Much experimental work has been done on the creep of metals and the longhyphen;time creep test is the standard means of rating resistance to slow deformation of metals under tensile stress. In engineering practice, frequently, cases are found in which the total strain and not the stress remains constant. In what has become known as relaxation, an initially pure elastic strain gradually is transformed into a permanent strain while the length of the bar remains unchanged. Several years ago some new apparatus was designed and built primarily to duplicate the above conditions in connection with the study of bolt materials for steam turbines. The unusual accuracy and exceptionally good test results obtained from the automatic relaxation machine during more than two years of operation indicate that the type of test may well become a means of comparison as standard as a creep test and at a great reduction of testing time.
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