Rotating Bending Loading Research Articles

Fatigue and corrosion‐fatigue behavior of the β‐metastable Ti‐5Al‐5Mo‐5V‐3Cr alloy processed by laser powder bed fusion

AbstractWe performed rotating bending tests and axial (tension‐compression) load‐increase and constant amplitude high‐cycle fatigue tests in air and Hanks' balanced salt solution (HBSS) on the β‐metastable titanium alloy Ti‐5Al‐5Mo‐5V‐3Cr, processed by laser powder bed fusion (LPBF‐M), solution‐treated and aged, and shot‐peened. Rotating bending loading in air revealed a strong influence of process‐induced flaws on fatigue endurance. Especially in the high‐cycle fatigue range and the transition region, the stochastic distribution of the flaws and flaw sizes led to a high scatter of the number of cycles to failure. The axial load‐increase tests yielded a good fatigue life estimation, with a negligible difference between air and HBSS. The cyclic deformation behavior in HBSS was also strongly influenced by the local microstructure and defect distribution, and, thus, by crack formation and propagation. Plastic deformation and microcrack growth interact, and their relative amount resulted in different progressions of the plastic strain amplitude over the number of cycles for different specimens. Changes in the free corrosion potential and the corrosion current were highly sensitive indicators for fatigue‐induced damage on the rough surfaces, which was correlated to the microscopic examination, fracture surface features, and the fatigue crack development.

The C2 isthmus screw provided sufficient biomechanical stability in the setting of atlantoaxial dislocation-a finite element study

BackgroundThe emerging of the C2 isthmus screw fixation technique is gaining popularity in the setting of atlantoaxial dislocation or other conditions requiring fixation of C2. However, the biomechanical stability of this fixation is poorly understood.PurposeTo compare and elucidate the biomechanical stability of C2 pedicle screw (C2PS), C2 isthmus screw (C2IS) and C2 short isthmus screw (C2SIS) fixation techniques in atlantoaxial dislocation (AAD).MethodA three-dimensional finite element model (FEM) from occiput to C3 was established and validated from a healthy male volunteer. Three FEMs, C1 pedicle screw (PS)-C2PS, C1PS-C2IS, C1PS-C2SIS were also constructed. The range of motion (ROM) and the maximum von Mises stress under flexion, extension, lateral bending and axial rotation loading were analyzed and compared. The pullout strength of the three fixations for C2 was also evaluated.ResultC1PS-C2IS model showed the greatest decrease in ROM with flexion, extension, lateral bending and axial rotation. C1PS-C2PS model showed the least ROM reduction under all loading conditions than both C2IS and C2SIS. The C1PS-C2PS model had the largest von Mises stress on the screw under all directions followed by C1PS-C2SIS, and lastly the C1PS-C2IS. Under axial rotation and lateral bending loading, the three models showed the maximum and minimum von Mises stress on the screw respectively. The stress of the three models was mainly located in the connection of the screw and rod. Overall, the maximum screw pullout strength for C2PS, C2IS and C2SIS were 729.41N, 816.62N, 640.54N respectively.ConclusionIn patients with atlantoaxial dislocations, the C2IS fixation provided comparable stability, with no significant stress concentration. Furthermore, the C2IS had sufficient pullout strength when compared with C2PS and C2SIS. C2 isthmus screw fixation may be a biomechanically favourable option in cases with AAD. However, future clinical trials are necessary for the evaluation of the clinical outcomes of this technique.

Finite Element and Design of Experiments Study on Stresses in Impact-Damaged Hourglass Specimens Subjected to Rotating Bending

Residual stresses and stress concentrations induced by impact-damage may shorten the fatigue life and cause premature failure of aeronautical components. Under cyclic loading, fatigue cracks may initiate at the points where high tensile stresses occur and propagate to failure. In this work, an experimentally validated finite element model was used to assess the stress state in impact-damaged 7075-T6 hourglass specimens subjected to rotating bending. In the first simulation step, the finite element method was used to model residual stresses in the specimens for various impact cases, with different masses of impacting objects and impact speeds and angles. In the subsequent simulation step, the damaged specimens were subjected to rotating bending. The total stresses in the impact region were obtained through the superposition of the residual stresses caused by the impact and the stresses due to the rotating bending load. The design of experiments was applied to the obtained finite element results to identify which impact parameters mostly influence the stress distribution in the damaged specimens. The analysis showed that the most significant parameter is the impact speed, followed by the material and the size of the impacting object while the influence of the impact angle is low.

Plain and fretting fatigue characteristics of 16MnCr5 steel under cyclic bending loading with the application of engine piston pin

The current study examined the plain fatigue and the fretting fatigue behaviors of the piston pin alloy (16MnCr5 steel) under fully-reversed rotating bending loading. The standard fatigue testing sample was cut out from the piston pin used in internal combustion engines. Furthermore, the failure mechanisms of samples were studied using field emission scanning electron microscopy. The obtained result indicated that the fatigue lifetime of 16MnCr5 steel was significantly affected by the fretting damage. The investigation of the failure mechanisms determined that the fracture behavior of the specimens under the plain fatigue and fretting fatigue conditions was brittle; however, it was considerably influenced by the casting defects in the samples. The test results can merely be used to compare the fatigue performance of the studied material under different conditions. More naturalistic experiments are required for further optimization in designing components made from this material to improve their reliability and service life, especially in contacting surfaces under rotating bending conditions.

Cumulative Fatigue Life Estimation Under Combined Shot Peening and Elevated Temperature for AA7001-T6

The fatigue life of aluminum alloys (7001–T6) and shot peening at various temperatures are predicted in this study. Shot peening (SP) steel balls is a surface treatment technique that can help minimize damage. This study set out to conduct an experimental investigation in order to ascertain the amount of damage caused by fatigue buildup for AA7001-T6 under rotating bending loading and a stress ratio R = -1. RT (room temperature), 330 °C, and SP + 330 °C were the temperatures used in the testing. To predict the fatigue life under high temperatures, it was suggested to use a modified damage stress model that had been established to take damage at different load levels into account. To determine the most damage (Miner's rule), the output of the current model was compared to experimental findings and the output from the fatigue damage model. The comparison showed that the current model had a respectable level of safety, whereas the miners' model had two models: one for low-high loading and the other for high-low loading, and the results were suitable for extending fatigue life. Despite the fact that H-L loading has a longer fatigue life (19477) cycles than the experimental (16433 cycles), L-H loading is conservative (Nf is 19477 cycles less than the experimental (24733 cycles) (non-conservative).

Finite element simulation of fretting wear on railway axle press-fit specimens

In this study, a finite element simulation method is proposed for railway axle press-fitted specimens that considers the fretting wear effect in slip zones. Based on the modified Archard wear model for calculating the fretting wear depth in slip zones, the real-time calculation of the specimen wear depth under rotating bending loading and the real-time update of the contact surface profile of the finite element model are realized. The results show that the fretting wear depth of the contact surface of the press-fitted axle specimen increases with the increase of number of cycles of rotational bending load, and the most severe instances of wear occurs at the edge of the contact surface and 0.1 mm from the edge; the existence of fretting wear leads to the redistribution of the contact fretting parameters.

Experimental study on fretting damage in the interference fit area of high-speed train wheels and axles based on specimen

Taking the high-speed train axles as the object, this paper designs and produces fretting fatigue specimens that simulate the interference fit of the high-speed train axles and conducts the fretting damage test on the interference fit area of the axles under rotating bending loads. The interrupted fretting fatigue tests were conducted based on the fretting fatigue limit to study the distribution, the damage of the wear debris and the characteristics of crack initiation of the specimen shaft in the contact area of the interference fit. Research shows that the fatigue limit of high-speed train axle materials is significantly reduced due to fretting damage in the interference fit area. The closer to the outer edge of the contact slip zone, the more concentrated the wear debris, the more severe the fretting fatigue damage. When the amount of wear debris reaches its maximum, the load cycle occurs 1 million cycles. Fretting wear and fretting fatigue coexist in the interference fit specimen under rotating bending loads, accompanied by the formation of third-body oxides between the contact surfaces.

Effect of the stress concentration factor on the final fracture zone of aluminium AW 6063 T6 for rotating bending specimens

The paper presents fracture surfaces of the polycrystalline material - AW 6063 T6 aluminium alloy - under a rotating bending load. The fatigue fracture surfaces were analysed for high-cycle fatigue at approximately 1 × 105, 8 × 105 cycles and stress amplitude level equal to 140 MPa. The specimens with four different stress concentration factors Kt (with values ~1, 1.4, 2 and 2.6) were made from a drawn bar. The fatigue tests were performed by rotating bending stand with a frequency of 50 Hz. Thirty (30) tests were carried out for each geometry of the specimen. Final fracture zones for unnotched specimens were 39.9%, 35.8% and 43.3% of the total cross-sectional area for 1 × 105, 8 × 105 cycles and 140 MPa stress amplitude, respectively, However, the final fracture zone for the notched specimen with Kt equal to 2.6 was less and had a value of 13.7%, 13.8% and 18.8% of the total cross-sectional area for 1 × 105, 8 × 105 cycles and 140 MPa stress amplitude, respectively. The research aimed to compare the ratio of the area of the final fracture zone to the total cross-sectional area. The authors have found a relationship that could be used to estimate the stress concentration factor based on the area of the final fracture zone. Based on this, the stress concentration factor can be determined. The estimates calculated using the equation and the test results show a good correlation between the stress concentration factor and the ratio of the area of the final fracture zone to the total cross-sectional area. The proposed method of determining the stress concentration factor can be used to verify different manufacturing processes (e.g. surface finish, notch radius) and the loading history (e.g. existing overload conditions).

Fatigue strength of LPBF Ti6Al4V machined under flood and cryogenic lubri-cooling conditions

Ti6Al4V specimens were manufactured by Laser Powder Bed Fusion (LPBF), heat treated and machined using two lubri-cooling conditions, i.e. flood or cryogenic, the latter being useful to improve the machined surface integrity. These specimens were characterised in terms of micro-hardness, microstructure, residual stresses and surface topography. Afterwards, they were fatigue tested under rotating bending loading and the fracture surfaces were analysed by SEM to identify the killer defects. Finally, the experimental fatigue results were compared with the theoretical estimations according to both the Murakami and El Haddad-Smith-Topper models.

Fatigue behavior of agricultural rims under rotating bending load

AbstractAgricultural rims are highly loaded components which affect the functionality and safety of tractors significantly. For this reason, it is essential to prevent a damage of the rims. However, fatigue‐initiated cracks along the bolt circle arise at any time during application. Until now, the determining load for the crack initiation is unclear. The paper investigates this fatigue problem by experimental, analytical, and numerical methods. Therefore, a test rig using hydraulic actuators is designed to load the rim by rotating bending in combination with a lateral force. The loads are deduced by an analytical model of the tractor under different driving situations like cornering. The finite element model shows the critical locations by performing a fatigue analysis of the driving situation. The experimental and numerical results verify the assumption that the rotating bending in combination with a lateral force leads to the fatigue cracks also found by tractors in reality.

The Fatigue Strength Analysis of ABS (Acrylonitrile Butadiene Styrene) Material Shaft Result of 3D Printing Process due to Rotating Bending Load

Prototyping a product using 3D (three-dimensional) printing process has been widely used. One of the materials commonly used is ABS (Acrylonitrile Butadiene Styrene). Currently, research did not refer to ASTM E-466 and tested specimens at 75% infill density without endurance limit analysis. The purpose of this research was to analyse the fatigue strength of 3D printed ABS material with infill density 100% due to rotating bending load according to ASTM E-466 standard, compare it with the 75% infill density test result and determine the value of its endurance limit. The research method used is experimental research by testing the fatigue strength of a number of ABS material specimens with four rotating bending load conditions until the specimen fails. The obtained result of the research is a S-N curve with maximum average cycle of 143702 at a stress of 26.87 MPa and minimum average cycle of 145 at a stress of 35.71 MPa. The shaft fatigue strength of ABS 3D printed with infill density 100% material has higher cycles at stresses below 37.1 MPa and lower cycles at stresses above 37.1 MPa compared to 75% infill density. The endurance limit obtained from the regression of the S-N curve is 16.25 MPa.

Experimental study of a CoCrMo alloy treated by SMAT under rotating bending fatigue

The main objective of this work is to understand the fundamental damage mechanisms involved in a SMAT treated CoCrMo alloy subjected to fatigue under rotating bending loads. For this purpose, different load amplitudes in rotating bending are imposed on cylindrical specimens, in as-machined and SMAT states. Different material characterizations are performed in order to determine which features play an important role in fatigue life of the studied alloy. Such characterizations are done via digital microscopy, electron backscatter diffraction (EBSD), roughness measurements and microhardness tests. The fatigue results presented in the form of S-N diagram show that SMAT with a moderate intensity (SMAT-2) can enhance the fatigue performance of the CoCrMo alloy, whereas SMAT with a higher intensity (SMAT-3) seems to deteriorate it. This fatigue life decrease is probably due to surface micro-cracks generated by an over-peening phenomenon.

Probabilistic Method to Estimate the Scatter of the Fatigue Strength of Shafts in the HCF Region

The fatigue strength of shafts is always subjected to scatter. Knowledge of this scatter is essential—especially in the high-cycle-fatigue (HCF) region—for producing safe shaft designs. Experimental determination is extremely time consuming and cost intensive. Therefore, this paper investigates the possibility of quantifying the scatter of (nominal) fatigue strength in the HCF region by means of a probabilistic model. The basis for establishing such a model is the identification of the parameters influencing the damage mechanism. In this context, the scatter-influencing parameters of external shape, surface and material condition were statistically modelled in a suitable manner. These influencing parameters act as input parameters in a local strength approach in addition to non-scattering parameters. Using a probabilistic model developed on the basis of Monte Carlo simulations, models of shafts and their surfaces can be randomly generated. The shafts so generated are submitted to local strength verifications by means of finite-element analyses of the entire failure-critical shaft surface. The stochastically generated shafts and the application of nominal stresses simulate the experimental testing at different nominal stress levels. By statistical evaluation of these fictitious nominal stress levels with respect to calculated failures and run-outs of the shafts, the probability distribution of the fatigue strength of the shaft population—and thus its scatter—can be determined. The probabilistic model is validated using a shaft population under non-scattering rotating bending load and compared with the experimentally determined scatter of the fatigue strength.

Heat Treatments Effects on the Fatigue Behaviors of Aluminum Nano-Composite Alloys

The fatigue is one of the major reasons for fracture of materials. Aluminum 7204 AA alloy with various heat treatments and (2.0) wt % of SiC nanoparticles were prepared by stir-casting method under rotating bending loading with ratio of stress (R= -1). The composite was strengthened by SiC particles size of) 10 (nanometre. The fatigue strength and life were obtained experimentally by the family of S-N curves for different heat treatments. The endurance limits (107cycles) for 7204 AA/ 2.0wt% SiC nano-composite fatigue strength as related to untreated nanocomposite was enhanced by 72 and 78.5% for T4 and T6, respectively.The improvement of fatigue properties is due to better spreading of SiC nanoparticles and increased porosity.

Influence of high initial porosity introduced by laser powder bed fusion on the fatigue strength of Inconel 718 after post-processing with hot isostatic pressing

Laser-based additive manufacturing (AM) of metallic materials can produce AM parts of high quality. The obtained density of metal parts manufactured by laser powder bed fusion (LPBF) is mostly greater than 99% and high mechanical strengths can be achieved; however, a long processing time is typically required to reach a high quality. Possibilities to shorten the LPBF processing time involve increasing either the scanning speed or the hatch distance, but both will result in greater porosity. In general, the porosity of AM parts can be reduced by subsequent post-densification of the materials by hot isostatic pressing (HIP). In this manner, not only can the LPBF process be accelerated but the fatigue strength of the parts can be increased by reliable reduction of porosity and the simultaneous homogenization of the microstructure. Nevertheless, argon porosity introduced by the LPBF process cannot be completely eliminated by HIP due to the insolubility of argon in metallic materials. In the present study, the influence of the initial porosity on the fatigue strength of IN718 specimens after HIP and different heat treatments were investigated with a view to understanding the impact of argon porosity. The fatigue strength under a rotating bending load was determined for four different test batches and one almost fully dense as-built state as a reference. For the test batches, two different initial porosities of 3.5% and 9.9% were introduced by increasing the hatch distance. These porous samples were subjected to the same HIP treatment but aged differently: half of the samples were annealed, quenched, and aged within the HIP vessel under pressure and the other half were annealed and quenched within the HIP vessel but aged in an ambient air atmosphere. HIP post-processing significantly improved the fatigue strength of IN718 samples produced by LPBF, even in the case of a high initial porosity and residual argon content. In the case of a 3.5% initial porosity, no difference was observed in fatigue behavior with respect to aging with or without pressure. In contrast, samples with an 9.9% initial porosity showed a large difference in fatigue strength according to different aging conditions.

Heat treatment effect on fatigue behavior of 3D-printed maraging steels

PurposeThis study aims to reveal that fatigue life is improved using heat treatment in the rotational bending fatigue test, which determines the fatigue behavior closest to service conditions.Design/methodology/approachIt is essential to know the mechanical behavior of the parts produced by additive manufacturing under service conditions. In general, axial stress and plane bending tests are used by many researchers because they are practical: the service conditions cannot be sufficiently stimulated. For this reason, the rotating bending fatigue test, which represents the conditions closest to the service conditions of a load-bearing machine element, was chosen for the study. In this study, the rotational bending fatigue behavior of X3NiCoMoTi18-9–5 (MS1) maraging steel specimens produced by the selective laser melting (SLM) technique was experimentally investigated under various heat treatments conditions.FindingsAs a result of the study, MS1 produced by additive manufacturing is a material suitable for heat treatment that has enabled the heat treatment to affect fatigue strength positively. Cracks generally initiate from the outer surface of the sample. Fabrication defects have been determined to cause all cracks on the sample surface or regions close to the surface.Research limitations/implicationsWhile producing the test sample, printing was vertical to the print bed, and various heat treatments were applied. The rotating bending fatigue test was performed on four sample groups comprising as-fabricated, age-treated, solution-treated and solution + age-treated conditions.Originality/valueMost literature studies have focused on the axial fatigue strength, printing orientation and heat treatment of maraging steels produced with Direct Metal Laser Sintering (DMLS); many studies have also investigated crack propagation behaviors. There are few studies in the literature covering conditions of rotating bending fatigue. However, the rotating bending loading state is the service condition closest to modern machine element operating conditions. To fill this gap in the literature, the rotating bending fatigue behavior of the alloy, which was maraging steel (X3NiCoMoTi18-9–5, 1.2709) produced by SLM, was investigated under a variety of heat treatment conditions in this study.

Mechanical properties and fatigue life detection of copper particle filled polyester composite material under rotating bending load

Mechanical properties and fatigue life detection of copper particle filled polyester composite material under rotating bending load

Rotating bending load tests of wheels. Methodological errors

Introduction (problem statement and relevance). Wheels are components that ensure the safety of vehicles. One of the main ways to test the fatigue strength of wheels is a rotating bending load test. The methodology of these tests, regulated by international and national regulatory documents, allows an indirect method for measuring the normalized force effect on the wheels, in which there are always risks of methodological errors.The purpose of the study was to identify potential sources of methodological errors when testing wheels in the bending-rotating mode.Methodology and research methods. Analytical research methods from the field of practical vibration theory were used in the article, considering the critical state of rotating shafts and rotors. Scientific novelty and results. The sources of potential methodological errors and their relationship with the design characteristics of the bench equipment and the wheel itself were determined.Practical significance. Practical recommendations have been given on the change and control of the stand components design characteristics aimed at minimizing errors. The high-speed test modes were determined, in which the error of the test effect on the wheel did not go beyond the normative limits.

Fatigue life prediction of glass fiber reinforced epoxy composites using artificial neural networks

In this work, fiber-reinforced composites, consisting of glass fibers with an epoxy matrix, have been considered to assess their fatigue life under combined rotating bending loads. Rotating bending fatigue tests were performed under fully reversed loading cycles at an operating frequency of 10 Hz. Fatigue test results revealed that the fatigue life of glass fiber reinforced with epoxy (GFRE) matrix composite decreased with an increase in stress levels. In addition, an artificial neural network approach was used in this study to demonstrate the impact of stress levels on the fatigue strength and failure modes of GFRE composites. The neural network was trained by the Levenberg-Marquardt algorithm using MATLAB. The feasibility of artificial neural networks for modeling and predicting the fatigue behavior of GFRE composites was verified by the correlation results (R2 = 0.99857) between the experimental data and ANN outputs. Three failure modes viz. matrix cracking, interfacial debonding and interfacial splitting of fibers were observed under low and high cycle fatigue tests. Further, ANN was successful in classifying these failure modes using a conjugate gradient backpropagation algorithm with 100% accuracy.

Biomechanical Effect of C5/C6 Intervertebral Reconstructive Height on Adjacent Segments in Anterior Cervical Discectomy and Fusion ‐ A Finite Element Analysis

ObjectiveTo investigate the biomechanical effect of different intervertebral reconstructive heights on adjacent segments following C5/C6 anterior cervical discectomy and fusion (ACDF) through finite element analysis.MethodsA finite element model of intact C4–C7 segments was developed and validated for the present study. Five additional C4–C7 postoperative models were constructed with 100%, 125%, 150%, 175%, and 200% of the benchmark height of C5/C6 on the basis of the intact model. The changes in intradiscal pressure (IDP) and range of motion (ROM) of adjacent segments before and after reconstruction of C5/C6 were analyzed.ResultsFor the upper adjacent segment (C4/C5), the IDPs under the different loading conditions all increased after reconstruction. The maximum IDPs were 0.387, 0.489, 0.491, and 0.472 MPa under flexion, extension, axial rotation, and lateral bending, respectively, observed at the reconstructive height of 200%. The minimum IDPs were observed at 150% reconstructive height under all loading conditions except extension, and were 57, 86 and 81% of the maximum IDPs under flexion, axial rotation, and lateral bending, respectively. The minimum IDP under extension occurred when the reconstructive height is 125% of the benchmark height. For the lower adjacent segment (C6/C7), the IDPs of postoperative models under all loading conditions also increased compared to the preoperative model. The maximum IDPs after reconstruction under flexion, extension, axial rotation, and lateral bending were 0.402, 0.411, 0.461, and 0.497 MPa, respectively, when the height of the reconstruction was 200% of the benchmark. The minimum IDPs were observed after a reconstruction at 150% of the benchmark, and were 59%, 85%, 82%, and 81% of the maximum IDPs under flexion, extension, axial rotation, and lateral bending loading conditions.ConclusionsThe reconstructive height is an important factor affecting the IDP and the ROM of adjacent segments after ACDF. To delay the adjacent segment disease, an intervertebral reconstructive height of 150% is an appropriate height in C5/C6 ACDF.