Laser surface-contouring and spline data-smoothing for residual stress measurement

We describe non-contact scanning with a confocal laser probe to measure surface contours for application to residual stress measurement. (In the recently introduced contour method, a part is cut in two with a flat cut, and the part deforms by relaxation of the residual stresses. A cross-sectional map of residual stresses is then determined from measurement of the contours of the cut surfaces.) The contour method using laser scanning is validated by comparing measurements on a ferritic steel (BS 4360 grade 50D) weldment with neutron diffraction measurements on an identical specimen. Compared to lower resolution touch probe techniques, laser surface-contouring allows more accurate measurement of residual stresses and/or measurement of smaller parts or parts with lower stress levels. Furthermore, to take full advantage of improved spatial resolution of the laser measurements, a method to smooth the surface contour data using bivariate splines is developed. In contrast to previous methods, the spline method objectively selects the amount of smoothing and estimates the uncertainties in the calculated residual stress map.     

A Cell-Centred CVD-MPFA Finite Volume Method for Two-Phase Fluid Flow Problems with Capillary Heterogeneity and Discontinuity

A novel finite volume method is presented that is applicable to discontinuous capillary pressure fields. The method is developed within the control-volume distributed multi-point flux approximation (CVD-MPFA) framework (Edwards and Rogers in Comput Geosci 02(04):259–290, 1998; Friis et al. in SIAM J Sci Comput 31(02):1192–1220, 2008). Results are computed on structured and unstructured grids that demonstrate the ability of the method to resolve flow in the presence of a discontinuous capillary pressure field for diagonal and full-tensor permeability fields. In addition to an upwind approximation for the saturation equation flux, the importance of upwinding on capillary pressure flux via a hybrid formulation is shown.

     

Viscoelasticity and diffusion in miscible blends of saturated hydrocarbon polymers

Linear viscoelasticity and tracer diffusion were investigated as functions of temperature, component molecular weight and blend composition for entangled, single-phase blends of nearly monodisperse poly(ethylene-alt-propylene) (PEP) and head-to-head polypropylene (HHPP). Both components are non-polar and, despite evidence for slight differences of component glass temperatures in their blends, the viscoelastic data obey time-temperature superposition rather well. The properties of the blends were compared at constant T-T _g (blend) with predictions of the tube-model theories. The composition dependence of viscosity agrees best with the double-reptation prediction, as had been found earlier for molecular weight blends. The variation in plateau modulus with composition is consistent with reptation, but the changes are too small to provide a definitive test. The tracer diffusion coefficients, D ^* _PEP and D ^* _HHPP are nearly independent of composition, consistent with the reptation prediction and in sharp contrast with tracer diffusion for blends with specific associations. Results for the recoverable compliance depart from this pattern, varying differently and much less strongly with composition than the predictions of either single or double reptation. It thus seems that microstructural blends may behave in significantly more complex ways than molecular weight blends even for components with only weak dispersive interactions and rather modest differences in glass temperature and plateau modulus.Dedicated to Prof. John D. Ferry on the occasion of his 85th birthday.     

Invariant Manifolds for Parabolic Partial Differential Equations on Unbounded Domains

In this paper finite-dimensional invariant manifolds for nonlinear parabolic partial differential equations of the form

Comparison of tensile and bulge tests for thin-film silicon nitride

The mechanical properties of thin-film, low-pressure chemical vapor deposited silicon nitride were measured in uniaxial tension and by a bulge test method suitable for wafer-level testing. This research compares the two approaches and presents additional data on silicon nitride. The common property from the two test methods is the Young's modulus. Tensile tests performed at the Johns Hopkins University provided a value of 257±5 GPa. Bulge tests conducted by Exponent, Inc., an engineering and scientific consulting firm, yielded a value of 258±1 GPa. It is concluded that this bulge test is a valid wafer-level test method. These tensile results, when added to earlier results, yield the following properties for low-stress silicon nitride: Young's modulus =255±5 GPa, Poisson ratio=0.23±0.02, and fracture strength=5.87±0.62 GPa.     

Simulations of hot, dense iron plasma opacity at 89 eV and comparison with experiment

Predictions of hot, dense iron plasma opacity at 89 eV photon energy are compared with experimental determinations from the transmission of laser-heated iron to extreme ultra-violet (EUV) laser radiation. The EUV laser was pumped using six beams of an Nd-Yag laser in a refraction compensating geometry, while another beam irradiated a tamped solid iron target with an intensity of 10¹⁴ W cm⁻². The Ehybrid hydrodynamic and atomic physics code was used to predict temperatures, densities and ionisation throughout the evolving iron plasma. The iron opacities were deduced taking into account free–free, bound–free and bound–bound absorption. Bound–bound absorption was considered using atomic data generated by the Opacity Project. Reasonable overall agreement between theory and experiment was obtained for the iron layer transmission. The simulations indicated the dominance of bound–bound absorption throughout most regions of the iron plasma, but also the potential importance of photoionisation from core levels where energetically possible.     

Scattering by periodic cracks and theory of comb transducers

Combs are distributed ultrasonic transducers for the generation of Rayleigh waves in solids. Synchronously excited by subsequent comb teeth, the surface wave grows along its propagation path under the comb. Although sliding contact between the comb and a solid sample is frequently assumed, the mechanical coupling is not weak. This modifies the surface wave propagation conditions to such an extent that the Rayleigh wave no longer exists at the comb–sample interface. Instead, an interface mode propagates, collecting power from each subsequent comb tooth and delivering it to the comb edge to be eventually transformed into a Rayleigh wave outside the comb. Generation efficiency is evaluated for the optimized angle of incidence of the longitudinal wave onto the comb–sample interface.     

Analysis of short crack growth from microscopic fatigue properties

Successful simulation of kinetics of small fatigue crack growth entails three aspects: Stage I, Stage II growth rate prediction and transition prediction. In this paper attention is focused on growth rate predictions. By using microstructurally-affected-zone and process zone concepts, microscopic fatigue behaviour of small fatigue crack propagation is logically linked with macroscopic fatigue behaviour, showing an intrinsic relation between small fatigue crack growth and macroscopic low-cycle fatigue properties during crack growth. Furthermore, variation of relatively big plastic zone size associated with a growing small fatigue crack is kinetically simulated. As a result a quantitative prediction model of growth rates for Stage I and Stage II growth has been developed whose explicit advantage is that the growth rate of small fatigue crack can now be predicted in terms of bulk fatigue properties in conjunction with local microstructural characteristics.     

Density functional theory: Foundations reviewed

Guided by the above motto (quotation), we review a broad range of issues lying at the foundations of Density Functional Theory, DFT, a theory which is currently omnipresent in our everyday computational study of atoms and molecules, solids and nano-materials, and which lies at the heart of modern many-body computational technologies. The key goal is to demonstrate that there are definitely the ways to improve DFT. We start by considering DFT in the larger context provided by reduced density matrix theory (RDMT) and natural orbital functional theory (NOFT), and examine the implications that N$N$-representability conditions on the second-order reduced density matrix (2-RDM) have not only on RDMT and NOFT but, also, by extension, on the functionals of DFT. This examination is timely in view of the fact that necessary and sufficient N$N$-representability conditions on the 2-RDM have recently been attained.     

Screening of textiles for contraband drugs using portable Raman spectroscopy and chemometrics

The impregnation of items of clothing with drugs of abuse that are then smuggled through airports and ports of entry is a growing problem for law enforcement. This work describes the application of portable Raman spectroscopic techniques for the analysis of a range of natural and artificial fibre items of clothing impregnated with drugs of abuse. Textile pieces were soaked with the solutions of the drugs then left overnight to dry prior to spectroscopic examination. The feasibility of detection of the characteristic Raman spectral bands in the presence of background matrix signals is demonstrated, even for dyed clothing. Definitive evidence for contamination of the items of clothing concerned can be acquired within 20–25 s, without any form of sample pre‐treatment or extraction being necessary. The feasibility of automatic spectral recognition of such illicit materials by Raman spectroscopy has been investigated by searching a database stored on the spectrometer computer and the use of principal component analysis. Copyright © 2014 John Wiley & Sons, Ltd.