The investigation of fibre reinforcement effects in thermoplastic materials: interfacial bond strength and fibre end parameter

Glass fibres used in the manufacture of fibre reinforced thermoplastic composites (FRTP) are normally sized with a film former which includes a silane coupling agent to improve the interfacial bond strength between glass fibre and matrix . However, during composite failure even an optimized interface cannot stop the initia tion of cracks at the fibre ends, which can lead to large transverse cracks in the matrix or failure by fibre pull-out. In order to help better understand the failure mechanisms of FRTP, thermoplastic microbond tests and photoelasticity experiments have been used to study the interface in model single fibre composites

Differentiation of silane adsorption onto model E-glass surfaces from mixed solutions of amino and glycidyl silanes

Mixed silanes are often used as coupling agents in sizings for glass fibres. A technique has been developed which enables the preferential adsorption of a particular silane onto a model E-glass from a mixed aqueous silane solution to be probed. It is shown that γ-Aminopropyltriethoxysilane (APS) is preferentially adsorbed over γ-glycidoxypropyltrimethoxysilane (GPS) onto model E-glass fibres. High resolution X-ray photoelectron spectroscopy (XPS) has been employed to investigate the nature of silane deposits. Differentiation between the hydrolysed silane deposit and the model silica-based glass substrate was achieved by Si2p curve fitting. The extent of total silane adsorption onto model E-glass fibres was determined from the intensity of CSiO3 peak. In the case of APS/GPS mixed silanes, the N1s peak intensity provides the concentration of APS in the deposit. By comparing the relative intensities of the components in the Si2p3/2 and Si2p1/2 peaks for SiO4 and CSiO3 with the intensity of the N1s peak an assessment of differential adsorption proved possible

The differential adsorption of silanes from solution onto model E-glass surfaces using high resolution XPS

γ-aminopropyltriethoxysilane (APS), γ-mercaptopropyltrimethoxysilane (MPS) and their mixture have been adsorbed onto acid-treated model E-glass fibres from aqueous solution with different concentrations. High resolution X-ray photoelectron spectroscopy (XPS) has been employed to characterize APS and MPS single silane coatings and the selective adsorption of APS/MPS mixed silane coating. It is found that the Si contribution from the silane can be distinguished from the Si contribution from the acid-treated E-glass fibres by fitting Si2p1/2 and Si2p3/2 peaks with components for CSiO3 and SiO4 environments. The adsorption isotherms of APS and MPS have been obtained by comparing the atomic concentrations of N, S and CSiO3 groups. APS and MPS are equally adsorbed from 0.1% APS/MPS mixed silane solution, however, MPS dominates the deposit on model E-glass fibres to a depth corresponding to the take-off-angle of 45º when it is adsorbed from 0.5% and 1.0% APS/MPS mixed silane solutions

Fracture mechanisms and failure analysis of carbon fibre/toughened epoxy composites subjected to compressive loading

This study investigates the failure mechanisms of unidirectional (UD) HTS40/977-2 toughened resin composites subjected to longitudinal compressive loading. A possible sequence of failure initiation and propagation was proposed based on SEM and optical microscopy observations of failed specimens. The micrographs revealed that the misaligned fibres failed in two points upon reaching maximum micro-bending deformation and two planes of fracture were created to form a kink band. Therefore, fibre microbuckling and fibre kinking models were implemented to predict the compressive strength of LID HTS40/977-2 composite laminate. The analysis identified several parameters that were responsible for the microbuckling and kinking failure mechanisms. The effects of these parameters on the compressive strength of the LID HTS40/977-2 composite systems were discussed. The predicted compressive strength using a newly developed combined modes model showed a very good agreement to the measured value (c) 2009 Elsevier Ltd. All rights reserve

Problem detection in legislative oversight:An analysis of legislative committee agendas in the U.K. and U.S.

This paper outlines a dynamic problem-detection model of legislative oversight where legislative committees engage in information-gathering to identify emerging policy problems. It is argued that activities of legislative committees are responsive to indicators of problem status across a range of policy domains. This enables committees to react to problems before, or at least simultaneously to, citizens. Our analyses use a new dataset on the policy agenda of UK Parliamentary Select Committees in combination with directly comparable data on US Congressional hearings. Aggregate measures of problem status (e.g. GDP, crime rates) and public opinion on the �most important problem� facing the country are used as independent variables. The comparison between a well-established and developing committee system offers insights into common dynamics across institutional contexts. The findings show that committee agendas in both the UK and US are responsive to problem status for the majority of issues

How to Stop (Worrying and Love) the Bubble: Boundary Changing Solutions

We discover that a class of bubbles of nothing are embedded as time dependent scaling limits of previous spacelike-brane solutions. With the right initial conditions, a near-bubble solution can relax its expansion and open the compact circle. Thermodynamics of the new class of solutions is discussed and the relationships between brane/flux transitions, tachyon condensation and imaginary D-branes are outlined. Finally, a related class of simultaneous connected S-branes are also examined.Comment: 47 pages; v2 introduction to Weyl cards added, comments added, references added, typos corrected, matches JHEP versio

Micro-Hall Magnetometry Studies of Thermally Assisted and Pure Quantum Tunneling in Single Molecule Magnet Mn12-Acetate

We have studied the crossover between thermally assisted and pure quantum tunneling in single crystals of high spin (S=10) uniaxial single molecule magnet Mn12-acetate using micro-Hall effect magnetometry. Magnetic hysteresis experiments have been used toinvestigate the energy levels that determine the magnetization reversal as a function of magnetic field and temperature. These experiments demonstrate that the crossover occurs in a narrow (~0.1 K) or broad (~1 K) temperature interval depending on the magnitude and direction of the applied field. For low external fields applied parallel to the easy axis, the energy levels that dominate the tunneling shift abruptly with temperature. In the presence of a transverse field and/or large longitudinal field these energy levels change with temperature more gradually. A comparison of our experimental results with model calculations of this crossover suggest that there are additional mechanisms that enhance the tunneling rate of low lying energy levels and broaden the crossover for small transverse fields.Comment: 5 pages, 5 figure

Restricted three body problems at the nanoscale

In this paper, we investigate some of the classical restricted three body problems at the nanoscale, such as the circular planar restricted problem for three C60 fullerenes, and a carbon atom and two C60 fullerenes. We model the van der Waals forces between the fullerenes by the Lennard-Jones potential. In particular, the pairwise potential energies between the carbon atoms on the fullerenes are approximated by the continuous approach, so that the total molecular energy between two fullerenes can be determined analytically. Since we assume that such interactions between the molecules occur at sufficiently large distance, the classical three body problems analysis is legitimate to determine the collective angular velocity of the two and three C60 fullerenes at the nanoscale. We find that the maximum angular frequency of the two and three fullerenes systems reach the terahertz range and we determine the stationary points and the points which have maximum velocity for the carbon atom for the carbon atom and the two fullerenes system

Thermal Density Functional Theory in Context

This chapter introduces thermal density functional theory, starting from the ground-state theory and assuming a background in quantum mechanics and statistical mechanics. We review the foundations of density functional theory (DFT) by illustrating some of its key reformulations. The basics of DFT for thermal ensembles are explained in this context, as are tools useful for analysis and development of approximations. We close by discussing some key ideas relating thermal DFT and the ground state. This review emphasizes thermal DFT's strengths as a consistent and general framework.Comment: Submitted to Spring Verlag as chapter in "Computational Challenges in Warm Dense Matter", F. Graziani et al. ed