Surface Crack Characterization: Geometry and Stress Intensity Factor Measurements

The reflection coefficient of a Rayleigh wave at a surface crack is measured in both the long wavelength and the short wavelength limits. from the long wavelength measurement, the maximum value of the stress intensity factor is evaluated. Using glass samples, we have formed surface cracks, measured their reflection coefficient, and predicted failure stress with an error of less than 5% from the measured fracture stress. In short wavelength limit, the reflection coefficient is measured versus frequency. Length and depth resonances of the crack are observed and used to estimate the crack geometry with an accuracy of 10-20% for EDM notches in steel

Detection and Characterization of Surface Cracks Using Leaky Rayleigh Waves

A number of ceramics such as silicon nitride, and zirconia are being considered for high temperature structural applications. The primary problem with these ceramics is their wide fracture strength variability. In consequence, non-destructive evaluation techniques are required to ensure their reliable use. The brittle nature of ceramics inhibits the strain energy release at flaws by plastic deformation. As a result, critical flaw size in these materials is small. For example, flaws in the size range of 20–100 µm are considered as “critical” in silicon nitride for engine applications. Surface cracks are particularly important since they are the major source of failure in ceramics (1). These cracks are generated during machining operations and usually consist of arrays of semi-elliptical cracks with random inclination to the surface, but a preferred alignment parallel to the direction of motion of the abrading particles (2).</p

Surface Crack Characterization: Geometry and Stress Intensity Factor Measurements

The reflection coefficient of a Rayleigh wave at a surface crack is measured in both the long wavelength and the short wavelength limits. from the long wavelength measurement, the maximum value of the stress intensity factor is evaluated. Using glass samples, we have formed surface cracks, measured their reflection coefficient, and predicted failure stress with an error of less than 5% from the measured fracture stress. In short wavelength limit, the reflection coefficient is measured versus frequency. Length and depth resonances of the crack are observed and used to estimate the crack geometry with an accuracy of 10-20% for EDM notches in steel.</p

Surface Crack Characterization: Geometry and Stress Intensity Factor Measurements

The reflection coefficient of a Rayleigh wave at a surface crack is measured in both the long wavelength and the short wavelength limits. from the long wavelength measurement, the maximum value of the stress intensity factor is evaluated. Using glass samples, we have formed surface cracks, measured their reflection coefficient, and predicted failure stress with an error of less than 5% from the measured fracture stress. In short wavelength limit, the reflection coefficient is measured versus frequency. Length and depth resonances of the crack are observed and used to estimate the crack geometry with an accuracy of 10-20% for EDM notches in steel.</p

Efficient Processing of Joins on Set-valued Attributes

Object-oriented and object-relational DBMS support set-valued attributes, which are a natural and concise way to model complex information. However, there has been limited research to-date on the evaluation of query operators that apply on sets. In this paper we study the join of two relations on their set-valued attributes. Various join types are considered, namely the set containment, set equality, and set overlap joins. We show that the inverted file, a powerful index for selection queries, can also facilitate the efficient evaluation of most join predicates. We propose join algorithms that utilize inverted files and compare them with signature-based methods for several set-comparison predicates.link_to_subscribed_fulltex