Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
6,431
result(s) for
"Fatigue resistance"
Sort by:
Mesoscale bicontinuous networks in self-healing hydrogels delay fatigue fracture
Load-bearing biological tissues, such as muscles, are highly fatigue-resistant, but how the exquisite hierarchical structures of biological tissues contribute to their excellent fatigue resistance is not well understood. In this work, we study antifatigue properties of soft materials with hierarchical structures using polyampholyte hydrogels (PA gels) as a simple model system. PA gels are tough and self-healing, consisting of reversible ionic bonds at the 1-nm scale, a cross-linked polymer network at the 10-nm scale, and bicontinuous hard/soft phase networks at the 100-nm scale. We find that the polymer network at the 10-nm scale determines the threshold of energy release rate G₀ above which the crack grows, while the bicontinuous phase networks at the 100-nm scale significantly decelerate the crack advance until a transition Gtran far above G₀. In situ small-angle X-ray scattering analysis reveals that the hard phase network suppresses the crack advance to show decelerated fatigue fracture, and Gtran corresponds to the rupture of the hard phase network.
Journal Article
Carbon Fibre-Reinforced Polymer (CFRP) Composites in Civil Engineering Application—A Comprehensive Review
In civil engineering, carbon fibre-reinforced polymer (CFRP) composites have emerged as a promising alternative to conventional materials. The article provides a comprehensive overview of the application of CFRP composites in various building structural elements and their characteristics and properties, such as their fatigue and corrosion resistance, stiffness and high strength, and incorporation of temperature factors. The advantages and disadvantages of CFRP composites and the current trends and prospects for CFRP composites in the construction sector are discussed. In addition, the article compares various studies on CFRP composites to shed light on their performance and potential limitations. This paper aims to provide useful information to researchers and practitioners interested in using CFRP composites in civil engineering applications. In addition, the article discusses emerging materials in CFRP, such as nanostructured carbon fibres, hybrid fibre reinforcement, and self-sensing CFRP. Additionally, the paper outlines how CFRP composites promote sustainability by increasing structural durability and longevity.
Journal Article
Fatigue Resistance and Cracking Mechanism of Semi-Flexible Pavement Mixture
Semi-flexible pavement (SFP) is widely used in recent years because of its good rutting resistance, but it is easy to crack under traffic loads. A large number of studies are aimed at improving its crack resistance. However, the understanding of its fatigue resistance and fatigue-cracking mechanism is limited. Therefore, the semi-circular bending (SCB) fatigue test is used to evaluate the fatigue resistance of the SFP mixture. SCB fatigue tests under different temperature values and stress ratio were used to characterize the fatigue life of the SFP mixture, and its laboratory fatigue prediction model was established. The distribution of various phases of the SFP mixture in the fracture surface was analyzed by digital image processing technology, and its fatigue cracking mechanism was analyzed. The results show that the SFP mixture has better fatigue resistance under low temperature and low stress ratio, while its fatigue resistance under other environmental and load conditions is worse than that of asphalt mixture. The main reason for the poor fatigue resistance of the SFP mixture is the poor deformation capacity and low strength of grouting materials. Furthermore, the performance difference between grouting material and the asphalt binder is large, which leads to the difference of fatigue cracking mechanism of the SFP mixture under different conditions. Under the fatigue load, the weak position of the SFP mixture at a low temperature is asphalt binder and its interface with other materials, while at medium and high temperatures, the weak position of the SFP mixture is inside the grouting material. The research provides a basis for the calculation of the service life of the SFP structure, provides a reference for the improvement direction of the SFP mixture composition and internal structure.
Journal Article
Optimization of Properties for Alumina-Spinel Refractory Castables by CMA (CaO-MgO-Al2O3) Aggregates
Aiming at optimizing properties of alumina-spinel refractory castables, coarse corundum particles were replaced partially with the particles of a novel porous multi-component CMA (CaO-MgO-Al2O3) aggregate in the same size. Properties including the bulk density, apparent porosity, strength, slag corrosion resistance, thermal shock resistance and thermal fatigue resistance of alumina-spinel refractory castables containing CMA aggregates were evaluated contrastively. The results demonstrated that the incorporation of CMA aggregates can significantly improve thermal shock resistance and thermal fatigue resistance of castables, although companying with slight decrease in the bulk density and strength. Moreover, slag penetration resistance of castables can also be enhanced by CMA aggregates with appropriate particle size. The influence of CMA aggregates on properties of alumina-spinel refractory castables depended strongly on their particle size.
Journal Article
A computational study of fatigue resistance of nitinol stents subjected to walk‐induced femoropopliteal artery motion
Fatigue resistance of nitinol stents implanted in femoropopliteal arteries is a critical issue because of their harsh biomechanical environment. Limb flexions due to daily walk expose the femoropopliteal arteries and, subsequently, the implanted stents to large cyclic deformations, which may lead to fatigue failure of the smart self-expandable stents. For the first time, this paper utilised the up-to-date measurements of walk-induced motion of a human femoropopliteal artery to investigate the fatigue behaviour of nitinol stent after implantation. The study was carried out by modelling the processes of angioplasty, stent crimping, self-expansion and deformation under diastolic-systolic blood pressure, repetitive bending, torsion and axial compression as well as their combination. The highest risk of fatigue failure of the nitinol stent occurs under a combined loading condition, with the bending contributing the most, followed by compression and torsion. The pulsatile blood pressure alone hardly causes any fatigue failure of the stent. The work is significant for understanding and improving the fatigue performance of nitinol stents through innovative design and procedural optimisation.
Journal Article
No sex differences in time-to-task failure and neuromuscular patterns of response during submaximal, bilateral, isometric leg extensions
BackgroundIn general, it has been suggested that females are more fatigue-resistant than males, with the magnitude of difference being most pronounced during low-intensity sustained contractions. However, the mechanisms for the apparent sex difference have not yet been fully elucidated in the literature. This study aimed to examine sex-related differences in fatigability and patterns of neuromuscular responses for surface electromyographic (sEMG) and mechanomyographic (sMMG) amplitude and frequency (MPF) characteristics during a sustained submaximal bilateral, isometric leg extension muscle action.MethodsA sample of 20 young recreationally active males and females with previous resistance training experience performed a sustained, submaximal, bilateral isometric leg extension until task failure. Time-to-task failure was compared using a nonparametric bootstrap of the 95% confidence interval for the mean difference between males and females. Additionally, patterns of response for sEMG and sMMG amplitude and MPF of the dominant limb were examined using linear mixed effect models.ResultsThere were no differences in time-to-task failure between males and females. Additionally, neuromuscular responses revealed similar patterns of responses between males and females. Interestingly, sEMG amplitude and sMMG amplitude and MPF all revealed non-linear responses, while sEMG MPF demonstrated linear responses.ConclusionThese data revealed that time-to-task failure was not different between males and females during sustained submaximal bilateral, isometric leg extension. Interestingly, the parallel, non-linear, increases in sEMG and sMMG amplitude may indicate fatigue induced increases in motor unit recruitment, while the parallel decreases in sMMG MPF may be explained by the intrinsic properties of later recruited motor units, which may have inherently lower firing rates than those recruited earlier.
Journal Article
Calculating the fatigue strength of load-bearing structures of special self-propelled rolling stock
This research primarily focuses on the strength indicators of the bearing structures of ADM-1 special self-propelled rolling stock. The special self-propelled rolling stock used by Uzbek railroads reaching the end of their functional life is a pertinent problem as Uzbekistan's railway system is growing rapidly, but there is a lack of enough funds to buy new special self-propelled rolling stock. Hence, it is vital to fix the issues with ADM-1 special self-propelled rolling stock by overhauling them. At the outset, the researchers divided the frame of a special a self-propelled rolling stock into multiple sections. Subsequently, these individual sections were analyzed closely to spot out issues. The precise location of the fatigue defect occurrence on the longitudinal beams was determined by the analysis of the individual sections of the special self-propelled rolling stock. During the motor carriage's modernization, which is an approach to extend the service life and improve the durability of special self-propelled rolling stock, this analysis helped in pinpointing exactly the location on the frame where the stress measurements had to be calculated. Pre- and post-modernization calculations were carried out on the vehicle to determine the optimal placement of the reinforcing plates. Additionally, normative calculations were also conducted and a new design mode distinct from the repair loads was implemented. The computation results revealed that the fatigue resistance reserve coefficient and service life value prior to the bearing structure’s modernization in section 1 were below the required values of n = 1.5 and 1.49, respectively. All the sections of the load-bearing structure fulfilled the fatigue resistance reserve coefficient standards after the modernization. The computational model of the motor carriage's structural strength was created in the ANSYS Workbench platform. This research intends to enhance the strength determination procedures and provides recommendations for design and restoration of modern structures of special self-propelled rolling stock.
Journal Article
A fatigue-resistance topology optimization formulation for continua subject to general loads using rainflow counting
Currently, fatigue-resistance topology optimization has received ever increasing attention, in which most of the literature considers this issue as a simple extension of stress-based topology optimization. However, previous approaches may not be applicable when considering general loads, as the conventional uniaxial rainflow counting method, commonly employed in prior studies, can result in significant errors. Furthermore, the inclusion of general loads introduces additional nonlinearity to fatigue-resistant topology optimization, posing challenges in identifying the optimal solution. To this end, a novel methodology for fatigue-resistance topology optimization considering general loads is proposed in this paper. The independent rainflow counting method is utilized during the process of structural damage estimation. The damage penalization model is subsequently adopted to reduce the nonlinearity by scaling the value of fatigue damage. To illustrate the necessity of an independent rainflow counting method, an example of a double
L
-shaped structure subjected to general loads is presented. The augmented Lagrangian (AL) approach is introduced to transform numerous damage constraint equations into the objective function, generating a sequence of box-constrained optimization sub-problems. After employing the typical SIMP technique, the relative sensitivities of the AL function regarding design variables are derived, which facilitates the efficient solution using the method of moving asymptotes (MMA). Through 2D and 3D numerical tests, the effectiveness of the proposed method is validated in comparison to the traditional method. Further investigation is conducted into the influences of general loads, damage penalization model, and manufacturing error robustness. In addition, the fatigue-resistance performance of a bearing support of a wind turbine is improved by the suggested approach, and its overall weight is decreased by 25.40%. The proposed method addresses the nonlinear and localized nature of fatigue-resistant topology optimization more efficiently. The results indicate that the proposed method can develop a lightweight design for structures under general loads.
Journal Article
Durability as an index of endurance exercise performance: Methodological considerations
Endurance athletes routinely complete physiological assessments to predict performance, inform training programmes and monitor subsequent training adaptations. This profiling is typically performed with the athlete in a ‘fresh’ (i.e., rested) condition, but physiological profiling variables deteriorate during prolonged exercise. Durability has been defined as the resilience to the deterioration of physiological variables and performance during or following prolonged exercise. Herein, we review the current approaches to measure durability. The construction of the fatiguing protocol affects durability profiles, with greater relative intensity and duration resulting in more marked deterioration of baseline measures. The design of durability assessments should control for factors that could impact durability measurements, such as nutrition and environmental characteristics, to ensure that outcomes are repeatable and can be compared between athletes or over time in the same athlete. The selection of these parameters should be based on the proposed research question or applied context and take account of the training status of the athlete. Accordingly, this review highlights important considerations to ensure that protocols for profiling durability in research and applied practice are appropriate. What is the topic of this review? The review discusses current approaches and essential considerations for assessing physiological durability. What advances does it highlight? The review summarizes various methodological approaches used to profile the resilience to deterioration of physiological variables during or after prolonged exercise, (i.e., durability). It highlights key considerations for durability profiling in research and applied settings, including exercise intensity, duration, nutritional and environmental factors, and the appropriateness of examining physiological decrements in the field or in the laboratory.
Journal Article