Rotating Bending Fatigue Tests Research Articles

Synergistic impact of corrosion pitting on the rotating bending fatigue of additively manufactured 316L stainless steel: Integrated experimental and modeling analyses

In this study, the ex-situ rotating bending corrosion fatigue behavior of laser powder bed fused stainless steel (SS) 316L has been studied incorporating experimental analyses and modeling. The findings revealed significant variations (almost 20 %) in fatigue lifetime in pre-corroded specimens relative to non-corroded (virgin) specimens because of corrosion-derived pitting phenomena on the surface. To this end, the fatigue strength of virgin (non-corroded) and pre-corroded SS 316L were recorded at 242 MPa and 203 MPa, respectively. Upon conducting the fatigue tests and extracting stress-life trends, advanced microstructural characterization and postmortem analyses were used to quantify fatigue crack behavior and fracture surface. An empirical model is also developed employing depth-sensing indentation testing, linear elastic fracture mechanics, and computer tomography scans to propose an optimum predictive trend. The analysis comparing existing models with our proposed model demonstrates reasonable agreement between experimental findings and the predicted life for the studied laser powder bed fused SS 316L material exposed to corrosion rotating bending fatigue test. The findings of this research carry important contributions to the structural integrity and longevity of marine engineering, ship construction, naval operations, and naval aviation where materials and components are exposed to cyclic loading and corrosion.

Fatigue crack extension mechanism and mode-type analyses of martensitic steels for proposing fatigue strength evaluation method: Example of 18% Ni BCC martensitic steel

The fatigue properties of martensitic steels tend to differ significantly from those of low- and medium-strength steels. Even if the hardness is the same, the fatigue strength varies substantially depending on the microstructure. Thus, for using martensitic steel rationally and developing materials with high fatigue strength, it is desirable to establish a fatigue strength evaluation method that can consider the microstructural effects on fatigue properties. For this purpose, 18% Ni bcc martensitic steel was used as a model metal to conduct rotating-bending fatigue tests in this study. The fatigue crack behavior on the smooth specimen surface was examined, and the fracture surface morphology on both sides of the broken specimen and the microplastic strain distribution near the fatigue crack tip were analyzed. The results clarified the mechanism underlying fatigue crack extension (FCE). The analytical results revealed three types of FCE mechanisms dependent on the stress amplitude, stress state (i.e., plane stress or plane strain), and martensitic microstructure. Considering these mechanisms, a unique stress–life curve was predicted, and a particular fatigue crack shape and fractography were confirmed. The material indices were speculated to be the representative properties of martensitic steels.

Fatigue performance testing and life prediction of welded fuel pipes

The external piping system which connects power devices, valve control devices, actuators, etc. is an essential system on the aero engine. Under the combined effects of high fluid pressure and external vibration, multiaxial fatigue failure is the main factor that seriously affects the safety of the piping system. The objective of this paper is to establish the multiaxial fatigue life model for the typical welded fuel pipe of the piping system by combining fatigue testing, simulation and theoretical analysis which is of great guiding significance for the engineering application of the piping system. Firstly, the fatigue limits of welded fuel pipes under no and 13.5 MPa internal pressure are obtained by rotational bending fatigue tests using the up-and-down method. Three additional stress levels of rotational bending fatigue tests under no internal pressure are supplemented and then the S-N curve is further obtained by the group method. Since the corresponding fracture surface of the specimens locates at the weld toe near the fixed end, peak stress method is adopted to evaluate the fatigue performance of the weld toe on the pipe specimens. In addition, by comparing the fatigue limit with no and 13.5 MPa internal pressured pipes, it is obvious that the equivalent uniaxial stress corrected by Gerber formula is not applicable for the multiaxial fatigue condition which is caused by the combined effect of fluid pressure and displacement load. The local stress concentration factor caused by the weld toe is determined and based on Findley critical plane model, the multiaxial fatigue life model is established which simultaneously takes the local stress concentration effect, mean stress effect and multiaxial stress effect into consideration. The results of rotational bending fatigue tests under 13.5 MPa internal pressure are within the triple error dispersion band and the accuracy of the proposed life model are verified.

Design and manufacturing of rotating bending fatigue test machine

Design and manufacturing of rotating bending fatigue test machine

A novel machine learning-based model for predicting the transition fatigue lifetime in piston aluminum alloys

The estimation of transition fatigue lifetimes for piston aluminum alloys was carried out using unsupervised machine learning (ML) with the K-means algorithm. For this purpose, an experimental dataset representing standard ISO specimens with piston aluminum alloy material, which was subjected to rotational bending fatigue tests under fully reversed cyclic load conditions, was utilized. Subsequently, the stress and fatigue lifetime data were employed to fit the algorithm of K-means clustering. Then, to enhance the K-means performance, various preprocessing methods and Kernel functions were employed to cluster fatigue lifetime and stress data. Furthermore, following the division of the data into multiple clusters, the middle cluster, which represents fatigue lifetime and stress, was identified as the transition fatigue region, and its center defines the estimated transition fatigue lifetime. Ultimately, the transition fatigue lifetimes were determined using the Coffin–Manson–Basquin equation for piston aluminum alloys and compared to the estimated transition fatigue lifetimes, along with the calculation of relative errors. The obtained results indicated that, among the different models employed in this study, the polynomial Kernel K-means clustering algorithm proved to be the most efficient for clustering data within stress and number of cycles plots (S–N plots). Moreover, employing the K-means algorithm with a polynomial Kernel function and five cluster numbers yielded the most accurate estimation of transition fatigue lifetime for piston aluminum alloys, exhibiting the lowest relative error.

A comprehensive study on the effects of surface post-processing on fatigue performance of additively manufactured AlSi10Mg: An augmented machine learning perspective on experimental observations

In this study, the efficacy of 21 distinct surface post-processing methods on the fatigue behavior of an additively manufactured (AM) material was investigated. Various treatments, encompassing single-step processes like sand blasting (SB), conventional shot peening (CSP), severe shot peening (SSP), gradient severe shot peening (GSSP), ultrasonic shot peening (USP), severe vibratory peening (SVP), ultrasonic nanocrystal surface modification (UNSM), laser shock peening (LSP), laser polishing (LP), tumble finishing (TF), chemical polishing (CP), electro-chemical polishing (ECP), and machining (M), as well as hybrid treatments, were systematically investigated for their impact on the fatigue behavior of hourglass laser powder based fused (LB-PBF) AlSi10Mg specimens. A comprehensive series of experimental tests were carried out, covering surface texture analyses, microstructural characterizations, porosity measurements, hardness, residual stresses (RS), monotonic tensile tests, and rotating bending fatigue tests at four stress levels. Following the experimental investigations, the acquired data were leveraged to develop a machine learning (ML)-based model to correlate the fatigue life with the influencing factors and conduct parametric and sensitivity analyses. The model utilized a deep learning approach to predict the fatigue response of LB-PBF AlSi10Mg, incorporating various artificial neural networks (ANNs) and considering input parameters such as yield strength, ultimate tensile strength, elongation to fracture, porosity, depth of pore closure, surface hardness, depth of hardness variation, surface RS, maximum compressive residual stresses (CRS), depth of the CRS field, top surface grain size, surface layer mean grain size, surface roughness, and stress amplitude. Depending on the life regime, the factors influencing fatigue behavior can vary significantly. In higher stresses, dominated by plastic strains, surface residual stress emerges as the primary factor. Conversely, in lower stresses, dominated by elastic strains, the significance of surface roughness becomes more pronounced, followed by surface residual stress, surface hardness and other factors. These findings underscore the contextual importance of different influencing factors for enhancing fatigue resistance based on varying loading conditions.

Complex-inclusion induced fracture mechanism of ultraclean 100Cr6 bearing steel under high cycle fatigue test

Fatigue property of an ultraclean 100Cr6 bearing steel was investigated by the high-cycle rotating bending fatigue tests. It was found that the cyclic loading below 1197 MPa led to the frequent cracking initiated from the complex inclusions with the two distinctly different features: the breaking and the debonding of complex inclusions, all of them have a core of oxide agglomerate containing many cavities and a nearly 2 μm-thick sulfide shell. Finite element simulation results reveal that this distinction depends on whether a sufficiently high residual stress (RS), which should be developed near the interface of inclusion and matrix during quenching and accumulated during the cyclic loading, can exceed the yield strength (YS) of steel matrix. Higher interfacial RS than the YS leads to the debonding of inclusion whilst lower one to the breaking of inclusion. A more uniform and thicker sulfide shell could relieve the RS to the greater extent, favoring the breaking of inclusion with longer fatigue life. Finally, we propose that the critical sizes for no fatigue crack initiated at the pure oxide, the complex inclusions with non-uniform and uniform sulfide shell are 11.2 μm, 12.8 μm and 17.0 μm respectively, and the optimum size ratio of oxide core to the entire complex inclusion is 0.56–0.76. Both are of great importance on tailoring the inclusions of ultraclean bearing steel for improving the fatigue life of bearing steel.

Analysis of the effect of deep-profile compressive residual stress induced by laser peening on fatigue strength of 7075 aluminum alloy

The effect of laser peening-induced compressive residual stress on the fatigue strength improvement of A7075 specimens was investigated. Rotary bending fatigue tests and residual stress distribution measurements using the sequential polishing method were conducted on untreated, shot-peened, and laser-peened specimens. The results revealed that laser peening provides a deeper compressive stress and a deeper fracture origin, resulting in higher fatigue strength. Furthermore, controlling the laser parameters could extend the depth of the compressive stress layer by approximately 5 mm, indicating the possibility of applying laser peening to thicker materials to improve the fatigue strength.

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.

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.

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.

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.

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.

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.

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.

Crack Propagation Behavior in Rotational Bending Fatigue Test of Nitrocarburized JIS SCM420 Steel

Crack Propagation Behavior in Rotational Bending Fatigue Test of Nitrocarburized JIS SCM420 Steel