D3MSC-LL 2012-02-29 Typical Fitting-part2

Fitting Stress Analysis Analysis Approach

Pedro Chou February 29, 2012

MSC Softw are Confidential

Agenda

Results from Linear and nonlinear material models Post-processing

Fringe plot options stress averaging Graph plots Contact body results as global variables Cross section stress plot

Using contact bodies for mesh refinement Using rigid contact bodies to apply loads

1


Model Review

2

fasteners

Material: Al 7050 T7451


Material model

Aluminum 7050 T7451 E = 71,000 MPa Poisson = 0.33 Density = 2.82E-6 Kg/mm^3 Yield stress = 455 MPa Plasticity modulus (H) = 744.91 MPa

3


RESULTS

4


Create Fringe Plot Options Form

Elm 1 Elm 2

Elm 4 Elm 3

*

Averaging Definition provides different options to determine the result values at nodes (*) shared by adjacent elements. The dots (red) represent element results at the node (*), not at element Gauss points. Domain

All Entities -- all result values at a node (from all elements using that node (*)) are averaged producing a single value

Material average the result values at a node, where the values corresponds to elements that have the same material property

Property average the result values at a node, where the values corresponds to elements that have the same element property set

nn

iiElementNode /)(

1=

=



Averaging Definition Domain

Target Entities average the result values at a node, where the values correspond to elements that have been selected under the Target Entities form of the Create/Fringe form

Element Type -- average the result values at a node, where the values correspond to elements of the same type, e.g. Quad4

None -- no averaging at nodes

Elm 1 Elm 2

Elm 4 Elm 3

*



Averaging Definition options Method

When both deriving and averaging of a result invariant, e.g. von Mises stress from the stress tensor, are to be performed the user has the following options

Derive/Average -- calculates the result invariant (Derive) at the integration points, extrapolates the result invariant to the element nodes, for all the elements, then causes plotting the average (Average) for the contribution of each element to each node

Average/Derive -- extrapolates the component values to the element nodes, averages (Average) them, then calculates the result invariant (Derive) using the average nodal component values

Difference causes plotting the absolute value of the difference between the largest and smallest of the values at a node. The plot is sometimes called a Stress Jump Plot when plotting stress. It is a quality check method. Must use Domain option other than None to make this work properly.

Sum causes plotting the sum of all values at an element node



Extrapolation of element results to the elements nodes can be done as follows

Shape Fn. -- result value at the elements nodes is determined from fitting an extrapolating surface through the known element result values

Average -- result is averaged within the element, then the value from averaging is assigned to the elements nodes

Centroid -- the centroidal value from the extrapolation surface is used at the elements nodes

mm

j

jiElementNodeiElement /)(

1=

=



Extrapolation (continued) Min -- the smallest of the integration point values is used

If the only result is at the centroid, the minimum value is set equal to the centroidal value

Max -- the largest of the integration point values is used If the only result is at the centroid, the maximum value is set

equal to the centroidal value


Averaging

Comments on averaging There are pluses and minuses about averaging Pluses

Great way to determine if the mesh has enough density to predict the results accurately. If the results from averaging appear to be the same as those from not averaging, then the mesh is considered adequate.

Smooths peaking results or results approaching a singularity Minuses

Blind averaging can hide peak results Never average

Across different material boundaries Across different thicknesses Across elements with different coordinate systems Across elements not in the same plane Amongst different element types


Patran Fringe Plots vs Nastran .f06

Settings that need to be used to have Patran display a fringe so its values are the same as those in the Nastran .f06 file Centroidal results read into Patran

Display Attributes: Element Fill; optionally, shrink fringe 100% and show fringe values Plot Options: Domain: None, Extrapolation: Centroid

Nodal results read into Patran Display Attributes: Discrete/Smooth; optionally, shrink fringe 100% and show fringe values Plot Options: Domain: None, Extrapolation: Shape Fn.


Results linear material model

12

Max avg VM stress = 917 MPa



13

Max non-avg centroid VM stress = 490 MPa



14

Initial contact status



15

Contact status full load application


Results nonlinear material model

16

Max avg VM stress = 561 MPa



17

Max non-avg centroid VM stress = 390 MPa



18

Max plastic strain = 0.011



19

Initial contact status



20

Contact status full load application

Display Attributes

Change scale factor and style


VM Stress Path Plot

21


Mesh Refinement

Fine mesh around areas of stress concentration Transition fine mesh to coarse mesh

OR Use CONTACT BODIES

Glue contact bodies

22


Using Glue Contact for Mesh Refinement

23

vs.


CONTACT BASICS

24


Contact Bodies

Deformable Contact Bodies Body is deformable Stress distribution on contact body

Rigid Contact Bodies Body is rigid Position controlled Velocity controlled Load controlled

25


Each deformable body consists of one or more finite elements. A deformable body does not need to completely correspond with a physical

body.

Nodes or elements must belong to NO MORE than one deformable body.

Deformable Bodies


Rigid Bodies

Each rigid contact body is defined by a number of geometrical entities: Curves for 2D analysis Surfaces for 3D analysis

27


Rigid Bodies

Velocity controlled

28


Rigid Bodies

Position controlled

29


Rigid Bodies

Load controlled (Force/Moment) First control node translations Second control node rotations

DOF for 2nd control node are UX (ROTX), UY (ROTY) and UZ (ROTZ)

Apply forces/moments to control nodes

Alternatively, control nodes can be constrained to obtain SPCFORCES

30


Contact Bodies

A

View A

Contact body 2

Contact body 1

Nastran uses the concept of contact bodies for general contact problems


Contact Bodies

32


Contact Detection

The user defines bodies (deformable or rigid) which are potential candidates for contact during the analysis

Grid points and segments defining the boundary of the deformable bodies are automatically determined

The contact algorithm automatically detects grid points entering contact and generates the appropriate constraints to ensure no penetration occurs

Two contact detection algorithms are available in Nastran Node-to-Patch contact

Beam-to-Beam contact


Node-to-node Patch Contact Detection

Following contact examples use the node-to-patch contact algorithm

Solid to solid contact

Shell surface to surface contact

Shell edge to edge glue Shell edge to solid glue

Shell edge to surface glue

Solid to Shell contact

Beam to solid glue

Beam to shell glue


Beam-to-beam Contact Detection

Following contact examples use the beam-to-beam contact algorithm

Shell edge to edge contact Beam to beam contact


Node-to-Patch Contact

Node-to-Patch contact A node from one body comes into contact with a patch on a second body. The touching node is the slave. It is located on the contacting body. The touched patch is the master. It is located on the contacted body. When contact is detected, a contact constraint is imposed. The touching node

becomes the tied node. Nodes on the patch become the retained nodes.

Touching (contacting) Node - Slave

Touched (Contacted) Patch - Master


Node-to-Patch Contact

The Master/Slave terminology is important to understanding how pairs of contact bodies are set up. Master = touched contact body Slave = touching contact body Rigid contact bodies are always the Master.

Defining which is which in a contact pair can be critical to achieving good contact results. This is not always clear in Patran.

Contact Search Methods will review this topic in detail.


Possible Contact Situations

Master

distance tolerance

2

2) Node outside element patch, inside distance tolerance

3

3) Node inside element patch, inside distance tolerance

4

4) Node inside element patch, outside distance tolerance

Slave

1

1) Node outside element patch, outside distance tolerance

View A


1) Node Outside Element, Outside Distance Tolerance

Bodies are not in contact Contacting node remains in current position


2) Node Outside Element, Inside Distance Tolerance

A multipoint constraint is imposed in order to close the gap between the contacting node and the patch

Remains in contact if normal tensile force is less than separation force


3) Node Inside Element, Inside Distance Tolerance

A multipoint constraint is imposed to resolve the penetration of the contacting node into the patch


4) Node Inside Element, Outside Distance Tolerance

Node penetrated Increment will be recycled with modified step Important: If this situation occurs at the beginning of analysis,

contact will not be found


Contact Table

43


Nastran Entries

44


Using Rigid Contact Bodies as BCs

Fasteners and anchor surfaces modeled as load controlled rigid contact bodies Control nodes constrained to extract

SPCFORCE

Load on the fitting applied through pin-load rigid contact body

45


Checking Equilibrium

Applied nodal load: FX = 8315 FY = 0 FZ = 1335

SPCFORCE:

46

Control Node X Component Y Component Z Component 80011 -2325.406738 -1634.408936 1828.627319 80021 -535.624756 -3579.358154 903.632751 80031 -3297.656982 -754.215637 -948.724609 80041 -2156.312012 774.207886 1006.236877 80051 0 5193.774902 -4124.771973

Resultant -8315.000488 6.1E-05 -1334.999635


Q & A

47


THANK YOU !!

48

Fitting Stress AnalysisAgendaModel ReviewMaterial modelresultsCreate Fringe Plot Options FormCreate Fringe Plot Options FormCreate Fringe Plot Options FormCreate Fringe Plot Options FormCreate Fringe Plot Options FormAveragingPatran Fringe Plots vs Nastran .f06Results linear material modelResults linear material modelResults linear material modelResults linear material modelResults nonlinear material modelResults nonlinear material modelResults nonlinear material modelResults nonlinear material modelResults nonlinear material modelVM Stress Path PlotMesh RefinementUsing Glue Contact for Mesh RefinementContact basicsContact BodiesDeformable BodiesRigid BodiesRigid BodiesRigid BodiesRigid BodiesContact BodiesContact BodiesContact DetectionNode-to-node Patch Contact DetectionBeam-to-beam Contact DetectionNode-to-Patch ContactNode-to-Patch ContactPossible Contact Situations1) Node Outside Element, Outside Distance Tolerance2) Node Outside Element, Inside Distance Tolerance3) Node Inside Element, Inside Distance Tolerance4) Node Inside Element, Outside Distance ToleranceContact TableNastran EntriesUsing Rigid Contact Bodies as BCsChecking EquilibriumQ & aThank you !!

D3MSC-LL 2012-02-29 Typical Fitting-part2

Documents

Transcript of D3MSC-LL 2012-02-29 Typical Fitting-part2