Realising the Potential of Carbon Fibre Composites in Compression

Transcription

1 Programme Grant Jakub Rycerz, Michael Wisnom, Kevin Potter

2 Outline 2/12 Introduction Material Properties: Carbon Non-linearity Carbon Fibre Theoretical Limits Shear Instability Hybrid Specimen Bending Study: Materials Investigated Results Non-linearity Acknowledgements

3 Carbon Non-linearity 3/12 Non-linearity in carbon well-documented Modulus drops as compressive strain increases Source: [1]

4 Carbon Fibre Theoretical Limits 4/12 Single fibre response shows high strain Metallic-like plateau Single Fibre Compressive Test Source: [2] Typical Carbon Composite ~1.2% Strain +15% Strain to Failure

5 Compressive Failure of Composites 5/12 Failure not due to fibre limit Structural phenomenon shear instability Source: [3] Compressed composite subject to shear stress Resulting shear deformation increases misalignment Shear increases until reaching equilibrium Loss of equilibrium at high enough stress causes failure

6 Parametric Study Materials 6/12 Name Table 1: Material properties (all 8552 resin) Fibre Measured Fibre Thickness Volume [mm] Compressive Modulus [GPa] Compressive Strength [MPa] Tensile Strain [%] S-Glass S2GL N/A Carbon IM7 57.8% Carbon IM7 42.3% N/A N/A N/A Parametric study on shear instability: Lay-up Shear test: Compression via bending:

7 Parametric Study Shear Results 7/12 Exponential fit material: Plateau before fibre rotation material: No plateau Early fibre rotation Shear Instability: Use fitted data to predict maximum compressive strain Two instability curves material stronger at low misalignment values Crossover point at ~0.75 initial misalignment

8 Instability Strain Parametric Study Shear Results 8/12 3% 2% 1% 0% Exponential fit Initial Misalignment [ ] material: Plateau before fibre rotation material: No plateau Early fibre rotation Shear Instability: Use fitted data to predict maximum compressive strain Two instability curves material stronger at low misalignment values Crossover point at ~0.75 initial misalignment

9 Instability Strain Parametric Study 4PB Results 9/12 Strain gauges top and bottom Rubber under loading noses Minimal geometric non-linearity 3.0% 2.5% 2.0% 1.5% 1.0% 0.5% 0.0% Initial Misalignment [ ]

10 Instability Strain Parametric Study 4PB Results 10/12 Strain gauges top and bottom Rubber under loading noses Minimal geometric non-linearity 3.0% 2.5% ε AVG =1.72% 2.0% 1.5% ε HIGH =1.72% ε LOW =1.56% 1.0% ε AVG Low =1.60% Vf 0.5% 0.0% α= Initial Misalignment [ ]

11 Non-linearity and Conclusions 11/12 Loading Artifacts Non-linearity: Change in centroid position due to carbon softening Consistent slope of change of position Conclusions: Shear instability explains well the difference in strains to failure Carbon modulus decreases in compression

12 Acknowledgements 12/12 Programme Grant References: [1] F. Tanaka, T. Okabe, H. Okuda, I. a. Kinloch, and R. J. Young, The effect of nanostructure upon the compressive strength of carbon fibres, J. Mater. Sci., vol. 48, no. 5, pp , Nov [2] M. Ueda, W. Saito, R. Imahori, D. Kanazawa, and T.-K. Jeong, Longitudinal direct compression test of a single carbon fiber in a scanning electron microscope, Compos. Part A Appl. Sci. Manuf., vol. 67, pp , Dec [3] M. Wisnom, The effect of fibre misalignment on the compressive strength of unidirectional carbon fibre/epoxy, Composites, vol. 21, no. 5, pp , Sep