BENDING PROPERTIES OF A FUNCTIONALLY GRADED POLYMERIC COMPOSITE REINFORCED WITH A HYBRID NANOMATERIAL

In this paper, functionally graded polymer hybrid nanocomposites have been produced by silica (SiO2) nanoparticles and alumina (Al2O3) nanoparticles distributed in a matrix of epoxy during the ultra-sonication via hand lay-up method. The variation in nanoparticles volume fraction (Vf.) has been given in the thickness direction for reaching the gradation. Each layer has a thickness of 1.2 mm through various concentrations of nanoparticles and is sequentially cast in acrylic moulds to fabricate the graded composite sheet with a 6 mm thickness. To fabricate the functionally graded layers, various concentrations of different nanoparticles (1.5% SiO2, 1% SiO2, epoxy, 2% Al2O3 and 3% Al2O3) have been used for tensile and compressive testing each isotropic layer of functionally graded material (FGM). The mechanical property that was studied for pure epoxy, isotropic and FGM was the flexural resistance. The flexural properties of FGM, isotropic nanocomposite (1% SiO2 + 2% Al2O3) and pristine epoxy, for evaluating their mechanical properties, including flexural stress-strain criteria and flexural Young's modulus, were determined via a Three-point bending test, with loading from the side of silica and alumina for the hybrid-FGM and at one side for the isotropic hybrid nanocomposite and pristine epoxy. The mechanical properties (tensile and compression) and the density of every layer were obtained for the epoxy resin and nanocomposites. They can benefit from the Finite Element Analysis (FEA) of the Three-point bending test via the Design Modeler (ANSYS workbench). The results of experiments were confirmed via building a detailed 3D FE model. Also, the advanced deformation results from the FE model were found in good agreement with the experimental outcomes.

The influence of heterogeneity and initial stress on the propagation of Love-type wave in a transversely isotropic layer subjected to rotation

Introduction: In this paper, a mathematical model of Love-type wave propagation in a heterogeneous transversely isotropic elastic layer subjected to initial stress and rotation of the resting on a rigid foundation. Frequency equation of Love-type wave is obtained in closed form. The material constants and initial stress have been taken as space dependent and arbitrary functions of depth in the respective media. Objectives: The dispersion equation is determined to study the effect of different types of parameters such as inhomogeneity, initial stress, rotation, wave number, the phase velocity on the Love-type wave propagation. Methods: The analytical solution has been obtained, we have used the separation of variables, method and the numerical solution using the bisection method implemented in MATLAB. Results: We present a general dispersion relation to describe the impacts as the propagation of Love-type waves in the structures. Numerical results analyzing the dispersion equation are discussed and presented graphically. Moreover, the obtained dispersion relation is found in well agreement with the classical case in isotropic and transversely isotropic layer resting on a rigid foundation. Finally, some graphical presentations have been made to assess the effects of various parameters in the plane wave propagation in elastic media of different nature.

Experiments and Numerical Implementation of a Boundary Value Problem Involving a Magnetorheological Elastomer Layer Subjected to a Nonuniform Magnetic Field

This study investigates experimentally and numerically the response of a magnetorheological elastomer (MRE) layer placed atop an electromagnetic coil. The MRE layer is deflected upon application of a current in the coil, which creates highly nonuniform magnetic fields. Isotropic and transversely isotropic layers (i.e., containing chains of magnetic particles) are tested experimentally, and the isotropic layer exhibits the largest deflection. To enhance the energetic efficiency of the model device, an iron core is introduced inside the electromagnetic coil, thereby leading to an increase in the resulting magnetic field near the center of the MRE layer. In parallel, the boundary value problem —including the MRE layer, the coil, the core (if present) and the surrounding air—is modeled numerically. For this, a magneto-mechanical, vector potential-based variational formulation is implemented in a standard three-dimensional finite element model at finite strains. For the material description, a recently proposed analytical homogenization-guided model is used to analyze the MRE in the “coil-only” configuration. It is then employed to predict the response of the layer in the “coil plus core” configuration, thus circumventing the need for a separate material characterization procedure. The proposed numerical simulation strategy provides a deeper understanding of the underlying complexity of the magnetic fields and of their interaction with the MRE layer. This study also reveals the importance of modeling the entire setup for predicting the response of MRE materials and, as a result, constitutes a step toward designing more efficient MRE-based devices.

Coupled vibrations of viscoelastic three-layer composite plates. 2. Numerical experiments

Results of numerical studies of the influence of reinforcement orientation of hard layers and the relative thickness of the soft layer of an isotropic viscoelastic polymer on the values of natural frequencies and coefficients of mechanical losses are discussed. In a symmetrical three-layer plate, a bending-torsion interaction arises, generating mutual transformations of the eigenmodes of the coupled vibration modes, if at least one of its own forms in plate directions is characterized by an even number quarters of a wave, and another proper form - an odd number of quarters the waves. In an unsymmetrical asymmetric three-layer plate, bending-bending interaction arises, generating mutual transformations eigenmodes of coupled vibration modes in two mutually orthogonal planes if in the main directions of the plate both of their own forms characterized by either an even or an odd number of quarters of a wave. It was found that each mode of natural vibrations of three-layer plates corresponds to the effective relative thickness of the soft isotropic layer viscoelastic polymer.

РАСЧЕТ ФУНДАМЕНТНЫХ СЕТЧАТЫХ ПЛИТ НА УПРУГОМ СЛОЕ

In this work, the authors have developed the procedure for calculation of mesh slabs on an elastic base modeled by an elastic homogeneous isotropic layer affected by the external load. The history of development of calculations of structures on an elastic basis demonstrates that, due to the scientific and technical progress, methods for calculation of aforementioned structures were improved and refined. This can be traced on various models of the elastic foundation that were used to simulate real soils in their natural occurrence or in an artificial base when setting up fundamentally new problems of structural analysis. Variety of practical tasks results in ambiguous modelling of the elastic base. The authors refer to the works of Tarasevich A. N., Kozunova O. V. and Semenyuk S. D. that provide extensive systematic review of elastic base models for calculation of foundation beams, beam and foundation slabs, as well as for calculation of cross tapes for shallow foundations. The relevance and timeliness of the proposed work is due to the fact that the issues of calculation of mesh slabs and the system of cross tapes on an elastic base have not yet been fully studied. The authors are familiar with the works of M. I. Gorbunov-Posadov, I. A. Simvulidi, G. Ya. Popov, S. D. Semenyuk, S. N. Klepikov, where various approaches are used to conduct the researches in calculation of mesh slabs and spatial monolithic foundations as the system of cross tapes on an elastic base. The procedure proposed is based on the Ritz variational method and the mixed method of structural mechanics using the Zhemochkin influence functions. To calculate the coefficients of canonical equations and the absolute terms for the mixed method of structural mechanics by way of the Zhemochkin method, the ratios of deflections with the normal restrained in the center of the slab are used in the calculation. The numerical implementation of the new general-purpose approach is carried out, as an example, for the rectangular foundation slab with holes, symmetrically loaded by the uniformly distributed load, on the elastic uniform isotropic layer. Graphical results of calculations are given, describing the settlements of the foundation mesh slab and the distribution of contact stresses under the slab. В рассматриваемой работе авторами разработана методика расчета фундаментных сетчатых плит на упругом основании, моделируемом упругим однородным изотропным слоем, под действием внешней нагрузки. Из истории развития расчета конструкций на упругом основании видно, что методы их расчета совершенствовались и уточнялись по мере развития научно-технического прогресса. Это можно проследить на различных моделях упругого основания, которыми моделировались реальные грунты в естественном залегании или в искусственном основании при постановке принципиально новых задач расчета конструкций. Разнообразие практических задач приводит к неоднозначному моделированию упругого основания. Авторы ссылаются на работы А. Н. Тарасевича, О. В. Козуновой и С. Д. Семенюка, в которых приведен обширный систематизированный обзор моделей упругого основания для расчета фундаментных балок, балочных и фундаментных плит, а также для расчета перекрестных лент фундаментов мелкого заложения. Актуальность и своевременность предлагаемой работы в том, что вопросы расчета сетчатых плит и системы перекрестных лент на упругом основании до настоящего времени не исследованы в полной мере. Авторам известны работы М. И. Горбунова-Посадова, И. А. Симвулиди, Г. Я. Попова, С. Д. Семенюка, С. Н. Клепикова, в которых различными подходами проведены исследования по расчету сетчатых плит и пространственных монолитных фундаментов, как системы перекрестных лент на упругом основании. Предлагаемая методика основана на вариационном методе Ритца и смешанном методе строительной механики с использованием функций влияния Жемочкина. Для определения коэффициентов канонических уравнений и свободных членов смешанного метода строительной механики через способ Жемочкина в расчете используются соотношения прогибов с защемленной в центре плиты нормалью. Численная реализация нового универсального подхода выполнена на примере симметрично нагруженной равномерно-распределенной нагрузкой прямоугольной фундаментной плиты с отверстиями на упругом однородном изотропном слое. Приводятся графические результаты расчета для осадок фундаментной сетчатой плиты и распределения контактных напряжений под плитой.

Non-muscle myosin-2 contractility-dependent actin turnover limits the length of epithelial microvilli

ABSTRACTEpithelial brush borders are large arrays of microvilli that enable efficient solute uptake from luminal spaces. In the context of the intestinal tract, brush border microvilli drive functions that are critical for physiological homeostasis, including nutrient uptake and host defense. However, cytoskeletal mechanisms that regulate the assembly and morphology of these protrusions are poorly understood. The parallel actin bundles that support microvilli have their pointed-end rootlets anchored in a highly crosslinked filamentous meshwork referred to as the “terminal web”. Although classic EM studies revealed complex ultrastructure, the composition, organization, and function of the terminal web remains unclear. Here, we identify non-muscle myosin-2C (NM2C) as a major component of the brush border terminal web. NM2C is found in a dense, isotropic layer of puncta across the sub-apical domain, which transects the rootlets of microvillar actin bundles. Puncta in this network are separated by ∼210 nm, dimensions that are comparable to the expected size of filaments formed by NM2C. In primary intestinal organoid cultures, the terminal web NM2C network is highly dynamic and exhibits continuous remodeling. Using pharmacological and genetic perturbations to disrupt NM2C activity in cultured intestinal epithelial cells, we found that this motor controls the length of growing microvilli by regulating actin turnover in a manner that requires a fully active motor domain. Our findings answer a decades old question on the function of terminal web myosin and hold broad implications for understanding apical morphogenesis in diverse epithelial systems.