Meccanica最新文献

Morrow’s model has been widely used in recent years as part of new methodologies for assessing the fatigue life of metallic materials through the laws of thermodynamics. It is used to quantify the rate of dissipated energy in the fatigue process, represented by the hysteresis loop of the stress–strain diagram of the material. Then, the dissipated energy is used to quantify the entropy generation of the fatigue process. Morrow’s model is a function of the amplitude of the cyclic loading, and a few constants that represent material properties. However, despite its apparent simplicity, the material properties, when are experimentally obtained, usually exhibit dispersions that can lead to inaccurate calculations. In this work, the sensitivity of Morrow’s model to the variability of these parameters is evaluated. In order to assess the sensitivity, a constant amplitude value was set, and the quotient ({{sigma }_f^{'}}/{{sigma }_U}), the fatigue strength coefficient (sigma_f^{'}), the fatigue ductility coefficient ({ epsilon_f^{'}}) and the cyclic strain hardening exponent (n^{'}) were varied. A factorial design was conducted to determine the effects of the interactions of the material parameters on the response of Morrow’s model. The results showed that Morrow’s model is strongly sensitive to the above mentioned parameters, affecting its accuracy. In an extended case study, the fatigue fracture entropy and the fatigue life of Al2024-T3 were determined using material parameters from different sources in order to determine the influence of the material parameters in the assessment of the estimation of fatigue damage. The study allowed concluding that a meticulous statistical treatment is required when characterizing the material properties and the design engineer must be aware of possible inaccuracies if Morrow’s model is used for estimating fatigue life, specially in the new thermodynamic approaches.

Large amplitude vibration of transmission line seriously affects the structural safety. Due to the low bending stiffness of superhigh transmission tower, vortex-induced excitation combining with support motion induced by the tower will cause significant complex dynamic behaviors of the transmission line. To reveal dynamic behaviors, this paper newly proposes a suspended cable model of the transmission line subjected to the boundary motion and vortex-induced vibration. Dynamic mechanism and vibration energy transfer are focused in the condition of primary and subharmonic resonances. Innovative behaviors of the transmission line under two excitations are revealed. Firstly, vortex-induced excitation is very weak and support motion usually plays a dominate role in the dynamic responses. Large amplitude vibration of transmission line observed in practice should be caused more by tower tip motion and the vortex-induced vibration is the incentive. Secondly, different weak support motion can cause different effect on dynamic responses of transmission line under vortex-induced vibration reflecting by different lock-in phenomenon, which leads us the application of active control measure in engineering.

We investigate the influence of elastic nonhomogeneity on compression of solid circular cylinders made of incompressible functionally graded neo-Hookean materials. The shear modulus is assumed varying in the axial direction. The fixed–fixed conditions are considered, i.e. two rigid platens are fixed to ends of sample surfaces. We transform the balance equations into ordinary differential equations (ODE) which are solved numerically. Based on, we investigate lateral deformed profiles of a solid circular cylinder. Furthermore, we compute von-Mises stress that governs the possible failure of the material.

We present a simple chemo-mechanical variational model for a fibrous material that describes (i) the emergence of the anisotropy due to microscopic buckling instabilities (ii) a diffusion in the substrate of the cell phase driven by the new created macroscopic bands characterized by intense compressive deformation. The model is applicable for simulating the spreading of cells within tissues and their interaction with tissue remodeling during mesenchymal migration.

Ocean surface wave profile due to the movement of an asymmetric (sloping) block of the ocean floor is analytically derived under the assumption of linearized water wave theory and by using the Fourier transformation method. A slight compressibility of the ocean water allows for generating acoustic-gravity modes that travel much faster than tsunami waves, the detection of which can contribute towards a possible warning mechanism. The influence of different parameters of interest, namely ocean depth, length, and slope of the block, on the surface wave profile is shown in the frequency domain. Finally, the frequency-domain solution is utilized to provide the surface profile in the time domain. The stationary phase approximation is applied to extract the far-field behavior of the surface waves. The individual impact of the acoustic-gravity and pure gravity modes is shown. Due to the asymmetry of the bottom motion, two different types of far-fields in opposite directions of each other from the source of initial ocean floor motion are obtained. The classical solutions of horizontal and flat moving ocean floors studied by Yamamoto (DOI:https://doi.org/10.1016/0261-7277(82)90016-X) in the frequency domain and Stiassnie (DOI: https://doi.org/10.1007/s10665-009-9323-x) in the time-domain are recovered as special cases. The envelope amplitude of the far-field surface fluctuates less when slope exists. The contributions from the acoustic-gravity modes in the far-field surface amplitude in the opposite directions are in opposite phases. The pure-gravity mode contribution is higher towards the direction of increasing slope with more oscillation. These results show insight into the surface profile when a submarine earthquake moves the ocean floor asymmetrically, and they could lead to a possible estimation of the fault geometry. These results can also be utilized to approximate arbitrary bottom movement using superposition of piece-wise asymmetric moving ocean floor arranged in a line and may provide important information for early tsunami detection mechanisms in the future.

Reliability of structures is evaluated by considering uncertainties present in the system, which can be characterized into aleatory and epistemic. Inherent randomness in the physical environment leads to aleatory, whereas insufficient knowledge about the system leads to epistemic uncertainty. For the reliability evaluation, ascertaining the sources of uncertainties poses a great challenge since both uncertainties coexist widely in structural systems. Aleatory uncertainties are quantified by probabilistic measures (such as first order reliability method, second order reliability method and Monte Carlo techniques), whereas epistemic uncertainties are quantified by various non-probabilistic approaches (such as interval analysis methods, evidence theory, possibility theory and fuzzy theory). However, major issues like interval extension problem and duality conditions that lead to overestimation hinder the versatility of application of such methods, thus uncertainty theory has been emerged to overcome these limitations. Given the existing uncertainties and limitations, a hybrid strategy has been constructed and referred to as “belief reliability”. A belief reliability metric is integration of three key factors: design margin, aleatory and epistemic uncertainty factor to evaluate the reliability of the structural system. In this paper, Monte Carlo simulation is adopted to account for aleatory uncertainty. On the other hand, epistemic uncertainty is quantified through adjustment factor approach using FMEA (failure mode effective analysis). Numerical examples are presented to substantiate the proposed methodology being applied to variety of problems both implicit and explicit nature in structural engineering.

A complete thermodynamical analysis for a blood model, based on mixture theory, is performed. The model is developed considering the blood as a suspension of red blood cells (solid component) in the plasma (fluid component), and taking into account the temperature effects. Furthermore, two independent scalar internal variables are introduced accounting for additional dissipative effects. Using Clausius-Duhem inequality, the general thermodynamic restrictions and residual dissipation inequality are derived. The thermodynamic admissibility with the second law of thermodynamics is assessed by means of the extended Coleman-Noll procedure; in one space dimension we exhibit a solution of all the thermodynamical constraints.