Use of SIMPACK in a CAE Process Chain for Fatigue Analysis Dipl.-Ing. Thomas Ille Dipl.-Ing. Roland Zettler
Content 01 Modelling of a spare wheel mount on virtual test rig 02 Simulation results 03 Benefits of the new SIMPACK interface LOADS for FEMFAT 04 Further development at MAN 2
Introduction Theory and method of modal superposition with LOADS for FEMFAT already discussed in lecture of Mr Dr Dietz at this User Meeting Corporate development with Intec: MAN engaged with financial resources and by support of diploma thesis of Mr Zettler about validation of software and method in the year 2002 Several specialists from different areas (FEA, MBS, fatigue, measurement) involved in the project by concurrent activities LOADS for FEFMAT 3
Validation of the process with auxiliary parts of truck frames Example: Spare wheel mount Spare wheel mount: Mass of complete wheel nearly 110 kg Non-linearities also caused by natural vibration of tyre Test rig Problems with truck frame auxiliary parts: Exhaust silencer Accumulator box Fuel tank Heavy components, cantilevered fixture under severe vibration and shock loads Low-frequency excitation in resonance Many loops in development Truck Spare wheel mount 4
ANSYS FEA model Specification Model size: 16000 elements 95000 degrees of freedom Reduction in FEMBS: 10 natural modes 6 frequency response modes Boundary conditions at spare wheel: Rim considered in FEA model Tyre will be added as MBS component in SIMPACK 5
SIMPACK MBS model Description Statically determinated, rheonomically driven (6 DOF) Simulation time 86 s (up to 610 s!) Sampling rate 400 Hz Drive signals based on measurements of accelerations, converted by RemuSIM 6
Conversion of measured data by RemuSIM Conversion of measured accelerations into a set of positions, velocities and accelerations for rheonomic excitation in SIMPACK by intelligent integration algorithm Independence of measured positions from testing cylinders or cut loads No taring or bearing of the models necessary Measuring on arbitrary places which aren t suitable for measuring of loads, e. g. free cutted frame 7
SIMPACK model Comparison of animation with reality Test rig Virtual test rig in SIMPACK 8
Process chains in simulation and measurement Comparison of results for evaluation of the process LOADS FF 9
Simulation results Vibration behaviour in SIMPACK 10
Simulation results Stresses at selected locations Mismeasurement! (strain gauge on double curved surface) Accurate dynamic behaviour of the MBS guarantees accurate modal stress calculation. 11
Simulation results Durability Durability plot FEMFAT results, visualized in ANSYS (logarithmic color scale) Fatigue Fatigueresults: results: J Simulation: 13 h J Simulation: 13 h J J Test Testrig: rig:27 27hh Damage on test rig: Location of primary crack Ille, Zettler / SIMPACK User Meeting Freiburg 2003 08.04.2003 12
Further development for process improvement FEA- and MBS-specific problems welds, welding spots screws, rivets contact friction natural damping FEA-specific MBS-specific 13
Required computing time 86 s simulation time Comparison of modal superposition by LOADS to transient FEM calculation * ) : Demand Modal superposition Transient FEM calculation CPU time approx. 7 hours approx. 2 weeks disk space < 5 GigaBytes > 1 TeraByte Computing times of single steps with the method of modal superpositon * ) : * ) all data based on Intel 1.7 GHz Xeon processor 14
Benefits of LOADS for FEMFAT compared to related methods Advantages compared to other established MBS methods: Consideration of natural vibration of components (cp. load cut method) Excellent stability of SIMPACK integrator allows even long simulation times (e. g. 10 minutes real time) without substantial loss of accuracy Advantages compared to conventional FEA calculation: Obvious improvement by consideration of vibrations opposite to static load assumptions Improved performance (faster and more efficient) compared to transient FEA calculation, because distribution of stress calculated only once per mode 15
Suggestions for improvement FEMBS - SIMPACK - LOADS FEMBS: Automated mode selection, e. g. by power density More ergonomic and easier handling especially in step declaration of frequency response modes Independency between reference coordinate and center of mass of FEA model SIMPACK: Improved visualization of elastic body deformation Stress visualization LOADS: Lower computing time at SIMPACK post processing by LOADS for FEMFAT Upgrade of the error-prone setup of calculation in loads_ortho.dat (redundant inputs) 16
Further development at MAN Future trends: Transfer to additional use cases: more frame auxiliary parts (e. g. battery box), axles, axle guidances, cabs, engine brackets, bus chassis,... Replacement of cost-intensive experiments by simulation, therefore increased use of test rigs for verification Relative fatigue-prediction at first, with increasing know-how for absolute prediction Parallel to presented process using measured accelerations: development of full vehicle simulation on virtual test track, probably by use of tyre model RMOD-K 17
End Thank you! MAN Nutzfahrzeuge AG Abteilung HTBD http://www.man-trucks.com Dachauer Straße 667 80995 München 18