Die Simulation von Crash- und Impaktvorgängen auf Faserverbundstrukturen: Eine Herausforderung in der Produktauslegung.

Transcription

1 Die Simulation von Crash- und Impaktvorgängen auf Faserverbundstrukturen: Eine Herausforderung in der Produktauslegung. Dr. André Haufe, Dr. Stefan Hartmann, Dr. Thomas Münz DYNAmore GmbH Stuttgart 1

2 DYNAmore GmbH Gesellschaft für FEM-Ingenieurdienstleistungen Stuttgart - Karlsruhe - Ingolstadt - Langlingen - Berlin Dresden - Linköping - Götheburg - Zürich Industriestraße 2 D Stuttgart Tel Fax info@dynamore.de Internet: 2

3 Portfolio LSTC Produkte LS-DYNA Modelle DYNAmore-Toolbox für LS-DYNA CAE Dienstleistungen Benchmarking Pilotprojekte Unterstützung vor Ort Support Training & Seminare Vor-ort Schulung Workshops Software-Entwicklung System- und Prozessintegration e-services Informations- veranstaltungen 3

4 8. LS-DYNA Forum 9. & 10. Oktober 2012 in Ulm Themen: Crash Insassensicherheit Optimierung Airbag, Dummy Metallumformung Impact und Falltest Herstellungsprozesse Glasumformung Durchstoßprobleme Fluid-Struktur-Interaktion Automotive Schiffbau Luft- und Raumfahrt Offshore Transportation Biomechanik Bauwesen... Weitere Informationen unter 4

5 Composites in technical applications 5

6 Composites: A rather broad term! Definition A combination of two or more materials (reinforcing elements, fillers, and composite matrix binder), differing in form or composition on a macroscale. The constituents retain their identities, i.e. they do not dissolve or merge completely into one another although they act in concert. The components can be physically identified and exhibit an interface between one another. Concrete (cement/stone/steel) Short fiber reinforced polymers (glass/pp) Long fiber reinforced polymers (glass/carbon/pa/pp/ep) Sandwich/Laminates (alloy/polymer/..glass/pvb/ ) 6

7 Composites: A rather broad term! Definition A combination of two or more materials (reinforcing elements, fillers, and composite matrix binder), differing in form or composition on a macroscale. The constituents retain their identities, i.e. they do not dissolve or merge completely into one another although they act in concert. The components can be physically identified and exhibit an interface between one another. Concrete (cement/stone/steel) Short fiber reinforced polymers (glass/pp) Long fiber reinforced polymers (glass/carbon/pa/pp/ep) Sandwich/Laminates (alloy/polymer/..glass/pvb/ ) short fibers long fibers particulate composite materials (particles in a matrix) fibrous composite materials (fibers in a matrix) laminated composite materials (layers of various materials) 7

8 Composites: A rather broad term! Definition A combination of two or more materials (reinforcing elements, fillers, and composite matrix binder), differing in form or composition on a macroscale. The constituents retain their identities, i.e. they do not dissolve or merge completely into one another although they act in concert. The components can be physically identified and exhibit an interface between one another. Properties that drive or limit the application in the automotive industry: & Weight & CO 2 A reduction compared to steel and/or light alloys is anticipated. Can be strongly dependent on composite setup, though! Stiffness & strength Depending on the type or combination of fiber and matrix. Can be higher or less that for comparable classic materials. Production issue Economic issue Part complexity Usually curing of matrix material is one order of magnitude lower than that of comparable engineering materials: Slow production cycle. At present, especially high performance composites are rather expensive. Can be higher than for steel/alloys. May compensate higher cost. 8

9 Manufacturing: Predictive producibility simulation? Short fibers: Injection Molding (even shorter fibers) Glass Mat Reinforced Thermoplatics (GMT) Sheet Molding Compound (SMT) matrix usually vinylester & polyester Bulk Molding Compound (BMT) matrix usually vinylester & polyester Long/continuous fibers: Pre-Pregs - pre-impregnated fibers - available in single plies or laminates - cooling chain necessary - curing in forming tools or autoclave (heat&pressure) Liquid composites molding (LCM): - draping of dry fibers (not impregnated) - injection/infusion of draped fibers in the tool - curing in the tool 9

10 Application: Predict serviceability in crashworthiness Status: Mostly shell like structures. Stiffness and/or deformation prediction possible IF fiber content and/or orientation is known. Failure prediction may be possible if failure mode can be engineered to be ductile. Brittle failure is hard to predict, because many different failure modes may exist due to mechanisms on different length scales: [ m ] [ mm ] [ cm] micro sub-ply meso macro Length scale 10

11 Application: Predict serviceability in crashworthiness Crushing/cracking/delamination/buckling on different length scales [ m ] [ mm ] [ cm] micro sub-ply meso macro Length scale T/C in plane T/C out of plane Shear smaller ele. 70ies 0.6k ele k ele k ele M ele. 11

12 Modeling failure: Interlaminar vs. intralaminar Interlaminar (between laminae): Intralaminar (within one lamina): Risc of delamination modeled by cohesive elements or tiebreak contacts [Camanho] Element: layered (thick/thin) shell or one solid for each layer Material: elasto(plastic) material models with damage behavior Element size in crashworthiness models is 1-2 orders of magnitude bigger, hence damage and failure cannot be described in detail. A smeared approach is unavoidable. stacked layered hybrid stacked coincident smeared stacked solid 12

13 Const. model mapping Composite process chain: Producibility2Servicability Problem: Different applications use different modeling techniques, constitutive models, standards and validation procedures. Producibility Serviceability Anisotropy and inhomogeneity GMT, SMC, BMC LMC or Prepreg?? Modeling technique Anisotropy and inhomogeneity Geometrical mapping 13

14 Const. model mapping Composite process chain: Producibility2Servicability Problem: Different applications use different modeling techniques, constitutive models, standards and validation procedures. Producibility Serviceability Anisotropy and inhomogeneity GMT, SMC, BMC LMC or Prepreg?? Length scale? Anisotropy and inhomogeneity Geometrical mapping?? 14

15 Producibility 15

16 Process simulation: Motivation [ m ] [ mm ] [ cm] Length scale Bundeled beam elements Automatic model setup Detailed studies Solid- or shell elements Automatic model setup Impact / draping simulation Single shell elements Autom. Model setup Draping simulation Smeared modeling Production-/Processsim. Draping and wrinkles 16

17 Process simulation: Motivation 1 ply 2 plies 3 plies m ] [ cm] Length scale homogeneous shell stacked solid or shell Single shell elements Autom. Model setup Draping simulation Smeared modeling Production-/Processsim. Draping and wrinkles membrane layered solid/shell 17

18 Simulation on the μm-scale Example: Generation of finite element model on the basis of CT data real Piqué structure full model diskretisation with single beam elements for each individual thread [ITV Denkendorf, Finckh] 18

19 Simulation on mm-scale Example: - Draping simulation of Piqué knitwear discretized with individual beams - Experimental validation of simulation results via optical system simulation experiment [ITV Denkendorf, Finckh] 19

20 stress Simulation on cm-scale Smeared approach: Homogenization of local structure and constitutive properties real structure structure of mech. model homogenized structure Validation of load bearing properties by basic experiments Homogenization strategy Homogenisierungsstrategie Longitudinal Perpendicular behavior behavior strain Shear behavior 20

21 Modeling techniques on cm-scale: Fabric materials available for draping simulation MAT_34 MAT_234 MAT_235 21

22 Picture Frame Test: MAT_MICROMECHANICS_DRY_FABRIC Single layer membrane element; Material parameters determined by optimization Sensitive parameter: and 12 lock 22

23 Draping: MAT_MICROMECHANICS_DRY_FABRIC / MAT_ELASTIC incl. lay-up Membrane formulation with coincident, elastic shell Three element layers stacked with contact formulation 23

24 Draping: Using discrete elements for strong anisotropy Modeling woven fabrics with beam elements: Warp and weft direction *MAT_LINEAR_ELASTIC_DISCRETE_BEAM (MAT_066) Diagonal behavior modeled with *MAT_CABLE_DISCRETE_BEAM (MAT_071) This approach allows also to model positive and negative shear loading. Optional matrix may be represented with shell elements and elastic/plastic material. 24

25 Process simulation: Draping with strong anisotropy Some fabrics (preforms) show extreme orthotropic behavior. Here modeling with shell elements using different constitutive models is possible: plain weave 5 harness weave and more modeling technique single layer 25

26 Process simulation: Draping with strong anisotropy Some fabrics (preforms) show extreme orthotropic behavior. Here modeling with shell elements using different constitutive models is possible. For stacked preforms a similar approach in finite element modeling is of course possible: Multiple layers of shell elements. y modeling technique three layers 26

27 Serviceability (crashworthiness) 27

28 The challenge to predict failure in crashworthiness Modeling complex failure modes on same length scale (detailed model) on higher length scale (smeared model) Simple failure criteria will often do! Complex failure criteria necessary! 28

29 The challenge to predict failure in crashworthiness Element erosion, which is often seen as the only adequate (or available) solution to failure modeling, leads to strong element dependency in space: in time: Laminated glass: Simple failure criteria on various meshes! Impact loaded composite tube: Shock front travelling through part Possible solution: Enhance discretization towards higher order modeling (and/or finer discretization) Separate brittle failure modes (usually tensile fiber failure) from more ductile mechanisms like compressive matrix failure. Enhance constitutive models with orthotropic damage formulations. Erode elements based on more complex criteria; use fading of elements. 29

30 LS-DYNA: Available models for composite structures Constitutive models for composite structures *MAT_022: (*MAT_COMPOSITE_DAMAGE) plane stress Chang-Chang failure criteria: fiber tension, matrix tension/compression fiber compression is missing sudden failure: E1,E2,nu12,G12 = 0.0 *MAT_054/055: (*MAT_ENHANCED_COMPOSITE_DAMAGE) plane stress failure criteria (54: Chang-Chang 55: Tsai-Wu): fiber tension/compression, matrix tension/compression failure: stresses kept constant till failure strain reached, then: E1,E2,nu12,G12 = 0.0 MAT_54 enhanced by inter-laminar shear damage and failure model plus minimum stress limits. *MAT_058: (*MAT_LAMINATED_COMPOSITE_FABRIC) plane stress Hashin failure criteria: fiber tension/compression, matrix tension/compression exponential damage model *MAT_059: (*MAT_COMPOSITE_FAILURE_Option_MODEL) Option: SHELL/SOLID 30

31 LS-DYNA: Available models for composite structures Constitutive models for composite structures *MAT_158: (*MAT_RATE_SENSITIVE_COMPOSITE_FABRIC) superposition of viscous stress tensor to strain rate independent def. in *MAT_058. *MAT_114: (*MAT_LAYERED_LINEAR_PLASTICITY) plasticity model that DOES use laminated shell theory (LAMSHT=1) *MAT_116: (*MAT_COMPOSITE_LAYUP) elastic behavior (pre-integration in thickness direction for stiffness matrix, saves CPU-cost) requires *INTEGRATION_SHELL resultant formulation (no stresses calculated) *MAT_117: (*MAT_COMPOSITE_MATRIX) elastic behavior (pre-integration in thickness direction outside of LS-DYNA) stiffness coefficients as material parameters given in material coordinate system *MAT_118: (*MAT_COMPOSITE_DIRECT) like *MAT_117 but stiffness coefficients given in element coordinate system (less storage required, no transformation necessary) *MAT_161/162: (*MAT_COMPOSITE_MSC) suitable for delamination strain rate dependent special license required (Material Science Corporation) Only available at extra cost. 31

32 LS-DYNA: Recent developments Constitutive models for composite structures *MAT_Camanho (Continuum-Damage-Model) plane stress coupled failure criteria bi-linear softening law based on fracture toughness 1D-plasticity-model (mixed hardening) for in-plane shear behavior *MAT_Pinho (Continuum-Damage-Model) 3D-stress space coupled failure criteria complex 3D-fibre kinking model linear softening law based on fracture toughness 1D-plasticity-model (mixed hardening) in in-plane shear behavior New options for composite (part) modeling Damage models with softening properties. Usable for inter- and intra-laminar modeling. Implemented in collaboration with Daimler AG. Available in future releases. *PART_Composite Easier definition of lay-ups in part-section by just defining MATID, thickness and orientation. *ELEMENT_(t)shell_composite Same input scheme as in *PART_Composite but on element level. Useful to define different lay-ups within one part (elementwise definition of lay-up). 32

33 Layered shell: No inter-laminar failure possible Impacting mass of 350kg with 10m/s, triggered to fail in shear UD carbon/epoxy composite with [90/0/-45/45] sym lay-up MAT_54 for intra-laminar damage and failure; laminate theory invoked Variation of softening behavior of neighboring elements via parameter SOFT in MAT_54 (crashfront algorithm). It is expected, that the failure mode becomes more ductile, however in this example the parameter set was chosen to be too brittle for the model to take effect. SOFT=0.5 SOFT=0.7 SOFT=0.9 SOFT=0.98 SOFT=0.0/1.0 33

34 4 stacked shells: Failure intra- and inter-laminar Impacting mass of 350kg with 10m/s, triggered to fail in shear UD carbon/epoxy composite with [90/0/-45/45] sym lay-up MAT_54 for intra-laminar damage and failure modeling Cohesive contact formulation for inter-laminar failure (debonding) 34

35 4 stacked shells: Failure intra- and inter-laminar Impacting mass of 350kg with 10m/s, triggered to deform in buckling mode UD carbon/epoxy composite with [90/0/-45/45] sym lay-up MAT_54 for intra-laminar damage and failure modeling Cohesive contact formulation for inter-laminar failure (debonding) 35

36 4 stacked shells: Failure intra- and inter-laminar Impacting mass of 350kg with 10m/s, triggered to deform in buckling mode UD carbon/epoxy composite with [90/0/-45/45] sym lay-up MAT_54 for intra-laminar damage and failure modeling Cohesive contact formulation for inter-laminar failure (debonding) 36

37 Summary Process simulation of different preforms is state-of-the-art and necessary to transport important orthotropic properties into the world of crashworthiness. A number of modeling techniques was presented. Mapping of relevant data from forming/draping to the crash application is available. However, the various modeling techniques require some adjustments. Prediction of failure and crushing in crashworthiness applications is an ongoing and very challenging topic. Transferring history variables is a must for more complex part designs that one expects in the near future. Simple failure models (stress or strain based) as used in the past will be replaced by more sophisticated orthotropic damage evolution models. Partially these are already available. Rigorous testing and validation of code-procedures but also of hard-testingprocedures is necessary to correlate models up to the needed quality. 37

38 FIN 38