材料定义

1 Rate Dependence Copyright 2006 ABAQUS, Inc. L3.2 Rate Dependence • Viscoplastic behavior is important at strain rates commonly encountered in manufacturing processes or dynamic events (101–103 per d) – Viscoplastic behavior can be included with the *RATE DEPENDENT material option (separable rate dependence) or by specifying the hardening curves as a direct function of the equivalent plastic strain rate (general rate dependence) second). • At these strain rates the yield stress of common structural metals increases by 20%–50% compared to their quasi-static yield values. pl& Copyright 2006 ABAQUS, Inc. Metal Inelasticity in ABAQUS rate, (general rate dependence). – Viscoplastic effects can be used only when the material hardening is isotropic (including perfectly plastic). – Strain-rate dependence is available in both ABAQUS/Standard and ABAQUS/Explicit. plε 2 L3.3 Rate Dependence • Separable strain-rate dependence • Separable strain-rate dependence is defined with the following expression: ( ) ( )0 l l& where is the static yield stress, is the yield stress ratio, and is the effective yield stress. • The static yield stress (hardening curve), is defined on the plastic material model hardening option. ( ) ( )0 , , , ,pl pli if R fσ σ ε θ ε θ= & ( )0 , ,pl ifσ ε θ ( ), ,pl iR fε θ&σ ( )0 , ,pl ifσ ε θ , Copyright 2006 ABAQUS, Inc. Metal Inelasticity in ABAQUS L3.4 Rate Dependence • The shape of the hardening curves will be similar for all values of when separable rate dependence is plε& σ 10plε =& 1plε =& 0plε =&separable rate dependence is used. ε 0ε = Separable rate-dependent behavior Copyright 2006 ABAQUS, Inc. Metal Inelasticity in ABAQUS 3 L3.5 Rate Dependence • The yield stress ratios are defined with the *RATE DEPENDENT option. • Rate dependence is a material sub-option ( ), ,pl iR fε θ& Rate dependence is a material sub option. Copyright 2006 ABAQUS, Inc. Metal Inelasticity in ABAQUS L3.6 Rate Dependence • can be defined directly as a tabular function of the equivalent plastic strain rate, (field variables). • Use the TYPE=YIELD RATIO parameter to indicate that this form of ( ), ,pl iR fε θ& pl ifε θ, , and& Use the TYPE=YIELD RATIO parameter to indicate that this form of rate dependence will be used. • The first data line must define 1 0plR ε= =when .& *PLASTIC 30.E3, 0.0 50.E3, 0.2 Copyright 2006 ABAQUS, Inc. Metal Inelasticity in ABAQUS 50.E3, 0.2 *RATE DEPENDENT, TYPE=YIELD RATIO 1.000, 0.0 1.076, 1.e-4 1.120, 1.e-3 4 L3.7 Rate Dependence • An overstress power law can be used to define It has the following form: ( ), ,pl iR fε θ .& • Use the TYPE=POWER LAW parameter to indicate that this form of rate dependence will be used. • The parameters D(θ, fi ) and ( )1 npl D Rε = − .& Copyright 2006 ABAQUS, Inc. Metal Inelasticity in ABAQUS i n(θ, fi ) are defined on the data lines of the *RATE DEPENDENT option. • Typical values are D = 30 − 100, n = 1 − 5. *PLASTIC 30.E3, 0.0 50.E3, 0.2 *RATE DEPENDENT, TYPE=POWER LAW 40., 5. L3.8 Rate Dependence • General strain-rate dependence • With the metal plasticity models it is possible to define hardening σ 10plε =& 1plε =& curves with different shapes at different strain rates. • Define general strain-rate dependency by specifying multiple hardening curves, each at a particular equivalent plastic strain rate, • The first hardening curve must ε 0plε =& General strain-rate dependent plasticity ( )0 , ,pl ifσ ε θ , plε .& Copyright 2006 ABAQUS, Inc. Metal Inelasticity in ABAQUS • The first hardening curve must define the static hardening curve (when ). General strain rate dependent plasticity 0plε =& 5 L3.9 Rate Dependence • Usage example: *PLASTIC 30 E3 0 030.E3, 0.0 50.E3, 0.2 *PLASTIC, RATE=1.0E-4 32.27E3, 0.0 53.79E3, 0.2 *PLASTIC, RATE=1.0E-3 33.60E3, 0.0 56.01E3, 0.2 Use the RATE parameter on Copyright 2006 ABAQUS, Inc. Metal Inelasticity in ABAQUS Use the RATE parameter on each occurrence of the *PLASTIC option to indicate the value of for the particular σ 0 being defined. plε&