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Mapping Stresses on Surfaces by Pulsed Photoacoustic Detection

IP.com Disclosure Number: IPCOM000051178D
Original Publication Date: 1982-Aug-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Tam, AC: AUTHOR

Abstract

Stressed areas on an opaque surface can be mapped out by using a pulsed photoacoustic technique. The pulsed photoacoustic stress identification technique is shown in the figure.

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Mapping Stresses on Surfaces by Pulsed Photoacoustic Detection

Stressed areas on an opaque surface can be mapped out by using a pulsed photoacoustic technique. The pulsed photoacoustic stress identification technique is shown in the figure.

Localized stresses are introduced onto a rectangular stainless steel slab by introducing two separate conical indentations (about 0.08 cm deep) on the steel surface by using a center punch. Then, the surface is machined flat and polished to a mirror finish, so that the indentations totally vanish, but the stresses are still present, although invisible. Optical pulses from a flash-lamp pumped dye laser, of duration about 1 Musec and energy about 1 mJ, are slightly focused (spot size about 1/4 mm) onto the polished steel surface in the vicinity of a stressed area. The pulsed photoacoustic signals, detected by the piezoelectric transducer attached to the stainless steel, are displayed on an oscilloscope. The photoacoustic signal at a delay time of 42-46 Musec after the laser pulse is characteristically different when the laser pulse is incident at the previously indented position compared to the other cases when the laser pulse position deviates from the stressed position by 1/2 mm. However, the earlier photoacoustic signal (before a time delay of 40 Musec) is unaffected; the earlier longitudinal wave first arriving at the transducer at time equals 17 Musec and the earlier shear wave first arriving at the transducer at time equal...