Fatigue Resistance Of Materials Research Articles

Fatigue performance and material characteristics of SiC/AlSi10Mg composites by selective laser melting

By using selective laser melting, the SiC/AlSi10Mg composites were created. Under various process parameters, the impacts of SLM producing SiC/AlSi10Mg composites on density, microstructure, tensile characteristics, and fatigue properties were investigated. The results demonstrated that the density of the SiC/AlSi10Mg composites was closely related to the laser energy density. The density of SiC/AlSi10Mg composites might reach 99.7% under the ideal conditions. The Al4SiC4 phase grew with the rise in laser energy density as the aluminum matrix and SiC reacted in situ to generate a new strengthening phase Al4SiC4, which was dispersed on the matrix in a granular way. Therefore, the composite's tensile strength and microhardness reached their maximum values at 190.17HV and 435 MPa, respectively, when the energy density was 151.79J/mm3. This was due to the mixed strengthening mechanism caused by the SiC and Al4SiC4 reinforcing phase Compared with AlSi10Mg alloy, the addition of reinforcing phase SiC could significantly improve the fatigue resistance of composite materials. The fatigue fracture mode was brittle fractures, and the source of the crack was mainly from the surface pore defects. The size of the fatigue source defect size was related to the fatigue performance. The smaller the size of the defect, the more beneficial the fatigue resistance of the composite material.

Fatigue resistance of metal construction materials and its relationship with changes in the state of thin surface layers

The paper considers the proven clear relationship between the fatigue resistance of a number of structural materials and the processes occurring in their thin surface layers. The fatigue studies of the samples were carried out over a wide range of temperatures and amplitudes of cyclic stresses under uniaxial tension-compression with simultaneous microhardness measurement of the thickness of the hardened surface layer. On the basis of experimental studies of the fatigue of metallic structural materials, using the microhardness method, the regularities of hardening (softening) of their surface layer are established depending on the level of the amplitude of high-cycle loading and temperature. A method for the accelerated determination of the fatigue limit of structural materials based on the determination of microhardness during cyclic loading has been developed and tested. The dependence of the formed hardened film of the surface layer on the level of plasticity of the material has been established - the greater its plasticity, the thicker the resulting hardened film. With an increase in the amplitude of cyclic loading, the thickness of the hardened surface layer decreases.

New Method for Prediction of Photochromic Textiles Fatigue Behavior

The main objective of this work is to study the fatigue behavior of photochromic textiles under different UV irradiance times and develop a rapid testing method. When considering their possible applications, the fatigue resistance of photochromic materials has been considered. The photochromic woven fabric was prepared using the screen-printing method. Previous studies have demonstrated the sensitivity of photochromic pigments to UV radiation's intensity during the experiment. This work provides different thoughts in testing the fatigue resistance of spiro-indolines-based pigment applied on textile fabric. We found that color intensity performance and photodegradation of the photochromic pigment can be evaluated using a relatively small amount of necessary irradiation cycles and an advanced setup of time/intensity UV radiation exposure. Keywords: Color intensity, Fatigue resistance, Photochromic phenomena, UV irradiance time

A benchmark activity on the fatigue life assessment of AlSi10Mg components manufactured by L-PBF

One of the challenges associated with additive manufacturing (AM) is the definition of an assessment route which considers the main process signatures of the AM process. To this end, this work presents a complete benchmark activity for the assessment of an AlSi10Mg component produced by a laser powder bed fusion process, aimed at advancing the understanding of the fatigue resistance of AM materials with particular focus on the comparison between the fatigue performances of small coupons and demonstrators. Four builds of AlSi10Mg specimen geometries were manufactured to: (i) determine the fatigue curves for both as-built and machined conditions; (ii) measure the fatigue crack growth rate; (iii) produce and test under fatigue a benchmark component used as a reference for the validation of the fatigue assessment procedure. Tools and concepts of flaw tolerance were then used to perform the fatigue assessment of the benchmark component and were shown to be successful in the life prediction. Results obtained from this wide database (related to internal defects and surface features) show that only a fracture-based fatigue assessment is able to provide precise life estimates consistent with material crack growth properties. Eventually, all the experimental results including specimens design, analysis of fracture surfaces and raw tests’ data will be made available in a database which can be accessed and used by the industrial and scientific communities to calibrate and validate alternative fatigue assessment procedures of AM parts.

Effect of reinforcement particle amounts on dry sliding wear behavior of shot-peened SiC/A356 composites

Abstract Aluminum matrix composites focus primarily on improving mechanical properties such as hardness and wear, however, the softness of the aluminum matrix and thermal coefficient difference between matrix and reinforcement adversely affect these properties. In the present paper, the wear properties of aluminum matrix composites including different amounts of reinforcement were investigated before and after the shot peening process which was used for decreasing the harmful effects as mentioned. The experimental studies clearly reveal that shot peening, which is a mechanical surface treatment and generally used for improving fatigue resistance of materials, has a beneficial effect on the poor wear behavior of metal matrix composites. Obtaining results also indicate that the microhardness is improved greatly up to a certain depth by shot peening due to the higher dislocation density/microstrain which is evidenced with the X-ray diffraction tests.

Predictive fatigue crack growth law of high-strength steels

The fatigue resistance of metallic materials is generally attributed to both strength and toughness. Unfortunately, these properties are mutually exclusive in most materials. Classical theories like Paris’ law only provide some data correlation schemes rather than a predictive capability, which cannot satisfactorily guide the anti-fatigue design. In this study, for the first time, the predictive fatigue crack growth rate law is proposed by considering the effects of both strength and toughness. Accordingly, a quantitative criterion is established for judging the fatigue crack resistance of high-strength steels. The predictive law would provide a unique view to the quantitative anti-fatigue design of metallic materials.

Resistance of frame polymer concrete to low-cycle loading

Low-cycle fatigue is the ability of a material or structure to resist cyclic loads in the range of 0–105 cycles. Low-cycle loads are sometimes referred to as repeated. Little work has been devoted to the low-cycle fatigue of polymer composite materials (PCM). Studies of low-cycle fatigue were carried out by A.I. Chebanenko, B.A. Bondarev, Bondareva A.B. Besides them, the works of Chernousov R.N., Nemtsev V.A., Biryukov K.S. are known. Much more publications and research are devoted to the static fatigue of polymer composites. Almost all the works of well-known polymer concrete researchers began with studies of their strength under various types of loading, including long-term static. Thus, analyzing the previous experience of studying the fatigue resistance of polymer composite materials, we can draw the following conclusions: • PCM static fatigue is the most studied; • quite a lot of work is devoted to the high-cycle fatigue of polymer concrete; • low-cycle fatigue of polymer concrete has not been studied enough; • physical fatigue of polymer composite materials is practically not studied; • there is no complexity in studying the issues of PCM fatigue. Thus, the relevance of this work is beyond doubt, and the studies presented in this work make it possible to fill in the missing knowledge on the fatigue of frame polymer composites under various types of loading. In the course of the study, equations of low-cycle fatigue for frame polymer concretes were obtained. Also, the values of reliability coefficients for polymer concrete based on furfural-acetone monomer, manufactured using frame technology, are determined. The analysis of the data obtained clearly showed the possibility of using frame polymer concrete in structures subjected to cyclic loads

Mullins Effect and Crack Growth in Natural Rubber Vulcanizates during Heat Aging and Cyclic Loading

The effect of thermal aging and cyclic loading on mechanical properties and development of cracks in natural rubber vulcanizates was studied. After aging at 70oC and 110oC vulcanizates were subjected to cyclic loading. At a certain number of loading cycles, the samples were conducted in a tension test. At the aging condition of 70oC, the static tensile properties of material stay almost unchanged even after 88 aged hours and 8000 loading cycles. On the contrary, the dynamic fatigue resistance of vulcanizates decreases with increasing aging time. These results are attributed to the post-curing and the development of microcracks that might be caused by Mullins effect: in the case of static loading, the strain-induced crystallization may prevent cracks growth, but in the case of cyclic loading the strain-induced crystallization does not occur, so cracks develop without hindrance. However, at 110oC both static properties and dynamic fatigue resistance of material reduced dramatically because at high temperature the heat degradation exceeds both post-curing and strain-induced crystallization. Crack formation and propagation were examined by a digital optical microscope in the progress of cyclic loading. Results showed that natural rubber vulcanizate filled with carbon black has the best crack growth resistance (CGR) while the addition of modified and unmodified silica reduces CGR of materials. Moreover, the vulcanizate with unmodified silica has the lowest CGR.

Thermal Fatigue Model of Aluminium Alloy Die Casting H-13 Dies under Thermo-Mechanical Cycle

In industrial fields, thermal fatigue behavior has recently acquired an important role which is mainly related to the interaction between mechanical and thermal conditions. This paper proposes a thermal fatigue model of H13 tool steel under thermos-mechanical cycles. A test apparatus was used to assess the thermal fatigue resistance of materials to estimate surface crack area when specimens are subjected to thermal cycling. Thermal cycling up to 700°C was used, and crack patterns were examined after 1850, 3000, and 5000 cycles. Temperature distributions were measured at different locations in the test specimens. A model was developed to establish a relationship between mechanical cycling and thermal analysis. From the results, the thermal fatigue resistance was significantly improved over the control parameter after heating and cooling during thermomechanical cycles. The model was applied to determine the best performance and in-service life of die casting tools.

Application of the concept of the criterion of equivalence of complex stress state to simple tension for assessing the fatigue resistance of structural materials. Part 1. Review of some experimental data with the preparation of the necessary information for subsequent use

A brief overview of the features of the fatigue resistance of some steels is given with the selection of terms, concepts and numerical data necessary for the subsequent compilation and verification of the equivalence criterion in relation to assessing the ability of structural materials to resist fatigue for a long time under the action of certain combinations of alternating and static loads. Keywords: regular loading cycle, extremely stressed state, static stressed state, bending, torsion, biaxial static tension. bdsho@nkmz.donetsk.ua

Study of the relationship among total oxygen, inclusions and fatigue properties of gear steel

In order to control non-metallic inclusions and improve fatigue performance of gear steel, the relationship among total oxygen, inclusion size and fatigue properties of gear steel was investigated. In the work, Mn–Cr system gear steels with different total oxygen contents were selected as the research objects. Inclusions and fatigue properties of gear steels with different total oxygen contents were studied by using traditional metallographic method, extreme value method and fatigue test. The experimental results demonstrates that with the decrease of total oxygen content（i.e., 0.0013%→0.0010%→0.0005%）, the number of small-size oxide inclusions in the range of 5–10 μm decreases greatly, whereas the number of large-size oxide inclusions over 10 μm has relatively little change. Meanwhile, it is found that the change of total oxygen content in different ranges has different influences on the size of maximum size oxide inclusion and fatigue properties. Reducing the total oxygen content of gear steel from 0.0013% to 0.0010% decreases the inclusion size of maximum oxide inclusion and improves fatigue resistance of materials, but these benefits do not extend to a total oxygen level of 0.0005%. Accordingly, we can conclude that no evident linear correlation exists between total oxygen content and maximum inclusion size or between the total oxygen content and the fatigue performance.

Bonded CFRP/Steel Systems, Remedies of Bond Degradation and Behaviour of CFRP Repaired Steel: An Overview.

This literature review has examined the use of FRP composite materials as a potential retrofitting technique for civil structures. Importantly, the various material properties, bond mechanisms, durability issues and fatigue resistance have been discussed. Studies exploring the performance of CFRP repaired steel have strongly indicated its potential as a rehabilitation material. These systems offer many improvements over the current bulky and less chemically resistant methods of bolting or welding steel plate patches. This review has established and highlighted the factors that affect CFRP/steel bond durability, namely surface preparation, curing, corrosion, fatigue loading, temperature and moisture ingress through studies that focus on their effect. These studies, however, often focus on a single influencing factor or design criteria. Only limited studies have investigated multiple parameters applied simultaneously, even though they commonly occur together in industrial practice. This review aimed to summarise the numerous influencing parameters to give a clearer understanding of the relevance of CFRP repaired steel structures.

High cycle fatigue behaviour of Inconel 625 weld overlay on AISI 316L plate

In this work, the high cycle fatigue (HCF) investigation was performed on Gas metal arc welding (GMAW) based Inconel 625 (IN625) hardfaced overlays in as-deposited condition. Tensile test and microstructural characterization were performed along with HCF analysis. The microstructure of the weld overlay was characterized with equiaxed, columnar and randomly oriented dendritic microstructures, these dendrites imparts improved mechanical properties. Higher amount of high angle grain boundaries (HAGBs) fraction at the IN625 section has direct effect on improving the toughness and strength of the overlay material. Monotonic tensile results indicate 5% increase in Ultimate tensile strength (UTS), 21% increase in Yield strength (YS) and 32% decrease in elongation to failure (PE) on hardfaced sample than the substrate. Fatigue strength was considered 143 MPa and 119 MPa for hardfaced and substrate samples respectively after sustaining infinite number of cycles. Fatigue resistance of hardfaced material was remarkable due to the presence of equiaxed dendrites and defect free overlays. Smooth crack growth area was noticed for the samples failed at higher number of cycles, expressing low stress-levels. Specifically, the fracture surfaces evidenced micro voids, riverine traces and dimples at the fracture point, which confirms the ductile failure.

A method of accounting for censored items as part of fatigue testing of composite materials

The Aim of the paper is to create a method for including information on censorship for the purpose of adjusting the estimates of the S-N diagram of composite materials. Censored items are such items that did not fail by the end of testing, for which a certain operation time has been registered. It must be noted that, currently, researchers often ignore the operation time data of the items that did not fail by the end of testing, which does not appear to be justified in terms of cost saving and reliability of statistical conclusions. Censorship information is very important in terms of assessing durability. It only needs the right tool to use it. The proposed Method consists in bootstrapping-based simulation, a method from the group of computer-intensive methods. In the process of the method’s development, the previously used approaches (for instance, as regards metals) were considered. In the examined example of the method’s application, the data was taken from literary sources. Results. The paper shows an example of fatigue testing conducted by the authors that produced a large number of censored items. The results obtained using the method were compared with real data. It is shown that the quality of statistical estimation improves with the use of the method. The paper sets forth certain observations regarding the mechanical testing tool for quality control. The source of data dispersion associated with fatigue testing is discussed. Conclusions. The application of the method will help include the information on censored items in the estimation of the S-N diagram. For scientists who are involved in the experimental research of the fatigue resistance of composite materials, the suggested method might prove to be quite useful. It takes into consideration the characteristic features of the strength analysis of composite materials (large properties dispersion and absence of unlimited fatigue range). The method will allow taking onto account an important, but not always so far used information on the items that operated a certain number of cycles, but did not fail.

Fatigue resistance and remaining life assessment of induction-hardened S38C steel railway axles

The remaining life assessment of damaged railway axles is an important topic primarily because of extending the maintenance interval. However, the fatigue resistance of surface-strengthened materials is extremely challenging due to the gradient-distributed microstructure, tensile properties, and residual stresses across the axle. To elucidate the fatigue cracking behaviors of induction-hardened S38C railway axles, the residual stress field ranging from −400 MPa to zero near the axle surface were rebuilt using a new unit pressure and proportional-integral approach (UPA) instead of complicated heat simulation. The fatigue life of full-scale S38C railway axles was then predicted by employing a real vertical load spectrum. The results show that in the presence of a 4.0-mm-deep crack, the remaining life of a damaged axle with compressive residual stresses is more than three times that of an axle without compressive residual stresses. In addition, the crack front is surrounded by a compressive stress field when the crack depth does not exceed 4.0 mm, which is the probable detection limit for the maximum crack depth extension. The present work is expected to serve a basic reference for the optimization and extension of the inspection intervals for induction-hardened S38C railway axles.

The mean stress and phase angle effect on multiaxial fatigue behavior of a TiAl alloy: Failure analysis and life modeling

In the presence of multiaxial fatigue loadings with multiple loading variables, fatigue behavior of material differs from those under in-phase (IP) multiaxial fatigue loadings. The co-existence of non-zero mean stress and phase angle could be extremely harmful to fatigue resistance of material. In this case, it is vital for researchers engaging in relative fields to put forward capable life prediction methods. In this study, the mechanical property of a TiAl alloy under combined tension-torsion (CTT) fatigue loadings is investigated through experiments. The applied fatigue load contains non-zero mean stress components as well as phase angle components. The fracture of specimen is observed by scanning electron microscope (SEM) to investigate the correspondence between multiaxial fatigue life and failure behavior. Susmel and Lazzarin's (S-L) fatigue criterion is critically reviewed to put forward a modification on its intrinsic drawback. In parallel, a correction factor is introduced to make the modified Wӧhler curve method (MWCM) feasible for multiaxial fatigue life prediction with multiple loading variables. Verified by experimental results of present work, the proposed method is of good accuracy compared with Matake method and McDiarmid method.

Improved fatigue resistance of gradient nanograined metallic materials: Suppress strain localization and damage accumulation

Compared to conventional metals with homogeneous microstructures, heterogeneously structured materials with spatially gradient nanostructures exhibit superior mechanical properties, especially enhanced fatigue resistance under cyclic loading by suppressing the strain localization and damage accumulation. In this paper, the basic features of fatigue properties, cyclic deformation, and damage mechanism of gradient nanostructured metallic materials are reviewed. The challenges and prospects on exploring fatigue resistance of gradient nanostructured materials in the future are also addressed.

Enhancement of Fatigue Endurance Limit through Ultrasonic Surface Rolling Processing in EA4T Axle Steel

Fatigue property is a key evaluation index for the service reliability of railway axle. In this work, the effect of ultrasonic surface rolling processing (USRP) on the surface characteristic and fatigue property was investigated in an EA4T axle steel used on high speed trains by several characterization techniques and the staircase method fatigue testing. The surface characteristics were initially studied in EA4T axle steel under different static loads of 1.0 kN, 1.5 kN and 2.0 kN, and served as the important USRP parameter. It was found that the larger static load greatly improved the surface microstructure, microhardness and compressive residual stress, but also increased the surface roughness. Furthermore, the rotating bending fatigue endurance limit of the USRP specimen with a static load of 1.5 kN was obviously enhanced by ~14% (from ~352 MPa to ~401 MPa) relative to the untreated specimen. The enhanced fatigue limit induced by USRP was attributed to the synergistic effect of the grain refinement, as evidenced by transmission electron microscope (TEM) observation, work-hardening, the increased compressive residual stress and the reduced surface roughness. Moreover, the fatigue limit of the USRP specimen was ~4% higher than that of the rolling specimen with turning off the ultrasonic system, ~386 MPa, which showed that the role of the ultrasonic impact could enhance the fatigue property. These findings demonstrate the validity of this technique in modifying the surface characteristics and thus improving the fatigue resistance of axle material, further ensuring its service safety and reliability.

Multi-Arch-Structured All-Carbon Aerogels with Superelasticity and High Fatigue Resistance as Wearable Sensors.

Compressible and ultralight all-carbon materials are promising candidates for piezoresistive pressure sensors. Although several fabrication methods have been developed, the required elasticity and fatigue resistance of all-carbon materials are yet to be satisfied as a result of energy loss and structure-derived fatigue failure. Herein, we present a two-stage solvothermal freeze-casting approach to fabricate all-carbon aerogel [modified graphene aerogel (MGA)] with a multi-arched structure, which is enabled by the in-depth solvothermal reduction of graphene oxide and unidirectional ice-crystal growth. MGA exhibits supercompressibility and superelasticity, which can resist an extreme compressive strain of 99% and maintain 93.4% height retention after 100 000 cycles at the strain of 80%. Rebound experiments reveal that MGA can rebound the ball (367 times heavier than the aerogel) in 0.02 s with a very fast recovery speed (∼615 mm s-1). Even if the mass ratio between the ball and aerogel is increased to 1306, the ball can be rebound in a relatively short time (0.04 s) with a fast recovery speed (∼535 mm s-1). As a result of its excellent mechanical robustness and electrical conductivity, MGA presents a stable stress-current response (10 000 cycles), tunable linear sensitivity (9.13-7.29 kPa-1), and low power consumption (4 mW). The MGA-based wearable pressure sensor can monitor human physiological signals, such as pulses, sound vibrations, and muscular movements, demonstrating its potential practicability as a wearable device.

High hardness and fatigue resistance of CoCrFeMnNi high entropy alloy films with ultrahigh-density nanotwins

Development of film materials has been limited by the hardness-fatigue resistance trade-off. The purpose of the present study was to obtain films with a combination of both high hardness and strong fatigue resistance. To achieve this, CoCrFeMnNi high entropy alloy films (HEAFs) were fabricated with three different structures: amorphous, high-density nanotwinned crystal structure with twin spacings of 2.2–5.6 nm, and ultrahigh-density nanotwinned columnar grains with twin spacings of 1.2–2.5 nm. Nanoindentation with dynamic mechanical analysis was used to measure the hardness and perform the fatigue tests. While higher twin densities could dissipate more energy by detwinning during fatigue loading to enhance the fatigue resistance, twin spacings larger than and small than 2 nm could, respectively, result in hardening and softening. Our results showed a high hardness of ~9 GPa and fair fatigue resistance (~104 cycles) for both amorphous and high-density nanotwinned crystalline layers. For the ultrahigh-density nanotwinned columnar grain structure, a high hardness of ~8.5 GPa and an excellent fatigue resistance (~106 cycles) were obtained. The outstanding fatigue resistance and high hardness were attributed to the synergistic effect of strain hardening and detwinning of ultrahigh-density nanotwins. The results not only enable CoCrFeMnNi HEAFs with a predominant combination of hardness and fatigue resistance, but also shed light on a new perspective for overcoming the conflict between hardness and fatigue resistance in film materials for microelectromechanical applications.