Forces in mechanics最新文献

Fracture networks are crucial in controlling rock mass permeability. Some of the important features of the fracture networks like the density, interconnectivity, spatial distribution, and fracture apertures determine the success of the subsurface operations. Fracture networks can be studied with analogue studies, physical experiments, and numerical modeling. In this study, we analyse the evolution of a two-dimensional fracture network under gravitational and shear loads using the lattice modeling capabilities of the microstructural modeling environment “Elle”. The simulation cases include varying gravitational loads and Young’s moduli of the formations. The topological progression of the modeled fracture network from isolated to interconnected nodes depicts a realistic network evolution process. The study shows that the rock stiffness exhibits a direct correlation with the number of fractures influencing the average aperture size of the network. A higher gravity load resulted in the development of a sparse fracture network. Stiffer rock models also showed an early onset of fracturing.

We propose a novel approach to optimize the design of heterogeneous materials, with the goal of enhancing their effective fracture toughness under mode-I loading. The method employs a Gaussian processes-based Bayesian optimization framework to determine the optimal shapes and locations of stiff elliptical inclusions within a periodic microstructure in two dimensions. To model crack propagation, the phase-field fracture method with an efficient interior-point monolithic solver and adaptive mesh refinement, is used. To account for the high sensitivity of fracture properties to initial crack location with respect to heterogeneities, we consider multiple cases of initial crack and optimize the material for the worst-case scenario. We also impose a minimum clearance constraint between the inclusions to ensure design feasibility. Numerical experiments demonstrate that the method significantly improves the fracture toughness of the material compared to the homogeneous case.

Present theory investigates the dimensionless vibration frequencies, deformations, and stresses for multilayered and sandwich arches using exponential shear and normal deformation theory (ESNDT). Present studies consider the effect of $\left[1+\left(z/R\right)\right]$radius of curvature while selecting the displacement field of arches under the action of uniform load. It includes the effects of transverse shear $\left({\gamma }_{xz}\ne 0\right)$ and transverse normal deformation$\left({\epsilon }_z\ne 0\right)$ i.e., effect of thickness stretching. The governing relations are obtained using the Navier's method, and Hamilton's virtual work principle. The proposed layered arches are completely free from shear correction, and its top and bottom surfaces is satisfies zero traction free end conditions. Present study obtained very accurate natural frequencies for layered sandwich arches than other theories because, available literature not considered the thickness stretching effect i.e.,$\left({\epsilon }_z=0\right)$. Hence, the present scientific investigation accounts the effect of thickness stretching i.e.,$\left({\epsilon }_z\ne 0\right)$. However, the non-availability of exact elasticity results of bending and dynamic responses for layered sandwich arches. Present theory is obtained vibration frequencies, displacements, and stresses of layered composite and sandwich arches; the results are compared and validates through prior published literature.

This paper deals with the flow of non-Newtonian nanoliquid past an unsteady stretched exterior in attendance of Stefan blowing/suction. Model for Casson liquid has been taken into account to represent the non-Newtonian liquid. Two phase fluid replica for nanofluid has been considered. Similarity alterations are applied to transform the leading pdes (partial differential equations) to ordinary ones. Runge–Kutta method of order four has been used to solve the altered equations numerically with the help of shooting technique. Wall shear stress, heat and mass transfer coefficients diminish with the rise in unsteadiness. Fluid's velocity and temperature are found to rise with the enhancement in Stefan blowing/suction parameter. Temperature of the fluid rises but fluid's velocity diminishes for the rising values of Casson parameter. Basically, the pertinent parameters affect the stream, warmth and accumulation transport significantly which can be viewed by the figures and tables presented here and also by their physical analysis.

Based on the Euler-Bernoulli beam theory, the coupling effect between bending vibration mode shape and longitudinal vibration mode shape of the beam is analyzed when the beam is supported by eccentric simply supported. Under the assumption of small deformation, the vibration control equations and the coupling boundary conditions are obtained through Hamilton's principle and the principle of virtual work variation. The numerical results under three different boundary conditions are given. It shows that the natural frequencies of the beam vary with the eccentricity distances are in complete agreement with the results obtained from finite element analysis and literature. The results strongly proved the validity and correctness of the coupling method in this paper. It also indicates that eccentric simply supported constraints have non-local effects.

The brake system is one of the most critical components in transportation, especially for massive machines such as trains. Brake components decelerate the train by using friction force between the train wheels and the brake block. The efficacy of a brake system strongly depends on the quality of the material components, especially the brake blocks. This study investigated the failure brake block on three different model of brake blocks used in Indonesia (grey cast iron, composite, and magnetic composite). Several characteristics and evaluations are used, i.e., non-destructive surface analysis, microhardness, Energy Dispersive X-Ray (EDX) analysis, and computational Finite Element Method (FEM). The microscopic analysis showed severe conditions at the non-magnetic brake, followed by the magnetic brake. The roughness test indicates that the Ra value for the magnetic brake is higher than the non-magnetic composite brake, with 4.59 and 4.08, respectively. The micro hardness test revealed that in metal-based materials indentation, the results showed magnetic composite has the highest value followed by cast iron and non-magnetic composite with 306, 283, and 218, respectively. In EDX examination, magnetic brakes have filler materials such as Calcium Carbonate and Wollastonite that create better performance. The study showed that the magnetic composite brake blocks demonstrate adequate resistance to failure due to the composite's filler material, which acts as a reinforcing agent.

This study aims to investigate the influence of radiation, thermal conductivity and variable viscosity on natural convective flow on a semi-infinite perpendicular plate. Variable viscosity, thermal conductivity and thermal radiation are considered for the given study. The dimensional governing equations are framed with the use of the mentioned parameters and then these equations were converted into dimensionless equations by applying non dimensional quantities. The main aim of this study is to find the Nusselt number and skin friction for both air and water for considered parameters. Using the finite difference method through Fortran software, numerical solutions to the governing heat equations and dimensionless momentum equations were computed. The results for the parameters thermal conductivity, variable viscosity, radiation, and Prandtl number for both air and water are displayed via various graphs. The skin friction coefficients, Nusselt parameter, and local Nusselt numbers were discussed for both the air and water. The key conclusions of this study are that the succeeding velocity declines as the radiation's increases. By increasing the radiation value and the fluctuation time, the temperature distribution increases. Notably, the temperature profile increases significantly when the variable viscosity parameter decreases.

Polymer nanocomposites are an important class of materials for engineering applications due to their high versatility and good mechanical properties combined with low density. By directly attaching the polymer chains to the nanofillers, the so-called grafting, a better load transfer between matrix and filler is achieved, and, in addition, a better dispersion of the fillers is obtained. Both result in enhanced mechanical properties. Since experimental investigations on the nanoscale are extremely challenging, complementary numerical studies are needed to unravel the mechanical behavior of polymer nanocomposites. To this end, molecular dynamics is ideally suited since it captures the microstructure, but is also numerically expensive. Therefore, this contribution presents a fast coarse-grained molecular dynamics model for the investigation of the mechanical behavior of grafted polymer nanocomposites. For this purpose, we extend an existing model by grafting bonds, which allows us to compare the effect of untreated and grafted fillers directly. In particular, we investigate the influence of filler content, grafting degree, and filler size on the stiffness and strength of the polymer (grafted) nanocomposites. We conclude that the grafting bonds have little effect on the stiffness, while the strength is significantly improved compared to the untreated fillers, which is in agreement with the literature. The presented molecular dynamics model for polymer grafted nanocomposites provides the basis for further investigations, particularly of the crucial matrix-filler interphase. In addition, this contribution translates molecular dynamics insights into mechanical properties, which bridges the gap to the engineering scale and thus represents a step towards exploiting the full potential of polymer (grafted) nanocomposites.

In order to acquire topographic/morphological images with superior resolution and depth of focus than an ordinary optical microscope, scanning electron microscopy (SEM) is used to take photographs of a surface of materials or specimens at a desired point. In the context of polymer and rubber materials science, SEM investigations frequently try to visualize phase morphology, surface and cross-sectional topography, and surface molecular order, and clarify damage mechanisms. In the case of rubber vulcanizates, test specimens are frequently put through a variety of mechanical property assessment procedures, including tensile, flexing, fatigue, abrasion, and tear tests, in order to finalize compounding parameters for required levels of quality. The damaged surface of the test specimens exhibits distinctive topographical characteristics, which are captured as an SEM picture and associated with relevant strength properties. However, the majority of the time, the relationship between strength attributes and the type of surface topography is qualitative. Surface roughness measurement metrics such as root mean square (r.m.s) roughness, average roughness, and peak-to-valley distance are frequently determined for quantitative research using standard software accessible in an SEM. The primary goal of this research is to use a statistical/spectral-based technique for quantitatively measuring surface topography using SEM. The Mullins stress-softening phenomenon of an isotropic, incompressible, hyperelastic rubberlike material is predicted using a phenomenological model. A simple exponential damage function characterizes the model, which represents deformation-induced microstructural degradation of rubberlike material.

This study aims at analyzing the effect of variable foundation parameters on the natural frequencies of a prestressed tapered Rayleigh beam having general elastically restrained ends. In this work, the elastic coefficients of the foundations are assumed varying along the beam major axis. In particular, the constant, linear and parabolic variations of the Pasternak foundation are considered. A semi-analytical approach known as differential transform method (DTM) is applied to the non-dimensional form of the governing equations of motion of the prestressed tapered Rayleigh beam and a set of recurrence algebraic equations are determined. Performing some direct algebraic operations on these derived equations and using some computer codes developed and implemented in MAPLE 18, the dimensionless natural frequencies and the associated mode shapes of the beam are obtained, the effects of these Pasternak foundation variations for various values of the slenderness ratio on the natural frequencies are investigated. It is found among others that : (i) an increase in foundation stiffness led generally to an increase in the natural frequencies; (ii) the constant elastic variations of Pasternak foundation produced highest values of natural frequencies; and (iii) the natural frequencies of tapered Rayleigh beam resting on Pasternak foundation are higher than those from the same beam on Winkler foundation. Finally, the efficiency and accuracy of differential transform method are illustrated by solving two numerical examples of vibration problems and validating the results obtained with those in the open literature, and are found to compare favorably well.