Research On The Structures And Propertes Of Spread Tow And Spread Tow Fbric Composites

Compared to conventional carbon fabric, fiber tow in the spread tow fab-ric(STF) is spread before weaving. Advantages of STF such as relatively straighterfibers, lesser crimp and better surface smoothness got established. Resin impregna-tion is also improved as impregnation and drying time are shorten. Thereby it re-sults in the final composite material product with better physical and mechanicalperformance. It meets the requirements with lightweight, high strength, highmoldulus, easy molding of advanced composites. Thus, it becomes one of the keytechnologies in the research of new materials. On the background of spread towfabric provided by OXEON AB, this paper studied the strucures and properties ofspread tow and spread tow faric and mainly discussed the following aspects:1) The mechanical properties, resin impregnation and compaction behavior ofcarbon fibre were tested before and after tow spreading. Results show that: aftertow spreading, fiber damage was controlled within1%; filaments in the tow werearranged in uniform; also, advantages of spread tow such as lesser void, better res-in impregnation and no resin-rich region got established; the compression amountof fibre will cause an increase in the preform compaction under a given pressure,and the increase in the preform compaction increases with the impregnation timeand spread tow.2） Structural parameters of STF were tested and effects of area weight ofSTF and gap content between fiber tows were studied. Results showed that thewarp and weft lineal density had influence on the area weight of STF.Gap contentcould be modified by adjusting the width of fiber tow. Each areal weight of STFhad an optimal fiber tows width. Under the case of the same width of fiber tows inthe STFs, the higher of the area weight of STF caused the gap content decrease re-spondingly. Gap content of STF was less than that of traditional fabric.3）Based on reasonable geometric hypothesis, a two-dimensional geometricstructural model of STF composite was proposed; crimp of fiber tows in the STFcould be predicted; an equation of fiber volume fraction of STF composite was al-so set up; variation of fibre volume fraction with fiber crimp percentage was ana- lysed. Comparison of the resulting analytical predictions with experimental resultsshowed that the proposed model was valid.4）The epoxy resins and VARTM(resin transfer molding) process were usedin spread tow fabric composite, and fully testing for spread tow fabric compositesmechanical properties were conducted, including tension, compressing, and inter-laminar shear strengths. Results showed that STF stacking configuration affectedon tension properties, STFs placed in random-phase mode (RPM) were better thanthat placed in Iso-phose mode (IPM). Comparing with1K,3K traditional carbonfiber, non crimp fabric (NCF) and unidirectional fabric(UD), STF has better ten-sion and compressing properties; however,due to its weak interface strength, STFcomposites didn’t have a good interlaminar shear strengths.5) Owing to mechanical multi-rollers tow spreading method is insufficient, anew ultrasonic tow spreading method was studied in this thesis. Results showedthat when this method is used, carbon fiber can be spread smoothly, but with lim-ited width and coarse phenomenon. In order to improve the quality of spread tow,a combination of ultrasonic and acoustic energy tow spreading method was pro-posed, then specific implementation modalities were introduced in detail.