The Study On Tensile Properties And Failure Modes Of Carbon Fiber Triaxial Woven Fabric Composites

The triaxial woven fabric is a flat fabric which is interwoven with each other at a certain angle(such as 0°,±60°)from three yarn systems and has an unique in-plane properties.The study on tensile properties of that fabric composites is one of the ways to characterize the mechanical properties of this kind of material and with a great significance to the improvement and widely application of the material in the future.In this paper,12K carbon fiber tow was used as a raw material to fabricate a single layer triaxial woven fabric by using the self-manufactured weaving machine in the lab.Then,having a preliminary study on the tensile properties of that one layer resin-based triaxial woven fabric composites and the main contents include the following:(1)The theoretical relationship between the basic parameters of carbon fiber triaxial woven fabrics was deduced by using geometric methods.The results show that the warp or weft density,the length of the side of the hexagonal cavity,and the porosity of the fabric are all functions of the braiding angle(?)and the width(d)of the tow.The hexagonal cavity side lengths,a and b,are both binary functions of the braid angle and the width of the tow,and both are proportional to the tow width,and inversely proportional to sin(2?)and tan(?),respectively;If the raw materials and specifications of the three groups of system yarns are the same and braiding angle?=60°,the values of the warp and weft densities of the triaxial woven fabrics are equal,that is,P_x=P_y=P_z,And besides,the corresponding fabric porosity reaches the maximum value of 33.3%.(2)According to the valid assumption of the sinusoidal buckling fluctuation of the tow in the triaxial fabric and the unit cell geometry,then the fiber volume fraction is theoretically calculated in combination with higher mathematics integration knowledge.The results show that the factors which affecting the volume fraction of fibers in the composites are not only the braiding angle of the fabrics and the width of the tow,but also the thickness of the composites and the geometrical length of the unit cell.(3)Through the tensile load analysis of the 0°and 90°specimens,it was found that when the applied load was about 1311N,the 0°direction tensile specimen showed a small mechanical attenuation phenomenon.And the specimen suddenly suffered a brittle fracture failure after the load continued to increase.However,the 90°direction specimen tensile load has two kinds of changes during the whole test process.First one is,it will continue to increase until a sudden failure of the specimen occurs after a small mechanical attenuation occurs.The other one is that the load will continue to increase after a large number of mechanical decays and eventually leads to tearing of the specimen,with a certain degree of torsion.(4)A comparative analysis of the tensile elongation at break and tensile strength of the 0°and90°specimens reveals that the elongation at break of the specimen in the 0°direction along the load direction is lower than that of 90°specimens under the sample preparation standards in this paper.While in the two kinds tested specimens with different tensile directions,the elongation at break perpendicular to the load direction is opposite to that case which parallel load direction,and that average value is about 0.40%for 0°specimens and 0.35%for 90°specimens.After the normalized cross-sectional area,the tensile strength at break for 0°direction specimens is higher than that of90°specimens.(5)By using the non-contact method to test the total field strain at the 0°and 90°direction tensile specimens,it is found that there are a significant differences in the size and distribution of the strain in the strain cloud diagrams of the tested regions.In addition,the tensile strain(|?_x|or?_y)of the 0°direction specimens at the yarn interweaving point and void-rich resin region along the load direction coincides with the tensile principal strain less than that of 90°tensile specimens.(6)According to the comparative analysis of the 0°and 90°specimen fracture failure process and the failure modes,it is found that the failure process of 0°direction tensile specimen can be classified into two types according to the location of that first obvious failure crack in the surface of samples.One is that the crack spreads laterally after the delamination at the interlacing point of the boundary,and finally leads to a brittle fracture failure of the specimen.The other is that,after the transverse cracks appear in the middle of the sample-rich resin zone,the cracks propagate to the two boundaries,and at last,the sample is macroscopically brittle after peeling delamination at the boundary or the directly fracture failure.At the same time,the weft yarns in the specimen parallel to the load were broken and monofilament extraction and breakage occurred.However,for the 90°tensile specimens the process and modes of fracture destruction are more complex.According to a comprehensive analysis of the corresponding cloud image,video and audio,the author summarized the three types of tear failure,resin failure and torsional failure.