Fatigue Resistance Of Materials Research Articles

Study on the improvement of fatigue and crack resistance of semi-flexible pavement materials using the mixing -molding method

This study focuses on two significant issues pertaining to conventional grout-molded semi-flexible pavement material (P-SFP): the difficult of achieving a high grouting rate and the limited scope for enhancing asphalt content, both of which contribute to the poor crack resistance of the SFP. To address these problems, the Mixed-Molding Method Semi-Flexible Pavement Material (M-SFP) is proposed, which utilizes a combination of mixed-molding method to enhance the crack resistance and fatigue life of SFP. In order to investigate the effects of asphalt film thickness and gradation type, four different gradations and five different asphalt contents of M-SFP were designed based on the volume filling theory. The effects of asphalt film thickness and gradation type on the cracking resistance and fatigue life of M-SFP were investigated through various tests, including low-temperature bending, semi-circular bending tensile, and four-point bending fatigue test. The results were then compared with those of the control P-SFP. The test results show that the strain energy density of M-SFP is increased by 24.9 % and the fracture energy is increased by 52.1 % compared with the conventional P-SFP; the number of fatigue life times under 200με, 225με, and 250με microstrain are increased by 53.6 %, 41.3 %, and 47.3 %, respectively. Based on crack resistance test results, it is recommended that the design asphalt film thickness of M-SFP exceed 10μm. Furthermore, measurements of the air void content reveal that the M-SFP exhibits significantly better compactness compared to the P-SFP. In conclusion, it shows that the Mixing-Molding method can be used to obtain semiflexible pavement materials with higher asphalt dosage, better cracking resistance, better degree of compactness, and longer fatigue life. In addition, the correlation analysis between the cracking resistance results and the rigid-flex ratio indicates that the recommended design rigid-flex ratio for SFP should be less than 2.06.

Materials Evolution in Dental Implantology: A Comprehensive Review

This comprehensive review navigates the dynamic landscape of dental implant materials, exploring historical milestones, mechanical intricacies, and emerging innovations. Tracing the evolution from early experimentation to the establishment of titanium as a benchmark, the review sheds light on the critical interplay of strength, elasticity, and fatigue resistance in materials' biomechanical performance. The diverse array of materials, including metals like titanium, ceramics such as zirconia, and polymers like polyetheretherketone (PEEK), is examined in depth, emphasizing their unique attributes and contributions to clinical needs. Surface modifications emerge as transformative elements, accentuating the role of precision engineering in optimizing implant performance. Challenges, encompassing biocompatibility, mechanical incongruity, and infection vulnerabilities, underscore the intricacies of material selection in implant dentistry. The ongoing pursuit of solutions to esthetic limitations and long-term stability constitutes a focal point for future research. Emphasizing the importance of ongoing research, the review highlights emerging materials, such as bioactive ceramics and advanced polymer composites, driven by nanotechnology and 3D printing. Smart implants, antimicrobial surfaces, and regenerative approaches signal a transformative era in precision dentistry. The journey towards refined materials transcends disciplines, uniting researchers, clinicians, and materials scientists in a collaborative pursuit. As the narrative of dental implant materials unfolds, the future beckons with promises of seamless integration with biological tissues, esthetic advancements, and redefined standards in oral rehabilitation. This review encapsulates a dynamic field in continual evolution, extending an invitation to collectively shape the future of dental implantology.

Rotating bending fatigue behavior of high-pressure diecast AlSi10MgMn alloy based on T5 heat treatment parameters

Abstract The study investigates fatigue failure, a common phenomenon in machine elements subjected to cyclic stresses. The analysis emphasizes that the actual stress experienced by materials often falls below their tensile and yield strengths due to repetitive variable stresses, leading to fatigue damage. Fatigue life is measured by the number of cycles endured before failure. This paper focuses on the aluminum alloy of AlSi10MgMn, extensively used in manufacturing due to its strength, low density, and corrosion resistance. Experimental procedures encompassed tensile testing, microstructural examination, SEM analysis, and fatigue testing. Tensile tests provided initial stress values for fatigue testing. Microstructure analyses verified that heat-treated samples exhibited precipitates. SEM analysis disclosed microstructural characteristics, while fracture surface examinations demonstrated higher fatigue resistance in heat-treated specimens. Hardness measurements were conducted, with heat-treated samples showing higher values. Theoretical calculations based on stress and cycle numbers were compared to experimental fatigue results. The derived equations aligned well with the tests. Ultimately, the study underlines the importance of heat treatment on material behavior and fatigue resistance, shedding light on alloy performance and durability enhancement.

Overhead conductor heating chamber and temperature effects on the fatigue life of aluminum alloy 6201‐T81 conductors

AbstractThis work investigates the impact of temperature on the fatigue life All Aluminum Alloy Conductors (AAAC) made of 6201‐T81. A heating chamber was developed to simulate thermal effects induced by electric current passage. Wöhler fatigue curves were generated under isothermal conditions at 75 and 150°C and later compared with the one at 20°C. The conductor exhibited similar fatigue life at 20 and 75°C; however, a significant increase of life was observed for tests at 150°C. Hardness tests and failure analysis of wire breakages were carried out on samples extracted from the conductor coil and on artificially aged samples maintained at controlled temperatures. The analyses revealed that at a temperature of 150°C, there is formation of small precipitates of magnesium and silicon within the aluminum matrix, which impeded the propagation of discontinuities, increasing the material's hardness and fatigue resistance.

Analysis of rolling contact and tooth root bending fatigue in a new high-strength steel: Experiments and micromechanical modelling

To find materials that meet the future requirements of increasing load density in wind turbine gear structures, the commonly used reference material, 18CrNiMo7-6, and another high-strength steel were analysed. Their fatigue properties were studied through rolling contact fatigue (RCF) and gear tooth root bending fatigue (TRBF) tests. The reference steel exhibited better fatigue performance under RCF conditions compared to the new steel; however, it was outperformed by the new steel under TRBF conditions. This study aims to understand gear contact fatigue at the microscopic level, moving beyond the macroscopic focus that dominates current research literature. To establish the causal link between the varied fatigue performance observed in these materials, we proposed a multiscale modelling workflow based on crystal plasticity. This crystal plasticity framework is combined with the fatigue indicator parameter (FIP) to explore the fatigue resistance of materials subjected to RCF and TRBF conditions. Emphasis has been placed on the role of retained austenite (RA) in fatigue performance. Utilizing representative elementary volumes (REVs) generated based on statistically representative crystallographic features and measured size distribution of RA, we examined the effects of various RA levels on fatigue resistance. Our findings reveals that the fatigue damage accumulation is significantly influenced by the level of RA. Different fatigue damage accumulation behaviours were observed under RCF and TRBF conditions. These insights offer new perspectives on RA’s role in fatigue resistance and highlight its complex influence under varied loading conditions.

Hydrothermal Hot Isostatic Pressing (HHIP)-Experimental Proof of Concept.

A new hydrothermal hot isostatic pressing (HHIP) approach, involving hydrothermal water conditions and no usage of inert gas, was hypothesized and tested on 3D-printed Al-10%Si-0.3%Mg (%Wt) parts. The aluminum-based metal was practically inert at the applied HHIPing conditions of 300-350 MPa and 250-350 °C, which enabled the employment of a long (6-24 h) HHIP treatment with hardly any loss of material (the overall loss due to corrosion was mostly <0.5% w/w). Applying the new approach on the above-mentioned samples resulted in an 85.7% reduction in the AM micro-pores, along with a 90.8% reduction in the pores' surface area at a temperature of 350 °C, which is much lower than the 500-520 °C applied in common argon-based aluminum HIPing treatments, while practically maintaining the as-recieved microstructure. These results show that better mechanical properties can be expected when using the suggested treatment without affecting the material fatigue resistance due to grain growth. The proof of concept presented in this work can pave the way to applying the new HHIPing approach to other AM metal parts.

Study on fatigue crack growth property of abrasive waterjet peened aluminum alloy

Abrasive waterjet peening is a favorable surface treatment method for improving the fatigue resistance of metal materials. An insight into the fatigue crack growth properties of AWJ peened specimens is meaningful for obtaining better strengthening performance. In present work, a numerical model of AWJ peening was established and experimentally validated for investigating the fatigue crack growth characteristics of Aluminum specimens. The effect of peening and loading conditions on the fatigue performance was also analyzed. The results indicated that the stress intensity factor at the peened region was enhanced and the crack propagation was significantly inhibited by the compressive residual stress. The influence of compressive residual stress on the effective stress factor range is greater under lower external load and higher loading ratio. The fatigue life for reaching the crack length of 40 mm is increased by 37%, 60% and 98% after peening by using the intensity of 0.6 mmA, 0.8 mmA and 1 mmA, respectively.

Optimization of energy storage performance in 0.8Na0.5Bi0.5TiO3-0.2Bi3.25La0.75Ti3O12 thin films via defect dipoles

Dielectric capacitors put forward higher requirements on the energy storage density, working stability and fatigue resistance of materials with the increasing shortage of energy. Herein, 0.8Na0.5Bi0.5TiO3-0.2Bi3.25La0.75Ti3O12-x%Mn (x = 0,2,4,6) thin film capacitors are designed to address above concern. The Mn ions inhibit the valence change of Ti ions and combine with oxygen vacancies to form defect dipoles, which improve breakdown strength and energy density of the films. As a result, high energy storage density of 92.7 J cm−3 and excellent efficiency of 70.2% are synchronously achieved for the 4% Mn-doped NBT-BLT film. Besides, outstanding stability of energy storage performance also exhibit over a wide range of temperature (25–200 °C) and cycle number (105). This result provides a novel strategy for the preparation of dielectric materials with high energy storage performance and high operational stability.

Laser shock-induced gradient twinning microstructure in AZ31B alloy

Magnesium alloys are highly promising in biodegradable materials for medical applications. However, their applications are limited by weaknesses in mechanical strength and corrosion resistance. In recent years, advancements in a novel laser method, Laser Shock Peening (LSP), have been explored. Researchers suggest that LSP can induce surface compressive stresses and induce changes in residual stress and grain size gradients, thereby enhancing the material's fatigue resistance, corrosion resistance, and resistance to stress corrosion cracking. However, there is ongoing debate about whether LSP treatment can, in effect, create a gradient microstructure. In this study, we focused on the AZ31B alloy, notable for its dense hexagonal close-packed (HCP) crystal structure. This material is particularly interesting because, due to its low stacking fault energy, it is more prone to twinning deformation than to dislocation slip when it undergoes plastic deformation. To analyze the changes wrought by LSP, we employed optical microscopy (OM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) for examining the microstructures both before and after LSP treatment. Our findings revealed that LSP treatment refined the grain size, leading to a gradient distribution. In addition, we observed a direct correlation between the volume fraction of twinning and grain size. In contrast, the geometrically necessary dislocation (GND) density exhibited an inverse relationship. By measuring hardness and residual stress in the region affected by LSP, we determined that LSP could introduce a layer of plastic deformation up to a depth of 800–1000 μm. We also established a link between the gradient microstructure and hardness and provided a thorough discussion on the types of twinning and the mechanisms behind the induction of gradient microstructure on the surface.

Assessing Fatigue Life Cycles of Material X10CrMoVNb9-1 through a Combination of Experimental and Finite Element Analysis

This paper uses a two-scale material modeling approach to investigate fatigue crack initiation and propagation of the material X10CrMoVNb9-1 (P91) under cyclic loading at room temperature. The Voronoi tessellation method was implemented to generate an artificial microstructure model at the microstructure level, and then, the finite element (FE) method was applied to identify different stress distributions. The stress distributions for multiple artificial microstructures was analyzed by using the physically based Tanaka–Mura model to estimate the number of cycles for crack initiation. Considering the prediction of macro-scale and long-term crack formation, the Paris law was utilized in this research. Experimental work on fatigue life with this material was performed, and good agreement was found with the results obtained in FE modeling. The number of cycles for fatigue crack propagation attains up to a maximum of 40% of the final fatigue lifetime with a typical value of 15% in many cases. This physically based two-scale technique significantly advances fatigue research, particularly in power plants, and paves the way for rapid and low-cost virtual material analysis and fatigue resistance analysis in the context of environmental fatigue applications.

Enhanced fatigue resistance of plasma modified pyrolysis carbon black filled natural rubber composites

Owning to the requirement of cost reduction and environmental protection, the application of pyrolysis carbon black (CBp) in dynamic rubber products becomes a hot topic in recent years. However, the fatigue resistance of CBp filled rubber composite is poor. Therefore, the evolution of micro- mesoscopic structure in modified CBp filled natural rubber (NR) composites during the tensile fatigue process is investigated to find the influencing factor for enhancing the fatigue resistance in this study. Results indicate that the particle/aggregate size distribution turns to be narrower after the aggregate size filtering treatment while a decreased particle/aggregate size and an improved polarity can be observed after argon plasma treatment. As a result, the average fatigue life of NR composites filled with CBp treated by air classifier, plasma modification and their combination are increased by 21%, 57% and 107%, respectively. It is found that the filler dispersion and the filler-polymer interaction deteriorate during the fatigue process. This evolution is inhibited by filler modification. Besides, the fatigue lives of filled rubber show a correspondence to their total and physical cross-linking densities as well as the bound rubber contents. The filler-polymer interaction can be proposed as an important factor in extending the fatigue life of rubber composites. These findings provide not only a promotion on the application value of CBp in fatigue resistance of rubber composite by different modification methods, but also an innovative perspective for exploring the fatigue resistance of rubber material from the aspects of filler-rubber interaction, and a scientific guidance for the development of long-life dynamic rubber products.

Analytical prediction of fatigue resistance of additively manufactured aluminium alloy based on Murakami method

This research is devoted to analyze the stress state and fatigue strength of two specimens made by a newly developed high-strength aluminium alloy produced by the wire arc additive manufacturing (WAAM) process. The relationship between fatigue strength and flaw size was calculated based on the root squared area – a parameter by conventional Murakami’s equation which is a widely used analytical approach for predicting fatigue resistance in metallic materials. The research involves the metallographic preparation process on two aluminum alloy labeled HS-Al-A and HS-Al-B followed by Vickers hardness measurement. Further, the image of the observed pores was processed and dimensioned using an open-sourced software ImageJ by considering pixels and actual distance as well as by defining image threshold value for measuring pore sizes. The analytical approach is conducted in order to describe the maximum stress intensity factor Kmax at the crack front and to assess the fatigue strength σFS. As final results, specimen A has an average pore area of ≈65 µm with Kmax of 333.75 MPa∙√m and σFS of 137 MPa, while specimen B has an average pore area of ≈42 µm with Kmax of 325.13 MPa∙√m and σFS of 153 MPa. Overall, this research allows the formulation of a method for estimating fatigue strength of large defects leading to a conclusion that flaws can influence the fatigue resistance of the material so that the bigger the flaw size is, the lower σFS and the higher the Kmax.

Surface integrity optimization for ball-end hard milling of AISI D2 steel based on response surface methodology.

This study focuses on systematically revealing how cutting parameters influence the surface integrity of ball-end hard milled surface of AISI D2 steel and proposing optimization scheme from surface integrity, wear resistance and fatigue resistance perspective based on response surface methodology respectively. Results can be summarized into three aspects. Firstly, radial depth of cut with percent contribution ratio (PCR) 62.05% has a decisive influence on surface roughness, followed by spindle speed 13.25% and feed per tooth 6.63%. The work hardening degree was raised from 12.5% to 38.4% when spindle speed changed from 8000 rpm to 2000 rpm. Spindle speed and radial depth of cut are the most significant factor influencing residual stress. The PCR of spindle speed and radial depth of cut reached 73.47% and 18.63% for residual stress in feed direction, 47.11% and 37.51% in step-over direction, respectively. High residual compressive stress can be generated by lowering spindle speed and radial depth of cut benefiting from the aggravated squeeze between ball-end milling cutter and workpiece. Secondly, too small feed per tooth or too small radial depth of cut should be avoided from wear resistance point because though the surface microhardness can be improved, the surface quality will also be deteriorated. The combination of high spindle speed, small feed per tooth together with small radial depth of cut can meet the wear resistance and the machining efficiency requirement. Finally, a medium-sized cutting parameter combination should be adopted to realize satisfying material removal rate and fatigue resistance. This study can be used to guide the selection of cutting parameters during ball-end milling of hardened AISI D2 steel for dies/molds manufacturing industries.

Fatigue response of a cast Al-Cu-Mg-Ag-TiB2 (A205) alloy: Stress relieved and aged

The purpose of this study is to assess the influence of heat treatment on the fatigue behavior of cast A205 alloy (i.e., Al-Cu-Mg-Ag-TiB2 nanocomposite). To do so, A205 samples were heat-treated and divided into two categories (i) stress-relieved (SR) and (ii) T7 stabilizing over-aged. This research delves further into the microstructure, mechanical properties, and fatigue performance of A205 alloy in SR and T7 heat-treated (i.e., T7 aged) conditions. After production and post-heat treatments, the samples underwent force-controlled fatigue experiments, tensile and depth-sensing indentation testing, and advanced microstructural characterizations (using electron backscattered diffraction and transmission electron microscopy). Microstructural characterization revealed exceptionally equiaxed, texture-free microstructure with uniform grain distribution and the existence of Al2Cu precipitates and TiB2 particles. The T7 heat treatment did not change grain size significantly (grain size: 46.4 ± 13.5 µm for SR and 48.5 ± 13.7 µm for T7 material). The T7 heat treatment was found to be very effective in improving the fatigue resistance of A205. The higher fatigue resistance of cast T7 material is attributed to the accelerated precipitation of Al2Cu along with different habit planes. The results of this study offer a critical understanding for choosing the optimum heat treatment parameters to control the fatigue behavior of cast A205, which is crucial considering their applications in the aerospace industry.

In situ observation of the pseudoelasticity of twin boundary

Twin boundary (TB) is a special and fundamental internal interface that plays a key role in altering the mechanical and physical properties of materials. However, the atomistic deformation mechanism of TB remains under debate, of which the most concerned aspect is how TB would affect the mechanical strength and plasticity of a material. Herein, we introduce our new discovery that the pseudoelastic strain of a TB can recover with decomposition and escape of pile-up dislocations, demonstrated by imposing a spontaneous pseudoelastic deformation with recoverable plastic bending strain up to 5.1% on a TB. We found that the steps on the curved TB gradually annihilated during the migration of the TB, which was induced by the slip of decomposition dislocations on the TB. The TB not only provides local strain hardening through interaction with dislocations during the loading stage but also acts as a channel for the fast movement of decomposition dislocations during the recovery stage. Beside, the TB can maintain excellent pseudoelasticity under a multicycle bending test, which may play an important role in improving the fatigue resistance of materials. These findings could open up a new avenue for optimizing the mechanical properties of materials by manipulating their twin boundaries at the nanoscale.

A dual physical crosslinking starch-based hydrogel exhibiting high strength, fatigue resistance, excellent biocompatibility, and biodegradability.

Simultaneous realization of high strength, toughness, and fatigue resistance in natural starch-based hydrogel materials is challenging. A facile method of in situ self-assembly and a freeze-thaw cycle was proposed to construct double-network nanocomposite hydrogels of debranched corn starch/polyvinyl alcohol (Gels). Rheology, chemical structure, microstructure, and mechanical property of Gels were investigated. Notably, short linear starch chains were self-assembled into nanoparticles and subsequently into 3D microaggregates, which were tightly wrapped by starch and PVA network. Compared with corn starch single-network and starch/PVA double-network hydrogels, the Gels reached up to a higher compressive strength (ca. 1095.7kPa), and then achieved to ∼20-30-fold improvement in compressive strength. Recovery efficiency exceeded 85% after 20 successive compression loading-unloading cycle tests. Furthermore, the Gels had good biocompatibility to L929 cells. Hence, the high-performance starch hydrogels are thought to serve as a biodegradable and biocompatible material to replace synthetic hydrogels, which can broaden their application fields.

In-situ SEM investigation of low-cycle fatigue behavior and microstructure evolution of CoCrNi medium entropy alloy

We performed an in-situ fatigue test by in-situ scanning electron microscope (SEM) to elucidate the deformation and failure behavior of equiatomic CoCrNi medium entropy alloy under cyclic loading. The SEM results indicate that the crack growth speed is slow at the initial stage, and the growth direction is perpendicular to the loading direction. As the cyclic loading continues, small cracks are generated in the material, which changes the direction of the main cracks and accelerates the growth of the main cracks. The deformation twins and elongated grains induced by cold rolling are frequently observed in samples before cyclic deformation. These grains are changed from nearly parallel elongated grains to irregular during cyclic deformation. However, deformation twins disappeared or became thinner after cyclic deformation. Molecular dynamics simulations are carried out to reveal the microstructure evolution mechanisms during cyclic deformation. The results show that the grain growth occurred after cyclic deformation in the model without deformation twins. However, the de-twinning, re-twinning and grain growth are observed in the models containing deformations twins. Molecular dynamic simulations also indicated that twin boundaries lead to higher strain energy density and significantly improve the material's fatigue resistance.

Fatigue-resistant, single-phase stretchable materials via crack bridging

Stretchable materials such as elastomers and hydrogels are vulnerable to the growth of a crack under repeated cycles of stretch. This is because in single-network/phase materials, the crack can easily propagate by fracturing a single layer of polymer chains. Therefore, to improve the fatigue resistance of stretchable materials, current methods focus on blocking the crack front by another intrinsically high-energy phase. Such high-energy phases, however, are often limited to specific polymers or compromise other properties, limiting its extension to other fields. Single material approaches have been used in structural materials but considered inapplicable to soft materials. Here we challenge this acknowledgement by demonstrating the crack bridging effect in micropatterned elastomers. Instead of resisting in front of crack tips, micropatterns shield polymer chains by bridging behind the crack front. To utilize the bridging effect, we create composites with one material. They are structurally one piece of material but have molecularly separated fibers and matrices due to different curing mechanisms of components. Single-phase composites of polydimethylsiloxane (PDMS) made by this strategy have a fatigue threshold three times higher than that of PDMS-hydrogel composites designed based on the classic high-energy strategy. This crack bridging strategy does not rely on the inter- and intra-polymer interactions provided by specific materials, and thus have a general usefulness.

Enhanced fatigue endurance limit of Cu through low-angle dislocation boundary

How to remarkably elevate the high-cycle fatigue resistance of metallic materials under cyclic loading is a crucial, yet technically challenging issue for major structural applications. Either traditional strengthening approaches or newly-developed hierarchical nanostructural modifications has been demonstrated to usually display a limited ability of enhancing the 107-cycle fatigue endurance limit. Here, we introduce massive nano-scaled low-angle dislocation boundaries in coarse grained pure Cu by means of simple drawing process, not only enhancing the tensile strength obviously, but also imparting a fatigue limit as high as 130 MPa and a fatigue ratio of 0.35, which is a record for pure Cu. Upon cyclic loading, the extensive activation of strongly confined dislocation slip within homogeneous dislocation cells (with cell size of about 300 nm) effectively mediates cyclic plastic strain with slightly cyclic softening. The elevated stress resistance of DC Cu to cyclic loading is primarily attributed to the high density of built-in low-angle dislocation cells, which are strong and also suppress local surface roughening and crack initiation, thereby contributing to an enhanced fatigue life.

Oxidation induced crack closure in a nickel base superalloy: A novel phenomenon and mechanism assessed via combination of 2D and 3D characterization

Understanding the mechanism of oxidation induced crack closure (OICC) is of great importance in understanding the fatigue resistance of materials operating at intermediate or high temperatures subjected to oxidation. Current work reveals that the occurrence of OICC is most closely related to the test frequencies and temperatures rather than the microstructure in a directionally solidified (DS) superalloy. Characterization techniques in three dimensions - X-ray scanning tomography (CT) and two dimensions - scanning electron microscopy (SEM) with attached energy-dispersive Xray spectroscopy (EDX) are combined to capture the oxides formed within the crack wake. These data are then incorporated into modified models to provide quantitative measurements of oxidation induced crack closure. Both the experimental and modelling results show that the external oxides forming close to the crack tip, result in a high crack tip opening displacement and thereby significant crack closure.