Instron 4400 Series Operator's Manual page 250

Glossary M10-94400-1
Proportional Limit.
Highest stress at which stress is directly proportional to
strain. It is the highest stress at which the curve in a
stress-strain diagram is a straight line. Proportional limit
is equal to elastic limit for many metals.
Rate of Strain Hardening.
Rate of change of true stress as a function of true strain
Proportional Limit
STRAIN
in a material undergoing plastic deformation. An alter-
nate term is modulus of strain hardening.
Recovery.
Index of a material's ability to recover from deformation
in the compressibility and recovery test (ASTM F-36),
the deformation under load test (ASTM D-621) and the
plastometer test (ASTM D-926). In the compressibility
and recovery test, it usually is reported with compressi-
bility and given as %. It is calculated by dividing the dif-
ference between recovered thickness and thickness
under load, by the difference between original thickness
B-24