Experimental Study On The Damage Mode Of Modified Silicon Nitride Fibers In Weaving

Based on the weaving damage of three-dimensional fabrics,this paper studied the bending and friction damage of silicon nitride fibers in the process of preparing three-dimensional fabrics.By analyzing yarn bending deformation and friction behavior between yarn and steel during fabric forming process,we established a simulation method for weaving damage experiment.The degree of damage was evaluated by the tensile properties after damage,and the influence of various parameters on the bending and friction damage of silicon nitride fiber during the weaving process was revealed.It provided predictive judgment for fiber damage and composite material performance during machine weaving,and provide guidance for optimizing the parameters of three-dimensional fabric.By simulating the bending damage of the z-binder yarn in the orthogonal fabric,it is found that the fiber tows damage increases as the weft density,the yarn tension and the bending depth increase.Among these parameters,the change of weft density has the most significant effect on the damage.As the increase of weft density reduces the bending radius of the fiber,the probability of bending fracture increases,and the dispersion of the strength of the fiber tows increases remarkably.The increase of tension leads to the increase of the maximum stress of the section during bending,which increases the risk of fiber failure.The increase of the bending depth leads to an increase in the length of the fiber during the sliding movement during bending,which causes more fibers to be bent and has a risk of failure,thereby increasing the damage..The friction experiments of steel and fiber tows by response surface method show that there is no interaction between the three variables of normal load,yarn tension and friction frequency,and only the normal load and friction frequency are the friction coefficient.The influence is large,and the friction coefficient decreases as the values of these two variables increase.The tensile test after friction experiments showed that the friction did not cause loss of performance of the fiber tows.By increasing the normal load and the number of frictions during the experiment did not cause performance loss.Electron microscopy observations show that the wear caused by the friction on the surface of the silicon nitride fiber is very slight,indicating that the silicon nitride fiber has strong wear resistance.By using TPU as the main slurry,PEG was used as the TPU modifier to prepare different concentrations of the combined sizing to modify the silicon nitride fiber.The test results after the second sizing showed that the addition of PEG changed the structural characteristics of the formed TPU film.The structural characteristics also make the properties of the silicon nitride fibers obtained after sizing different.At higher TPU concentration,the tensile properties and wear resistance of the fiber after sizing are greatly improved,but the fiber volume fraction and bending performance are poor,and the performance is also different with the PEG addition rate.For evaluation,a sizing formulation suitable for weaving is preferred.