title: Effect of adhesion force between crack planes on subharmonic and DC responses in nonlinear ultrasound.
abstract: Subharmonic and DC responses in nonlinear ultrasound have been expected as a possible means of detecting closed cracks. Recently, it has been reported that subharmonics in a closed crack markedly increases above a certain input wave amplitude. Such a phenomenon is called "threshold behavior". However, the mechanism of threshold behavior has yet to be elucidated. To clarify this, we introduced adhesion force as a short-range force into the previous analytical model, which expresses the nonlinear contact vibrations of crack planes with intense ultrasound and provides a DC displacement as an approximation of the subharmonic response. Consequently, upward convex curves of displacement against input wave amplitude above the threshold were reproduced for the first time. The validity of the derived analytical solution is discussed by comparison with experimentally observed subharmonics.
authors.affiliation: Tohoku University, Department of Materials Processing, Aoba 02, Aramki-aza, Sendai City, Miyagi 980-8579, Japan.
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ohara
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Mihara
authors.forename: Kazushi
authors.initials: K
authors.lastname: Yamanaka