Definitions for "Proportional limit"
Keywords:  strain, elastic, stress, ceases, hooke
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.
The maximum stress at which strain remains directly proportional to stress; the upper end of the straight-line portion of the stress-strain or load-elongation curve.
Stress at which the deformation ceases to be proportional to the load as determined by straino-meter (also, by a extensometer for tension, compressometer for compression and deflectometer for transverse tests, value being read from plotted results). See "Elastic Limit."