Plastic Stress-Strain Relationships：塑性应力应变关系.ppt

Plastic Stress-Strain Relationships Plastic Stress-Strain Relationships UAA School of Engineering CE 334 - Properties of Materials Lecture # 5 Outline Plastic Stress-Strain Relationships Plastic deformation - Metal as a ductile material What is plastic stress-strain relation? Definitions about plastic stress-strain curves Inelastic Material Behavior Limitations on the Use of Uniaxial Stress-Strain Data Tension or compression tests are usually run at room temperature in testing machines that have head speeds in the range of 0.20 to 10 mm/min. Rate of Loading If a tension test is run at a high rate of loading then the material response is less ductile. Temperature -Temperature Lower than Room Temperature A metal tension specimen may fail in a brittle manner. -Temperature Higher than Room Temperature: Creep Effect of Unloading and Load Reversal ? ·??The accrual unloading path does not follow the ideal linear elastic unloading path ·?The yielding strength in compression is reduced below the original value ? Bauschinger Effect. Nonlinear Material Response If the unloading path coincides with the loading path, the process is reversible and the material is said to be Elastic. If the unloading path does not follow the loading path, the behavior is said to be Inelastic. If after the load is released, the permanent deformation remains, the behavior is said to be Plastic. If after load removal, the response continues to change with time, its response is Viscoelastic or Viscoplastic. If a viscous material, after complete unloading, the material will return to an unstrained state in time, it is Viscoelastic In a Viscoplastic material, after complete unloading, the response will change with time. However, some permanent strain will remain. Metal as a Ductile Material The Crystals that Make the Metal  Lets take a look at a paper clip. A typical paper clip is made up of 1,000,000,000,000,000,000,000 atoms of iron. These atoms are tightly packed