天然橡胶伸张疲劳结构演变及破坏发展机理分析

摘要

研究了未填充天然橡胶(NR)硫化胶动态伸张疲劳破坏历程中的结构演变,并从化学反应和微观破坏角度对破坏机理进行了探讨.采用红外光谱(FT-IR)对伸张疲劳过程进行了分析,认为橡胶材料疲劳是机械外力引发、氧化反应和力化学反应增长的过程,且氧化反应增长为主破坏增长过程.硫化橡胶发生伸张疲劳破坏存在一个最小临界拉伸比,约为0.8.拉伸比小于0.8时,橡胶材料的耐疲劳性能较好,拉伸比大于0.8时,耐疲劳性能明显下降.采用差示扫描量热法(DSC)和 X-射线衍射(XRD),分析了在不同的拉伸比(或形变量)下未填充硫化胶分子链的趋向和结晶,结果表明,硫化胶分子链随着拉伸比(或形变量)的增加,趋向和结晶程度增加.扫描电镜(SEM)分析结果表明,在小伸张形变下,NR结晶对疲劳发展影响较小,断面显示出明显的韧带和空穴.在大的伸张形变下,橡胶断面脊痕线明显降低,呈现出脆性断裂的特征.%In this paper,the evolution of the structure of unfilled NR vulcanizates during dynamic tensile fatigue is studied.The mechanism of failure is discussed from chemical reaction and microscopic destruction.Results of FT-IR analysis showed that the fatigue process of rubber material is the process of mechanical external force initiation,oxidation reaction and chemical reaction,and the oxidation reac-tion grow th is the main damage grow th process.Vulcanized rubber undergoes fatigue failure with a minimum critical draw ratio(λ)of approximately 0.8.When the stretch ratio is less than 0.8,the fa-tigue resistance of the rubber material is better,and the fatigue resistance is decreased obviously w hen the draw ratio is more than 0.8.Results of DSC and XRD analysis of the molecular structure of vulcani-zates,from the different tensile ratio(or deformation),unfilled vulcanizate molecular chain trends and crystallization,showed that vulcanized rubber molecular chain with the stretch ratio or(the amount of deformation)increased,the trend and the degree of crystallization increased.For SEM analysis the fa-tigue failure mechanism of vulcanized rubber was analyzed from the point of view of microscopic damage development.The results showed that NR crystal has little effect on fatigue development and showing obvious ligaments and cavities in the small deformation.Under the large tensile deformation, the ridge line of the rubber section is obviously reduced,showing the characteristics of brittle fracture.