Мониторинг разрушения волокон композитных материалов с применением системы акустической эмиссии, виброанализатора и высокоскоростной видеосъемки

The initial cause of the acoustic emission (AE) in the process of deformation and destruction of solids is considered. A theoretical analysis of the processes of transformation and energy dissipation during the destruction of structural bonds of an idealized solid model is carried out. The research of wave process arising in the deformation and rupture of fiber reinforced composites is conducted using AE system A-line32D and PCI-2, vibration analyzer Onix, high speed camera Videosprint and numerical simulation in the software LS-DYNA. The obtained experimental and calculated data showed that the main energy in the time interval after the fiber rupture is released in the range of audio frequencies less than 2 kHz. The peak values energy recorded in the ultrasonic frequency range does not exceed a few percent relative to the maximum level at the carrier frequency in the audio range.

Correction of the Doppler distortion generated by a vibrating baffled piston

The Doppler effect is a phenomenon inherent to source motion, which introduces a variable propagation time between the source and a listening point. In the case of a vibrating piston, this is responsible for distortion of the radiated sound pressure. This moving-boundary phenomenon is part of the nonlinear effects involved in loudspeaker radiation. The present paper investigates the significance of this distortion, usually considered as neglectible, and addresses its correction. First, the direct problem is solved by: (a) converting the (Lagrangian) position of the moving source into its equivalent (Eulerian) velocity field at a fixed position; (b) deriving the acoustic pressure radiated from this velocity field. A series solution of (a) is derived and time-domain simulations of (b) are built from the truncated series combined with a baffled piston radiation model. Simulations show that Doppler distortion can be significant for realistic loudspeaker diaphragm motion with a wide spectral content. Second, the inverse (anti-Doppler) problem is examined, that is, the derivation of a piston displacement that generates a targeted Eulerian velocity field. The corrected piston velocity solution proves to be an uncentered signal, leading to a diverging displacement. In order to remove this practical problem, a centered approximation is preferred, based on modified inverse Volterra kernels. The anti-Doppler algorithm is reliable in the audio range.

3. Sound waves

Sound is a small fraction of the pressure wave spectrum. In terms of wavelength, we can hear far more than we can see: while deep red light has waves about twice as long as those of deep violet, the lowest-pitched sound waves we can hear are about ten times longer than the highest. ‘Sound waves’ explains infrasound, the lower frequencies detectable by touch rather than hearing, and the audio range, describing the fundamental differences between sound power and loudness, and frequency and pitch. It also considers sound underwater. Sonar systems can be passive systems that simply detect sounds, while active sonar transmits sounds and detects those that are reflected.

Wear Monitoring of Connecting Rod Bearing via Air-Borne Method Analyzed by Using I-KazTM Multi Level Value

Different techniques have been developed in the area of bearing wear monitoring. This paper proposes a different experimental study on bearing wear monitoring by using an airborne technique. The data captured in the airborne technique will be analyzed by using I-kazTM Multi Level (7Z) coefficient and then will be correlated with the conventional specific wear rates, K. The wear tests were carried out by using a pin-on-disc configuration at a sliding speed of 7.85 m/s. A set of sliding distance ranging from 20 160 km at a fixed load of 200 N was utilized and the K value was measured at every interval of 20 km for the speed. SAE40 type lubricant was used in the test to simulate the actual operation of the connecting rod bearing. The audio range frequency below 20 kHz in the airborne technique was obtained through a microphone 40SC type which was placed 10 mm from the pin-disc contact. The analysis result showed that the wear rate, K increased from 1.82 to 6.70x10-8 mm3/Nm as the sliding distance increased, indicating that a mild-abrasion wear regime had occurred. The curve fitting of K as a function of I-kazTM Multi Level coefficient showed a similarity to an established of Taylor Tool Life curve. Thus, it was possible to correlate the Taylor curve and worn bearing, mainly in monitoring and identifying the bearing condition with respect to the sliding distance. The trend of I-kazTM Multi Level coefficient was found to be consistent with the increase of sliding distance which indicates that the I-kazTM Multi Level value can positively be used as wear response indicator for bearing.