Nonlinear Elasto-Plastic Material Properties

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Nonlinear Elasto-Plastic Material Properties

Nonlinear material properties in LUSAS Modeller can be assembled by an appropriate combination of the elastic, plastic, creep, damage, etc. datasets. Details of the elasto-plastic material models available in LUSAS are presented in the following table.

Material Type	Model Name	Stress Potential Type	Yield Criteria	Model Number	Hardening Type	Stress Return Method	Different Tensile & Compressive Yield Stress?	Flow Rule
Isotropic	Stress Resultant	-	von Mises (plastic moment)	29	Isotropic	N/A	8	Associated
	Tresca	-	Tresca	61	Isotropic	Explicit forward Euler	8	Associated
	Stress Potential	von Mises	von Mises	72	Isotropic	Implicit backward Euler	8	Associated
		Modified von Mises	von Mises	77	Nonlinear isotropic	Implicit backward Euler	4	Associated
	Optimised Implicit von Mises	-	von Mises	75	Isotropic/ Kinematic	Steepest Descent (radial return)	8	Associated
	Mohr-Coulomb	-	Mohr-Coulomb	65	Isotropic	Implicit backward Euler	8	Non-associated
	Drucker-Prager	-	Drucker-Prager	64	Isotropic	Explicit forward Euler	8	Associated
	Cracking Concrete	-	Cracking Concrete	82	Isotropic	Implicit backward Euler	8	Associated
Orthotropic	Stress Potential	Hill	Hill	76	Nonlinear isotropic	Implicit backward Euler	8	Associated
		Hoffman	Hoffman	78	Nonlinear isotropic	Implicit backward Euler	4	Associated
Specialised	Interface	-	von Mises (normal) Mohr Coulomb (shear	26, 27	Isotropic	Steepest Descent (sub-incrementation)	8	Associated

Notes:

See the LUSAS Theory Manual I ("Chapter 4.0: Constitutive Models" section) for more information on the terms used in the table
The stress return methods used for each material model cannot be manipulated. They are embedded in the material model
The column title "Different Yield Stress in Tension and Compression" means that not only is the specified yield stress assumed the same, but also any hardening characteristics
The kinematic input units are the same as those for the isotropic hardening (Force/Length²). Kinematic hardening not a parameter defined between 0 and 1, it is a kinematic hardening tangent and is available from experimental testing
Search for "Isotropic/Orthotropic Material Definition" in the online help for more general information on these material models
It is not possible to input a mathematical curve tp specify a nonlinear hardening response. Most of the models do, however, accept a piecewise-linear input
Note that, when the hardening behaviour is specified as a gradient, both the isotropic and kinematic hardening parameter need to be converted from the elasto-plastic modulus, Ep, to the slope of the uniaxial yield stress against equivalent plastic strain curve. Search for "Nonlinear Material Hardening Convention" in the online help for more information

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