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Thin ply composites: Experimental characterization and modeling

Thin ply composites: Experimental characterization and modeling. In partnership with North-TPT, FHNW, RUAG Technology, RUAG space, and Connova. ICCM19 Montréal 2013. Robin Amacher , Joël Cugnoni , John Botsis Ecole polytechnique fédérale de Lausanne , Switzerland.

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Thin ply composites: Experimental characterization and modeling

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  1. Thin ply composites: Experimental characterization and modeling In partnership with North-TPT, FHNW, RUAG Technology, RUAG space, and Connova ICCM19 Montréal 2013 Robin Amacher, Joël Cugnoni, John Botsis Ecole polytechnique fédérale de Lausanne , Switzerland

  2. Why Thin Ply composites? Thin ply : below 125 g/m2, down to 15g/m2 today Intro • Advantages: • Improved delamination resistance, higher onset of damage & ultimate failure • Improved fatigue properties and in some case damage tolerance • More design degrees of freedom = more optimal laminate • Easier to design ply drops / small angle laminates / local reinforcements • Can produce “homogeneous” laminates, no more dependency on stacking • Can produce mixed “thin & thick” laminates for structures with large shell thickness variations. • Thin ply materials are now commercially available • Challenges: • Characterization and understanding of ply-thickness effect for a wide range of constituents • Efficient and accurate models for prediction of thin ply composite performance • Flexible manufacturing (assembly of complex preform) & automation to reduce layup time • Develop & validate efficient design method to account for the performance benefit without blowing up the degree of complexity of the problem Relevant literature (small subset): [1] S. Sihn, R.Y. Kim, K. Kawabe, S. Tsai, Experimental studies of thin-ply laminated composites, Composites Science and Technology,67, 2007 [2] M.R. Wisnom, B. Kahn, S.R. Hallet, Size effects in unnotched tensile strength of unidirectional and quasi-isotropic carbon/epoxy composites, Composite Structures, 84, 2008 [3] A. Arteiro, G. Catalanotti, J. Xavier, P.P. Camanho, Notched response of non-crimp fabric thin-ply laminates, Composites Science and Technology,79, 2013 Lamina level Laminatelevel Elementlevel Simulation Design Conclusion

  3. Objectives & Method Intro Objectives:Understand, characterize and model thinply composites from the plylevel to part level. Experimentalstudy of thinply size effects • Constant specimenthickness • UD prepregs of varyingplythickness& number of sub-laminaterepetitions Material • North TPT Thinplycomposites UD prepregwith ATL production of complexlaminates • Thick= 300 (2x150) g/m2 ~300 microns / ply • Intermediate = 100 g/m2 ~100 microns / ply • Thin = 30 g/m2 ~30 microns / ply • M40JB fiber / NTPT TP80ep (80°C epoxyresin) fromthe samebatchesand production on the same machine the sameweek. Autoclaveproduction, 55% fiber volume fraction Lamina level Laminatelevel Elementlevel Simulation Design Conclusion

  4. Experimental characterization of Thin-ply size effects

  5. UD plylevelproperties • Overall no change in intrinsic lamina properties when reducing ply thickness • One exception: 0° compression Thick 300 g/m2 Intro • Thin Ply : more uniform microstructure and improved 0° compressive strength Compressive strength(ASTM D5467*) Lamina level Laminatelevel Intermediate 100g/m2 Elementlevel Simulation Design Thin 30g/m2 Conclusion

  6. Quasi isotropic laminate, tensile ASTM D3039, constant thickness, sub-laminate scaling: [+45°/90°/-45°/0°]ns with n=1 for thick, n=3 for interm. and n=10 for thin ply. Intro Lamina level Laminatelevel Elementlevel Simulation Design Conclusion Damage (Acoustic emission) Applied stress

  7. QISO tensile properties [+45°/90°/-45°/0°]ns Intro Ultimate strength: +42% • Onset of damage: +227% Lamina level n=10 & n=3 n=3 Laminatelevel • Change of failure mode: • Thick: extensive matrix cracking & delamination • Thin: brittle rupture by fiber failure (max strain of fiber) • Little effect of n n=1 Elementlevel Simulation Design Conclusion

  8. Open Hole Compression Open Hole Compression [+45°/90°/-45°/0°]ns (ISO 14126 / ASTM D6484) Intro Lamina level +18% Laminatelevel OHC Strength [Mpa] Elementlevel Checklist Simulation Design

  9. Open Hole Tensile fatigue Open Hole Tensile: static and fatigue (ASTM D5766 & D7615, R=0.1) [+45°/90°/-45°/0°]ns Intro • Lower static ultimate strength. No damage around hole means no stress concentration relief but better predictability (Wisnom & al) Lamina level -34% Laminatelevel +31% Thick plies 300g/m2, n=1 @12k cycles, 316MPa Thin plies 30g/m2, n=10 @1M, 316MPa Elementlevel Simulation Design Ruin = -10% stiffness Conclusion • Strong improvement in fatigue life (<20k vs >1M cycles)

  10. Bolted joint bearing strength Single lap bearing test, standard and Hot Wet condition (ASTM 5961), fastener type EN-6115 Hot Wet cond. 95%RH/70°C, test 90°C [+45°/90°/-45°/0°]ns Intro • Strength improvement for as produced @ 20°C  +18% • Strength improvement for Hot Wet @ 90°C  +58% Lamina level Intermediate 100g/m2, n=5 Thin Ply 30g/m2, n=18 Thick Ply 300g/m2, n=2 sbr_ult = 584 MPa sbr_ult = 573 MPa sbr_ult = 476 MPa Laminatelevel As Produced, 20°C Elementlevel Hot Wet 90°C sbr_ult = 372 MPa sbr_ult = 294 MPa sbr_ult = 156 MPa Simulation As produced, 20°C Design Conclusion Hot Wet 90°C

  11. Low energy impact • Rectangular specimen clamped on the short sides; bending is dominant • QI [0°/+45°/90°/-45°]ns, 300 x 140 x 2.4 mm • Thick (300 g/m2) n=1, Intermediate (100g/m2) n=3, Thin (30g/m2) n=10 • Energy: 11.5 J & 18J THICK, n=1 INTERMEDIATE, n=3 THIN, n=10 Intro • Transition of failure mode from delamination to fiber failure • An optimal ply thickness can be found to achieve the smallest damage area • Thin-Ply technology allows tailoring the material properties wrt impact induced damage Lamina level Backside Laminatelevel Elementlevel Summary Simulation Design mostly fiber failure delamination & fiber failure delamination

  12. Modeling of Thin-ply size effects

  13. Modelingthin-ply size effects Intro Plythicknesseffects: • reduction of interlaminarshear stresses at the free edges& delayed free edgedelamination • Constrained intra laminar transverse cracks => apparent 90° and in-planeshearstrengthincrease=> in-situ plystrength model (*) • Matrix cracking induceddelaminationalsodelayedby constraining plies • Othermechanisms(bridging?, plasticity of matrix?) Lamina level 2D generalized plane strain or 3D continuum model Laminatelevel Elementlevel In-situ shear / normal strength (*) + coarse 3D model Or high fidelity 3D continuum model + cohesive zone Simulation Design Conclusion High fidelity 3D continuum model + cohesive zone Fracture mechanics : onset ~ 1/sqrt(t) (*) Camanho et al., Composites Part A, 37, 2006

  14. Simulation of ‘thin ply’ effects Intro • Goal: capture the transition in dominant failure mode in order to understand and predictply size effectswithinteracting damage modes • Hypotheses: no change in intrinsicproperties of ply and interface wrtplythickness Lamina level Cohesiveelements => Intralaminarmatrix cracking 2ndply: -45° 3rd ply: 90° First ply: 0° (symetry) User materialwith fiberfailure (subroutine) Cohesiveelements > lateral cracking User materialwith fiberfailure (subroutine) Laminatelevel Elementlevel 45° 90° -45° Simulation Symmetry BC 0° Between the layers: cohesive surfaces => delamination UD mx. withoutfiberfailure Simulation: force controlled (sigmoidramp, quasi-static) Design Conclusion • High fidelity 3D modelingof quasi isotropicunnotchedtensile test in AbaqusExplicit, [45°/90°/-45°/0°]ns laminate. • All material properties coming from tests, no fitting parameters.

  15. Simulation of ‘thin ply’ effects • Damage models: cohesive interfaces between plies, cohesiveelements for transverse cracking, continuum damage model for fiberfailure • Meshconvergence study: 6 linearhex. element C3D8R per plythickness, 0.5mm in plane elem. size, up to 650k elements, 2.1M dofs • Mass scaling & time step convergence study: dt = ~5e-6 s, ~500’000 time steps Intro Lamina level Laminatelevel Elementlevel Simulation Design Conclusion

  16. Thick ply (300 g/m2) QISO tensile Intro Lamina level Laminatelevel Elementlevel Simulation Design Intra laminar cracking (matrix failure) Conclusion Delamination damage Fiber failure

  17. Thick ply (300 g/m2) QISO tensile Intro Lamina level Laminatelevel Elementlevel Simulation Design • Damage sequence: • cracking of 90° ply, then cracking of 45° plies & delaminationfromedges • Final failureafter extensive delamination / damage of all off-axis plies • Ultimatestrength: fiberfailure in 0° plies with all other plies broken Conclusion

  18. Intermediate ply (100 g/m2), n=3 Intro Lamina level Laminatelevel Elementlevel Simulation Design • Damage sequence: • cracking of 90° plies thenouter 45° plythen final failure (localization of damage startingfrom the free edgesand fiberfailurein 0° plies • Transverse normal and shear cracking delayed, Delaminationnearlysuppressed Conclusion

  19. Simulation of ‘thin ply’ effects FE Analysis Intermediate 100 g/m2 Thick 300 g/m2 • Good predictions for thick & intermediate ply thickness for both onset of damage and ultimate strength. • High fidelity FE model can capture the change of damage mode sequence wrt ply thickness (with constant intrinsic properties) • Coarse 3D FE Models (1 elem/ply) with in-situ strength (scaled by 1/sqrt(t)) provide comparable results, could be extended towards shell modeling (work in progress)

  20. Towards part level modeling and design High fidelity 3D FE modeling All damage modes with interactions Intro Delamination follows intra laminar cracking(no complex interaction) Lamina level Computation time Separate damage models for transverse cracking and delamination Coarse 3D FE modelingwith in-situ strength Laminatelevel Elementlevel Ply thickness small enough to avoid delamination Shell models or CLT with in-situ strength Simulation Damage models for transverse cracking Delamination Design • Thin Ply composites : closer to classical laminate theory as no delamination!! Conclusion

  21. Why Thin Ply composites? Thin ply : below 125 g/m2, down to 15g/m2 today Intro • Advantages: • Improved delamination resistance, higher onset of damage & ultimate failure • Improved fatigue properties and in some case damage tolerance • More design degrees of freedom = more optimal laminate • Easier to design ply drops / small angle laminates / local reinforcements • Can produce “homogeneous” laminates, no more dependency on stacking • Can produce mixed “thin & thick” laminates for structures with large shell thickness variations. • Thin ply materials are now commercially available • Challenges: • Characterization and understanding of ply-thickness effect for a wide range of constituents • Efficient and accurate models for prediction of thin ply composite performance • Flexible manufacturing (assembly of complex preform) & automation to reduce layup time • Develop & validate efficient design method to account for the performance benefit without blowing up the degree of complexity of the problem Lamina level Laminatelevel Elementlevel Simulation Design Conclusion

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