WITHDRAWN: Multiscale cutting and damage mechanisms of flax fiber reinforced biocomposites under hygrothermal conditioning

Abstract

Manufacturing processes of biocomposite materials made of natural plant fibers and biobased polymers are subjected to many issues that slow down their industrial expansion. Among these issues, the hygrothermal conditions are the most relevant because natural plant fibers are highly sensitive to humidity due to their hydrophilic properties, and their ability to absorb water molecules is accelerated by increasing the temperature, which affects their mechanical performances. This paper addresses the cutting and damage mechanisms that occur when machining flax fiber reinforced polylactic-acid (PLA) biocomposites under hygrothermal conditioning. The moisture content, the chip morphology, the tool-chip friction calculated from the machining forces, and the machined surface state observed with a scanning electron microscope are considered in this study to evaluate the machinability and identify the involved mechanisms. Results show that the conditioning temperature and the fiber orientation affects considerably the moisture diffusion behavior inside the biocomposite structure, which modifies the cutting contact interaction and leads to a change in the form of the chip in terms of curling. The tool-chip friction is also dependent on both the hygrothermal conditioning and the fiber orientation that control the different involved mechanisms such as adhesion, plastic deformation, and fiber shear. The microscopic observation of the machined surfaces describes the shearing efficiency of flax fibers regarding the hygrothermal conditioning in addition to the effect of interface and microstructural fiber damages after a long hygrothermal conditioning time.