Elastic Characterization of Orthotropic Composite Materials from Ultrasonic Inspection through Non-Principal Planes

Transmission of bulk ultrasonic waves through materials immersed in water is a well appropriated method to measure the stiffness matrix of anisotropic composite materials. This matrix can be deduced from velocities measurements by simple [1,2,3] or double transmission [4,5] or from amplitudes of double reflected bulk waves [4]. All these methods are working very well for unidirectional composites when transverse isotropy is assumed and the stiffness matrix has only five independent elastic constants.</p

Elastic Wavefield Modeling for Arbitrarily Oriented Orthotropic Media

Composite materials have gained a considerable importance, being widely applied e.g. in aerospace industries as unidirectional, layered or woven structures. Through their complex build-up these materials exhibit anisotropic elastic behavior, raising considerable difficulties for ultrasonic nondestructive testing techniques. In modeling the interaction of elastic waves with such media a simple tool of assisting analysis is available. In this respect, simulation and optimization allow for a reduction of experimental work and an increase in reliability of applied testing procedures. For materials exhibiting orthotropic elastic symmetry, fundamental plane wave characteristics are presented in this contribution. These relationships are further applied for transducer-field modeling using the Generalized Point Source Synthesis method [1]. Since for complex-shaped components the material’s natural symmetry planes are in general not identical with the component’s surfaces, a respective transformation has been applied recently to yield a compact elastic tensor representation for such configurations [2]. Based on this formulation, all analytical results are obtained in a coordinate-free form, where the material’s spatial orientation appears as an additional parameter. Since orthotropy includes the higher symmetries tetragonal, transversely isotropic, cubic and isotropic, the results presented cover most of the materials of today’s industrial interest. Numerical results cover slowness and group velocity diagrams as well as field pattern calculations for commercial transducers including time-depedent rf-impulse modeling

Ultrasonic NDE of Laser-Damaged Organo-Matrix Composites

The ultrasonic attenuation and velocity in graphite/epoxy (Gr/Ep) composites damaged by real and simulated laser radiation were measured. The measurements were carried out with composite ultrasonic test equipment (CUTE), a water-tank testbed constructed to study the elastic properties of samples subjected to CO2 laser radiation at several different scan rates. Parallel simulation studies were carried out on samples subjected to temperatures high enough to cause pyrolysis. The ultrasonic measurements were made in the 1 to 5 MHz frequency range for varying angles of incidence. The damage manifests itself in differing degrees of porosity depending on the intensity of irradiation. Both attenuation and velocity were found to be sensitive to this damage.</p

Temperature dependence of the energy of a vortex in a two-dimensional Bose gas

We evaluate the thermodynamic critical angular velocity Omega_c(T) for creation of a vortex of lowest quantized angular momentum in a strictly two-dimensional Bose gas at temperature T, using a mean-field two-fluid model for the condensate and the thermal cloud. Our results show that (i) a Thomas-Fermi description of the condensate badly fails in predicting the particle density profiles and the energy of the vortex as functions of T; and (ii) an extrapolation of a simple Thomas-Fermi formula for Omega_c(0) is nevertheless approximately useful up to T = 0.5 T_c.Comment: 9 pages, 4 figure

2-(2-Benzyl­phen­yl)propan-2-ol

There are two mol­ecules in the asymmetric unit of the title compound, C16H18O, a tertiary alcohol featuring a 2-benzyl­phenyl substituent. Co-operative O—H⋯O hydrogen bonds connect the mol­ecules into tetra­mers

Measurement of Anisotropic Elastic Constants of an Aluminum Composite Plate Using a Double Reflection Method

Various ultrasonic methods[1–3] have been proposed for determination of anisotropic elastic stiffness and constants of composite materials. Among them, the double through transmission method[2] is effective because of direct measurement of the phase velocity as well as simple experimental set-up of use of single transducer. However, this method requires to install a reflector plate in the opposite side of the transducer. For determining anisotropic elastic properties of fabricated structural parts, which have different shape from flat panels, however, the application of the double transmission method is difficult

Optimized Determination of Elastic Constants of Anisotropic Solids from Wavespeed Measurements

Ultrasonic measurements have been used for a long time to quantitatively determine the elastic properties of solids from wavespeed measurements. The determination is based on measuring the speeds of propagation of various wave modes, propagating in specific directions of the solid. Various methods have been developed for these measurements including both continuous wave and pulsed or burst techniques. A traditional distinction can be done in the way the transducer(s) interact with the solid to be characterized. Contact techniques [1,2] have been supplemented by immersion systems [3,4] which often yield more reproducible results and which permit measurements to be easily made along different directions in the test specimen. For instance, an advanced immersion system using the principle of digital interferometry with the help of a cross-correlation technique and normal mode tracking algorithms was recently designed [51. By using the mode conversion process at a liquid-solid interface, quasi-longitudinal and quasi-transverse bulk modes can be generated in numerous directions in the interior of the solid. The design and implementation of specialized optimization algorithms [6] permit a precise determination of the elastic constants for various synthetic and natural composite materials [7,8]. Nevertheless, a principal limitation of the existing optimization procedures for recovering a material’s elastic constants has been the requirement of wavespeed data measured in principal planes, where some analytical expressions, providing the slowness curves, generally exist [9]

Demonstration of quantum Zeno effect in a superconducting phase qubit

Quantum Zeno effect is a significant tool in quantum manipulating and computing. We propose its observation in superconducting phase qubit with two experimentally feasible measurement schemes. The conventional measurement method is used to achieve the proposed pulse and continuous readout of the qubit state, which are analyzed by projection assumption and Monte Carlo wave-function simulation, respectively. Our scheme gives a direct implementation of quantum Zeno effect in a superconducting phase qubit.Comment: 5 pages, 4 figure

Free expansion of two-dimensional condensates with a vortex

We study the free expansion of a pancake-shaped Bose-condensed gas, which is initially trapped under harmonic confinement and containing a vortex at its centre. In the case of a radial expansion holding fixed the axial confinement we consider various models for the interactions, depending on the thickness of the condensate relative to the value of the scattering length. We are thus able to evaluate different scattering regimes ranging from quasi-three-dimensional (Q3D) to strictly two-dimensional (2D). We find that as the system goes from Q3D to 2D the expansion rate of the condensate increases whereas that of the vortex core decreases. In the Q3D scattering regime we also examine a fully free expansion in 3D and find oscillatory behaviour for the vortex core radius: an initial fast expansion of the vortex core is followed by a slowing down. Such a nonuniform expansion rate of the vortex core may be taken into account in designing new experiments.Comment: 10 pages, 4 figure