Study On The Mechanical Behaviors Of Natural Bamboo Fiber Reinforced Poly-benzoxazine Composites

Due to the serious environmental pollution and energy shortage in the world,researchers pay great attention to the development of renewable natural fiber resources.European and American countries have been actively guiding and supporting the development of natural fiber materials and energy.In the National Long-term Scientific and Technological Development Plan,China has also promoted the priority theme of comprehensive development and utilization of agricultural and forestry biomass and the focus of strategic emerging industries.As a potential substitute for man-made fibers such as glass fiber and carbon fiber,natural fibers have many excellent characteristics such as low cost,pollution-free,renewable,light weight and high strength,thus demonstrating great potential in making new environmentally-friendly and sustainable fiber composites.However,similar to man-made fiber reinforced polymer composites,natural fiber reinforced polymer composites also face a series of challenging in practical engineering applications,such as hygrothermal aging,high temperature environment,high speed impact load and so on.In addition,natural fibers generally have strong hydrophilicity,and the interfacial strength between fibers and polymer matrix is relatively weak in the blending process.Therefore,in this thesis,the interfacial properties between natural bamboo fiber and polymer matrix were improved by alkali treatment,and the mechanical behaviors and failure mechanisms of the composites under different working conditions were systematically studied.The main contents of this paper are as follows:(1)The natural bamboo fiber with great application prospect was selected as the research object,and the bamboo fiber was pretreated by different concentrations of alkali solution.With the help of single fiber tensile test,single fiber pull-out test and scanning electron microscopy(SEM),the changes of surface morphology and mechanical properties of bamboo fibers before and after alkali solution treatment with different concentrations were compared and analyzed.Finally,the suitable alkali solution concentration for bamboo fiber pretreatment was obtained.(2)The preparation technology of chopped bamboo fiber reinforced poly-benzoxazine composite was developed by using hot pressing method.The effects of alkali treatment on the tensile and flexural mechanical properties of bamboo fiber composites were studied.In addition,in order to further expand the application of this kind of composite,the mechanical behavior of bamboo fiber composite after hygrothermal aging and at high temperatures was studied.With SEM technology,the failure mechanism of composite after hygrothermal aging and the mechanism of mechanical behavior at high temperatures were explored.The thermal and dynamic mechanical properties of bamboo fiber and its composites before and after alkali treatment were studied by thermogravimetric analysis(TGA)and dynamic mechanical analysis(DMA).(3)The compression behavior of bamboo fiber reinforced poly-benzoxazine composites under high-velocity impact loading was studied by using split-Hopkinson pressure bar device(SHPB)and high-speed camera.By capturing the real-time images of neat benzoxazine and its bamboo fiber reinforced composite under impact loading,the effect of adding bamboo fiber on the progressive failure and energy absorption of the composite under high-speed impact loading was analyzed.This study can provide theoretic guidance for the application of such composites in the field of impact engineering.(4)The tensile behavior of bamboo fiber reinforced poly-benzoxazine composites under different strain rates was further studied.By split-Hopkinson tensile bar device(SHTB),digital image correlation(DIC),high-speed camera and SEM techniques,the effect of bamboo fiber on the tensile properties of composites under different strain rates was investigated.(5)The geometric model of randomly-dispersed chopped bamboo fiber reinforced polybenzoxazine composite was established by using Matlab and Python.With the help of ABAQUS finite element software,a new simulation method-embedded element method,was used to simulate the tensile behavior of chopped bamboo fiber reinforced composites.In addition,the prediction model of tensile strength of chopped bamboo fiber reinforced polybenzoxazine composite is presented and the strain rate factor is taken into account in this thesis.