轮胎疲劳损伤过程的数值监测

利用系统分析的方法和信号处理技术,建立了轮胎在疲劳损伤过程的数学模型,结合大量的试验结果,定义了轮胎的疲劳损伤参数,并在此基础上以在线的方式,对轮胎疲劳损伤过程进行监测和数值跟踪描述、经轮胎耐久性疲劳试验结果表明：基于系统分析的方法所定义的轮胎疲劳损伤参数,能够有效跟踪在轮胎的复合层、橡胶层和复合层与橡胶层之间的结构内部的疲劳损伤的发展时间、疲劳裂纹扩展过程以及各层间结合的疲劳强度、裂纹扩展阻力等数值结果．     

聚酯增强橡胶疲劳破坏实验研究

采用特殊设计的夹具和疲劳测试系统,借助软Ｘ射线技术和ＳＥＭ技术研究了聚酯增强橡胶的疲劳破坏机理,给出了疲劳寿命图。研究表明,定应变控制的聚酯增强橡胶的疲劳过程呈现明显的阶段性,其疲劳破坏机理表现为三种类型：基体裂纹、聚酯／橡胶界面脱粘、帘线断裂。疲劳过程的不同阶段对应不同的基体、界面以及帘线纤维的损伤机理。另外,对材料疲劳过程中的热效应进行了定性分析。     

裂纹生长方法在橡胶疲劳分析中的应用研究

橡胶因能承受大应变而不发生永久变形或断裂而得到广泛应用。如轮胎、隔振器、缓冲器和鞋类。这些应用长期承受随时间变化的大应变,耐久性尤其重要。在影响耐久性的诸多因素中,机械疲劳是首要因素。文章回顾了裂纹生长方法在橡胶件疲劳寿命分析中的应用。介绍了现有理论,讨论了其优点和局限性,给出其在工程分析中应用的实例。     

金属疲劳累积损伤理论的研究

一、前言 大量的工程实践表明,机械及结构物的破坏,大多是疲劳造成的。一般情况下,在零件或结构物的局部,由于应力或应变集中,在循环载荷的作用下,就会产生局部塑性变形的累积,从而形成了微观疲劳裂纹,在循环载荷的连续作用下,裂纹会不断扩展至宏观裂纹,最终达到临界尺寸,导致破坏。疲劳破坏大致可以分成四个阶段:疲劳成核、微观裂纹形成、宏观裂纹扩展、最后断裂。一般把前二个阶段统称为疲劳的无裂纹寿命阶段,把后二个阶段统称为疲劳的有裂纹寿命阶段。 断裂力学的发展,对宏观疲劳裂纹扩展的研究起了很大的推动作用,现在已经可以用断裂力学的方法定量地计算有裂纹阶段的疲劳寿     

轮胎结构中层间裂纹扩展过程的数值模拟

轮胎是一个十分复杂的橡胶基复合材料结构,在使用过程中常常发生层间脱层破坏。提出了一种新的复合材料结构中层间脱层裂纹扩展模型,并利用Irwin的虚拟裂纹闭合技术和有限元分析技术对轮胎结构带束层中的层间脱层裂纹扩展过程进行了数值模拟。结果表明,提出的模型能够比较真实地揭示复杂复合材料结构层间脱层裂纹扩展复杂性的特点。     

发电机转子疲劳开裂原因分析

对某发电机转子出现的裂纹从结构、材质、局部应力及裂纹面的宏、微观检查,得出了其低应力高周疲劳破坏的开裂性质.分析了其失效原因.     

热处理工艺对50CrVA高强弹簧钢超高周疲劳损伤机制的影响

研究了50CrVA高强弹簧钢在不同热处理状态下(淬火+中温回火和退火)的超高周疲劳破坏行为及其裂纹萌生机理。结果表明,50CrVA高强弹簧钢在107~109循环周次内发生疲劳破坏,两种热处理状态的S-N曲线下降形态不同,均未出现疲劳极限。热处理工艺改变50CrVA的微观组织,从而影响超高周疲劳阶段(寿命107周次)的疲劳破坏损伤机制:经淬火+中温回火处理材料破坏多起源于内部夹杂物,夹杂物周围存在的应力场与溶质原子发生弹性交互作用,吸引间隙原子向其周边扩散、富集,使间隙原子富集区材料性能下降,导致裂纹在内部夹杂物处萌生;退火热处理后材料微观组织对间隙原子向材料内部夹杂物扩散起到阻碍作用,所以超高周疲劳裂纹易于在材料表面萌生。     

橡胶疲劳性能计算方法与机理研究进展

从橡胶疲劳性能的计算方法和疲劳机理两方面对其疲劳问题研究进行了回顾。计算方法主要有裂纹萌生方法、裂纹扩展方法及人工神经网络计算模型。橡胶疲劳的机理主要从填料对疲劳性能的影响和应变结晶型橡胶疲劳增强机理两个方面进行回顾。最后对橡胶疲劳问题研究的发展趋势进行了展望。     

基于开裂能密度及裂纹扩展特性的橡胶隔振器疲劳特性预测

基于开裂能密度的连续介质力学参数及橡胶材料裂纹扩展特性(裂纹扩展速率与撕裂能之关系),获得橡胶部件多轴疲劳特性计算公式,并计算某汽车动力总成橡胶隔振器的疲劳特性。计算与试验对比表明,橡胶隔振器疲劳特性预测(寿命、开裂位置及开裂方向)与实测较一致。预测疲劳寿命分布在实测疲劳寿命的1/2倍分散因子内,满足工程疲劳寿命预测要求。提出的橡胶隔振器多轴疲劳特性预测方法,可用试验效率较高、投入较少的材料裂纹扩展试验代替耗时较多的材料疲劳破坏试验,不仅能为橡胶部件前期疲劳设计提供参考,亦能大幅缩短产品疲劳设计周期。     

AlSi10Mg(Cu)铸铝合金的热疲劳裂纹萌生及早期扩展行为

微观观察AlSi10Mg(Cu)铸铝合金在热疲劳裂纹的萌生和早期扩展过程,重点研究共晶硅粒子对热疲劳裂纹行为的影响。结果表明:热疲劳裂纹萌生于脱粘共晶硅粒子与铝基体间的开裂界面,原因是共晶硅粒子与铝基体的热膨胀系数不同,引起热循环过程中两相热应变不协调,从而在两相界面处产生循环应力而引起疲劳破坏。热疲劳裂纹的扩展在长度和宽度上同时进行,具有良好塑性的铝枝晶对疲劳裂纹的扩展起阻碍作用。对热疲劳过程中共晶硅粒子周围应力场的模拟分析进一步解释了实验现象。     

Evaluation of fatigue property of PET tyre cord and rubber by using thermoluminescence

The experimental analysis of thermoluminescence (TL) activation energy, E, and frequency factor, S, by changing heating rate was applied to the investigations of fatigue and fatigue resistance performances of poly(ethylene terephthalate) (PET) tyre cords and tyre rubber. The TL frequency factor, S, was found to be very sensitive to the process of the fatigue of the PET cords and rubber sheet. A strong correlation between TL frequency factor and fatigue process was found which is expected to be applied as a new approach to the studies of fatigue in polymers.     

轮胎钢圈开裂失效分析

某公司生产的轮胎钢圈在安装服役15d左右后出现批量开裂现象,采用宏观分析、化学成分分析、力学性能测试、金相检验及断口分析等方法对轮胎钢圈的开裂原因进行了分析。结果表明:该批轮胎钢圈失效为早期疲劳开裂;轮胎钢圈轮辋侧焊缝熔合线处存在机加工刀痕,产生缺口应力集中,加之裂源处焊缝熔深不足降低了其疲劳性能,加速了疲劳裂纹的萌生和扩展,最终导致轮胎钢圈早期疲劳开裂。     

橡胶复合材料疲劳破坏特性

分别对[00 ]和[ ±200 ]橡胶复合材料在拉伸循环载荷下的疲劳损伤进行了实验研究。两类材料的周期最大应变随循环周次的变化遵循三阶段规律, 三个阶段对应着疲劳损伤从萌生、稳定扩展到加速扩展直至整体破坏的过程。单层和双层材料的疲劳破坏分别为帘线控制和基体控制。实验表明, 用加载最大应力表征的疲劳寿命与循环周次的对数近似成线性关系。疲劳过程中材料的滞后损失基本保持不变。滞后损失和导热系数的差异是造成不同种类试件表面温升差异的主要原因。     

轮胎螺栓断裂失效分析

某汽车轮胎螺栓在使用过程中发生断裂。采用宏、微观检验和化学成分分析等方法对失效件进行了检测。结果表明，其断裂形式为弯曲疲劳断裂。疲劳裂纹的形成是由于螺纹牙底存在脱碳和折叠裂纹等缺陷，这些缺陷的存在使该材料产生了较大的应力集中，从而导致螺栓开裂失效。     

Fatigue life prediction of a rubber mount based on test of material properties and finite element analysis

Failure analysis and fatigue life prediction are very important in the design procedure to assure the safety and reliability of rubber components. The fatigue life of a rubber mount was predicted by combining test of material properties and finite element analysis (FEA). The natural rubber material material’s fatigue life equation was acquired based on uniaxial tensile test and fatigue life tests of the natural rubber. The strain distribution contours and the maximum total principal strains of the rubber mount at different loads in the x and y directions were obtained using finite element analysis method. The critical region cracks prone to arise were obtained and analyzed. Then the maximum total principal strain was used as the fatigue parameter, which was substituted into the natural rubber’s fatigue life equation, to predict the fatigue life of the rubber mount. Finally, fatigue lives of the rubber mount at different loads were measured on a fatigue test rig to validate the accuracy of the fatigue life prediction method. The test results imply that the fatigue lives predicted agree well with the test results.     

疲劳荷载对橡胶混凝土损伤和断裂性能的影响

虽然橡胶混凝土塑性和疲劳性能较好,但由于掺入橡胶,其在疲劳荷载下离散性增大,损伤过程及最终的断裂机制均不明确。为研究橡胶混凝土在疲劳荷载下的损伤和断裂性能,基于声发射开展了不同橡胶掺量的混凝土在疲劳荷载下的三点弯曲疲劳断裂试验。计算有效裂缝长度,分析疲劳荷载下不同橡胶掺量的混凝土裂缝长度a的变化规律,并利用裂缝长度a和声发射累积能量E_AE分别定义了损伤变量D_a和D_AE;分析疲劳荷载下不同橡胶掺量的混凝土断裂能G_F的变化规律;利用声发射中的信号持续时间分析疲劳荷载下橡胶混凝土中裂缝出现和扩展的规律。结果表明,混凝土的断裂能随橡胶掺量的增加呈线性增加;在疲劳荷载下,裂缝长度a和D_a均呈倒S型规律变化,而D_AE呈正S型规律变化;声发射信号持续时间表明,在疲劳荷载下,橡胶混凝土中的裂缝总在荷载较小时出现或发生扩展。      

硅酸铝纤维增强铝基复合材料的疲劳断裂特征

采用压力铸造法, 制得Al₂O₃?SiO₂短纤维增强的铝合金复合材料, 对其弯曲疲劳性能进行了测试, 并详细观察了疲劳裂纹的形成及扩展方式。结果表明: Al₂O₃?SiO₂f/ ZL 108复合材料存在 多种疲劳源; 疲劳裂纹的扩展是通过主裂纹与裂尖前方孔洞的相互联接而进行的, 是不连续的, 沿着纤维及渣球密集的路径扩展; 疲劳过程中主裂纹的形成消耗了大部分的疲劳寿命, 一旦主裂纹形成就快速扩展瞬间断裂。该复合材料的断裂宏观上是脆性的, 但微观上显示出塑性的特征。     

Influence of temperature on fracture initiation in PET and PA66 fibres under cyclic loading

The fatigue of single thermoplastic fibres has been well documented to occur in a reproducible manner when they are subjected to certain cyclic loading conditions. The fatigue fracture morphologies of these fibres are very distinctive and differ markedly from other types of failure. This type of behaviour, which is clearly seen with the unambiguous tests on single fibres, must reflect behaviour of fibres in more complex structures which are subjected to cyclic loading. Only limited numbers of reports have, however, shown similar fracture morphologies with fibres extracted from fibre bundles embedded in a matrix material such as rubber. Usually the fractured ends of fibres taken from structures are seen to be shorter than those obtained in single fibre tests and also they show more complex and confused crack growth. The present study reveals that the low thermal conductivity of the fibres, exacerbated when they are embedded in a rubber matrix, leads to very high temperature rises, which is not the case in single fibre tests and under these conditions, crack initiation occurs across the fibre section instead of being restricted to the near surface region. Tests on single fibres at temperatures up to and beyond the glass transition temperature have shown how the fracture morphologies become modified. The fatigue process has been seen to become generalised throughout the fibre and failure occurs due to the coalescence of several cracks, some of which are initiated in the core of the fibre. In all cases, the cracks can be seen to have been initiated by solid inclusions in the fibres.     

Fatigue crack orientation in NR and SBR under variable amplitude and multiaxial loading conditions

The orientations of cracks as they develop in a material indicate the planes that have experienced the maximum damage. For the purpose of fatigue life analysis and prediction, these planes are referred to as the failure or critical planes. In order to study the planes on which cracks develop for different types of loading, the development of cracks was observed during constant and variable amplitude experiments using the multiaxial ring specimen. Two filled rubber materials were compared in this study: NR, which strain crystallizes, and SBR, which does not. Multiaxial test signals composed of alternating blocks of axial and torsion cycles (each of which acts on different critical planes) produced crack orientations that fell between those occurring for signals composed only of axial or of torsion cycles. Plane-specific fatigue damage parameters of cracking energy density and normal strain were evaluated for their ability to predict the experimentally observed planes of crack development.