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Thin ply technology advantages An overview of the TPT-TECA project Joel Cugnoni, Robin Amacher, John Botsis Laboratory of applied mechanics and reliability.

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Presentation on theme: "Thin ply technology advantages An overview of the TPT-TECA project Joel Cugnoni, Robin Amacher, John Botsis Laboratory of applied mechanics and reliability."— Presentation transcript:

1 Thin ply technology advantages An overview of the TPT-TECA project Joel Cugnoni, Robin Amacher, John Botsis Laboratory of applied mechanics and reliability (LMAF) Ecole polytechnique fédérale de Lausanne (EPFL), Switzerland In partnership with North-TPT, FHNW, RUAG Technology, RUAG space, and Connova

2 Introduction to Project TPT-TECA Swiss industry-academic project with 4 companies and 2 academic partners: o North TPT, Connova, RUAG Technology, RUAG Space, EPFL, FHNW ( ) Goal o Characterize, optimize and demonstrate the technical and economical advantages of the Thin-ply technology developed by North TPT Scientific & technical objectives o fully characterize and optimize two TPT thin ply composite materials, and their processing parameters: M55/cyanate-ester for autoclave production and high Tg and M40JB / TP80ep epoxy for low temperature, autoclave or out-of-autoclave process o evaluation of the ply size effects and determination of the optimal ply thickness with respect to mechanical performance o complete material characterization and evaluation of the predictability of the performance of the final composite parts o design optimization using the flexibility of thin ply technology and production of two benchmark parts to compare the performance and system cost

3 Introduction to Project TPT-TECA TPT-TECA CTI project Industrial / academic collaboration project Material development Production technology & implementation Mechanical performance Prediction models Optimal design of benchmark parts Bearing strength Satellite panel demonstrator part Rheo-kinetics testing and modeling Process cycle optimisation Helicopter structural part demonstrator Evaluation of production time and cost savings Goal: Characterize, optimize and demonstrate the technical and economical advantages of the Thin-ply technology developed by North TPT

4 Introduction to Project TPT-TECA TPT-TECA CTI project Today End: march 2014 Project timeline 24 months start March 1st 2012 WP6: vaccuum bag process optimization

5 Study of ply size effects Method: o Comprehensive study of composite properties and thin ply effects o Properties at Lamina/Laminate/Element levels (same as Mil Hdbk 17) o Resin and fibre fixed (same batch) : UD prepreg TP80ep toughened epoxy / 55%vol M40JB, autoclave production o Tests perfomed at three ply thicknesses: 30g/m2, 100g/m2, 300g/m2 o Constant laminate thickness and specimen dimension, only change ply thickness o Scaling: Ply or sub-laminate repetition (+ half-angle / optimized laminates) Questions to be addressed: o Will thin plies make my part stronger – qualitatively? o How to simulate / predict ply size effects? o Design methods towards part level modeling and design?

6 ThinPly composites: design performance advantages Lamina & Laminate Open Hole & Fatigue Bolted joint & Ageing Impact Damage Resistance Part Design & Analysis ? Click one of the icons below to learn more about Thin Ply composites performance in a specific area … or just continue reading normally to have a full overview

7 Ply and interface failure Ply size effect Measurements: Strain gages Acoustic emission Digital image correlation C-Scan (*)

8 Lamina properties TP80ep/M40JB 55%vol o Overall no change in intrinsic lamina properties except compression ThinPregTM80EP 55%vol M40JB

9 Lamina level thin ply effects o Thin Ply leads to a more uniform microstructure and improved 0° compressive strength Compressive strength UD 0° (ASTM D5467*) Thick 300 g/m2 Intermediate 100g/m2 Thin 30g/m2 +20%

10 Laminate properties Quasi isotropic laminate tensile test (ASTM D3039) [45°/90°/-45°/0°]ns +42% +227% Thin 30g/m2 & Interm. 100g/m2 Thick 300g/m2 Laminate level Failure mode transition from progressive transverse cracking & delamination to quasi brittle failure For thick ply (n=1), onset of damage at ~50% of ult. strength Nearly no damage in thin ply before failure Acoustic emission damage monitoring n=10 n=3n=1

11 Laminate properties Quasi isotropic laminate tensile test (ASTM D3039) [45°/90°/-45°/0°]ns Laminate level o Thin Ply ply-level scaling not better than Thick => Thin ply effect is not an intrinsic ply property. o Strong effect of number of ply thickness is related to the number of sub- laminate repetition: o Thick, n=1 : progressive damage, low onset of damage o Intermediate, n=3 : mixed failure (delamination and macro through crack), improvement in strength and damage onset o Thin, n=10: brittle failure with one macro through crack, best strength and damage onset, behaves like an homogeneous brittle solid o Half angle laminate slightly weaker than standard QISO

12 Open Hole Tensile fatigue o Strong improvement in fatigue (10k vs 1M cycles) o Lower ultimate strength. No damage around hole means no stress concentration relief but better predictability (Wisnom & al, Mollenhauer ) Open Hole Tensile: static and fatigue [45°/90°/-45°/0°]ns (ASTM D5766 & D7615, R=0.1) -34% +31% Thick plies cycles, 316MPaThin plies 316MPa Element level Thick, n=1 Thin, n=10 Fatigue criterion = -10% stiffness

13 Open Hole Compression Element level +18% Open Hole Compression [+45°/90°/-45°/0°]ns (ISO / ASTM D6484) OHC Strength [Mpa]

14 Bolted joint bearing strength o Strength improvement for as 20°C +18% o Strength improvement for Hot 90°C +58% Single lap bearing test *, Hot Wet condition (ASTM 5961), fastener type EN-6115 ThinPregTM80EP 55%vol M40JB as and Hot Wet cond. 95%RH/70°C, test 90°C br_ult = 156 MPa br_ult = 476 MPa br_ult = 573 MPa br_ult = 294 MPa br_ult = 584 MPa br_ult = 372 MPa Thick Ply 300g/m2 Intermediate 100g/m2Thin Ply 30g/m2 Hot Wet 90°C As Produced, 20°C As produced, 20°C Element level *[+45°/90°/-45°/0°]ns n=2 n=18n=5

15 Structural element properties o OHT: lower ult. strength but higher onset of damage, more brittle o Strong improvement of most properties, delamination and damage in off axis plies are nearly suppressed o Much improved hot wet properties as weakening of the matrix is less critical in thin plies (still no delamination) o No damage means a better predictability and durability. Element level

16 Low energy impact o Transition of failure mode from delamination to fiber failure o An optimal ply thickness can be found to achieve the smallest damage area o Thin-Ply technology allows tailoring the material properties wrt impact induced damage o 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/m 2 ) n=1, Intermediate (100g/m 2 ) n=3, Thin (30g/m 2 ) n=10 o Energy: 11.5 J & 18J THICK INTERMEDIATE THIN Backside THICKINTERMEDIATETHIN delamination delamination & fiber failure mostly fiber failure Element level n=1 n=3 n=10

17 Thin ply effects at different scales At the lamina level o More uniform microstructure, lower local variation of fiber Vf and finer voids o Improved longitudinal compressive strength At the laminate level o Delay or suppression of delamination as damage / failure mechanism o Delayed transverse cracking => apparent increase of transverse tensile strength o Increased QI laminate onset of damage and ultimate strength o Increased laminate fatigue strength At the structural component level o Notched tests: improved onset of damage and fatigue life increase; more brittle response but better predictability o Bolted joint strength: strong strength improvement in hot-wet conditions o Impact effects: from delamination to fiber failure, optimal ply thickness is « intermediate ». Checklist Microstructure Change of failure mode (delayed delamination) But more brittle, sensitive to stress concentrators !

18 Will thin plies make my part stronger ? If it has one or more of the following features : o Compressive strength critical o Free edges o Open holes (damage onset) o Fastener connections o Fatigue and impact loading o Delamination cracks are the main concern o Optimization is limited by ply thickness … the answer is probably yes ! But how to quantify the benefits in a predictable manner? Need new analysis models and better design & optimization methods to deal with potentially more design degrees of freedom.. but as the failure modes are simpler, predictability should be easier to reach too! Read further for on going developments towards that goal… Checklist

19 Simulation of thin ply effects o Goal: capture the transition in dominant failure mode in order to understand and predict ply size effects o Hypotheses: no change in lamina and interface properties Work in progress First ply: 0° (symetry) User material with fiber failure (subroutine) UD mx. without fiber failure Cohesive elements > lateral cracking 2 nd ply: -45°3rd ply: 90°4th ply: +45° Between the layers: cohesive surfaces > delamination Simulation: force controlled (sigmoid ramp, quasi-static) o 3D modeling of quasi isotropic unnotched tensile test in Abaqus Explicit o Damage models: cohesive interfaces between plies, cohesive elements for transverse cracking, continuum damage model for fiber failure Simulation All data = from testing !

20 Simulation of thin ply effects o First results on thick ply QISO unnotched tension Work in progress o Results: THICK Cohesive elements = transverse cracking (all layers) 0°-45°90°+45° Interface 0° / -45° Blue dots = fibre failure Interface -45° / 90° Interface9 0° / 45° Blue = undamaged >>> Red = delamination Force – dsp. Damage sequence: o cracking of 90° & 45° plies, delamination 90° / -45° plies from free edges o shear failure of 45° plies, delamination 0° / -45° from free edges o fiber failure in 0° plies Clic to play video Simulation

21 Simulation of thin ply effects Work in progress Thick, n=1 – EXPERIMENTAL (c-scan) Thick, n=1 – NUMERIC (CSDMG) Intermediate, n=3 – NUMERIC (CSDMG) 250 MPa 300 MPa 350 MPa 400 MPa 450 MPa 500 MPa 550 MPa 600 MPa 650 MPa 700 MPa Simulation

22 Simulation of thin ply effects o Damage energy, QISO unnotched tension Work in progress o Good predictions for thick ply composites (300g/m2) for both onset of damage and ultimate strength. Numerical modeling Experimental results (normalized for vf 55%) Simulation Failure at a « boundary » condition to be improved Onset THICK = 248 MPa Onset THICK = 253 MPa Ult. str. THICK = 595 MPa Ult. str. THICK = 685 MPa [+45°/90°/-45°/0°] ns o Future: parametric study, extension to open hole and other cases [mJ]

23 Towards part level modeling and design o Even though ply size effects might be captured by detailed 3D FE modeling, computation cost makes it unsuitable for part level analysis; we need a way to up-scale the analysis (i.e shell models) ! o Homogenization and parametric meso-scale analysis could provide laminate level failure envelopes for shell models. Specific strategy needs to be developed of free-edge crack stability analysis though. o As delamination and transverse cracking are less an issue, standard shell models and laminate theory might be closer to the reality of Thin Ply composites than standard composites! Open questions: o Ply size effects in standard impact tests and compression after impact? o Transverse crack propagation in laminates? Next steps: o Optimization of scarf joints, ply size effects without free edges (tubes) o Design optimization of two demonstrator parts; project continuation? Design ModelFirst ply failure0° ply failureExperimentDamageUlt strength CLT no damage 287 MPa819 MPa Thin ply 30g/m2 821 MPa847 MPa CLT with damage 287 MPa609 MPa Thick ply 300g/m2 248 MPa595 MPa Example: QISO unnotched tensile test, Classical laminate theory analysis

24 Next steps within TECA project Design Scarf joint optimization Parametric FE Experiment Scarf joint optimization Parametric FE Experiment Thin ply effects without free edges Test and FE on tubular specimens Thin ply effects without free edges Test and FE on tubular specimens Thin ply Design Guidelines Simple design rules Where to use thin ply? Failure envelopes (limit cases) Thin ply Design Guidelines Simple design rules Where to use thin ply? Failure envelopes (limit cases) Demonstrator Design & Opt Performance & production time / cost optimization to benefit from thin-ply effects and complex building block production approach Demonstrator Design & Opt Performance & production time / cost optimization to benefit from thin-ply effects and complex building block production approach Demonstrator Production & testing 1)Satellite sandwich panel CE/M55 2)Helicopter part (gear box support structure) Demonstrator Production & testing 1)Satellite sandwich panel CE/M55 2)Helicopter part (gear box support structure)

25 Perspectives (new project?) o Moving further towards Part level performance prediction & design criteria Design o Combined experimental / modeling work based on realistic demonstrator parts is required. Performance vs cost vs complexity (=1/quality) optimum need to be identified for representative cases o Open for collaboration for a continuation project This may look complex, but Thin ply composites behaviour is simpler (less damage mechanisms) than traditional composites. Current designs methods do not consider much damage but 1 st ply failure

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