Mechanical Property And Interfacial Property Of Glass Fiber Composites With Different Reinforced Fiber Length

In recent years, with the development of the automotive industry and the increasing of car ownership, energy consumption, safety, and environment protection issues are also increasingly prominent. Automotive lightweight is one of the most important ways to reduce energy consumption and reduce pollutant emissions. Automotive lightweight means to reduce automobile weight as far as possible without weakening the strength and safety performance of the automobile but improving fuel efficiency and reducing emissions. There are many ways to reduce the automobile weight, one of which is the development of lightweight, high-strength materials. Composite materials are defined as a key research due to its high strength and stiffness, high corrosion resistance, good fatigue resistance and the ability to mass production, in which the fiber reinforced composite material is a hot research for scholars.In this study, glass fiber and polypropylene were used to produce short fiber reinforced pellets S3 and long fiber reinforced pellets L7, L11, L15. After the injection molding process dumbbell-shaped specimens were obtain, and then the four kinds of composites were subjected to the tensile, bending and impact test. Residue fiber length after the injection molding of glass fibers were also measured, and the influence of different length of the reinforcing fibers of glass fiber /polypropylene composites on mechanical properties were studied. In addition to the study of the mechanical properties, optical microscope observation and X-ray CT scanning were conducted. The fiber alignment inside material was observed and fiber orientation angle and fiber orientation factor were calculated. According to the modified Kelly-Tyson equation fiber critical length was obtained and then the interfacial shear stress between glass fibers and polypropylene resin was calculated.Conclusions from the above experiment were as follows:1) residual fiber length of the four composites was seriously decreased by over 50% after the injection molding, but with the original fiber length increases from 1.5mm to 15mm, the residual fiber length also increased from 0.68mm to 4.18mm.2) When the residual fiber length increased from 0.68mm to 3.02mm, the tensile strength and flexural strength both improved significantly, but when the residual length increased from 3.02mm to 4.18mm, the tensile strength and flexural strength kept stable. The impact strength got improved with the longer fiber length.3) X-ray CT scan image showed that short fiber reinforced composite material S3 had the small fiber orientation angle and good fiber orientation. While the long fiber-reinforced composite materials had a wide "random zone" in the core layer where fiber arrangement and fiber orientation is poor.4) By calculating the interfacial shear stress it was found that with the increasing of reinforcing fiber length, interfacial shear stress decreased.5) Through the study of L11/S3 hybrid composites, it was found that when L11/S3 at the mixing ratio of 90/10, the tensile strength and flexural strength are slightly higher than the L11, and meantime maintain a high impact strength.6) X-ray CT scan results of L11 and L11/S3 (90/10) showed that L11/S3 (90/10) had better fiber arrangement and orientation compared to L11. It is considered that mixing a small proportion of short fiber into long fiber reinforced composite materials, such as 10%, would improve the fiber orientation and strength.