Taizo Maruyama

Improved ultrasonic SAFT imaging of flaws in structures with curved surfaces

A time domain synthetic aperture focusing technique (SAFT) for flaw imaging of immersed structures with curved surfaces is improved in conjunction with approximate wave solutions, which were obtained in an explicit form by Schmerr (1998). In the improved SAFT, the approximate solutions are used to normalize A-scan waveforms and then the normalized waveforms are superimposed to obtain images with high contrast for a flaw in a structure in curved surfaces. As examples, the proposed SAFT is applied to experimental data for a side drilled hole (SDH) in an immersed round bar.

Steady-state anti-plane shear wave scattering by a crack with friction

The present article describes the steady-state numerical modeling of anti-plane shear wave scattering by a crack with frictional boundary conditions. The system is composed of an unbounded elastic solid that includes a closed crack under static compressive stress. A time-harmonic anti-plane shear wave is incident, and dynamic friction between the crack faces is induced as a nonlinear phenomenon. The anti-plane wave scattering can be described in a retarded potential integral equation by taking the nonlinearity into account. The present article introduces the steady-state expression as an asymptotic vibration of crack faces after a sufficient elapsed time. In order to solve the equations describing nonlinear steady-state vibration, a harmonic balance method is integrated into a boundary element method. Fourier coefficients of crack opening displacement distributed on the crack face are treated as unknown variables. The system of nonlinear equations is solved by means of a numerical continuation method. The present numerical results show almost complete agreement with those obtained by the conventional time-domain analysis after a sufficient elapsed time. Furthermore, the robustness and effectiveness of the proposed method are demonstrated numerically.

Simulation for air-coupled ultrasound testing using time-domain BEM

Air-coupled ultrasound testing is known as one of attractive non-contact ultrasonic NDE methods. However, the sensitivity of the air-coupled method greatly depends on the positioning of transducers, because the difference of acoustic impedance between air and solid is very large. In order to use this method for quantitative detection and evaluation of material flaws, it is necessary to simulate ultrasonic wave propagation and scattering in a solid. For a coupling problem between two media, in which ultrasonic waves travel at greatly different velocities, it is difficult to obtain stable solutions by means of a conventional time-domain boundary element method (BEM). A convolution quadrature time-domain fast multipole BEM (CQ-FMBEM) has been developed for the simulation of ultrasonic wave propagation and scattering in a solid. In the CQ-FMBEM, a convolution quadrature method (CQM) is introduced to make BEM solutions stable by evaluating a convolution integral in a very accurate numerical manner, while a fas...