Stress Analysis SW Simulation

7/28/2019 Stress Analysis SW Simulation

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Ken Youssefi Mechanical Engineering Dept.1

Engineering Analysis using Simulation (SW)

The process of dividing the model into small pieces is called meshing. Thebehavior of each element is well-known under all possible support and load

scenarios. The finite element method uses elements with different shapes.Elements share common points called nodes.


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Uploading Simulation (SW)



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SW Simulation

Designer (SW Simulation)

Linear static load analysis (SimulationXpress)

Professional (SW Simulation Professional)Linear static load analysis, Thermal analysis,

Buckling analysis, Frequency analysis, Drop test

analysis, Fatigue analysis Optimization analysis

Advance Professional (SW Simulation Premium)

The features of the Professional

package plus: Nonlinear analysis and

Dynamic loading condition

(Includes many limitations)


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SolidWorks Simulation -Advance Professional

Select New Study


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Plot Type Options

Right click on results

and select plot types

2009

2008

Safety factor applied to

strength, less than 1


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SW Simulation Professional

Stress analysis due to static loads - Static studies calculatedisplacements, reaction forces, strains, stresses, and factor of safety

distribution.A factor of safety less than unity indicates part failure.

Large factors of safety in a contiguous region indicate low stresses and

that you can probably remove some material from this region.

Frequency (Vibration) analysis -A body in motion tends to vibrateat certain frequencies called natural frequencies. The lowest natural

frequency is called the fundamental frequency. For each natural frequency,

the body takes a certain shape called mode shape. Frequency analysiscalculates the natural frequencies and the associated mode shapes.

High stresses are produced if a body is subjected to a dynamic load

vibrating at one of its natural frequencies. This phenomenon is called

resonance. Frequency analysis can help you avoid failure due to

excessive stresses caused by resonance.


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Thermal analysis- Thermal studies calculate temperatures, temp.

gradients, and heat flow considering heat generation, conduction,

convection, and radiation conditions. Thermal studies can help in avoiding

undesirable thermal conditions like overheating and melting.

Buckling analysis - Slender structures, called columns, subject toaxial loads can fail due to buckling at load levels lower than those

required to cause material failure. Buckling can occur in different

modes. In many cases, only the lowest buckling load is of interest.

Optimization - Optimization studies automate the search for theoptimum design based on a geometric design. The software is

equipped with a technology to quickly detect trends and identify

the optimum solution using the least number of runs.


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Fatigue analysis - Repeated (cyclic) loading weakens objectsover time even when the induced stresses are considerably less than

allowable stress. The number of cycles to failure depends on the

material and the stress fluctuations. This information, is provided by a

curve called the S-N curve (stress vs number of cycle to failure).

Fatigue studies evaluate the consumed life of an object based on

fatigue events and S-N curves.

Drop Test Studies - Drop test studies evaluate the effect of droppingthe design on a rigid floor. The dropping distance or the velocity at the time

of impact, in addition to gravity, can be specified. The program solves a

dynamic problem as a function of time. Due to the large amount of data,

the program saves results at certain instants and locations as instructed

before running the analysis. It is possible to plot and graph displacements,

velocities, accelerations, strains, and stresses.


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Nonlinear analysis - When the assumptions of linear staticanalysis do not apply, you can use nonlinear studies to solve the

problem. The main sources of nonlinearity are: large displacements,

nonlinear material properties, and contact. Nonlinear studies calculatedisplacements, reaction forces, strains, and stresses at incrementally

varying levels of loads and restraints.

Nonlinear studies refer to nonlinear structural studies. For thermal

studies, the software automatically solves a linear or nonlinearproblem based on material properties and thermal restraints and loads.

Solving a nonlinear problem requires much more time and resources

than solving a similar linear static study.


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Mesh Elements used by SW Simulation

Solid elements (3D)

Beam elements (1D)

Shell elements (2D)

Draft quality High quality


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Draft quality High quality

Mesh Elements used by SW Simulation

Certain shapes can be modeled using either solid or shell elements

such as a plate.


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The model's degrees of freedom (DOF) are assigned at

the nodes.Usually solid elements have three DOF, all translational.

Rotations are accomplished through translations of a

node relative to another node.

Shell elements, on the other hand, have six DOF pernode: three translations and three rotations. The

addition of rotational DOF allows for evaluation of

bending stresses due to rotation of one node relative to

another. This bypasses the necessity of modeling thephysical thickness. The assignment of nodal DOF also

depends on the class of analysis.

For a thermal analysis, only one temperature DOF

exists at each node.

Nodal Degree of Freedom (DOF)


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Mesh Type in SW Simulation

Use the solid mesh for bulky models. All elements are tetrahedralwith straight or curved edges

Solid

Node


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Mesh Type in SW SimulationShell mesh using mid-surfaces

Use this option forsheet metals and simple thin solid parts made of a

single material. During meshing, the software creates shell elements based onmidsurfaces. The thickness of elements is calculated automatically based on

surface pairs.This option is not available for assemblies and surface modelsand can fail to generate the proper mesh for complex parts and parts with

intersections. View the mesh and see if it represents the actual model before

proceeding with the solution.


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Shell mesh using surfaces

This option allows you to create shells on selected faces or surfaces. Foreach shell, you can specify thickness, material, and formulation. It is available

for solid parts, solid assemblies, and surface models. Shell elements are

placed such that the associated face or surface is located at the middle of the

element across the thickness.


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Use this option to simulate frames, and truss structures. The program

creates elements automatically from weldments or you can defineelements manually . A beam element is a line element defined by two

end points and a cross-section. Beam elements are capable of

resisting axial, bending, shear, and torsional loads. Trusses resist

axial loads only.

Beam Mesh

This option is available only if you have a solid body in thedocument. It is possible to create shells as well as solids. When

meshing, the software creates shells with shell elements and solids

with tetrahedral solid elements. Use this option if the modelincludes bulky as well as thin objects.

Mixed Mesh

Optimization and fatigue studies do not require mesh type.


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Automatic Meshing


When you mesh a model, the software generates a mixture of solid,

shell, spring, and contact elements based on the created

geometry. The program automatically creates the following

meshes:

Solid mesh

Shell mesh

Beam Mixed mesh


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SW Simulations Help

SW Simulation provides

extensive on-line help and

tutorials


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SW Simulation Menu

Tool bars

Main

Loads

Result Tools


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SW SimulationTo start analyzing the model, you should start with the definition

of a study.

Study name

Mesh type, not in

2009, selection is

done automatically

by the program

Select analysis

type

Select Study


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SW SimulationOption menu

Set Mesh

quality to High


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Creating Mesh


Right click the Meshfolder to display the

pop-up menu.

Select Create Mesh

Use the bar to set the

mesh density


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Effect of Mesh Size


Coarse FineMedium


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Mesh Characteristics


Global element

size

Tolerance is set at 5%.

Nodes are merged ifthe distance between

them is less than 5% of

the element size.

Increasing the tolerance

may resolve meshing

problems

Automatic transition - theprogram automatically

applies mesh controls tosmall features, holes, fillets,

and other fine details of your

model. Uncheck Automatictransition before meshinglarge models with many small

features and details to avoidgenerating a very large

number of elements.


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Mesh Characteristics


J acobian Points - Parabolic elements can mapcurved geometry much more accurately than linear

elements of the same size. In extremely sharp or

curved boundaries, it is possible to generate distorted

elements with edges crossing over each othercausing the mesh generation to fail.

The Jacobian check is based on a number of points

located within each element. The default value of 4

should be fine for most applications. Increase that for

extremely curved surfaces.


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Mesh Quality

The ideal shape of a tetrahedral element is aregular tetrahedron with the aspect ratio of 1.Analogously, an equilateral triangle is the ideal

shape for a shell element.

Sometimes, Irregular tetrahedra are created

by the program. These distorted elementshave high aspect ratio. An aspect ratio that is

too high causes element degeneration, which

in turn affects the quality of the results.

i


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Aspect Ratio


Right click theMesh icon andselect CreateMesh Plot

Select Aspect ratio


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SW Automesher



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Mesh Quality Automesher (SW)

Standard mesh (automesher)

It is preferred to use the Standard automesher (default). The program

uses the Voronoi-Delaunay meshing technique, it is faster than theCurved-based mesh method (Alternate automesher).

The Delaunay triangulation

with all the circumcircles and

their centers (in red).

By far the most popular of the triangle (2D) and

tetrahedral (3D) meshing techniques are those

utilizing the Delaunay criterion. The Delaunaycriterion, sometimes called the "empty sphere"

property. Simply stated, it says that any node

must not be contained within the circumcircle of

a triangle or circumsphere of any tetrahedral

within the mesh

Delaunay triangulations maximize theminimum angle of all the angles of the

triangles in the triangulation. The process

avoids narrow triangles, as they have

large circumcircles compared to their area

Triangleelement


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Connecting the centers of the

circumcircles produces the

Voronoi diagram (in red)

The Delaunay criterion in itself, is not an algorithm

for generating a mesh. It merely generates a set

of existing points in space. As such it is necessary

to provide a method for generating node locations

within the geometry. A typical approach is to first

mesh the boundary of the geometry to provide an

initial set of nodes. The boundary nodes are then

triangulated according to the Delaunay criterion.

Nodes are then inserted incrementally into theexisting mesh, redefining the triangles or

tetrahedra locally as each new node is inserted to

maintain the Delaunay criterion. It is the method

that is chosen for defining where to locate the

interior nodes that distinguishes one Delaunay

algorithm from another.

A Voronoi segment can be defined as the line segment between the circumcircle

centers of two adjacent triangles or tetrahedra. The new node is introduced at a

point along the Voronoi segment in order to satisfy the best local size criteria.

This method tends to generate very structured looking meshes with six triangles

at every internal node.


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Curved Based mesh (Alternate automesher)

The Curved based mesh method uses the Advancing Front meshing

technique. The mesher creates more elements in higher-curvature areas

automatically (without need for mesh control). The technique disregards

the mesh control and automatic transition settings. It should only be

used when the Standard automesher fails

Another very popular family of triangle and tetrahedron meshgeneration algorithms is the advancing front, or moving front

method. Two of the main contributors to this method are

Rainald Lohner at George Mason University and S. H. Lo at

the University of Hong Kong. In this method, the tetrahedra

are built progressively inward from the triangulated surface.

An active front is maintained where new tetrahedra areformed. The figure shows a simple two-dimensional example

of the advancing front, where triangles have been formed at

the boundary. As the algorithm progresses, the front will

advance to fill the remainder of the area with triangles.


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SW Simulation - Materials

Right click on

the materialicon to edit

To assign

material select

Material and

choose ApplyMaterial to All


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Type of Restraints (supports)Select the Fixtures (Restraints) option

Fixtures menu

Standard option:

Fixed support

Sliding support

Pin support

T f R t i t ( t )


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Type of Restraints (supports)


Advanced supports


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This is used for build-in or rigid supports. For solid elements, this

restraint type sets all translational degrees of freedom to zero (solidelements do not have rotational degrees of freedom). For shell

elements, it sets the translational and the rotational degrees of

freedom to zero. When using this restraint type, no reference

geometry is needed.

Selectable entities: vertices, edges, and faces

Fixed (no rotation and translation)

This restraint type sets all translational degrees of freedom to zero.

This is the same as fixed If solid elements are used. The rotational

degrees of freedom are not constrained for shell elements. No

reference geometry is used.

Immovable (no translation) SW 2008

Selectable entities: vertices, edges, and faces


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Symmetry requires that geometry, restraints,

loads, and material properties be symmetrical.

In general, using symmetry is notrecommended for buckling and frequency

studies.

Symmetry

For shell models, symmetry requires that faces coinciding with planes

of symmetry should be prevented from moving in the normal directionand rotating about the other two orthogonal directions.

You can use symmetry to analyze a portion of the model instead of thefull model. When appropriate, taking advantage of symmetry can help

you reduce the size of the problem and obtain more accurate results.

The procedures to apply the symmetry restraint type to solid meshesand shell meshes using mid-surface are identical.

Plane of symmetry

T f R i S (S lid M h)


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Type of Restraints Symmetry (Solid Mesh)

DOFs restrained for solid

meshes: 1 translation

Analyze one half of the model by applying

the Symmetry constrained to the faces of

symmetry.

The model

Plane of symmetry


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Analyze one quarter of the model by

applying the Symmetry constraint to thefaces of symmetry.

The model is symmetrical with

respect to two planes


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DOFs restrained for solid meshes: 1 translation

Axisymmetrical model, use a wedge, apply the Symmetry restraints to

analyze the whole model. Make sure the wedge angle is not too small.

T f R t i t S t (Sh ll M h)


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Type of Restraints Symmetry (Shell Mesh)For studies created with Shell mesh using mid-surfaces, symmetry restraints are

applied on the faces coinciding with the planes of symmetry of the model along the

model thickness.

Displacement (translation) normal to theface is restrained, circumferential direction

Rotation about radialand axial directions arerestrained.

Axial symmetry

The axisymmetrical model can be studied

by analyzing a wedge of the model

Mid-Surface

element

T f R t i t S t (Sh ll M h)


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Type of Restraints Symmetry (Shell Mesh)

Mid-Surface

element

Planar symmetry

The model is symmetric about two planes, xz and yz planes. A

quarter of the model can be analyzed



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For studies created with Shell mesh using surfaces, symmetry restraints are

applied manually on shell edges located on the planes of symmetry of the model

Surface model with

Axial Symmetry

Select the axis of the shell as a

reference and set the rotations about

radial and axial and translation in the

circumferential directions to zero on

the vertical edges..`


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Type of Restraints

Use the Roller/Sliding restraint to specify that a planar face can move

freely on its plane but CANNOT move in the direction normal to its

plane. The face can shrink or expand under loading.

Roller/Sliding

Use the Hinge restraint to specify that a cylindrical face can ONLY

rotate about its own axis. The radius and the length of the cylindrical

face remain constant under loading. This condition is similar to

selecting the On cylindrical face restraint type and setting theradial and axial components to zero.

Hinge

T f R t i t O C li d i l F


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Type of Restraints On Cylindrical Face

You can use this option only when

all the selected faces are

cylindrical. Each face can have adifferent axis. The radial,

circumferential, and axial

directions for each face are based

on its own axis.

DOFs restrained for solid meshes:

3 translations

DOFs restrained for shell meshes:

3 translations and 3 rotations

f i l


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Type of Restraints On Flat Face

You can use this option only when all the selected faces are planar. Each face can

be in a different plane. Each face is restrained relative to its own directions

(Direction 1, Direction 2, and Normal).

The selected face can only slide

in the direction shown (dashedred line). Translation in the other

two directions, Dir. 2 and Normal

are set to zero



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Type of Restraints - On Flat Face

The selected face can slide in the directions 1 and 2. Translation in the

normal direction is set to zero.



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It is required to have the inner

slider free to slide along the

direction shown

Use the On Flat Face restraint

and specify zero displacementalong Face Dir 2 and Normal to

the face. The face is allowed to

move in Face Dir 1.


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The desk is free to slide on the ground

(dashed red arrows) but not to move up

and down (normal direction, blue arrow)

The selected flat faces can slide freely

in Dir 1 and Dir 2 but are restrained in

the Normal direction

Type of Restraints On Spherical Face


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Type of Restraints On Spherical FaceYou can use this option only when all the selected faces are spherical. Each

face can have a different center. The radial, longitude, and latitude directions for

each face are based on its own center.

DOFs restrained for solid meshes:

3 translations

DOFs restrained for shell meshes:

3 translations and 3 rotations

The spherical face of the

reflector can only rotate in the

latitude direction. Set the

translations in the other two

directions to zero to achieve this.



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A handle

Type of Restraints Use Reference Geometry


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Type of Restraints Use Reference GeometryYou can use a selected reference geometry to apply restraints. The reference can

be a plane, axis, edge, or face. Using this option you can prescribe restraints on

vertices, edges, and faces.

Reference plane



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You can use an axis as a reference to apply restraints. You can prescribe

the translations in the radial, circumferential, and axial directions. For shell

meshes, you can prescribe rotations in reference to these directions.

The selected face of the cylindrical

hole can rotate about or move along

the reference axis (in blue)

Type of Restraints Cyclic Symmetry


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Type of Restraints Cyclic Symmetry

Cyclic symmetry allows you to analyze a model with circular patterns around

an axis by modeling a representative segment. The segment can be a part or an

assembly . The geometry, restraints, and loading conditions must be similar for

all other segments making up the model. Turbine, fans, flywheels, and motor

rotors can usually be analyzed using cyclic symmetry.

Model one sixth of the wheel and apply Cyclic Symmetry to the cut faces

The Cyclic Symmetry restraint can be applied to a solid model and for a static case

only. Apply it to two sections and define the axis of revolution for the symmetry.

Stress Analysis Example


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Stress Analysis- Example

Select Study and choose New Study from the toolbar or Simulation menu

Name the study

Select study

type, Static

Stress Analysis Material selection


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Stress Analysis- Material selectionSimulation menu choose Apply Material.

Create a new material by

specifying its mechanical

properties or edit the exciting

one in the library.

Stress Analysis- Material selection


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Stress Analysis Material selection

From Library files select 1023 steel

Stress Analysis Restraint Selection


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Stress Analysis Restraint Selection

Select the desired type of restraint

(support), fixed.

Select the

entity, face

Symbols used to show

translational and

rotational restraints

Rotation

Translation

Stress Analysis - Apply Load (Force)


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Stress Analysis - Apply Load (Force)Select the type of load, location, direction, and magnitude.



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Select the edge

for load location

Specify value,

units and directionof the force Choose the direction of the load

by selecting the edge

Stress Analysis - Run Command


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Stress Analysis Run Command

Select Run

After selecting study type, mesh type, material, load, and restraints,

you are ready to run the solver.

Stress Analysis - Results


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Stress Analysis Results

Yield strength = 282.7 MPa, max. stress around the hole = 14030 MPa

Stress distribution

Stress Analysis Results


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Stress Analysis - Results

Displacement

Maximum deflection at the tip is 16.45 mm.

Stress Analysis Mesh Control


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Mesh control refers to specifying different element sizes at different regions in the

model. A smaller element size in a region improves the accuracy of results in that

region. You can specify mesh control at vertices, edges, faces, and components

From the SolidWorks

Simulation manager,select Mesh and right

clickChoose Apply Mesh

Control option

St A l i M h C t l


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Select the edges of the two holes (max. stress location) to

create finer mesh.



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Finer mesh at the hole

Without mesh control

With mesh control



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Max. stress = 14370 MPa,

with finer mesh around the

holes, 2.5% higher.

Max. stress = 14030 MPa,

without finer mesh around

the holes

Stress Analysis Effect of Restraint Type


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Stress Analysis Effect of Restraint Type

Change the back face restraint from

fixed to immovable.No change in max.

stress


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Stress Analysis SW Simulation

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