Study On Cutting Fracture Behavior And Mechanism Of Synthetic Fiber Monofilament Based On The Model Of Friction Between Strands

As the earliest textile products,ropes have irreplaceable functions in carrying and transferring.In recent years,high-performance ropes have gradually become development trends of rope industry.Synthetic fibers have high modules,high strength to weight ratio,high chemical resistance,high temperature resistance and other high performance and high reliability characteristics.It is widely used in ropes and cables,cut resistant products,parachute cords,protective clothing and other important occasions where superior properties are needed.Once the rope breaks in the work,it will cause extremely serious consequences.Therefore,the research on the fracture mechanical properties of fiber ropes has been paid more and more attention by scholars at home and abroad.The fracture failure test of rope synthetic fiber rope starts with the fracture of the strands.In view of the fracture of the strand,the synthetic fiber monofilament is selected as the research object.It carries out the experimental research on the breaking process and mechanism of the synthetic fiber monofilament under the action of simulated friction between the strands and different cutting parameters.The work is summarized in detail.(1)A test method to simulate the tangential friction state of the strands under the normal load was proposed,and the BTF-300 cutting experiment machine was developed independently.The testing machine can detect changes in parameters such as cutting resistance and cutting speed in real time during the cutting process.At the same time,parameters such as the initial speed of the cutter and the loading quality can be adjusted within a certain range.The testing machine can meet the cutting fracture performance tests of synthetic fiber monofilament in two different ways: no braiding and simulated braiding.(2)Based on the contact analysis of synthetic fiber and cutter,a physical model of Hertz contact is established,and the formula of cutting contact stress is deduced.The cutting stress of synthetic fiber monofilament under different initial speeds and loading qualities is calculated under two cutting states.The influence rules of different cutting parameters on the breaking strength of synthetic fiber monofilament are obtained.(3)An energy balance equation is established for the cutting fracture process of synthetic fibers under without the action of braiding and friction between strands.It is proposed to divide the total cutting fracture energy into effective cutting fracture energy and loss cutting fracture energy.According to the proportion of the two parts of energy in the total energy,the role of different cutting parameters on the cutting fracture process and cutting fracture toughness of synthetic fiber are discussed.(4)Based on the micro-morphological characteristics of synthetic fiber monofilament cutting fractures,the strain behavior and mechanism of synthetic fiber monofilaments during cutting fractures are studied.The process of cutting synthetic fiber is divided into three stages:cutting deformation,cutting and brittle fracture.According to the micro-morphological characteristics of different stages of the fracture,different deformation mechanisms are studied,and the deformation mechanism of different cutting parameters on different stages is discussed.(5)The effects of different cutting methods,initial velocity,loading mass and elastic modulus on the fracture mechanism of synthetic fiber samples during impact cutting are studied.Finally,the fracture mechanism of synthetic filament in impact cutting is revealed based on macroscopic mechanical properties and microscopic deformation mechanism.(6)According to the law of cutting fracture behavior and mechanism of synthetic fiber monofilament under different parameters,the influence of different cutting parameters on the essential factors of fracture deformation mechanism of synthetic fiber monofilament is analyzed.The physical model of molecular chain segment motion under different fracture mechanism is established.The results show that the fracture mechanism of synthetic fiber monofilaments is the coupling of forced high-elastic deformation and viscoelastic deformation.Different parameters have different effects on the mechanism of synthetic fiber monofilaments.Different braiding state,initial speed,loading mass and elastic modulus of synthetic fiber monofilament have significant influence on cutting fracture behavior and mechanism.The essential factors affecting the fracture behavior and mechanism of synthetic fiber monofilament are the loading rate and loading stress.Changing the initial speed of the cutter has a significant effect on the loading rate,and the cutting deformation is mainly viscoelastic deformation.When the deformation rate of synthetic fibers can keep up with the loading rate,the viscoelastic deformation is sufficient and the fracture surface of the fiber is smooth in the cutting deformation stage.However,the deformation rate of the molecular segment lags behind the loading rate,the fracture surface of the cutting deformation zone has obvious tear fissures.The change of loading quality has a significant effect on the loading stress,and the cutting deformation is mainly forced high elastic deformation.While the loading stress is increased,the plastic deformation of fiber fracture is more significant.When the synthetic fiber monofilament is woven,due to the tangential friction between the strands,the action time between the cutter and the fiber sample is long,and the more energy is consumed during the breaking process,which effectively buffers the loading impact force and improves the cutting fracture toughness and cutting resistance of synthetic fiber monofilament.In this paper,an experimental model of tangential friction force between strands is designed,establishes a mathematical model of the contact stress between synthetic fiber monofilament and cutter,deduces an energy balance based on the fracture balance theory.The macro fracture behavior and micro fracture morphology of synthetic fiber monofilament are combined to confirm the rationality and correctness of the fracture mechanism.The action rules of the fracture deformation mechanism of synthetic fiber monofilaments under different parameters are obtained,which provides certain theoretical basis for the research of fracture behavior of synthetic fiber monofilament under different braided states.The research work in this paper has perfected the theoretical basis of the cutting fracture of synthetic fiber to a certain extent,which is helpful to improve the engineering design and application of synthetic fiber,and also provides a reference for the theoretical research of fracture deformation mechanism of synthetic fiber monofilament.