Page 340 - Mechanics Analysis Composite Materials

Chapter I. Environmental, special loading, and manufacturing effects 325

The corresponding creep diagram is shown in Fig. 7.17. As follows from this figure,
~(t-+ m) = oo/El, where E1 is specified by Fiq. (7.40). This means that there exists
some limit for the creep strain, and materials that can be described with this model
should possess the so-called limited creep.
Now assume that the model is loaded in such a way that the apparent strain is
constant, i.e., that E = EO. Then, the solution of Eq. (7.39) that satisfies condition
o(0) = Eleo is

The corresponding dependence is presented in Fig. 7.18 and illustrates the process
of stress relaxation. Parameter tr is called the time of relaxation. During this time the
stress drops by the factor of e.
Consider again Eq. (7.39) and express El, E2, and q in terms of Ei, El, and t,.. The
resulting equation is as follows

(7.41)

Fig. 7.17. Creep diagram corresponding to mechanical model in Fig. 7.16.

Fig. 7.18. Relaxation diagram corresponding to mechanical model in Fig. 7.16.