CREEP OF 2618 ALUMINUM UNDER STEP STRESS CHANGES PREDICTED BY A VISCOUS-VISCO-ELASTIC MODEL

Nonlinear constitutive equations are developed and used to predict from constant stress data the creep behavior of 2618 Aluminum at 200° C (392°F) for tension or torsion stresses under varying stress history including stepup, stepdown, and reloading stress changes. The strain in the constitutive equation employed includes the following components: linear elastic, time-independent plastic, nonlinear time-dependent recoverable (viscoelastic), nonlinear time-dependent nonrecoverable (viscous) positive, and nonlinear timedependent nonrecoverable (viscous) negative. The modified superposition principle, derived from the multiple integral representation, and strain-hardening theory were used to represent the recoverable and nonrecoverable components, respectively, of the timedependent strain in the constitutive equations. Excellent-to-fair agreement was obtained between the experimentally measured data and the predictions based on data from constant-stress tests using the constitutive equations as modified. © 1980 by ASME.