The Research On The Preparation Technology And Mechanical Properties Of LGFRP Composite For Application In Vechicle Body

Lightweight design is one of key technologies in energy-saving and environmental protection for automobile. Among all approaches to achieve lightweight, fiber reinforced resin composites are leading the trend for their unique performance when manufactured for the automobile bodies. Long glass fiber reinforced polypropylene(LGFRP) composite is widely used in consideration for its design-ability, recyclability and cost superiority. However, the current difficulties mainly consist in several aspects, such as few researches report the influence of process parameters during mold thermoforming, rules of material design parameters and strain rate effect upon its mechanical properties, stress concentration effect after hole opening and the application design in automobiles, etc. The thesis lucubrates into the preparation technology, mechanical properties and connection performance of LGFRP composite through experiments and numerical analysis. Furthermore, the design of battery pack and bumper beam with LGFRP composite for electric vehicles are also be studied. Detailed contents are listed as follow:(1) Influence of mold thermoforming process parameters upon the mechanical properties of LGFRP composite.To reveal the rules and optimize the mechanical performance of LGFRP composite, this thesis studies the tensile and bending strength under influencing of preheating temperature, preheating time, pressure and pressure duration. The results show that for tensile strength, the rate of contribution is preheating temperature, pressure, preheating time, pressure duration from large to small order, while for bending strength, the rate of contribution is pressure, preheating temperature, pressure duration, preheating time from large to small order. The optimal tensile and bending strength of LGFRP composite are reached when preheating temperature is 215.5℃, preheating time is 16 minutes, pressure is 3.8MPa and pressure duration is 3 minutes. These values lay foundation for follow research of LGFRP composite.(2) Influence of fiber content and strain rate upon mechanical properties of LGFRP composite.Considering the diversity in mechanical properties and loading condition requirements of different parts of automobile bodies, this thesis studies the mechanical properties and failure modes under different fiber contents. Based on Rule of Mixtures, a microscopic mechanical model is proposed through which mechanical properties with different fiber contents can be predicted. Moreover, the mechanical properties of LGFRP composite under dispersion and relevant strain rate effect are studied.(3) Stress concentration effect and failure modes of LGFRP composite with opening hole.The stress concentration effect during opening connection for LGFRP composite applied for in automobile bodies is investigated. With digital image correlation(DIC) method, the experimental results show the stress concentration area is 4 times of opening radius for LGFRP composite. The concentration factor increases as the radius enlarges, but less than the factor in metal under same condition. Theory model and numerical analysis method including damage co-efficiency and opening radius are established, which can be used to estimate stress concentration effect of LGFRP composite with different length and content of fiber. Thus, this study provides design basis for opening connection and safety evaluation of LGFRP composite.(4) Applications of LGFRP composite in automobile bodies.Based on above-mentioned research, this thesis studies the designs of battery pack and bumper beam with LGFRP composite for electric vehicles. With fulfilling different restrictions and regulation and compared with metal battery pack and bumper beam, 80% and 11.2%of weight can be reduced through battery pack and bumper beam with LGFRP composite, respectively, indicating promising application of the LGFRP composite.