The effect of the measurement frequency on the elastic anisotropy of fibre laminates

Static tests and ultrasonic measurements (2.25 MHz) have been carried out on a series of composite laminates of glass fibres in a polypropylene matrix. A range of angle ply laminates were prepared for this study, with laminate angles θ of ±0, 10, 20, 30 and 40^∘. The high frequency measurements were made using the ultrasonic immersion technique, which allows the determination of a complete set of the elastic constants of a material. The relationship between the ultrasonically determined elastic constants of the angle ply laminates was found to be in excellent agreement with theoretical predictions, as previously validated for carbon fibre/epoxy angle ply laminates. A comparison between the ultrasonic and statically measured values was made for two of the angle ply laminates (θ = 0 and 20^∘). It was found that the static values were lower than those measured at ultrasonic frequency, particularly those constants that were more matrix dominated (for example the transverse moduli of the laminates). Measurements on a pure polypropylene sample at both testing frequencies confirmed that the change in matrix properties with frequency was the cause of this difference. The change in properties with test frequency is likely to be much larger in this system than in other composite materials because the glass transition temperature of polypropylene is close to ambient temperature. Dynamic mechanical tests (1 Hz) were carried out on a sample of pure polypropylene to assess this effect. We also give an appropriate method of estimating the dependence of glass transition temperature on frequency. The results for polypropylene are compared with those for other commonly used polymer matrix materials: epoxy resin, nylon and polyetheretherketone (PEEK): DMTA measurements were also made on these samples. The effect of test frequency on matrix properties, for the glass/PP laminates, was further investigated by examining the relationship of the Poisson's ratios with laminate angle using a mixture of ultrasonic experiments and theoretical predictions. Previously we have shown that the degree of anisotropy between the reinforcing fibre and the matrix phase is paramount in determining whether the material will show a negative Poisson's ratio at a critical laminate angle. The ultrasonic measurements carried out in this study on the glass/PP laminates showed a minimum in one of the Poisson's ratio at a laminate angle of 32°, but the value did not become negative. However, theoretical predictions showed that for a static frequency measurement (1 Hz), where the matrix is softer and hence the anisotropy of each laminate ply is higher, the laminate will show a negative Poisson's ratio with a minimum at a laminate angle of around 28°.     

Enhanced adhesion of PMMA to copper with black oxide for electrodeposition of high aspect ratio nickel-iron microstructures

 Copper is widely used as a plating base for soft magnetic alloy electrodeposition in sensors and actuators. PMMA, the X-ray resist used in the LIGA process, typically has poor adhesion with copper. The use of black oxide of copper to enhance PMMA-copper adhesion was investigated. In this work, peel strength as a function of treatment time and the method of bonding was evaluated using an ASTM standard T-peel test. Peel strength increased with increasing treatment time. The feasibility of producing microstructures with predictable 3-D geometry for use in resonating sensors was investigated using the process developed. Nickel-iron structures of 100-1000 micrometers wide and 500 micrometers tall were successfully electrodeposited. Growth of other representative microstructures is being investigated. Received: 25 August 1997/Accepted: 3 September 1977     

Rough Terrain Autonomous Mobility—Part 1: A Theoretical Analysis of Requirements

A basic requirement of autonomous vehicles is that of guaranteeing the safety of the vehicle by avoiding hazardous situations. This paper analyses this requirement in general terms of real-time response, throughput, and the resolution and accuracy of sensors and computations. Several nondimensional expressions emerge which characterize requirements in canonical form.The automatic generation of dense geometric models for autonomously navigating vehicles is a computationally expensive process. Using first principles, it is possible to quantify the relationship between the raw throughput required of the perception system and the maximum safely achievable speed of the vehicle. We derive several useful expressions for the complexity of terrain mapping perception under various assumptions. All of them can be reduced to polynomials in the response distance.The significant time consumed by geometric perception degrades real-time response characteristics. Using our results, several strategies of active geometric perception arise which are practical for autonomous vehicles and increasingly important at higher speeds.     

Experiences using lightweight formal methods for requirementsmodeling

The paper describes three case studies in the lightweight application of formal methods to requirements modeling for spacecraft fault protection systems. The case studies differ from previously reported applications of formal methods in that formal methods were applied very early in the requirements engineering process to validate the evolving requirements. The results were fed back into the projects to improve the informal specifications. For each case study, we describe what methods were applied, how they were applied, how much effort was involved, and what the findings were. In all three cases, formal methods enhanced the existing verification and validation processes by testing key properties of the evolving requirements and helping to identify weaknesses. We conclude that the benefits gained from early modeling of unstable requirements more than outweigh the effort needed to maintain multiple representations     

Effect of dissolved tungsten on the deformation of 70Ni-30Fe alloys

A series of Ni-Fe alloys containing various levels of tungsten in solid solution have been prepared as a means to assess the influence of solid solution strengthening on the mechanical behavior of monolithic 70Ni-30Fe. In particular, 70Ni-30Fe alloys plus equilibrium concentrations of tungsten in solid solution nominally correspond to the compositions associated with the matrix-only portion of certain tungsten heavy alloys, that is, alloys comprised of a high volume fraction of nominally pure tungsten particles embedded within a minority Ni-Fe-W based matrix. The study shows that the working solubility of tungsten within the 70Ni-30Fe base composition increases slightly with temperature, from approximately 21 wt pct at room temperature to approximately 23 wt pct at 1400 °C. Increasing the level of tungsten in solid solution leads to increases in room-temperature yield strength, tensile strength, and ductility. In contrast, the deformation characteristics of the alloys, as quantified by the power-law work-hardening exponent, n, and the strain-rate-sensitivity exponent, m, show little variation with tungsten solute concentration.     

Updating Situation Models: Reply to Zwaan and Madden (2004).

E. J. O'Brien, M. L. Rizzella, J. E. Albrecht, and J. G. Halleran (1998) demonstrated that, consistent with the memory-based text processing view, outdated or incorrect information can be reactivated through a passive resonance process. Once reactivated, this outdated information can still influence comprehension. R. A. Zwaan and C. J. Madden (2004) suggested that the O'Brien et al. findings resulted from problems with the materials used. The present authors show that the possible "problems" identified by Zwaan and Madden do not adequately explain the findings of O'Brien et al. and that Zwaan and Madden's Experiment 3 lacks sufficient control or power to support their alternative interpretation of O'Brien et al. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fluid, solid and fluid-structure interaction simulations on patient-based abdominal aortic aneurysm models

This article describes the use of fluid, solid and fluid-structure interaction simulations on three patient-based abdominal aortic aneurysm geometries. All simulations were carried out using OpenFOAM, which uses the finite volume method to solve both fluid and solid equations. Initially a fluid-only simulation was carried out on a single patient-based geometry and results from this simulation were compared with experimental results. There was good qualitative and quantitative agreement between the experimental and numerical results, suggesting that OpenFOAM is capable of predicting the main features of unsteady flow through a complex patient-based abdominal aortic aneurysm geometry. The intraluminal thrombus and arterial wall were then included, and solid stress and fluid-structure interaction simulations were performed on this, and two other patient-based abdominal aortic aneurysm geometries. It was found that the solid stress simulations resulted in an under-estimation of the maximum stress by up to 5.9% when compared with the fluid-structure interaction simulations. In the fluid-structure interaction simulations, flow induced pressure within the aneurysm was found to be up to 4.8% higher than the value of peak systolic pressure imposed in the solid stress simulations, which is likely to be the cause of the variation in the stress results. In comparing the results from the initial fluid-only simulation with results from the fluid-structure interaction simulation on the same patient, it was found that wall shear stress values varied by up to 35% between the two simulation methods. It was concluded that solid stress simulations are adequate to predict the maximum stress in an aneurysm wall, while fluid-structure interaction simulations should be performed if accurate prediction of the fluid wall shear stress is necessary. Therefore, the decision to perform fluid-structure interaction simulations should be based on the particular variables of interest in a given study.     

Calorimetric and thermodynamic analysis of palladium-deuterium electrochemical cells

An analysis is made of the chemical heats liberated from a palladium-deuterium electrochemical cell operating inside a calorimeter. It is important, in such an analysis, to carefully identify the chemical and electrochemical sources of heat, before any “excess heats” can be ascribed to non-chemical reactions.⁽¹⁾ The calorimeter measures the enthalpy (ΔH _r ) of the reaction; whereas, the electrochemical voltage of the cell reflects the free energy (ΔG _r ) of the reaction within the Pd-D electrolysis cell. The heat energy from the calorimeter cell therefore doesnot equal the electrical energy supplied to the cell, as might initially be expected. The magnitudes of the differing calorimetric and electrochemical energies were found to be related through the “thermoneutral potential” (ξ_H) of the electrochemical reaction. The chemical heat theoretically expected from the calorimeter is given by (1) I(ξ_L-ξ_H), the cell current (I), multiplied by the difference between the operating cell voltage (ξ_L) and the thermoneutral potential (ξ_H), rather than (2) Iξ_L, the electrical input power. This was verified empirically using a freon vaporization calorimeter, which operates on the principle of accurate measurement of the vaporization rate of liquid freon which completely surrounds the electrochemical cell. The calorimetrically-measured heats observed from a Pt/D₂O, 0.1M LiOD/Pd electrochemical cell were within 2% of the thermoneutral potential predicted value, I(ξ_L-ξ_H); but were found to be 15–30% less than the electrical work supplied to the cell, Iξ_L. Measurements of D₂O consumed by the cell reactions also verified that essentially no significant recombination of D₂ and O₂ gases occurred within the cell. No “excess heats” were observed from this Pd cell during the 36 days of its electrolytic operation. Likewise, no increase in the neutron flux around the cell was found, using three³He radiation detectors.     

Molecular cloning, expression, and characterization of a functional single-chain Fv antibody to the mycotoxin zearalenone

The heavy-chain and kappa light-chain variable region genes of an antizearalenone hybridoma cell line (2G3-6E3-2E2) were isolated by PCR and joined by a DNA linker encoding peptide (Gly4Ser)3 as a single-chain Fv (scFv) DNA fragment. The scFv DNA fragment was cloned into a phagemid (pCANTAB5E) and expressed as a fusion protein with E tag and phage M13 p3 in Escherichia coli TG1. In the presence of helper phage M13K07, the scFv fusion protein was displayed on the surfaces of recombinant phages. High-affinity scFv phages were enriched through affinity selection in microtiter wells coated with zearalenone-ovalbumin conjugate. The selected recombinant phages were used to infect E. coli HB2151 for the production of soluble scFv antibodies. One selected clone (pQY1.5) in HB2151 secreted a soluble scFv antibody (QY1.5) with a high zearalenone-binding affinity (concentration required for 50% inhibition of binding, 14 ng/ml), similar to that of parent monoclonal antibody in a competitive indirect enzyme-linked immunosorbent assay. However, scFv QY1.5 exhibited higher cross-reactivity with zearalenone analogs and had greater sensitivity to methanol destabilization than the parent monoclonal antibody did. Nucleotide sequence analyses revealed that the light-chain portion of scFv QY1.5 had a nucleotide sequence identity of 97% to a mouse germ line gene VK23.32 in mouse kappa light-chain variable region subgroup V, whereas the heavy-chain nucleotide sequence was classified as mouse heavy-chain subgroup III (D) but without any closely related members having highly homologous complementarity-determining region sequences. The potential of soluble scFv QY1.5 for routine screening of zearalenone and its analogs was demonstrated with zearalenone-spiked corn extracts.