3.3 Element Technology

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NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
1

3.3 Element Technology

Overview
:


In this chapter, we will present a brief overview to
the following topics:

A. Beam Enhancements

1. Cross
-
Section Mesh Refinement

2. Built
-
Up Sections

3. Plasticity

B. Mixed U
-
P Formulations

C. Pressure Load Stiffness

D. 20
-
Noded Layered Solid

E. Initial Stress

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
2


Cross
-
Section Enhancements


Shear center, warping rigidity and
shear correction factors

are calculated for all sections, including user mesh


No hard limits on section size (number of section cells)


Cross
-
section mesh refinement


Needed for accurate shear correction factors & direct shear
stress calculations


Built
-
up (multi
-
material) cross
-
sections


Applications:


sandwich beams


airfoils


MEMS


reinforced beams

Element Technology

A. Beam Enhancements

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
3

Element Technology

… Beam Enhancements


Transformed section method is used for multi
-
material cross sections


Sparse solver used for efficient section solution


Extensive material library


Orthotropic elasticity, BISO, MISO, BKIN, MKIN, KINH,
NLISO, Creep, Chaboche, Rate Dependent plasticity, User
material


Initial Stresses supported for built
-
up beams


assign initial stress based on the cell material number


3D post processing (/ESHAPE, /EFACET)


visualization of direct shear stress

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
4

Element Technology

… Beam Enhancements


Cross
-
Section Mesh Refinement


Available for common and custom sections


Refine with slider bar


Refine by picking elements (EREFINE)

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
5

Element Technology

… Beam Enhancements


Built
-
Up Sections for BEAM188 and BEAM189


Ability to specify a cross
-
section made up of different
materials (EMODIF)


Available for common and custom sections

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
6

Element Technology

… Beam Enhancements


Plasticity for BEAM188 and BEAM189


At revision 5.6, the treatment of material nonlinearities at
the section points is based on uncoupled behavior
between the stress components


Axial and the torsional shear stress components behave
independently


As a result of this approximation, the equivalent stress output
by PRSSOL may at times exceed yield stress and yet no active
yielding is reported


At revision 5.7, the
actual

state of stress within the beam is
used to perform the plasticity calculation


The new formulation will release the restriction on the beam
elements of handling complete state of stress in plasticity and
will provide more realistic state of stress in the beam elements

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
7

Element Technology

B. Mixed U
-
P Formulations


Mixed U
-
P formulation option added to elements:
PLANE182, PLANE183, SOLID185, SOLID186, SOLID187


Includes hydrostatic pressure as an independent DOF


Applications


hyper
-
elastic materials (typically fully incompressible)


elasto
-
plastic materials undergoing large plastic strains


linear elastic materials with Poisson’s ratio > 0.4999


Advantage
-

better convergence and more robust


Disadvantages


Additional DOF’s
(longer solution time per equilibrium iteration)



Does not support modal and buckling analyses

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
8

Element Technology

… Mixed U
-
P Formulations


Activation


keyopt(6) = 0, regular formulation (default)


keyopt(6) = 1 (or 2 for SOLID187), mixed U
-
P formulation


The solver (EQSLV command) must be either the frontal solver
(default) or the sparse solver
-

(frontal is recommended)


Internal nodes used for pressure DOF’s


Created automatically


Not accessible by user


*** NOTE *** CP= 54.625 TIME= 14:28:22


Internal nodes from 2360 to 3831 are created.


1472 internal nodes are used for 18x elements with mixed formulation.

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
9

Element Technology

… Mixed U
-
P Formulations


The examples below were solved with mixed U
-
P
formulations

Inflation and pinch flat of
a bicycle tire

Inflation of a
hyperelastic membrane

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
10

Element Technology

C. Pressure Load Stiffness


Pressure load stiffness option added to elements:
PLANE2, PLANE42, SOLID45, SOLID46, SOLID64, SOLID65, PLANE82, VISCO88, VISCO89,
SOLID92, SOLID95, SURF153, PLANE182, PLANE183, SOLID185, SOLID186, SOLID187


Benefits models with element pressure loads


Improved convergence for large deflection analyses


Improved accuracy for linear buckling analyses


New options on existing commands:


Pressure load stiffness controlled by a new field (
Key3
) on
the SOLCONTROL command


Unsymmetric stiffness matrix controlled by a new
Option

on
the NROPT command

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
11

Element Technology

… Pressure Load Stiffness


SOLCONTROL
,
Key1
,
Key2
,
Key3



Key3

=
NOPL


Do not include pressure load stiffness for any elements


Key3

=
no entry (default)


Include pressure load stiffness for elements
SURF153, SURF154, SHELL181,
PLANE182, PLANE183, SOLID185, SOLID186, SOLID187, BEAM188, and BEAM189


Do not include pressure load stiffness for elements
PLANE2, PLANE42,
SOLID45, SOLID46, SOLID64, SOLID65, PLANE82, VISCO88, VISCO89, SOLID92, SOLID95, and SOLID191


Key3

=
INCP


Include pressure load stiffness for elements
PLANE2, PLANE42, SOLID45,
SOLID46, SOLID64, SOLID65, PLANE82, VISCO88, VISCO89, SOLID92, SOLID95, SURF153, SURF154, SHELL181,
PLANE182, PLANE183, SOLID185, SOLID186, SOLID187 BEAM188, BEAM189, and SOLID191

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
12

Element Technology

… Pressure Load Stiffness


NROPT
,
Option
,
--
,
Adptky


Option

=
UNSYM


Use full Newton
-
Raphson with unsymmetric matrices of
elements where the unsymmetric option exists


If an unsymmetric matrix is needed for pressure load
stiffness effects, use NROPT,UNSYM


For analyses involving friction, using NROPT,UNSYM is
useful (and, in fact, sometimes required) for problems
where the normal and tangential (sliding) motions are
strongly coupled, such as in a wedge insertion problem


You should first try NROPT,FULL; then try NROPT,UNSYM
if you experience convergence difficulties

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
13

Element Technology

D. 20
-
Noded Layered Solid


New element: SOLID191

3D 20
-
Noded
Layered

Structural Solid


Enhances element library for composites


Uses SHELL91 data structure


stable, fully integrated


Uses SOLID95 displacement shapes


Better accuracy for curved boundaries


Input similar to SOLID46


Includes stress stiffening capability


Does not support nonlinear materials or large deflections

NEW FEATURES 5.7

Training Manual 001419

15 Aug 2000

3.3
-
14

Element Technology

E. Initial Stress


Enhancements made to Initial Stress loading


New commands


ISTRESS


Defines a set of initial stress values


ISWRITE


Determines whether an initial stress file is written (or not)


New options


Ability to apply initial stresses only to specified materials


Existing command


ISFILE


Reads an initial stress state from a file into ANSYS


Lists initial stresses


Deletes initial stresses