Experimental Study On Fatigue Properties Of Carbon-aramid Hybrid Two-dimensional Braided Composites After Impact

Two-dimensional(2D)braided fabric manufacturing process is relatively simple and the braiding parameters can be designed flexibly.2D braided composites have the advantages of high surface strength and modulus,impact and fatigue resistance and overall performance.The Carbon fiber has high strength and high rigidity.The aramid fiber has high elongation and good fracture toughness.The carbon and aramid braided hybrid composites make the mechanical properties of them well preserved,and the purpose of reducing weight and improving the fracture toughness of the composites is achieved.Therefore,the mechanical performance of hybrid composites could be realized through the design of carbon-aramid fiber hybrid style.The following three different hybrid styles of carbon-aramid/epoxy composites were produced and tested:(1)K-CC(aramid fiber as axial yarn and carbon fiber as braiding yarn),(2)C-CK(carbon fiber as axial yarn and carbon-aramid fiber as braiding yarn)and(3)K-CK(aramid fiber as axial yarn and ccarbon-aramid fiber as braiding yarn).Non-hybrid carbon composites were also tested for comparison.The impact resistance and compression fatigue after impact properties of them were evaluated by low velocity impact(LVI)and compression fatigue test.The effects of the hybrid structure on the impact properties such as the peak load,elastic strain energy,dent depth and damage area were discussed.We can preliminary conclude the impact resistance of composites.For the peak load,K-CC and C-CK are 14.4%? 7.0%higher than C-CC.It shows that their carrying capacity is better than C-CC.For elastic strain energy,the three kinds of hybrid composites are 82.4%,140.1%and 105.5%higher than C-CC respectively,which indicating that the absorption energy of C-CK is the lowest.For dent depth,C-CC is the largest(0.878mm).The three hybrid composites is lower 39.4%,85.1%and 86.3%than C-CC respectively.For damage area from the C-scan imaging and B-scan imaging,C-CC and K-CC are 371.65mm2 and 373.13mm2,respectively.C-CK and K-CK is 65.4%and 69.3%less than C-CC respectively.The compression test was carried out for the composites before and after the impact.Among undamaged composites,the compression load of C-CC is the biggest(37.45kN).The compression load of hybrid composites decrease significantly,Compared with C-CC,which are decreased by 30.6%,32.9%and 56.4%respectively.Compared with the composites before and after the impact,the compression strength and modulus of C-CC decreased by 20.19%and 9.37%respectively.For K-CC,the compression strength of it is 16.85%lower than K-CC-CAI.There is no obvious change for the modulus.The performance parameters of C-CK is similar with K-CC.The decrease percentage of the modulus K-CK is the largest.The strain mode of non-hybrid carbon composites before and after impact is mainly bending tensile strain,both of them have serious damage.In the three kinds of hybrid composites with or without damage,the compressive strain of C-CK is the least.Also,the damage degree and damage area are the lowest.C-CK represents strong ability to resist failure and elastic deformation.Three kinds of composites with impact damage were tested under the 60%stress level to evaluate their fatigue properties preliminarily.The results show that the fatigue life K-CK(443197)is the longest,followed by C-CK(77523).However,the latter has the lowest stiffness-drop(11.84%),which indicates that it has excellent resistance to elastic deformation and fatigue performance.