摘要:

We demonstrate a new artificial fracture source for quantitative acoustic emission (AE) characterization. The source utilizes the break-down of silicone oil (or other liquids) placed inside a crack (or a slit). This is a dipole source with a rise time under 0.1 &mgr;s. It is much faster than a pencil-lead-break source and allows the calibration of a sensor-structure system to 7–10 MHz. We irradiated a focused Q-switched Nd-YAG laser beam (15 to 90 mJ energy) on silicon placed in a slit on a cylindrical block. The out-of-plane displacement produced by the resultant bulk waves was monitored on the outside surface using a heterodyne-type laser interferometer. This break-down source was employed to determine the transfer functions of an AE transducer and propagation medium. Finally, we studied AE signals due to the delayed fracture of a butt-welded dual-phase stainless steel, using the break-down source for calibration. Brittle-fracture events were successfully characterized. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301975

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In order to study the progression of internal damages in a cross-ply CFRP plate impacted repeatedly by a flying steel ball, we detected Lamb-wave acoustic emission (AE) using a small sensor. Lamb-wave AE revealed internal damages at ball velocities higher than 15 m/s, leading to delamination and transverse cracks at ball velocities of 41 m/s. Damage-induced changes of plate vibration were clearly seen with the AE/wavelet analysis. We also deduced the impact force, which increased linearly with velocity, but the impact duration remained constant under 19 m/s. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301976

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The algorithm of a three dimensional AE (acoustic emission) source location for anisotropic materials was developed to investigate the crack propagation of orthotropic GFRP (glass fiber reinforced plastic) thick plate which has variable wave velocities along different directions. Wave velocities used for AE source location were calculated from the elastic modulus of materials by the basic elastic relation. The algorithm was applied in the tensile loading test with CT (compact tension) specimen to monitor the crack propagation in GFRP. The results of source location clearly demonstrated the forming of fracture process zone in the material, that is, the three dimensional shape and size of process zone could be estimated. The process zone was dilated with increasing load while the load-COD (crack opening displacement) curve is linear. The propagation of the main crack was also observed at the beginning of the nonlinear part of load-COD curve. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301977

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Fracture behavior of Al/sapphire bulk joint fabricated by SAB (surface activated room temperature bonding) was investigated by AE (acoustic emission) method. Direct bonding at atomic level without formation of reaction products restricted the sources of AE generation into interfacial debonding and aluminum fracture itself. In order to reveal the effects of bonding conditions on fracture behavior by non-destructive method, specimens having different bonded area fraction were prepared. The sequential process of interfacial defect growth and propagation of main crack was elucidated by AE source characterization and real time observation of interface through transparent sapphire. Classification of AE signals was carried out by means of source characterization, which well agreed to observed results. While the coalescence of unbonded dominated in Al 2nine (99.5&percent;)-bonded at 40 MPa, both coalescence of unbonded and ligament Al fracture resulted in crack propagation in Al 5nine (99.999&percent;)-bonded at 20MPa. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301978

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The laser interferometer enables us to detect accurate, quantitative and noncontact measurement of local velocity. By using laser interferometer in the acoustic emission (AE) measurement, the limitations of conventional PZT transducer are expected to be overcome. The purpose of this work is to measure AE during the thermal cycle test by laser interferometer and to evaluate fracture behavior in plasma-sprayed ceramics coatings onto steel substrate. The results showed that it is possible to use laser facility as acoustic emission measurement method. Moreover, by analyzing detected waves due to the AE source analysis, the fracture behavior of coatings during thermal cycle tests was quantitatively evaluated. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301979

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In cold heading manufacturing processes, complete or partial fracture of the punch-pin leads to production of out-of-tolerance parts. A process monitoring system has been developed to assure that out-of-tolerance parts do not contaminate the batch of acceptable parts. A four-channel data acquisition system was assembled to collect and store the acoustic signal generated during the manufacturing process. A genetic algorithm was designed to select the smallest subset of waveform features necessary to develop a robust artificial neural network that could differentiate among the various cold head machine conditions, including complete or partial failure of the punch pin. The developed monitoring system is able to terminate production within seconds of punch pin failure using only four waveform features. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301980

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Acoustic Emission techniques have been used in a variety of applications in industrial plant, and the special techniques developed by Metacoustics can provide real time defect location; identify processes and procedures damaging pressurised equipment; provide a structural integrity evaluation, and after a number of tests and analysis operations provide an estimate of remnant life of the structure monitored. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301981

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The behavior of short fatigue cracks of about 100 &mgr;m in length has been monitored by using acoustic emission (AE). By introducing wavelet de-noising technique, AE signals due to short fatigue cracks appeared to be separable from those due to various sources of background noise. With its extremely high sensitivity and the real-time capability, AE can be a unique means to detect the onset of fatigue damage, which is known to be otherwise impossible or extremely difficult to be accomplished. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301982

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Detection and evaluation of glass properties, such as the degree of anisotropy, is an important issue in glass making industry. In addition, a nondestructive means by which glass tensile strength may be correlated to some measurable parameter is also desirable. Microwave nondestructive material characterization techniques have shown great potential for evaluating glass properties. In this study these techniques have been utilized at S- and X-band to determine the potential of evaluating anisotropy and obtain some useful correlation to tensile strength in glass fibers. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301983

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Microwave assisted Non-Destructive Evaluation (NDE) technologies have been utilised in industry for materials characterization and quality assessment. This paper discusses the potential of using broadband variable frequency microwaves(2.5−18&hthinsp;GHZ)for diagnosing materials integrity, especially during processing in resonant cavities. The technique is compared to conventional microwave based NDE. Details regarding system configuration with on-line process control and volumetric quality control capabilities are included for microwave curable epoxy test pieces. The principles of microwave interactions with these materials are explained and experimental findings presented. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301984

出版商:AIP    

年代:1999

数据来源: AIP