Determination of absolute material nonlinearity with air-coupled ultrasonic receivers

Abstract

Quantitative evaluation of the microstructural state of a specimen can be deduced from knowledge of the sample's absolute acoustic nonlinearity parameter, β, making the measurement of β a powerful tool in the NDE toolbox. However, the various methods used in the past to measure β each suffer from significant limitations. Piezoelectric contact transducers are sensitive to nonlinear signals, cheap, and simple to use, but they are hindered by the variability of the interfacial contact between transducer and specimen surface. Laser interferometry provides non-contact detection, but requires carefully prepared specimens or complicated optics to maximize sensitivity to the higher harmonic components of a received waveform. Additionally, laser interferometry is expensive and relatively difficult to use in the field. Air-coupled piezoelectric transducers offer the strengths of both of these technologies and the weaknesses of neither, but are notoriously difficult to calibrate for use in nonlinear measurements. This work proposes a hybrid modeling and experimental approach to air-coupled transducer calibration and the use of this calibration in a model-based optimization to determine the absolute β parameter of the material under investigation. This approach is applied to aluminum and fused silica, which are both well-documented materials and provide a strong reference for comparison of experimental and modeling results.

Characterization of Microcrack Orientation Using the Directivity of Secondary Sound Source Induced by an Incident Ultrasonic Transverse Wave

“…In the past decades, due to the fact that the harmonic generated by primary ultrasonic wave propagation can carry microstructural information of materials, the nonlinear ultrasonic technique has received great attention in nondestructive evaluation (NDE) for its high sensitivity to microdamage and has been proven to be an effective potential for microdamage detection and evaluation [ 6 , 7 , 8 ]. Generally, the nonlinearity of ultrasonic wave propagation in an elastic solid with microcrack comes from three main sources: the elastic nonlinearity of material [ 9 ], the geometric nonlinearity [ 10 ], and the contact acoustic nonlinearity (CAN) (or the boundary nonlinearity of contact) [ 11 ]. In the field of NDE, there are mainly five techniques for nonlinear ultrasonic detection: vibration acoustic modulation [ 12 ], nonlinear wave modulation spectroscopy technique [ 13 , 14 ], nonlinear resonance technique [ 15 ], second-harmonic generation [ 16 ] and wave-mixing technique [ 17 , 18 ].…”

Applying multiparametric ultrasonic nondestructive test for structural characterization of age hardened aluminum alloy

“…Other authors applied the ultrasonic technique to evaluate elastic modulus, grain size, and yield strength of steel and titanium alloys. The results proved the potentials of NDT to quality control of materials manufacturing [13][14][15][16][17][18][19][20]. To analyze the microstructure of the samples by scanning electron microscopy (Jeol model JSM-5700 SEM), the samples were ground, polished and chemically attacked with Weck solution.…”

“…During the propagation through the bulk material, ultrasonic waves interact with materials interfaces (discontinuities, grain boundaries, precipitates, and secondary phases). These interactions influenced the wave velocity and attenuation, providing a correlation between materials ultrasonic and microstructural properties [14][15][16][17][18][19][20].…”

Compensation of a Second Harmonic Wave Included in an Incident Ultrasonic Wave for the Precise Measurement of the Acoustic Nonlinearity Parameter

“…For this, the acoustic nonlinearity parameter β , defined by the displacement amplitudes of the fundamental and second harmonic waves, is generally employed [ 4 ]. Furthermore, contact transducers have been frequently used for transmitting and receiving an ultrasonic wave because they have a higher signal-to-noise ratio and it is simple to set up the measurement system [ 5 ]. However, they detect the ultrasonic wave in the form of an electric signal, the amplitude of which is not a displacement signal.…”