Mechanical Property 기계적 성질 Associate Professor Su-Jin Kim School of Mechanical Engineering Gyeongsang National University 1
Tension test Tension test (인장 실험) is the most common test for determining the stress-strain characteristics of materials.
Stress strain curve Stress strain curve (응력 변형율 곡선)
Elastic (탄성) Stress (응력, MPa) = applied load / original area Strain (변형율) = extended l. / original length Stiffness (강성, GPa) E: Modulus of elasticity, Young’s modulus Hook’s law F Ao l0 d
Strength(강도) Yield Strength(항복강도): Stress at which noticeable plastic deformation has occurred. Tensile, Ultimate Strength(인장,극한강도): Maximum stress on engineering stress-strain curve. Noticeable necking of metal starts. Polymer backbone chains are aligned and about to break. strain stress Yield strength ep = 0.002 sy su Ultimate strength
Toughness (인성) • Toughness(인성,韌性) is the ability of material to absorb energy and plastically deform without fracturing. • Approximate by the area under the stress-strain curve. Ductility strain stress ceramic plastic metal Toughness Brittle fracture: elastic energy Ductile fracture: elastic + plastic energy
Ductility (연성) Ductility(연성, 延性) is ability to deform under tensile stress; to be stretched into a wire. Ductility is measured by elongation or reduction of area. Malleability(가단성,可塑性) is ability to deform under compressive stress; to form a thin sheet by hammering or rolling. ㅣf Ao Af ㅣo
True stress and true strain True stress is defined as where A is the actual area supporting the load True strain is defined as A true stress–true strain curve is approximated as True strain True stress
Effects of temperature (온도) Increasing temperature: - Decrease the modulus of elasticity, yield strength, and ultimate tensile strength - increases ductility and toughness
Hardness test (경도) The most common standardized hardness tests are as follows. HRC hardness is suggested for steels.
Hardness Diamond HRC