Slide 1

A Physically-Based Model for the Notched Strength of Woven Quasi- Isotropic CFRP Laminates H.M.S. Belmonte a, S.L. Ogin a, P.A. Smith a, R. Lewin b a School of Engineering, University of Surrey b Rolls Royce plc. HMS Belmonte School of Engineering University of Surrey Guildford, Surrey GU2 7XH, UK Slide 2 Introduction In previous work, it was shown that in woven GFRP laminates with circular central holes there was matrix cracking and fibre tow fractures at the hole edge prior to ultimate load and catastrophic failure. HMS Belmonte Slide 3 Introduction A physically based model (CDG Model) was shown to give good predictions of notched strength with out reliance of fitted parameters. Present work investigates the ability of the CDG model to predict the notched strength of quasi- isotropic woven CFRP laminates. Slide 4 Experimental Material: Six different Quasi-isotropic CFRP Laminates. Reinforcement: Plain Weave (PW) and Five Harness Satin Weave (5HS). Thickness: 3 thicknesses investigated for each weave. Fibre : Toray T300 high strength carbon fibre. Matrix : Vantico MY750 epoxy resin system. Preparation: C-scanning, sectioning, end tabbing & notching Testing: Volume fraction, Mechanical testing and damage investigations. HMS Belmonte Slide 5 Experimental Testing Mechanical Testing: Un-notched - Young's Modulus, Poissons Ratio and Un- notched Strength. Notched 2.5, 5 and 10 mm Circular Centre Holes in 25 mm Wide Coupons and 20 mm Circular Centre Holes in 120 mm Wide Coupons. Fracture Mechanics: SEN Calibration & SEN Fracture. Damage Studies Loading notched coupons to just below ultimate load. HMS Belmonte Slide 6 Material Properties Slide 7 HMS Belmonte Slide 8 Analysis HMS Belmonte Slide 9 Fracture Mechanics Properties Slide 10 Damage Investigations HMS Belmonte Slide 11 Layer 1 Layer 2 Layer 4 Slide 12 HMS Belmonte Layer 4 Layer 8 Layer 7Layer 10 Slide 13 Notched Strength Modelling Whitney Nuismer (WN) failure criteria (Whitney Nuismer 1974) Semi-empirical Require elastic properties, unnotched and notched strength Parameter must be calculated for each laminate investigated Critical Damage Growth (CDG) fracture model (Soutis and Fleck 1990) Uses physically meaningful parameters Considers the growth of a notch edge crack Slide 14 Whitney Nuismer Point Stress Criterion (PSC) - failure occurs when the stress reaches the unnotched laminate strength at a characteristic distance, d 0, ahead of the notch. Average Stress Criterion (ASC) - failure occurs when the average stress over a distance from the notch edge, a 0, reaches the unnotched laminate strength. Slide 15 HMS Belmonte WN Criteria Strength Predictions Slide 16 HMS Belmonte Slide 17 Critical Damage Growth Crack Growth - defined using the ASC of WN model Failure predicted when stress required for crack propagation is equal to stress required for crack growth. Crack Propagation - given by a fracture mechanics approach Analysis is based upon the stable growth and subsequent catastrophic failure of a damage zone at the notch edge Slide 18 HMS Belmonte CDG Strength Predictions Slide 19 HMS Belmonte Slide 20 CDG Parametric Study Slide 21 HMS Belmonte Slide 22 Conclusions Range of mechanical property has been obtained for quasi-isotropic CFRP laminates Fracture from circular holes studied showing tow fracture occurring at hole edge prior to catastrophic failure WN models result in accurate predictions (ASC more accurate than PSC), however fitted parameters need to be re-evaluated for each new case CDG model produced good results for quasi-isotropic CFRP laminates as it did for quasi-isotropic GFRP laminates Parametric study showed that varying both the CDG input parameters by 10% only gives a variation of 10% in the notched strength predictions. HMS Belmonte