SiGnal Processing Techniques For Nondestructive Evaluation Using Laser Ultrasonics
Laser ultrasonics is a form of ultrasonic evaluation in which a pulsed laser generates an ultrasonic wave in a sample which interrogates a specific feature. When this wave returns to the surface a separate laser interferometer detects the small resulting displacement. This technique is strictly noncontact and is thus suitable for in-process inspection of parts at high temperature or moving at high speed. In many applications the acquired temporal signals have features which differ from those acquired using conventional transducers. In this paper we will describe these features and discuss techniques which have been used to process these signals.
Applications of Laser Ultrasonics in the Pipeline Industry
Managing pipe damaged by Stress Corrosion Cracking (SCC) ha s been a formidable challenge to the pipeline industry. The development of a practical solution f or the measurement and evaluation of SCC has been marred by the complexity of crack shapes, their distrib ution within a crack colony, and the lack of non-destructive technology capable of reliably measuring th e crack depths. Laser ultrasonics is a promising noncontact technique for pipeline inspection. The large frequency bandwidth and small footprint make laser ultrasonics ideally suited for applicat ion as a depth sizing tool for closely-spaced cracks in a colony. It has been conclusively proven that laser ultrasonic inspection, using the time of flight diffraction (TOFD) technique, can reliably and accurately measure the depth of naturally occurring SCC, and potentially, other cracks and seam weld anomalies.
Using the International Classification of Impairments, Disabilities, and Handicaps in surveys: the case of Spain.
A survey was conducted in Spain in 1986 to estimate the number of people with disabilities and to identify the impairments which had given rise to them. The survey also set out to identify the causes of these impairments and to analyse the nature and extent of the handicaps resulting from these impairments and disabilities. The frame of reference for the survey was the WHO International Classification of Impairments, Disabilities, and Handicaps (ICIDH), which was adapted in a number of ways. The most radical departure was to begin the survey with disabilities, which were considered easier to identify. 15% of the population presented a disability, the rate mostly increasing with age, with substantial differences between the sexes and pronounced gradients in relation to socioeconomic status in some cases. Analysis of disabilities and impairments by administrative area also revealed some significant geographical variations. The study of handicaps posed some particularly complex problems of methodology. In conclusion, the work of the Spanish survey was facilitated by the use of the ICIDH, but this classification requires several substantial modifications before it can be systematically used in surveys of this type.