A simplified modelling approach of front car structures for a shortened design study

Transcription

1 A simplified modelling approach of front car structures for a shortened design study Robert Szlosarek, Rico Neuber TU Bergakademie Freiberg, Institute for machine elements, design and manufacturing TU Bergakademie Freiberg Institute for machine elements, design and manufacturing Chair of machine elements Robert Szlosarek Agricolastr. 1, Freiberg robert.szlosarek@imkf.tu-freiberg.de

2 Motivation Kinetic energy 9 % splashboard 79 % 12 % front structure engine Load scenario: Euro NCAP, frontal crash, 50 km/h Source: D. Anselm Allianz Zentrum für Technik 2

3 Motivation Kinetic energy 9 % splashboard 79 % 12 % front structure engine 4 % fender 57 % main chassis beam 18 % wheel guard Load scenario: Euro NCAP, frontal crash, 50 km/h Source: D. Anselm Allianz Zentrum für Technik Goal: Increased occupant protection by changing the design of the main chassis beam improved energy absorption behavior 3

4 How to rate the crash behavior? Occupant load criterion A1 A2 65 mm 235 mm car occupant Velocity v Inclination = Occupant load criterion (OLC) Time t no coupling between occupant and car ideal coupling 4

5 Motivation Idea of a degressive front car structure Original state Original state car Car degressive Original state occupant Occupant degressive Degressive front car structure Occupant original state Occupant degressive front car structure Velocity v Time t OLC can be reduced by a higher acceleration in the first crash phase degreessive front car structure 5

6 Motivation Reducing the OLC by using a degressive front car structure State of the art Degressive front car structure Crashbox Main chassis beam Force F Displacement u 6

7 Motivation Validated crash model of a Toyota Yaris Sedan Load scenario: frontal crash, 56 km/h, against rigid wall Idea: Reducing the OLC value by modifying the front car structure 7

8 Motivation Development process (Re-) Design 8

9 Motivation Development process (Re-) Design New FE mesh/model 9

10 Motivation Development process (Re-) Design Computation New FE mesh/model 10

11 Motivation Development process Analysis of results (Re-) Design Computation New FE mesh/model 11

12 Motivation Development process Analysis of results Time reduction by looping only these steps using a simplified modelling approach (Re-) Design Computation New FE mesh/model 12

13 Front car submodel Investigation of the front car structure Rigid wall, m= 1246 kg Fixed boundary 13

14 Front car submodel Investigation of the front car structure Rigid wall, m= 1246 kg (=mass of the car), v 0 =56 km/h submodel 14

15 Front car submodel Investigation of the front car structure full car model submodel Velocity [m/s] Time [ms] - Good match in the first 30 ms 15

16 Front car submodel Force-displacement curve of the original front structure Force F [kn] Displacement u [mm] - Original design shows an progressive characteristic of the front car structure 16

17 Simplified modelling approach Generic front car structure Spring elements Reducing the shell-thickness of the crash box and the main chassis beam Implementing spring elements with an adjustable force-displacement curve 17

18 Simplified modelling approach Aim Variation of the force-displacement behavior of the front car structure Implementation Using spring elements in the full car model Reduction of the stiffness of the original components (contact are still working) thickness reduction Force F Deformation spring 18

19 Simplified modelling approach Force-displacement curve of the spring Front end of the car Force F [kn] Spring deformation s F [mm] Using SPRING elements 19

20 Simplified modelling approach Force-displacement curve of the simplified front structure original front car structure degressive front car structure Force F [kn] Displacement u [mm] 20

21 Simplified modelling approach Comparison of different spring modifications Load scenario: frontal crash, 56 km/h, against rigid wall F FH F FU OLC Version kn 1.5 kn Version kn 30 kn Version kn 50 kn 31.4 Original structure Investigation of variants without redesign and remesh of the model! saves time and money The Version 01 shows of the best result high average force of the crash box and low force of the main chassis beam 21

22 Possible solutions Displacement controlled crash structure Crashbox Pipe Split die Two fixed U-shaped profiles 22 22

23 Possible solutions Displacement controlled crash structure Hinges 23

24 Possible solutions Results of a drop tower test Test conditions : v = 10 m/s ( h 5,10 m) m = 150 kg Degressive characteristic of the front car structure 24

25 Degressive front car structure Simulation using the full car model Load scenario: frontal crash, 56 km/h, against rigid wall Original front car structure Degressive front car structure OLC=35.12 OLC=30.5 Reduction of the OLC value from to

26 Degressive front car structure Simulation using the full car model Δa=10 g No coupling of the occupant Reduced maximum acceleration of the car 26

27 Summary Using simplified modelling approaches can help to reduce the product development time Found approach can be transferred to other components using beams for modelling the bumper First try to build a degressive front car structure was successful but not proper for a car Modifying the main chassis beam by notches could be better 27

28 FIN Thank You! Robert Szlosarek /