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In the late 1960s and early 1970s research and

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In the late 1960s and early 1970s, research and development in acoustic emission testing was undertaken in the United States by national laboratories and in the aviation, nuclear and petroleum industries. In the United Kingdom, the method was developed at Imperial College, London, and at the Atomic Energy Research Establishment, Harwell. In the spring of 1967, a number of researchers were investigating the phenomena of acoustic emission and publishing reports of their work but without a means of centralized communication. There were differences in terminology and experimental techniques, generally reflecting the researchers’ educational background and field of expertise. Jack C. Spanner contacted a dozen people with interest or experience in the field of acoustic emission and invited them to participate in the formation and organization of the Acoustic Emission Working Group. The first meeting was held, informally, in 1967. Acoustic emission working groups were also organized in Japan and Europe. Through the forum provided by these groups, an international exchange of information and cooperation developed for addressing specific areas. Information on the history of acoustic emission developments has been published in more detail elsewhere. 14,31 In the closing years of the twentieth century, the publication of the acoustic emission volume of the Nondestructive Testing Handbook in 1987 and the certification of inspectors together demonstrated that the technology was mature and had found widespread acceptance by industry. 4 24 Acoustic Emission Testing
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Origin and Use of the SI System In 1960, the General Conference on Weights and Measures established the International System of Units. Le Systéme International d’Unités (SI) was designed so that a single set of measurement units could be used by all branches of science, engineering and the general public. Without SI, the Nondestructive Testing Handbook series would contain a confusing mix of obsolete centimeter-gram-second (CGS) units, imperial units and the units preferred by certain localities or scientific specialties. SI is the modern version of the metric system and ends the division between metric units used by scientists and metric units used by engineers and the public. Scientists have given up their units based on centimeter and gram and engineers have abandoned the kilogram-force in favor of the newton. Electrical engineers have retained the ampere, volt and ohm but changed all units related to magnetism. Table 6 lists the seven SI base units. Table 7 lists derived units with special names. Table 8 gives examples of conversions to SI units. In SI, the unit of time is the second (s) but hour (h) is recognized for use with SI. For more information, the reader is referred to the information available through national standards organizations and specialized information compiled by technical organizations. 32-35 Multipliers In science and engineering, very large or very small numbers with units are expressed by using the SI multipliers, prefixes of 10 3 intervals (Table 9). The
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  • Fall '19
  • Nondestructive testing, Acoustic Emission

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