Scaling Effects in the Structural Response of Plain Woven Composite Laminates

Obtaining a clear understanding of scaling effects in the mechanical response of composites is an indispensable prerequisite for successful design of load-bearing composite structures. The aim of this research is to investigate scaling effects in the structural response of plain woven composites using a combined experimental and numerical approach, with an emphasis on scaling effects in the load-displacement response, damage mechanisms and energy absorption. In the experimental part of the study, scaled test models have been designed based on the similitude approach, and several sets of tests with different combinations of specimen geometrical shapes (i.e. rectangular beams and square panels) and loading conditions (i.e. low-velocity perforation, low-velocity bending, quasi-static perforation and quasi-static bending) have been conducted for a typical plain woven composite. An examination of the experimental results suggests that the load-displacement response of the composite specimens does not obey simple scaling laws, with the curve increasingly extended (or shrunken) with scale size under perforation (or flexural) loading at both quasi-static and low-velocity rates. Additionally, it has been highlighted that there was no obvious transition in the appearance of damage in all perforation cases, with fibre fracture being the primary failure mechanism and becoming more severe with scale size. Further, it has been analysed that scaling effects in the severity of damage are associated with the discrepancy between the scaling of input energy and that of the energy absorbed during the perforation event. In the numerical part, a multiscale model has been developed to predict the deformation and damage of plain woven composites under low-velocity loadings. The multiscale model includes a unit cell model that describes the geometrical architecture of the woven fabric analytically, aiming to account for the influence of the microscopic features on the macroscopic response. In addition, at the intra-ply scale, the nonlinearity and rate-dependence of polymer matrix are characterised based on a viscoplasticity based model, and the damage evolution of yarn material is evaluated by using a Weibull function based formulation. Further, at inter-ply scale, the initiation and evolution of interlaminar delamination are identified based on the bilinear damage model that has been built in the commercial finite element (FE) software ABAQUS. A user-defined material subroutine implementing the multiscale model has been incorporated into the FE solver ABAQUS/Explicit to simulate the low-velocity perforation and flexural tests. Based on these numerical examples, it has been demonstrated that the proposed model is capable of reasonably predicting scaling effects in the load-displacement response, impact damage and energy absorption of plain woven composites. The significance of this research includes quantitative identifications of scaling effects in the structure response of plain woven composite laminates, and the development of a multiscale model capable of replacing experimental routes for studying scaling effects in plain woven composites

SHMS-based fatigue reliability analysis of multiloading suspension bridges

Author name used in this manuscript: Z. W. Chen2011-2012 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe

Magneto-optical visualization of vortices penetration into Ba(Fe1.8Co0.2)As2

Vortices penetration into oxygen-free superconducting compounds FeAs-122 system is of interest in understanding superconductivity. This work studies the vortices motion in Ba(Fe1.8Co0.2)As2 single crystal by means of magneto-optical imaging technique in zero field cooled and field cooled conditions. The captured magneto-optical images and corresponding flux profiles show that, at zero field cooled condition, vortices penetrate into the crystal from the edges as external magnetic field increases. A vortices-free region is observed at the center of sample as applied field is less than full penetration field. In field cooled condition, the introduced vortices leave the sample at the edges as field decreases and polarization of the vortices at the edges are opposite as decreasing field approaches to zero. The pinning strength decreases with increasing temperature. The observed vortex behavior is very similar to that in high Tc superconducting materials with strong pinning strength

A Simple Method to Synthesize Cadmium Hydroxide Nanobelts

Cd(OH)2nanobelts have been synthesized in high yield by a convenient polyol method for the first time. XRD, XPS, FESEM, and TEM were used to characterize the product, which revealed that the product consisted of belt-like crystals about 40 nm in thickness and length up to several hundreds of micrometers. Studies found that the viscosity of the solvent has important influence on the morphology of the final products. The optical absorption spectrum indicates that the Cd(OH)2nanobelts have a direct band gap of 4.45 eV

An experimental and numerical study on scaling effects in the low velocity impact response of CFRP laminates

Scaling effects in the low velocity impact response of plain weave carbon-fibre-reinforced plastic (CFRP) panels have been investigated both experimentally and numerically. The experimental tests were undertaken using an instrumented drop-weight impact tower and the numerical simulations were conducted using the commercially-available finite element (FE) solver ABAQUS/Explicit. Here a rate-dependent damage model was implemented through the ABAQUS user-defined material interface, VUMAT, to describe the mechanical behaviour of the composite laminates. The experimental tests and numerical simulations both indicate that at energies above the damage threshold, damage does not obey a simple scaling law, becoming more severe as the scale size is increased. An examination of the damaged samples in the tests and numerical simulations indicated that, for a given scaled impact energy, fibre damage, in the form of large cracks extending in the warp and weft directions, was more severe in the larger samples. It is argued that the energy absorbed in fibre fracture scales with the square of the scale factor, i.e. n2, whereas the initial impact energy scales as n3. This discrepancy results in increased levels of energy needing to be absorbed in larger scale sizes, leading to greater levels of impact damage in the larger scale sizes

Current distribution analysis for high temperature superconducting cable considering hysteresis characteristics

This paper presents a hysteresis model for Type-II high temperature superconductor (HTS) by using simplified Preisach Model, in which the Preisach distribution function μ-kα, β) is determined only based on the B-H limiting loop. The nonlinear dynamic circuit model of the superconductor is established. In the circuit model, the hysteresis inductance and hysteresis loss described by using simplified Preisach Model are deduced. Applying the hysteresis circuit model, the currents flowing in different superconductor layers of high temperature superconducting cable are simulated, as well as the hysteresis loss of the superconducting cable. The simulation results are verified by comparison with the data recorded in literatures. Finally, the influences of hysteresis on superconducting cable are analyzed and discussed. © 2010 - IOS Press and the authors. All rights reserved

Correcting atmospheric effects on InSAR with MERIS water vapour data and elevation-dependent interpolation model

Author name used in this publication: X. L. Ding2011-2012 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Fast empirical Bayesian LASSO for multiple quantitative trait locus mapping

<p>Abstract</p> <p>Background</p> <p>The Bayesian shrinkage technique has been applied to multiple quantitative trait loci (QTLs) mapping to estimate the genetic effects of QTLs on quantitative traits from a very large set of possible effects including the main and epistatic effects of QTLs. Although the recently developed empirical Bayes (EB) method significantly reduced computation comparing with the fully Bayesian approach, its speed and accuracy are limited by the fact that numerical optimization is required to estimate the variance components in the QTL model.</p> <p>Results</p> <p>We developed a fast empirical Bayesian LASSO (EBLASSO) method for multiple QTL mapping. The fact that the EBLASSO can estimate the variance components in a closed form along with other algorithmic techniques render the EBLASSO method more efficient and accurate. Comparing with the EB method, our simulation study demonstrated that the EBLASSO method could substantially improve the computational speed and detect more QTL effects without increasing the false positive rate. Particularly, the EBLASSO algorithm running on a personal computer could easily handle a linear QTL model with more than 100,000 variables in our simulation study. Real data analysis also demonstrated that the EBLASSO method detected more reasonable effects than the EB method. Comparing with the LASSO, our simulation showed that the current version of the EBLASSO implemented in Matlab had similar speed as the LASSO implemented in Fortran, and that the EBLASSO detected the same number of true effects as the LASSO but a much smaller number of false positive effects.</p> <p>Conclusions</p> <p>The EBLASSO method can handle a large number of effects possibly including both the main and epistatic QTL effects, environmental effects and the effects of gene-environment interactions. It will be a very useful tool for multiple QTL mapping.</p