PSI - Issue 8

A. Pantano et al. / Procedia Structural Integrity 8 (2018) 517–525 A. Pantano, B. Zuccarello/ Structural Integrity Procedia 00 (2017) 000–000

8

524

a

100 120 140 160 180

b

c

σ L [MPa]

0 20 40 60 80

Biocomposite with rectilinear fibers Biocomposite with sinusoidal fibers (middle section) Biocomposite with sinusoidal fibers

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020

ε L [ mm/mm ]

Fig.9. (a) Tensile curves of the biocomposites with rectilinear and wavy fibers having a/l = 0.05 and V f =0.2, and (b, c) images of the relative specimens after failure.

From Fig.9 it is possible to observe that the biocomposite with straight fibers exhibits a longitudinal Young modulus of 9.3 GPa and a tensile strength of 156 MPa. The biocomposite with sinusoidal fibers instead, has a tensile strength of about 134 MPa and a Young modulus of 9.1 GPa (green curve in Fig.9), which corresponds to a deviation of the Young modulus of about 2%. The central zone of the specimen, monitored by the MTS extensometer, exhibits instead a more significant decreasing of the Young modulus that is equal to about 8.2 GPa (blu curve in Fig.9), which corresponds to a deviation of about 12% with respect to the biocomposite with rectilinear fibers (red curve). In percentage terms, it is observed a more significant reduction of the tensile strength of about - 14%. The comparison between such results and that provided by the numerical analysis above exposed, i.e. the decreasing of the Young modulus provided from Fig.6, equal to 2%, shows a very good accordance. However, the experimental results allow to observe that, as it is easy to understand, the effects of the natural fiber undulation are not uniform in the specimen (as it can occur in a generic structural component), but they are maximum near the zone where there is the higher misalignment between the fiber direction and load direction. In other words, the local effects are more significant (in the examined specimens they change from a global effect of 2% to a local effect of 12%) and they lead to localized phenomena that influence significantly the mechanical behavior of the biocomposite. The experimental analysis has proved that, unlike it has been observed into the specimens with rectilinear fibers in which the failure can occur in different transversal sections of the same specimen, the failure of the specimens with sinusoidal fibers occurs always at the middle transversal section of the specimen, characterized by the presence of fibers having the maximum misalignment with the loading direction. The numerical and experimental study carried out in this work allowed to analyze the effects of natural fiber waviness on the longitudinal module of long fiber unidirectional biocomposites with green epoxy matrix. In particular, by approximating the wavy form of natural fibers with sinusoids, whose form is uniquely defined by the elongation ratio a/l between the amplitude a of the sinusoid and the relative wavelength l , suitable FEM models have been implemented able to simulate the behavior of orthotropic biocomposites laminates made by a pair of sinusoidal fibers arranged in opposition of phase. Parametric modeling performed allowed to analyze the effects on the longitudinal modulus of the biocomposite of the variation of the key parameters such as the volume fraction of the fibers V f and their average curvature, represented synthetically by the ratio a/l . In summary, the numerical models developed show that, similar to what happens to a perfectly straight fiber composite, the longitudinal module of long 4. Conclusions