Noncontact evaluation of acoustic nonlinearity of a laser-generated surface wave in a plastically deformed aluminum alloy

A noncontact method to evaluate the acoustic nonlinearity of surface waves in a plastically deformed aluminum alloy is proposed. Line-arrayed laser beams modulated with slit masks were used for the generation of narrowband surface waves. A laser-ultrasonic detector using a two-wave mixing (TWM) approach was also employed to detect the surface waves. The specimens were deformed by a stroke-controlled tensile tester so as to generate various degrees of tensile deformation. The experimental results showed that the acoustic nonlinearity of the laser-generated surface waves increased according to the level of tensile deformation. This tendency was in good agreement with our previous results obtained using a contact piezoelectric (PZT)-transducer as the receiver. These results imply that our noncontact technique is suitable for the evaluation of acoustic nonlinearity and can be applied to practical damage assessment.