The Effect Of The Pulp On The Suture On The Low-speed Impact Properties Of The Stitched Composite

In the course of the application,the stitched composites will be squeezed,collisions and other injuries,so the impact resistance is a key factor affecting the service life.The suture will be rubbed by the needle and the preform repeatedly during the sewing process,resulting in tensile,bending,torsion and other deformations.After the suture was rubbed many times,fibers at the surface of suture would be broken,which not only affect the progress of the suture process,but also make the mechanical properties of suture composites decreased,so it is urgent to improve the carbon fiber suture to improve its property performance.In this paper,modified sizing agent was used to size the carbon fiber suture,the study results show that sizing can significanty increase its tensile strength and hook pull strength,the tensile strength of carbon fiber suture which was sized had been improved 47.7%than unsized carbon fibers,and the hooking strength increased by 29.3%compared with unsized one.The wear resistance of carbon fiber suture is obviously improved after sizing and it was the best when the concentration of slurry is 3%.The number of wear resistant reached 936 times,which was 3.9 times of that unsized carbon fiber.Sizing of carbon fiber suture was an effective way to improve the amount of wool yam on the fiber surface,reduce its surface defects and improve the suture mechanical properties and wear resistance.But the concentration of the slurry can not be more than 3%,otherwise,the excess of pulp will be enriched on the fiber surface,which would improve the probability of fiber brittle fracture and reduce its mechanical and wear resistance.Polyurethane sizing made the groove on the surface of carbon fiber become deeper,but the surface of fiber tended to be smooth with the increase of sizing rate.The surface of unsized carbon fiber mainly consists of C,O two elements,but after sizing N elements and Si elements had been introduced to the fiber surface and the ratio O/C is increased by 11.04%.The contact angle between carbon fiber and epoxy resin is reduced by 9.8%through sized the carbon fiber,so the wettability of the resin to the fiber is improved.However,with the increase of sizing rate,the contact angle increased gradually.Carbon fiber sizing treatment increased the interfacial shear strength of carbon fiber epoxy composites by 16.3%,but when sizing rate is too high,the interfacial shear strength will be decreased.The impact morphology of stitched composites that the carbon fiber sized and unsized is similar and the internal impact damage is obviously "butterfly type".However the low speed impact damage area of the suture composite is reduced by 8.05%after the suture sized.The critical force of delamination(Pcrit)and the maximum load(Pmax)are greater than the stitched laminates made of sized suture,and their maximum load was 4.546KN and 5.749KN respectively,the ability to withstand load increased by 20.93%after the suture was sized.