Mechanical modelling of composites with reinforcements in finite deformation

Although the mechanical behaviour of particle-reinforced and fibre-reinforced composites have been studied extensively in infinitesimal deformation regime, their properties under finite deformation are still not well understood due to the complex interaction mechanisms between matrix and reinforcement, the intrinsic material and geometry nonlinearities. In this work, theoretical analysis, numerical simulation, and experimental data in the literature are employed to investigate the mechanical properties of composites with reinforcement in finite deformation. First, a three-dimensional Representative Volume Element (RVE) is developed for neo-Hookean composite, in which the incompressible neo-Hookean matrix is reinforced with spherical neo-Hookean particles. Four types of finite deformation (i.e., uniaxial tension/compression, simple shear and general biaxial deformation) are simulated using the RVE models with periodic boundary conditions enforced. The simulation results show that the overall mechanical responses of the incompressible particle-reinforced neo-Hookean composite (IPRNC) can be well predicted by another simple incompressible neo-Hookean model. The results also indicate that the effective shear modulus of IPRNC with different particle volume fraction and different particle/matrix stiffness ratio can be well predicted by the classical linear elastic estimation. In the second half of the study, the significance of the fibre-matrix interaction in the Human Annulus Fibrosus (HAF) is identified and analysed in detail. Based on the experimental results in the literature it is shown that the mechanical behaviour of the matrix can be well simulated by the incompressible neo-Hookean type model, but the effective stiffness of the matrix depends on fibre stretch ratio, which can only be explained by fibre-matrix interaction. Furthermore, it is found that this interaction takes place anisotropically between the matrix and the fibres distributed in different proportions in different directions. The dependence of the tangent stiffness of the matrix on the first invariant of the deformation tensor can also be explained by this fibre orientation dispersion.EThOS - Electronic Theses Online ServiceChinese Scholarship CouncilUniversity of GlasgowNewcastle UniversityGBUnited Kingdo

Mechanical modeling of incompressible particle-reinforced neo-Hookean composites based on numerical homogenization

In this paper, the mechanical response of incompressible particle-reinforced neo-Hookean composites (IPRNC) under general finite deformations is investigated numerically. Threedimensional Representative Volume Element (RVE) models containing 27 non-overlapping identical randomly distributed spheres are created to represent neo-Hookean composites consisting of incompressible neo-Hookean elastomeric spheres embedded within another incompressible neo-Hookean elastomeric matrix. Four types of finite deformation (i.e., uniaxial tension, uniaxial compression, simple shear and general biaxial deformation) are simulated using the finite element method (FEM) and the RVE models with periodic boundary condition (PBC) enforced. The simulation results show that the overall mechanical response of the IPRNC can be well-predicted by another simple incompressible neo-Hookean model up to the deformation the FEM simulation can reach. It is also shown that the effective shear modulus of the IPRNC can be well-predicted as a function of both particle volume fraction and particle/matrix stiffness ratio, using the classical linear elastic estimation within the limit of current FEM software

Numerical Simulation of the Effect of Smooth Muscle Layer Thickening on Stress Distribution in the Airway Wall

Many chronic respiratory diseases are associated with airway remodeling such as hyperplasia and/or hypertrophy of the smooth muscle cells. It is well known that the hyperplasia and hypertrophy of the smooth muscle cells directly affects the mechanical properties of the smooth muscle layer. Consequently, it may cause uneven distribution of stress and thus local stress stimulation of the cells and tissues in the airway wall, possibly leading to pathogenesis of airway dysfunction such as airway hyperresponsiveness. However, it is difficult to experimentally study the effect of smooth muscle layer on stress distribution in the airway wall. Therefore, in the present work, we built a finite element model which simplified the anatomical structure of the airway wall as a three-layer structure that included an inner wall layer, a smooth muscle layer and an adventitia layer. Based on this model, we varied the smooth muscle layer thickness either uniformly or locally and then computed the stress distribution in the modeled airway wall. The results revealed that the minimum stress occurred in the adventitia layer, and the maximum stress occurred in the smooth muscle layer. More importantly, the smooth muscle layer thickening, occurred either uniformly or locally, led to elevated stress level and enhanced stress concentration in the smooth muscle layer. And the enhancement of stress level and concentration was variable depending on the pattern of smooth muscle layer thickening. For a given extent of smooth muscle layer thickening, the stress level and concentration appeared to be determined by the number of locations and the separation distance between the locations at which the smooth muscle layer thickening occurred. In other words, the maximum stress level in the smooth muscle layer increased from 2.712kPa to 2.842KPa depending on whether the local thickening occurred at one location, 3 or 5 equally separated locations, 2 connected and 1 distanced location, or 3 all connected locations. These simulation results provide important insight for better understanding the mechanism through which the airway smooth muscle is involved in the alteration of airway dysfunction in health and disease, which may be helpful in developing novel diagnosis/therapy via targeting smooth muscle hyperplasia and/or hypertrophy for the prevention/treatment of asthma

Bitter Taste Receptor Agonist (Quinine) Induces Traction Force Reduction and Calcium Flux Increase in Airway Smooth Muscle Cells from Ovalbumin-Sensitized and Challenged Rats

Recently, bitter taste receptors (TAS2Rs) have been found in the lung, which can be stimulated with TAS2R agonist such as quinine to relax airway smooth muscle cells (ASMCs) via intracellular Ca2+ signaling generated from restricted phospholipase C activation. This provides a promising new therapy for asthma because enhanced contractility and impaired ability of relaxation of the ASMCs within the bronchial wall of asthmatic patients are thought to be ultimately responsible for airway constriction in asthma. However, further study is required for characterization of the effect of TAS2R agonist on the mechanical behaviors of ASMCs, in particular the traction force generation and associated mechanism in asthma model. Here, we sensitized Sprague Dawley rats with ovalbumin (OVA) for up to 12 weeks to simulate chronic asthma symptoms. Subsequently, we isolated ASMCs from these rats, and studied the traction force and intracellular Ca2+ signaling of the cells with/out treatment of quinine hydrochloride, a well-known TAS2R agonist. The results demonstrated that quinine hydrochloride relaxed the ASMC in a dose dependent manner. It also evoked dose-dependent increase of intracellular calcium ([Ca2+]i) in the ASMCs. Perhaps more importantly, the quinine-induced traction force reduction and Ca2+ flux increase were correlated. Taken together, our findings indicate that TAS2R agonists (e.g. quinine hydrochloride) could reduce the ability of ASMCs to generate traction force via activation of the intracellular calcium signaling, which may contribute as one of the mechanisms for TAS2R agonist-induced ASMC relaxation. This provides additional evidence to support TAS2R agonists as a new class of compounds with potential in treatment of chronic asthma

Bismuth-induced phase control of GaAs nanowires grown by molecular beam epitaxy

In this work, the crystal structure of GaAs nanowires grown by molecular beam epitaxy has been tailored only by bismuth without changing the growth temperature and V/III flux ratio. The introduction of bismuth can lead to the formation of zinc-blende GaAs nanowires, while the removal of bismuth changes the structure into a 4H polytypism before it turns back to the wurtzite phase eventually. The theoretical calculation shows that it is the steadiest for bismuth to adsorb on the GaAs(111) B surface compared to the liquid gold catalyst surface and the interface between the gold catalyst droplet and the nanowire, and these adsorbed bismuth could decrease the diffusion length of adsorbed Ga and hence the supersaturation of Ga in the gold catalyst droplet. (C) 2014 AIP Publishing LLC

Nondestructive Damage Testing of Beam Structure Based on Vibration Response Signal Analysis

Nondestructive damage-testing technology based on vibration signal analysis makes full use of the response characteristics of wave and energy. With the advantages of wide bandwidths of response frequency and high sensitivity, the nondestructive testing technology based on vibration signal analysis has a superiority in the application for the detection and characterization of structural defects, and has become one of the important methods for the nondestructive testing of structural material defects and damage. This paper presents a novel method of detection localization and quantitative analysis for local damage in beam structures, based on the response analysis of vibration signals. A damage-detection and -identification algorithm based on a unscented Kalman filter (UKF) was designed, which greatly reduces the computational workload in the process of damage identification over that in conventional methods. The method presented in this paper has significances to widen the application scope of the nondestructive testing method, and increase the recognition efficiency and effectiveness of this kind of method in engineering

Experimental study of the application of micro-PIV on the flow characteristics detection of micro-gap rotational flow field

For a micro-gap rotational flow field with a large horizontal extent, tiny gap and fast flow velocity, the two-dimensional images shot by the micro-scale Particle ImageVelocimetry(Micro-PIV) technique are not sufficient for the study of local or whole flow characteristics. In this paper, by establishing a test bench of a rotational flow field with the functions of driving, positioning, adjustment and sensing, all the local states of the micro-gap rotational flow field can be obtained by horizontally moving the rotating axis to observe point by point. While measuring some local flow fields, two-dimensional pictures are taken by adjusting the focusing height of the objective lens, and then superposed and interpolated according to their shooting order to obtain a quasi-three-dimensional distribution image of the local flow fields, thus obtaining the flow condition of the vertical section of the flow field. The position of the focusing plane and mutual distance are adjusted to realize the measurement of wall shear force in the flow field, providing a feasible reference method for detecting the rheological property of the gap flow field and the effect of surface drag reduction

Direct air CO2 capture using coal fly ash derived SBA-15 supported polyethylenimine

Designing an amine modified silica derived from coal fly ash (CFA) towards direct air CO2 capture (DAC) provides an economic way to manage increasing atmospheric CO2 concentration utilizing solid wastes. In this work, rod-like SBA-15 (SBA-15-R) and wheat-like SBA-15 (SBA-15-W) with distinct pore lengths are synthesized from CFA by controlling the synthesis conditions and then modified by PEI via the wet impregnation method. Their CO2 adsorption behaviors under sub-ambient conditions are investigated to explore their feasibility under aggressive conditions. The adsorbents with various silica morphologies exhibit distinctive CO2 adsorption performance under ambient and sub-ambient conditions. At 35°C under dry conditions, the CO2 adsorption capacity increases with amine loading. The CO2 adsorption capacity (qe) of SBA-15-W-PEI with long channels reaches the highest qe of 1.92 mmol/g with 70 wt.% PEI loading due to a large amount of strong chemisorption sites. Under the sub-ambient conditions (-20°C, 400 ppm), SBA-15-R-PEI30 with short channels having weaker CO2 diffusion resistance exhibits promising CO2 uptake of 0.83 mmol/g. These findings indicate that the ultra-dilute CO2 adsorption at ambient temperature requires an adsorbent with large amounts of adsorption sites, whereas the adsorbents for cold temperature application should reconcile amine loading with CO2 diffusion resistance inside pores. The co-adsorption of H2O and CO2 significantly improves CO2 capacity from 0.83 mmol/g and 1.92 mmol/g to 1.81 mmol/g and 3.48 mmol/g for SBA-15-R-PEI30 (-20°C, 400 ppm) and SBA-15-W-PEI70 (35°C, 400 ppm), respectively. Furthermore, the CFA derived SBA-15-PEI shows good cyclic stability during five consecutive TSA cycles. Preparing the amine silica adsorbents from coal fly ash potentially reduces the adsorbent cost of DAC devices. Moreover, the systematic exploration of amine silica adsorbents at a wide range of temperatures guides the design of high-performance CO2 adsorbents employed under various climatic conditions

Comparison of Membrane Inlet and Capillary Introduction Miniature Mass Spectrometry for Liquid Analysis

Membrane inlet mass spectrometry (MIMS) is commonly used for detecting the components in liquid samples. When a liquid sample flows through a membrane, certain analytes will permeate into the vacuum chamber of a mass spectrometer from the solution. The properties of the membrane directly determine the substances that can be detected by MIMS. A capillary introduction (CI) method we previously proposed can also be used to analyze gas and volatile organic compounds (VOCs) dissolved in liquids. When CI analysis is carried out, the sample is drawn into the mass spectrometer with no species discrimination. The performance of these two injection methods was compared in this study, and similar response time and limit of detection (LOD) can be acquired. Specifically, MIMS can provide better detection sensitivity for most inorganic gases and volatile organic compounds. In contrast, capillary introduction shows wider compatibility on analyte types and quantitative range, and it requires less sample consumption. As the two injection methods have comparable characteristics and can be coupled with a miniature mass spectrometer, factors such as cost, pollution, device size, and sample consumption should be comprehensively considered when choosing a satisfactory injection method in practical applications