ANSYS Mechanical Tips-Tricks - Radhakrishnan

28 Pages·2011·1.33 MB·English

ANSYS Mechanical
Tips & Tricks
Harish Radhakrishnan
1 © 2011 ANSYS, Inc. September 8, 2011
Material Library
Elastic
Plasticity
Linear /
Multilinear Isotropic / Kinematic
hardening
Hyperelastic
Drucker Prager
Cap Model
Viscoelastic
Mullins effect
Bergstrom-Boyce model
2 © 2011 ANSYS, Inc. September 8, 2011
Plasticity
UTS
Failure
Yield
Hardening Necking
  2   2   2 6 2  2  2
  xx yy yy zz zz xx xy yz zx
eq 2
Equivalent stress calculates Splits the stress to two components –
the distortional energy in the hydrostatic stress + deviatoric stress
material
No role!!! Causes plastic
yielding
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Hardening
Isotropic hardening
Kinematic hardening
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Plasticity….Multilinear hardening
F
Required for  
true A
modeling
current
F
UTS Available from
S 
Failure
experiments A
Yield
0
Hardening Necking
 
  S 1 e
true
 
 ln 1e
NOTE: Using Engineering stress
instead of true stress will cause
instabilities!!
5 © 2011 ANSYS, Inc. September 8, 2011
Modeling Contact in ANSYS
Contact definition requires three
Penetration occurs when contact
compatibility is not enforced. components
1. Normal behavior &Tangential
(sliding) behavior
2. Contact detection behavior
3. Formulation
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Penalty Method F  K x
normal contact penetration
• As K   , penetration goes
contact
to zero
Integration Point

Detection
• Large values of K lead to
contact
contact chattering – change the
Normal stiffness factor

• For highly Nonlinear materials
use update stiffness

• Consider Asymmetric contact
for dissimilar materials - ratio of
Young’s modulus is large
(>100)

7 © 2011 ANSYS, Inc. September 8, 2011
Other Contact formulations
•
In the Lagrange Method, we seek to solve for the constraint –
penetration is zero.
•
Lagrange multipliers are used to enforce the constraint – result in extra
degrees of freedom (DOF)
F
• Zero penetration
• Can be computationally
expensive

•
Augmented Lagrange Method uses the best of both worlds
• F  K x  pressure
Less sensitive to the value of contact stiffness
normal contact pentration

•
Multipoint Constraints (MPC) is for bonded contacts – ties the nodes
between the two surfaces
8 © 2011 ANSYS, Inc. September 8, 2011
General Tips on Modeling Contact
• A plateau in the force convergence plot could be attributed to large
contact stiffness
• MPC method is preferred over the Penalty method for bonded
contacts
• Plot the Newton-Raphson residuals to identify problem contact regions
• For contact between dissimilar materials, consider using
– Asymmetric contact
– Modeling the stiff body as rigid

9 © 2011 ANSYS, Inc. September 8, 2011
Contact Tool
• Keep track of contacts with large penetration -
Consider refining mesh

• If penetration is intended consider using Add
Offset with / without ramped effects
10 © 2011 ANSYS, Inc. September 8, 2011