Fatigue Testing Device Research Articles

In situ SEM fatigue testing technology for metallic materials: a review.

Fatigue failure is one of the most common fracture modes of structural materials in the industrial field. The study of material fatigue mechanisms and methods for predicting fatigue life has always been of significant interest to researchers due to the abrupt and catastrophic failure mode. In recent decades, the performance and functionality of scanning electron microscopy (SEM) have been continuously improved and expanded. Based on this, the development of in situ fatigue testing in SEM has been rapidly developed. This technology plays a crucial role in providing insights into the deformation behavior of materials under fatigue. Keeping this in view, a comprehensive review of the development and application methods of in situ SEM fatigue testing technology is provided here. The development of in situ SEM fatigue testing devices is provided in brief overview, and the application and research progress of this technology in some representative metal structural materials (nickel-based single-crystal superalloys, steel, aluminum alloys and additive manufacturing materials) are analyzed in detail. Moreover, the perspectives on evaluating fatigue damage, particularly about small cracks and the plastic accumulations fatigue behavior, are presented in this study, utilizing the latest advancements in in situ SEM fatigue testing. Remarks about the present and outlook for future work to be done are then provided.

Design of a continuously repeated impact method with constant amplitude based on Hopkinson bar: Principle and impact fatigue life testing

The lack of reliable testing methods and standards hinders systematic research on the impact fatigue performance of materials. The aim of developing an impact fatigue test method is to generate repeated impact loads with a constant amplitude, which is difficult to achieve using various existing impact test devices. This study investigated the principles of cyclic loading-resetting and constant-amplitude loading based on the split Hopkinson pressure bar (SHPB) system, established a novel impact fatigue test device, and verified the developed method by testing the impact fatigue life of a Ti-6Al-4V alloy. Electromagnetic valves, laser sensors, and a vacuum pump were used in the developed device to launch and reset the striker bar; a servo motor and laser sensors were used to reset the loading bars and specimen, and the entire system was controlled by a programmable controller to achieve continuously repeated loading. To achieve constant-amplitude loading, the conditions required to ensure that the specimen moves away from the incident bar before the returning stress wave reloads the specimen was derived. It was found that a constant-amplitude repeated impact on the specimen could only be achieved through the precise design of the geometric configuration and material of the loading bars. This method is considerably simpler than various existing methods based on energy absorption and is more applicable to impact fatigue tests. The verification tests showed that the highest loading frequency of the device was 0.5 Hz, the loading rate exceeded 105 kN/s, and the amplitude error of the repeated impact loads did not exceed 2.45 %. Under loads with the same amplitude, the impact fatigue life of a Ti-6Al-4V alloy was considerably shorter than the non-impact (low strain rate) fatigue life, which indicates the necessity of investigating the strain rate effect on the fatigue performance of materials.

Torsional fatigue behaviour and damage mechanisms of martensitic spring steel in the HCF regime

This study investigates the fatigue behaviour and damage mechanisms of the martensitic spring steel SAE 9254, with emphasis on short crack propagation. Shear stress-controlled torsional fatigue tests are performed at stress ratio R = -1 and test frequency f = 79 Hz using structure-sensitive measurement techniques to detect the relevant damage mechanisms. An in-situ torsional fatigue testing device is applied for shear-controlled fatigue tests at two amplitudes of the torsion angle using R = –1 and f = 5 Hz, and the microstructural-dependent short crack propagation path is documented by means of confocal laser microscopy and electron backscattering analysis. It is found that the early development of fatigue damage is characterised by the formation of slip bands, which serve as crack initiation sites. In this process, crack initiation occurs preferentially at or near prior austenite grain boundaries. Furthermore, prior austenite grain boundaries were identified as obstacles for the propagation of short cracks, because of the change of the crystallographic orientation leading to an oscillating propagation rate of short cracks. The short crack density ρCD, which is an important parameter for fatigue damage, is rapidly growing with increasing shear stress amplitude ΔτT/2 and reveals a stress type specific behaviour.

Effect of Wear on Alternating Bending Fatigue Life of 20CrNi2Mo Martensitic Steel

Bending fatigue failures are commonly related to the wear behavior in an active system. The surface wear and plastic deformation of the tribolayer play crucial roles in the wear–bending fatigue behaviors of steels. In particular, the lamellar structure of martensitic steel leads to its unique wear–bending fatigue behavior. In this work, the wear–bending fatigue testing method and device were introduced to explore the wear–bending fatigue behavior of the martensitic steel. The effect of wear on the alternating bending fatigue life of 20CrNi2Mo martensitic steel was studied under low and high fatigue stress. The influence of wear debris on the fatigue life at two different sliding speeds was also analyzed. The results show that the fatigue life decreased with the wear load increased under high bending stress. Moreover, for systems with nanoscale wear debris on the steel surface, the wear–bending fatigue lifetimes are significantly enhanced compared with large wear debris.

Bending fatigue performance of high-strength seven-wire monostrand

Large-amplitude cable vibrations are remarkably common in cable-stayed bridges subjected to wind and mechanical loading due to low inherent damping of these structures. Although the high slenderness ratio of cables means that bending moments are not normally significant over their free length, local effects near the cable anchorage induce non-negligible bending stress variation under dynamic loading, which could lead to fatigue failure of stay cables. In modern parallel strand stay cables, the fatigue performance depends on the fatigue properties of the individual seven-wire monostrands which together make up the cable. We introduce a new bending fatigue testing device for seven-wire monostrand which can control the fatigue loading in the axial and transverse directions of the cable independently. The fatigue endurance of monostrand with guide deviators is significantly longer than without guide deviators present, especially for smaller bending fatigue amplitudes. We found that bending fatigue life of monostrand is also reduced by increased constant or dynamic axial stress, but over-tensioning of the monostrand (e.g. during construction) had no consistently adverse effect on fatigue life. For monostrand loaded in severe bending, fatigue occurs due to the bending stress variation caused by the combination of bending moments and axial forces at the extreme edges of the monostrand cross-section, rather than due to relative movement and fretting between adjacent wires within the monostrand.

Influence of hot corrosion on thermal fatigue behavior of Ni-based single crystal superalloy: Invisible and accelerated crack

As an important failure model for single crystal materials in service, with the increasing complexity of working environments, the thermal corrosion fatigue failure needs to be studied urgently. In this study, the thermal corrosion fatigue crack initiation and propagation behaviors of an Ni-based single crystal superalloy in both air and hot corrosion environments at 25–900 °C were studied by using a designed precise thermal fatigue test device. The microstructure characteristics and crack composition were analyzed by SEM, TEM and EDS, and the internal stress and recrystallization during thermal fatigue were characterized by EBSD. Moreover, the detailed and comprehensive crack morphology was characterized with different surface treatments. The results showed that the crack morphology was invisible in the hot corrosion environment, which is worthy of being highlighted. The initiation and propagation of thermal fatigue cracks were also accelerated in the hot corrosion environment, which contributed to the sufficient thermal stress, the accelerated material degradation of the inner/outer layers in the crack region, and the rapid forward diffusion of O2 in the inner crack layer. Finally, the influence mechanism of hot corrosion on the thermal fatigue behavior of the Ni-based single crystal superalloy is proposed.

Structure Design and Driving Dynamics Research of Crane Wheel Fatigue Test Device

In order to explore the fatigue damage of the crane wheel, the contact stress between the crane wheel and the steel rail was calculated. Moreover, the fatigue mechanism of crane wheels was also discussed by deriving the theoretical wheel pressure formula. As a result, a device design idea based on the fatigue mechanism of the crane wheel was proposed, where the device can be used to detect the bearing capacity, wear resistance and fatigue resistance of crane wheels. By using the simulation methods, the structure requirements and driving dynamics of the test device for different wheel diameters and wheel pressures were investigated and validated. Finally, the structural diagram of the fatigue test device is presented to provide the design guidance for the experiment research of the fatigue properties and reliability of crane wheels.

Investigation on the Design and Application of Hydraulic Loading Fatigue Test Device for Non-Vascular Stent

Investigation on the Design and Application of Hydraulic Loading Fatigue Test Device for Non-Vascular Stent

Development and Verification of Fatigue Testing Device for Rail Fastening Clamps

Development and Verification of Fatigue Testing Device for Rail Fastening Clamps

Amazing epsilon-shaped trend for fretting fatigue characteristics in AM60 magnesium alloy under stress-controlled cyclic conditions at bending loads with zero mean stress.

In the present article, fatigue properties (pure and fretting) of magnesium alloys (AM60) under cyclic bending loading were compared. For this objective, a rotary fatigue testing device was utilized with a fretting module on standard cylindrical samples under bending loads with zero means stress. The fretting fatigue condition decreased fatigue lifetime compared with pure fatigue but in an amazing Epsilon-shaped trend. Comparatively speaking to the state of pure fatigue, the fatigue lifetime of the fretting fatigue condition reduced by 91.0% and 44.8%, respectively, between the lowest level of stress (80 MPa) and the greatest level of stress (120 MPa). To study the fracture behavior and the fractography analysis, field-emission scanning electron microscopy (FESEM) was utilized. In general, since both quasi-cleavage and cleavage were seen; therefore, the fracture behavior for all samples was brittle. In both test conditions (fretting fatigue and pure fatigue), at higher stress levels, the average crack length was higher than at low-stress levels. In addition, the number of cracks (in high- and low-stress levels) was observed to be less in fretting fatigue conditions than in pure fatigue conditions, but the average crack length in fretting fatigue conditions in high-stress levels and low-stress levels was 212.82% and 259.47% higher than the average crack length under the pure fatigue condition, respectively.

Clamping Fatigue Properties of Shrink-Fit Holder.

In order to explore the clamping fatigue properties of shrink-fit holders, ANSYS software was used in this study to analyze the thermal and contact stresses during the clamping process of the shrink-fit holder, and the fatigue analysis was performed by selecting the dangerous areas based on the two stresses. A numerical control shrink-fit holder clamping fatigue test device was manufactured, and the automatic clamping of the shrink-fit holder was executed in this study. After 500 clamping repetitions, a milling test was carried out on the shrink-fit bracket. By collecting the vibration signal of the workpiece during processing and measuring the change in the surface roughness of the workpiece, and then analyzing the change in the machining performance of the shrink-fit holder under different clamping times, we were able to compare and verify the accuracy of the finite element fatigue analysis.

Design Theory and Experimental Research of Ultrasonic Fatigue Test

Ultrasonic fatigue testing is a key technology that is more efficient and energy saving compared to conventional fatigue testing. In order to investigate the behavior of metallic materials at ultra-high frequencies and to verify the validity of ultrasonic fatigue test results, this paper builds a test apparatus that can be used to conduct ultrasonic fatigue tests, and this paper proposes a complete procedure from theoretical analysis to the investigation of test laws for 20 kHz tensile and the compression test. Firstly, the initial sizes of the sample are calculated with an analytical method, then the three-dimensional model is simulated and optimized with finite element software, and the optimum result for the sample size is then obtained according to the sensitivity of the sample size to the effect of frequency. The next step is to analyze the influenced trend of the sample size, including L1, L2, L3, R1 and R2, on the resonant frequency and maximum stress of the sample. According to the optimized results, the sample was processed, and an ultrasonic fatigue test was carried out to ensure the sample fatigue fracture finally occurred. Finally, the S-N curve of the material was plotted based on the data recorded in the test and compared with the conventional fatigue life curve to verify the feasibility of the ultrasonic fatigue test device and test method. The fracture of the sample was observed using an optical microscope, and its macroscopic fracture morphology was analyzed. The fracture morphology of the sample can be divided into three typical zones: the fatigue crack source zone, the extension zone and the transient zone, where the fatigue cracks all originate from on the surface of the sample. The results demonstrate the validity of the ultrasonic fatigue test results and provide new ideas for the design and optimization of ultrasonic fatigue samples and shorter processing times, providing a reference for subsequent ultrasonic fatigue tests on typical materials.

Research on evolution behavior of 42CrMo microscopic fatigue short crack based on microstructure effect of material

To investigate the causes of damage dispersion in fatigue life of alloy materials, fatigue tests on 42CrMo are carried out under microscope with the aid of a micro fatigue testing device. The fatigue crack initiation and propagation evolution process of 42CrMo are studied on the micromechanical scale. The fatigue short crack and short crack growth rates are measured respectively under loads of 1400, 1550, and 1650 N. The experimental result shows that the initiation of fatigue short cracks is related to the randomness of microstructure defects. The initiation and propagation of fatigue short cracks on the surface of samples are random and local, while the propagation is characterized by first deceleration and then acceleration.

Assessment of cyclic fatigue resistance of Protaper Next and WaveOne Gold in different kinematics

BackgroundThe purpose of the current study was to inspect and compare the influence of applying continuous rotation and reciprocation motions on the cyclic fatigue resistance of Protaper Next (PTN) file (X2) and WaveOne Gold (WOG) Primary file in simulated canals. Twenty Protaper Next files(X2) and 20 WaveOne Gold Primary files were included in this study. A cyclic fatigue testing device was employed to test the cyclic resistance of each file in different motions. The testing device has an artificial custom-made stainless-steel canal with a 60° angle of curvature and a 2-mm radius of curvature. The files were randomly divided into 4 groups; group 1: PTN in continuous rotation, group 2: PTN in reciprocation, group 3: WOG in continuous rotation and group 4: WOG in reciprocation. All the instruments were rotated until fracture occurred, and the time to fracture was recorded in seconds using a digital chronometer. The number of cycles to fracture (NCF) was calculated. The data were analyzed statistically (p < .05).ResultsResults represented that when using either continuous rotation motion or reciprocating motion, WOG files showed a significantly longer time until failure than PTN files (p < 0.001). The time till fracture increased significantly, when using both types of files with a reciprocating filing motion.ConclusionWithin the confinement of this study, WOG file in reciprocation showed higher cyclic fatigue resistance than PTN in both continuous rotation and reciprocating motion. The reciprocating motion enhances both files behavior in terms of cyclic fatigue resistance.

Corrosion fatigue and electrochemical behaviour of steel wires used in bridge cables

AbstractIn‐service bridge wires often fail prior to the design life subjected to alternating stresses and environmental erosion. In this paper, a novel corrosion fatigue test device, integrating fatigue testing machine and electrochemical accelerated corrosion assemblies, was developed to characterize the corrosion fatigue and electrochemical behaviour of the wires. Using the developed device, corrosion fatigue tests of corroded bridge wires under different corrosion and loading conditions were conducted. Electrochemical characteristics, corrosion fatigue behaviour, failure mechanism, and so forth were investigated according to electrochemical measurements, fracture morphologies and the lifetime of wires. Results evidence the synchronization of corrosion and fatigue and show the accelerated corrosion due to static and fatigue stresses. Additionally, cracking and fracture induced by multiple crack initiation was dominant in corrosion fatigue of corroded wires, and the coexistence of multiple corrosion pits decreased the lifetime significantly.

Fretting manifestations in total hip prosthesis

This paper analyses the fretting and fretting wear phenomena to the classical and modular hip prostheses. Theoretical and experimental manifestations are studied, at the interface of the femoral stem with the bone cement mantle, at the taper junction between the femoral stem and the femoral head of the prosthesis, as well as at the tapering of the femoral neck adapter’s connections with the stem and the femoral head. The aim of the paper is to highlight the modularization implications of the femoral component of the Total Hip Prosthesis, especially its tribological implications (fretting wear of modular junctions, fatigue and corrosion by fretting) which can contribute to wear and increasing ion concentrations of the metal in the blood, and the possibility of the femoral shaft fracture at the femoral head junction. Theoretical approach described, allows the “Archard” law implementation to predict the fretting wear. Experimental laboratory studies focused on the analysis of the tribological phenomena occurring at the taper junctions between the femoral head and neck, as well as the neck and femoral stem, highlighting the relevant qualitative tribological aspects. For this purpose, experimental junctions were fabricated and tested on a universal MTS mechanical machine, equipped with a fatigue testing device.

In situ synchrotron ultrasonic fatigue testing device for 3D characterisation of internal crack initiation and growth

AbstractThis work presents a new ultrasonic fatigue testing device for studying the initiation and propagation mechanisms of internal microstructurally short fatigue cracks using in situ synchrotron tomography. Its principle is described as well as the method used for automatically detecting crack initiation and its subsequent growth. To promote internal crack initiation, specimens containing internal casting defects were tested between the high cycle and very high cycle fatigue regimes (107‐109cycles). Preliminary results show the ability of this new device to initiate an internal microstructurally short crack in a reasonable testing time and monitor its growth.

The Crack Nucleation Life of the TLP Flexjoint

Since the tension leg platform (TLP) needs to work in the ocean for a long time, it requires a high cost to replace any components. The working life is a key design element. The flexjoint is the crucial load-bearing component in the TLP mooring system. It has a multilayer metal/elastomer structure, and its working life generally depends on the rubber portion. In this paper, the fatigue life of flexjoint is calculated by crack nucleation method. Firstly, the dumbbell test piece is used to perform the uniaxial tensile fatigue test. The strain-fatigue life curve of the rubber material is obtained. The fatigue life of the flexjoint is calculated by the crack nucleation method. The fatigue test device of the flexjoint is developed, and the calculation result of crack nucleation life is verified by experiments.

A comparative analysis of cyclic fatigue of a new preheated machined CM wire endodontic files after exposure to different irrigants

AIM: Analysis of cyclic fatigue of a new preheated machined CM wire MPro endodontic files after exposure to lycopene, curcumin and Soduim hypochlorite for two different immersion observation periods; 5 minutes and 10 minutesMethodology: Eighteen size 20 MPro files were used in this study, divided into three groups of 6 files each according to irrigant used: Group I lycopene, Group II curcumin and Group III Soduim hypochlorite. All files were immersed in irrigants for either 5 or 10 minutes. The cyclic fatigue tess were performed on all files of both immersion periods using a static cyclic fatigue testing device, which have an artificial stainless steel canal and tested using a custom-made static cyclic fatigue testing apparatus. Parameters recorded were time to fracture, number of cycles to failure (NCF) and mean length of fractured segments.Results: Results showed no statistically significant difference between the different irrigants at the two observation periods and within the same group regarding time to fracture, number of cycles to failure (NCF) and mean length of fractured segments.Conclusion: All tested irrigants lycopene, curcumin and Soduim hypochlorite had same effect on cyclic fatigue of the preheated machined CM wire Mpro endodontic files when used for 5 or 10minutes.

The stress intensity factor calculation for combined sliding wear and fatigue of GH4169 superalloy based on three-dimensional simulation

In this paper, a sliding fatigue-wear methodology based on conventional rotating bending fatigue testing device is proposed. The crack propagation characteristics of GH4169 superalloy under plain fatigue and sliding fatigue-wear conditions are investigated by fatigue tests and SEM. In addition, the crack propagation and wear analysis are carried out with the finite element program ABAQUS and the three-dimensional fracture analysis software FRANC3D. The influence factors of crack growth rate including bending stress, contact stress and wear depth are investigated based on the stress intensity factor calculation and experimental measurements. The results show that the fatigue strength is severely decreased from 780 MPa to 200 MPa due to wear, although both contact stress state and material removal mechanism have positive effects on restraining the crack propagation acceleration. This competition between fatigue and wear is discussed and it is concluded that the fatigue defeats the resisting effect of wear and occupies the dominate position after the nominal crack length reaches a critical value. However, the wear volume and depth would increase the fatigue stress and accelerate crack propagation. Therefore, the positive and negative influence of wear on material fatigue lives also have a competitive mechanism and a correction model is carried out based on the classic Paris law.