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Pedro P. Camanho DEMec , University of Porto, Portugal Hannes Körber

High strain rate characterization of unidirectional carbon-epoxy IM7-8552 in transverse compression and in-plane shear via digital image correlation. Pedro P. Camanho DEMec , University of Porto, Portugal Hannes Körber DEMec , University of Porto, Portugal

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Pedro P. Camanho DEMec , University of Porto, Portugal Hannes Körber

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  1. High strain rate characterization of unidirectional carbon-epoxy IM7-8552 in transverse compression and in-plane shear via digital image correlation Pedro P. Camanho DEMec, University of Porto, Portugal Hannes Körber DEMec, University of Porto, Portugal TechnischeUniversitätMünchen, Lehrstuhlfür Carbon Composites, Germany José Xavier UTAD, Vila Real, Portugal

  2. 1. Introduction Contents Introduction. Longitudinal compression tests. Off-axis compression tests. Analysis model. Conclusions.

  3. 1. Introduction • Aircraft dynamic threats • Crashworthiness. • Bird strike. • Tyre debris impact. • Hard debris impact. • Hail impact. Hail damage Bird strike [www.aviation-safety.net] Longitudinal Compressive Modulus Longitudinal Compressive Strength No consensus reachedin previous studies; further investigations are required

  4. 1. Introduction • Objectives • To perform an experimental investigation of strain rate effects on the mechanical response of unidirectional carbon-epoxy composites: • elastic, plastic and strength properties. • uni-axial and multi-axial loading. • To provide a sound scientific basis for the development of a strain rate dependent constitutive model. Materials and methods • Hexcel IM7-8552 CFRP used. • Unidirectional test specimens. • High-strain rate tests performed using a Split-Hopkinson Pressure Bar. • The same specimen configurations and load introduction systems used in-quasi static tests performed in an universal test machine.

  5. SHPB Experiment Simulation IM7-8552 longitudinal compressive stress 2. Longitudinal compression [0]12 UD laminate; nominal dimensions: 23x7x1.5mm3 (Koerber and Camanho, Composites – Part A, in press, 2011).

  6. 2. Longitudinal compression Longitudinal stress-strain diagram Longitudinal modulus is not rate-dependent. Longitudinal compressive strength increases by 40% under dynamic loading.

  7. 3.Off-axis compression Experimental Setup Dynamic test setup Quasi-static test setup [θ]32 UD laminate; θ=15˚, 30˚, 45˚, 60˚, 75˚, 90˚; nominal dimensions: 20x10x4mm3 (Koerber and Camanho, Mechanics of Materials, Vol. 42, 1004-1019, 2010).

  8. 3.Off-axis compression High strain rate failure modes In-plane shear dominated failure modes 15° off-axiscompression (front view) 30° off-axiscompression (front view) Transverse compression dominated failure modes 45° off-axiscompression (sideview) 60° off-axiscompression (sideview) 75° off-axiscompression (sideview) 90° transversecompression (sideview)

  9. 3.Off-axis compression 15° off-axis compression 30° off-axis compression 45° off-axis compression 60° off-axis compression 75° off-axis compression 90° transverse compression

  10. 3.Off-axis compression 45° In-plane shear stress-strain response Extrapolation of in-plane shear strength 30° 15°

  11. 3.Off-axis compression Failure domain, dynamic. Failure domain, quasi-static. Elastic domain, dynamic. Elastic domain, quasi-static.

  12. 3.Off-axis compression Transverse compressive modulus Shear modulus In-plane shear strength Transverse compressive strength

  13. 4. Analysis model Failure criterion:

  14. 4. Analysis model Two-parameter plasticity model Plastic potential (plane stress, no plastic deformation in the fiber direction): Associated flow: Equivalent stress: Effective plastic strain increment: (Sun and Chen, J. Composite Materials, Vol. 23, 1009-1020, 1989).

  15. 4. Analysis model Identification of model parameters selected so that all curves collapse into one master curve master

  16. 4. Analysis model Model implemented in ABAQUS explicit as a material model using a VUMAT user subroutine. Forward-Euler integration scheme used for the stress update.

  17. 4. Analysis model 15⁰ 30⁰ 45⁰ 60⁰ 75⁰ 90⁰

  18. 5. Conclusions Conclusions • The proposed modifications to the SHPB test methods enable a reliable measurement of the dynamic modulus and strengths of polymer composites. • The longitudinal compressive modulus of elasticity in not strain rate sensitive up to the strain rates considered in this work. • The longitudinal compressive strength increased 40% under dynamic loading. • Under dynamic loading the transverse compression modulus of elasticty, yield strength and failure strength increased by 12%, 83% and 45% respectively. • Under dynamic loading the in-plane shear modulus of elasticty, yield strength and failure strength increased by 25%, 88% and 42% respectively. • The failure angle and friction coefficients used in the failure criteria are not affected by the strain rate. • The experimental data obtained can be used to identify simple models that simulate the effect of strain rate on the plastic deformation and failure of composite materials.

  19. 5. Conclusions Future work • Tests at strain rates higher than 1000s-1. • Investigate the effect of strain rate on the fracture toughness of composites. • Enhancement of existing plastic-damage model by including strain rate effects.

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