ANSYS Workbench Static

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Training Manual

Linear Stat ic Structu ral Analysis

February 2, 2004

Inventory #002010

4-2

Chapter Overview

•

In this chapter, performing linear static structural analysesin Design Simulation will be covered:

– Geometry and Elements

– Contact and Types of Supported Assemblies

– Environment, including Loads and Supports

– Solving Models

– Results and Postprocessing

• The capabilities described in this section are generally

applicable to ANSYS DesignSpace Entra licenses andabove.

– Some options discussed in this chapter may require more

advanced licenses, but these are noted accordingly.

– Modal, harmonic, and nonlinear static structural analyses are

not discussed here but in their respective chapters.


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Basics of L inear Stat ic Analysis

•

For a linear static structural analysis, the displacements {x}are solved for in the matrix equation below:

This results in certain assumptions related to the analysis:

– [K] is essentially constant

• Linear elastic material behavior is assumed

• Small deflection theory is used

• Some nonlinear boundary conditions may be included

– {F} is statically applied

• No time-varying forces are considered

• No inertial effects (mass, damping) are included

• It is important to remember these assumptions related to

l inear static analysis. Non linear static and dynamic

analyses are covered in later chapters.

F x K


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A. Geometry

•

In structural analyses, all types of bodies supported byDesign Simulation may be used.

• For surface bod ies , thickness must be

supplied in the “Details” view of the

“Geometry” branch.

• The cross-section and orientation of l ine bod ies is defined

within DesignModeler and is imported into Design

Simulation automatically.

– For line bodies, only displacement results are available.

ANSYS License Availability

DesignSpace Entra x

DesignSpace x

Professional xStructural x

Mechanical/Multiphysics x


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… Elements Used

•

In Design Simulation, the following elements are used: – Solid bodies are meshed with 10-node tetrahedral or 20-node

hexahedral elements

• SOLID187 and SOLID186

– Surface bodies are meshed with 4-node quad shell elements

•

SHELL181 using real constants• Section definition (and offsets) are not used

– Line bodies are meshed with 2-node beam elements

• BEAM188 (with 3rd orientation node)

• Section definition and offsets are supported

Advanced ANSYS Details


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… Material Properties

•

The required structural material properties are Young’sModulus and Poisson’s Ratio for linear static structural

analyses

– Material input is under the “Engineering Data” branch, and

material assignment is per part under the “Geometry” branch

– Mass densi ty is required if any inertial loads are present

– Thermal expansio n coeff ic ient and thermal cond uct iv i ty are

required if any thermal loads are present

• Thermal loading not available with an ANSYS Structural license

– Stress Lim i ts are needed if a Stress Tool result is present

–Fatigue Propert ies are needed if Fatigue Tool result is present• Requires Fat igue Modu le add-on license

– Specific loading and result tools will be discussed later


DesignSpace Entra x

DesignSpace x

Professional xStructural /



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B. Assemb l ies – Sol id Body Contact

•

When importing assemblies of solid parts, contact regionsare automatically created between the solid bodies.

– Surface-to-surface contact allows non-matching meshes at

boundaries between solid parts

– Tolerance controls under “Contact” branch allows the user to

specify distance of auto contact detection via slider bar


DesignSpace Entra

DesignSpace x




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… Assemblies – Sol id Body Contact

•

In Design Simulation, the concept of contact and target surfaces are used for each contact region.

– One side of the contact region is comprised of “contact”

face(s), the other side of the region is made of “target” face(s).

– The integration points of the contact surfaces are restricted

from penetrating through the target surfaces (within a given

tolerance). The opposite is not true, however.

• When one side is the contact and the other side is the target, this

is called asymmetr ic contac t . On the other hand, if both sides are

made to be contact & target, this is called symmetr ic co ntac t since

neither side can penetrate the other.

•

By default, Design Simulation usessymm etr ic contac t for solid assemblies.

For ANSYS Professional licenses and

above, the user may change to asymmetric

contact, as desired.


DesignSpace Entra

DesignSpace /




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•

Four contact types are available:

– Bonded and No Separation contact are basically

linear behavior and require only 1 iteration

– Frict ionless and Rough contact are nonlinear

and require multiple iterations. However, no te

that small def lect ion theory is s t i l l assumed.

• When using these options, an interface treatment

option is available, set either as “Actual Geometry (and Specified Offset)” or “Adjusted to Touch.”

The latter allows the user to have ANSYS close the

gap to ‘just touching’ position.


DesignSpace Entra

DesignSpace x



Contact Type Iterations Normal Behavior (Separation) Tangential Behavior (Sliding)

Bonded 1 Closed Closed

No Separation 1 Closed Open

Frictionless Multiple Open Open

Rough Multiple Open Closed


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•

For the advanced user, some of thecontact options can be modified

– Formulation can be changed from “Pure

Penalty” to “Augmented Lagrange” or “MPC”.

• “MPC” is applicable to bonded contact only

• “Augmented Lagrange” is used in regular ANSYS

– In bonded contact, the pure Penalty method canbe thought of as adding very high st i f fness

between interface of parts to prevent relative

movement. This results in negligible relative

movement between parts at contact inter face .

– MPC formulation writes con straint equat ions

relating movement of parts at interface , so norelative movement occurs. This is sometimes

an attractive alternative to penalty method.


DesignSpace Entra

DesignSpace




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•

Advanced options (continued): – As explained in Chapter 3, the pinball

region can be input and visualized

• The pinball region defines location of near-

f ield open co ntact . Outside of the pinball

region is far-f ield open con tact .

• Originally, the pinball region was meant tomore efficiently process contact searching,

but this is also used for other purposes,

such as bonded contact

• For bond ed or no separat ion co ntact , i f gap

or penetrat ion is sm al ler than pinbal l region,

the gap/penetrat ion is autom atical lyexcluded

– Other advanced contact options will be

discussed in later chapters.


DesignSpace Entra

DesignSpace



In this case, the gap between

the two parts is bigger than the

pinball region, so no automatic

gap closure will be performed.


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• Internally, the solid face contact regions are modeled in

ANSYS as CONTA174 and TARGE170 elements

– By default, pure penalty method is used with relative contact

stiffness of 10 with symmetric contact pairs being generated

– For bonded and no separation contact, any geometric

penetration or gap is ignored i f wi th in the pinbal l region .

– For frictionless and rough contact, considering “actualgeometry” makes any initial gap or penetration ramped

whereas “adjust to touch” closes gap with auto CNOF

– NEQIT is set to 1 for if only bonded or no separation contact

exist; it is set higher otherwise (15-40, depending on model).

Contact Type KEYOPT(2) KEYOPT(5) KEYOPT(9) KEYOPT(12)

Bonded 1 0 1 5

No Separation 1 0 1 4

Frictionless, Actual Geometry 1 0 2 0

Frictionless, Adjusted to Touch 1 1 1 0

Rough, Actual Geometry 1 0 2 1

Rough, Adjusted to Touch 1 1 1 1



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… Assemblies – Surface Body Con tact

• For ANSYS Profess ional 1 licenses and above, mixed

assemblies of shells and solids are supported

– Allows for more complex modeling of assemblies, taking

advantage of the benefits of shells, when applicable

– More contact options are exposed to the user

–

Contact postprocessing is also available (discussed later)


DesignSpace Entra

DesignSpace

Professional x1

Structural x

Mechanical/Multiphysics x 1 For ANSYS Professional, surface contact supported with ANSYS 8.0 Service Pack 1 and above


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• Edge contact is a subset of general contact

– For contact including shell faces or solid

edges, only bonded or no separation

behavior is allowed.

– For contact involving shell edges, only

bonded behavior using MPC formulation is

allowed.

• For MPC-based bonded contact, user can set

the search direction (the way in which the

multi-point constraints are written) as either

the target norm al or pinbal l region .

• If a gap exists (as is often the case with

shell assemblies), the pinbal l region can be

used for the search direction to detect

contact beyond a gap.


DesignSpace Entra

DesignSpace

Professional x1Structural x



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• Internally, any contact including an edge (solid body edge

or surface edge) results in asymmetric contact with

CONTA175 for the edge and TARGE170 for the edge/face

– Contact involving solid edges default to pure penalty method

– Contact involving surface edges use MPC formulation.

Instead of “target normal,” if search direction is “pinball

region,” KEYOPT(5)=4 set on companion TARGE170 element.

– For bonded contact (default), both use KEYOPT(12)=5 and

KEYOPT(9)=1.

• For surface faces in contact with other

faces, standard surface-to-surfacecontact is used, namely CONTA174

and TARGE170Example of Design Simulation-

generated edge-to-edge

contact, which results in

CONTA175 on one edge and

TARGE170 on the other.Advanced ANSYS Details


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… Assemblies – Contact Summary

• A summary of contact types and options available in

Design Simulation is presented in the table below:

– This table is also in the Design Simulation online help.

Referring to this table will aid in determining what options areavailable to the user.


DesignSpace Entra

DesignSpace /



Contact Geometry Solid Body Face Solid Body Edge Surface Body Face Surface Body Edge

All types Bonded, No Separation Bonded, No Separation Bonded only

All formulations All formulations All formulations MPC formulation

Symmetry respected Asymmetric only Symmetry respected Asymmetric only

Bonded, No Separation Bonded, No Separation Bonded only

All formulations All formulations MPC formulation

Asymmetric only Asymmetric only Asymmetric onlyBonded, No Separation Bonded only

All formulations MPC formulation

Symmetry respected Asymmetric only

Bonded only

MPC formulation

Asymmetric only

Solid Body Face

Solid Body Edge

Surface Body Face

Surface Body Edge


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… Assemblies – Spot Weld

• Spot welds provide a means of connecting shell assemblies

at discrete points

– For ANSYS DesignSpace licenses, shell contact is not

supported, so spotwelds are the only way to define a shell

assembly.

– Spotweld definition is done in the CAD software. Currently,

only DesignModeler and Unigraphics define spotwelds in a

manner that Design Simulation supports.

– Spotwelds can also be created in

Design Simulation manually, but

only at discrete vertices.

ANSYS License AvailabilityDesignSpace Entra

DesignSpace Structural x

DesignSpace x

Professional x

Structural x


DesignModeler x

Pro/ENGINEER

Unigraphics x

SolidWorks

Inventor

Solid Edge

Mechanical Desktop

CATIA V4

CATIA V5

ACIS (SAT)Parasolid

IGES


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… Assemblies – Spot Weld

• Internally, spot welds are defined as a set of BEAM188

elements. The spot weld is defined with one beam element,

and the top and bottom of the spot weld is connected to the

shell or solid elements with a ‘spider web’ of multiple

beams.

– The BEAM188 elements use

same material properties as

underlying materials but

with an appropriate circular

cross-section with radius=

5*thickness of underlying

shells

– Figure on right shows spot-

welds between two sets of

shell elements, which are

made translucent for clarity.



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C. Loads and Suppo rts

• There are four types of structural loads available:

– Inertial loads

• These loads act on the entire system

• Density is required for mass calculations

– Structural Loads

•

These are forces or moments acting on parts of the system – Structural Supports

• These are constraints that prevent movement on certain regions

– Thermal Loads

• Structurally speaking, the thermal loads result in a temperature

field, which causes thermal expansion on the model.


DesignSpace Entra x

DesignSpace x

Professional x

Structural /



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… Acceleration & Gravity

• An acceleration can be defined on the system

– Acceleration acts on entire model in length/time2 units.

– Users sometimes have confusion over notation of direction. If

acceleration is applied to system suddenly, the inertia resists

the change in acceleration, so the inertial forces are in the

oppos i te direction to applied acceleration

– Acceleration can be defined by Components or Vector

• Standard Earth Gravity can also be applied as a load

– Value applied is 9.80665 m/s2 (in SI units)

– Standard Earth Gravity direction can only be defined along

one of three World Coordinate System axes.

– Since “Standard Earth Gravity” is defined as an acceleration,

define the direction as opposite to gravitational force, as noted

above.


DesignSpace Entra x

DesignSpace x




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… Rotational Velocity

• Rotational velocity is another inertial load available

– Entire model spins about an axis at a given rate

– Can be defined as a vector, using geometry for axis and

magnitude of rotational velocity

– Can be defined by components, supplying origin and

components in World Coordinate System

– Note that location of axis is very important since model spins

around that axis.

– Default is to input rotational velocity in radians per second.

Can be changed in “Tools > Control Panel > Miscellaneous >

Angular Velocity” to revolutions per minute (RPM) instead.


DesignSpace Entra x

DesignSpace x




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… Inertial Loads in ANSYS

• Inertial loads are modeled in ANSYS as follows:

– Acceleration and Standard Earth Gravity are represented via

ACEL command

– Rotational velocity is defined via CGLOC (defines origin) and

CGOMGA (defines rotational velocity about CGLOC)



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… Forces and Pressures

• Pressure loading:

– Pressures can only be applied to surfaces and always act

normal to the surface

– Positive value acts into surface (i.e., compressive)

negative value acts outward from surface (i.e., suction)

– Units of pressure are in force per area

• Force loading:

– Forces can be applied on vertices, edges, or surfaces.

– The force will be distr ib uted on al l ent i t ies . This

means that if a force is applied to two identical

surfaces, each surface will have half of the forceapplied. Units are mass*length/time2

– A force is defined via vector and magnitude or by

components


DesignSpace Entra x

DesignSpace x




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… Bolt Load

• Bolt Load:

– A bolt load is for cylindrical surfaces only. Radial component

will be distributed on compressive side using projected area.

Example of radial component distribution shown below.

Axial component is distributed evenly on cylinder.

– Use only one bolt load per cylindrical surface. If the

cylindrical surface is split in two, however, be sure to selectboth halves of cylindrical surface when applying a bolt load.

– Load is in units of force

– Bolt load can be defined via

vector and magnitude or by

components.


DesignSpace Entra x

DesignSpace x

Professional x

Structural x



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… Moment Load

• Moment Load:

– For solid bodies, a moment can be applied on any

surface

– If multiple surfaces are selected, the moment load

gets apportioned about those selected surfaces

– A vector and magnitude or components can define the

moment. The moment acts about the vector using the right-

hand rule

– For surface bodies, a moment can also be applied to a vertex

or edge with similar definition via vector or components as

with a surface-based moment

– Units of moment are in Force*length.


DesignSpace Entra x

DesignSpace x

Professional x

Structural x



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… Remote Load

• Remote Load:

– Allows the user to apply an offset force on a surface

– The user supplies the origin of the force (using vertices, a

cylinder, or typing in (x, y, z) coordinates)

– The force can then be defined by vector and magnitude or by

components

– This results in an equivalent force on the surface plus a

moment caused by the moment arm of the offset force

– The force is distributed on the surface

but includes the effect of the moment

arm due to the offset of the force

– Units are in force (mass*length/time2)


DesignSpace Entra x

DesignSpace x

Professional x

Structural x



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… Structural Loads in ANSYS

• Structural loads are modeled in ANSYS as follows:

– Pressures are applied directly on surfaces via SF,,PRES

– Forces on vertices and edges are applied as nodal loads via

F,,FX/FY/FZ

– Forces on surfaces are applied as pressures on face 5 of

surface effect elements SURF154 with KEYOPT(11)=2

• KEYOPT(11)=2 to use full area, including tangential component

– Bolt loads are applied as pressures on face 5 of surface effect

elements SURF154 along compressive half of cylinder

• KEYOPT(11)=0 uses projected area w/ tangential component

– Moments on vertices or edges of shells are applied as nodal

loads via F,,MX/MY/MZ



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… Structural Loads in ANSYS

• Moment load on surface is defined by surface constraint

– Surface constraint is RBE3-type of distributed loading

– Pilot node at surface CG defined by TARGE170 with

KEYOPT(2)=1 and KEYOPT(4)=xxx000

– Surface is defined by CONTA174 with KEYOPT(2)=2,

KEYOPT(4)=1, KEYOPT(12)=5

– Moment applied as nodal load on pilot node

• Remote force load is defined by surface constraint

– Surface constraint is RBE3-type of distributed force

– Pilot node at force origin defined by TARGE170 with

KEYOPT(2)=1 and KEYOPT(4)=000xxx

– Surface is defined by CONTA174 with KEYOPT(2)=2,

KEYOPT(4)=1, KEYOPT(12)=5

– Force applied as nodal load on pilot node



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… Supports (General)

• Fixed Support:

– Constraints all degrees of freedom on vertex, edge, or surface

– For solid bodies, prevents translations in x, y, and z

– For surface and line bodies, prevents translations and

rotations in x, y, and z

• Given Displacement:

– Applies known displacement on vertex, edge, or surface

– Allows for imposed translational displacement in x, y, and z

– Entering “0” means that the direction is constrained

–

Leaving the direction blank means that the entity is free tomove in that direction


DesignSpace Entra x

DesignSpace x

Professional x

Structural x



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… Supports (Solid Bodies)

• Frictionless Support:

– Applies constraint in normal direction on surfaces

– For solid bodies, this support can be used to apply a

‘symmetry’ plane boundary condition since ‘symmetry’ plane

is same as normal constraint

•Cylindrical Constraint: – Applied on cylindrical surfaces

– User can specify whether axial, radial, or tangential

components are constrained

– Suitable for small-deflection (linear) analysis only


DesignSpace Entra x

DesignSpace x

Professional x

Structural x



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… Supports (Solid Bodies)

• Compression Only Support:

– Applies a compression-only constraint normal to any given

surface. This prevents the sur face to move in the po si t ive

normal direct ion on ly .

– A way to think of this support is to imagine a ‘rigid’ structure

which has the same shape of the selected surface. Note that

the con tact ing (compressiv e) areas are not known beforehand.

– Can be used on a cylindrical surface to model a

“Pinned Cylinder Support”, which was available

in 7.1 but is a special case of the “Compression

Only Support”. Notice the example on the right,

where the outline of the undeformed cylinder isshown. The compressive side retains the shape

of the original cylinder, but the tensile side is free to deform.

– This requ ires an iterat ive (nonl in ear) so lut ion .

• Compressive behavior is not known a pr ior i , so an iterative

solution is required to determine what sides exhibit

compressive behavior.


DesignSpace Entra x

DesignSpace x

Professional x

Structural xMechanical/Multiphysics x


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… Supports (Line/Surface Bodies)

• Simply Supported:

– Can be applied on edge or vertex of surface or line bodies

– Prevents all translations but all rotations are free

• Fixed Rotation:

– Can be applied on surface, edge, or vertex of surface or line

bodies

– Constrains rotations but translations are free


DesignSpace Entra x

DesignSpace x

Professional x

Structural x



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… Structural Supports in ANSYS

• The following are applied internally in ANSYS:

– Fixed support constraints result in D,,ALL for given entity

– Given displacement is D,,UX/UY/UZ for specified direction

– Frictionless surface involves nodal rotation such that UX is in

normal direction, and D,,UX is applied

–

Cylindrical constraint rotates nodal coordinates in cylindricalCS and constrains appropriate direction with D,,UX/UY/UZ

– Simply supported constraints apply D on UX, UY, and UZ on

shells or beams

– Fixed rotation constraints apply D on ROTX, ROTY, and ROTZ

on shells or beams

– For compression-only supports, the surface mesh is copied to

form a rigid target surface (TARGE170) on top of the original

surface (CONTA174). Standard contact behavior is used to

model this support, and that is why it is a nonl inear solution.



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… Summary of Supports

• Suppor ts and Contact Regions may both be thought of as

being boundary con d i t ions .

– Contact Regio ns provides a ‘flexible’ boundary condition

between two existing parts explicitly modeled

– Suppor ts provide a ‘rigid’ boundary condition between the

modeled part an a rigid, immovable part not explicitly modeled

• If Part A, which is of interest, is connected to Part B,

consider whether both parts need to be analyzed (withcontact) or whether supports will suffice in providing the

effect Part B has on Part A.

– In other words, is Part B ‘rigid’ compared to Part A? If so, a

support can be used and only Part A modeled. If not, one may

need to model both Parts A and B with contact.

Type of Support Equivalent Contact Condition at Surfaces of Part

Fixed Support Bonded contact with a rigid, immovable part

Frictionless Support No Separation contact with a rigid, immovable part

Compression Only Support Frictionless contact with a rigid, immovable part


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… Thermal Loading

• Temperature causes thermal expansion in the model

– Thermal strains are calculated as follows:

where is the thermal expansion coefficient (CTE), T ref is the

reference temperature at which thermal strains are zero, T is

the applied temperature, and eth is the thermal strain. – Thermal strains do not cause stress by themselves. It is the

constraint, temperature gradient, or CTE mismatch that

produce stress.

– CTE is defined in the “Engineering” branch

and has units of strain per temperature

– The reference temperature is defined in the

“Environment” branch

ref

z

th

y

th

x

th T T a e e e


DesignSpace Entra x

DesignSpace x

Professional x

Structural



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… Thermal Loading

• Thermal loads can be applied on the model

– Any temperature loading can be applied (see Chapter 6 on

Thermal Analysis for details)

– Design Simulation will always perform a thermal solution first,

then use the calculated temperature field as input when

solving the structural solution.


DesignSpace Entra x

DesignSpace x

Professional x

StructuralMechanical/Multiphysics x


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… Thermal Loading in ANSYS

• In ANSYS, for any thermal loads present in the model:

– ANSYS will always solve a thermal solution first

• Even if a uniform temperature field is applied, a thermal solution

will be performed. This is why temperature body loads in a

structural analysis is not possible with an ANSYS Structural

license.

– Reference temperature is defined with TREF (not MP,REFT) – Coefficient of thermal expansion per material is supplied with

MP,ALPX (not MP,CTEX or MP,THSX)

– Temperature loading is input via BF commands after thermal

solution



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… Solution Options

– Weak springs can be added to stabilize model

• If “Program Controlled” is set, Design Simulation

tries to anticipate under-constrained models. If no

“Fixed Support” is present, it may add weak springs

and provide an informative message letting the user

know that it has done so

• This can be set to “On” or “Off”. To set the default

behavior, go to “Tools > Control Panel > Solution> Use Weak Springs”.

• In some cases, the user expects the model to be in

equilibrium and does not want to constrain all

possible rigid-body modes. Weak springs will help

by preventing matrix singularity.

• It is good practice to constrain all possible rigid-bodymotion, however.


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… Solution Options

– Informative messages are also present:

• The type of analysis is shown, such as “Static

Structural” for the cases described in this section.

• If a nonlinear solution is required, it will be indicated

as such. Recall that for some contact behavior and

compression-only support, the solution becomes

nonlinear. These type of solutions require multiple

iterations and take longer than linear solutions.

• The solver working directory is where scratch files

are saved during the solution of the matrix equation.

By default, the TEMP directory of your Windows

system environment variable is used, although this

can be changed in “Tools > Control Panel > Solution

> Solver Working Directory”. Sufficient free space must be on that partition.

• Any solver messages which appear after solution

can be checked afterwards under “Solver Messages”


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… Solving the Model

• To solve the model, request resu lts f i rst (covered next) and

click on the “Solve” button on the Standard Toolbar

– By default, two processors (if present) will be used for parallel

processing. To set the number of processors, use “Tools >

Control Panel > Solution > Number of Processors to Use”

– Recall that under “Worksheet” tab of the “Solution” branch,

the details of the solution output can be examined.


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… Solution Options in ANSYS

• The solver selection for direct vs. iterative:

– The solvers used are either the direct sparse solver

(EQSLV,SPARSE) or the PCG solver (EQSLV,PCG)

– A simplified discussion between the two solvers:• If given the linear static case of [K]{x} = {F}, Direct solvers factorize [K] to solve for [K]-1.

Then, {x} = [K]-1{F}.

–

This factorization is computationally expensive but is done once.• Iterative solvers use a preconditioner [Q] to solve the equation [Q][K]{x} = [Q]{F}. Assume

that [Q] = [K]-1. In this trivial case, [I]{x} = [K]-1{F}. However, the preconditioner is not

usually [K]-1. The closer [Q] is to [K]-1, the better the preconditioning is, and this process

is repeated - hence the name, i terat ive solver .

– For iterative solvers, matrix multiplication (not factorization) is

performed. This is much faster than matrix inversion if done entirely in

RAM, so, as long as the number of iterations is not very high (which

happens for well-conditioned matrices), iterative solvers can be moreefficient than sparse solvers.

– The main difference between the iterative solvers in ANSYS — PCG,

JCG, ICCG — is the type of pre-condit ioner used.



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• Weak spring option:

– If used, weak springs are added to the mesh. These are

modeled with COMBIN14 with small stiffness and added to the

extreme dimensions of the part.

• Solver working directory:

–The ANSYS input file is written as “ds.dat” in the solverdirectory. The output file is “solve.out” and can be viewed in

the “Worksheet” tab of the “Solution” branch.

– ANSYS is executed in batch mode (-b) as a separate process.

During solution, the results file .rst is written. The results are

also read in and XML results files are generated in batch

mode. The XML files are then read into Design Simulation.

– All associated ANSYS files have default jobname of “file” and

are deleted after solution, unless changed in “Tools > Control

Panel > Solution > Save Ansys Files”.



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• Various defaults in ANSYS are turned off when solving in

Design Simulation:

– Solution control (SOLCON,OFF) is turned off

– Multiframe restart is turned off (RESCON,,NONE)

– ANSYS shape checking is turned off (SHPP,OFF)

–

Number of equilibrium iterations (NEQIT) is set to 1 if contactis not present or if all contact is bonded or no separation.

• Otherwise, it is automatically determined, such as NEQIT,20

(frictionless contact) or NEQIT,40 (rough contact). NSUBST,1,10,1

is also set in these cases.

– Only requested results is output with OUTRES, not everything

by default

• Results are later written to XML files in /POST1, which are then

read back into Design Simulation. Hence, Design Simulation does

not directly read the results from the .rst file



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E. Resu l ts and Postpro cessing

• Various results are available for postprocessing:

– Directional and total deformation

– Components, principal, or invariants of stresses and strains

– Contact output

• Requires ANSYS Professional and above

–

Reaction forces

• In Design Simulation, results are usually requested before

solving, but they can be requested afterwards, too.

– If you solve a model then request results afterwards, click onthe “Solve” button , and the results will be retrieved. A

new solution is not required i f that type of result h as been

requested previously (i.e., total deformation was requested

previously but now direction deformation is added).


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… Plotting Results

• All of the contour and vector plots are usually shown on the

deformed geometry. Use the Context Toolbar to change the

scaling or display of results to desired settings.


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… Deformation

• The deformation of the model can be plotted:

– Total deformation is a scalar quantity:

– The x, y, and z components of deformation can be

requested under “Directional.” Because there is

direction associated with the components, if a

“Coordinate System” branch is present, users can

request deformation in a given coordinate system.

• For example, it may be easier to interpret displacement for a

cylindrical geometry in a ‘radial’ direction by using a cylindrical

coordinate system to display the result.

– Vector plots of deformation are available.

Recall that wireframe mode is the easiest

to view vector plots.

222

z y xtotal U U U U


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Li St t i St t l A l i


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… Deformation

• Deformation results are available for line, surface, and solid

bodies

– Note that “deformation results” are associated with

translational DOF only. Rotations associated with the DOF of

line and surface bodies are not directly viewable

– Because deformation (displacements) are DOF which Design

Simulation solves for, the convergence behavior is well-behaved when using the Convergence tool

– Vector deformation plots cannot use“Alert” or “Convergence”

tools because they are vector quantities (x, y, z) rather than a

unique quantity (x or y or z). Use Alert or Convergence tools

on “Total” or “Directional” quantities instead. – “Total” deformation is an invariant, so “Coordinate Systems”

cannot be used on this result quantity. Also, “Vector”

deformation is always shown in the world coordinate system.


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… Stresses and Strains

• Stresses and strains can be viewed:

– “Strains” are actually elastic strains

– Stresses and (elastic) strains are

tensors and have six components

(x, y, z, xy, yz, xz) while thermal

strains can be considered a vector

with three components (x, y, z)

– For stresses and strains, components can be

requested under “Normal” (x, y, z) and “Shear” (xy, yz, xz).

For thermal strains, components are under “Thermal”

• Can request in different results coordinate systems

•Not available with an ANSYS Structural license

• Only available for shell and solid bodies. Line bodies currently do

not report any results except for deformation.


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… Stresses and Strains

• Safety Factors can be used to evaluate designs:

– Because stress is a tensor, it is hard to evaluate

the response of the system by looking solely at

stress components

– The “Stress Tool” allows the user to

have Design Simulation calculate

scalar results related to factors ofsafety

– In the next slides, stress results will

be discussed, along with different

criteria of evaluating material response,

as available from the Stress Tool.

– The “Stress Tool” branch controls

what theory will be used and what

type of stress limit will be used.


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… Principal Stresses

• Principal Stresses and Strains:

– From basic mechanics review, the stress tensor can

be rotated such that only normal stresses appear.

These are the three pr inc ipal stresses s1 < s2 < s3.

– Principal values of stress and strain results can be requested.

The three principal values also have direction associated with

them, and a “Vector Principal” output can be selected. • Principal values can be exported to Excel with Euler angles

– In the example shown on the right, one

can easily see the three principal

stresses (white=max, blue=min). From

this, one can see that the part is under-going bending with one side in tension

and the other in compression.


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Linear Stat ic Str ct ral An al sis


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• Maximum Tensile Stress Theory:

– The maximum tensi le st ress theory can be used for the

“Stress Tool”. It utilizes the maximum principal stress and is

generally suitable for brittle materials.

– The criterion can be thought of as the following:

where st is the ultimate (or yield) tensile strength

– If plotted in two-dimensional principal stress space, the failuresurface results in a square as shown below. A stress state

lying inside the square is assumed to be fine but any stress

state lying on the edges of the square will fail.

– The max tensile stress criterion, as its

name implies, only considers the tensilebehavior. For many brittle materials, the

compressive strength is much greater,

so this assumption may be valid.


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s1

s2

st

st

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s t safety F

Linear Stat ic Structu ral An alysis


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• Mohr-Coulomb Theory:

– The Mohr-Coulom b theory can be used for the “Stress Tool”.

It utilizes the maximum and minimum principal stresses and is

suitable for brittle materials.

– The criterion is as follows:

where st and sc are the ultimate (or yield)

tensile and compressive strengths. – The failure surface is plotted in two-dimensional principal

stress space below. Unlike the maximum tensile stress

theory, the Mohr-Coulomb theory considers the

effects of the compressive strength.


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1

31

ct

safety F s

s

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… Equivalent Stress

• Equivalent Stress:

– The von Mises or equivalent stress se is defined as:

– This criterion is commonly used for ductile metals.

–When uniaxial tensile tests of specimens are performed todetermine the yield strength and stress-strain relationships,

the engineer needs a way to relate the uniaxial data to the

stress state (tensor). Hence, the equivalent stress is a

commonly used scalar invariant for this purpose.


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… Equivalent Stress

• Maximum Equivalent Stress Theory:

– The Maximum Equ ivalent Stress Theory can be used for the

“Stress Tool”. It compares the equivalent stress with the yield

(or ultimate) strength and is suitable for ductile materials.


where sy is the tensile yield (or ultimate) strength.

– The failure surface is plotted in two-dimensional principalstress space below.

– A stress state can be separated into hydrostatic and

distortional terms. The hydrostatic term

contributes to volume change but the

distortional term is associated withyielding. Hence, the maximum equivalent

stress criterion is also known as the

disto r t ion energy cr i ter ion.

e

y

safety F s

s


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Inventory #002010

4-57

… Maximum Shear Stress

• Maximum Shear Stress:

– The maximum shear st ress tmax is defined as

which results in the largest principal shear stress

– This value can be compared to the yield strength to predictyielding for ductile materials

• Stress Intensity:

– The stress intensity is twice the value of the maximum shear

stress.

– The stress intensity provides the value of the largest

difference between principal stresses

2

31

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s s

t


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4-58

… Maximum Shear Stress

• Maximum Shear Stress Theory:

– The Maximum Shear Stress Theory or the Tresca c r i ter ion can

be used for the “Stress Tool”. It is suitable for ductile

materials.


where sy is the tensile yield (or ultimate) strength

and f is a factor (default=0.5) – The failure surface is plotted in two-dimensional principal

stress space below with the von Mises criterion superimposed

on in with a thin line. The two criteria are

quite similar, although the Tresca criterion

is slightly more conservative (maximum

difference between the two does not

exceed 15%).

maxt

s y

safety

f F

s1

s2

sy

sy

sy

sy


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4-59

… Contact Results

• Contact Results:

– Contact results can be requested for selected

bodies or surfaces which have contact elements.

– Contact elements in ANSYS use the concept of

contact and target surfaces. Only co ntact sur faces

repor t contact resul ts . MPC-based contact, the target surfaces

of any contact, and edge-based contact do not report results.Also, line bodies do not report any contact results.

• Contact Pressure shows distribution of normal contact pressure

• Contact penetration shows the resulting amount of penetration

whereas contact gap shows any gap (within pinball radius).

• Sliding distance is the amount one surface has slid with respect to

the other. Frictional stress is tangential contact traction due to

frictional effects.

• Contact status provides information on whether the contact is

established (closed state) or not touching (open state).

• For the open state, near-field means that it is within pinball

region, far-field means that it is outside of pinball region.


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… Reaction Forces

• Reaction forces and moments are output for each support

– For each support, look under the “Details” view

after solution. Reaction forces and moments are

printed. X, y, and z components are with respect

to the world coordinate system. Moments are

reported at the centroid of the support.

– The reaction force for weak springs, if used, isunder the “Environment” branch Details view

after solution. The weak spring reaction forces

should be small to ensure that the effect of weak

springs is negligible.


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4-61

… Reaction Forces

• The “Worksheet” tab for “Environment” branch has a

summary of reaction forces and moments

– If a support shares a vertex, edge, or surface with another

support, contact pair, or load, the reported reaction forces may

be incorrect. This is due to the fact that the underlying mesh

will have multiple supports and/or loads applied to the same

nodes. The solution will still be valid, but the reported valuesmay not be accurate because of this.


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• Workshop 4 – Linear Structural Analysis

• Goal:

– A 5 part assembly representing an impeller type pump is

analyzed with a 100N preload on the belt.

F. Workshop 4
http://localhost/var/www/apps/conversion/tmp/scratch_3/workshops/DS80_Workshop_04.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_3/workshops/DS80_Workshop_04.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_3/workshops/DS80_Workshop_04.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_3/workshops/DS80_Workshop_04.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_3/workshops/DS80_Workshop_04.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_3/workshops/DS80_Workshop_04.ppthttp://localhost/var/www/apps/conversion/tmp/scratch_3/workshops/DS80_Workshop_04.ppt

ANSYS Workbench Static

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