Study On Dynamic Fatigue Mechanism Of Fiber/Rubber Composites Under Harsh Working Conditions

The interfacial bonding between the fiber and the rubber matrix in the tire industry determines the mechanical properties of the fiber-reinforced rubber compound,which is directly related to the safety and durability of the product.The dynamic fatigue performance of the cord-reinforced rubber compound has a significant impact on the load carrying capacity and fatigue resistance of the tire,which is subjected to cyclic alternating load during driving.Due to the limitation of test technology and testing instruments,many dynamic fatigue research works are conducted at low frequency and room temperature,which cannot simulate the use conditions of automobile tires and large aircraft tires.In addition,the dynamic fatigue mechanism of nylon fiber and aramid fiber reinforced rubber composites under severe operating conditions(high frequency,high strain,and wide temperature domain)has rarely been mentioned.Therefore,the dynamic fatigue characteristics of fiber/rubber composites under wide frequency range,wide temperature domain and high strain are investigated with RFL impregnated nylon 66 and aramid fibers,and the fatigue failure mechanisms of fiber/rubber composites at different frequencies and temperatures are elucidated.The main research contents are as follows:(1)The effect of frequency(5～30Hz)on the dynamic fatigue performance of nylon 66 fiber/rubber composites was investigated,and the fatigue failure mechanism of the composites at different frequencies was elucidated by the interfacial energy dissipation,interfacial heating rate and fatigue failure location.The fatigue life of nylon 66 fiber/rubber composite at low frequency of 5Hz is the highest,283,000 times,and the fatigue failure location is the rubber matrix,which is because the interface hysteresis effect and internal consumption are smaller at low frequency,and the interface loss factor is small,resulting in low heat generation rate and less damage to the interface during dynamic fatigue.In the high frequency 30 Hz,the fatigue life(277,000 times)is similar to the low frequency and the damage location is the same as the rubber substrate,because the deformation at high frequency can not keep up with the stress,the interface loss factor and the interface heat generation rate is still low.13 Hz is in the middle region between low frequency and high frequency,but the fatigue life is the lowest(205,000 times)and the damage location is the interface,because the interface hysteresis phenomenon is obvious at this time,the interface loss factor is high,resulting in the highest heat generation rate and the largest damage to the interface in the dynamic fatigue process.(2)The effect of temperature(-20～120℃)on the dynamic fatigue performance of nylon 66 fiber/rubber composites was studied,and the fatigue failure mechanism of the composites at different temperatures was elucidated by the relative deformation of the interface,the fiber/rubber modulus ratio and the interface heat generation rate.At-20℃,the fatigue process of nylon 66fiber/rubber composites is in two stages of destruction,but the performance after the first destruction can no longer meet the service demand,and the fatigue life should be judged on the basis of the first destruction,which is corrected to 150,000 times.25℃ and 80℃,although the destruction position is at the interface,the fatigue life of the composite at 80℃(205,000 times)is higher than that at 25℃(91,000 times).This is because the glass transition of nylon 66 fiber at 80℃ leads to its fiber/rubber modulus ratio and relative deformation of the interface is lower than 25℃,resulting in its interface heat generation rate is lower than 25℃,and the interface shear effect is weaker in the fatigue process.The fatigue life(49,000 times)is the lowest at 120°C,and the damage location is the rubber matrix.The reason is that the modulus of rubber decreases significantly at high temperature,resulting in a sharp increase in the fiber/rubber modulus ratio,and the interface shear and stress concentration effects are enhanced,which makes it easy to produce cracks and expand to the matrix.(3)The dynamic fatigue performance and failure mechanism of aramid fiber/rubber composites at different frequencies(5～30Hz)were investigated.Similar to the nylon 66 fiber/rubber composite,the fatigue life of the aramid fiber/rubber composite at low frequency 5 Hz and high frequency 30 Hz is high,42,000 and 47,000 cycles respectively,and the damage location is the rubber matrix,but the fatigue life at 13 Hz is only 9,000 cycles and the damage location is the interface.This is because at 13 Hz,the interface hysteresis is large and the interface loss factor is large leading to the highest heat generation rate,and the interface damage during dynamic fatigue is higher than 5 Hz and 30 Hz,so the fatigue life is the lowest.(4)The dynamic fatigue performance and failure mechanism of aramid fiber/rubber composites at different temperatures(-20～120°C)were investigated.The fatigue life(39,000 cycles)was the highest at-20°C,and the fatigue lives of the composites at 25°C and 80°C were 30,000 and 8,000 cycles,respectively,with the damage location at the interface.This is due to the increase of the fiber/rubber modulus ratio with the increase of temperature,which leads to the increase of the interfacial shear and stress concentration effect,which is manifested by the high rate of interfacial heat generation,and therefore the fatigue life decreases.The lowest fatigue life(3,000 cycles)at120°C is due to the severe softening of the rubber matrix at high temperatures,the sharp increase in the fiber/modulus ratio,and the stress concentration between the interface and the rubber matrix,which expands into cracks at the rubber and leads to matrix fracture.The fatigue life of aramid composites is much lower than that of nylon 66 composites,because the relative deformation of the interface and the interfacial loss factor of aramid composites are much higher than that of nylon 66 composites.