Fatigue Characteristics Research Articles

Evaluation and prediction of material fatigue characteristics under impact loads: review and prospects

PurposeThe properties of materials under impact load are introduced in terms of metal, nonmetallic materials and composite materials. And the application of impact load research in biological fields is also mentioned. The current hot research topics and achievements in this field are summarized. In addition, some problems in theoretical modeling and testing of the mechanical properties of materials are discussed.Design/methodology/approachThe situation of materials under impact load is of great significance to show the mechanical performance. The performance of various materials under impact load is different, and there are many research methods. It is affected by some kinds of factors, such as the temperature, the gap and the speed of load.FindingsThe research on mechanical properties of materials under impact load has the characteristics as fellow. It is difficult to build the theoretical model, verify by experiment and analyze the data accumulation.Originality/valueThis review provides a reference for further study of material properties.

Replacement working body material as a way to increase reliability of road construction machines

Introduction. On the example of a motor grader knife, ways of increasing the reliability of road construction machines (RCM) operation are evaluated. For this purpose, the analysis of force effects nature on the working body of the RCM is carried out and its design features are highlighted (the presence of a welded joint). Based on the analysis, the range of characteristics necessary for making a decision on the possibility of replacement the material of the RCM working body is determined. Additionally, its thermocyclic treatment (TCT) is carried out. Experimental studies of the effect of this thermal impact type on the structure and properties of steels are described.Materials and methods. With the help of metallographic analysis, the author investigates the influence of the number of thermal effects cycles on the grain size and the complex of various materials physical and mechanical characteristics of road construction machines working body at various stages of the thermocyclic treatment.Results. It is determined that an increase in the level of the investigated steels physical and mechanical characteristics is possible through the use of TCT due to the obtaining of a fine-grained metal structure. The dependences of the main physical and mechanical characteristics of the investigated steels (ultimate strength and yield strength) on the number of thermal effects cycles are considered. Correlation relationships are selected to describe these dependencies. The relationship between the yield strength and ultimate strength of 09G2S and 30MnB5 steels and the grain size is considered. In addition, studies of the steels fatigue characteristics are carried out; data on determining the microhardness are presented for the welded joint. For various operating temperatures, fractographic studies are carried out on samples after cyclic loading.Discussion and conclusion. Based on a comparative analysis of the complex of physical and mechanical characteristics, the author made a conclusion about the possibility of replacing steel 09G2S with steel 30MnB5.

Effect of Material Change from 20MnCr5 to EN 353 on Fatigue Performance of Crown Wheel Pinion ( Hypoid Gear Sets) of Full Float Axles - Case study

Crown wheel pinion is a prime member in transferring the power from transmission to wheel ends in automotive truck axles. Gear material is one of the deciding factors to estimate the fatigue life of the part. Higher the fatigue characteristics of the material better the fatigue performance of the part. In this case study, heavy truck axle with particular size having deep gear ratio is considered for material change from DIN 20MnCr5 to BS-EN 353, because its challenging to meet the life requirement in deeper gear ratios typically above 6. The basic material comparison conducted for metallurgical properties, jominy values, heat treatment properties, fatigue endurance limits, impact strength & fracture toughness. The analysis shows the EN 353 has 50% better impact strength, 35% better fracture toughness & 6.5% better endurance limit than that of 20MnCr5. The impact strength of EN 353 is 50J where as 20 MnCr5 is 25J, the fracture toughness of EN353 is 99.5 MPa√m & that of 20MnCr5 is 64.3MPa√m. The fracture toughness is calculated using Roberts-Newton formula. The endurance limit for EN 353 is 1000MPa & that of 20MnCr5 is 935MPa. The case carburized results show EN 353 has better case structure than 20MNCr5. The total 12 Numbers of gear sets, 6 each for 20 MnCr5 & EN 353, are validated for gear set fatigue on bench for particular torque. The performance of EN 353 is 24% better than 20MnCr5. The fatigue life of EN 353 is 39983 Cycles & that of 20MnCr5 is 30212 Cycles. The fracture mode is same in both the grades & typical fracture is on the Pinion. This study shows us the material change over is contributed significantly by improving the fatigue life of crown wheel pinion particularly for deeper gear ratios in heavy truck axles.

Study on the P-S-N Curve of Sucker Rod Based on Three-Parameter Weibull Distribution.

During the oil production process, sucker rods are subjected to cyclic alternating load. After a certain number of cycles, a sucker rod can experience fatigue failure. The number of cycles is called fatigue life (N), and the accurate relationship between maximum stress (S) and fatigue life (N) under a certain reliability (P), namely the P-S-N curve, is an important basis for the reliability analysis and fatigue life prediction of sucker rods. The Basquin model, based on log-normal distribution, is widely used for fitting the P-S-N curves of sucker rods. Due to the limitation of this model, it is difficult to extrapolate the conclusion obtained from a finite fatigue region to the high-cycle or ultra-high-cycle fatigue region, which makes it impossible to estimate the fatigue limit of the sucker rod. Compared to the log-normal distribution, Weibull distribution causes the sucker rod to have a minimum safety life, namely the safety life at 100% survival rate, which complies with the fatigue characteristics of the sucker rod and is more in line with the actual situation. In this study, the fatigue data for ultra-high-strength HL and HY grade sucker rods were obtained through experimental fatigue tests. A new fatigue life model was established and the P-S-N curves of two types of ultra-high strength sucker rods were obtained. For HL- and HY-type ultra-high strength sucker rods, the average error between the fitting result and fatigue test value is 1.25% and 4.39%, respectively. Compared to the S-N curve fitting result obtained from the Basquin model commonly used for sucker rods, the new model based on three-parameter Weibull distribution provides better fitting precision and can estimate fatigue limit more accurately, so this model is more suitable for estimating fatigue life and can better guide the design of ultra-high strength sucker rod strings.

Investigation on Strain Characteristics and Fatigue Constitutive Model of Limestone under Osmotic Pressure and Cyclic Disturbance Coupling

The existing fatigue models are not sensitive to load cycles and do not consider the effect of osmotic pressure. To study the strain characteristics and fatigue constitutive model of limestone under osmotic pressure and cyclic disturbance coupling, 300 cycles of loading and unloading tests under different osmotic pressures were carried out and the evolution characteristics of irreversible accumulative deformation curve were analyzed. Then, an improved Nishihara fatigue model was established based on the theoretical results of rheological model by introducing the nonlinear function into Nishihara model. The results show that the irreversible cumulative deformation under different osmotic pressures experiences three evolutionary processes of initial deformation stage, stable deformation stage, and accelerated deformation stage with increasing cycle indexes, showing the typical fatigue deformation characteristics. The axial deformation at initial deformation stage increases significantly, the stable deformation stage shows approximately linear growth and accounts for 40% to 73% of total cycle indexes, and the accelerated deformation stage shows a sudden increase indicating the overall instability of limestone. The nonlinear function is introduced into the Nishihara fatigue model based on rheological theory, and a fatigue deformation model that can reflect the entire process of irreversible accumulative deformation curve is established. The physical meanings of model parameters are discussed, and the relationships between model parameters and cycle indexes are inverted. The model parameters have good convergence and verify the rationality and applicability of the fatigue constitutive model based on experimental data. The results have reference value for revealing the fatigue characteristics of rock under osmotic-cyclic stress coupling.

Applications of continuum fatigue risk monitoring in riser connectors system integrity management

This paper discusses the effects of marine riser connectors (MRCs) on fatigue failure risk using multi-coupling models. When MRCs are subjected to vortex-induced fatigue, a risk early warning strategy is used for effective risk monitoring as a preventive measure for the operation of MRCs. To ensure safe marine oil and gas production and to improve fatigue failure prevention and control, research on offshore structural fatigue risk failure theory criteria and evaluation and the vibration fatigue characteristics of MRCs over time and frequency is characterized. By coupling data-driven technological means, including rain-flow counting (RFC), Hilbert–Huang transform (HHT), power spectral density (PSD), artificial neural network (ANN), risk-based inspection (RBI), and risk management measures (RMM) to assess the fatigue risk characteristics of in-service members in special offshore environments. The fluid-structure interaction characteristics of MRCs and a load spectrum are analysed by empirical mode decomposition (EMD) to determine the changes in the components of an intrinsic mode function (IMF) and investigate the degree of fatigue damage. The fatigue damage of MRCs is predicted using the PSD of the IMF and the RFC of the IMF-coupled ANN time series prediction model. The results show that using any IMF component or combined component data as input to the ANN and training set facilitates cross-validation of the analysis. When the input layer and a hidden layer of the ANN are optimized and properly trained, the predicted performance is suitable. Through early warnings and coordination, the spread of fatigue failure risk trends can be predicted, and warning information is issued accordingly.

Effect of stress on the phase transition and optimizing electric-induced strain behavior of Bi0.5Na0.5TiO3-SrTiO3 lead-free co-fired multilayer piezoactuators

A series of (1-x)Bi1/2Na1/2TiO3-xSrTiO3+0.05 wt% MnO2 lead-free multilayer piezoactuators was prepared using a tape casting method, and the field-induced strain performance, temperature stability, electric fatigue and load characteristics were evaluated to assess potential practical applications. In contrast to traditional PZT ceramics, the fabrication of BNT bulk ceramics into multilayer piezoactuators provides significantly decreased strain (S)-electric field (E) characteristics as a result of internal compressive residual stress. The inactive edge distance, sintering temperature and layer thickness were all found to affect the compressive residual stress of the actuator. Through reconstructing the material composition and structure of BNT-ST actuators, active strain (0.168 %, 2 kV/mm), total strain (>0.15 %, E ≤ 2.5 kV/mm) and blocking stress (42.6 MPa) were realized in BNT-based cofired multilayer actuators, displaying a better performance than commercial PZT actuators. These results indicate that environmental-friendly BNT-based lead-free multilayer piezoactuators are promising candidates with regard to practical applications.

Effect of operating parameters on functional fatigue characteristics of an Ni-Ti shape memory alloy on partial thermomechanical cycling

In this study, the influence of upper cycle temperature (maximum temperature in a cycle) and the magnitude of applied stress on the functional properties of an SMA during partial thermomechanical cycling has been studied. A near-equiatomic NiTi SMA was chosen and tested under different upper cycle temperatures (between martensite finish (Mf) and austenite finish (Af) temperatures) and stress level (below and above the yield strength of the martensite). The upper cycle temperature was varied by controlling the magnitude of the current supply. The results show that a raise in the upper cycle temperature causes the permanent strain to increase and also lowers the stability. However, decreasing the stress imposed to a value lower than the yield strength of the martensite improves cyclic stability. The upper cycle temperature was found to influence the crack nucleation, whereas the applied stress level the crack propagation during partial thermomechanical cycling of SMAs. Therefore, decreasing the upper cycle temperature as well as the magnitude of stress applied to lower than the yield stress of martensite have been found to be suitable strategies for increasing the lifespan of SMA-based actuators during partial thermomechanical cycling.

Evaluations of microstructure and fatigue properties of Ti-Ta alloys

In recent years, the demand for implants has increased in the orthopedic field due to the aging of the population. Among them, Ti-6Al-4V alloy is very often used. However, its high Young's modulus and cytotoxicity are regarded as problems. Therefore, we are focusing on titanium and tantalum, which are highly corrosion-resistant elements, and are developing Ti-Ta alloy, which is a β-type titanium alloy that exhibits low Young's modulus and low cytotoxicity. Furthermore, from the viewpoint of safety and durability, both high strength and low elasticity and excellent fatigue characteristics are required. In this study, we identified the microstructure and crystal structure of 4-types of heat-treated Ti-Ta alloys. In addition, torsional fatigue and plane bending fatigue tests were performed. By comparing these results, we investigated the relationship between structure and fatigue characteristics. From SEM and TEM observation, EBSD and EDS results, it was found that Tantaulum was dissolved in the β-Ti matrix in any heat treatment conditions. Furthermore, α-Ti was deposited at the grain boundaries by 500℃ aging. It was also found that the average crystal grain size increased due to the increase in the solution temperature and the aging treatment. Then, the torsional fatigue characteristics improved as the crystal grain size became smaller. The plane bending fatigue characteristics were improved by strengthening precipitation with α-Ti.

A Novel Learning Model of Driver Fatigue Features Representation for Steering Wheel Angle

In the field of advanced driver assistance systems (ADAS), effective learning of driver fatigue characteristics representation is a major challenge due to uncertainties of both real roads and drivers. To tackle this problem, this paper proposes a novel model of learning interpretable representations for fatigue features, so as to improve the performance of the monitoring system on real roads through the learned features. First, the approximate entropy of the Steering Wheel Angle (SWA)sequence is used to crop adaptive lengths of the Recurrent Neural Network (RNN) input data. Then, it will learn statistical indexes to discover the random steering characteristics. The Long Short-Term Memory (LSTM) unit can memorize drivers’ long-term operating characteristics and instantaneous change patterns, and mine their fatigue characteristics. Finally, the information gain method is used to discover the strong correlation between potential characteristics and fatigue levels, thereby obtaining the best feature representation for driver fatigue. The proposed method makes use of the advantages of recurrent neural network learning to explicitly capture various potential characteristics of fatigue driving and interactions between non-linear characteristics in driving. Experimental results on real driving data validate the effectiveness of our proposed method.

Stress Analysis and Fatigue Life Prediction of Contact Wire Located at Steady Arms in High-Speed Railway Catenary System

In an electrified railway system, the pantograph on the train roof is used to collect the electric current through a sliding contact with the contact wire (CW) of the catenary. The CW is mounted laterally in a zigzag relative to the track centerline with the help of a steady arm to ensure symmetrical wear on the pantograph’s strip, which is beneficial to slow the wear process and extend the service life. Under the pantograph’s impact, the CW around the steady arm forms a stress concentration and has been recognized as a vulnerable point in the catenary system. This article performed a uniaxial tensile test and high-cycle fatigue test to measure the mechanical properties and fatigue characteristics of Cu–Mg alloy that is used for manufacturing high-speed CW. A stress analysis method is proposed based on the combination of the pantograph–catenary interaction model and the solid CW specimen model. In the pantograph–catenary interaction simulation, the catenary is modeled using the Euler–Bernoulli beam element. The 3-D solid element is used to model the CW segment. The nodal displacements of the CW segment obtained from the pantograph–catenary interaction simulation are transferred to the CW specimen model. The stress distribution on the CW section and the entire multiaxial transient stress field are analyzed. Based on fatigue test results and stress time history data obtained by simulation, using the nominal stress method, the uniaxial fatigue and multiaxial fatigue analyses are performed to reveal the fatigue characteristics with different speed classes. The results indicate that the weakest points appear at both the wing point and the top point on a CW section. The CW’s fatigue life reduces by over 50% when the speed class is upgraded from 350 to 400 km/h.

Study on the impact of Nano-reinforcements on the fatigue strength of adhesive joints

Single overlap joints had been created by combining two AISI 302 stainless steel sheets with the help of 3 M DP270 grade epoxy and their fatigue characteristics were examined under shear stress condition. Further, the effect of adding three distinct proportions of nano-titania with epoxy, on the mechanical characteristics of the joint was analyzed. The overlap lengths was selected as 20 mm and nano-titania proportions were elected as 1.0%, 2.0% and 4.0%, respectively during shear load condition. When the experimental findings were analyzed, it was shown that the mean damaging load associated with the usage of nano-dispersed adhesives rose significantly in general. As a consequence of the trials, it was discovered that the most effective nanoparticles proportion for boosting the fracture strength of adhesive joints is 4.0 percent, and the enhancement in rate of failure strength increase was noted as 85.52 percent. Additionally, it was shown that strain of nanoparticle had a noteworthy role in the shear characteristics of the adhesive junctions. Additionally, it has been shown that incorporating nanoparticles into the glue enhances junction extension. When the adhesive interfaces of the specimens were inspected, impairment was detected as adhesion dissociation, but nanoparticle replenishment had been detected as a combination of cohesive as well as adhesive characteristics.

ИССЛЕДОВАНИЕ ХАРАКТЕРИСТИК ПРОЧНОСТИ СИНТЕЗИРОВАННОГО СПЛАВА СИСТЕМЫ Co–Cr–Ni–W–Ta

Additive manufacturing is increasingly used in the aviation industry. Its main feature is the manufacture of parts of complex external and internal geometric shapes without increasing the cost of their production. To calculate the resource of nodes and reliable operation of new equipment, it is necessary to have a set of calculated values of characteristics of structural strength, including the characteristics of tensile, creep rupture and high-cycle fatigue (HCF). The study of characteristics of tensile, creep rupture and HCF of the Co–Cr–Ni–W–Ta alloy obtained by the method of selective laser melting (SLM) is presented in this paper.

A study on dynamic characteristics of muscle strength and muscle fatigue in hip abduction of healthy subjects:

A study on dynamic characteristics of muscle strength and muscle fatigue in hip abduction of healthy subjects:

Micro-mechanism associated with very high cycle fatigue crack initiation of advanced DQ&P processed steel

In the present study, very high cycle fatigue (VHCF) characteristics and properties of a direct quenched and partitioned (DQ&P) medium carbon (0.4 wt.% C) steel having ultrahigh-strength (UTS > 2 GPa) was investigated using an ultrasonic-fatigue testing technique (∼19 kHz frequency) up to ∼1010 cycles at the load ratio (R) of −1 (fully reversed tension-compression). The occurrence of crack initiation in the VHCF regime was observed at interior non-metallic inclusions. The microstructural changes following VHCF failure underneath the fracture surfaces near the crack initiation sites were further investigated through transmission electron microscopy. Formation of a clear nanograined subsurface layer adjacent to the crack initiating site at the interior inclusion was noticeably evident. The variation of average grain size (60 − 140 nm) and thickness (300 − 1200 nm) of nanograined layers at different number of cycles to failure were measured in detail. Apparently, localized plastic deformation caused the fragmentation of martensitic laths and hence, the formation of aforesaid ultrafine-grained layers in the microstructures.

Effects of Microstructure on the Buckling Fatigue and Functional Degradation Characteristics of the Tape-shaped Cu-Al-Mn Shape Memory Alloy Element

Shape memory alloys (SMAs) are functional materials with high shape memory and super elasticity effects that are used in a wide range of fields, including medical and engineering fields. Our research group has focused on the negative stiffness characteristics of plate-shaped SMA during buckling deformation and has attempted to apply them to vibration-isolation devices. The buckling properties of Cu-Al-Mn SMA, which exhibits almost the same super elastic properties as Ti-Ni SMA, were evaluated in comparison with those of Ti-Ni SMA. The results showed that Cu-Al-Mn SMA is more suitable for vibration isolators because of its smaller change in post buckling properties due to temperature change and smaller hysteresis compared with Ti-Ni SMA. In addition, the buckling fatigue and functional degradation properties of Cu-Al-Mn SMA were studied. As a result, it was clarified that fatigue failure is basically caused by the propagation of cracks originating from grain boundaries, and that the increase of these cracks is the cause of the decrease in buckling load. In this study, the buckling fatigue properties of Cu-Al-Mn SMA material in which bainite phase is formed at the grain boundary by changing the heat treatment conditions were investigated, and the effects of the differences in internal microstructures on the buckling fatigue and functional degradation properties of plate-like Cu-Al-Mn SMA with different internal microstructures were compared with those of conventional Cu-Al-Mn material. The effects of different internal microstructures on buckling fatigue and functional degradation properties of plate Cu-Al-Mn SMA with different internal structures were investigated. The results show that the specimens with bainite phase have superior fatigue properties, but in terms of functional degradation properties, they increase the rate of decrease in Pcr and increase the rate of increase in tangential stiffness after buckling.

FATIGUE IN MULTIPLE SCLEROSIS

The article discusses and analyzes literature data on the phenomenon of fatigue in patients with multiple sclerosis. More than 80% patients with multiple sclerosis complain of fatigue, which significantly limits their functional capacity and negatively affects the quality of life. In general, fatigue is a complex, multidimensional phenomenon that consists of subjective (one's own feeling of fatigue) and objective (quantitative characteristics of fatigue when performing a certain activity) components. At present, the most accessible method of fatigue assessment is patient survey. In multiple sclerosis, fatigue can be primary (as a direct consequence of the disease) or secondary (as a consequence of reduced functional capabilities, sleep disorders, chronic pain, side effects of medications, etc). In general, fatigue in multiple sclerosis is a heterogeneous phenomenon based on various etiopathogenetic mechanisms. We reviewed neuroimaging markers of global and focal lesions of the white and gray matter of the brain that are associated with the presence of fatigue in patients with multiple sclerosis. The impact of peripheral immune-inflammatory processes on the fatigue occurrence was shown which was realized via humoral, cellular, and neuronal mechanisms. We analyzed the role of inflammatory processes in the brain and spinal cord in the form of activation of microglia with hyperproduction of cytokines, which ultimately disrupts dopamine metabolism and reduces the affinity of dopamine receptors. The excess activity of certain functional components of the nervous system in the form of higher engagement of the motor structures of the brain and spinal cord during the performance of standard motor tasks was highlighted. The role of disruption of interoceptive mechanisms (perception and monitoring of the body's internal environment via hormonal, immune, metabolic, temperature, pain, and visceromotor signals) in the occurrence of fatigue in multiple sclerosis was shown. The paper underlines modern principles of fatigue correction based on these mechanisms.

Some problems of the new radiation-resistant rubber mechanics in vibrating machines at hard γ-radiation

AnnotationToday, the sources of ionizing radiation are present in various spheres of human activity: during the uranium ore extraction, processing and benefication, in medicine, at exploration of outer space, in nuclear power plants, etc. Here rubber is used as insulating and protective materials, sealers, elastic links, dampers and wear-resistant linings of machines. Therefore, a problem of creating new radiation-resistant rubbers capable to operate in a radiation zone for a long time with no significant changes in their physical and mechanical parameters and durability is of great importance. In this work, some aspects of creating such rubber for use in vibrating machines (screens, feeders, conveyors) operating under extreme conditions while mining and processing of uranium ores are discussed. In our case, the extreme conditions include high long-term stationary cyclic loads, high and low temperatures and exposure to hard γ-radiation. Under such conditions, rheological and fatigue characteristics of rubber differ from those demonstrated under normal conditions, and such factors as dissipative heating, changes in characteristics over time (aging effects), development of damageability, etc., become essential and must be taken into account when choosing a proper type of rubber.

3-Dimentional Elucidation of Fatigue Characteristics and Fracture Morphologies in Spot Welding Joints of High Strength Steel

In order to investigate the three-dimensional fatigue properties of resistance spot welded joints made of high strength steel, this study was carried out observed three-dimensional fatigue cracks and calculated stress intensity factors using fem analysis. In addition, this study was conducted under shear mode and pure shear mode to investigate the influence of loading mode during fatigue testing. As a result, it was found that a new crack growth behavior branched in the welding circumferential and width direction under the low loading force range. However, all the cracks leading to final fracture were of the same type, and it was confirmed that the fatigue strength was not affected by a new crack growth behavior. Moreover, the results of observed initial fatigue crack growth angles and the calculated stress intensity factor, KIθ, were in close agreement, which proved that the fatigue crack growth behavior was strongly influenced by the fracture mechanics.

Characteristic evaluation of wear of mass finished surface of medical-grade Co-Cr alloys with shot-peening

The design life of artificial joints is 10 to 20 years and in an aging society, improvements in durability are expected. Therefore, as a method for improving fatigue characteristics, the authors have expected the effect of shot peening and reported that the fatigue properties of the Co-Cr alloy, which used as an artificial joint material, treated with Shot peening (SP) are significantly improved. In addition, mass finishing (MF) was applied to smooth the surface of the shot-peened Co-Cr alloy. It was confirmed that the high-performance layer obtained by the SP remained and was maintained. However, the wear properties using this method have not been verified.