International Journal of Engineering Science最新文献

A riot-control water cannon is a large, supposedly nonlethal apparatus that uses pressurized water to control and disperse crowds. However, riot-control water cannons may cause personal injury if directly aimed at the human forehead, for example. Therefore, we systematically analyzed, via a numerical model, the spatio-temporal evolution of the equivalent pressure of a water cannon and its influence on the human body dynamic response, especially considering the head and neck body regions. The simulation results suggest that 10 m is a critically dangerous working distance because the impact of a water cannon can lead to skull, cervical vertebra and brain injuries. In addition, compared to side/back impacts, frontal impacts are much more dangerous due to a more extensive range of head movement. Oblique impact induces rotational movement on the human body, resulting in a significant risk of injury. A quantitative injury risk analysis is presented to provide safety guidance for water cannon usage.

The aim of this article is to analyse the nonlinear biomechanics of diseased carotid arteries as a potential tool for predicting the onset of cerebral strokes. A two-way coupled three-dimensional (3D) hyperelastic fluid-structure interaction (FSI) analysis of a diseased carotid artery with abnormal luminal projections at the carotid bulb known as carotid web (CaW) is conducted on the geometry of a patient artery, built upon employing CT angiography images. The blood-flow model incorporates non-Newtonian pulsatile turbulent fluid, and the artery wall is considered hyperelastic subject to blood-induced motion. The hemodynamics of artery induced by transient boundary conditions is determined, specifically focusing on shifts in crucial hemodynamic parameters such as wall shear stress (WSS) and alterations in the blood velocity pattern. Structural assessment of the artery wall involves quantifying the von Mises (VM) stress and deformation field. The analysis demonstrates that different CaW models result in different flow patterns for a selection of time steps in a cardiac cycle. The findings reveal that the presence of the web, as the most common disease among younger adults, can significantly influence the hemodynamic parameters and potentially accelerate the formation of thrombus and atherosclerosis. Hemodynamic analysis can potentially predict specific sites prone to plaque formation and rupture within the carotid artery.

Considering the prominent properties of nanocomposites, the closer their modeling is to reality, the more suitable it is for engineering applications. One of the steps that can be taken for this purpose is to include the waviness of the reinforcements in the study of nanocomposites. In this article, for the first time, the effects of the waviness of reinforcing nanotubes in spherical nanocomposites on the behavior of mechanical waves have been studied. Several different ideas, such as adopting random contact model, the excluded volume of two spherocylinders, microscopic images and experimental results, are used for modeling wavy nanotubes in spherical nanocomposites, each of which has its own characteristics. For modeling the spherical nanocomposite itself, three-dimensional elasticity theory in spherical coordinates is used. For several different cases, the results of the present models are compared and calibrated with the results of experimental tests, which adds to the attractiveness of the work. The influences of various parameters such as radius of spherical nanocomposite, waviness factor, nanotubes volume fraction and wave number on the results are also investigated. From the results of this article, the idea can come to mind that the effects of the waviness of the nanotubes cannot be ignored in some cases and should be included in the modeling, otherwise it will produce significant errors in the results.

Effective elastic and conductive properties of 2-D random (“disordered”) mixtures of several types are examined by computational means. It is found that an “equivalent” material of simple microgeometry – a continuous matrix with elliptical inhomogeneities – can be identified, that matches both the elastic and the conductive properties, in the entire range of property contrast between constituents. Moreover, the ellipse eccentricities are almost the same for different types of the random mixtures in the volume fraction range (0.3 – 0.7); in this range, there is no need in specifying the type of a mixture, as far as the effective properties are concerned. It is also found that the effective properties of the considered random mixtures are well described by the Mori-Tanaka-Benveniste model (in spite of the fact that this model was not intended for them).

We also examined the effect of inhomogeneity interactions in a matrix composite on the cross-property connections between the elastic and conductive properties. Whereas the interactions generally produce strong effect on each of the properties, their effect on the connections is negligible (the latter can be taken from the non-interaction approximation).

It is argued that most findings related to 2-D random mixtures should apply to 3-D ones as well.

In this paper we propose an approach for calculating the effective physical properties of porous materials (for example, sedimentary rocks) which is based on the unified structure of the pore space. This approach is based on the Generalized Differential Effective Medium (GDEM) method. This method generalizes the classical differential scheme (DEM) for the case of many types of inclusions. The physical properties of a composite calculated using the GDEM depend on how the solution is constructed.

A porous medium is represented by the elastic weakly conductive matrix with embedded inclusions of two types (spheroidal and cylindrical), saturated with a conductive liquid. The cylindrical inclusions appear in the system when the porosity value exceeds the void percolation. Parameters, that characterize the inclusions (the aspect ratio of spheroidal inclusions and the relative part of cylindrical inclusions), are determined in the inverse problem solving process for the experimental data approximation of the effective conductivity as a porosity function. These parameters, obtained by solving the inverse problem, were used to calculate the effective elastic moduli, electrical conductivity, and dielectric permittivity of porous media. The results obtained describe well the available experimental data for different effective physical properties.

In this paper, thermoelastic stresses of a functionally graded annular rotating disc subjected to internal and external pressure has been studied. Elasticity modulus, thermal conductivity, coefficient of thermal expansion and density of the disc are presumed to vary radially in accordance with three distinct power-law functions and the Poisson's ratio remains constant. A gradient index parameter is opted among -0.5 and 0.5. When this parameter equals zero, the disc turns into an isotropic disc. The distributions of radial and tangential stresses on the disc are obtained for various gradient parameters.

This study presents an original and novel investigation into the mechanics of piezo-flexo-magneto-elastic nanocomposite doubly-curved shells (PFMDCSs) and the ability to detect the lower and higher levels of electro-magnetic fields. In this context, by utilizing the first-order shear deformation shell model, stresses and strains are acquired. By imposing Hamilton's principle and the von Kármán approach, the governing equations have been obtained. The intelligent shell model consists of size-dependent influences, viz., strain gradients. This will take place via Mindlin's strain gradient elasticity theory and the subsequent re-establishing of the mathematical framework by incorporating this concept. The strain gradient results in a flexoelectric/flexomagnetic effect. The converse effect of the magnetic field on the basis of a close circuit has been assumed. The developed bending equations have been transferred into the algebraic ones by substituting an analytical technique based on homogeneous immovable simple support for the four edges. The problem has been solved according to the Newton-Raphson iteration scheme, and transverse deflections have been computed. For researching the rightness and precision of the shell models together with the solution process, a comparison is prepared by the finite element method (FEM) results for simplified shells, and a good correlation has been observed. At last, by examining several factors governing the problem, the conditions under which the magnetic effects can be noticeable and dominant in doubly-curved shells have been sought. This study could serve as a benchmark reference for piezoceramic-DCSs, as the presented governing equations are original. The most interesting outcome of this research is that the electro-magnetic response of intelligent structures can be entirely geometry-dependent.

A mathematically well-posed nonlocal model is formulated based on the variational approach and the transfer matrix method to investigate the size-dependent elastostatics of nonuniform miniaturized beams. The beams are composed of an arbitrary number of sub-beams with diverse material and geometrical properties, as well as small-scale size dependency. The model adopts a stress-driven nonlocal approach, a well-established framework in the Engineering Science community. The curvature of a sub-beam is defined through an integral convolution, considering the bending moments across all cross-sections of the sub-beam and a kernel function. The governing equations are solved and the deflections are derived in terms of some constants. The formulation uses local and interfacial transfer matrices, incorporating continuity conditions at cross-sections where sub-beams are joined, to define relations between constants in the solution of a generic sub-beam and those of the first sub-beam at the left end. The boundary conditions are then imposed to derive an explicit, closed-form solution for the deflection. The solution significantly simplifies the study of nonuniform beams with multiple sub-beams. The predictions of the model for two limiting cases, namely local nonuniform and nonlocal uniform beams, are in excellent agreement with the available literature data. The flexural behavior of nonuniform miniaturized beams, composed of two to five different sub-beams and subjected to different boundary conditions, is studied. The results are presented and discussed, emphasizing the effects of the material properties, nonlocalities, and lengths of the sub-beams on the deflection. It is demonstrated that the flexural response of nonlocal nonuniform beams is more complex than local counterparts. Unlike the local beams, dividing a nonlocal uniform beam into multiple sub-beams and then reconnecting them changes the overall stiffness of the beam. The study highlights the potential to design nonuniform miniaturized beams with specific configurations to control their flexural response effectively.

A differential scheme is proposed for the calculation of the components of the effective electrical conductivity tensor of a microinhomogeneous material taking into account the Hall effect. The presence of the Hall effect results in an appearance of asymmetry of the components of the conductivity tensor and a dependence of these components on the magnitude of the magnetic field applied to the material. In this case, the differential scheme leads to a system of matrix differential equations that were solved numerically in the current work. This solution was obtained for materials containing spherical or cylindrical inclusions. In the case of cylindrical inclusions, the results were obtained for inclusions with the symmetry axes parallel or orthogonal to the magnetic field. A comparison of the results obtained by the proposed methodology to the low concentration approximation was carried out.

We introduce a new rheological nonlinear model for some granular media such as masonries. The latter may demonstrate a rather complex behaviour. In fact, considering a masonry one can see that relative rotations of bricks are most important in comparison with deformation of bricks themselves. As a result, one gets stresses and couple stresses as static characteristics of such a medium. Using the Cosserat point approach for modelling of orientational interactions between masonry elements we provide a deformation energy for such a medium which takes into account both material and geometrical nonlinearity.