Ultrasonic Immersion Research Articles

Nondestructive characterization of metal matrix composite by ultrasonic measurement

Nondestructive characterization of a composite using ultrasonic technique has been conducted systematically on A1 2O 3 short fiber reinforced AC8A aluminium metal-matrix composites. For this purpose, A1 2O 3/AC8A with volume fraction of A1 2O 3 short fiber varying up to 30% were fabricated by the squeeze casting technique. Ultrasonic properties of composites were measured by the ultrasonic immersion technique based on pulse-echo method. It was found that ultrasonic velocities were primarily correlated with the volume fraction of A1 2O 3 short fiber. The elastic constants of composites including Young's modulus, shear modulus, and bulk modulus were determined on the basis of the longitudinal and shear wave velocities measured by an ultrasonic technique. The Young's modulus of the composites obtained by ultrasonic technique demonstrated a slightly more conservative value than those measured by the three-point bend test and showed relatively good agreement with the results predicted from the equal stress condition. It was also found that the attenuation and the backscattering behaviors of the composites were primarily related to the volume fraction of fiber and these relations could be used to predict the condition of fiber distribution in matrix nondestructively.

Backscattered microstructural noise in ultrasonic toneburst inspections

A model is presented which relates the absolute backscattered noise level observed in an ultrasonic immersion inspection to details of the measurement system and properties of the metal specimen under study. The model assumes that the backscattered noise signal observed for a given transducer position is an incoherent superposition of echoes from many grains. The model applies to normal-incidence, pulse-echo inspections of weakly-scattering materials using toneburst pulses from either a planar or focused transducer. The model can be used in two distinct ways. Measured noise echoes can be analyzed to deduce a “Figure-of-Merit” (FOM) which is a property of the specimen alone, and which parameterizes the contribution of the microstructure to the observed noise. If the FOM is known, the model can be used to predict the absolute noise levels that would be observed under various inspection scenarios. Tests of the model are reported, using both synthetic noise echoes, and measured noise echoes from metal specimens having simple and complicated microstructures.

Non destructive ultrasonic evaluation of fibrous metal matrix composites

An iterative numerical elastic constants optimization method associated to a classical ultrasonic immersion device is used for the entire characterization of two kinds of metal matrix composites. The usual methods of optimization are generally based on Newton's algorithm. Sometimes this algorithm converges towards relative minima that gives elastic constants which do not correspond to the physical reality of the material. As a remedy, we have developed a numerical analysis technique based on a different algorithm allowing a better convergence to the unique global solution. Using the Levenberg-Marquard algorithm, the methodology to recover the elastic constant, consists in minimizing the square deviation between calculated velocities and the experimental ones measured under variable incidence from a computer controlled ultrasonic immersion device.

Ultrasonic immersion test equipment

Ultrasonic immersion test equipment

Surface roughness and the ultrasonic detection of subsurface scatterers

The influence of surface roughness on the detection of subsurface scatterers using phase-coherent, ultrasonic immersion transducers is reported. Experiments were conducted with phase-coherent transducers, immersed in a liquid bath, that insonified samples with roughened surfaces. Measurements were made of: (1) the signal-to-noise ratio for a subsurface void when viewed through a rough surface; (2) the frequency-dependent loss (between 2 and 20 MHz) that was induced in the transmission and reflection coefficients of the coherent beam for flat aluminum plates with root-mean-square roughness varying between 5 and 50 μm; and (3) the effects of surface roughness on the material noise. The following results were found. First, surface roughness greatly degraded the signal-to-noise ratio (S/N) for some typical inspection geometries. Second, after appropriate normalization, the transmission and reflection coefficients for the coherent beam were found to be nearly universal functions of the angle of incidence, except near the critical angles. Large reductions (several orders of magnitude) in the phase-coherent signal S resulted for some typical inspection setups. The noise, on the other hand, remained nearly unchanged for the same setups. The degradation in S/N was attributed to the randomization of the phase of the coherently transmitted and reflected beams. Both the sensitivity of the signal and the relative insensitivity of the backscatter noise are explained in terms of the phase-screen approximation. This simple approximation is also used to explain the nearly universal form of the normalized transmission and reflection coefficients, and to predict that the backscatter noise may be either slightly enhanced or slightly decreased by surface roughness.

Modelling the elastic properties of fibre-reinforced composites: II theoretical predictions

This paper evaluates different models for predicting the elastic properties of fibre reinforced composites. The modelling is broken into two discrete components. First, the properties of the individual composite unit, envisaged as a fibre embedded in a circular sheath of matrix, are determined. Four models for determining the elastic properties of the unit are evaluated. The second stage in the modelling is to predict the effects of a range of orientations of the simple composite unit. This is achieved by applying the aggregate model proposed by Ward. The orientation averages needed for the second stage were obtained by image analysis, and their measurement was detailed in a previous paper. Finally the predicted elastic constants were compared with experimental values determined using an ultrasonic immersion technique.

The elastic constants of moulded polymeric composites

AbstractThe paper makes an approach to the determination of the five independent elastic constants of uniaxial symmetric material with the ultrasonic immersion technique. Only five ultrasonic wave velocities are required during measurement. The elastic constants of the moulded composites comprised of poly(phenylene sulfide), poly(aryl ether sulfone) with cardo side groups, short carbon fiber and carbon black are measured by using the suggested treatment. The results exhibit a close relationship between the elastic properties and the structure of the materials.

Elastic anisotropy in unidirectional fibre reinforced composites

A theory is presented to calculate bounds on the elastic constants for unidirectional fibre reinforced composites, where the fibres and matrix both show transverse isotropy. This, and a more intuitive theory due to Brody and Ward (1971) tested using new comprehensive measurements for the elastic constants of a range of unidirectional composites using the ultrasonic immersion technique. These composites are based on epoxy resin reinforced either by glass fibres or with ultrahigh modulus polyethylene fibres and polyetheretherketone reinforced with carbon fibres (APC2). Agreement between experimental data and the theoretical bounds is very satisfactory considering the present uncertainties in some of the fibre elastic constants.

Characterization of ultrasonic immersion transducers : Review of progress in quantitative nondestructive evaluation, Brunswick, maine (United States), 23–28 Jul. 1989. Vol. 9A, pp. 781 – 788. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990)

Characterization of ultrasonic immersion transducers : Review of progress in quantitative nondestructive evaluation, Brunswick, maine (United States), 23–28 Jul. 1989. Vol. 9A, pp. 781 – 788. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990)

Characterization of ultrasonic immersion transducers: new applications in the nuclear industry : Proceedings of the 10th international conference on NDE in the nuclear and pressure vessel industries, Glasgow (Scotland), 11–14 Jun. 1990. pp. 743–746. Edited by M.J. Whittle, J.E. Doherty and K. Iida. ASM international, (1990)

Characterization of ultrasonic immersion transducers: new applications in the nuclear industry : Proceedings of the 10th international conference on NDE in the nuclear and pressure vessel industries, Glasgow (Scotland), 11–14 Jun. 1990. pp. 743–746. Edited by M.J. Whittle, J.E. Doherty and K. Iida. ASM international, (1990)

Mechanical characterization of a unidirectional composite by ultrasonic methods

The anisotropy of fibrous composite materials makes it difficult to determine their elastic constants nondestructively. Quantitative ultrasonic methods were studied to determine elastic constants of a transversely isotropic laminate. Comprehensive relationships of the measured ultrasonic data and material properties were developed. The mode conversion phenomenon at the specimen–liquid interface with oblique incidence ultrasonic immersion testing provided all the necessary information. Determination of elastic constants was possible by measuring wave speeds and critical angles. Phase velocities were determined by the multiple reflection technique utilizing ultrasonic spectroscopy. A special scanning technique was developed to determine the phase velocities and wave propagation angles in the anisotropic plane from the measured group velocities. The method developed was applied to the characterization of a unidirectional graphite/epoxy composite.

PAC Delivers UltraPAC II to Marshall Space Centre

PHYSICAL Acoustics Corporation (PAC) recently delivered the computerised ultrasonic immersion system, UltraPAC II, complete with a 7′ × 4′ × 4′ tank to Marshall Space Centre in Huntsville, Alabama for testing composite components of the space shuttle. The Marshall System will be able to locate and size structural flaws, such as delaminations, cracks and voids. Designed to meet Marshall Space Centre requirements, UltraPAC II will be used to inspect parts of the space shuttle intertank door, located on the External Tank, and other associated flight hardware. Positioned between oxygen and hydrogen tanks on the underbelly of the shuttle, the intertank door provides access to electronics, attaching shuttle struts and fuel lines. This area is where the tanks feed three main engines on the shuttle.

Ultrasonic Immersion Testing System

WELLS Krautkramer has introduced a new range of British designed and built ultrasonic immersion testing systems for detecting minute flaws in large, safety‐critical components such as aero engine turbine discs and rings.

Dynamic Distribution of Displacement and Stress Considerations in the Ultrasonic Immersion Nondestructive Evaluation of Multilayered Plates

A unified theoretical treatment is presented for the calculation of displacements and stresses within multilayered media subjected to incident ultrasonic waves. The wave is supposed to be incident from water, at an arbitrary angle, upon a plate consisting of an arbitrary number of different isotropic material layers. In the first part of the analysis displacements and stresses are determined as functions of position within the plate while all layer interfaces are assumed to be rigidly bonded. A smooth interface is subsequently introduced to simulate debonding of two material layers. The composite plate is assumed to be bounded at the bottom by either a free surface, a fluid half-space or an elastic solid half-space. A byproduct of the analysis is the derivation of the reflection and transmission coefficients for the systems. Extensive numerical results are given in order to delineate the influence of the plate material orderings, layer thicknesses and interfacial conditions on the displacements and stresses within the plate. The model developed here will be of value in material characterization and in the nondestructive evaluation of advanced material applications.

Nondestructive evaluation of ceramic preforms

In order to identify and eliminate flawed ceramic preforms prior to metal infiltration, several approaches for nondestructive evaluation were studied. The techniques chosen include immersion ultrasonics, scanning acoustic microscopy (SAM), and radiography. Undesirable irregularities in the preforms include cracks, voids, density gradients, and shot. The latter represents spherically shaped particles of alumina, with diameters that may exceed ten times that of the fibers, and that are incorporated into the porous fiber preform. It is generally thought that shot with sizes greater than 100 μm affects the mechanical properties of the resulting metal matrix composite. With the aid of SAM and scanning electron microscopy (SEM), shot in near-surface areas could be evaluated. Cracks and voids could also be located using SAM and SEM. On a larger scale, the ultrasonic immersion equipment was capable of detecting and quantifying density gradients, which were verified using radiographic techniques. Examples will be given to illustrate the sensitivity and resolution of the various techniques with regard to examination of the flawed preforms. [Work supported by Center for Advanced Materials, Pennsylvania State University.]

Correlation method for normal mode tracking in anisotropic media using an ultrasonic immersion system

This paper considers the problem of normal mode tracking using an ultrasonic immersion system. Due to mode conversion at the liquid-solid interface, two quasi-waves coexist in the solid medium. The spatial and temporal separation of the two modes are limited in certain conditions. The aim of this study, is to analyse the optimum possibilities offered by a correlation method for time-of-flight measurements when mixing of the different modes is present. To describe such a problem, a simple mathematical modelization is introduced and a numerical simulation using experimental waveforms is performed. A criterion for the separation of the different modes, the systematical error associated with their overlapping and an algorithm for unravelling them are described. Some experimental results illustrating the improvements when using a windowing procedure are also presented.

Ultrasonic immersion transducer is upgraded

Ultrasonic immersion transducer is upgraded

Ultrasonic Inspection Tank Features 7 Axis Computer Control

A new ultrasonic immersion tank, announced by Hocking NDT Ltd, of St. Albans, Herts., features 7 axis computer control in the precision inspection of aero engine turbine discs and other critical aerospace components.

DESIGN, CONSTRUCTION AND TRIALS OF A PRECISION DOUBLE-PROBE ULTRASONIC CONIOMETER FOR HIGH FREQUENCY MEASUREMENTS.

Abstract A precision double-probe ultrasonic goniometer and two air-backed ultrasonic transducers were designed and constructed for use in the investigation of the surface and sub-surface structures of engineering materials, using the ultrasonic water immersion technique. The instrument has specifications which are a considerable improvement over those described elsewhere. Measurements with high frequency Lamb waves in thin films are described.

Design, manufacture and performance of narrowband ultrasonic immersion probes for multiple frequency operation in the range 3–170 MHz

This paper describes the design, construction and performance of a set of immersion probes which provided useful frequency coverage in the range 3–170 MHz by simple methods, that is harmonic excitation of commercially available lead zirconate titanate and quartz piezoelectric elements. A comparison of the two transducer materials and a comprehensive study of their output power as a function of frequency are presented.