Metal_Inelasticity_in_ABAQUS英语教案.ppt

Ductile Metal Response Overview Uniaxial Test at Low Temperatures Stress and strain measures Yield Strain reversal after yield Cyclic loading Necking Temperature and strain-rate dependence Uniaxial Test at Elevated Temperatures Uniaxial Test at Low Temperatures A uniaxial test, when performed in tension or compression at a relatively low temperature (below two-thirds of the metal’s melting temperature on an absolute scale), exhibits several phenomena that are basic to the formulation of the classical theories of metal plasticity. A typical response is shown in the figure below: Uniaxial Test at Low Temperatures Stress and strain measures The results are plotted as stress versus strain. Because nominal strains of 20%–100% are possible in tension for typical metals at room temperature, a precise definition of strain is needed. The dominant micromechanical mechanism for ductility in polycrystalline materials is dislocation motion. The mechanism driving dislocation motion is the force, or resolved stress, associated with the dislocation mechanism. Thus, the important stress measure on the microscopic scale is the true (or Cauchy) stress: the force per unit of current area transmitted across a surface in the material. Uniaxial Test at Low Temperatures Data from tension and compression tests correspond when true stress is adopted on the macroscale and the conjugate logarithmic strain measure is used. True stress s and logarithmic strain e are conjugate in the sense that se = work per unit volume. Uniaxial Test at Low Temperatures Yield data should always be given in ABAQUS as true stress versus logarithmic strain. Logarithmic strain, e, is defined as where l is the current gauge length, l0 is the original gauge length, and e nom is the engineering or nominal strain. True stress, s , is defined as where s nom is the engineering or nominal stress (s nom = F/A0). Uniaxial Test at Low Temperatures Yield Yield is the point at which the deformation is no longer fully