Yield. UTS.
Elongation. Toughness.
Engineering terms.
Material properties glossary for engineers. Yield strength, ultimate tensile, elongation, toughness, fatigue, modulus. Standard definitions for design calculations.
Key principles.
Permanent deformation start
Stress at which permanent deformation begins. Design limit for most applications.
Maximum stress
Maximum stress before fracture. Higher than yield. Brittle materials fracture at UTS.
% stretch before failure
Ductility measure. Steel 20-30%, aluminum 8-15%, brittle materials < 5%.
Stiffness
Ratio of stress to strain. Steel 200 GPa, aluminum 69 GPa, plastics 1-4 GPa.
Lateral contraction
Ratio of lateral to axial strain. Most metals 0.3, rubber near 0.5.
Cyclic loading
Stress below which infinite cycles. Steel ~50% UTS. Aluminum: no true limit.
Toughness
Energy absorbed in impact fracture. Indicates ductility under shock.
Surface deformation resistance
Indentation resistance. Correlates loosely with strength.
Per °C dimensional change
Steel 12, aluminum 23, plastics 80-200 µm/m·°C.
FAQ
Yield vs ultimate strength?
Yield: permanent deformation begins. Ultimate: fracture. Design typically to yield (with safety factor 1.5-3). Brittle materials fracture at UTS.
What is fatigue?
Material failure under repeated cyclic loading at stresses below static yield. Critical for parts seeing many cycles (engines, springs, bearings).
Modulus vs strength?
Modulus: stiffness (deflection per load). Strength: failure point. High modulus materials don't flex much. High strength materials don't fail until high load.
Why does CTE matter?
Different CTE in mating parts causes thermal stress, dimensional drift over temperature. Critical for precision instruments, optics.
How is hardness measured?
Indenter pushed into surface; resistance measured. Various scales (Rockwell, Brinell, Vickers, Shore). Each suitable for different ranges.
Toughness vs strength?
Toughness: energy to fracture (area under stress-strain curve). High strength + high ductility = high toughness. Brittle materials low toughness.