CHARACTERIZATION OF LINEAR VISCOELASTIC MATERIALS TESTED IN CREEP AND RELAXATION

The experimental creep and relaxation functions determined by a set of independent experiments may not fulfill identically the equation 0tE(τ)D(t-τ)dτ=t of linear viscoelasticity, where E(t) and D(t) are the relaxation modulus and creep compliance, respectively. The consistency of the experimental data can be improved by the introduction of appropriate error functions. Two different methods have been suggested in order to compute the error functions so that the above equation is satisfied. In Method I, the error function is a solution of a Volterra nonlinear integral equation which is solved by a numerical procedure. In Method II, the error functions are defined in the Laplace domain; the application of the convolution theorem reduces the determination of the error functions to the solution of an algebraic equation. These methods are applied to creep and relaxation tests performed on a sand-asphalt composite. The computations show the extent of the improvement achieved by making the transient functions D(t) and E(t) consistent. © 1969 The American Institute of Physics.