Fatigue Properties Of Materials Research Articles

Basic mechanical and fatigue properties of rubber materials and components for railway vehicles: A literature survey

Abstract Rubber material is widely used in railway vehicles due to its superior damping performance. The testing methods, fatigue, and aging theories of rubber materials are of great significance to improve the design, manufacture, and application of rubber components for railway vehicles. This work systematically introduces the constitutive theory, mechanical testing standards, and testing methods of rubber materials. Then, the aging mechanism is described and the research progress of rubber fatigue properties is reviewed from the perspectives of fatigue crack initiation and fatigue crack propagation. Moreover, the reinforcement methods of rubber materials are presented. Finally, according to the working conditions of rubber components in railway vehicle, the technical difficulties and future research trends of fatigue characteristics analysis of rubber materials and components are pointed out.

A compendious review on fatigue properties of the bio‐nanocomposites

AbstractIn this present work, a review of fatigue strength on bio‐nano composites was presented. Generally, the biocomposites possessed higher fatigue strength than the conventional materials. Because the propagation in biocomposites can be arrested due to their internal structure, whereas the damages occur in the matrix and/or at the fiber/matrix interface region. In the case of conventional materials, the cracks would rapidly grow until a catastrophic failure occurs. Thus, the S–N curves of composites show a flatter curve when compared to the conventional materials. In terms of fatigue properties, conventional fiber‐reinforced composites (e.g., glass and carbon‐reinforced composites) were more extensively studied than bio‐based reinforced composites. Examining the fatigue properties of materials is significant for all engineering‐based applications. Because the fatigue failures can occur below the ultimate tensile strength of materials. However, the fatigue performance of the composites can be enhanced by improving the fiber‐matrix interfacial bonding resulting from surface treatment of fibers and incorporating nanofillers within the matrix, and so forth. Since the nanocomposites have a larger surface area and aspect ratio, they are preferred to use in many applications: aerospace, automotive, biotechnology, construction, and building, electronics, marine, and packing industries. Thus, this chapter starts with the unique advantages of bio‐nano composites. Then, the fatigue properties of bio‐nano composites, the significance of the S–N diagram, and the pattern of fatigue testing were discussed. In order to understand the fatigue behavior, several factors such as structure, fillers, fabrication techniques, and so forth were included. Challenges of fatigue strength of biocomposites were also summarized.

Fracture mechanism of a Ni-base alloy under high-temperature cyclic deformation: Experiments and microstructure characterization

The components of power generations are subjected to the repeated thermal strain, owing to the temperature fluctuations associated with start-up and shut-up. Therefore, fatigue properties of the candidate materials are essential to be understood. To fully elucidate the fracture mechanism and microstructure evolution of the Nickel-based alloy under high-temperature cyclic loading, low cycle fatigue tests were carried out under the strain amplitude of 0.4%, in which temperature was in the range of 700–800 °C and strain rates from 5 × 10−4 s−1 to 5 × 10−3 s−1. The fatigued specimens were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), and electron backscatter diffraction (EBSD) observations. Slip band deformations mainly dominated under the temperature of 700 °C and 720 °C, and paralleled dislocation transmissions around twin boundaries were dominant under 750 °C. While free dislocation lines were typical dislocation configurations in 800 °C. Due to stress concentration caused by the accommodated dislocations, some cracks preferred to propagate along the twin boundary. Molecular dynamics simulated the dynamic interaction between dislocation and twin boundary at 750 °C. Dislocation movement was constrained on the twin boundary, which was verified by molecular dynamics simulations. As the temperature increased, the strength of the grain boundary degraded, and the fracture pattern changed from totally transgranular to both transgranular and intergranular cracking.

A critical comparative review of cavitation peening and other surface peening methods

Mechanical surface modification such as shot peening offer powerful enhancement of fatigue properties of metals and other materials. Cavitation usually causes surface damage in hydraulic machineries. However, careful selection of process parameters allowed developing an approach known as “cavitation peening.” Its advantage is surface roughness increase is lower than in conventional shot peening as there are no solid collisions involved. As cavitation is a hydrodynamic phenomenon, an understanding of both fluid dynamics and materials science is required. Cavitation peening is distinguished from “water jet peening,” in which water column impulse is used. Another flavor is “Submerged laser peening” that involves the use of a pulsed laser and can be considered a type of cavitation peening where cavitating bubbles are generated due to laser ablation. Ultrasound vibration, a popular method for generating cavitation for cleaning, has also been adapted for cavitation peening. The present comparative review presents key insights and achievements and addresses future directions that are required for advancing cavitation peening technology by considering the mechanisms of cavitation peening based on the reported data for water jet, pulsed laser, and ultrasonic cavitation peening. The data and methods are critically considered and summarized in comparison with shot peening. Strategic view of future challenges is presented. • Fatigue resistance enhancement using water jet, pulsed laser and ultrasonic cavitation peening was quantified • Cavitation peening using jet, pulsed laser & ultrasonic enhanced fatigue properties • Cavitation peening clearly distinguished from water jet peening • Cavitation peening benefits shown to exceed those by shot peening • Dislocation density induced by cavitation peening was lower than by shot peening • Importance of vortex cavitation is shown for experimental and numerical future work

High cycle fatigue performance evaluation of a laser powder bed fusion manufactured Ti-6Al-4V bracket for aero-engine applications

Due to the stringent certification requirements and complex engine operating environment, the design of AM components for aero-engine application remains a challenging task. The high cycle fatigue performance of a weight-optimised bracket made using the Laser Powder Bed Fusion (LPBF) process was studied through shaker table testing. The results are discussed together with the observed mechanical and fatigue strengths in conjunction with material characterisation of microstructure, surface roughness, defects, micro-hardness and fracture surfaces. The debits in mechanical and fatigue strengths are expected due to process dependent surface roughness and the density of defects present. From the shaker table test results, it was concluded that the proposed weight-optimised LPBF bracket is capable of meeting the performance targets. The fundamental vibration mode of the bracket assembly was 84 Hz, which was much higher than the 1st Low Pressure shaft speed (48 Hz) of the target engine and thus avoids potential resonance. The bracket achieved its target inertial g load capability of 20 g and it was demonstrated that the bracket had enough redundancy in its load transfer paths should a strut fail during service of the engine. Lack of fusion voids and micro-cracks present on or near the surface were the prime sites for crack initiation. It has been shown that the as-built surface can cause a significant reduction (up to 40%) in the fatigue strength when compared to machined Ti-6Al-4V. A safe life regime for LPBF component design has been presented based on the Kitagawa-Takahasi diagram, modified using the Chapetti curve, which effectively links the material fatigue properties and performance of LPBF parts with intrinsic defects.

Fuzzy Approach for Reliability Modeling of Lead-Free Solder Joints in Elevated Temperature Environmental Conditions

The mechanical and fatigue properties of microelectronic interconnection materials are important issues in critical applications in the life of electronic assemblies. Due to the growth in the applications of electronic components in new technological products used in tough conditions, evaluating the reliability of solder alloys has become crucial to the prediction of product life. SAC (Sn-Ag-Cu) solder alloys are common lead-free alloys used to form solder joints. In the current study, the reliability of individual SAC305 solder joints in actual setting conditions with an organic solderability preservative (OSP) surface finish was examined using an accelerated shear fatigue test at different load levels (16 MPa, 20 MPa, and 24 MPa). Four operating temperature levels (−10, 25, 60, and 100 °C) were also used. Seven samples were utilized at each experimental condition. An orthogonal array (L12) was employed for this experiment. The fatigue behavior of the SAC305 solder joints in actual setting conditions was described by a two-parameter Weibull distribution. The characteristic life and the shape parameter were extrapolated from the Weibull distribution for each experimental condition. Characteristic life was employed to represent the fatigue resistance of the solder joints. For each sample, the inelastic work per cycle and plastic deformation were determined. The results indicated a notable increase in the inelastic work per cycle and the plastic strain as a result of increasing either the stress load or the working temperature. Combinations of stress amplitude, working temperature, inelastic work, and plastic deformation were applied as inputs to the fuzzy system for computing a comprehensive output measure (COM-Value) using the Mamdani method. A negative relationship was observed between the solder life and the four fuzzy inputs. To fuzzify the inputs of the fuzzy system, two membership functions, “MFs”, were formed for each input, and five MFs were set for the output. The center-of-gravity (COG) theorem was utilized as a defuzzification method in the fuzzy inference system. The characteristic life of the solder joints was predicted by the COM-Value, which was used as an independent variable. Finally, The COM-Value was used to generate a general predicted reliability model for SAC305 solder joints with an acceptable model adequacy index.

Influence of Wet or Dry Conditions on the Fatigue Life of Grout Cementitious Materials under Cyclic Loading

Grouting cementing material is a kind of sealing cementing material widely used in underground space. However, the influence of the fatigue life after cementation hardening is often ignored when subjected to, for example, cyclic traffic loads. Therefore, it also often causes engineering problems such as joint cracking, leakage, and plate bottom emptiness. The prediction of fatigue life of grouting cementation material is of great significance to the stability of underground tunnel structure. In this paper, the fatigue characteristics of hardened grout specimens under different fatigue loads and cycle frequencies are studied. Test the cyclic compression load repeatedly in different environments (dry or wet). The results show that the fatigue properties of grout materials are reduced in both air and water and significantly reduced when the stress level is 65% or above of static compressive strength in wet environment, especially when the loading frequency in water drops from 10 to 35 Hz. The main mechanism of fatigue life decline is splitting effect caused by water extrusion in the sample under cyclic loading. Water washes away abrasive action in the cracks. The dry-wet fatigue aging characteristics of superhigh strength grout cement materials lay a foundation for the evolution simulation of underground foundation structures under cyclic loading.

The Impact of Conventional Power Block Startup Procedures on the Fatigue Behavior of Drum Materials

Varying demands for electricity within the energy sector require the modification of operating modes to ensure both an uninterrupted electricity supply and the upholding of safety standards. This paper presents a method for the prediction of drum fatigue life, via the local analysis of stress–strain fields and low-cycle fatigue tests of the drum material. The analysis compares the fatigue properties of an unused material and a material that has undergone many years of operation. In addition, this paper suggests drum operating conditions based on the results of load testing under industrial conditions. The drum model was developed on the basis of technical documentation. The analysis includes the calculations of time-dependent temperature distributions, stresses, and strains for various drum startup modes. The drum material fatigue properties are determined under low-cycle conditions. Using the modeling results and fatigue properties, predictions of drum life for different startup modes are presented. The paper summarizes the impact of a range of startup procedures and the drum material fatigue properties on the fatigue life of a working drum, under various mechanical and thermal loads. In addition, this paper proposes a methodological approach to fatigue life assessment, as a combination of multiple research methods.

Experimental and Numerical Investigation on Fatigue Properties of Carbon Fiber Cross-Ply Laminates in Hygrothermal Environments.

The fatigue properties of composite materials are degraded seriously in hygrothermal environments, so taking into account their influence is very important when evaluating the fatigue life of composite structures. Tensile fatigue experiments of carbon fiber reinforced resin composite cross-ply laminates were conducted in room temperature/dry (RTD), cool temperature/dry (CTD) and elevated temperature/wet (ETW) conditions. The S-N curves and fatigue failure modes of the cross-ply laminates were obtained in three conditions. On this basis, a finite element model was established to discuss the influence of temperature and moisture content on the fatigue properties, as well as a method for determining environmental factors of fatigue life of cross-ply laminates was established. The results show that the saturation moisture absorption and temperature have a significant influence on the tensile fatigue properties of cross-ply laminates. The high-cycle fatigue property is weakened significantly by the saturation moisture absorption and high temperature, but the low-cycle fatigue properties were strengthened in cool temperature conditions. The delamination failure mode in ETW is the most severe, presenting with an obvious necking phenomenon. The influence of temperature has a greater effect than that of moisture content, but moisture absorption would play its affect obviously when temperature exceeds 40 °C.

Literature Review on the Fatigue Properties of Materials Processed by Surface Mechanical Attrition Treatment (SMAT)

As a promising surface treatment technique, the surface mechanical attrition treatment (SMAT) has been applied to enhance mechanical properties of various materials. Through multidirectional severe plastic deformation, SMAT is able to nanocrystallize the near surface region of materials. The nanostructured layer associated with high compressive residual stresses coupled with a work hardening layer can provide the treated materials with an improved fatigue resistance. The present work gives a comprehensive review on the fatigue strength of SMATed materials. First of all, a brief introduction is given on the basic elements of SMAT and surface modifications induced by this treatment. The fatigue strength of a large variety of SMATed materials with different loading conditions is reviewed, including low-cycle fatigue (LCF), high-cycle fatigue (HCF) and very-high-cycle fatigue (VHCF). Then, the mechanism of enhancement or reduction is explained through a detailed review on the effects of several factors, such as residual stress, surface quality and nanocrystalline grains. In addition, the combined effect of SMAT coupled with other processes is also reviewed. Trends and prospects of the current research are summarized at the end.

Effect of Cr, Mo, and V Elements on the Microstructure and Thermal Fatigue Properties of the Chromium Hot-Work Steels Processed by Selective Laser Melting

Thermal fatigue is the main failure mode for chromium hot-work steels. In this study, pre-alloyed chromium hot-work steel powders with three different Cr, Mo, and V addition levels (low content (LH), medium content (MH), and high content (HH)) were used for selective laser melting (SLM). The microstructure and thermal fatigue properties of these SLM-processed materials were investigated. After thermal fatigue tests, LH possessed the lowest hardness (approximately 573 HV5) and longest crack length, MH possessed the highest hardness (approximately 688 HV5) and HH (with the hardness of approximately 675 HV5) possessed the shortest crack length. It can be concluded that the increase of V content in MH is the main reason for the refined grains which result in an enhanced hardness and thermal fatigue resistance compared to LH. The further increase of the Cr and Mo content in HH leads to the grain coarsening and hardness decreasing, which is supposed to degrade the thermal fatigue resistant properties according to the conventional theory. However, HH exhibited an enhanced thermal fatigue resistance compared to MH. That is because the higher stored energy in MH deteriorated its thermal fatigue resistance compared to HH.

Experimental study on low-cycle fatigue and recovery properties of viscous material for viscous damping wall

This paper aims to study the low-cycle fatigue property and recovery properties of viscous material. The authors designed a Self-Stabilization Dynamic Sandwich-Type Shear (S-DSTS) test device, which allows the static recovery of semisolid materials that can not be achieved in the traditional rheometer. A series of recovery tests with different static recovery times and low-cycle fatigue tests with different strain amplitudes and loading frequencies were conducted on the polyisobutylene-B12 (PIB–B12) by this device. The test data on low-cycle fatigue and recovery properties of PIB-B12 were evaluated by the storage modulus, loss modulus, loss factor, velocity exponent, parameter decay ratio, and recovery coefficient. The results show that each parameter's degradation rate and degradation degree increase significantly with the rise of strain amplitude. The low-cycle fatigue property of PIB-B12 is less affected by the loading frequency, and the degradation rate and degradation degree of all parameters are similar under different loading frequencies. The PIB-B12 has excellent recoverability and static recovery showing that the mechanical parameters of PIB-B12 could restore to more than 65% and 92% of the original magnitude after short-term and long-term intervals, which ensures a reliable energy absorption property during aftershocks. The velocity exponent of PIB-B12 shows minor variations under different strain amplitudes and loading frequencies.

An Investigation on Fatigue Resistance of Notched Long Fiber-Reinforced Composite Materials

A new type of specimen is proposed for further research on the structure of glass-fiber-reinforced resin matrix composite lamina, which holds the potential to significantly improve the fatigue property of materials while having limited effect on the tensile strength. Herein, the fatigue life, based on the monotonic tensile test, was simulated utilizing ANSYS and nCode analysis software. The results show that the tensile strength of the local notched fiber specimens is slightly lower than that of the continuous long-fiber specimens. However, when extending the notches’ longitudinal distance, the impact to tensile strength becomes smaller and smaller. The results show that, when the longitudinal distance of the notched fiber is greater than 80 mm, the reduction in tensile strength is less than 0.65%. At the same time, the fatigue property of the specimens is improved considerably. It has been found in this experiment that when the notches’ longitudinal distance is 100 mm, the notches’ length is 1.5 mm, and the notches’ width is 1.75 mm, the fatigue cycles number of the specimens reaches 126,000 cycles, which is about 180% higher than that of the 0-0 type long fiber specimens without notches. This investigation provides a robust foundation and is a compelling basis for further exploration of new fatigue specimens.

Investigation of the Effect of Dwell Period in Load Controlled Fatigue Tests of Inconel718 Superalloy

The mechanical property of Inconel718 is examined in terms of fatigue behavior. The main concern of this work is to determine the material's fatigue properties under pure bending fatigue conditions with additional interruptions and thermal effects. Test conditions will include room temperature, 450°C, and dwell times to simulate the material's operating environment in the engine application. Additional to fatigue testing hardness measurements and nano indentation testing were performed at ambient temperature. Fractographic and microstructural examinations of the tested specimens are performed with an optical microscope and SEM (scanning electron microscope) to understand the material's reaction to different deformation factors.

Use of elastomers as pressure media for fatigue testing of cold forging tools

Cold forging has high potential as a sustainable production technology. With net-shape production, only the material needed for the produced part is used. By not heating up the workpiece, energy consumption is also low. However, this leads to high forming forces and consequently critical stresses in the tools. An accurate prediction of tool life is therefore necessary; both to find measures for its increase and to plan tool changes with minimal machine downtime. Currently there is little data about the fatigue properties of cold forging tool materials. Existing tests to determine this data strongly simplify the tools’ stress state to a uniaxial load. Therefore, a new fatigue test is presented in this paper, which incorporates the actual load conditions of cyclically swelling inner pressures. For this purpose, a high-strength elastomer is used as pressure medium. Its low compressibility and high elasticity allow for cyclic testing with pressures up to at least 2000 MPa. This load causes wear on the elastomer, as it is pressed into the gap between the punch used to apply the load and the fatigue specimen. Therefore, the gap between punch and fatigue specimen should be as low as possible to ensure stable test conditions. Within the scope of the research, fatigue failure already occurred in one specimen. This shows that the compression of elastomers is able to generate very high loads comparable to the cold forging of steel.

EFFECTS OF SLIP RATIO ON WEAR PERFORMANCE OF CLASS B WHEEL STEELS AGAINST SOFTER R260 RAIL STEELS USING THE TWIN DISC SETUP

A train experiences different slip ratios at the wheel/rail contact point as it moves along the rail track, which influences the rolling contact fatigue (RCF) and wear properties of wheel and rail materials. This variation in slip ratios is caused by a change in contact area between the wheel and rail head at curves, as the slip ratio increases compared with when a train is moving on a straight track. When the train is moving on a straight track, the wheel is found to be in contact with the rail head; but that changes when moving around curves, as the wheel flange will now be in contact with the gauge corner of the rail, affecting the severity of wear. Therefore, more research needs to be done to understand the role that slip ratio plays in the wear performance of wheel and rail materials in order to be able to develop models or systems that could be used to predict preventive maintenance. The aim of this work was to investigate the effect of the slip ratio on the wear performance of class B wheels against softer R260 rail steels under rolling and sliding conditions, using a twin-disc setup developed at the University of Pretoria. The results showed that the severity of wear was heavily dependent on the slip ratio – i.e., it increased with the slip ratio, with class B wheels performing better than the softer R260 rail.

Proposal of Evaluation Method of Elastic and Plastic Properties of Mechanical Surface Modified Layer of Metallic Materials by Indentation Test

In order to improve fatigue properties of metallic materials, mechanical surface modification such as shot peening is one of powerful methods. Major key parameters of the material properties on the improvement are work hardening and introduction of compressive residual stress. In the case of measurement by using an indentation test, hardness which relates resistance on plasticity such as yield stress is evaluated, and residual stress is also affected by residual stress. Namely, elastic properties such as compressive residual stress can be measured by the indention test as well as material flow stress characteristic of the transition from elastic to plastic deformation. In the present paper, an evaluation method of elastic and plastic properties of mechanical surface modified layer by the indentation test was proposed. In view point of practical application, as the indentation test which was similar to Rockwell superficial hardness was useful, the ratio of preliminary minor load and additional major load was investigated.

Research on low cycle fatigue life prediction considering average strain

To address the difficult problems in the study of the effect of average strain on fatigue life under low-cycle fatigue loads, the effect of average strain on the low-cycle fatigue life of materials under different strain cycle ratios was discussed based on the framework of damage mechanics and its irreversible thermodynamics. By introducing the Ramberg-Osgood cyclic constitutive equation, a new low-cycle fatigue life prediction method based on the intrinsic damage dissipation theory considering average strain was proposed, which revealed the correlation between low-cycle fatigue strain life , material properties, and average strain. Through the analysis of the low-cycle fatigue test data of five different metal materials, the model parameters of the corresponding materials were obtained. The calculation results indicate that the proposed life prediction method is in good agreement with the test, and a reasonable characterization of the low-cycle fatigue life under the influence of average strain is realized. Comparing calculations with three typical low-cycle fatigue life prediction models, the new method is within two times the error band, and the prediction effect is significantly better than the existing models, which is more suitable for low-cycle fatigue life prediction. The low-cycle fatigue life prediction of different cyclic strain ratios based on the critical region intrinsic damage dissipation power method provides a new idea for the research of low-cycle fatigue life prediction of metallic materials.

Designing very high-cycle fatigue specimens of additively manufactured Ti-6Al-4V with different porosities and microstructures

High cycle fatigue properties of material obtained with additive manufacturing (AM) processes such as LPBF (Laser Powder Bed Fusion) remain misunderstood. These properties are complex due to the porous and anisotropic features of AM parts. Moreover, a high number of process parameters can influence the obtained fatigue behavior. In this context, a rapid determination of the high and very high cycle fatigue properties is necessary in order to optimize process parameters with regard to fatigue response. This first work aims to produce test pieces with different porosity rates and microstructures. The processing and post-processing parameters leading to different porosity rates, porosity size distribution and microstructure are determined and presented. In a future work, the fatigue response will be then compare using two accelerated fatigue determination methods: ultrasonic fatigue testing and fatigue limit evaluation through lock-in thermography.

Ускоренная оценка влияния технологических факторов на прочностные характеристики Ti-6Al-4V И Al-Cu-Mg

Introduction. The strength of construction materials when used under cyclic loads is of great importance in design engineering. A significant number of factors that affect the fatigue resistance have predetermined the creation of numerous methods that consider such influence. Nondestructive methods that are based on the connection of the physical degradation of material with strain properties enable evaluating experimentally the fatigue properties of materials. Purpose of study: the analysis of the processes of energy dissipation and strain accumulation during the inelastic cyclic strain of samples, using the VT6 (Ti-6Al-4V) titanium alloy and the D16 (Al-Cu-Mg) aluminum alloy before and after the technological impact. The work experimentally investigates the physical processes of degradation of the VT6 and D16 alloy samples that accompany the process of fatigue failure in materials with homogeneous and inhomogeneous stress-strain states in the concentrator (in the form of a hole and a weld). Typical modes are used to reach the fatigue testing that determine the critical stress in a material sample – the stress at which physical properties (temperature, strain) change without reaching the fatigue failure of samples. Critical stress amplitudes in the cycle, based on the data obtained during the experiment and the results of mathematical simulation, are compared. The effect of stress concentrators on critical loads that a detail can withstand after a unit operation is estimated by the finite-element method (FEM). As a result, the effect of the operational and technological factors on critical stress determined by strain and temperature is estimated. Comparative tests of the VT6 and D16 alloy samples with and without stress concentrators showed that the amplitudes of critical stress decrease by more than 30% in comparison with the ones that are without stress concentrators. The low-cycle fatigue tests of the D16 alloy samples are carried out. Mathematical simulation of the cyclic strain of the samples is carried out using MSC.Marc package. The results of the cyclic loading tests, which show that the characteristics of the technological process reduce the amplitudes of the critical stress of the VT6 and D16 alloys and affect the fatigue properties of the D16 aluminum alloy, are discussed. Mathematical simulation corresponded positively to the experimental data. Such correspondence indicates the possibility of conducting qualitative numerical assessments of the beginning of the inelastic strain accumulation process in structures with stress concentrators under the cyclic stress and the increasing stress amplitude, using the typical sample made of hardening elastoplastic material.