Materials for engineering, 3rd Edition - (Malestrom)

64
Materials for engineering
III
a
log d d
t
II
I
K I EAC K K Ic
2.21 Diagram showing three stages of environment-assisted cracking
under sustained loading in an aggressive atmosphere. Lower and
upper K limits of plot determined by K I EAC and K Ic , respectively.
2.7.5 Time-dependent elastic properties
Vibrating solids
If a material is loaded elastically to a stress σ, the stored elastic energy per
unit volume is:
∫
σ max
U = σde
0
If it is loaded and then unloaded it dissipates an energy
∆U
= de
∫ σ
The specific damping capacity D is defined by the ratio:
D = ∆U/U [2.32]
Another measure of damping is the logarithmic decrement δ which is the
log of the ratio of successive amplitudes of natural vibration of the solid. The
effect arises because the elastic forces acting may also assist thermal energy