The effects of small defects on the fatigue strength of Ti-6 Al-4V were investigated in tension-compression fatigue tests.specimens (Series A). Another series of specimens (Series B) were prepared to investigate the effect of a burr or a pre-crack which was introduced at the edge of the artificial hole. For Series A specimens, the fatigue limit was defined as the threshold for crack initiation from the edge of the hole. For Series B specimens, the fatigue limit was defined as the threshold for crack propagation from the burr or the tip of the pre-crack fatigue limit of Series A specimens, but the model accurately predicted the fatigue limit defined by crack-growth threshold for Series B specimens. In addition it was noted that the presence of abun resulted in a decrease in fatigue life, since the bun facilitated the crack initiation process.

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During the last two decades, significant advances in the field of laser generated ultrasounds have been made. In the conventional pulse echo technique, a discontinuity in the specimen can be detected only if an ultrasonic detector is properly oriented to the discontinuity. The 2-D Scanning Laser Source (SLS) technique allows detection of surface-breaking cracks of arbitrary orientation with respect to the direction. This technique also makes detection possible on rough and curved surfaces by scanning changes in ultrasonic amplitude and frequency when the laser source scans over flaws. Conventional ultrasonic scanning technique requires immersion of specimen or water jet for transferring ultrasonic wave between transducer and specimen. However, this SLS technique does not need contacting and couplant to generate surface wave and to get flaw images. Therefore, this SLS technique has several advantages, for complicated production inspection, high speed scanning, non-contact, remote from specimen, and high resolution. In this study, ultrasonic SLS images of fatigue cracks on turbine blade of aircraft and steel plates were obtained to describe shapes of defects by SLS technique.

The purpose of this research is to identify and recommend methods of inspection, surveillance, and monitoring that would provide timely detection of valve degradation and service wear so that maintenance or replacement could be performed prior to loss of safety functions. This research is focused on the capability of acoustic emission (AE) technique to provide diagnostic information on the determination of check valve aging and degradation, check valve failures and undesirable operating modes. Several commercially available check valve diagnostic-monitoring methods were evaluated, especially for the techniques based on measurements of acoustic emission, ultrasonic, and accelerometers. In the present paper, acoustic emission signals due to leak from check valve with artificially leakage and artificially worn disk were studied both analytically and experimentally. The results of development of advanced signal processing and de-noising techniques also have been presented.