompts a shift in TC11's fatigue initiation source from the interior to its surface. Furthermore, under both fatigue loading condition, fatigue cracks initiate at droplets on the coating surface and propagate to the surface of the substrate and eventually its interior. And the fatigue failure of the TC11 substrate is accelerated due to the coating causing balanced tensile stress. The inherent compressive characteristics and lack of tensile strength in TiN ceramic materials render them more susceptible to premature cracking when subjected to tensile fatigue loads. This vulnerability leads to heightened damage to the fatigue performance of TC11.

Rotating bending fatigue behaviour and quasi‐static tensile properties of Wire Arc Additively Manufactured 308L stainless steel

AbstractWire Arc Additive Manufacturing (WAAM) is a direct energy deposition method used to manufacture steel components by using an electric arc as a heat source to melt a metal wire and deposit it layer by layer. In this study, monotonic tensile tests, standardized Charpy impact tests, and rotating bending fatigue tests are executed to characterize the mechanical properties of WAAM 308L stainless steel using specimens extracted from additively manufactured plates. In particular, monotonic tensile properties are investigated in three directions: that is 0, 90, and 45 degrees with respect to the plane of deposition, whereas the fatigue strength is quantified for one direction only, i.e. 90 degrees since this is deemed to be the weakest.The mechanical characterization highlights that WAAM 308L SS shows an anisotropic behaviour, an enhanced strain‐rate sensitivity, and an overall reduced yield strength as compared to the base material 308L. The anisotropic material behaviour is explained by the microstructure morphology since the austenite grains form anisotropic columnar zones due to an uneven heat profile during production. During the fatigue tests, the relatively high strain rate sensitivity causes susceptibility to self‐heating at relatively low loading frequencies, i.e. below 100Hz.

Effect of Laser Shock Peening on the Fatigue Life of 1Cr12Ni3Mo2VN Steel for Steam Turbine Blades

In the present study, laser shock peening (LSP) was employed to enhance the rotating bending fatigue life of 1Cr12Ni3Mo2VN martensitic stainless steel used in steam turbine blades, addressing the issue of insufficient fatigue performance in these components. The aim of this study was to investigate the effect of LSP on the microhardness, residual stress, and rotating bending fatigue life of 1Cr12Ni3Mo2VN steel samples. The microhardness of LSP-treated samples was increased by 10.5% (LSP-3J sample) and 15.3% (LSP-4J sample), respectively, compared to high-frequency hardening samples. The residual compressive stress of the LSP-4J sample was the largest, reaching −689 MPa, and the affected layer depth was about 800 μm. Fatigue tests showed that the number of cycles at the fracture point for the LSP-3J and LSP-4J samples increased by 163% and 233%, respectively. The fatigue fracture morphology of the four samples showed that the microhardness and residual compressive stress distribution introduced by LSP could effectively inhibit the initiation of surface cracks, slow down the crack growth rate, and improve the rotating bending fatigue life of 1Cr12Ni3Mo2VN.