Experimental Study On The Tensile Properties Of Two-dimensional Braided Ropes

High-performance fiber braided ropes have been adopted in aerospace applications such as satellites,airships,solid rockets,space shuttles,and space stations.The old two-dimensional braiding is a relatively simple process,with high efficiency and flexible tailorability,which lays a foundation for the application of high-performance fiber ropes.A series of research work have been carried out on the stress relaxation of high performance fiber braided ropes under long-term tension.Firstly,10 types of polyarylate(Vectran)fiber and 7 types of aramid(Kevlar)fiber ropes were designed and braided to evaluate the tensile properties of the braided rope.The effects of twisting,sample length,braiding structure,braiding angle,knotting,preloading and hydrothermal treatment on the tensile properties of braided ropes were compared and analyzed.And then,a minitype stress relaxation testing system for the braided ropes was self-developed.The stress relaxation behaviors of both the two categories of braided ropes was monitored and evaluated within 20 days.The tested results are as follows:Twisting can increase the breaking strength of Vectran fiber up to 14.69%,however,the strength improvement of its braided rope is only 3.75%.When twisting parameter is 10 twist/10 cm for single yam and 5 twist/10 cm for the braid yam,it may be due to the further bending of fibers during the braiding process,which leads to the increase of fiber prestressing force and impact the strength of braided rope.When the braiding angle is 10°,the braided rope.with 2 × 2 structure has the highest tensile fracture strength among the 1 ×1,2×2 hybrid,1×1 and 2 × 2 braided structures.Preloading with 25%fracture strength of braided rope improves the inhomogeneous of fiber orientation along the length direction,which can be used to connect and load the rope component in stress relaxation test of braided rope.The 1000 hours hydrothermal treatment(temperature 80℃,relative humidity 85%)has little effect on the tensile properties of the Vectran fiber braided rope,but the tensile fracture strength of the Kevlar fiber braided rope decreased by 2.66%.The above experiment results can provide reference for the engineering application of polyarylate and aramid fiber braided rope.From the stress relaxation tests within 40 days,it is shown that the relaxation rate of the Kevlar fiber rope is about 2.13 times of the Vectran fiber braided rope.The Vectran fiber braided rope and the Kevlar fiber braided rope were rapidly relaxed at 2 and 5 days at the beginning of the experiment,respectively.The relaxation rate of the Kevlar fiber braided rope was 22.1(N/day),which was about 1.21 times the relaxation rate of the Vectran fiber braided rope.However,when the relaxation rate of the braided rope is stabilized,the Kevlar fiber braided rope with the relaxation rate of 2.36(N/day)of about 2.36 times the relaxation rate of the Vectran fiber braided rope.Both categories of ropes with excellent relaxation resistance.However,under similar process conditions,Vectran fiber braided rope has better damp hydrothermal stability and relaxation resistance than Kevlar fiber braided rope.Therefore,in the case where the stress relaxation properties is strictly required,the polyarylate fiber braided rope is preferable.