橡胶复合材料在循环载荷下的疲劳损伤特性

利用自行建立的疲劳试验系统，以单向聚酯帘线增强橡胶复合材料为对象，研究了循环载荷作用下影响橡胶复合材料疲劳性能的因素。结果表明，应力幅值和加载频率对橡胶复合材料疲劳性能影响较大，而平均应力影响较小。聚酯／橡胶复合材料的疲劳强化现象主要与组分材料本身的特性有关。     

单向帘线增强橡胶复合材料在疲劳过程中的温升

哈尔滨工业大学刘宇艳等人以单向帘线增强橡胶复合材料为研究对象 ,利用自行建立的疲劳试验系统 ,研究了周期载荷作用下橡胶复合材料表面温升的一般规律 ;讨论了实际热生成对材料疲劳行为的影响。为评价轮胎疲劳特性提供了有效的手段。《宇航材料工艺》 ,1 999,(5) :3 0单向帘线增强橡胶复合材料在疲劳过程中的温升     

芳纶/聚酯复合帘线性能研究

通过改变芳轮／聚酯复合帘线的初捻捻度比和复捻捻系数对比了复合帘线的强伸性能变化规律，并优选加捻参数，研究了芳轮、聚酯、芳纶／聚酯复合帘线在不同温度下老化不同时间的静态及往复拉伸疲劳后的粘合性能和不同受力条件下动态往复疲劳后的粘合性能以及不同受力条件下动态往复疲劳后的粘合强度保持率，比较了３种帘线的耐疲劳性能。结果表明，复合帘线的静、动态老化后粘合性能均优于芳纶、聚酯帘线，耐疲劳性能比芳纶帘线略有提     

芳纶/聚酯复合帘线性能研究

通过改变芳纶／聚酯复合帘线的初捻捻度比和复捻捻系数对比了复合帘线的强伸性能变化规律，并优选加捻参数，研究了芳纶、聚酯、芳结／聚酯复合帘线在不同温度下老化不同时间的静态及往复拉伸疲劳后的粘合性能和不同受力条件下动态往复疲劳后的粘合性能以及不同受力条件下动态往复疲劳后的粘合强度保持率，比较了３种帘线的耐疲劳性能。结果表明，复合帘线的静、动态老化后粘合性能均优于芳纶、聚酯帘线，耐疲劳性能比芳纶帘线略有提高，成本比芳纶帘线降低４４％。     

橡胶复合材料疲劳性能研究进展

本文综述了橡胶复合材料疲劳的研究现状，分别介绍了橡胶的疲劳、帘线的疲劳以及橡胶－帘线界面间疲劳研究的国内外最新进展，并着重介绍了断裂力学方法和疲劳－寿命图在橡胶复合材料疲劳研究中的应用。     

纤维帘线/橡胶复合材料的压缩性能

对纤维帘线／橡胶复合材料进行了压缩性能试验，结果表明帘线体积分数是影响纤维帘线／橡胶复合材料压缩性能的主要因素，帘线的类型、规格、结构性能对纤维帘线／橡胶复合材料的抗弯曲能力也有明显影响。     

用多功能胺改性聚酯帘线的浸渍组分

聚酯帘线具有很高的强度和耐疲劳性能,与尼龙帘线比较,在机械负荷作用下不易被破坏,因此被认为是目前生产子午线轿车胎胎体的有发展前途的帘线。但是聚酯帘线的粘合指标要比通常采用的粘胶帘线和尼龙帘线差,这是国为聚乙二醇对苯二甲酸酯(ПЭТФ)无论对浸渍组分,还是对橡胶改性剂都具有化学惰性。传统的浸渍组分配方不能保证它同橡胶的粘附强度,РУ型改性剂也不奏效。现在,通过国内外实践,积累了大量经验,并且开发了一些粘合剂,能将聚酯帘线用于轮胎工业,不过改进聚酯帘线粘合剂仍然是当前的任务。     

用于半钢子午线轮胎胎体增强的二股聚酯帘线的开发

研究二股聚酯帘线替代三股聚酯帘线在半钢子午线轮胎胎体中的应用.结果表明:2220dtex/2聚酯帘线的物理性能、耐弯曲疲劳和圆盘压缩拉伸疲劳性能与1440dtex/3聚酯帘线相当;2500dtex/2聚酯帘线的物理性能和耐圆盘压缩拉伸疲劳性能与1670dtex/3聚酯帘线相当,且耐弯曲疲劳性能更优.二股聚酯帘线完全可以替代三股聚酯帘线进行应用.     

橡胶－织物帘线粘合的静态和动态评价

使用两种天然橡胶胶料和用于聚酯和尼龙－６６帘线的两种浸渍液，对橡胶－帘线体系的静态和动态粘合疲劳进行了比较，其它变量是热处理的温度和时间。静态和动态粘合疲劳的相关性出乎意料地差，表明如果增强的橡胶在动态下使用，则在进行静态粘合测量时应同时进行粘合疲劳试验。     

橡胶-织物帘线粘合的静态和动态评价

使用两种天然橡胶胶胶料和用于聚酯和尼龙－６６帘线的两种浸渍液，对橡胶－帘线体系的静态和动态粘合疲劳进行了比较，其它变量是热处理的温度和时间。静态和动态粘合疲劳的相关性出乎意料地差。表明如果增强的橡胶在动态下使用，则在进行静态粘合测量时应同时进行粘合疲劳试验。     

层层接结三维角联锁机织复合材料的三点弯曲疲劳破坏

本文主要研究一种层层接结三维角联锁机织复合材料在三点弯曲交变循环载荷下的疲劳破坏与失效模式,以此阐述材料破坏的结构特征。在不同应力水平下对材料施加正弦波式应力进行三点弯曲疲劳实验,得到材料疲劳寿命(S-N)曲线,说明材料寿命与施加载荷之间的关系,随着应力水平的增加,材料的疲劳寿命呈现下降趋势。此外,观察材料的典型疲劳破坏模式,发现破坏主要集中于经纱屈曲起伏的最大曲率区域,应在结构设计中予以重点关注。     

Fatigue life prediction for circular rubber bearings subjected to cyclic compression

The fatigue life of circular rubber bearings under cyclic compression is theoretically and numerically analyzed based on a previously proposed fatigue failure mechanism. The energy release rate at any point in circular rubber bearings under cyclic compression, which depends on the cracking energy density and crack length along the predicted crack propagation path, is derived first theoretically. Then, the corresponding fatigue crack growth rate and fatigue life are determined numerically by introducing the fatigue parameters of three different rubber compounds before and after suffering from thermal aging. Meanwhile, the effects of intrinsic flaw size and maximum compressive stress on the fatigue life of circular rubber bearings are also investigated. It is found that the enlargement in the Regime 1 range of the crack growth rate of rubber increases the fatigue resistance of circular rubber bearings. Therefore, the effects of the mechanical properties, intrinsic flaw size, threshold value, and maximum cyclic compressive stress on fatigue life are significant and should be taken into account in designing rubber bearings. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Improvement of the mechanical and electrical properties of waste rubber with carbon nanotubes

The effect of carbon nanotubes (CNTs) on the stability of the mechanical and electrical properties of recycled waste rubber was experimentally investigated. The stress–strain curves of the composites were studied. The results show that the toughness, the area under the stress–strain curve, of the recycled rubber increased monotonically as a result of the addition of CNTs. The modulus of the nanocomposites increased by 28 times when only 5 wt % CNTs was added to the recycled rubber matrix. The effects of the cyclic fatigue and hysteresis for the composites were also examined. The strain energy density, dissipation energy, and linear damage accumulation versus the number of cycles are discussed for all of the samples. The analysis of the results showed that the strain energy density increased by 15 times at a CNT concentration of 5 wt %. The electrical properties were measured for all of the samples. The results indicate that the addition of CNTs to the recycled rubber improved its electrical conductivity by more than two orders. © 2011 Wiley Periodicals, Inc. J Polym Sci, 2011     

Failure behavior of adhesively bonded joints with a rubber modified epoxy adhesive under tensile-shear combined cyclic loading

Rubber-modified epoxy adhesives are used widely as structural adhesive owing to their properties of high fracture toughness. In many cases, these adhesively bonded joints are exposed to cyclic loading. Generally, the rubber modification decreases the static and fatigue strength of bulk adhesive without flaw. Hence, it is necessary to investigate the effect of rubber-modification on the fatigue strength of adhesively bonded joints, where industrial adhesively bonded joints usually have combined stress condition of normal and shear stresses in the adhesive layer. Therefore, it is necessary to investigate the effect of rubber-modification on the fatigue strength under combined cyclic stress conditions. Adhesively bonded butt and scarf joints provide considerably uniform normal and shear stresses in the adhesive layer except in the vicinity of the free end, where normal to shear stress ratio of these joints can cover the stress combination ratio in the adhesive layers of most adhesively bonded joints in industrial applications.

In this study, to investigate the effect of rubber modification on fatigue strength with various combined stress conditions in the adhesive layers, fatigue tests were conducted for adhesively bonded butt and scarf joints bonded with rubber modified and unmodified epoxy adhesives, wherein damage evolution in the adhesive layer was evaluated by monitoring strain the adhesive layer and the stress triaxiality parameter was used for evaluating combined stress conditions in the adhesive layer. The main experimental results are as follows: S–N characteristics of these joints showed that the maximum principal stress at the endurance limit indicated nearly constant values independent of combined stress conditions, furthermore the maximum principal stress at the endurance limit for the unmodified adhesive were nearly equal to that for the rubber modified adhesive. From the damage evolution behavior, it was observed that the initiation of the damage evolution shifted to early stage of the fatigue life with decreasing stress triaxiality in the adhesive layer, and the rubber modification accelerated the damage evolution under low stress triaxiality conditions in the adhesive layer.     

Fatigue resistance and damage mechanisms of 2D woven SiC/SiC composites at high temperatures

Fatigue resistance and damage mechanisms of 2D woven SiC/SiC composites at high temperatures were investigated in this research. Fatigue behavior tests were performed at 1200℃ and 1000°C at 10 Hz and stress ratio of 0.1 for maximum stresses ranging from 80 to 120 MPa, and the fatigue run-out could be defined as 10⁶ cycles. Evolution of the cumulative displacement and normalized modulus with cycles was analyzed for each fatigue condition. Fatigue run-out was achieved at 80 MPa and 1000°C. It could be found that the cycle lifetimes of the composites decreased sharply with the increasing maximum stress and temperature conditions significantly affected the fatigue performance under matrix cracking stress. The cumulative displacement showed no noticeable increase before 1000 cycles and the modulus of the failed specimens decreased before fracture. The retained properties of composites that achieved fatigue run-out, as well as the microstructures, were characterized in order to understand the fatigue behavior and failure mechanisms. The composites exhibited similar fracture morphology with matrix crack extension and glass phase oxidation formation under different conditions. In general, the high-temperature fatigue damage and failure of composites could be affected by combination of stress damage and oxidative embrittlement.     

A fatigue damage model for composite materials

Composite materials using polymer resins as matrices possess viscoelastic properties such that the fatigue behavior of the composite could be changed by different stress levels, stress ratio, stress frequency, or temperature. Based on a physical phenomenon of damage growth, this work develops a fatigue damage model including the nonlinear effects of stress ratio and stress frequency on the damage processes for carbon/epoxy composites. A damage index is defined and used to confirm the damage evolution behavior, and a series of fatigue tests of unidirectional specimens under monotonous loading and two‐stress level loading are conducted to test the proposed fatigue damage model. The results reveal that the proposed model could reasonably predict the fatigue life of composite materials under complicated loading conditions and it also includes the sequence effect of cyclic block loadings. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Tensile fatigue of glass fibers and composites with conventional and surface compressed fibers

The mechanism of tensile cyclic fatigue failure in conventional glass fiber dominated composites has been investigated using single fibers, strands, and composites. Surface damage to the fibers resulting from a fretting type of contact is identified as the dominant mechanism. Macrofibers of glass or glassceramic with residual surface compression have been developed to overcome the sensitivity both to cyclic and static fatigue. The macrofibers and their composites with several different matrices show greatly improved tensile fatigue resistance.     

The hygrothermal effect on the fatigue behavior of carbon fiber/ peek laminate composites (I)

The hygrothermal effects on the fatigue behavior of the Carbon/PEEK laminated composites before and after impact damage were examined in this study. The [0/45/90/-45]_2s AS-4/PEEK laminated composites were immersed in 80°C hot water for 45, 90 and 200 days,and subjected to falling weight impact with an energy of 8.58 J and then immersed in 80°C hot water for 45 days. It was found that the tensile strength of AS-4/PEEK laminated composites decreased with the increase of exposure period. The injured AS-4/PEEK composites were subjected to a static load and a tensiontension fatigue load at various levels of stress amplitudes. The effect of stress amplitude on the fatigue life was studied. The experimental fatigue life under different stress amplitude tests were estimated by the median rank order statistic cumulative distribution function. Then,the fitting curves for estimated data were analyzed by the Weibull distribution function. The S-N curves for a series of cyclic loads at various survival probabilities were presented. The damage behaviors of composites after fatigue load test were also investigated by scanning electron microscope(SEM). Results indicated the fatigue lives of immersed specimens were shorter than those without hygrothermal effect, the impact damage affects the fatigue life of composite significantly.     

Damage development and lifetime prediction of cross-ply ceramic-matrix composites subjected to cyclic loading at room and elevated temperatures

ABSTRACT

In this paper, the damage development and lifetime prediction of fibre-reinforced ceramic-matrix composites subjected to cyclic loading at elevated temperatures in oxidising atmosphere have been investigated. Considering the damage mechanisms of matrix cracking, interface debonding, interface wear and interface oxidation, the damage evolution of fatigue hysteresis dissipated energy, fatigue hysteresis modulus, fatigue peak strain, interface shear stress and broken fibres fraction have been analysed. The relationships between damage parameters and internal damage of matrix cracking, interface debonding and slipping, and fibres fracture have been established. The experimental fatigue hysteresis, interface slip lengths, peak strain, and the fatigue life curves of cross-ply CMCs under cyclic loading at elevated temperature have been predicted. The different fatigue behaviour in unidirectional and cross-ply CMCs at room and elevated temperatures subjected to low-cycle and high-cycle fatigue has been discussed.