Fatigue damage evaluation on austenitic stainless steel using nonlinear
ultrasonic method
Abstract
The closed crack and micro damage are liable to be underestimated in
conventional (linear) ultrasonic nondestructive testing, which lead to
unpredictable safety hazards. The objective of this work was to detect
the fatigue damage in the stainless steel samples by use of nonlinear
ultrasonic method. In the first, the macro cracks of fatigue specimens
were measured by metallographic method. Secondly, the finite amplitude
method of nonlinear ultrasonic testing was employed to evaluate the
micro damages, and both the linear and the nonlinear characteristics of
testing signals were investigated. Thirdly, the influences of excitation
voltage on the finite amplitude method were discussed. The results
indicate that the maximum value of the relative nonlinearity parameter
is sensitive to the closed cracks and micro damages which are unable to
be detected by the amplitude of linear ultrasonic testing. Higher
excitation voltage is beneficial for exciting the nonlinear response of
closed crack, which can be used to evaluate the degree of fatigue
damage.