Development of a solver system for an inverse problem of defect shape determination with elastic wave

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1. Development of a workstation code for the time domain elastodynamic crack determination with BIEMWe could develop computer codes for 2 and 3 dimensional time domain elastodynamic crack determination problems with BIEM.These codes are found to run fast on a portable workstation. The investigation of this subject made more progress than planned ; actually, we proceeded to the crack determination problems where the crack has many geometrical degrees of freedom. At this moment we can solve 2 and 3 dimensional crack determination problems for the wave equation with the collocation BIEM, rather than the variational one. In 2D problems, in particular, we can determine quite complicated crack shapes with the help of the Tikhonov regularisation. We now plan to extend these studies to elastodynamics including anisotropic cases, which are important in the non-destructive evaluation of composite materials.2. Measurement of scattered waves from a crackAn ultrasonic measurement is carried out with a circular duralumin test piece using PZT transducers. The measurement is of the pitch-catch type. We first made the experiment first with an intact specimen, and then repeated the same experiment with the same specimen but with a saw cut. We tried to convert the output voltage from the transducer into displacements by using Fourier transform, but the resolution was not satisfactory. A similar trial with a semi-conductor strain gauge was not very successful, either. We therefore decided to use a statistical method to reconstruct the crack from the transducer output. We plan to continue this investigation looking into the possibility of using laser measurements.3. Inversion of the experimental dataThe data obtained in 2. was processed statistically to determine the location of the crack, with a moderate success. The use of the BIEM for the inversion, however, needs more investigation.