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FATIGUE EVALUATIONUSING ANSYS NCODE
DESIGNLIFE
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Short overview of fatigue
Introduction to nCode Design Life products
nCode Design Life basic procedure
Main Glyph items
Duty Cycle procedure example
New features for nCode 6.0
OBJECTIVES
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To make it simple, fatigue is a special structural failurestructural failure, dueto crack growth caused by repeated loading cyclesrepeated loading cycles.
Usually loads that result in fatigue failure cause stress levels
that are below the yield stress limit of the material. In other words, a specific load magnitude may not cause failure in anot cause failure in asingle applicationsingle application, but it may result in fatigue failure after severalfatigue failure after several
cyclescycles.
FATIGUE ANALYSIS
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Why perform a fatigue analysis?Why perform a fatigue analysis? Cant the resistance tofatigue be estimated from a stress analysis?
Sometimes it can!Sometimes it can!
Other design factors may contribute to fatigue life. Parts subjected to very simple loading conditions.
But, if the component is subjected to complex loads thatcomplex loads that
vary with timevary with time, a simple stress study can lead to incorrect
results. In this case, a fatigue analysis is recommended.
FATIGUE ANALYSIS
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nCode Design Life is an advanced tool for fatigue evaluation,developed by HBM.
Fully integrated with ANSYS WorkBench 11.0 SP1.
New version (for ANSYS 12.1) to be released this month.
INTRODUCTION TO NCODE DESIGN LIFE PRODUCTS
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Different modules are available, with specific capabilities.
INTRODUCTION TO NCODE DESIGN LIFE PRODUCTS
Package/Module Description
ANSYS nCode DesignLife Standard Base package including Stress-Life, Strain-
Life and Dang Van analyzers
ANSYS nCode DesignLife Modules/add-ons
ANSYS nCode DesignLife
Vibration
Adds ability to do vibration fatigue
analysis. Simulate swept sine and PSD
loadings
ANSYS nCode DesignLife
Accelerated Testing
Signal processing package complementary
to vibration option. Design accelerated virtual
and physical vibration tests.
ANSYS nCode DesignLife
Welds
Fatigue life prediction for seam welds and
spot welds.
ANSYS nCode DesignLife
Parallelization
DesignLife is multi-threaded and licensed
per core with one core included in the base
package.
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What does nCode Design Life and ANSYS Fatigue tools havein common?
They are both postpost--processorsprocessors, reading results from ANSYS.
Some basic featuresbasic features are available in both modules.
nCode Design Life provides some additional advanced
features, unavailable in ANSYS Fatigue Tools:
Several signal treatment toolssignal treatment tools, for load time histories;
More material modelsmaterial models (like Dang Van multiaxial method);
More complex fatigue calculationscomplex fatigue calculations (like vibration analysis and
accumulated damage evaluation); Easier to capture fatigue design intentdesign intent (with workflow templates
and reference files);
More detailed postpost--processingprocessing (like hot-spot identification).
NCODE DESIGN LIFE x ANSYS FATIGUE TOOLS
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nCode Design Life reads the stress results from the ANSYSsimulation.
Loading histories can be defined directly in Design Life.
NCODE DESIGN LIFE BASIC PROCEDURE
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nCode Design Life main screen
NCODE DESIGN LIFE BASIC PROCEDURE
Desktop
Reference Files
(*.RST, loading curves...)
Glyph Library
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A GlyphGlyph is a tool that represents a specific stage or operationfrom the fatigue calculation.
For example, there are glyphs for geometry import, material definition,
postprocessing
Each glyph has input and output connections.
Right-clicking a glyph provides advanced properties
configuration. In Design Life, the user can define a fatigue calculation
procedure by assembling some glyphs, creating a workflowcreating a workflow.
NCODE DESIGN LIFE BASIC PROCEDURE
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Some Glyph libraries available in nCode Design Life.
NCODE DESIGN LIFE BASIC PROCEDURE
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Considering a typical SN fatigue calculation, the followingglyphs are used:
FE Input : FEA results import and load case combination
SN Analysis : material definitions, loading conditions and fatigue solution
advanced properties
Hot Spot Detection : identification of critical points for damage plots
FE Display : result plots
Data Values Display : result tables
NCODE DESIGN LIFE BASIC PROCEDURE
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Glyphs are connected, sharing and transferring information. This fatigue map can be savedcan be saved as a Design Life workflow.
NCODE DESIGN LIFE BASIC PROCEDURE
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Direct recognitionDirect recognition of ANSYS results files (*.RST); Several cases can be combined in one single results file.
Results from the FEA model can be visualized in the Design
Life interface;
FINITE ELEMENT INPUT
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nCode DesignLife automatically recognizes groupsautomatically recognizes groups, basedon FEA file information.
Parts, materials, element types
User defined groupsUser defined groups can be created, with on-screen
selection of nodes or elements.
FINITE ELEMENT INPUT
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nCode DesignLife allows the definition of several fatiguematerial models, including:
SN curvesSN curves (standard, mean multi-curves, R-ratio multi-curves, Haigh
multi-curves, Bastenaire and temperature multi-curves);
N curvesN curves (standard, mean multi-curves, R-ratio multi-curves andtemperature multi-curves);
Dang VanDang Van multiaxial safety factor;
Spot WeldSpot Weld analysis;
Seam WeldSeam Weld analysis;
MATERIAL MODELS
nCode Design Life comes
with a demo materialdatabase, with 100+
example materials, with
different curves!
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Fatigue curves can be derived from mechanical propertiesderived from mechanical properties. For example, curve based on ultimate tensile stress of the material.
The curves can also be manually specifiedmanually specified.
For example, a list of stress-cycle pairs to define a SN curve.
MATERIAL MODELS
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Time Series Time history is obtained from transient analysis.
Constant Amplitude
Creates a 2 point stress history, by scaling and linear superposition.
Time Step
Combination of static loadcases to generate stress/strain history.
Vibration
Determines the rain flow to be used for further analysis.
Duty Cycle
Evaluates the combined effect of repeating loading events, with
accumulated damage calculation.
These loading conditions can be derived from FEA results,
from static, transient, modal and harmonic analysis.
LOADING CONDITIONS
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The fatigue solver provides some advanced setup optionsadvanced setup options,such as:
Result to be readResult to be read from FEA (stress, strain, displacement );
Method for combinationMethod for combination of stress/strain components (Absolute Max
Principal, Signed von Mises, Signed Shear, Critical Plane);
Mean stress correctionMean stress correction (Goodman, Gerber, Morrow, SWT);
Elastic plastic correctionElastic plastic correction (Hoffmann-Seeger, Neuber);
Duty cycle event processingevent processing (independent, combined);
Calculations on surface nodes onlysurface nodes only;
GroupsGroups to be processed;
Unit systemUnit system of the imported file;
Check for static failurestatic failure;
ADVANCED OPTIONS
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The fatigue solver provides results like damage, life, biaxialityratio and dominant stress direction.
Results are available in contour plotscontour plots and data tablesdata tables.
The hotspot glyph identifies the most critical regionsmost critical regions.
POST-PROCESSING FEATURES
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DUTY CYCLE EXAMPLE
A
B
Tension Force, applied on the hole,
in the X-direction
Remote Force, aligned with holes
axis, at Z = 30mm, in the Y-direction
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Two simulations are performed (max. and min. angles). Each simulation includes 4 loadsteps (one for each class).
DUTY CYCLE EXAMPLE
2 RST files are created.They are renamed for
easier reference, as
MAX.RST and MIN.RST
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Design Life is available on the WorkBench launcher. A working directory is selected, where the RST files are.
DUTY CYCLE EXAMPLE
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Workflow for the fatigue duty cycle calculation.
DUTY CYCLE EXAMPLE
Reads FEA results
Combine files
Material Properties
Loading Definition
Advanced Run Options
Critical Regions
Contour Plots
Data Tables
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RST files are dragged to the FE Input glyph. Since a duty cycle analysis will be performed, those files are
combined in a single one.
Mesh and FEA results can be visualized in this glyph as well.
DUTY CYCLE EXAMPLE
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A demo material will be used, with fatigue behavior derivedfrom mechanical properties (UTS = 400 MPa).
DUTY CYCLE EXAMPLE
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Loading history must be defined as a duty cycle. Each class is a duty cycle event (time step load provider).
Number of cycles (repeats) is defined for each event.
DUTY CYCLE EXAMPLE
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In each event, results can be selected from the global file,defining the loading conditions of this event.
DUTY CYCLE EXAMPLE
Class #1 is defined by the results from
loadstep 1, from both simulations
(MAX.RST and MIN.RST).
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It is important to check if the run options are properly defined,in the Advanced Edit window.
DUTY CYCLE EXAMPLE
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The solution is ready to run. Diagnostic messages can beobtained during the calculation for debug purposes.
DUTY CYCLE EXAMPLE
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In the results post-processing, damage values can be studied. The hotspot feature identifies the 10 most critical nodes, showing
their location over the geometry.
DUTY CYCLE EXAMPLE
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Fully-integrated with ANSYS 12.1, available in May 2010 Main new features:
Virtual Strain Gage
Glyph for fatigue crack propagation
Better integration with optimization tools like DesignXplorer and
modeFrontier
Named Selections recognition from WorkBench
NEW FEATURES FOR NCODE 6.0
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FOR MORE INFORMATION ABOUT
NCODE DESIGN LIFE,CONTACT OUR TEAM
THANK YOU
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