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Effects of mesostructure on the in-plane properties of tufted carbon fabric composites

Effects of mesostructure on the in-plane properties of tufted carbon fabric composites. CompTest 2011, 14 th February 2011 Johannes W G Treiber Denis D R Cartié Ivana K Partridge j.treiber@cranfield.ac.uk. Tufting process. - Modified one-sided stitching process

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Effects of mesostructure on the in-plane properties of tufted carbon fabric composites

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  1. Effects of mesostructure on the in-plane properties of tufted carbon fabric composites CompTest 2011, 14th February 2011 Johannes W G Treiber Denis D R Cartié Ivana K Partridge j.treiber@cranfield.ac.uk

  2. Tufting process - Modified one-sided stitching process - Automated insertion of carbon, glass or aramid thread - For dry composite preforms 0.5% carbon tufted NCF Top Automated KSL KL150 tufting head Hollow needle Presser foot Dry fabric Bottom Tuft thread loop Support foam Tufting process Meso-structure Exp. database FE-Models

  3. Introduction Main purpose: Through-the-thickness reinforcement technique + 460%/+60% mode I/II delamination toughness for only 0.5% areal tuft density (Cranfield) Tuft bridging Delamination crack DCB of 0.5% carbon tufted NCF Drawback: Potential reduction of in-plane properties Stitching: - considerable database Stiffness: -15% to +10% Tensile strength: -25% to +25% Tufting: - to date only 3 experimental studies (KU Leuven, Cranfield) Tensile strengths: -14% to +10% no agreement Need for detailed testing database on wider range of tufted materials Tufting process Meso-structure Exp. database FE-Models

  4. Materials - Carbon Preforms: Uni-weave - [0°]7 , [0°]10 balanced NCF - [(0°/90°)s]2 - Tufted with 2k HTA carbon thread in at sx = sy = 5.6 mm (0.5%) /2.8 mm (2%) Square arrangement • Cross-over • Pattern shift Free loop height: 3.5 – 5 mm - RTM injection of epoxy resin (ACG MVR 444) for dimensional control Tufting process Meso-structure Exp. database FE-Models

  5. In-plane tension behaviour Tensile tests (BS EN ISO 527-4:1997): Property changes depend on fabric and tuft morphology Tufting process Meso-structure Exp. database FE-Models

  6. Meso-structure In-plane disturbance (x-y): Triangular UD 4° w ,φ UD: 6° NCF: 10° Resin pocket Fabric deviation Tuft 0.5% 2.0% Square w Thermal crack Square w,φ 2φ UD: 3° NCF: 4° 7° NCF Tufting process Meso-structure Exp. database FE-Models

  7. Meso-structure Out-of-plane disturbance (x-z/y-z): Thread seam Surface crimp z x Vf = f(wi,tloop, tthread) Thread layer tth Loop layer tl • Surface seam causes local fabric crimp • Resin rich layers and pockets affect global and local Vf z y Tufting process Meso-structure Exp. database FE-Models

  8. Numerical Unit Cell model φ= cosine fct. Loop Vf= f(tl,tth,wi) ¼ UC Resin channel Tuft y Thread y x wi ‘Smeared’ UD x Parametric 3D Unit Cell model (Marc): UD, NCF, square and triangular arrangement Isotropic, linear elastic material + ‘Rule of mixtures’ (Chamis) Failure and degradation: Ply: Puck (FF + 3 modes of IFF) Resin: Maximum strength Knops, Comp. Sci. Tech. 2006 Tufting process Meso-structure Exp. database FE-Models

  9. Failure prediction – NCF 0° Ply ¼ UC A Transverse tension failure A Longitudinal splitting 0.5% NCF|| Cracks • Accurate modulus and strength, also for 2% density (error < 2/4%) • Fabric straightening leads to transverse tension failure in fabric and longitudinal splitting of resin pocket Longitudinal splitting Tufting process Meso-structure Exp. database FE-Models

  10. Failure prediction – NCF 0° Ply B ¼ UC B Fibre failure initiation 0.5% NCF|| Rupture Tuft 0° • Ultimate fabric fibre failure in close vicinity of tuft Tufting process Meso-structure Exp. database FE-Models

  11. Vf distribution 0.5% NCF|| • Local fabric fibre distribution affects both stiffness and strength prediction • Gradient Vf model agrees best with true morphology and tension results Tufting process Meso-structure Exp. database FE-Models

  12. Fibre misalignment φ 0.5% square wmin • Fabric fibre deviation critical on tensile strength, effect on modulus negligible • UD strength more sensitive to fabric deviation Tufting process Meso-structure Exp. database FE-Models

  13. Tuft arrangement UD|| • Upper and lower strength bounds defined by square and triangular pattern • Triangular pattern causes most critical strength reduction Tufting process Meso-structure Exp. database FE-Models

  14. Conclusions • Tuft introduces structural complexity into Z-reinforced composite • Critical meso-structural tuft defects: resin rich pockets, fibre deviation, matrix cracking and local fibre compaction • Tufting has no effect on longitudinal tensile stiffness of UD and biaxial NCF composite, but surface loops increase matrix dominated transverse stiffness • Reduction in longitudinal tensile strength most prominent for UD (<-19%) • Fibre undulation most critical contributing factor, fibre breakage limited effect on tensile strength • High quality experimental morphology data allows accurate tensile stiffness and strength prediction of tufted composites

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