208 Rock dynamics and time-dependent aspects
Figure 13.1 Examples of visible effects of (a) high and (b) low strain rates on rock.
loading-unloading stress-strain curve. The area under this curve
represents energy, so the presence of such hysteresis loops indicates the
non-recovery of energy, which causes an increase in entropy.
13.2 Stress waves
Stress waves are the manifestation of dynamic stress changes. They occur
when the body is not in static equilibrium as described so far, and are
essentially sound waves in solid material. The differential equations of
equilibrium, represent the fact that, for any given axis, the resultant force
on a body is zero when the body is in equilibrium. Considering now that