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Investigation of the brittle fracture of ceramic materials using microcomputer processing of acoustic emission signals
Ultrasonics International 87 abstracts Assessment of heat-cracking tower and piping by use of AE technique
B.Q. Zhang, Daqing Petroleum College, Province Heilongjiang, PR China AE on-line monitoring was carried out for the feed-nozzle of the heat-cracking tower (465°C) and butt-weld seams (335°C) between the piping and flanges for a pipe-line in the high-pressure reform process of an ammonia plant by use of a two-channel waveform recorder and a AE analyser (PAC3000/3004, USA). To avoid degradation of PZT sensors from high-temperature, two sensors were separately coplanted on the cold top surfaces of two wave-guides (D.12 mm, L.1400 mm) through which the feed-nozzle and the butt-weld-seam was monitored under operation conditions to evaluate whether cracking of material or fluid-leak of the feed-nozzle was going on or not. Inspection and X-ray examination after stopdown proved that the result of AE on-line monitoring for the feed-nozzle and butt-weld seam was effective.
Investigation of the brittle fracture of ceramic materials using microcomputer processing of acoustic emission signals
J. RanachowskL F. Rejmund, W. Mikiel and Z. RanachowskL Institute of Fundamental Technological Research, Warsaw, Poland The method of investigation of the subcritical crack growth in brittle ceramic materials with AE signals is reported. To obtain a relationship between the velocity of crack growth and the stress intensity factor SIF, double torsion samples were examined at constant strain rate. The AE registration was used to observe the initiation of the crack growth and to obtain the SIF dependence of AE signals density. The automatic method of processing the values of loading and number of AE signals is reported. The results of such measurements are presented for specimens cut off from ceramic long-rod insulators produced by different European factories.
Broad-band ultrasonic transducers based on fractured piezoelectric ceramics
F.R. Montero de Espinosa, J.L. San Emeterio, P. Y. Sanz and A. Ramos, Instituto de AcDstica, Madrid, Spain Some papers have been recently presented dealing with various techniques to make a new type of connectivity piezoelectric composite. These techniques consist of fracturing through the poling direction a commercial piezoelectric ceramic and pouring an epoxy resin into the fractures. Depending on the fracturing technique employed, the epoxy volume fraction can be less than 10%. The epoxy then acts only as a glue to ensure the mechanical integrity of the fractured ceramic. The ceramic-epoxy system behaves as a piezoelectric ceramic, with material properties very similar to those of the initial piezoceramic but with additional mechanical losses introduced in the fracturing process, rather than as a typical composite. These mechanical losses can be controlled and depend on the fracture density. This poster deals with a correlation between theoretical and experimental behaviour in time and frequency domains of some samples of fractured ceramics at thickness resonance when varying the fracture density. The agreement between theory and experiment confirms that the fractured ceramic behaves as
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Ultrasonics 1987 Vol 25 November
a compact ceramic with added internal mechanical losses. These results can facilitate the design of broad-band ultrasonic transducers because it is possible to eliminate the backing material using a fractured ceramic. The volume and total mass of the transducer can be drastically reduced allowing the construction of very small broad-band transducers. Moreover, the fracturing techniques used in that case allow us to make fractured ceramics very easily. Conical, convex and more complicated surface geometries have been made and tested showing corresponding acoustic behaviour. Finally, some transducers, made using the fracturing techniques, with different types of focalization, especially adapted for NDT proposes, are presented.
Focussed high-power ultrasonic transducer with stepped-plate radiator for industrial application in gases
G. Rodriguez-Corral, J.L. San Emeterio and J.A. GallegoJuarez, Instituto de Acu'stica, Madrid, Spain Flexural axisymmetric vibrating plates with an extensive surface area and a stepped profile in one of their faces have proved to be very useful high-directional ultrasonic radiators. We have already presented a commercial version for highpower applications in gases of a highly-directional and highly-efficient stepped-plate transducer. This transducer, with a maximum power capability of about 200 W, has been successfully applied in industrial defoaming. The radiating element of this transducer was a titanium plate of about 34 cm diameter, stepped in one face and slightly grooved in the other. The special profile of this plate provides, together with a uniform distribution of maximum displacements (due to the added mass of the steps), the dual possibility of using the transducer as a piston-like generator or as a focussed transducer. From the stepped face this transducer generates a very directional pattern while from the grooved face it produces an appreciable focussing effect. This focussing effect, which is very useful in many applications where energy concentration is needed, can be notably improved with some changes in the design of the radiating plate. In fact, the profile of the non-stepped face can be modified by shifting the internodal zones so that the radiation arrives in phase at a selected point on the axis (focus). A number of extensive plate radiators with different focussing profiles vibrating with five and seven nodal circles and diameters up to 500 mm have been designed, constructed and tested. As a result we have arrived at a relatively simple and effective profile for this new kind of radiator. We present the characteristics and performance of a focussed high,power transducer constructed with this new radiator. The transducer, designed for a resonant frequency of about 21 kHz, incorporates a radiating plate of 480 mm diameter made of a specially fabricated titanium alloy with high fatigue strength. It is capable of handling a maximum applied power of about 400 W. The development of this new ultrasonic transducer represents a remarkable advance in the generation of highintensity ultrasonic radiation in gases and interphases (gassolid, gas-liquid).
New techniques in the characterization of ultrasound beams
M.J. Alty, Frazer-Nash (Electronics) Ltd, Leatherhead, UK In 1981, the National Physical Laboratory initiated a project to develop test gear which could be used in the field to analyse the beam characteristics of medical ultrasound equipment.
B.Q. Zhang, Daqing Petroleum College, Province Heilongjiang, PR China AE on-line monitoring was carried out for the feed-nozzle of the heat-cracking tower (465°C) and butt-weld seams (335°C) between the piping and flanges for a pipe-line in the high-pressure reform process of an ammonia plant by use of a two-channel waveform recorder and a AE analyser (PAC3000/3004, USA). To avoid degradation of PZT sensors from high-temperature, two sensors were separately coplanted on the cold top surfaces of two wave-guides (D.12 mm, L.1400 mm) through which the feed-nozzle and the butt-weld-seam was monitored under operation conditions to evaluate whether cracking of material or fluid-leak of the feed-nozzle was going on or not. Inspection and X-ray examination after stopdown proved that the result of AE on-line monitoring for the feed-nozzle and butt-weld seam was effective.
Investigation of the brittle fracture of ceramic materials using microcomputer processing of acoustic emission signals
J. RanachowskL F. Rejmund, W. Mikiel and Z. RanachowskL Institute of Fundamental Technological Research, Warsaw, Poland The method of investigation of the subcritical crack growth in brittle ceramic materials with AE signals is reported. To obtain a relationship between the velocity of crack growth and the stress intensity factor SIF, double torsion samples were examined at constant strain rate. The AE registration was used to observe the initiation of the crack growth and to obtain the SIF dependence of AE signals density. The automatic method of processing the values of loading and number of AE signals is reported. The results of such measurements are presented for specimens cut off from ceramic long-rod insulators produced by different European factories.
Broad-band ultrasonic transducers based on fractured piezoelectric ceramics
F.R. Montero de Espinosa, J.L. San Emeterio, P. Y. Sanz and A. Ramos, Instituto de AcDstica, Madrid, Spain Some papers have been recently presented dealing with various techniques to make a new type of connectivity piezoelectric composite. These techniques consist of fracturing through the poling direction a commercial piezoelectric ceramic and pouring an epoxy resin into the fractures. Depending on the fracturing technique employed, the epoxy volume fraction can be less than 10%. The epoxy then acts only as a glue to ensure the mechanical integrity of the fractured ceramic. The ceramic-epoxy system behaves as a piezoelectric ceramic, with material properties very similar to those of the initial piezoceramic but with additional mechanical losses introduced in the fracturing process, rather than as a typical composite. These mechanical losses can be controlled and depend on the fracture density. This poster deals with a correlation between theoretical and experimental behaviour in time and frequency domains of some samples of fractured ceramics at thickness resonance when varying the fracture density. The agreement between theory and experiment confirms that the fractured ceramic behaves as
374
Ultrasonics 1987 Vol 25 November
a compact ceramic with added internal mechanical losses. These results can facilitate the design of broad-band ultrasonic transducers because it is possible to eliminate the backing material using a fractured ceramic. The volume and total mass of the transducer can be drastically reduced allowing the construction of very small broad-band transducers. Moreover, the fracturing techniques used in that case allow us to make fractured ceramics very easily. Conical, convex and more complicated surface geometries have been made and tested showing corresponding acoustic behaviour. Finally, some transducers, made using the fracturing techniques, with different types of focalization, especially adapted for NDT proposes, are presented.
Focussed high-power ultrasonic transducer with stepped-plate radiator for industrial application in gases
G. Rodriguez-Corral, J.L. San Emeterio and J.A. GallegoJuarez, Instituto de Acu'stica, Madrid, Spain Flexural axisymmetric vibrating plates with an extensive surface area and a stepped profile in one of their faces have proved to be very useful high-directional ultrasonic radiators. We have already presented a commercial version for highpower applications in gases of a highly-directional and highly-efficient stepped-plate transducer. This transducer, with a maximum power capability of about 200 W, has been successfully applied in industrial defoaming. The radiating element of this transducer was a titanium plate of about 34 cm diameter, stepped in one face and slightly grooved in the other. The special profile of this plate provides, together with a uniform distribution of maximum displacements (due to the added mass of the steps), the dual possibility of using the transducer as a piston-like generator or as a focussed transducer. From the stepped face this transducer generates a very directional pattern while from the grooved face it produces an appreciable focussing effect. This focussing effect, which is very useful in many applications where energy concentration is needed, can be notably improved with some changes in the design of the radiating plate. In fact, the profile of the non-stepped face can be modified by shifting the internodal zones so that the radiation arrives in phase at a selected point on the axis (focus). A number of extensive plate radiators with different focussing profiles vibrating with five and seven nodal circles and diameters up to 500 mm have been designed, constructed and tested. As a result we have arrived at a relatively simple and effective profile for this new kind of radiator. We present the characteristics and performance of a focussed high,power transducer constructed with this new radiator. The transducer, designed for a resonant frequency of about 21 kHz, incorporates a radiating plate of 480 mm diameter made of a specially fabricated titanium alloy with high fatigue strength. It is capable of handling a maximum applied power of about 400 W. The development of this new ultrasonic transducer represents a remarkable advance in the generation of highintensity ultrasonic radiation in gases and interphases (gassolid, gas-liquid).
New techniques in the characterization of ultrasound beams
M.J. Alty, Frazer-Nash (Electronics) Ltd, Leatherhead, UK In 1981, the National Physical Laboratory initiated a project to develop test gear which could be used in the field to analyse the beam characteristics of medical ultrasound equipment.