At the proportional limit
state, SDR of the two-layer reinforced cushion was similar to that of the one-layer reinforced cushion, while at the stable state, there was a big difference between them.
The difference lies in the attempt to use equations developed for materials that have a proportional limit
on materials that do not have a true proportional limit
and not considering the properties of copper strain hardening.
Therefore, there is a concern that bending properties, including Young's modulus, proportional limit
stress, and bending strength, cannot be evaluated appropriately by the conventional bending tests.
To simplify the calculations, it was taken, that cyclic proportional limit
[[bar.s]sub.T] is independent on [[bar.e].sub.con] , the number of semicycles k and on stress ratio [r.sub.[sigma]].
For high loads, stress and strain exceed proportional limit
and elastic plastic strain occurs.
* Proportional limit
. The point where the curve starts to deviate from a straight line.
Figure 1 shows the initial portion of a tensile stress-strain curve that identifies the proportional limit
. This is the last point on the stress-strain curve where the stress and strain are in proportion.
No difference in modulus of elasticity and modulus of rupture, work to proportional limit
, work to maximum load, or fiber stress at proportional limit
between samples steamed following treatment and those only treated was shown.
For many materials this proportional limit
takes place even below 0.5% strain.
The research conducted herein focused on nondestructive identification of damage in wood that has occurred via bending load in excess of the proportional limit
, yet below breaking strength.