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Nonlinear ElastoPlastic 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 elastoplastic 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 

MohrCoulomb 
 
MohrCoulomb 
65 
Isotropic 
Implicit backward Euler 
8 
Nonassociated 

DruckerPrager 
 
DruckerPrager 
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 (subincrementation) 
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/Length^{2}).
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 piecewiselinear 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
elastoplastic 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

