Strain ($\Delta L$/L) Stress (Pa) P Proportional Limit E Elastic Limit Y Yield Point U Ultimate Stress B (Break) Slope = Y (Young's modulus) ← Elastic → ←— Plastic —→

Key labels: P = Proportional Limit (Hooke's law holds up to here), E = Elastic Limit (full recovery up to here), Y = Yield Point (plastic deformation begins), U = Ultimate Stress (maximum stress), B = Breaking Point. The slope of the P-E linear region = Young's modulus Y.