Studies On CBF Weft Fleecy Fabric Reinforced Composites And Their Mechanical Properties

Currently,the studies based on weft knitted reinforced composites, are mainly in ordinary knitted fabrics,such as jersey,rib,Cardigan,etc. They have many defects as low modulus,large deformation,tenuous density and their reinforced composites are of poor mechanical properties.If combined with some high performance fibers and their knittability,the weft-knitting applied to composites may be less.The tensile properties of ordinary weft knitted composites,especially the horizontal tensile properties are very low.In order to increase the horizontal tensile properties,the fleecy yarn in fleecy structures was studied.And knitting of the CBF on an electronic flat knitting machine is a new trial.The knittability of CBF on a computerized flat knitting machine is studied little.Firstly,the tensile strength and dynamic friction coefficient of CBF were tested and compared with glass fiber in order to analyze its knittability.Derived jersey and fleecy structures with different fleecing proportion are designed on the M1 pattern design system.In the knitting process,considering CBF knittability and fabrics quality,the optimize knitting parameters were fixed through trials,such as cam setting, take-down force,feeding yarn's tension and knitting speed.The fabrics off the machine were relaxed properly because of crimping.The weft knitted fabric reinforced composites were fabricated by VARTM process.Four layers of fabrics were symmetrically laid in parallel.In order to reduce the crimping interference during the composites production process,the edges of effective part were seamed. The proportion of resin,hardener and accelerator were determined by gel test.Composites with good quality and appearance were produced by optimizing test program,such as vacuum pressure,injection and exhausting,etc.According to tensile and flexural test standards,composites were made into specified samples,whose vertical and horizontal tensile and flexural properties were tested on testing instruments.Then,the vertical and horizontal tensile and flexural properties were respectively compared and analyzed.The results indicate that the properties of CBF composites are better than glass fiber composites at the same reinforcement structure.It can meet strength requirements,and can make up for ordinary glass fiber's shortcomings in the alkali resistance and high temperature.As to different structures,with the increasing of fleecy proportion,the vertical and horizontal tensile and flexural properties,especially horizontal properties,were improved,which was a breakthrough in the development of common knitting reinforced composite.CBF knitting fabrics have good combination with resin,and with the fiber's high breaking strength and modulus,CBF has great potential in knitting reinforced composites.The research results have important reference value for weft knitted composites in structural design,as well as to overcome the composites' defects of low stiffness and strength,especially poor horizontal mechanical properties.CBF weft fabrics knitted on a computerized flat knitting machine provide a way to develop industrial knitting fabrics, especially knitting reinforced composites and it also has great significance of applying CBF in the field of composites.