Measurement of Residual Strains and Stresses in Transparent Materials,
MEASUREMENTS GROUP INC RALEIGH NC
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Measurement of birefrigence is a straight forward process that can be accomplished on any transparent or partly transparent material by using methods described in presently existing standards. Present methods permit observation and inspection of large non-flat objects by using either transmission or reflection photoelastic techniques. The method is applicable to a large variety of polymers, as shown in Table I. In some partly crystalline polymers, the birefringence is observed even in a totally strain-relieved condition, and special care must be exerted to avoid misinterpretation. Using material constants from Table I or by obtaining via the calibration process described above, one can calculate residual strains from the measured birefrigence, and thus obtain valuable information revealing the quality or safety margin of the tested part.