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