Showing papers on "Acoustic emission published in 1970"

Acoustic emission crack monitor

Abstract: A system for monitoring crack growth in a structure in which acoustic energy released as a result of a crack event is sensed and integrated to provide a binary signal representative of the number and intensity of individual crack events. The binary crack energy data signals are accumulated and a warning device is activated when the stored crack data exceeds a predetermined level. Means may be provided to discriminate crack event signals from similar acoustic signals resulting from noise and impact or vibration.

Probing of elastic surface waves in piezoelectric media

Abstract: Data are presented which indicate that detection of the rf electrical potential associated with an acoustic surface wave in a piezoelectric medium by a simple point probe can yield extensive information about the propagation characteristics of such waves. Such a probe, in mechanical contact with the propagating surface of a 107‐MHz LiNbO3 delay line, has been used to measure the diffraction pattern of the acoustic energy, spreading of the acoustic beam, insertion loss due to misalignment of the transducer axis with the crystal symmetry axis, and the amplitude and phase variations of the acoustic wave near the output transducer.

The application of acoustic emission to in-process inspection of welds

Abstract: EXPERIMENTAL RESULTS SHOW THAT CRACKS AND POROSITY IN THE WELDS DISCUSSED IN THIS PAPER EMIT ACOUSTIC SIGNALS DURING AND AFTER JOINT FUSION; THAT SOME WELD DEFECTS NOT DETECTED BY RADIOGRAPHY WERE DETECTED BY SPECIALLY DESIGNED TRANSDUCERS SENSITIVE TO THE ACOUSTIC SIGNALS EMITTED BY THE WELD DEFECTS, THE VERIFICATION BEING BY METALLOGRAPHIC SECTIONING; THAT THE ACOUSTIC EMISSION RATE FROM WELD DEFECTS IS A FUNCTION OF THE WELD DEFECT TEMPERATURE; THAT THERE IS A RELATIONSHIP BETWEEN THE ACOUSTIC EMISSION COUNT AND THE NUGGET DIAMETER OF RESISTANCE WELDS, AND THAT THE WELD BEAD CONFORMATION ON SUBMERGED ARC WELDS IS RELATED TO THE CHANGES IN THE ACOUSTIC-EMISSION RATE RECORDED DURING WELDING. /AUTHOR/

Means for generating (a source of) surface and bulk elastic wares

Abstract: A source of high frequency elastic waves are generated by placing a Gunn effect oscillator in close proximity to a piezoelectric or an electrostrictive solid. The device creates a moving source of sound near the surface of the solid. The sound will be radiated from the surface of the solid as bulk or surface elastic waves. Elastic waves can be generated from both surfaces in certain situations.

Mechanism Of Sand LiquefactionAs Studied By Acoustic Emission

Abstract: The mechanism of sand liquefaction was studied by performing a series of undrained triaxiai test with measurement of Acoustic Emission (AE). The AE measurement is a technique to monitor minute sounds which are generated by slippages of sand particles during loading. By detecting the initiation of AE as sand being loaded, the yielding stress of sand can be determined since the AE should indicate the irrecoverable movements of sand particles. Isotropically consolidated sand was subjected to a cycle of undrained triaxiai loading first, and then the yield locus of sand after such loading was determined by performing various stress probing tests with AE measurement under drained loading condition. The shape of yield locus of the isotropically consolidated sand before undrained loading was found to be elliptic on the p (i.e., mean principal stress) q (i.e., deviator stress) stress plane with its axis of symmetry coincides with the p axis. However, the shape of yield locus has been drastically altered after sand being subjected to undrained shear. The yield locus is translated to the direction of undrained shear indicating the kinematic hardening property of sand, but more importantly the size of yield locus has been reduced towards the origin of p

Plastic stress and acoustic emission as predictors of fatigue life

Abstract: The high rate of acoustic emission from AISI E4340 annealed steel when it is stressed can be used to accurately indicate the yield stress. Predictive equations for the fatigue life of AISI E4340 annealed steel have been developed by the use of “Multiple Classification Analysis” and “Stepwise Regression” computer programs based on an experimental study of 175 specimens. The acoustic emission from the fatigue specimens was investigated prior to fatiguing, but no parameter of the emission was found to correlate significantly with fatigue life. The high-rate emission which occurs at yield is found to be useful in determining the value of the yield stress. The value of the stress into the plastic range determined in this manner was defined by both statistical approaches as the best predictor of fatigue life. The fatigue stress level was rejected as a lesser predictor. Surface finish in the range of 90 to 350 μin. was found to have little correlation with fatigue life of this material.

Acoustic emission as a technique for nondestructive testing

Abstract: A PROMISING METHOD FOR NONDESTRUCTIVE TESTING AND INSPECTION IS TO OBSERVE THE ACOUSTIC EMISSION FROM MATERIALS WHEN THEY ARE STRESSED. OBSERVATIONS CAN BE MADE ON TENSILE SPECIMENS OR ON MANUFACTURED PARTS. EXCEPT FOR THE NOISE PRODUCED BY CRACK NUCLEATION OR PROPAGATION, THE EXACT MECHANISMS WHICH CAUSE ACOUSTIC EMISSION ARE NOT CLEAR AT THE PRESENT TIME. THE AMOUNT OF NOISE HAS BEEN SHOWN TO BE DEPENDENT UPON MICROSTRUCTURE AND THE LEVEL OF THE APPLIED STRESS. THE TECHNIQUE APPEARS TO OFFER CONSIDERABLE PROMISE FOR THE "IN-SERVICE" MONITORING OF CRITICAL STRUCTURES. /AUTHOR/