PSI - Issue 12

P.M. Giuliani et al. / Procedia Structural Integrity 12 (2018) 296–303 P.M. Giuliani, O. Giannini, R. Panciroli / Structural Integrity Procedia 00 (2018) 000–000 M. Giuliani, O. Giannini, R. Panciroli / ctural Integrity Procedia 0 (2 18) 0–000

302

7

100 125 150 175 200 225 250 275

0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 1 . 4

Stress [ MPa ]

25 50 75

Normalized Stress

0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 1 . 4 1 . 6 1 . 8 2 0

0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 1 . 4 1 . 6 1 . 8 2 0

Strain [%]

Strain [%]

Figure 6. Left: Original stress-strain curves for a set of BioTex/SuperSap specimens cyclically loaded. Right: Results with normalized stress data. Fig. 6. Left: Original stress-strain curves for a set of BioTex / SuperSap specimens cyclically loaded. Right: Results with normalized stress data.

4. Conclusions We presented some preliminary results of an experimental campaign on flax composites fabricated through a LRTM process. Results evidenced that the LRTM process can be e ff ectively utilized to manufacture flax composites, obtaining mechanical properties which are in line with the best properties found in the literature. The behavior of flax composites is found to be both viscoelastic, being highly dependent from the strain rate, and viscoplastic, since inelastic strain is found to accumulate when stains exceed 0 . 1% . The inelastic strains are never recovered and make the apparent modulus of the material to increase at every increasing load cycle. At low strain rates, creep is found to further influence the inelastic strain accumulation. The use of a bio-epoxy instead of a traditional epoxy system has been found to decrease the laminate properties in terms of elastic moduli and ultimate stress by roughly 50%, while the ultimate strain remains approximately constant. Intra-laminate repeatability of the mechanical properties is found to be very high, but results are also found to be highly related to the quality of the manufacturer’s rough material. Tests on specimens with varying fiber volume ratio evidences that the ratio between E 1 and E 2 remains constant, and that the location of the transition point is stable at Á = 0 . 2% . Results also clearly show that failure strain can be used as design criterion. Acknowledgements This work was supported by the Italian ministry for higher education through the grant PRIN2015 n.2015RT8Y45. Views expressed herein are those of the authors and not of the funding agency. The use of a bio-epoxy instead of a traditional epoxy system has been found to decrease the laminate properties in terms of elastic moduli and ultimate stress by roughly 50%, while the ultimate strain remains approximately constant. Intra-laminate repeatability of the mechanical properties is found to be very high, but results are also found to be highly related to the quality of the manufacturer’s rough material. Tests on specimens with varying fiber volume ratio evidences that the ratio between E 1 and E 2 remains constant, and that the location of the transition point is stable at ε = 0 . 2%. Results also clearly show that failure strain can be used as design criterion. Acknowledgements This work was supported by the Italian ministry for higher education through the grant PRIN2015 n.2015RT8Y45. Views expressed herein are those of the authors and not of the funding agency. References Baley, C., 2002. Analysis of the flax fibres tensile behaviour and analysis of the tensile sti ff ness increase. Composites - Part A: Applied Science and Manufacturing 33, 939–948. doi: 10.1016/S1359-835X(02)00040-4 . Deseri, L., Mares, R., 2000. Class of viscoelastoplastic constitutive models based on the maximum dissipation principle. Mechanics of Materials 32, 389–403. doi: 10.1016/S0167-6636(00)00011-9 . Mahboob, Z., Bougherara, H., 2018. Fatigue of flax-epoxy and other plant fibre composites: Critical review and analysis. Composites Part A: Applied Science and Manufacturing 109, 440–462. URL: https://doi.org/10.1016/j.compositesa.2018.03.034 , doi: 10.1016/j. compositesa.2018.03.034 . Mahboob, Z., El Sawi, I., Zdero, R., Fawaz, Z., Boughe ara, H., 2017. Tensile and compressive damaged response in Flax fibre reinforced epoxy composites. Composites Part A: Applied Science and Manufacturing 92, 118–133. URL: http://dx.doi.org/10.1016/j.compositesa. 2016.11.007 , doi: 10.1016/j.compositesa.2016.11.007 . Marklund, E., Eitzenberger, J., Varna, J., 2008. Nonlinear viscoelastic viscoplastic material model including sti ff ness degradation for hemp / lignin composit s. Composites Science and Technology 68, 2156–2162. doi: 10.1016/j.compscitech.2008.03.011 . Mattei, G., Ahluwalia, A., 2018. A new analytical method for estimating lumped parameter constants of linear viscoelastic models from strain rate tests. Mechanics of Time-Dependent Mat rials , 1–9URL: http://dx.doi.org/10.1007/ 11043-018-9385-0h tp://link. s ringer.com/10.1007/s11043-018-9385-0 , doi: 10.10 7/s 1043-018-9385-0 . Pil, L., Bensadoun, F., Pariset, J., Verpoest, I., 2016. Why are designers fascinated by flax and hemp fibre co posites? Composites Part A: Applied Science nd Manufacturing 83, 193–205. URL: http://dx.doi.org/10.1016/j.compositesa.2015.11.004 , doi: 10.1016/ j.c mpositesa.2015.11.004 . Poilaˆne, C., Ch rif, Z.E., Richard, F., Viv t, A., Ben Doudou, B., Chen, J., 201 . Polymer reinforced by flax fibres as a viscoelastoplastic mat ri l. Composite Structures 112, 00–112. d i: 10.1016/j.compstruct.2014.01.043 . References Baley, C., 2002. Analysis of the flax fibres tensile behaviour and analysis of the tensile sti ff ness increase. Composites - Part A: Applied Science and Manufacturing 33, 939–948. doi: 10.1016/S1359-835X(02)00040-4 . Deseri, L., Mares, R., 2000. Class of viscoelastoplastic constitutive models based on the maximum dissipation principle. Mechanics of Materials 32, 389–403. doi: 10.1016/S0167-6636(00)00011-9 . Mahboob, Z., Bougherara, H., 2018. Fatigue of flax-epoxy and other plant fibre composites: Critical review and analysis. Composites Part A: Applied Science and Manufacturing 109, 440–462. URL: https://doi.org/10.1016/j.compositesa. 2018.03.034 , doi: 10.1016/j.compositesa.2018.03.034 .