Abstract

Most creep-time relations for materials are obtained for short periods of time—usually for 1000 hr or about 40 days. In many applications, however, the life of the member is much greater than 1000 hr. In the design of these members, therefore, it is necessary to provide for creep deformations which cover periods of time much greater than 40 days. To do this, it is common practice to obtain a stress-creep-time empirical relation based on 1000-hr test data, and to extrapolate these relations to periods of time representing the service life of the part. The purpose of this paper is to determine the accuracy of this extrapolation. This is accomplished by comparing the extrapolated tension and compression creep-time relations based on 1000-hr test data with actual 10,000-hr creep-test data. Long-time creep-test data also were obtained for pure bending and pure torsion. These creep-time relations were compared with theoretical values based on empirical relations for 1000-hr tension and compression creep data. For the relations used and for the material tested, it was found that the extrapolated values gave good engineering approximations to the actual values.

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