Scale effect on tribo-mechanical behavior of vegetal fibers in reinforced bio-composite materials

Abstract

The nature of friction of vegetal fiber and polymeric matrix in bio-composite materials is very important for many industrial applications. In order to design natural fiber composites for structural applications, the scientific understanding of tribo-mechanical phenomena inside the heterogeneous structure of natural fibers and also the overall heterogeneous structure of the bio-composite is required. This implies a special focus on the fundamental aspects of vegetal fiber friction at the macro-, meso-, and microscale. This research paper investigates the multiscale mechanical and friction properties of natural fibers. The mechanical properties of flax fibers, glass fibers (as a reference) and polypropylene matrix has been evaluated at microscale and mesoscale by Atomic Force Microscopy (AFM) and Nanoindenter XP (MTS Nano Instruments), respectively, using nanoindentation technique. At the macroscale, the mechanical behavior has been considered for the global composite structure. The micro-friction response of each composite component has been measured by instrumenting AFM for scratch test technique. The results show the scale dependence of mechanical behavior for flax fibers, unlike glass fibers and polypropylene matrix where their mechanical performances are independent of the analysis scale. Tribological results in terms of dynamic friction coefficient show that flax fibers induce more friction than glass fibers, while polypropylene matrix generates the highest friction. This is sign that vegetal fiber friction is scale dependent property as shown when referring to the contact mechanics theory. The arisen results are very important for many technical applications in PMCs surface engineering based on plant fibers.

Mechanics of material removal when cutting natural fiber reinforced thermoplastic composites

“…Indeed, unlike glass fibers, plant fibers present a scale effect since their mechanical properties depends on the mechanical scale used for the analysis as demonstrated in Ref. [19].…”

New Multiscale Approach for Machining Analysis of Natural Fiber ReinforcedBio-Composites

“…This founding has been also confirmed by an orthogonal cutting investigation on UD flax fibers reinforced PP matrix [33] which proves that the multiscale behavior of NFRP composites is independent of the process type. Indeed, the intimate relationship between the relevant scales and the fibrous structure size has been previously confirmed by nanoindentation and scratch test measurements where the authors show the scale effect on the tribo-mechanical performances of flax fibers [46,47].…”

Tribo-functional effects of double-crossed helix on surface finish, cutting friction and tool wear mechanisms during the milling process of natural fiber composites

“…The strong demand for bio-composite materials requires deep investigations into their manufacturing processes to optimize their production [13], especially during machining operation where the cutting behavior of natural fibers presents some issues due to their complex cellulosic structure [14] that makes them highly sensitive to the variation of process parameters. Because of this cellulosic structure, mechanical properties of NFRP composites have a multiscale dependence on the analysis contact scale [15,16]. A particular problem in the milling of NFRP is that of holding good surface finish, which is significantly dependent on the fiber type [17] and the tool geometry such as the cutting edge sharpness [18] and the helix angle of the cutting flutes [19].…”