Influence of surface roughness on the measurement of acoustic nonlinearity parameter of solids using contact piezoelectric transducers

• Published in: Ultrasonics 2018-03, Vol.84, p.112-118
• Main Authors: Chakrapani, Sunil Kishore, Howard, Alexander, Barnard, Daniel
• Format: Article
• Language: English
• Subjects: Acoustic nonlinearity parameter; Surface roughness; Transducer calibration
• ISSN: 0041-624X; 1874-9968
• DOI: 10.1016/j.ultras.2017.10.022

•Present study investigates the influence of surface condition on β measurement.•Up to 35% variation in β was observed for aluminum, compared to 1.5% for steel.•Most variation was observed when the receiver was placed on the rough side.•β changed by 1.5%, whereas β′ changed by 52%.•Aluminum samples had surface deformation and scuff marks due to transducer loading. The current article reports on the experimental study of the influence of surface roughness on the measurement of the acoustic nonlinearity parameter. The nonlinearity parameter was measured using contact piezoelectric transducers, which were calibrated using the reciprocity based technique. Aluminum and steel samples were chosen to study the influence of hardness of the sample on the measurement of the nonlinearity parameter. While, lower Ra value (average asperity height) aluminum samples were more susceptible to surface deformation and scratches from coupling the transducer to the sample, the same could not be observed for steel samples. Results demonstrate a large variation in nonlinearity parameter for aluminum (∼35%) compared to steel (∼2%) between two consecutive experiments, suggesting flattening of asperities after the first experiment. Experiments were also performed with 3 different setup configurations; (1) receiver and transmitter on rough sides, (2) receiver on smooth and transmitter on rough side and (3) receiver on rough and transmitter on smooth side. Results show that least variation in the measured nonlinearity parameter was observed when the receiver was placed on the smooth side, and a 10% variation was observed between the three setup configurations. Finally, a comparison of relative nonlinearity parameter calculated using current or voltage ratio and absolute nonlinearity parameter showed large discrepancies. Conclusions were drawn from the experimental observations.