Usage of the software nCode for fatigue evaluation of … · · 2017-01-16The nCode Software...

Marenco Swisshelicopter AG © Marenco Swisshelicopter AG | Waldemar Schäfer 1 |

Usage of the software nCode for fatigue evaluation of helicopter structure M. Malnati - Marenco Swisshelicopter - Pfäffikon ZH


Marenco Swisshelicopter SKYe SH09 Project

Light helicopter concept in 2002 (Alternative engines, Business plan)

Decision 2.5 to class, largest turbine segment (highest numbers)

Intensive search for an investor

Founding of Marenco Swisshelicopter AG in 2007

Start of the development of the SKYe SH09 December 2009

Founding of Marenco Germany in 2012

P1 Roll out 2013

P1 First Flight 2014

P2 First Flight 2016

Usage of the software nCode for fatigue evaluation of helicopter structure



SKYe SH09 Project


The nCode Software

ANSYS nCode DesignLife integrates nCode capabilities in Ansys

Software for performing fatigue-life analyses on the basis of FEM-Results

Efficiently analyse large finite element models and complete usage schedules

Wide range of fatigue analysis capabilities including stress-life, strain-life, multi-axial, weld analysis, virtual shaker table, and more

Highly configurable for the expert user

Single environment for both Test and CAE data

Enables standardization of analysis processes and reporting



Helicopter fatigue spectra and loads

1. Definition of a flight-manoeuvres sequence Manoeuvre Duration [s]

1 Start-Up 1 2 Vertical Take Off at MCP 8 3 Hover 5 4 Autorotation - Entry 2 5 Autorotation - Descent 10 6 Autorotation - Flare 2 7 Hover 5 8 Straight forward flight 80kts 30 9 Straight forward flight 120kts 57

10 Pull-up 2 11 Steady Climb 66 12 Straight forward flight 140kts 14 13 Level banked turn 45° 5 14 Straight forward flight 140kts 14 15 Level banked turn 45° 5 16 Straight forward flight 140kts 14 17 Level banked turn 30° 5 18 Straight forward flight 140kts 14 19 Level banked turn 30° 5 20 Straight forward flight 140kts 14 21 Level banked turn 30° 5 22 Straight forward flight 140kts 14 23 Level banked turn 30° 5 24 Straight forward flight 140kts 14 25 Level banked turn 30° 5 26 Straight forward flight 140kts 14 27 Level banked turn 30° 5 28 Straight forward flight 140kts 14 29 Level banked turn 30° 5 30 Straight forward flight 140kts 14 31 Level banked turn 30° 5 32 Straight forward flight 140kts 14 33 Level banked turn 30° 5 34 Straight forward flight 140kts 14 35 Level banked turn 30° 5 36 Straight forward flight 140kts 26 37 Push-Over 2 38 Descent 66 39 Straight forward flight 120kts 57 40 Straight forward flight 80kts 30 41 Hover 10 42 Vertical Landing 8 43 Shut-Off 1

-300

-200

-100

0

100

200

300

0 50 100 150 200 250 300 350 400 450 500 550 600 650

The mission used for calculating fatigue is characterised by a sequence of manoeuvres defining the spectrum



Helicopter fatigue spectra and loads 2. Calculation of loads on each subpart or component of the

helicopter structure

By MSH the Load Dpt. provides loading acting on the structural system submitted to analysis during all the phases describing the mission-flight

F3 [N]

Force acting in the different flight-phases during a blade revolution (0° to 360°)



ANSYS Finite Element Model

Unit fatigue load cases are defined and calculated on the component. For ex. for F3 (s. previous page) a load case is created with unit force 1000 N



nCode module

nCode is provided as a specific module within a ANSYS-Workbench session



Input data setting for nCode

1. Time Series describing the load history

The coefficients of each FEM input load case can be provided to a nCode in form of a Time Series. For instance in the previous example the coefficients describe the entire blade revolution period for each of the three forces and for each single manoeuvre.


The stress contribution of load case k at each point of the FEM is calculated at the instant t as:

( c(t) · Scale Factor + Offset ) · sij(k)FEM

Divider sij(t;k) =

sij(t) = Sk sij(t;k)

Then a sum of stresses from all load cases provides the stress at the point




2. Combination of Time Series in "Duty Cycles" to form the complete flight

Each defined Time Series is used to build-up the scheduled flight by use of a sequence and a number of repetitions (corresponding to number of blade revolutions for the analysed component) occurring in the single manoeuvre’s phase.




3. Definition of settings for fatigue analysis




4. Definition of material data

Material SN-Curve can be entered either in the ANSYS Engineering Data …




4. Definition of material data

… or in the nCode Materials Manager module



Running the nCode analysis



Life Repeats shown here are intended as the number of the whole "flights“ defined by the Duty Cycle above

nCode results

1. Results in graphical form



nCode results 2. Results in tabular form



Usage of in-flight measured data for nCode analysis

The forces acting on same component shown above are continuously measured during prototype P2 flight-testing programme. This allows continuous monitoring of fatigue-life consumption. In this case nCode input is a simple Time Series.

Recalculation of safe fatigue life projection from measured data



Splitting analysis using different multiaxial criteria

It is useful under complex spectra and for huge FE models to use firstly a rough but less time-consuming fatigue criterion (ex. SignedVonMises) only to select the group of critical nodes of the analysis. Then the more reliable but more time consuming Critical Plane criterion can be used on the critical nodes only.



Example of fatigue analyses on helicopter components

Tail Rotor Gear Box

This component has

• Complex geometry (casting part)

• Strongly multiaxial loading (multiple forces not in phase acting simultaneously)

• Complex spectrum (flight manoeuvres combination: s. above)

Classical fatigue hand-analysis is practically unfeasible. A test campaign is anyway necessary for certification but this is extremely costly and needs to be performed when all the design parameters are certain and frozen

The capability to perform a reliable fatigue analysis in advance appears indispensable for economizing resources during development and for testing different possible solutions (for ex. weight saving)




Tail Rotor Gear Box

Inputs for nCode

Sequence of manoeuvres Operational Loads acting on the component are available for each manoeuvre.

For ex. Vertical Take-Off +3° pitch:




Tail Rotor Gear Box

Inputs for nCode Material Working SN Curve




Tail Rotor Gear Box

Results from nCode analysis: Life duration in number of repeats.

The allowable safe-life Flight-Hrs can be then calculated


Thank you for your attention!

Questions?



M. Malnati - Marenco Swisshelicopter - Pfäffikon ZH

Usage of the software nCode for fatigue evaluation of … · · 2017-01-16The nCode Software...

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