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Ultrasonic techniques and ceramic integrity
_Tech A Ultrasonic techniques and ceramic integrity Progress is reported in developing ultrasonic nondestructive techniques to assess the integrity of ceramics and the quality of ceramic-ceramic and ceramic-metal bonds. The progress follows work at the Oak Ridge National Laboratory, TN, USA. A report describes techniques for characterizing ceramics and detecting flaws. It has been shown that it is possible to determine which face of a 60/am-thick layer of braze filler material is unbonded, thus" giving information on the integrity of ceramic-metal bonds. Also described is the development of a rapid technique using Lamb waves to probe the bond between alumina coupons in flexure-strength specimens. Since attenuation of ultrasonic waves through ceramic structural materials is critical in determining the minimum detectable flaw size, a technique was developed that permits a material transfer curve, or attenuation versus frequency response, to be determined for any ceramic. This process corrects for all known material-independent losses. The transfer curve is highly sensitive to changes in the ceramic microstructure. When testing joints between ceramic coupons, it is often impossible to introduce ultrasonic waves at normal incidence to the bond because of specimen geometry. Instead of angle-beam testing, with its limitations, an approach using Lamb waves was studied. Two transducers were used: the first launches a Lamb wave into one plate of the specimen
To order reports Unless otherwise indicated, reports are available from TechAlert, Microinfo Ltd, PO Box 3, Newman Lane, Alton, Hants GU34 2PG, UK. Cheques should be in Pounds Sterling and drawn on a UK bank. Non-UK customers should add £2. The report's reference number should always be quoted.
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and the second receives the wave in the other plate after propagation through the joint. The amplitude of the received wave indicates the condition of the bond in the region between the transducers. Dispersion curves for alumina coupons were calculated and a system was assembled for evaluating the bond by these waves. The system easily detected a
simulated bond fault; inspection of a second sample revealed an unbonded area that was not detected by angle-beam testing.
Further information: a 56-page report, reference 2290-NDT(M), price £ 10.00 + £1.50 VAT, is available from TechAlert. If a paper copy is required the price will be £27.90 + £ 1.65 postage and packing.
Ultrasonic characterization of composites Work has been performed at the Johns Hopkins University, MA, USA, on the characterization of the nonlinear elastic properties of unidirectional graphite/epoxy composites. The work, described in a report, concentrated on the behaviour of fibre-reinforced composites, where the deformation is recoverable but is nonlinearly related to the applied load. The theoretical treatment of linear and nonlinear elasticity in a unidirectional fibre-reinforced composite is developed, and measurements for a unidirectional graphite/epoxy composite are presented. Linear elastic properties were measured by both ultrasonic and strain gauge methods. The
nonlinear properties were determined as a function of stress and temperature by measuring changes in ultrasonic 'natural' phase velocity with a pulsed phase locked-loop interferometer. The measurements provide the basis for further investigations into the relationship between nonlinear elastic properties and other important properties of graphite/epoxy composites, such as strength and fibre-matrix interfacial strength.
Further information: a 198-page report, reference 2751-NDT ( M ), price £10.00 + £1.50 VAT, is available from TechAlert. If a paper copy is required the price will be £37.90 + £2.00 postage and packing.
X-ray imaging" status and trends Technological developments are bringing about a renaissance in Xray imaging. The methods and applications of X-ray imaging and the developments that are contributing to this renaissance are outlined in a report from the Lawrence Livermore National Laboratory, CA, USA. X-ray imaging by radiography is a highly developed technique in medicine and industry. Highresolution imaging has not generally been practicable, however, because sources have been relatively dim and diffuse, optical elements have been nonexistent for most applications and detectors
have been slow and of low resolution. Sources, optics and detectors, together with the related issue of signal processing, are seen as the four key areas for progress in X-ray imaging. The technology in these areas determines the sensitivity, resolution and practicality of X-ray imaging techniques. Recent progress in these areas forms the bulk of the report. Further information: a 19-page report, reference 2770-NDT(M), price £ 10.00 + £1.50 VAT, is available from TechAlert. A paper copy costs £23.90 + £1.15 postage and packing.
NDT International October 1988
To order reports Unless otherwise indicated, reports are available from TechAlert, Microinfo Ltd, PO Box 3, Newman Lane, Alton, Hants GU34 2PG, UK. Cheques should be in Pounds Sterling and drawn on a UK bank. Non-UK customers should add £2. The report's reference number should always be quoted.
358
and the second receives the wave in the other plate after propagation through the joint. The amplitude of the received wave indicates the condition of the bond in the region between the transducers. Dispersion curves for alumina coupons were calculated and a system was assembled for evaluating the bond by these waves. The system easily detected a
simulated bond fault; inspection of a second sample revealed an unbonded area that was not detected by angle-beam testing.
Further information: a 56-page report, reference 2290-NDT(M), price £ 10.00 + £1.50 VAT, is available from TechAlert. If a paper copy is required the price will be £27.90 + £ 1.65 postage and packing.
Ultrasonic characterization of composites Work has been performed at the Johns Hopkins University, MA, USA, on the characterization of the nonlinear elastic properties of unidirectional graphite/epoxy composites. The work, described in a report, concentrated on the behaviour of fibre-reinforced composites, where the deformation is recoverable but is nonlinearly related to the applied load. The theoretical treatment of linear and nonlinear elasticity in a unidirectional fibre-reinforced composite is developed, and measurements for a unidirectional graphite/epoxy composite are presented. Linear elastic properties were measured by both ultrasonic and strain gauge methods. The
nonlinear properties were determined as a function of stress and temperature by measuring changes in ultrasonic 'natural' phase velocity with a pulsed phase locked-loop interferometer. The measurements provide the basis for further investigations into the relationship between nonlinear elastic properties and other important properties of graphite/epoxy composites, such as strength and fibre-matrix interfacial strength.
Further information: a 198-page report, reference 2751-NDT ( M ), price £10.00 + £1.50 VAT, is available from TechAlert. If a paper copy is required the price will be £37.90 + £2.00 postage and packing.
X-ray imaging" status and trends Technological developments are bringing about a renaissance in Xray imaging. The methods and applications of X-ray imaging and the developments that are contributing to this renaissance are outlined in a report from the Lawrence Livermore National Laboratory, CA, USA. X-ray imaging by radiography is a highly developed technique in medicine and industry. Highresolution imaging has not generally been practicable, however, because sources have been relatively dim and diffuse, optical elements have been nonexistent for most applications and detectors
have been slow and of low resolution. Sources, optics and detectors, together with the related issue of signal processing, are seen as the four key areas for progress in X-ray imaging. The technology in these areas determines the sensitivity, resolution and practicality of X-ray imaging techniques. Recent progress in these areas forms the bulk of the report. Further information: a 19-page report, reference 2770-NDT(M), price £ 10.00 + £1.50 VAT, is available from TechAlert. A paper copy costs £23.90 + £1.15 postage and packing.
NDT International October 1988