PragTicPragTic

Use of Finite Element Analysis Use of Finite Element Analysis Data Data

in Fatigue Analysesin Fatigue Analyses

Jan PapugaJan Papuga

Czech Technical University in Prague

Dept. of Mechanics, Biomechanics and Mechatronics

Workshop on Computational Fatigue Analysis 2008 & 2ndWorkshop on Computational Fatigue Analysis 2008 & 2nd PragTic PragTic UsersUsers’ Meeting’ MeetingKamenice nad Lipou, Czech Rep., Oct. 29-31, 2008Kamenice nad Lipou, Czech Rep., Oct. 29-31, 2008

Software PragTicSoftware PragTic Started as a support tool for preparation of my PhD thesisStarted as a support tool for preparation of my PhD thesis

Present focus: research tool usable for fatigue computationPresent focus: research tool usable for fatigue computation

Freeware (Freeware (www.www.pragticpragtic..comcom))

MS Windows MS Windows

basedbased

English interface English interface

onlyonly

v.0.2v.0.2beta -beta -

v.0.2v.0.2betaDbetaD

developdevelopmentment

sponsored bysponsored by

EvektorEvektor

Previous versions Previous versions

sponsored by CTU sponsored by CTU

in Praguein Prague

PragTicPragTic Features Features Works on dataWorks on data

of FE-modelof FE-model

at isolated points with no relation to any FE-model (strain at isolated points with no relation to any FE-model (strain

gauges)gauges)

Own database of all data processedOwn database of all data processed Preparation and analysis of loading by more load Preparation and analysis of loading by more load

channelschannels Easy to use graphical interfaceEasy to use graphical interface Complex setup of calculation methodsComplex setup of calculation methods Unique coverage of multiaxial methodsUnique coverage of multiaxial methods Approx. 20 high-cycle and 10 low-cycle fatigue Approx. 20 high-cycle and 10 low-cycle fatigue

computation methodscomputation methods

Fatigue Calculation on FE-Fatigue Calculation on FE-ModelModel

FE-modelFE-model TopologyTopology ResultsResults

Essentials

Material dataMaterial data Knowledge about load historyKnowledge about load history Availability of suitable Availability of suitable

calculation method calculation method

FEM-Model RequirementsFEM-Model Requirements Adequately detailed Adequately detailed

mesh around the mesh around the

critical localitiescritical localities

Use the submodel of Use the submodel of

the critical place if the critical place if

availableavailable Some rough rulesSome rough rules: :

A quarter of circleA quarter of circle ~ ~

5 element5 elementss Avoid linear Avoid linear

tetrahedronstetrahedrons At least three At least three

elements over the elements over the

thickness, otherwise thickness, otherwise

shellsshells

Woehlerovy křivky

100

150

200

250

300

350

400

450

500

550

600

1E+3 1E+4 1E+5 1E+6 1E+7 1E+8

Počet kmitů N [-]

Am

pli

tud

a n

apět

í s a

[M

Pa]

ČSN 41 1523.1 (w ~21)

AISI 4340 (L-CM3) (w ~15)

7175-T37511 (w ~8)

5E+

5

ČSN 41 1523.1 AISI 4340 7175-T375110% 100% 100% 100%2% 66% 67% 82%5% 36% 38% 62%

10% 13% 17% 39%

Vzrůst napětí

Pokles na životnostČSN 41 1523.1 AISI 4340 7175-T375110% 100% 100% 100%2% 66% 67% 82%5% 36% 38% 62%

10% 13% 17% 39%

Vzrůst napětí

Pokles na životnostLoad increase

Decrease of fatigue life

Use of Result DataUse of Result Data – Part I – Part I Results can be printout Results can be printout atat

nodes of elementsnodes of elements can be significantly discontinuous (coarse meshes)can be significantly discontinuous (coarse meshes) the measure of conservativeness can be doubtfulthe measure of conservativeness can be doubtful

integration points integration points the only the only “exact” values“exact” values

nodes as averagenodes as averagedd value value smooth in comparison to nodes of elementssmooth in comparison to nodes of elements the same results on edgesthe same results on edges

element centroidselement centroids used e.g. in FemFat on shell elements and welds (the used e.g. in FemFat on shell elements and welds (the

load values on load values on edgesedges are not decisive – structural are not decisive – structural stresses)stresses)

more points to be analyzed

much slower calculation

}

Use of Result DataUse of Result Data – Part II – Part II Shell elementsShell elements

obvious demand by the most of industrial partners obvious demand by the most of industrial partners (automotive, airplane, transport, etc. industry)(automotive, airplane, transport, etc. industry)

further complicationfurther complication as regards listing as regards listing – results on – results on top and bottom sidetop and bottom sidess

questionable results at typical crack initiation areas questionable results at typical crack initiation areas – junctions, toes, etc.– junctions, toes, etc.

these localities are moreover often affected by weldsthese localities are moreover often affected by welds use of results at element centroids should be preferreduse of results at element centroids should be preferred

Bar elements?Bar elements? does the computation make sense?does the computation make sense? description of potential notches on elements close description of potential notches on elements close

to zero (if not input e.g. in the fatigue post-to zero (if not input e.g. in the fatigue post-processor)processor)

notches at junctions are not described in notches at junctions are not described in acceptable detailacceptable detail

Data Import to PragTicData Import to PragTic FE-dataFE-data

commonly formatted (rows & columns) ASCII file (solid commonly formatted (rows & columns) ASCII file (solid

elements only)elements only)

MSC.Nastran (*.nas/*.dat files - topology, *.pch – FE-results)MSC.Nastran (*.nas/*.dat files - topology, *.pch – FE-results)

ABAQUS (ASCII file *.fil) – suspended at present (is there ABAQUS (ASCII file *.fil) – suspended at present (is there

anybody to sponsor it?)anybody to sponsor it?)

Isolated pointsIsolated points direct input through the PragTic’s interface expecteddirect input through the PragTic’s interface expected

possibility to import as a commonly formatted ASCII filepossibility to import as a commonly formatted ASCII file

Other entitiesOther entities load regimes, calculation methods – possibility to read data load regimes, calculation methods – possibility to read data

from other PragTic’s tasksfrom other PragTic’s tasks

Example of ANSYS InputExample of ANSYS InputOperations done in points 1-6 can be saved and read during any future import on a similar data structure

FE-Model DescriptionFE-Model Description Topology dataTopology data

NodeNode description (ID, coordinates) description (ID, coordinates) ElementElement description description

IDID Related Related materialmaterial Related Related element groupelement group Related Related real constantsreal constants Related Related coordinate systemscoordinate systems

(definition, output)(definition, output) Related nodes (element table of Related nodes (element table of

incidencies)incidencies) Result dataResult data

Data Data Structure of TaskStructure of Taskss in PragTicin PragTic

hard-disc representationhard-disc representation *.fdb file with description of the task (data_base)*.fdb file with description of the task (data_base) directory * (the same name as the task) full with directory * (the same name as the task) full with

binary files of individual items in the data_base binary files of individual items in the data_base (data_vectors)(data_vectors)

each file consists of data of uniform type and each file consists of data of uniform type and lengthlength

memory representationmemory representation data_base – specialized data_vector describing data_base – specialized data_vector describing

complete content of the taskcomplete content of the task data_vectordata_vector

class build around the data read from filesclass build around the data read from files data are cached, read only their part, not the whole filedata are cached, read only their part, not the whole file

PragTic interface representationPragTic interface representation

InterfaceInterface

data_vectors are represented as items with unique ID-names (big letters)

function of each data_vector identified by its header and categorized to appropriate sections

data_vectors opened for viewing by right hand click on their ID-names

data_base tree

Interface II – Popup MenuInterface II – Popup Menu Opened by a click on the right Opened by a click on the right

mouse buttonmouse button Differs for various selected itemsDiffers for various selected items Remove Remove commandcommand

removes the data_vector from the removes the data_vector from the task, but leaves the file task, but leaves the file representation on the hard-discrepresentation on the hard-disc

DeleteDelete command command removes also the file removes also the file

Note:Note: Some data_vector serve as Some data_vector serve as a synergic part of another a synergic part of another data_vector – you will be warned data_vector – you will be warned that the delete/removal is that the delete/removal is forbiddenforbidden

When When complete:complete:

Report window – errors, warnings, output of some commands

Interface IIIInterface III

Status bar - reports on current calculation results

Main menu

Data Items Data Items DifferentiationDifferentiation

Each data_vector has a header at its Each data_vector has a header at its beginning, where are among others data beginning, where are among others data on:on: Its meaning (e.g. Stress, Strain, Nodes, Its meaning (e.g. Stress, Strain, Nodes,

etc.)etc.) Related location (e.g. variable described Related location (e.g. variable described

at element centroids)at element centroids) Number of items, dimension of one itemNumber of items, dimension of one item Related sets (e.g. nodal)Related sets (e.g. nodal)

Quick view: Select the data_vector and then click on the right button of the mouse

View / Edit Window – Type IView / Edit Window – Type I Description of elements, nodes, isolated points, sets, results, Description of elements, nodes, isolated points, sets, results,

loadsloads Use of clipboard enabled Use of clipboard enabled

Ctrl+C (or the command from the right-hand click menu) for View Ctrl+C (or the command from the right-hand click menu) for View modemode

Ctrl+V (or the command from the right-hand click menu) for Edit Ctrl+V (or the command from the right-hand click menu) for Edit modemode

Fast ASCII CopyFast ASCII Copy – copies whole content of the table to a – copies whole content of the table to a file, using the tabulators and enters as separatorsfile, using the tabulators and enters as separators

FilterFilter – see its strength on the next slide – see its strength on the next slide

Note the hints

View / Edit Window – Type IView / Edit Window – Type IFilterFilter

Leaves only dataLeaves only data belonging to belonging to

specified setspecified set with specific values with specific values

in the chosen columnin the chosen column

Resulting set can be saved

Filtering can be used in a consecutive Filtering can be used in a consecutive seriesseries

View / Edit Window – Type IIView / Edit Window – Type II no command no command BackBack or or UndoUndo, every , every SaveSave is final is final not not SavedSaved changes can be returned back by the changes can be returned back by the

SkipSkip Changing the ID-name to a new one and saveChanging the ID-name to a new one and save is is

not equal to rename but to a copy to a new itemnot equal to rename but to a copy to a new item

edition of each item in the data_vector (load regimes here) has to be finished by Save if you want to continue to another one

individual items

View / Edit Window – Type IIView / Edit Window – Type II Popup-menu enabled only for Edit modePopup-menu enabled only for Edit mode Some items in the Command menu enabled also in Some items in the Command menu enabled also in

View modeView mode Reorder:Reorder: Currently enabled only for Load Currently enabled only for Load

Regimes and Setups of AnalysesRegimes and Setups of Analyses

Popup-menu

Command menu

View / Edit Window – Type IIView / Edit Window – Type II

Apply to setApply to set button button Enables correction of FE-model properties, if Enables correction of FE-model properties, if

they were inadequaely imported to PragTicthey were inadequaely imported to PragTic

Assignment of a chosen property to specified set of e.g. nodes

LoadLoadss DescriptionDescriptionLoad RegimeLoad Regime ( (LOAD_REGLOAD_REG))

a combination of all entities necessary for creation of local load histories a combination of all entities necessary for creation of local load histories extern extern load history + FE-results file + knowledge of load applied to the FE-load history + FE-results file + knowledge of load applied to the FE-

modelmodel local load history in hte FE-result file local load history in hte FE-result file = transient analysis= transient analysis

extern loadsextern loads (Hooke) (Hooke) math formulamath formula load by data sequenceload by data sequence load spectrumload spectrum / rain-flow / rain-flow

matmatrixrix

transient analysis (transient analysis (no no Hooke)Hooke) local load history read local load history read

from FE-solver from FE-solver (ABAQUS)(ABAQUS)

In preparation:In preparation: buildup buildup of transient analysis of transient analysis from a sequence of FE-from a sequence of FE-results results

LoadingLoading Linear FEALinear FEA

The individual load channels can be The individual load channels can be combined by simple superpositioncombined by simple superposition

If the resulting loads pass over the yield If the resulting loads pass over the yield limit, some kind of reduction to elastic-limit, some kind of reduction to elastic-plastic value can be necessaryplastic value can be necessary

Non-linear FEANon-linear FEA No superposition allowedNo superposition allowed More challenging way due to necessity More challenging way due to necessity

to include all the interacting channels to include all the interacting channels and contacts into one modeland contacts into one model

Load History DefinitionLoad History Definition Transient analysis – local loads over Transient analysis – local loads over

the structurethe structure History of the acting load – must be History of the acting load – must be

in a known relation to the load in a known relation to the load acting on the FE-modelacting on the FE-model real record (time – force)real record (time – force) mathematical formulationmathematical formulation load spectrum (upper force – lower load spectrum (upper force – lower

force – occurence)force – occurence) load spectra load spectra as e.g. as e.g. required by standardsrequired by standards rain-flow matricesrain-flow matrices

Load Input toLoad Input to PragTic PragTic Use of the Use of the Import Import function from the main menufunction from the main menu Creation in PragTic (Creation in PragTic (NewNew command at the right- command at the right-

hand click menu opened on hand click menu opened on Time Scales, Load Time Scales, Load Sequencies Sequencies and and Load SpectraLoad Spectra)) direct editingdirect editing use of Copy and use of Copy and

Paste function Paste function (Ctrl(Ctrl+V) at the +V) at the void cells of void cells of Edit window – Edit window – be sure that the be sure that the size of the size of the clipboard and clipboard and the edit window the edit window coincidecoincide

Various data_vectors used for load definitions

Load ScalingLoad Scaling Optimum setup:Optimum setup:

FEA solution for unit load (e.g. 1 N, 1 kN, etc. – FEA solution for unit load (e.g. 1 N, 1 kN, etc. – something with what can be easily worked further)something with what can be easily worked further)

FEA result FEA result input for a input for a desired load desired load

e.g. the e.g. the load equal load equal to the load to the load amplitudeamplitude

not so not so handy for handy for further further modificatiomodificationsns

Loads, Results and Node descriptions can be scaled as whole data_vectors by the use of Scale By command available from the database tree popup-up menuAttention: Do not scale results from elastic-plastic FEA!

Setup of Calculation Setup of Calculation MethodsMethods

1. Selection of the method affects the content of combo boxes below as well as of all the tables2. Selection of this partial procedures affects the content of the tables

Only the material parameters necessary for selected setup of the method are shown

Check before any calculation that the M.Ps. are defined for all materials included into the selected calculation scope

Transient AnalysisTransient Analysis

Local load history built for cases, where Local load history built for cases, where the linear Hooke’s law is not validthe linear Hooke’s law is not valid

Two ways of creationTwo ways of creation local load history recorded for each local load history recorded for each

node/element (node/element (FE-postprocessor buildsFE-postprocessor builds the the transient analysis)transient analysis)

set of results at different times chained set of results at different times chained together (together (fatigue solver buildsfatigue solver builds the the transient analysis)transient analysis)Transient S-E Tensor Pairs (SET_Pair item)

are placed to the Results / FEA Results groups and not to Loads

1.

2.

Material ParametersMaterial Parameters(MATERIAL)

Even a complete import of the FE-model e.g. from *.nas file Even a complete import of the FE-model e.g. from *.nas file provides only several static parametersprovides only several static parameters

Material definition common Material definition common also with Isolated Points – it also with Isolated Points – it should precede before their should precede before their definitiondefinition

Material parameters Material parameters definition opened from:definition opened from:

1.1. MATERIAL MATERIAL ID-name of ID-name of data_vectordata_vector

2.2. MaterialMaterial item of the item of the main menumain menu

Some material parameters Some material parameters preset in dependency on the preset in dependency on the chosen material groupchosen material group

Note:Note: Use of a decimal Use of a decimal comma or dot depends on comma or dot depends on your local Windows setupyour local Windows setup

Note: The meaning of the material parameter on the edited line is explained at the bottom of the window

Eventual Setup of Material Eventual Setup of Material ParametersParameters

Use the Methods dialogueUse the Methods dialogue

You are not defining the setup of methods, i.e. Methods can You are not defining the setup of methods, i.e. Methods can

be opened even in the otherwise passive View modebe opened even in the otherwise passive View mode

You can see much more efficiently, which material You can see much more efficiently, which material

parameters you really need in order to get to resultsparameters you really need in order to get to results

Any your change of a

table cell starts a

dialogue asking

whether to save your

input into the

Material data_vector

Setup of Calculation Setup of Calculation Methods Methods ((METHODSMETHODS))

Properties of Structure Properties of Structure ((LOCPROPLOCPROP))

The dialogue covers facts on the specimens that The dialogue covers facts on the specimens that

are included neither in the FE-model nor in are included neither in the FE-model nor in

material parameters descriptionmaterial parameters description Surface qualitySurface quality

Up to 3 technologies Up to 3 technologies

affecting the surface affecting the surface

layerlayer

Size effectSize effect

Values in text fields Values in text fields

override the selected override the selected

items in comboboxesitems in comboboxes

Activated for LESA Activated for LESA

method onlymethod only

Coordinate SystemsCoordinate Systems((COORDSYSCOORDSYS))

New coordinate systems can be defined on basis New coordinate systems can be defined on basis

of other previously defined coordinate systemsof other previously defined coordinate systems

Used both for Isolated Points and the FE-modelUsed both for Isolated Points and the FE-model

Definition of a new item:Definition of a new item: the values in the values in

the first the first

column column

(nodes, IPs) (nodes, IPs)

override the override the

next next

positionspositions

3 rows only 3 rows only

define the define the

c.s.c.s.

Coordinate SystemsCoordinate Systems((COORDSYSCOORDSYS))

Thanks to Thanks to Apply to setApply to set buttons the c.ss. can be buttons the c.ss. can be applied to imported data additionallyapplied to imported data additionally

ResultsResults, , LoadsLoads, , Node descriptionsNode descriptions can be can be transformed in the View mode to another c.ss.transformed in the View mode to another c.ss.

Unsolved yet: Unsolved yet: The results imported to PragTic could be The results imported to PragTic could be

printout in another c.s.printout in another c.s.A further data_vector descriptor marking the A further data_vector descriptor marking the

related c.s. has to be implemented in some related c.s. has to be implemented in some next PragTic versionnext PragTic version

The results on shell elements can be defined in The results on shell elements can be defined in their native coordinate systems (i.e. cs intrinsic their native coordinate systems (i.e. cs intrinsic to every particular element). Note thatto every particular element). Note that

it should not affect the fatigue calculationsit should not affect the fatigue calculationsbut it affects transformations between but it affects transformations between

individual c.ss.individual c.ss.

Setups of Analyses Setups of Analyses ((ANA_SETUPANA_SETUP))

Each setup consists Each setup consists of:of: at least one item at least one item

from load regimesfrom load regimes at least one item at least one item

from methodsfrom methods at least one set of at least one set of

nodes, elements or nodes, elements or isolated pointsisolated points

Calculations loopsCalculations loops for each load regimefor each load regime

at each pointat each point for each for each

methodmethod

Note the preselection of the calculation scope by its localization.If there are e.g. only load regimes defined at element centroids, this choice is selected by PragTic automatically.

Specifies the focus of the Specifies the focus of the calculation:calculation:

where (localities) where (localities) on which data (load on which data (load

regimes) regimes) by which method by which method

(methods)(methods)

Setups of Analyses Setups of Analyses ((ANA_SETUPANA_SETUP))

Replaces the common Replaces the common RunRun window in PragTic v.0.2betaH window in PragTic v.0.2betaH

Introduced in order to quicken repeated starts of fatigue analyses in various modifications

Results of Fatigue Results of Fatigue CalculationCalculation

Spreadsheet summary of damage and calculation Spreadsheet summary of damage and calculation related variablesrelated variables

Graphical interpretation of resultsGraphical interpretation of results:: import back to import back to

the original the original FE-post-FE-post-processorprocessor

export of export of fatigue results fatigue results into into aa FEMAP FEMAP neutral file neutral file (*.neu)(*.neu)

export to a export to a batch file that batch file that can be can be imported to imported to AnsysAnsys

PragTic’s HelpPragTic’s Help freely downloadablefreely downloadable created as a context created as a context

helphelp *.chm version*.chm version

common context common context manual inmanual in Windows Windows

started from the started from the PragTic’s interface PragTic’s interface ((HelpHelp buttons?, Alt+H buttons?, Alt+H, , F1F1 key key))

*.html version*.html version either for download or either for download or

accessed via Internet (accessed via Internet (www.www.pragticpragtic.com.com))

content coincident to content coincident to the *.chm versionthe *.chm version

does not have Index, does not have Index, thus any search thus any search without knowing the without knowing the structure is structure is problematicproblematic