Anisotropy

Biomechanical studies suggest that one determinant of abdominal aortic aneurysm (AAA) rupture is related to the stress in the wall. In this regard, a reliable and accurate stress analysis of an in vivo AAA requires a suitable 3D constitutive model. To date, stress analysis conducted on AAA is mainly driven by isotropic tissue models. However, recent biaxial tensile tests performed on AAA tissue samples demonstrate the anisotropic nature of this tissue. The purpose of this work is to study the influence of geometry and material anisotropy on the magnitude and distribution of the peak wall stress in AAAs. Three-dimensional computer models of symmetric and asymmetric AAAs were generated in which the maximum diameter and length of the aneurysm were individually controlled. A five parameter exponential type structural strain-energy function was used to model the anisotropic behavior of the AAA tissue. The anisotropy is determined by the orientation of the collagen fibers (one parameter o...

An increase in random molecular vibrations of a solid owing to heating above the melting point leads to a decrease in its long-range order and a loss of structural symmetry. Therefore conventional liquids are isotropic media. Here we report on a light-induced isothermal transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the

Resumen En la presente investigación se ha encontrado una nueva familia de soluciones de estrellas anisótropas con densidad variable que dependen de dos parámetros ajustables C y α, relacionados al grado de anisotropía del fluido. En este modelo se ha ...

This paper presents the effect of loading rate, (ELR), and direction of formation, (DF), of rigid polyurethane foams, (PUR 40 and PUR 140), on fracture toughness. Nominal densities of used foams in the experimental program were 140 kg/m 3 , (for ELS) and 40 kg/m 3 , (for DF), which is closed-cell rigid foams widely used for sandwich cores. Determination of fracture toughness for Mode I fracture of studied materials has made by three-point bending tests, (3PB), on specimens with notches, at room temperature (20 ± 2 ºC). All the specimens were cut from one and the same plate. The specimens were subjected to 3PB at a loading speed of 2 mm/min, except samples for determining the ELR where 2, 20, 200 and 400 mm/min loading speeds were used, and were taken into account the fact that the load must act exactly on the notch direction. All the specimens present brittle failure without plastic deformation.

This paper aims to improve current understanding of the subsurface fracture system in the Coso geothermal field, located in east-central California. The Coso reservoir is in active economic development, so that knowledge of the subsurface fracture system is of vital importance for an accurate evaluation of its geothermal potential and day-to-day production. To detect the geometry and density of fracture systems we applied the shear-wave splitting technique to a large number of high-quality seismograms from local microearthquakes recorded by a permanent, 16-station, down-hole, 3-component seismic array running at 480 samples/s. The analysis of shear-wave splitting (seismic birefringence) provides parameters directly related to the strike of the subsurface fractures and their density (number of cracks per unit volume), and, consequently, is an important technique to outline zones of high permeability. Three major fracture directions N10–30W, N0–20E, and N40–50E, of which the first and the second are the most prominent, were identified from the seismograms recorded by the 16-station down-hole array. All orientations are consistent with the known strike of local sets of faults and fractures in local wells and at the surface, as well as with previous analyses of seismic anisotropy in the region. The high quality of the recordings has allowed us to launch an unprecedented investigation into the characteristics of the temporal variations in crack polarization and crack density in a producing geothermal environment. Preliminary results point to significant temporal changes in shear-wave time delays, probably influenced by temporal changes in crack density within a period of 5 years (1996–2000). They are tentatively interpreted as due to a local ∼3% increase in shear-wave velocity in the southwestern part of the field during 1999.

Die Planung und Ausführung von tiefen Baugruben in weichen Böden im innerstädtischen Bereich ist für alle Beteiligten eine große Herausforderung. In diesem Beitrag wird die Herstellung einer 8 m tiefen Baugrube mit unmittelbarer Nachbarbebauung in Konstanz vorgestellt. Hierzu werden umfangreiche Messergebnisse gezeigt, die im Rahmen der bei Baugruben in weichen Böden unverzichtbaren Beobachtungsmethode erfasst wurden, und mit den Ergebnissen einer numerischen Analyse unter Berücksichtigung der räumlichen und zeitabhängigen Effekte verglichen. Darüber hinaus werden die erforderlichen Nachweise für den Grenzzustand der Tragfähigkeit unter Berücksichtigung der komplexen Baugrund-Tragwerk-Interaktion präsentiert. Insbesondere wird ein modifizierter Ansatz zur Berechnung der Aufbruchsicherheit einer verankerten Baugrubensohle nach den Vorgaben des Eurocodes EC7-1 in Anlehnung an die Empfehlungen des Arbeitskreises „Baugruben“ der Deutschen Gesellschaft für Geotechnik vorgestellt.
Die Baugrube mit einem annähernd quadratischen Grundriss wurde im Jahr 2008 in weich-breiigem Seeton mit zwei Untergeschossen hergestellt. Als Verbauwand wurde eine eingepresste Spundwand verwendet, die in einer Höhe von –1,80 m durch einen oberen Aussteifungsring aus einer Gurtung mit diagonalen Ecksteifen und mit einer abschnittweise hergestellten Unterbetonsohle in einer Tiefe von –7,80 m ausgesteift wurde. Die räumlichen Einflüsse der Baugrund-Tragwerk-Interaktion, die für dieses Projekt durch den Einbau einer rautenförmigen oberen und unteren Aussteifung und den abschnittweisen Einbau der Betonsohle bestimmt wurden, konnten in einer zweidimensionalen numerischen Analyse mit Mobilisierungsfaktoren und unter Berücksichtigung der spannungspfadabhängigen Steifigkeit des Seetons zutreffend erfasst werden.
Dieses Ausführungsbeispiel einer tiefen Baugrube in weichen Böden verdeutlicht besonders die Wichtigkeit eines umfangreichen begleitenden Messprogramms im Hinblick auf die Anwendungsgrenzen der Finiten Elemente Methode bei Verwendung derzeit kommerziell verfügbarer höherwertigerer Stoffgesetze. In dem Beitrag wird darüber hinaus eine Methode zur Berücksichtigung der spannungspfadabhängigen Steifigkeit von weichen Böden vorgestellt.

Additive manufacturing offers an exclusive way of anisotropic microstructure control with a high degree of freedom regarding variation in process parameters. This study demonstrates a unique texture formation in Inconel 718 (IN718) using a bidirectional laser scan in a laser powder bed fusion (LPBF) process for tailoring the mechanical properties. We developed three distinctive textures in IN718 using LPBF: a single-crystal-like microstructure (SCM) with a < 110 > orientation in the build direction (BD), crystallographic lamellar microstructure (CLM) with a < 110 >-oriented main layer and < 100 >-oriented sub-layer in the BD, and polycrystalline with a weak orientation. The microstructure observations and finite element simulations showed that the texture evolution of the SCM and CLM was dominated by the melt-pool shape and related heat-flow direction. The specimen with CLM exhibited a simultaneous improvement in strength and ductility owing to the stress-transfer coefficient between the < 110 >-oriented main and < 100 >-oriented sub-grains, showing superior mechanical properties compared to cast-IN718. This behavior is largely attributed to the presence of the boundary between the main and sub-layers (crystallographic grain boundary) lying parallel to the BD uniquely formed under the LPBF process. Furthermore, the strength-ductility balance of the part with the CLM can be controlled by changing the stress-transfer coefficient and the Schmidt factor through an alteration of the loading axis. Control of the crystallographic texture, including the CLM formation, is beneficial for tailoring and improving the mechanical performance of the structural materials, which can be a promising methodology.

In this work, we characterized streptavidin-conjugated quantum dots (QDs) manufactured by Quantum Dot Corporation. We present data on: (1) two-photon excitation; (2) fluorescence lifetimes; (3) ensemble and single QD emission anisotropy; (4) QDs as donors for Förster resonance energy transfer (FRET); and (5) spectral conversion of QDs exposed to high-intensity illumination. We also demonstrate the utility of QDs for (1) imaging the binding and uptake of biotinylated transferrin on living cells, and (2) resolving by fluorescence lifetime imaging microscopy (FLIM) signals originating from QDs from those of spatially and spectrally overlapping visible fluorescent proteins (VFPs). Microsc. Res. Tech. 65:169–179, 2004. © 2005 Wiley-Liss, Inc.