Approximate analysis of structures in the presence of moderately large creep deformations
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where en is the tensile strain rate caused by uniaxial tension in direction 1, <ru is the corresponding tensile stress, and K and n are constants. When the creep strains are large (of the order of magnitude of 0.01), the elastic deformations can often be neglected in the calculations, as will be demonstrated by means of an example. Thus the limiting state of stress and strain approached as the creep strain becomes large as compared to the elastic strain can be determined on the basis of a simple non-linear stress-strain rate law. It is believed that structural analyses based on the assumptions stated are satisfactory for supersonic guided missiles whose surface is heated to high temperatures by the air flow. As guided missiles are generally used only for a single flight and not over long periods of time like piloted airplanes, their structure can be permitted to undergo large permanent deformations. 2. The elastic analogue. It will now be shown that the stress distribution in a body whose deformations are governed by a generalized version of the non-linear creep law of Eq. 1 is the same as that in a non-linear perfectly elastic body provided the elastic stress-strain law and the boundary conditions are suitably chosen. Following Prager's suggestions for the representation of the stress-strain laws of strain-hardening materials [l]f, the uniaxial stress-strain rate law of Eq. 1 is generalized to read
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