The application of acoustic emission method for ultrasonic fatigue testing monitoring

The ultrasonic fatigue testing (USFT) is an effective method for rapid determination of the fatigue properties of structural materials under high cycle (≥106 cycles) loading. However, the occurrence and accumulation of fatigue damage with this test method remain uncertain due to the limitations of the existing measurement methods. Currently used monitoring methods allow detecting the fatigue cracks, but only in the late stages of failure. Despite the superior sensitivity to localized processes in materials, the use of the acoustic emission (AE) method in ultrasonic testing is extremely difficult due to the presence of resonant noise. This work aimed to suppress resonant noise and extract the signal for early detection of fatigue damage. The authors tested the samples of the AlSi9Cu3 aluminum alloy under the asymmetric cyclic loading (R=0.1) at a resonant frequency of 19.5 kHz with a non-threshold AE registration. The fracture surfaces were analyzed by electron and optical microscopy. The authors processed AE by two different methods: (1) the digital filtering method consisted of detecting resonant noise and removing it from the spectrum; (2) the φ-function method consisted of differentiating the spectrogram by time. The processed spectrograms were integrated by the frequency with further extraction of the AE events using the threshold method. The digital filtering method revealed a correlation between AE signals and fatigue damage, whereas the undamaged control sample showed no signals. The φ-function technique demonstrated ambiguous results, showing high AE activity on the control sample.

Modeling and Dynamic Analysis of an Electrical Helmholtz Resonator for Active Control of Resonant Noise

This paper describes a theoretical and experimental investigation into an electrical Helmholtz resonator (EHR): that is, an active noise control (ANC) loudspeaker used in conjunction with a microphone and a feedback controller for suppressing resonant noise in an acoustic cavity. The microphone is collocated with the loudspeaker and a band pass filter of second-order is used as the control filter inside the controller. The EHR is configured as such in order to suppress an acoustic mode that is within the volume velocity drive frequency range of the loudspeaker used. The concepts of impedance and passivity are used to develop the mathematical model as well as to study its dynamics. From these, it is theoretically shown that the EHR for single-mode suppression is an extremely low-impedance acoustic damping device that electrically realizes the pressure neutralization mechanism of a conventional Helmholtz resonator (HR). Experimental work is also presented, in which an EHR is constructed to suppress the Helmholtz mode of an acoustic cavity at about 40 Hz by more than 40 dB, to justify the mathematical model and also to verify the dynamic control mechanism.

Slabičné Rozhrania V Modeloch Trojčlenných Konsonantických Skupín V Slovenčine

The paper analyzes the criteria for the determination of the syllabic boundary in consonant clusters in the intersonantic position of three-syllable words (material base is standard Slovak), while the applicability and „weight” of individual criteria for the determination of syllable boundaries, as well as their „cooperative” and „contradicting” character, are manifested. The interpretative procedure is realized on the abstract level of phonic units, on which three groups of nonsonants (resonant, noise occlusives and noise fricatives) are determined. As a result, a limited number of model combinations of examined consonant (nonsonant) clusters has arisen. This kind of analysis proceeds from a closer interconnection between differentiated levels of individual and universal in phonic units according to J. Sabol’s synthetic phonological theory.

A Study on Timing Belt Noise (How to Reduce Resonant Noise)

Tow methods of suppress the resonant noise of timing belts are proposed. One method is to vary the belt tension periodically by the use of an eccentric pulley and the other method is to vary the mass density of the belt. It was experimentally confirmed that the resonant noise of timing belts is reduced by about 10 dB by the use of each method.