| Natural rubber(NR)is widely used in vibration damping products such as air spring because of its high strength,low heat generation and high adhesion.However,rubber vibration damping products inevitably undergo aging due to the invasion of oxygen in the air during storage,and long-term fatigue aging during use,which result in serious performance and service life decline.Therefore,it is very important to study the properties and structural changes of natural rubber materials during storage and use.Firstly,the effects of types and contents of carbon black and the antioxidants on the hot air aging and fatigue aging performance of NR were studied.It was found that carbon black had little effect on the thermal oxygen aging properties of NR vulcanizate,but could significantly reduce fatigue life of NR.The comprehensive performance of carbon black N660 is better than N774,which is more suitable for NR formulation used in vibration damping products.Antioxidant RD has better protection effect on hot air aging,but poor protection effect on fatigue aging,by contrast Antioxidant 4020 was the opposite to RD.For natural rubber used for vibration damping products,it is necessary to ensure good thermal and oxygen aging resistance in storage and good fatigue aging resistance during use.Therefore,carbon black N660 with a relatively high fatigue life of was selected as filler with a content of 38 phr in NR,and the combination of RD and 4020 was used as antioxidant in NR.Secondly,the changes of structure and properties of NR used for vibration damping products during room temperature storage and hot air aging were studied.The results showed storage of NR at room temperature had little effect on the structure and properties of NR,while storage of NR under constant stress at room temperature could cause a decrease in crosslink density,modulus at 100% and 300%,E’,and E " of NR vulcanizates,and the greater the constant stress,the greater the decrease.With the increase of hot air aging temperature and aging time,the hardness,modulus at 100%and 300%,storage modulus(E ’)and loss modulus(E "),the initial stress of stress relaxation and 15 min stress of NR specimen gradually increased,and the overall trend was similar to that of crosslinking density.Tensile strength and elongation at break of NR decreased with the increase of aging temperature and time,and the loss factor(tanδ)rapidly decreased at initial aging,and tended to stabilize with the increase of aging time.he dynamic and static stiffness ratio showed a trend of first decreasing and then slowly rising with the increase of aging time.The tensile strength and elongation at break of NR at different temperatures and aging times were fitted by mathematical models,and it was found that both of them showed exponential decay characteristics.The fatigue properties of NR were studied under different tensile fatigue times,different tensile strain,and different compressive deformation amounts were studied.The results showed that the fatigue life of NR vulcanizate was about 120 000 times under 100% dynamic tensile fatigue.When the number of tensile fatigue is20,000 times,the hardness,elongation at break,crosslinking density and modulus decreased slightly,and then the above mentioned properties remained unchanged with the increased fatigue,when the tensile fatigue times exceeded 60,000 times,the above properties would decline signficantly.The strain of tensile fatigue had a significant impact on the dynamic fatigue life of NR vulcanizates,the results showed that the fatigue life calculated by using the empirical formula of maximum elongation rate matched the experimental results the best.The amplitude of tensile fatigue also affects the dynamic fatigue performance.By analyzing the fatigue test results of rubber samples under different strains,three methods are used to predict the fatigue life times of rubber samples.The comparison shows that the fatigue times calculated by the empirical formula of maximum elongation provided the best match with the experimental results.Under the compression fatigue condition,the properties of NR vulcanizate did not change significantly when the compression fatigue strain was less than 20%,and the crosslinking density,hardness,resilience,and modulus of the NR vulcanizate all decrease significantlyIn this paper,natural rubber used in vibration damping products was taken as the research object.By systematically changing the temperature,time,stress level,fatigue type(compression,tensile)and working conditions and ozone aging conditions of hot air,modern testing equipment is used to test the related properties of natural rubber after aging,and the nonlinear finite element model of rubber samples in different working conditions is established.It is of great theoretical significance and practical engineering value to simulate and predict the change of mechanical properties and obtain the change rule and evolution mechanism of properties after aging or fatigue. |
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