Increase Of Acoustic Nonlinearity Research Articles

Strategies for reliable second harmonic of nonlinear acoustic wave through cement-based materials

The strategies for retrieving reliable nonlinear second harmonic in cement-based materials are proposed in this paper using high-performance test system, piezoelectric transducers with central frequency in MHz, monochromatic tone-burst excitation and robust data process method.The Fundamental and second-order harmonics are measured to retrieve reliable acoustic nonlinearity with the input power level increased from ∼50 V to ∼280 V. About 173 times repeatable measurements are conducted to verify the stability of the experimental system. Specimens with three distinct aggregate sizes are used to measure the acoustic nonlinearity under uniaxial load. The results show a decrease in the measured acoustic nonlinearity at early damage stage, then a slight increase when large cracks coalesce. The rapid increase in acoustic nonlinearity at the final stage indicates the imminent failure. Our results also suggest that the nonlinear ultrasonic method is more sensitive than P-wave velocity for damage evaluation.

Creep damage characterization of Ni-based superalloy by acoustic nonlinearity

The creep damage of Ni-based superalloy has been experimentally investigated by acoustic nonlinearity measured by the finite amplitude method. The creep test is conducted and interrupted after a specified fraction of creep life time. The cuboidal γ′ precipitates coarsen preferentially in the direction perpendicular to the applied stress axis. The aspect ratio (a/b) of the γ′ precipitate increases monotonously with creep duration. The increase in acoustic nonlinearity is discussed in relation to the directional coarsening of the γ′ precipitates, which proves to be closely related to the scattering and distortion of the ultrasonic waves. We have determined that acoustic nonlinearity is a potential diagnostic method for determining creep damage in Ni-based superalloys.

Investigation of the second ultrasonic harmonic generation in Sn2P2S6and Sn2P2Se6crystals

Abstract The results of the second longitudinal ultrasonic harmonic measurements in ferroelectric semiconductive Sn2P2S6 and Sn2P2Se6 crytals in the vicinity of phase transitions are presented for X crystallographic direction. It is shown, that there are unusual anomalies of the second harmonic amplitude at the phase transition region. Such harmonic behaviour is determined by the increase of acoustic nonlinearity and also by the ultrasonic attenuation maximum at the phase transition temperature. The temperature dependences of the nonlinear elastic coefficients for Sn2P2S6 and Sn2P2Se6 crystals have been calculated using ultrasonic data. The elastic nonlinearity is markedly higher in the temperature interval where an incommensurate phase exists