sensor of acoustic emissions produced by each small section specimens under tensile stress

摘要

1414537 Piezoelectric transducers COMMISSARIAT A L'ENERGIE ATOMIQUE 11 June 1973 [15 June 1972] 27711/73 Heading H4J Apparatus for picking up acoustic signals emitted by metal rods, wires or fibres 15 under tension comprises a piezoelectric ceramic cylinder 6 having internal and external metal coatings 7, 8. Two end plates 10 secure a cyclindrical metal casing 9 around the cylinder 6 without touching it. Rubber rings 14 are preferably also provided to maintain a constant air-filled space 12 between cylinder 6 and casing 9. A cover 13 of sound permeable material seals the air-filled space 12. A rod 2 is secured to the casing 9 and terminates in a co-axial connection 5 (Fig. 3). Rod 2 contains two conductors 3, 4 connecting between the metal coatings 7, 8 and the coaxial connection 5. In use, the apparatus is in a liquid-filled tank 16 and the rods, wires or fibres 15 are coaxially arranged in the cylinder 6. Rod 2 is mounted on the tank 16 by an acoustically insulating ring 19 and a device 26 allows for adjustment to provide the coaxial arrangement. The rods, wires or fibres 15 are held between a stationary head 20 and a head 21 secured to a device 18 for exerting tensile stress. The base 22 of tank 16 is connected to head 21 by a bellows 23. Device 18 is preferably of the kind in which water flows into a vessel 25. The coating 13 is resistant to corrosion by the liquid 17. Cylinder 6, preferably of barium lithium titanate has a radial resonance of 185 kHz and the device, uses the response in the region of this resonance frequency.