5th International CFK-Valley Stade Convention Numerical simulation of the crash behaviour of braided composites Stade, Dipl.-Ing. Ralf Matheis Institut für Kraftfahrzeuge RWTH Aachen University #110410 11rm0033.pptx Slide No. 1
Presentation of the Institute Overview ika Basic data : Founded in 1902 (ika) and 1981 (fka) ika has approx. 230 employees: 60 engineers, 40 workers and technicians as well as apprentices,130 student workers Together with co-operation partner fka access to a total staff of approx. 300 employees Project structure: 55 % Advanced engineering 20 % Serial vehicle development 25 % Future development and others References: Automotive customers from Europe, USA und Asia 17 % OEM and 45 % suppliers 38 % Public funded research #110410 11rm0033.pptx Slide No. 2
Presentation of the Institute Body Department Fields of Activity > Concept design > Lightweight design > Simulation and testing > Passive safety > Benchmarking > Durability #110410 11rm0033.pptx Slide No. 3
Agenda Motivation Physical Testing Numerical Simulation Summary & Outlook #110410 11rm0033.pptx Slide No. 4
Motivation FRP in Automotive Applications Lightweight structures CO 2 -targets demand a sustainable reduction of fuel consumption Electrification of vehicles (weight compensation) Limited resources Advantages of FRP Mass reduction Energy absorption Part and functional integration Formability Styling and image Challenges of FRP Material Process Use phase Braided structures for crash absorbers Highest specific energy absorption of all textile pre-forms offer lightweight potential Large progress in braiding technology in recent years #110410 11rm0033.pptx Slide No. 5 [Sources: KTM, Daimler, ZF, BMW, LCC München]
Force [kn] Motivation CFRP Crash Absorbers Main purpose of a crash management system is absorption on a low energy level AZT (v = 15 km/h) IIHS (v = 10 km/h) Application of a braided energy absorption elements in an automobile front structure Rectangular progression of the force over displacement is aspired Efficiency of the crash absorber: 100 80 E abs η= F max s def Efficiency: Metallic crash box: 40 % - 50 % CFRP absorber: 80 % 60 40 20 MB SLR McLaren #110410 11rm0033.pptx Slide No. 6 0 0 10 20 30 40 50 60 70 80 Deformation [mm] [Source: Daimler]
Fibre stress (E+G) Motivation FEM Simulation of Braided FRP Appropriate modelling mandatory Simulation of FRP still issue of numerous research activities Several approaches for braided structures No flexible modelling yet No testing procedures for braided structures for direct data input defined yet 3 2.5 2 1.5 1 0.5 Material Model A mat 2 B mat 22 C mat 54 D mat 58 E mat 59 E11T (XT = fibre tensile strength) DFAILT ERODS 0 0 0.05 0.1 0.15 0.2 0.25 XT XT*SR XT*SLIMT Fibre strain LS-Dyna common explicite FEM solver Several material models for FRP Usability for such structures has been shown Special approach has to be found in order to take account of all damage effects #110410 11rm0033.pptx Slide No. 7 [Source: Dynamore]
Agenda Motivation Physical Testing Numerical Simulation Summary & Outlook #110410 11rm0033.pptx Slide No. 8
Physical Testing Manufacturing Process Axial 0 -Fäden fibres Braiding Flechtfäden fibres Braiding Flechtringe rings Braiding Flechtwinkel angle +/- 30 +/- 60 +/- 45 Axialfadenanteil fibre share 0 % 20 % 50 % Fibre: Carbon roving HTS 5631 12k Matrix: Infusion resin RIM 135 Lay-down of six pre-form layers on a steel core Variation of the production parameters braiding angle and axial fibre share Impregnation of the pre-forms via vacuum resin infusion Cutting to the test specimen s length after consolidisation #110410 11rm0033.pptx Slide No. 9
Physical Testing Tensile Tests Testing derived from DIN EN ISO 527 Flat specimen Same manufacturing process as shown before No homogenous results No transfer to material model of tubular braiding structures possible #110410 11rm0033.pptx Slide No. 10
Physical Testing Drop Tower Tests (1/4) Drop mass Guidance Displacement transducer Hollow steel profiles Accelerometer Specimen Load cell Trigger geometry: 30 chamfer Steel plug Energy application of 10 kj Evaluation of the first 180 mm of displacement in order to obtain comparable force displacements curves for all nine structures #110410 11rm0033.pptx Slide No. 11
Physical Testing Drop Tower Tests (2/4) Exemplary behaviour of a tube with a braiding structure with 45 braiding angle without axial fibres #110410 11rm0033.pptx Slide No. 12
Physical Testing Drop Tower Tests (3/4) Averaged force displacement curves for all series: The structure with 60 braiding angle and no axial fibres shows a different behaviour than the other series #110410 11rm0033.pptx Slide No. 13
F max [kn] / E spez [kj/kg] F max [kn] / E spez [kj/kg] E def [kj] E def [kj] Physical Testing Drop Tower Tests (4/4) E spec 70 70 60 60 50 50 40 40 14 14 Average efficiency 80 % 14 14 12 12 12 12 10 10 10 10 8 8 8 8 30 30 6 6 6 6 6 6 20 20 4 4 4 4 4 4 10 10 2 22 2 22 0 0 0 0 30 /0% 30 /50% 45 /20% 60 /0% 60 /50% 30 /20% 45 /0% 45 /50% 60 /20% 0 0% 0% 30 20% 30 20% 45 0% 45 0% 45 50% 45 50% 0% 0% 60 20% 60 20% 30 /0% 30 /50% 45 /20% 60 /0% 60 /50% 30 /20% Spezifische Spezifische Energieaufnahme 45 /0% Kraftpeak Kraftpeak Deformationsenergie 45 /50% bei 180 bei mm 180 mm 60 /20% 0 0 Kraftpeak Force Peak Spezifische Specific enery Energieaufnahme absorption Deformationsenergie energy bei at bei 180 180 mm mm #110410 11rm0033.pptx Slide No. 14
Agenda Motivation Physical Testing Numerical Simulation Summary & Outlook #110410 11rm0033.pptx Slide No. 15
Numerical Simulation Material Model Application of Material *MAT_LAMINATED_COMPOSITE FABRIC (MAT_58) Macroscopic elastic damage model defined by Matzenmiller based on Hashin criterion Implemented for fabrics and unidirectional fibres Additional shear failure criterion for numeric stability *MAT_ADD_EROSION σ Fibre Faserbruch failure Matrix Matrixbruch failure τ τ S c S lim,s S c S lims S cc Under-integrated elements Smeared approach Layered shell approach - three integration points: Positive braiding angle Axial fibre Negative braiding angle Hauptfaserorientierung +45 +90-45 S lim,i σ i,max S lim,i σ i,max i,max ε ε γ MS γ MS MS [Source: Dynamore] #110410 11rm0033.pptx Slide No. 16
Force Kraft [N] Kraft [N] Kraft [N] Kraft [N] Numerical Simulation Delamination Model Contact tiebreak Contact definition for delamination *CONTACT_AUTOMATIC_ONE_WAY_ SURFACE_TO_SURFACE_TIEBREAK Stacked shell approach with six shell layers Contact definition considers pressure and shear failure as well as a critical crack length 45 40 45 40 45 40 45 40 No direct transfer of matrix values possible 35 30 35 30 35 30 35 30 Simulation of a DCB test in order to obtain appropriate initial values for contact failure 25 20 15 10 25 20 15 10 25 20 15 Abzugsgeschwindigkeit v = 80 mm/s 10 25 20 15 10 5 5 5 5 z Kraft-Weg-Verlauf x DCB-Test Kraft-Weg-Verlauf DCB Kra y 0 0 0 0 0 1 0 2 1 30 02 14 13 25 24 63 35 4 Displacement Weg [mm] [N] Weg [mm] Weg [mm] Weg [mm] #110410 11rm0033.pptx Slide No. 17
Numerical Simulation Model Set-up v = 7.85 m/s Sectional view Element size 3 mm, congruent meshing Rigid solids for impactor and basis with plug Modelling of the trigger chamfer significant for first force peak and further deformation behaviour Separate material model card for trigger in order to take account of the material pre-damage g z y x First approach for material values calculative respectively determined by literature Validation of the crash behaviour by parameter variation #110410 11rm0033.pptx Slide No. 18
Force [kn] Numerical Simulation Result: 45 Braiding Angle / 0% Axial Fibres Averaged 45 / 0% Simulation Displacement [mm] #110410 11rm0033.pptx Slide No. 19
Force [kn] Numerical Simulation Result: 30 Braiding Angle / 0% Axial Fibres Averaged 30 / 0% Simulation Displacement [mm] #110410 11rm0033.pptx Slide No. 20
Force [kn] Numerical Simulation Result: 45 Braiding Angle / 20% Axial Fibres Averaged 45 / 20% Simulation Displacement [mm] #110410 11rm0033.pptx Slide No. 21
Force [kn] Numerical Simulation Result: 45 Braiding Angle / 50% Axial Fibres Averaged 45 / 50% Simulation Displacement [mm] #110410 11rm0033.pptx Slide No. 22
Agenda Motivation Physical Testing Numerical Simulation Summary & Outlook #110410 11rm0033.pptx Slide No. 23
Summary & Outlook Summary Series of component tests: Testing of flat tensile specimen background of further research activities High specific energy absorption of tubular specimen [64 kj/kg] High components efficiencies [90%] Lower braiding angles lead to higher force peaks and hence to a better energy absorption Simulation of the specimen: Good accuracy for the braiding structure with 45 braiding angle and 0 % axial fibres Direct transfer to the models of other structures not always possible High axial fibre shares show inadequate model behaviour Higher axial fibre shares augment the specific energy absorption #110410 11rm0033.pptx Slide No. 24
Summary & Outlook Outlook Open questions: In general: Quality monitoring RTM Fundamental material testing Transfer of measured material parameters to simulation Strain rates Simulation model: Validity of the approach for: High axial fibre share Higher number of layers Different load application Different materials Different geometries Numerical stabilisation of the delamination behaviour 3,57 mm 2,63 mm [Source: IVW Kaiserslautern] #110410 11rm0033.pptx Slide No. 25
Thank you for your attention! Dipl.-Ing. Ralf Matheis Institut für Kraftfahrzeuge RWTH Aachen University Phone E-Mail Internet +49 241 80 25610 matheis@ika.rwth-aachen.de www.ika.rwth-aachen.de #110410 11rm0033.pptx Slide No. 26