Composite Geometry Research Articles

Extinction law in ultraluminous infrared galaxies at z∼ 1

We analyse the multiwavelength photometric and spectroscopic data of 12 ultraluminous infrared galaxies (ULIRGs) at z∼ 1 and compare them with models of stars and dust in order to study the extinction law and star formation in young infrared (IR) galaxies. Five extinction curves, namely the Milky Way (MW), the pseudo-MW which is MW-like without the 2175 Å feature, the Calzetti and two supernova (SN) dust curves are applied to the data by combining with various dust distributions, namely the uniform dust screen, the clumpy dust screen, the internal dust geometry, and the composite geometry with a combination of dust screen and internal dust. Employing a minimum χ2 method, we find that the foreground dust screen geometry, especially combined with the 8–40 M⊙ SN extinction curve, provides a good approximation to the real dust geometry, whereas internal dust is only significant in two galaxies. The SN extinction curves, which are flatter than the others, reproduce the data of eight (67 per cent) galaxies better. Dust masses are estimated to be in excess of ∼108 M⊙. The inferred ages of the galaxies are small, eight of which range from 10 to 650 Myr. The SN-origin dust is the most plausible to account for the vast amount of dust masses and the flat slope of the observed extinction law. The inferred dust mass per SN ranges from 0.01 to 0.4 M⊙ per SN.

Analytic solutions for some basic problems in electricity involving intersecting sphere and circular cylinder pairs

The method of electrical inversion in classical electrostatics is employed to obtain exact solutions for basic electrostatic problems pertaining to overlapping spheres/cylinders. The problems considered here include (1) a pair of overlapping conducting spheres, intersecting at a vertex angle π/n, n an integer, placed in a constant potential field; (2) a pair of infinitely long conducting circular cylinders, intersecting at a vertex angle π/n, n an integer, placed in a uniform field; and (3) a composite hybrid geometry consisting of two orthogonally intersecting infinitely long circular cylinders whose boundary is a combination of conducting and dielectric surfaces (with mixed boundary conditions) submerged in a uniform field. Applying the basic idea of Kelvin’s inversion repeatedly, solutions for the electric potentials are derived in each case. An exact expression for the capacitance in terms of the two radii, center-to-center distance, and the vertex angle is found for the twin sphere geometry. The capacity is then used to find the steady-state rate coefficient of a perfectly absorbing body placed in a thermally conducting environment of lower temperature. The equipotentials are plotted using the exact solutions of the two-dimensional problems and their features are discussed as well. The simple method illustrated here can be useful both as a teaching tool and as a building block for further computations.

Non-destructive examination of interfacial debonding using acoustic emission

Objectives This study aims to assess the viability of using the acoustic emission (AE) measurement technique to detect and monitor in situ the interfacial debonding in resin composite restorations due to build-up of shrinkage stresses during polymerization of the composite. Materials and methods The non-destructive testing technique that measures acoustic emission (AE) was used to detect and monitor the interfacial debonding in resin composite during curing of the composite. Four groups of specimens, n = 4 each, were tested: (1) intact human molars with Class-I cavities restored with the composite Z100 (3M ESPE, USA); (2) intact human molars with Class-I cavities restored with the composite Filtek™ P90 (3M ESPE, USA); (3) ring samples prepared from the root of a single bovine tooth and ‘restored’ with Z100; (4) freestanding pea-size specimens of Z100 directly placed on the AE sensor. The restorations in Groups (1)–(3) were bonded to the tooth tissues with the adhesive Adper™ Scotchbond™ SE Self-Etch (3M ESPE, USA). The composites in all the specimens were cured with a blue light (3M ESPE, USA) for 40 s. The AE signals were recorded continuously for 10 min from the start of curing. Non-destructive 3D imaging was performed using X-ray micro-computed tomography (micro-CT) to examine the bonding condition at the tooth–restoration interface. Results The development of AE events followed roughly that of the shrinkage stress, which was determined separately by the cantilever beam method. The number of AE events in the real human tooth samples was more than that in the ring samples, and no AE events were detected in the pea-size specimens placed directly on the AE sensor. The number of AE events recorded in the specimens restored using Z100 was more than that found in specimens restored with Filtek P90. The micro-CT imaging results showed clear interfacial debondings in the tooth specimens restored with Z100 after curing, but no clear debonding was found in the P90 specimens. Conclusions The AE technique is an effective tool for detecting and monitoring in situ the interfacial debonding of composite restorations during curing. It can potentially be employed to evaluate the development of shrinkage stress and the quality of interfacial bonds in teeth restored with different composite materials, cavity geometries, and restorative techniques.

Erratum to: Kim Model of Transport ac Loss with Position Dependent Critical Current Density in a Superconducting Cylinder

In this article, the dependence of the transport ac loss on field and position is investigated for a hard superconducting cylinder, which is consisted of two concentric shells with different critical current density. The Kim model is considered for the critical state in which the critical current density is assumed to depend on the flux density. Based on Norris’ equations, the analytic expression of the loss with field and position dependence is derived for the cylindrical specimen having a composite geometry. The results obtained show that the field and position dependent critical current density have obvious effects on the loss, which may explain why Norris’ predictions and the theoretical results have small differences.

Crystallization Morphology and Behavior of Polypropylene Composites Containing Microencapsulated Flame Retardant

With shells of melamine-formaldehyde (MF), urea-melamine-formaldehyde (UMF), or poly(vinyl alcohol)-melamine-formaldehyde (VMF), microencapsulated ammonium polyphosphate (APP) was prepared by in-situ polymerization for use as a flame retardant in polypropylene (PP). Microencapsulated APP showed rougher surface, smaller size, and narrower size distribution compared with APP. The results of polarized optical microscopy (POM) showed that the additives resulted in a decrease of the spherulite size and less perfection in crystal geometry of PP composites. Due to the interaction and alignment of the PP polymer chains at the surface, the surface modification of APP influenced the formation and further development of PP crystals remarkably. The crystallization and melting behaviors of the PP composites were affected by the rough surface of the microencapsulated APP, which was helpful for the formation of β-crystals and decreased the crystal growth rate compared with APP.

Development of Anti-Ballistic Board from Ramie Fiber

A laminate of a composite was developed from Kevlar 29-ramie fiber reinforced by polyester resin for hard body armor. The focused given to the ballistic limit, maximum energy absorption, composite failure mode, lifetime rupture, target geometry and environmental effects. The results indicated that the maximum ballistic limit at impact speed is 623.97 m/s for a 15-mm target thickness and 837 m/s for a target thickness of 25 mm. The targets were improved in terms of the impact response with increasing relative humidity in the range of 50% ± 20% but were relatively decreased in terms of resistance with increasing temperature.

A lubrication approach to friction in thermoplastic composites forming processes

Friction is an important phenomenon that can dominate the resulting product geometry of thermoplastic composites upon forming. A model was developed that predicts the friction between a thermoplastic laminate and a rigid tool. The model is based on the Reynolds equation for thin film lubrication and assumes hydrodynamic lubrication on a meso-mechanical level. The frictional properties are calculated, solely based on the rheological properties of the matrix constituent and the fabric weave geometry. The results have been validated against pull-out experiments of a 2 × 2 twill polypropylene (Twintex) weave at melt temperatures.

Fabrication and realistic modeling of three-dimensional metal-dielectric composites

Historically, the methods used to describe the electromagnetic response of random, three-dimensional (3D), metal-dielectric composites (MDCs) have been limited to approximations such as effective-medium theories that employ easily-obtained, macroscopic parameters. Full-wave numerical simulations such as finite-difference time domain (FDTD) calculations are difficult for random MDCs due to the fact that the nanoscale geometry of a random composite is generally difficult to ascertain after fabrication. We have developed a fabrication method for creating semicontinuous metal films with arbitrary thicknesses and a modeling technique for such films using realistic geometries. We extended our two-dimensional simulation method to obtain realistic geometries of 3D MDC samples, and we obtained the detailed near- and far-field electromagnetic responses of such composites using FDTD calculations. Our simulation results agree quantitatively well with the experimentally measured far-field spectra of the real samples.

TIME-DOMAIN ITERATIVE PHYSICAL OPTICS METHOD FOR ANALYSIS OF EM SCATTERING FROM THE TARGET HALF BURIED IN ROUGH SURFACE: PEC CASE

In this paper, time-domain physical optics (TDPO) method is extended to its iterative version (TDIPO) to consider the coupling efiects between two regions, and the latter is employed to investigate electromagnetic scattering from three dimensional target half-buried by a two dimensional rough surface. By using iterative scheme, more accurate transient response re∞ected from combinative target with multi-scattering efiects would be obtained than that by using TDPO alone. The TDIPO could also be enhanced by time-domain equivalent edge current (TDEEC) to further determine the far-fleld characteristics of the combinative target with rough surface. An accurate composite geometry model technique which combines 2D perfectly electrically conducting (PEC) rough surface and half-buried 3D PEC target is introduced and employed to assist the meshing work. The validity of the presented method is verifled by comparing the scattering results for dihedral targets with those obtained through TDPO and flnite difierence in time domain (FDTD), as well as multi-level fast multiple algorithm (MLFMA). Then simulations of EM scattering from the target embedded in rough surface for difierent incidence directions are carried out to test the availability of TDIPO/EEC. Discussions on the efiects of incidence direction and the presence of the target on the backscattering in far- zone are also given.

EMFIE and MEFIE formulations for the analysis of scattering from dielectric and composite bodies of revolution

AbstractIn this article, the electromagnetic scattering from dielectric and composite bodies of revolution are analyzed by the electric‐magnetic field integral equation (EMFIE) and the magnetic‐electric field integral equation (MEFIE), which are customarily overlooked in the literature. A standard method‐of‐moments (MoM) technique is applied for the numerical solution of the surface integral equations. Several dielectric and composite geometries are analyzed through the bandwidth and results are compared with those of well‐established Müller and PMCHWT (a solution proposed by Poggio, Miller, Chang, Harrington, Wu, and Tsai) integral equation formulations. Investigated case studies indicate that the MoM Z‐matrices yielded by the EMFIE and MEFIE are as well‐conditioned as those provided by the Müller and PMCWHT formulations. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:398–402, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25720

Tiled Composite Laminates

This article describes our efforts to develop a meso-scale in-plane tiling technique for fiber-reinforced composite laminates. Such a technique expands the design space of the laminate, and the ability to tailor local laminate properties may provide a means, for example, to mitigate stress concentrations that arise in places such as along free edges of the laminate. Preliminary fabrication of tiled laminates produced material with an elastic modulus that is nearly equal to that of continuously reinforced laminates; however, the strength of these first specimens was significantly reduced. Finite element analyses were then performed to characterize the effects of features unique to tiled composite laminates, such as the existence of resin-rich tile-to-tile interfaces, and to explore the effects of relative arrangement of tiles through the thickness of the laminate. This led to a novel composite joint geometry as well as recommendations to minimize strength reduction. Strength retention of laminates fabricated using the new design guidelines was experimentally found to exceed 92% in comparison with the traditional analogs. Finally, we discuss the potential application of composite tiling for the suppression of free-edge delamination.

Microstructure and unit-cell geometry of four-step three-dimensional rectangular braided composites

This article investigates the microstructure of 3D four-directional rectangular braided composites produced by the four-step 1 × 1 procedure. The planar and spatial yarn paths are analyzed systematically based on 3D braiding process. Three different types of microstructural unit cell models are established with respect to the interior, surface, and corner regions of a braided preform. These models truly simulate the microstructure of the braided composites. Furthermore, they are oriented in the same reference frame of the preform cross-section, which coincides with the actual configuration of composites and suits for the analysis of mechanical properties. The mathematical relationships among the structural parameters, such as braiding dimensions, fiber orientation, braiding pitch, the yarn packing factor, fiber volume fraction, are deduced. The calculated results are in good agreement with the measured values of the geometric characteristics of braided composite samples.

Nanoscale strain characterization in microelectronic materials using X-ray diffraction

The engineering of strained semiconductor materials represents an important aspect of the enhancement in CMOS device performance required for current and future generations of microelectronic technology. An understanding of the mechanical response of the Si channel regions and their environment is key to the prediction and design of device operation. Because of the complexity of the composite geometries associated with microelectronic circuitry, in situ characterization at a submicron resolution is necessary to verify the predicted strain distributions. Of the measurement techniques commonly used for strain characterization, synchrotron-based X-ray microbeam diffraction represents the best nondestructive method to provide spatially resolved information. The mapping of strain distributions in silicon-on-insulator (SOI) features induced by overlying silicon nitride structures and embedded heteroepitaxial features adjacent to SOI device channels are presented. The interaction regions of the SOI strain were observed to extend large distances from the SOI/stressor interfaces leading to significant overlap in the strain distributions at technically relevant dimensions. Experimental data were also compared to several mechanical models to assess their validity in predicting these strain distributions.

Modeling for piezoelectric-shape memory alloy composites

A new concept of a piezoelectric ceramic/shape memory alloy (SMA) composite is proposed with aim of using this as a new actuator material with fast actuation speed and large strain. To prove the new concept, a new model is constructed based on Eshelby formulation where linear piezoelectric constitutive equations and bi-linear superelastic equations of SMA are used. The predictions of the strain induced by applied stress and electric field are made for two simple designs of piezo–SMA composites, 1-D series and 1-D parallel laminated composites. The proposed model indicated that 1-D parallel laminate provides the highest strain induced under bias stress and applied electric field among other composite geometries.

Internal geometry evaluation of non-crimp 3D orthogonal woven carbon fabric composite

Measurements of the internal geometry of a carbon fiber non-crimp 3D orthogonal woven composite are presented, including: waviness of the yarns, cross sections of the yarns, dimensions of the yarn cross sections, and local fiber volume fraction. The measured waviness of warp and fill yarns are well below 0.1%, which shows that the fabric termed here “non-crimp” has nearly straight in-plane fibers as-produced, and this feature is maintained after going through all steps of fabric handling and composite manufacturing. The variability of dimensions of the yarns is in the range of 4–8% for warp and fill directions, while the variability of the yarn spacing is in the range of 3–4%. These variability parameters are lower than respective ranges of variability of the yarn waviness and the cross-sectional dimensions in typical carbon 2D weave and 3D interlock weave composites, which are also illustrated in this work for comparison.

Real-Time Rendering Method and Performance Evaluation of Composable 3D Lenses for Interactive VR

We present and evaluate a new approach for real-time rendering of composable 3D lenses for polygonal scenes. Such lenses, usually called "volumetric lenses," are an extension of 2D Magic Lenses to 3D volumes in which effects are applied to scene elements. Although the composition of 2D lenses is well known, 3D composition was long considered infeasible due to both geometric and semantic complexity. Nonetheless, for a scene with multiple interactive 3D lenses, the problem of intersecting lenses must be considered. Intersecting 3D lenses in meaningful ways supports new interfaces such as hierarchical 3D windows, 3D lenses for managing and composing visualization options, or interactive shader development by direct manipulation of lenses providing component effects. Our 3D volumetric lens approach differs from other approaches and is one of the first to address efficient composition of multiple lenses. It is well-suited to head-tracked VR environments because it requires no view-dependent generation of major data structures, allowing caching and reuse of full or partial results. A Composite Shader Factory module composes shader programs for rendering composite visual styles and geometry of intersection regions. Geometry is handled by Boolean combinations of region tests in fragment shaders, which allows both convex and nonconvex CSG volumes for lens shape. Efficiency is further addressed by a Region Analyzer module and by broad-phase culling. Finally, we consider the handling of order effects for composed 3D lenses.

Kim Model of Transport ac Loss with Position Dependent Critical Current Density in a Superconducting Cylinder

In this article, the dependence of the transport ac loss on field and position is investigated for a hard superconducting cylinder, which is consisted of two concentric shells with different critical current density. The Kim model is considered for the critical state in which the critical current density is assumed to depend on the flux density. Based on Norris’ equations, the analytic expression of the loss with field and position dependence is derived for the cylindrical specimen having a composite geometry. The results obtained show that the field and position dependent critical current density have obvious effects on the loss, which may explain why Norris’ predictions and the theoretical results have small differences.

Plasmonic Modes of Metallic Semishells in a Polymer Film

The symmetry-broken geometry and variation of metal composition of semishells induce new plasmonic properties. A system of separated metallic semishells embedded in a poly(dimethylsiloxane) polymer film provides an ideal platform to investigate the localized surface plasmon resonance modes of semishells. We demonstrate experimentally that silver, gold, copper, and aluminum semishells can offer distinct plasmonic responses due to the wide range of their material parameters. Numerical calculations combined with the plasmon hybridization theory render us a clear understanding and assignment of the plasmonic modes of the semishells.

Experimental measurement and predictive modelling of bending behaviour for viscous unidirectional composite materials

It is widely accepted that the key deformation mechanisms during forming of viscous textile composite (prepreg) sheets are in-plane shear and out-of-plane bending. This paper focuses on the bending deformation mechanism, including experimental characterisation and theoretical modelling of bending behaviour during viscous composite forming. Experimental measurements are obtained by means of a large-displacement buckling test at a variety of displacement rates and temperatures. Some important aspects, such as viscoelastic behaviour, are also investigated. A bending model based on elastic theory combined with uniaxial continuum theory for ideal fibre-reinforced fluids for viscous shear deformation has been developed, using material parameters obtained from industrial manufacturers as input data, such as composite geometry, fibre properties, fibre volume fraction and matrix rheology. Model predictions demonstrate that the model can capture the main characteristics of material properties, such as rate dependence. This bending model can be used in formability analysis for viscous unidirectional composite materials, and might be applied in a finite element forming simulation to account for the bending stiffness.

Electrooptical properties of polarization holographic gratings formed in liquid-crystal composites

The results of experimental study of the electrooptical properties of polarization holographic gratings formed in a liquid-crystal composite by polarization holography are presented. The influence of the formation conditions, the parameters of the controlling ac electric field, and the composite geometry on the diffraction efficiency of such gratings is considered.