Virtual Vehicle Research Center b. Engineering System International GmbH d. TU Darmstadt, Fachgebiet Konstruktiver Leichtbau und Bauweisen e

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1 Simulation of the Damage and Failure Behaviour of Flow Drill Screw Joints between Fibre-Reinforced Plastics and Aluminium by using User- Materials Szlosarek, R. a, Karall, T. a, Hahne, C. b, Berger, A. c, Meyer, N. d, Enzinger, N e a Virtual Vehicle Research Center b AUDI AG c Engineering System International GmbH d TU Darmstadt, Fachgebiet Konstruktiver Leichtbau und Bauweisen e TU Graz, Institut für Werkstoffkunde und Schweißtechnik COMET K2 Competence Center - Initiated by the Federal Ministry of Transport, Innovation & Technology (BMVIT) and the Federal Ministry of Science, Research & Economics (BMWFW). Funded by FFG, Land Steiermark and Steirische Wirtschaftsförderung (SFG)

2 Motivation o US-NCAP o 56 km/h o rigid wall o Chrysler Neon Numerical Modelling of the Damage and Failure Behaviour of Flow Drill Screw Joints between Fibre-Reinforced Plastics and Aluminium 2

3 Flow Drill Screw Joints between CFRP-Aluminium micrograph test specimen flow drill screw CFRP aluminium only a one-sided accessibility is necessary low thermal impact minor requirements for part preparation chipless process the thread in the aluminium part is perfectly connected to the screw with no clearances 3

4 Joining Process (1) Placement of the screw in the pre-hole (2) Forming of the through draught (3) Yielding of the aluminium starts (4) Forming of the through draught (5) Forming of the through draught (6) Pre-stressing of the screw by a defined torque 4

5 Roadmap Flow drill screw joint between CFRP - aluminium micrograph test specimen experiment detailed simulation ViF K2 Projekt: Audi, ESI, KLuB, IWS analogous model 5

6 Roadmap Flow drill screw joint between CFRP - aluminium micrograph test specimen experiment ViF K2 Projekt: Audi, ESI, KLuB, IWS 6

7 Experiment Modified KSII-Test Facility aluminium: EN-AW6060-T6; thickness 2,5 mm CFRP: laminate with 8 layers (0/90/45/-45) s ; thickness 1,2 mm modified LWF KS2 test facility of the Laboratory for Materials and Joining Technology of the University of Paderborn 0 test specimen 7

8 Damage and Failure under Cross Tension Video recording of the damage and failure behaviour under cross tension 8

9 Damage and Failure under shearing Load good reproducibility of the tests bearing as dominant failure mode 9

10 Force-Displacement-Curves Test results under various loading angles 100 % 75 % 50 % 25 % nearly the same maximum force under all tested loading angles for the tested combination of CFRP and aluminium 10

11 Roadmap Flow drill screw joint between CFRP - aluminium micrograph test specimen experiment detailed simulation ViF K2 Projekt: Audi, ESI, KLuB, IWS 11

12 Why a Detail Simulation? Modelling of the elastic behaviour Simulation of the damage and failure behaviour Study of additional loading situations Analysis of other material combinations virtual design real experiments numerical experiments 12

13 Finite Element Model Real test facility Finite element model Using symmetries and the results of the optical displacement measurement reduction of the model reduction of computation time within the same result quality 13

14 Pre-load of the Joint Multi-stage analysis to regard the pre-stressing F 1. Stage: pre-load of the screw to take the joining process into account stress transfer 2. Stage: loading of the screw strength analysis u u u 14

15 Pre-load of the Joint Pre-stress of the laminat stress σ

16 Material Modelling Material Models Screw, aluminium, clamp rigid body Test facility (steel S370 and aluminium) material models are available 0 CFRP, 8 layers (0/90/45/-45)s user-material by using the inter-fibre failure criteria of Puck 16

17 User-material model Modelling of inter-fibre fracture - inter-fibre fracture criteria of Puck is based on the fracture hypothesis of Mohr transformation of the stresses into an action plane determination of the fracture angle is mandatory 17

18 Modelling of the Degradation Modelling of an increasing crack density (smeared crack modelling) stress-strain extrapolation method after Schürmann the stress is kept constant with an increasing crack density no additional stress could be transferred after inter-fibre fracture occurs 18

19 Degradation model Stresses on the action plane are kept constant constant: constant: degradation model depends on the fracture angle! 19

20 Degradation model Example: single element σ 3 in GPa

21 Roadmap Flow drill screw joint between CFRP - aluminium micrograph test specimen experiment detailed simulation ViF K2 Projekt: Audi, ESI, KLuB, IWS analogous model 23

22 force force Analogous Model Using shell and beam elements for large structures - non-linear force-displacement-curves - user-defined rupture model - usage of MPC-Links N2 Link-Element (0/90/45/-45)s shearing load N1 (0/90/45/-45)s cross tension test simulation average tests test 1 test 2 test 3 simulation average tests test 1 test 2 test 3 displacement displacement 24

23 Visualization of the LINK Elements Example: multi material profile Aluminium CFRP FDS - length for the normal force - diameter for the shearing force - colours for the damage 25

24 Visualization of the LINK Elements Example: crushing test damage 26

25 Conclusion Modified test facility and data analysis due to test specimens made of CFRP User-defined material model which enables a detailed simulation of the damage and failure behaviour of FRP Analogous model for the use joint modelling in large structures 27

26 Robert Szlosarek Thomas Karall Clemens Hahne André Berger Nils Meyer Norbert Enzinger iws.tugraz.at The authors would like to acknowledge the financial support of the "COMET K2 - Competence Centres for Excellent Technologies Programme" of the Austrian Federal Ministry for Transport, Innovation and Technology (bmvit), the Austrian Federal Ministry of Science, Research and Economy (bmwfw), the Austrian Research Promotion Agency (FFG), the Province of Styria and the Styrian Business Promotion Agency (SFG). The authors would, furthermore, like to express their gratitude to their supporting industrial and scientific project partners, namely Audi AG, ESI GmbH, Institut für Werkstoffkunde und Schweißtechnik at Technical University of Graz, Fachgebiet Konstruktiver Leichtbau und Bauweisen at Technical University of Darmstadt.