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

Training Manual 00141915 Aug 2000

3.3-1

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.73.3 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


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.7

• 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


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.7Element 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


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• Cross-Section Mesh Refinement

– Available for common and custom sections• Refine with slider bar

• Refine by picking elements (EREFINE)


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• 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


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• 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


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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


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… 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.


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… 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


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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


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… 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


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… 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


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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


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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

Documents

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