introduction to ansys ncode designlife

1 © 2015 ANSYS, Inc. September 7, 2016 ANSYS Confidential

Introduction to ANSYS nCode DesignLife

Lecture 7

Duty Cycles


Agenda

• Discuss duty cycles

• Explain how to create duty cycles

• Explain how to post-process duty cycles


5 Box Trick

• CAE fatigue process can be described in 5 basic steps

Load mapping converts FE results into

stress/strain histories

FE Input

Material

Mapping

Load Mapping

CAE Fatigue

Analysis

Fatigue Results

Display


Load Mapping

• Constant Amplitude, Time Series, and Time Step are common loading mappings

– applicable to both stress-life (SN) and strain-life (EN) fatigue

– Constant Amplitude load mapping

• assumes FE stresses/strains cycle between min and max values

• linear superposition

– Time Series load mapping

• pairs FE results with loading channels to generate stress/strain histories

• linear superposition

– Time Step load mapping

• directly uses FE stress/strain histories


Duty Cycles

• Real-world loading is often a combination of different types of events with associated repeats

– cannot be represented simply as constant amplitude, time series, or time step loading

• Duty Cycles are a combination of sequences and repeats of loadings

– powerful, flexible technique for representing complicated loadings

– can include any combination of constant amplitude, time series, and time step loadings

– can include other duty cycles


Duty Cycles

• Duty cycles are a user defined combination of events

– each event has defined number of repeats

• Events are loadings

– can be constant amplitude, time series, or time-step loadings

• types can be mixed within a duty cycle

– can be other duty cycles

• nested duty cycles

• For example, a duty cycle could contain

– 10 repeats of a constant amplitude loading

– 2 repeats of a time series loading

– 5 repeats of another duty cycle

• Miner’s rule used to sum damage from all events and repeats


Duty Cycles

• Duty cycles can be created interactively using the Edit Load Mapping option in the Analysis Engine

– saved to a file

– simplest method

• Duty cycles can also be created using Schedule Create or from an external text file


Create Duty Cycles Interactively

• Set-up analysis with any type of Load Mapping and the switch the Loading Type to Duty Cycle

– Analysis Engine > RMB > Edit Load Mapping > Loading Type > Duty Cycle


Create Duty Cycles

• Set Configuration Method to Interactive and use RMB to add Events

LoadProviderDutyCycle > RMB >

pick type of load provider


Create Duty Cycles

• Construct duty cycle by selecting multiple load providers

RMB to access property editor

reposition load

providers


Event Processing

• Event Processing defines how cycles are counted within a duty cycle

• Three options

– Independent

• each event is processed independently per Miner’s Rule

• total damage is the sum of the damage per event

– fastest, but can miss overall largest cycle

– Combined Fast

• similar to Independent method but residual cycles between events are processed

– next fastest method with good accuracy

– Combined Full

• all events are processed in their entirety, including all repeats

– slowest, but most accurate method


Independent Event Processing

• Damage for each event is calculated independently as if the event is repeated until failure

– all rainflow cycles are closed within each event

– total damage is the sum of the damage for each event times the number of repeats for each event

A

B

C D E


Combined Fast Event Processing

• Calculates damage for each event and corresponding repeat factor

– residual from all events is combined to handle cycles that cross events

– fast analysis because only one pass of each event is processed

– more precise than Independent method because it accounts for cycles that cross events

• incorporates some assumptions and hence does not give as precise answer as Full method

A

B

C D EFG


Combined Full Event Processing

• Concatenates the events including repeat factors

– for large repeat factors can create very long time histories with long analysis times

A

B

CD E

F G


Comparison of Event Processing Methods

• Combined Full and Combined Fast methods should produce similar results, regardless of the duty cycle

• Independent method can give un-conservative answers when the damage due to cycles that cross events causes is significant

– occurs when the limits between events is substantially different and the events are relatively short


Set Event Processing

• Analysis Engine > RMB > Advanced Edit > EventProcessing


Output Events

• Results can be calculated for entire duty cycle and for each event within the duty cycle

– allows examination of fatigue damage per event

• Analysis Engine > RMB > Advanced Edit

– ResultsHandler > Compressed results > ChannelPerEvent > True

– Analysis Engine > OutputEventResults > True


Summary

• Duty cycles are a combination of other loading types

– powerful, flexible technique for representing complicated loadings

– user defined combination of events

• independent sequences and repeats

– can be constant amplitude, time series, or time-step loadings

• types can be mixed within a duty cycle

– can be other duty cycles

• nested duty cycles

• Duty cycles can be created interactively using the Edit Load Mapping

– can also be created using Schedule Create or from an external text file


Workshop 6

• Workshop 6: Duty Cycles

– restore archive

– solve Mechanical model

– link nCode SN Time Series system to Mechanical model

– open DesignLife

– create duty cycle

– solve

– post-process

introduction to ansys ncode designlife

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