Krishnan Balasubramaniam

Inversion of composite material elastic constants from ultrasonic bulk wave phase velocity data using genetic algorithms

In this paper, efforts on the reconstruction of material stiffness properties of unidirectional fiber-reinforced composites from obliquely incident ultrasonic bulk wave data, employing an inverse technique based on genetic algorithms, is described. Computer-generated ultrasonic phase velocity data, as a function of the angle of refraction in both symmetry and nonsymmetry through the thickness planes of unidirectional composites were used as the input to the genetic algorithm. A simple genetic algorithm, with optimal parameters chosen from the literature and numerical analysis (reported here), was implemented for the reconstruction. The inversion using this novel technique was found to be extremely promising in the characterization of the material stiffness properties. Stability to noise in the input phase velocity data set was also investigated. Advantages and disadvantages of the genetic reconstruction technique over conventional methods are also discussed.

High temperature ultrasonic sensor for the simultaneous measurement of viscosity and temperature of melts

An ultrasonic sensor that simultaneously measures temperature and viscosity of molten materials at very high temperature is described. This sensor has applications as a process monitor in melters. The sensor is based on ultrasonic shear reflectance at the solid–melt interface. A delay line probe is constructed using refractory materials. A change in the time of flight within the delay line is used to measure the temperature. The results obtained from this sensor on various calibration glass samples demonstrate a measurement range of 100–20 000 P for the viscosity and 25–1500 °C for the temperature.

Measuring Newtonian viscosity from the phase of reflected ultrasonic shear wave

In this paper, an acoustic shear impedance model is employed to obtain a relation between the viscosity of a Newtonian fluid and phase characteristics of ultrasonic shear wave reflection from a solid-fluid interface. The phase and magnitude of the reflection coefficient can be decoupled in this model. The decoupling allows an independent relation between the acoustic shear impedance (viscosity-density product) and phase of the reflection coefficient. The model was experimentally verified for different fluid-solid combinations. Comparison of the results with the commonly used absolute reflection coefficient method demonstrates that phase measurement provides improved measurements.

Effect of viscosity on ultrasound wave reflection from a solid/liquid interface

A study of the simulated reflection of a wideband ultrasound shear wave from the solid/viscous fluid interface is presented. Various parameters affecting reflection factors including the material properties of the solid, fluid properties like density and viscosity, and the operating frequency are discussed. Simulated ultrasonic response waveforms are compared with the experimentally obtained data for NIST traceable calibration standards of viscosity. A good agreement was observed between the simulated and experimental waveforms at various viscosities and for different solid substrates.

Ultrasonic through-transmission characterization of thick fibre-reinforced composites

Abstract Thick composites pose a significant challenge to the ultrasonic nondestructive evaluation process due to the increased attenuation as well as the influence of material anisotropy. The physics of ultrasonic wave propagation in anisotropic material involves understanding such phenomena as beam skewing, material focusing/defocusing, unsymmetrical beam profiles, etc. This ultrasonic behaviour can be considered to be relatively insignificant in the nondestructive evaluation of thin anisotropic composite structures, but cannot be neglected in thick composites. In this paper, the ultrasonic characterization of thick glass-epoxy composites using an immersion through-transmission method employing a standard ultrasonic robot scanner system is discussed in detail. An inverse technique for computing material elastic constants from the acquired data is discussed. The experiment measures group velocity is a function of energy propagation angle (group angle), from which phase velocity is numerically computed as a function of phase angle. Then, the material constants are determined from phase velocity profiles using commercially available parameter identification software. Both uni-directional (five independent elastic constants) as well as cross-ply (nine independent elastic constants) were considered. Through-transmitted ultrasonic beam characteristics in thick composites are then analysed using feature extraction procedures and compared with the isotropic plexiglass structure.

Torsional Waveguide Sensor for Molten Materials

Viscosity of the molten glass is a key variable in determining the quality of the final glass product. At low viscosities the melt can be highly corrosive. At high viscosities the melter can become plugged. “Melt viscosity is the most important processing property; it controls processing rate, product homogeneity, and heat transfer within the molten glass [1]. “ Thus, the viscosity is an important parameter which can be used by the vitrification industry for the processing of waste material and by the glass industry for production of high quality glass products. The major problem in measuring the viscosity of the molten waste product is the extremely hot and corrosive environment.

Viscosity measurement with laser-generated and detected shear waves

A technique is described in which laser-generated shear waves can be used to measure the viscosity of liquids. The technique involves measuring the shear wave reflection coefficient at a solid–liquid interface. To accommodate this procedure, a wedge was designed to launch laser-generated shear waves into the material at nearly normal incidence to the solid–liquid interface. The reflected laser-generated shear waves are detected at a second interface with a laser interferometer. The angle of incidence at this second interface is at an angle greater than the critical angle. The purpose of this arrangement is to maximize the out-of-plane displacement at this second interface so that detection with the interferometer can be more easily accomplished. Calculations that support the design of the wedge and experiment are outlined and experimental results are presented and discussed. This technique would be most applicable in those situations in which conventional techniques are not suitable, such as those involvi...

On a numerical truncation approximation algorithm for transfer matrix method

A numerical truncation technique is described for reducing the numerical instability problems associated with the utilization of the transfer matrix method, especially in cases where the frequency of ultrasound, the number of layers, or the thickness of the layers become very large. This rather simplistic modification to the numerical coding extends the transfer matrix method to a wide range of applications, without any complex and computationally intensive reformulation.

Guided Wave Behavior Analysis in Multi-Layered Inhomogeneous Anisotropic Plates

homogeneous anisotropic plates. It has been reported before that guided waves in inhomogeneous plates tend to follow preferred directions based on the location of ply-groups as well as the orientation of the fibers [1]. The pattern obtained by imaging the leaked energy into the surrounding fluid (earlier called as Plate Wave Flow Patterns) has been shown to indicate fiber orientations [2]. In this paper, a model based on the Thomson-Haskell transfer matrix is employed to obtain the internal distributions of the energy vector within the inhomogeneous plate. Based on the theoretical results, the plate wave flow patterns can be predicted and compared with the experimental results. The results provide insight into the understanding of the generation mechanism of guided wave mode patterns in inhomogeneous plates. THEORETICAL BACKGROUND Consider a general anisotropic multilayered plate immersed in water. The plate consists of an arbitrary number of general anisotropic layers n, rigidly bonded at their interfaces as shown in Figure 1. Without losing generality, it is assumed that leaky plate waves propagate along the Xl direction. First consider the plane wave propagation in a general anisotropic multi-layered structure as shown in Figure 1. The displacements of the wave are given by

Ultrasonic and vibration methods for the characterization of pultruded composites

Abstract Characterization of unidirectional fiber reinforced glass/epoxy pultruded composites using ultrasonics (high frequency, 1-5 MHz) and the impulse-frequency response vibration (intermediate frequency, 50-100 Hz) technique, is demonstrated here. This paper compares the response of both of these non-destructive test techniques to the changes in the pultrusion process variables and to the indeed contaminants introduced during manufacturing. The ultrasonic methods use multi-mode techniques of wave velocity and attenuation measurements to measure the viscoelastic constants of the pultruded composite while the vibration technique provides the dynamic flexural modulus and loss factor (damping) measurements. Quasi-destructive assays were also performed using a low frequency (1-50 Hz) Dynamic Mechanical Analyser (DMA) to verify the state of pultruded samples with induced contaminants (simulated porosity and interfacial debonding) and the results compared with the non-destructive measurements. Mathematical models to describe the influence of porosity and debonding agents on the material properties were derived based on statistical regression analysis procedures. Results indicate that the peak damping value of the tan δ curve obtained from the DMA is a sensitive parameter to detect abnormalities in the finished product. The ultrasonic velocity and dynamic flexural modulus measurements provide useful information on the stiffness characteristics while the attention and loss factor can be related to the anomaly-sensitive damping properties of the material.