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Dr R. Moulart, Prof. F. Pierron

High strain rate photomechanics on composites: use of a ultra high speed camera and the virtual fields method. Dr R. Moulart, Prof. F. Pierron. Arts et Métiers ParisTech Châlons-en-Champagne, France. Dr S.R. Hallett, Prof. M.R. Wisnom.

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Dr R. Moulart, Prof. F. Pierron

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  1. High strain rate photomechanics on composites: use of a ultra high speed camera and the virtual fields method Dr R. Moulart, Prof. F. Pierron Arts et Métiers ParisTechChâlons-en-Champagne, France Dr S.R. Hallett, Prof. M.R. Wisnom ACCIS, Aerospace Engineering, University of Bristol, UK Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  2. Objectives • Perform full-field deformation measurements with a ultra high speed camera • Evaluate performances (quantitative measurements) • Process the deformation data to identify stiffnesses • Use of acceleration maps to make up for the lack of force data Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  3. Test set-up Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  4. Quasi-isotropic lay-up: [-452/902/452/02]s 20 Thickness: 2 y Ø = 3.17 x Input tensile wave 16 50 Test set-up • Test specimen: glass-epoxy composite • Cross-line grid: 200 mm pitch • Transferred onto specimen • Displacements obtained by spatial phase shifting Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  5. Test set-up • Ultra high speed camera: Cordin 550-62 • Time resolution: 3.3 ms (300.000 fps) – light issues • Maximum frame rate: 4 Mfps! • Spatial resolution: 1 Mpixel Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  6. Measurements • Grey level images Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  7. Problem of bias caused by sensor positions Measurements Ux in mm • Need for a first set of 62 still images • Phase maps obtained sensor by sensor • Final resolution: 5 mm (2.5% of grid pitch) Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  8. Measurements • Longitudinal displacement Ux in mm Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  9. Measurements • Acceleration maps: double temporal differentiation • 4th order polynomial fit over time • Sliding window of 9 images • Resolution: between 1 and 2.105 m.s-2 m.s-2 Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  10. Strain maps: spatial differentiation Local smoothing (diffuse approximation) Resolution: 10-3 Measurements Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  11. Strain rate maps (s-1): temporal differentiation Calculated through point to point finite difference Resolution: about 400 s-1 Measurements Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  12. The virtual fields method y F -F x L Linear elastic isotropy Integrate over x Homogeneous material Plane stress Identification Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  13. Identification • Principle of virtual work 1 VF: 1 linear equation • No force measurement • In “static”: • Only stiffness ratios (n) • No force measurement • In dynamic • Acceleration forces: distributed volumic load cell! Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  14. L y x Spatial differentiation of Ux Spatial differentiation of Uy Double time differentiation of Uy Identification • Choice of virtual fields: field 1 Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  15. L y x Linear system Identification • Choice of virtual fields: field 2 www.camfit.fr Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  16. Identification • Results Young’s modulus (GPa) Reference: 24.5 GPa Mean: 17.2 GPa Time (ms) Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  17. Identification • Results Poisson’s ratio Reference: 0.35 Mean: 0.28 Time (ms) Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  18. CONCLUSION • Measurements • Use of a UHS speed camera • Quantitative data obtained (novel) • Quality can be improved • Increase frame rate (limit: 4 Mfps) • Improve lighting, improve spatial resolution (grid pitch) • Understand origin of bias and noise • Identification • Quantitative data obtained • Use of acceleration forces (novel) • Huge future potential: no need for Hopkinson bar setup • Need for better (and cheaper) cameras • Need for new test designs Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

  19. ACKNOWLEDGEMENTS • Grant EP/G001715/1 for sabbatical of R. Moulart • Access to the Cordin camera through the EPSRC pool of instruments Engineering and Physical Sciences Research Council Moulart, Pierron, Hallett, Wisnom - SEM 2009 Albuquerque

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