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Applications
Published in Cameron Coates, Valmiki Sooklal, Modern Applied Fracture Mechanics, 2022
Cameron Coates, Valmiki Sooklal
In this case study, a failed railway rail which was used for heavy cargo trains is investigated in order to find out its root cause. In addition to the fatigue load, rails are also subjected to other high mechanical loads and harsh environmental conditions. The main loading components are rolling contact pressure, shear and bending forces from the vehicle weight, thermal stresses due to restrained elongation of continuously welded rails, and residual stresses from manufacturing and welding in the field. The latter makes it more difficult to control in terms of weld quality, due its dependence on the operator. In this study, a failed railway rail shown in Figure 4.27, which was used for heavy cargo trains, was investigated in order to find out its root cause. The analysis involved performing macroscopic inspections, chemical analysis, scanning electron microscope (SEM) observations, and metallographic examinations.
Friction and Wear in Extreme Conditions
Published in Ahmed Abdelbary, Extreme Tribology, 2020
Surface features that correlate to the above macroscopic travel were examined using a high-resolution scanning electron microscope (SEM). The collective remark is that the wear intensity is highly nonuniform along the contact surfaces. However, the overall features were similar in all devices irrespective of the test conditions. Based on this observation, the mechanisms responsible for material removal during the wear process are classified into: adhesion-dominated wear, as shown in Fig. 8.10, in which the contact regions and wear tracks appear polished on the surface of the friction pad. The possible reason for this observation is that the asperities were sheared off or were plastically deformed during early wear cycling. third-body wear (associated with device failure), where the agglomerates formed in the previous regime are trapped between the friction pad and the wear track. The applied normal force causes these agglomerates to stick to one of the contact surfaces and form debris patches along the wear track, as shown in Fig. 8.11. The severe wear in this localized region caused the debris patch on one of the clamps to get lodged in the trench of the counter surface. Finally, the clamps undergo “severe wear” characterized by a trench formation where the contact surfaces get locked and cause device failure.
Continuum theory of granular materials
Published in M. Oda, K. Iwashita, Mechanics of Granular Materials, 2020
The relative importance of the higher order stress μij is obviously determined by the ratio of the characteristic length of the microstructure (= l in the present example) to the length scale of the macroscopic deformation pattern.
Three-dimensional phase field modeling of progressive failure in aramid short fiber reinforced paper
Published in Mechanics of Advanced Materials and Structures, 2022
Song Zhou, Tong Wang, Xiaodi Wu, Zhi Sun, Yan Li, Filippo Berto
Composites can be studied from different length scales, ie., microscopic length scale, mesoscopic length scale and macroscopic length scale. In macro-scale models, the composite is normally treated as homogeneous material with anisotropic properties, and proper homogenization technique is required [20]. Such models without consideration of microstructures of composites is more proper for modeling large sized structures. However, local failure processes in different material phases cannot be captured. Under mesoscopic length scale, each lamina is modeled separately as an orthotropic plate. In this case, cohesive elements are normally inserted into the neighboring laminas to capture possible delamination [21–26]. For micro-scale models, the microstructure of fiber, matrix, and the interface between then are all considered, and thus provide a precise model to dig into the local failure mechanism involving failure processes in matrix, fiber, and the interface [27, 28]. In order to investigate the complicated failure mechanics, and the role of microstructure, material property, porosity of the composite, it is investigated from microscopic length scale in this paper.
Models for Droplet Motion on Hydrophilic and Hydrophobic Surfaces
Published in Heat Transfer Engineering, 2022
Mustafa Sengul, Esra H. Isik, I. Bedii Ozdemir
However, the contact angle of a droplet can vary depending on its past, in particular, on the initial formation process. The variations occur in a range of contact angles from a receding contact angle, to an advancing contact angle, and this feature is called the hysteresis [44]. In order to consider these variations, further model modifications are necessary. When the local Reynolds number on the contact line, is less than 1, the Cox model [11] can be evolved into, where l is characteristic length, is a macroscopic length scale and is the split length. Yokoi et al. [10] further developed the dynamic contact angle model following the Tanner’s law [45]. where and are material-based properties of receding and advancing angles and are experimentally [10] given as 9 × 10–9 and 9 × 10–8, respectively.
Thermodynamics from Lagrangian theory and its applications to nanosize particle systems
Published in Molecular Physics, 2021
Eduardo Hernández-Huerta, Ruben Santamaria, Tomás Rocha-Rinza
The laws of thermodynamics represent the pillars of thermodynamics. For example, the Zero Law of Thermodynamics establishes the heat flux from hot bodies to cold bodies to reach the thermal equilibrium, and the First Law of thermodynamics states that every physical system has internal energy that can be changed by the action of external factors, like mechanical work and heat. This law is different to the mechanical law of energy conservation due to the presence of the heat term in the expression of the first law. The thermodynamic laws are the outcome of experimental observations, which give them an empirical character [1]. Yet, we know they have a microscopic origin, and there should be a derivation from a more fundamental theory [2]. The first attempts to link the microscopic theory to the macroscopic theory are attributed to the creators of kinetic theory [3–5]. In fact, they established the foundations of Statistical Mechanics, where statistical approaches are combined with (classical and quantum) mechanics to determine the properties of the macroscopic bodies with ensemble averages.