Improved Fatigue Resistance Research Articles

Probing fatigue resistance in multi-layer DLC coatings by micro- and nano-impact: Correlation to erosion tests

DLC coatings have seen recent use as protective coatings for flow control devices in the oil and gas industries. Improving fatigue resistance for multi-layered DLC coatings on hardened steel is key for improving their performance in this harsh environment of highly loads repetitive contact. This has been studied directly by micro-scale repetitive impact tests at significantly higher strain rate and energy than in the nano-impact test, enabling the study of coating fatigue with spherical indenters and dry erosion testing. Nano-impact has also been used to assess the initial fatigue behaviour of the coatings. Good correlation between micro-impact results and erosion results was found. Hard multi-layered a-C:H and Si-a-C:H coatings were found to be significantly less durable under fatigue loading than a-C:H:W. The influence of the coating mechanical properties and structure on these differences is discussed. The results of this study provide further strong evidence that in highly loaded mechanical contact applications requiring a combination of load support and resistance to impact fatigue, the optimum lifetime of coated components may be achieved by designing the coating system to combine these properties rather than by solely aiming to maximise coating hardness as this may be accompanied by brittle fracture and higher wear.

Calcium entry units (CEUs): perspectives in skeletal muscle function and disease

In the last decades the term Store-operated Ca2+ entry (SOCE) has been used in the scientific literature to describe an ubiquitous cellular mechanism that allows recovery of calcium (Ca2+) from the extracellular space. SOCE is triggered by a reduction of Ca2+ content (i.e. depletion) in intracellular stores, i.e. endoplasmic or sarcoplasmic reticulum (ER and SR). In skeletal muscle the mechanism is primarily mediated by a physical interaction between stromal interaction molecule-1 (STIM1), a Ca2+ sensor located in the SR membrane, and ORAI1, a Ca2+-permeable channel of external membranes, located in transverse tubules (TTs), the invaginations of the plasma membrane (PM) deputed to propagation of action potentials. It is generally accepted that in skeletal muscle SOCE is important to limit muscle fatigue during repetitive stimulation. We recently discovered that exercise promotes the assembly of new intracellular junctions that contains colocalized STIM1 and ORAI1, and that the presence of these new junctions increases Ca2+ entry via ORAI1, while improving fatigue resistance during repetitive stimulation. Based on these findings we named these new junctions Ca2+ Entry Units (CEUs). CEUs are dynamic organelles that assemble during muscle activity and disassemble during recovery thanks to the plasticity of the SR (containing STIM1) and the elongation/retraction of TTs (bearing ORAI1). Interestingly, similar structures described as SR stacks were previously reported in different mouse models carrying mutations in proteins involved in Ca2+ handling (calsequestrin-null mice; triadin and junctin null mice, etc.) or associated to microtubules (MAP6 knockout mice). Mutations in Stim1 and Orai1 (and calsequestrin-1) genes have been associated to tubular aggregate myopathy (TAM), a muscular disease characterized by: (a) muscle pain, cramping, or weakness that begins in childhood and worsens over time, and (b) the presence of large accumulations of ordered SR tubes (tubular aggregates, TAs) that do not contain myofibrils, mitochondria, nor TTs. Interestingly, TAs are also present in fast twitch muscle fibers of ageing mice. Several important issues remain un-answered: (a) the molecular mechanisms and signals that trigger the remodeling of membranes and the functional activation of SOCE during exercise are unclear; and (b) how dysfunctional SOCE and/or mutations in Stim1, Orai1 and calsequestrin (Casq1) genes lead to the formation of tubular aggregates (TAs) in aging and disease deserve investigation.

Chemical and biological properties of puffed Dendrobium officinale extracts: Evaluation of antioxidant and anti-fatigue activities

Abstract Dendrobium officinale (D. officinale, DO) is a traditional medicinal herb used in China. Phytochemicals and its antioxidant activity of puffed dendrobium extract was measured for antioxidant capacity. Physiological mechanism on skeletal muscle was analyzed by blood glucose, lactic acid, glycogen and ATP content and mRNA gene expression. Antioxidant effect of the extract on liver were measured. The extraction yield and phytochemical contents in DO extract were increased by the change of puffing pressure. In addition, antioxidant activities creased after explosive puffing process. DO extract treated with explosive puffing at high dose was significantly prolonged in swimming time. The glycogen content of puffing DO at high dose was significantly different. The expression of the PGC1-α and the level of ATP in PHD was higher. Explosive puffing DO strongly improve fatigue resistance of mice correlated with inhibiting the depletion of glycogen stores, regulating oxidation related enzymes, and modulating the activation of PGC-1α.

Improving Fatigue Resistance of Dihydropyrene by Encapsulation within a Coordination Cage.

Photochromic molecules undergo reversible isomerization upon irradiation with light at different wavelengths, a process that can alter their physical and chemical properties. For instance, dihydropyrene (DHP) is a deep-colored compound that isomerizes to light-brown cyclophanediene (CPD) upon irradiation with visible light. CPD can then isomerize back to DHP upon irradiation with UV light or thermally in the dark. Conversion between DHP and CPD is thought to proceed via a biradical intermediate; bimolecular events involving this unstable intermediate thus result in rapid decomposition and poor cycling performance. Here, we show that the reversible isomerization of DHP can be stabilized upon confinement within a PdII6L4 coordination cage. By protecting this reactive intermediate using the cage, each isomerization reaction proceeds to higher yield, which significantly decreases the fatigue experienced by the system upon repeated photocycling. Although molecular confinement is known to help stabilize reactive species, this effect is not typically employed to protect reactive intermediates and thus improve reaction yields. We envisage that performing reactions under confinement will not only improve the cyclic performance of photochromic molecules, but may also increase the amount of product obtainable from traditionally low-yielding organic reactions.

Effect of nano montmorillonite on the multiple self-healing of microcracks in asphalt mixture

This study investigated the effect of nano montmorillonite at different damage degree on the multiple self-healing properties of asphalt mixture by semicircular bending (SCB) test. Four kinds of asphalt binder were used to prepare the asphalt mixture. The cumulative fatigue life was measured and the multiple healing index (MHI) was proposed as an index to evaluate the multiple healing. The test results of different healing temperatures and damage degrees were fitted to obtain the threshold conditions of multiple self-healing. The fatigue life of asphalt mixture was evaluated by four-point bending beam test. Results showed that montmorillonite (MMT) could improve fatigue resistance and the self-healing ability of asphalt mixture, especially when the damage degree was small. The multiple healing capacity of the mixture decreased with the increased of the degree of damage. After freezing-thawing cycle, the self-healing ability decreased significantly. In addition, the results of multivariate nonlinear fitting showed that when the damage degree of montmorillonite modified asphalt mixture was less than 30% and the ambient temperature reaches 50°C, multiple times of self-healing can be effectively achieved. The fitting results can also be used to calculate the self-healing threshold conditions of other asphalt mixtures.

Microstructure, tensile and fatigue properties of high strength Al 7075 alloy manufactured via twin-roll strip casting

High strength Al 7075 alloy was manufactured via twin-roll strip casting (TRC) process, and its microstructure, tensile and fatigue properties were investigated. Commercial Al 7075 alloy fabricated via direct-chill (DC) casting process was also used for comparison. T6 and T651 heat treatments were implemented for both the materials to precipitate MgZn2(η) phases. The TRC alloy showed globular grain shape with η phases evenly distributed at the grain boundary and matrix interior, while the DC alloy showed elongated grains due to hot forging process and η phases clumped together at grain boundaries. The TRC alloy’s yield strength was 518.5 MPa, tensile strength was 578.2 MPa, and elongation was 6.9%. Comparing both the alloys’ mechanical properties, the TRC alloy’s strength was at least about 40 MPa higher and elongation was about 4% lower than the DC alloy. The TRC alloy showed about 20 MPa higher fatigue (fatigue limit) than the DC alloy. The DC alloy was observed to have coarse cracks on fatigue fractured surface. By contrast, the TRC alloy showed uniform fractured surface without coarse cracks, and the evenly-distributed η phases improved fatigue resistance efficiently. The present study sought to examine the correlation among TRC process-led microstructure, tensile and high-cycle fatigue properties while discussing the strengthening mechanism.

Regular endurance exercise of overloaded muscle of young and old male mice does not attenuate hypertrophy and improves fatigue resistance

It has been observed that there is an inverse relationship between fiber size and oxidative capacity due to oxygen, ADP, and ATP diffusion limitations. We aimed to see if regular endurance exercise alongside a hypertrophic stimulus would lead to compromised adaptations to both, particularly in older animals. Here we investigated the effects of combining overload with regular endurance exercise in young (12 months) and old (26 months) male mice. The plantaris muscles of these mice were overloaded through denervation of synergists to induce hypertrophy and the mice ran on a treadmill for 30 min per day for 6 weeks. The hypertrophic response to overload was not blunted by endurance exercise, and the increase in fatigue resistance with endurance exercise was not reduced by overload. Old mice demonstrated less hypertrophy than young mice, which was associated with impaired angiogenesis and a reduction in specific tension. The data of this study suggest that combining endurance exercise and overload induces the benefits of both types of exercise without compromising adaptations to either. Additionally, the attenuated hypertrophic response to overload in old animals may be due to a diminished capacity for capillary growth.

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.

Fatigue behavior of additively manufactured 17-4 PH stainless steel: The effects of part location and powder re-use

In laser beam powder bed fusion (LB-PBF), an additive manufacturing method, powder is often reconditioned and re-used multiple times to save cost. Considering the assumption that powder characteristics may affect the LB-PBF part quality, it is essential to understand how such characteristics change by re-using the powder and how these changes affect the mechanical properties of the fabricated part. Therefore, this study systematically investigates the effect of powder re-use on the powder characteristics, microstructural features, and mechanical properties of LB-PBF 17−4 precipitation hardening (PH) stainless steel (SS) specimens in both as-built and machined surface conditions. In addition, the dependency of microstructural features and mechanical properties on the location of the specimen on the build plate and how the powder re-use affects such location dependencies are studied. No significant effect of powder re-use and location dependency was observed on tensile or fatigue behavior of LB-PBF specimens in the as-built surface condition. However, an improved fatigue resistance, specifically in the high cycle regime, was observed for machined specimens fabricated by heavily re-used powder. In addition, considerable location dependency on the fatigue behavior was observed for machined specimens fabricated by unused powder. This location dependency, however, decreased with increasing powder re-use. The observed dependency of the fatigue behavior to the location and the improved fatigue resistance are explained by the better flowability and less compressibility of the re-used powder due to the decreased number of very fine particles and agglomerates within the powder batch. These improved powder characteristics resulted in a more uniform powder distribution on the build plate and less and smaller defects in the specimens.

Performance evaluation of asphalt concrete mixes under varying replacement percentages of natural sand

Frequently, load associated mode of failure, rutting and fatigue, are the main failure types found in some newly constructed roads within Baghdad, the capital of Iraq, and some suburban areas. The use of excessive amount of natural sand in asphalt concrete mixes which is attractive to local contractors could be one of the possible causes to the lack of strength properties of the mixes resulting in frustration in the pavement performance. In this study, the performance properties of asphalt concrete mixes with two natural sand types, desert and river sands, were evaluated. Moreover, five replacement rates of 0, 25, 50, 75, and 100% by weight of the fine aggregate finer than 4.75 mm were used. The performance properties including moisture susceptibility, resilient modulus, permanent deformation, and fatigue characteristics were evaluated using indirect tensile strength, uniaxial repeated loading and repeated flexural beam tests. Also, as a part of the research objective, the laboratory tests result were used to predict the performance using VESYS computer software. Results showed that mixes with high natural sand content (NSC) are more susceptible to moisture damage and rutting, lower resilient modulus and some improvement in fatigue resistance. Based on the obtained results, the necessity has rise to revise the current local specification for asphalt concrete which specifies the limits of natural sand content in the mixes of wearing and binder courses with 25% whereas for base course mixes no limit exist yet.

Quantitative Measurements of Backside Wear in Acetabular Hip Joint Replacement: Conventional Polyethylene Versus Cross-Linked Polyethylene.

As shown in previous studies, the modification of conventional polyethylene (CPE) to cross-linked polyethylene (XLPE) and the contribution of antioxidants result in a reduction in total wear. The aim of this study was to evaluate XLPE inserts with vitamin E and CPE regarding their resistance to the backside wear mechanism. A cementless hip cup system (Plasmafit® Plus 7, Aesculap) was dynamically loaded using CPE and XLPE inserts. The backside wear was isolated, generated and collected using the two-chamber principle. The chambers were filled with ultrapure water. After 2 × 106 cycles, the fluids were examined for wear particles according to a particle analysis. Using XLPE inserts, the backside wear was significantly reduced by 35%. While XLPE backside wear particles are significantly larger than CPE particles, they do not differ in their morphology. This study confirms the greater resistance to backside wear of XLPE compared to CPE. It can be assumed that the improved fatigue resistance of the vitamin E-stabilized XLPE inserts demonstrates XLPE’s effectiveness against micro-motion and the resulting changing tensions in interface areas like surface breakdown, pitting and the release of very small particles.

Improving fatigue resistance of railway axles by cold rolling: Process optimisation and new experimental evidences

Cold rolling is a relatively simple process known as a method to increase the surface hardness and the mechanical fatigue resistance of metal components by the introduction of residual compressive stresses. Cold rolling is also particularly convenient as it is applied in the final part of the manufacturing process. Despite the process being quite common in the manufacturing of various mechanical components, very limited information is available about the actual advantages that are achievable on safety critical components like railway axles. This paper focuses on both optimisation of the process parameters adopted on the Lucchini RS and on the advantages that are obtained when a well calibrated process is applied. The process is optimized by an analytical model, validated by means of an extensive number of residual stress measurements using the X-ray Diffraction method, that estimates the residual stress profile that is generated under the surface depending on different parameters (force, roller geometry, roller feed, axle geometry and steel grade). An overview of various advantages, demonstrated by an extended series of experimental full-scale tests, is then shown: an increase in the fatigue limit even in the presence of artificial micro-notches and corrosion fatigue. An analysis of the driving force at the crack tip is able to confirm the experimental evidences.

Microtissue Engineering Root Dentin with Photodynamically Cross-linked Nanoparticles Improves Fatigue Resistance of Endodontically Treated Teeth

IntroductionMicrotissue engineering root canal dentin with biopolymeric nanoparticles has the potential to improve mechanical properties of iatrogenically compromised root dentin. This study aims to characterize the surface mechanical property, bulk biomechanical response, and fatigue resistance of microtissue-engineered root dentin using photodynamically (photodynamic-activated [PDA]) cross-linked chitosan nanoparticles (CSnps). MethodsExperiments were conducted in 3 parts: part 1, root canal dentin sections were subjected to nanoindentations before/after treatment with CSnps and chemically (1-ethyl-3-[3-dimethylaminopropyl]carbodiimide [EDC] cross-linked CSnps) and photodynamically cross-linked CSnps to determine the properties of treated surfaces (n = 84 points/group); part 2, root canal dentin specimens treated with PDA cross-linked CSnps were subjected to strain analysis using customized moiré interferometry (n = 5/group); and part 3, root canal dentin specimens treated with EDC cross-linked CSnps, PDA cross-linked CSnps, and instrumented controls were tested using an accelerated fatigue loading protocol to evaluate the sustained loads and cycles at failure (n = 15/group). Data were analyzed using the paired sample t test, trend analysis, and Kaplan-Meier with log-rank tests at a significance of .05 in each experiment. ResultsRoot dentin microtissue engineered with PDA cross-linked CSnps showed a 16.8% increase in elastic modulus and a conspicuous decrease in strain distribution in cervical root dentin (P < .01). There was a significant reduction in the tensile strain formed at the apical region of the instrumented root dentin after treatment (P < .05). Survival analysis showed a statistically significant difference (P < .05) among evaluated conditions in fatigue resistance (ie, PDA cross-linked CSnps > EDC cross-linked CSnps > control). ConclusionsThis study highlighted the potential of root canal dentin microtissue engineering with PDA cross-linked CSnps to diminish radicular strain distribution and improve resistance to fatigue loads in endodontically treated teeth.

Improving fatigue resistance of high strength bolt under cyclic transverse loading by fine particle peening

In order to avoid the fatigue failure of high strength bolt under cyclic transverse loading, fine particle peening (FPP) treatment was conducted to the bolt using steel beads. The surface roughness, residual stress and surface hardness of the treated bolts were examined. Fatigue tests were performed for bolts with or without FPP treatment under transverse loading. The test results show that FPP treatment effectively improves the fatigue resistance of high strength bolt through reducing the surface roughness, increasing the surface hardness and introducing high compressive residual stress in the surface layer. For the FPP treated bolts, failure location changes from the bolt head fillet to thread root as loading displacement decreases to 0.3 mm. A finite element analysis was performed to analyze the failure behavior before and after FPP treatment.

Exercise May Ameliorate the Detrimental Side Effects of High Vitamin D Supplementation on Muscle Function in Mice.

ABSTRACTVitamin D is commonly prescribed to normalize deficiencies and to treat osteoporosis. However, the effect vitamin D supplements have on skeletal muscle health is equivocal. Although vitamin D is known to play a role in the various processes that maintain muscle integrity and function, recent studies utilizing high bolus dose vitamin D supplementation has demonstrated an increased risk of falls. Thus, the aim of this study was to investigate the effects of high vitamin D supplementation on skeletal muscle function with and without exercise enrichment. Four‐week old C57BL/10 mice (n = 48) were separated into either normal vitamin D (1500 IU/kg diet; unsupplemented) or high vitamin D (20,000 IU/kg diet; supplemented) treatment groups. Each dietary group was further separated into interventional subgroups where mice either remained sedentary or received exercise‐enrichment for 8 weeks in the form of voluntary running. Following the intervention period, whole body in vivo and ex vivo contractile analysis were performed. High vitamin D supplementation decreased force production in the slow‐twitch soleus muscles of sedentary mice (p < .01); however, exercise normalized this effect. Eight weeks of exercise did not improve fatigue resistance of the extensor digitorum longus (EDL) or soleus muscles in unsupplemented mice, likely due to low levels of activation in these muscles. In contrast, fatigability was improved in the EDL (p < .01) and even more so in the soleus (p < .001) in the supplemented exercise‐enriched group. Our data highlights that increasing vitamin D levels above normal reduces postural muscle force as seen in the soleus. Thus, unnecessary vitamin D supplementation may contribute to the increased risk of falls observed in some studies. Interestingly, when vitamin D supplementation was combined with exercise, force production was effectively restored, and fatigue resistance improved, even in muscles lowly activated. Regular exercise may modulate the effects of vitamin D on skeletal muscle, and be recommended for individuals receiving vitamin D supplements. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Asphalt self-healing with encapsulated rejuvenators: effect of calcium-alginate capsules on stiffness, fatigue and rutting properties

Asphalt self-healing with encapsulated rejuvenators is a new promising approach to extend the service life of asphalt pavements. Although the research performed so far has demonstrated the crack healing mechanism, no formulation/design for the capsule-bituminous mixture system, aiming to optimize its performance properties, has yet been proposed. This study investigates the effect of calcium-alginate capsules, containing sunflower oil, on the mechanical properties of bituminous mixtures. Performance-related properties of a continuously-graded bituminous mixture (stiffness, fatigue and rutting) were evaluated for different dosages of capsule incorporation (0.50, 0.75 and 1.00 wt%). The results showed that the stiffness properties of the bituminous mixture are affected by capsules and that this effect evolves with bitumen ageing. The stiffness modulus after ageing treatment was close to the bituminous mixture with 0.50 wt% and 0.75 wt% capsules and to the reference material. The fatigue resistance of all bituminous mixtures was similar and the bituminous mixtures with capsules did not show an improvement in fatigue resistance after resting, in comparison with the reference material. However, the results clearly indicated that the rejuvenator was released from the capsules and diffused into the bitumen. The bituminous specimens with capsules showed a strong rutting resistance, and the performance was even improved after the rest period.

In vivo characterization of skeletal muscle function in nebulin-deficient mice.

The conditional nebulin knockout mouse is a new model mimicking nemaline myopathy, a rare disease characterized by muscle weakness and rods within muscle fibers. We investigated the impact of nebulin (NEB) deficiency on muscle function in vivo. Conditional nebulin knockout mice and control littermates were studied at 10 to 12 months. Muscle function (force and fatigue) and anatomy (muscles volume and fat content) were measured in vivo. Myosin heavy chain (MHC) composition and nebulin (NEB) protein expression were assessed by protein electrophoresis. Conditional nebulin knockout mice displayed a lower NEB level (-90%) leading to a 40% and 45% reduction in specific maximal force production and muscles volume, respectively. Nebulin deficiency was also associated with higher resistance to fatigue and increased MHC I content. Adult nebulin-deficient mice displayed severe muscle atrophy and weakness in vivo related to a low NEB content but an improved fatigue resistance due to a slower contractile phenotype.

The Popeye mythology may be true: eating spinach can make you fatigue resistant!

The Popeye mythology may be true: eating spinach can make you fatigue resistant!

Influence of Pore Size and Crystallography on the Small Crack HCF Behavior of an A357-T6 Cast Aluminum Alloy

The high-cycle fatigue, small crack propagation behavior of an A357-T6 cast aluminum alloy is investigated. Laboratory X-ray micro-computed tomography \((\mu {\text {CT}})\) is used to assist in the manufacturing of two flat fatigue specimens containing subsurface shrinkage pores of different sizes (Pore 1 \(\sqrt{A} = 522\,\mu {\text {m}}\) against Pore 2 \(\sqrt{A} = 280\,\mu {\text {m}}\)). Surface crack monitoring is performed by means of optical microscopy and the cracked specimens are analyzed via scanning electron microscopy and electron backscatter diffraction techniques. The subsurface pores tend to induce intergranular crack nucleation, principally when the grain boundaries are oriented perpendicular to the loading direction. Pore 1 induces a fatigue life reduction of 500.000 cycles when compared to Pore 2. The crystallography is able to influence small crack propagation by slightly decelerating the crack growth rates as well as by altering the crack path topography. Tailoring of the crystallography for improved fatigue resistance requires an investigation of the optimal largest defect to grain size ratio.

Comparison of cyclic fatigue resistance of three NiTi glide path files with different cross-sectional geometric characteristics: An in vitro experimental study

Aim: New nickel-titanium file systems with improved fatigue resistance are being introduced to the market. This study aimed to compare the cyclic fatigue resistance (CFR) of G1 (#12) file of G file system (Micro Mega, Besancon, France), ProGlider (Dentsply Maillefer, Ballaigues, Switzerland) single-file rotary pathfinding system, and the #13 file of the Flex Glide system (Neoendo, Gurugram, India). Materials and Methods: Each group had a sample size of 10 files. The cyclic fatigue test was conducted in an artificial stainless steel canal in a customized device. The artificial canal contained an inner diameter of 1.5 mm with 60° angle of curvature and 5 mm radius of curvature. The file tip was positioned at 18 mm with a stopper and then rotation began, synchronized with timing by a digital stopwatch (Timex, Middlebury, CT) to the thousandth of a second. The center of the curvature was located at 7 mm from the tip of the device. For each instrument, time to fracture and the number cycles to fracture (NCF) were recorded. The data were analyzed statistically. Results: ProGlider files had a significantly higher resistance to cyclic fatigue than G1 files, which in turn had significantly higher CFR than Flex Glide instruments (P < 0.05). The lengths of the fractured segment of ProGlider files and G1 files were significantly higher than the Flex Glide files. Conclusion: Thus, it can be inferred that the ProGlider files had the highest resistance to cyclic fatigue and can be advocated for glide path preparations in severely curved canals.