Showing papers on "Acoustic emission published in 1971"

Relationship between Acoustic Emission and Dislocation Kinetics in Crystalline Solids

Abstract: The sounds emitted from single crystals of irradiated LiF, annealed LiF, NaCl, and zinc during constant‐strain‐rate compressive deformation were recorded and analyzed. The acoustic emission consisted of discrete pulses of varying amplitudes, and the rate of pulsing changed with total strain during the continuous deformation experiments. A reasonable correlation between acoustic‐emission pulse rate and the rate of change of mobile dislocation density was found and led to the conclusion that the pulses were generated by dislocation breakaway from pinning points. The measured dislocation densities were used to estimate that several thousand centimeters of dislocation line length had been involved in the generation of an individual acoustic pulse. It was suggested that some 105−106 segments of dislocation line were involved in a cumulative fashion due to the stimulating effect of the moving acoustic wave on bowed dislocation segments. The concept of stimulated dislocation breakaway from pinning points appeare...

Factors Affecting Acoustic Emission Response From Materials

Abstract: THE MANY FACTORS THAT CAN INFLUENCE THE ACOUSTIC EMISSION RESPONSE FROM MATERIALS ARE DISCUSSED. A BETTER UNDERSTANDING IS GIVEN OF THE NEED FOR CHARACTERIZATION OF THE ACOUSTIC EMISSION RESPONSE OF MATERIALS PRIOR TO APPLICATION OF THE TECHNIQUES FOR DETERMINATION OF STRUCTURAL INTEGRITY. /AUTHOR/

Acoustic Emission Studies of a Boron-Epoxy Composite

Abstract: Acoustic emission and stress wave emission are terms used to describe the release of stored acoustic energy from a material when it undergoes plastic deformation, phase transformation, or fracture. This energy is released in discrete pulses characteristic of the process. If a transducer is attached to a specimen of the material emission above the threshold of the transducer can be amplified and read as acoustic emission counts. The response of the count rate measuring device depends upon the amplifier gain setting, and the number and amplitude of the pulses monitored by the transducers. Using a totalizer, the count rate can be integrated to give the sum of counts. Count rate and sum of counts (2:AE) printouts produce a pattern of energy release characteristic of a given process. This note describes how acoustic emission has been correlated with the breaking of fibers during the fracture of a boron-epoxy composite. The boron-epoxy composite material containing 66 volume percent of aligned fiber

Acoustic emission monitoring system for detection of cracks in a complex structure

Abstract: AN ACOUSTIC EMISSION MONITORING SYSTEM DESIGNED TO DETECT, IN REAL TIME, INITIATION AND GROWTH OF CRACKS IN A COMPLEX STRUCTURE DURIING STATIC AS WELL AS FATIGUE TESTING HAS BEEN DEVELOPED. THE SYSTEM CONSISTS OF ARRAYS OF ACOUSTIC SENSORS, LOGIC CIRCUITS AND OUTPUT DEVICES. AN EFFECTIVE SPATIAL- AND FREQUENCY-FILTER COMBINATION PERMITS THE USE OF THE SYSTEM IN THE PRESENCE OF THE HEAVY BACKGROUND NOISE ORDINARILY ENCOUNTERED IN THE TESTING OF A LARGE, COMPLEX STRUCTURE. THE SYSTEM IS BEING USED SUCCESSFULLY IN STATIC AND FATIGUE TESTING OF FULL-SCALE AS WELL AS SMALL-SCALE SPECIMENS OF AIRCRAFT COMPONENTS AND STRUCTURES. /AUTHOR/

Detection of paster welds with acoustic emission

Abstract: Method and apparatus for the nondestructive detection of paster welds wherein the test piece is repeatedly flexed at the weld to be tested, and then any acoustic emission produced by such flexing, indicative of the presence of a paster weld, is detected. The invention provides for apparatus to convert the acoustic emission to electrical pulses which may then be integrated to provide a signal dependent upon the amplitude and rate of such acoustic emission.

Acoustic Emission Test Facility

Abstract: An acoustic emission test facility was designed and constructed to allow constant strain rate compressive deformation of samples up to an applied load of approximately 180 kg. Strain rates of from 1.6×10−3 to 3.2×10−6 sec−1 were obtained with total system noise limited to less than 10 μV peak‐to‐peak referred to the input of the pre‐amplifier. Over‐all signal amplification was 9900±100 over a bandwidth of 200 Hz–200 kHz.

Assessment of structural integrity by acoustic emission

Abstract: THE APPLICATION PHILOSOPY AND METHODS OF THE ACOUSTIC EMISSION TECHNIQUE ARE DISCUSSED. CASES IN WHICH THE TECHNIQUE IS APPLIED TO MEASURE STRUCTURAL INTEGRITY OUTSIDE THE LABORATORY ALSO ARE PRESENTED. THESE RANGE FROM THE MONITORING OF WELDS FOR CRACK FORMATION TO THE SURVEILLANCE OF BUILDINGS AND EARTH STRUCTURES FOR STRUCTURAL DETERIORATION./ AUTHOR/

Acoustic emission simulation test set

Abstract: IN ORDER TO DESIGN AND CONDUCT AN EFFECTIVE ACOUSTIC EMISSION EXPERIMENT, THE TEST DESIGNER SHOULD HAVE A MEANS OF DETERMINING (1) THAT ALL TRANSDUCERS OR SYSTEM CHANNELS OR BOTH ARE FUNCTIONING PROPERLY, (2) THAT THE OPTIMUM TRANSDUCER FOR THE TEST IS BEING USED, (3) THE DIRECTIVITY OF THE TRANSDUCERS, (4) THE RESPONSE OF THE TRANSDUCER TO A KNOWN INPUT WAVEFORM, (5) PULSE DISTORTION AS A FUNCTION OF DISTANCE TRAVELED THROUGH THE STRUCTURE, (6) THAT APPARENT ATTENUATION IS WITHIN ACCEPTABLE LIMITS, (7) THE GROUP VELOCITY OF SOUND WAVES IN THE TEST STRUCTURE, (8) THAT TRIANGULATION CALCULATIONS ARE CORRECT, AND (9) THAT SYSTEM PERFORMANCE IS MAINTAINED THROUGHOUT LONG DURATION TESTS. SO FAR, THERE HAS BEEN NO EFFECTIVE, UNIVERSALLY ACCEPTED MEANS FOR MAKING THESE DETERMINATIONS OR FOR CHECKING OUT THE ACOUSTIC EMISSION MONITORING SYSTEM ON THE TEST STRUCTURE. IN AN ATTEMPT TO FILL THIS NEED, THE ACOUSTIC EMISSION SIMULATION TEST SET HAS BEEN DEVISED. /AUTHOR/

Detection of a low-level critical stress in geologic materials using ultrasonic techniques

Abstract: Recent studies of inelastic behavior and acoustic emission in geologic materials further validate the concept that such materials may be considered to consist of an elastic media containing an array of pores and cracks. This concept is investigated further by experiments in which the mechanical behavior of a number of geologic materials were studied in detail at low stress levels using ultrasonic pulse methods. Experiments were conducted on cylindrical test specimens of Indiana Limestone, Tennessee Sandstone and Barre Granite under relatively low confining pressure (0 to 5000 psi). Analysis of data from these experiments indicated that there existed a low-level critical stress at which there appeared to be a transition in the mechanical behavior of the material. Under triaxial stress, results indicated that the differential critical stress was relatively independent of confining pressure, i.e., the mechanism responsible for the transition in mechanical behavior was governed by a maximum shear stress criteria. (24 refs.)

Magnetostriction transducers of acoustic emission, impulse, vibration, and noise analysis

Abstract: MAGNETOSTRICTIVE TRANSDUCERS OFFER AN ALTERNATIVE TO PIEZOELECTRIC TRANSDUCERS FOR USE IN ACOUSTIC EMISSION, VIBRATION, AND NOISE ANALYSIS. THEY ARE FINDING WIDER USE IN ULTRASONIC MEASUREMENT OF ELASTIC MODULI AND TEMPERATURE, AND AS COMPONENTS IN AN ACOUSTIC EMISSION SIMULATION TEST SET. MAGNETOSTRUCTIVE MATERIALS INCLUDE NICKEL AND NICKEL ALLOYS (E.G. PERMENDUR, REMENDUR, ELINVAR). SUCH MATERIALS MAY BE PREFERRED TO PIEZOELECTRIC IN CASES (1) WHERE HIGH TEMPERATURE OR NUCLEAR RADIATION OR BOTH ARE PRESENT, (2) WHERE REMOTE SENSING IS REQUIRED, (3) WHERE THE PART TO BE MONITORED IS ROTATING. MAGNETOSTRICTION TRANSDUCERS RESPOND TO FREQUENCIES UP TO APPROXIMATELY MHZ. BANDWIDTH IS CONTROLLED THROUGH CHOICE OF GEOMETRY. MECHANICALLY, MAGNETOSTRICTIVE METALS ARE MUCH MORE RUGGED THAN PIEZOELECTRIC CERAMICS. /AUTHOR/

Deslocation mechanisms as possible sources of acoustic emission

Abstract: THE GENERATION OF PACKETS OF SOUND WAVES IN SOLID BODIES IS DISCUSSED, AND SOME POSSIBLE SOURCES OF ACOUSTIC EMISSIONS IN CRYSTALLINE SOLIDS ARE ENUMERATED. SOURCES INVOLVING DISLOCATION MOTION ARE CONSIDERED TO BE GENERALLY IMPORTANT AND ARE DISCUSSED QUALITATIVELY. /AUTHOR/