Mechanical Behavior of metallic Materials e Elastic-homogeneous plastic deformation E B 000 A Gage length ③大季
Mechanical Behavior of Metallic Materials ⚫ Elastic-homogeneous plastic deformation
Mechanical Behavior of Metallic materials Strain Hardening An increasing resistance to further plastic deformation Hollomon relation: o=KE n: strain hardening coefficient, sensitive to thermo-mechanica treatment Material Strain hardening coefficient, n stainless steel 0.45-0.55 brass 0.35-04 copper 0.3-0.35 aluminum 0.15-0.25 Iron 0.05-0.15 ③大季
Mechanical Behavior of Metallic Materials An increasing resistance to further plastic deformation Strain Hardening Hollomon relation: n = K n: strain hardening coefficient, sensitive to thermo-mechanical treatment. Material Strain hardening coefficient, n stainless steel 0.45-0.55 brass 0.35-0.4 copper 0.3-0.35 aluminum 0.15-0.25 iron 0.05-0.15
Mechanical Behavior of metallic Materials o The magnitude of n reflects the ability of the material to resist further deformation o n=l, represent ideally elastic behavior n=0, represent ideally plastic behavior o n is generally larger for materials in the annealed conditions and smaller in the cold-worked conditions o n generally increases with decreasing strength level and with decreasing mobility of certain dislocations in the crystalline lattice ③大季
Mechanical Behavior of Metallic Materials ⚫ The magnitude of n reflects the ability of the material to resist further deformation. ⚫ n = 1, represent ideally elastic behavior ⚫ n = 0, represent ideally plastic behavior ⚫ n is generally larger for materials in the annealed conditions and smaller in the cold-worked conditions ⚫ n generally increases with decreasing strength level and with decreasing mobility of certain dislocations in the crystalline lattice
Mechanical Behavior of metallic Materials Plastic instability and necking Uniform plastic deformation: Initial plastic flow higher stress another plastic flow strain hardening increasing resistance to further plastic deformation Necking point: localized plastic deformation The strain hardening capacity is exhausted and the further plastic deformation is localized in the necking region ③大季
Mechanical Behavior of Metallic Materials Uniform plastic deformation: Plastic instability and necking Necking point: localized plastic deformation The strain hardening capacity is exhausted and the further plastic deformation is localized in the necking region. Initial plastic flow strain hardening increasing resistance to further plastic deformation another plastic flow higher stress
Mechanical Behavior of Metallic materials The amount of uniform strain is related to the magnitude of the strain-hardening exponent. It can be proved that: O da Kan=knan-l The true plastic strain at necking insta bility is numerically equal to the strain-hardening coefficient ③大季
Mechanical Behavior of Metallic Materials The amount of uniform strain is related to the magnitude of the strain-hardeningexponent. It can be proved that: n = The true plastic strain at necking instability is numerically equal to the strain-hardening coefficient. n n 1 d d K Kn − = =