Flax Reinforced Resin Matrix Composite Materials Development And Research

Flax is abundant in China and flax fiber has higher strength and modulus--density ratio compared with other inorganic fibers such as glass fiber. It is easy to cultivate and its growth period is shot. As a result flax fiber can be decomposed naturally;it could be used as an ideal reinforcing material of environmental protection composites. Flax fiber was used to fabricate with thermo-setting and thermo-plastic resins in this research. Laminates with high property-cost ratio were developed and researched;the results may be important reference for engineering applications theoretically.Flax reinforced thermo-plastic composites were mainly analyzed in this paper. For comparison, first flax fiber was needle-punched to form the mats, then fabricated with unsaturated polyester (UP) and epoxy (EP) separately. The mechanical properties of these composites were tested and analyzed.Polypropylene (PP), which has the lowest density among man-made fibers, was used as the thermo-plastic matrix. Te overcome the difficulties of resin penetrating during the composite processing because of the high viscosity, commingled yarns were produced by PP filaments wrapping around the linen yarn. The even distribution of flax and PP in the yarn gave a better mixture of the matrix and reinforcing material, and the reduction in cost was also realized to some extend.Commingled yarns with volume fraction of 45%, 50% and 60% were processed and woven into fabric as the pre-pregnant. Then fabric was sandwiched into laminates by optimum hot-pressing technology that was chosen through testing the parameters such as pressure and temperature during experiment. The laminates with different volume fractions, layers, and woven structures were tested by the tensile and impact instruments. Analysis revealed that fiber status in laminates was the most important factor affecting the mechanical properties. Since the weft yarns straightened better than warp yarns in laminates with the same manufacture technology, the tensile property in fill direction and impact behavior in warp direction were much better. As far as the woven structures were concerned, the mechanical properties of laminateswith twill structure were better than those with plain structure.The fiber impregnation process was analyzed with the help of model and the shaping process was numerically simulated. The reason of the void was analyzed and the numerical value of the content was calculated as well. As for the tensile results, the revised formula for tensile strength was conducted. Two yarn straightened coefficients a,, aw were quoted to the formula, which were related to the extending ratio at break of laminates, and the expressions were defined by polynomial fit.The tensile processes of flax reinforced thermo-setting & thermo-plastic composites were programmed and simulated by using ANSYS, the software of Finite Element Analysis (FEA). The mechanisms of fiber reinforcing and fracture were discussed through examining the fracture photographs of Scanning Electronic Microscope (SEM).