Applied Mechanics and Materials Vols. 239-240

Abstract: ASTM C78 standard tests for flexural strength of concrete were conducted on cellulose fiber reinforced concrete (CFRC) specimens using varying percentages of ultimate load. During testing, Acoustic Emission (AE) signals were recorded while after testing, a scanning electron microscope (SEM) was used to visually observe surface features. SEM results appear to illustrate three important stages of the fracture process: cement cracking, fiber-cement debonding, and fiber breakage/pullout. AE results were used to bound ranges for a relationship between AE amplitude and CFRC fracture mechanisms.

Abstract: This paper presents a comparison of high-frequency hydrophone calibration by a heterodyne interferometer and two-transducer reciprocity method respectively. For the calibration using the heterodyne interferometer, a vertical arrangement is applied to avoid the acousto-optical interaction which is a major uncertainty source in previous studies. For the demodulation of the acoustic displacement, a PC-based digital demodulation using arctangent algorithm is applied which has overcome the drawback of analog demodulation and achieved a higher demodulation accuracy. The demodulation is independent of the intensity of the carrier signal and thus can avoid the correction for the frequency response of the photodiode which is another uncertainty source. Comparison results between these two methods showed a good agreement. Owing to the optical measurement is independent of the acoustic field generating by the transducer, it has wider usage compared to the reciprocity method and can be easily extended to higher frequency and higher acoustic power application.

Abstract: Based on the mobile rail flash butt welding machine UN5-150ZB, the synchronous data acquisition hardware system was designed to collect welding current, welding voltage and flash acoustic signal in welding process, and the software platform with the functions of signal collecting, waveform display and data operation was developed by higher-level programming language LabVIEW. After the welding current, welding voltage and flash acoustic signal in welding process had been collected, the mean, variance and mean square value of flash acoustic signal in time-domain were analyzed. Through comparison, the relationship between these characteristics and the stability of flash was analyzed. The result shows that the changes of mean and variance of flash acoustic signal are not obvious, and do not correlate with stability of flash, but the mean square value in time domain is closely associated with the stability of flash, and the stability of flash can be indicated by the mean square value.

Abstract: The present study was conducted on sensitized 304 stainless steels in 0.5mol/L Na₂S₂O₃ solution under the slow strain rate testing (SSRT). To monitor the evolution of intergranular stress corrosion cracking (IGSCC) occurring, acoustic emission (AE) technology was applied in this test. Besides, signal characteristics of different AE sources, including the dissolution along susceptible grain boundaries, the plastic deformation ahead of the crack tip and the mechanical fractures of material ligaments, were identified distinctly with fractography and clustering analysis.

Abstract: Based on the principle of photoacoustic,blood glucose can be non-invasive monitoring of in the NIR region.The system irradiates to the glucose solution by opo laser,then the signals are received by photoacoustic probe and processed by the oscilloscope, finally imported into the computer.By the least squares method,the data repeatedly fits to make the mean square error of the glucose concentration less than 5mg/dl.The experimental results show that:photoacoustic measurement method can achieve a certain precision, with the value of further research.

Abstract: A cavity acoustic modal of a medium-sized commercial vehicle was tested and analyzed based on LMS Test.Lab modal analysis system. Acoustic modal characteristics, including modal frequencies and modal shapes of the cavity, were obtained. By comparing the results of acoustic modal frequencies to the structure modal ones, the acoustic-structure coupling at critical frequencies could be avoided and the noise in low frequency range could be reduced. Meanwhile, the simulation of the acoustic modal is analyzed by establishing the finite element model of the cavity, which may be a reference to improve the interior acoustic properties of the cavity.

Abstract: A real-time and high precision ultrasonic ranging method is proposed here. Ultrasonic ranging system based on MCU was established, which is composed of MCU, ultrasonic sending and receiving circuit, temperature compensate circuit, alarm, key and display circuit. Counting pulse method was used to measure the ultrasonic transmission time, and then the distance is calculated. In order to improve the ranging accuracy, temperature compensation was used in this system. Preliminary experiment showed that the system meet the requirements. This system has advantages such as low price, small volume, reliable operation, high accuracy, and can be employed in car backing, obstacle avoiding of robots, industrial logging, reservoir level measuring etc.

Abstract: Aiming at the acoustic emission signals of oil storage tank bottom injured, hidden Markov algorithm is proposed to identify the tank bottom corrosion signal. Typical corrosion acoustic emission signal is divided into transient acoustic signal, continuous acoustic emission signal and mixed acoustic emission.Baum-Welch algorithm is used to train these typical corrosion acoustic emission signals model, then establish HMM model library. The forward-backward algorithm is used to compute each acoustic emission model’s output probability. The simulation experiments shows that the hidden Markov algorithm can correctly identified the acoustic emission signals.

Abstract: The Parametric Acoustic Receiving Array achieves the directional reception characteristics through an end-fire array of virtual sources by the use of only two transducers (pump and hydrophone). With a radial size much smaller than linear receiving array whose radial size is too wide to fit in laboratory measurement of low frequency transducers, and with the ability of totally suppressing the inversely traveling signals, parametric acoustic receiving array can be used to measure low frequency complex waveform signals with large pulse length and broad bandwidth in reverberant tank. This paper gives a detail analysis and setups for this application.