呼吸式裂纹梁的振动疲劳裂纹扩展耦合分析

为提高结构振动疲劳分析的精度,提出一种呼吸式裂纹梁的振动疲劳裂纹扩展耦合分析方法。分析过程中,采用双线性弹簧描述呼吸式裂纹,广义的Forman方程模拟疲劳裂纹扩展;运用Galerkin法把裂纹梁简化为单自由度系统,振动分析与疲劳裂纹扩展计算交替进行,并考虑了振动疲劳裂纹扩展耦合行为。结果表明,对于含裂纹结构的振动疲劳裂纹扩展,采用呼吸式裂纹可以更客观地描述振动过程和裂纹扩展现象;激励频率和阻尼效应对疲劳寿命具有重要影响,尤其对共振疲劳裂纹扩展而言,阻尼效应特别明显。     

某型地铁车辆车下帽型梁裂纹扩展寿命预测

针对某型地铁车辆车下帽型梁螺栓孔边开裂问题,本文通过统计大量开裂结构的裂纹情况,分析了裂纹分布规律,并利用有限元仿真技术探究导致帽型梁开裂的主要载荷;对送试验的5根帽型梁开展疲劳台架试验,并基于Paris公式和Minear线性损伤理论实现了该帽型梁裂纹扩展寿命的预测。研究结果表明:帽型梁结构的裂纹分布主要沿车身纵向,横向排布的帽型梁受横向振动的影响大,其次为垂向和纵向,垂向振动对纵向排布帽型梁的影响明显大于其余两向振动;5根帽型梁试样的剩余疲劳寿命均在1.07以上,与台架试验的结论相同,结构满足标准要求。     

直齿轮弯曲疲劳裂纹的扩展行为预测与分析

以渐开线圆柱齿轮为研究对象,在其齿根部存在初始裂纹的前提下,研究齿根疲劳裂纹扩展特性及其寿命;将齿轮啮合过程的动力学计算等效为多个啮合位置的静力分析,得到不同位置的应力强度因子;根据线弹性断裂力学,将裂纹扩展过程线性等效,以K判据分析裂纹是否发生扩展,根据Paris准则计算裂纹扩展量,采用最大周向应力准则确定裂纹扩展角度,得到整个计算周期的应力强度因子、疲劳裂纹扩展路径及疲劳寿命;采用高频试验台对齿轮进行疲劳试验,得到齿轮的疲劳扩展路径,与有限元计算结果进行对比验证;最后分别分析了初始裂纹的尺度、位置和载荷的不同对疲劳裂纹的扩展及疲劳寿命的影响。     

含裂纹板的振动疲劳裂纹扩展耦合分析

为提高含裂纹板的振动疲劳分析精度,提出一种振动疲劳裂纹扩展耦合分析方法。首先,利用附加载荷等效代替裂纹作用,由力学平衡原理推导含裂纹板的振动方程,基于Rice与Levy应力关系式形成方程的裂纹项;然后,运用Paris方程模拟裂纹扩展,通过振动分析与裂纹扩展计算同步进行的方式考虑振动与裂纹扩展的耦合作用,讨论振动对含裂纹板裂纹扩展的影响。分析表明,结构固有频率与裂纹大小和板厚密切相关;阻尼大小和激振力变化对裂纹扩展速率的影响显著。     

基于临界曲面的改进Paris定律球轴承疲劳寿命预测方法

通过场发射扫描电镜对球轴承疲劳故障点微观结构进行观察,发现裂纹总是沿着某个曲面进行萌生和扩展,扩展到一定程度后发生断裂形成近似椭圆形状的剥落点,随着球轴承的运转,不仅断裂后的裂纹发生二次剥落,而且剥落点将在新的曲面上发生多次剥落,形成断层形貌。基于此种现象,提出球轴承临界曲面的概念,假定裂纹的萌生和扩展均在此临界曲面上,将三维裂纹扩展问题转化为二维裂纹扩展问题进行分析。在临界曲面概念的基础上,提出改进的Paris疲劳寿命预测模型,将疲劳寿命分为裂纹扩展和剥落点增大两部分,分段采用改进的Paris定律预测球轴承的疲劳寿命。通过多套SKF 6205深沟球轴承疲劳寿命试验数据进行验证,与传统的SKF L-P公式预测结果相比,提出的方法能够较好地预测球轴承的疲劳寿命。     

镍基单晶涡轮叶片榫头疲劳裂纹扩展寿命研究

设计航空发动机涡轮叶片榫头/榫槽接触模拟试验件,基于涡轮叶片的实际工况,进行了榫头/榫槽接触疲劳试验。基于Paris公式提出了榫头接触疲劳裂纹扩展寿命模型,并采用晶体滑移有限元程序对涡轮榫头/榫槽接触进行了有限元模拟。有限元分析得到的疲劳裂纹扩展寿命与试验结果相符,表明提出的疲劳裂纹扩展寿命模型可用于指导分析榫头寿命。     

基于应变模态的振动筛横梁损伤诊断及疲劳剩余寿命预测研究

基于模态理论对振动筛横梁进行了位移和应变模态分析,结果表明横梁损伤前、后同阶模态频率的相对偏差较小,位移模态振型亦无明显突变,而应变模态振型在横梁损伤后产生了突变峰值。据此构建了应变模态变化率作为横梁损伤诊断指标,分析结果表明应变模态变化率随横梁损伤程度的增加而增大,然后用最小二乘法拟合了二者的对应关系。由横梁的损伤程度可确定横梁初始疲劳裂纹尺寸,进而可由Paris公式预测振动筛横梁的疲劳裂纹扩展剩余寿命。应变模态变化率作为损伤诊断指标具有敏感、可靠的优点,可以较好地确定横梁损伤位置和损伤程度。对振动筛横梁的裂纹扩展剩余寿命的预测,可为横梁的预报维修提供参考,以保证振动筛的安全可靠运行。     

含任意数目裂纹梁的振动分析

基于递推方法研究多种边界条件下含任意数目裂纹梁的振动分析。将梁的裂纹模拟为无质量的等效扭转弹簧。通过递推方法可以把裂纹梁的特征微分方程转换成递归代数公式,然后利用边界条件和裂纹位置的连续性条件推导可以得到该裂纹梁的无量纲固有频率以及相应的振形函数解析表达式。通过与参考文献中的计算结果相比较,验证了方法的正确性和有效性。文中还给出了具体的算例,计算出了简支梁的模态振型,并分别讨论了裂纹的数量和深度对于固有频率的影响。     

硬涂层阻尼结构的随机振动疲劳寿命分析

为了研究硬涂层阻尼结构的疲劳寿命合理的分析方法和对结构寿命影响的基本规律，利用有限元模拟技术进行带硬涂层阻尼的悬臂薄壁梁结构的随机振动疲劳寿命计算。以一个悬臂薄壁梁为对象，首先，对该结构涂敷硬涂层前后的模态和谐响应进行计算，获得模态频率和危险部位应力响应函数；其次，采用随机振动疲劳寿命频域分析法对涂层前后悬臂梁进行有限元仿真计算，获得相应的寿命和损伤云图；最后，在电磁振动台上进行随机振动基础激励的编谱加载，获得涂层前后悬臂梁的振动疲劳寿命和损伤行为。结果表明，硬涂层能够延长悬臂梁振动疲劳寿命，可以减缓疲劳裂纹扩展速率。通过对比模拟和试验结果的误差分析，证明振动疲劳寿命模拟方法的合理性。     

基于应变模态的振动筛上横梁疲劳损伤分析

基于模态理论建立了振动筛位移和应变模态参数识别模型,仿真分析了振动筛上横梁产生疲劳损伤裂纹时位移和应变模态参数的变化。分析结果表明上横梁产生疲劳裂纹后的模态频率和位移振型较疲劳损伤前均无显著变化,而应变模态振型在疲劳裂纹处发生了显著的突变,其中弯曲应变模态较扭转应变模态对疲劳损伤裂纹更敏感。以振动筛上横梁产生疲劳损伤裂纹前、后的应变模态变化率为指标判定疲劳损伤程度,由损伤程度即可确定上横梁疲劳裂纹尺寸,进而可由Paris公式的积分形式计算振动筛上横梁的疲劳剩余寿命。基于应变模态变化预测振动筛上横梁的疲劳损伤程度和疲劳剩余寿命,将有助于对其进行动态优化设计,从而提高振动筛的使用寿命。     

基于裂缝梁动力特性和自振频率的参数敏感性

基于Bernoulli-Euler理论,将开口裂缝梁视为变截面梁,利用模态摄动方法建立了一种求解带任意数量开口裂缝简支梁和连续梁动力特性的半解析分析方法。在等截面无损梁的模态子空间内将裂缝梁的变系数微分方程的求解转化为非线性代数方程组的求解;利用无损梁的自振频率和振型函数摄动求解裂缝梁的模态参数;通过矩形开口裂缝简支梁和两跨连续梁的动力试验验证了笔者方法的准确性;最后,利用开口裂缝梁动力特性的半解析解研究了简支梁和两跨连续梁的自振频率对裂缝尺寸和位置的敏感性。     

Second Generation Wavelet Finite Element and Rotor Cracks Quantitative Identification Method

The presence of cracks in the rotor is one of the most dangerous and critical defects for rotating machinery. Defect of fatigue cracks may lead to long out-of-service periods, heavy damages of machines and severe economic consequences. With the method of finite element, vibration behavior of cracked rotors and crack detection was received considerable attention in the academic and engineering field. Various researchers studied the response of a cracked rotor and most of them are focused on the crack detection based on vibration behavior of cracked rotors. But it is often difficult to identify the crack parameters quantitatively. Second generation wavelets (SGW) finite element has good ability in modal analysis for singularity problems like a cracked rotor. Based on the fact that the feature of SGW could be designed depending on applications, a multiresolution finite element method is presented. The new model of SGW beam element is constructed. The first three natural frequencies of the rotor with different crack location and size were solved with SGW beam elements, and the database for crack diagnosis is obtained. The first three metrical natural frequencies are employed as inputs of the database and the intersection of the three frequencies contour lines predicted the normalized crack location and size. With the Bently RK4 rotor test rig, rotors with different crack location and size are tested and diagnosed. The experimental results denote the cracks quantitative identification method has higher identification precision. With SGW finite element method, a novel method is presented that has higher precision and faster computing speed to identify the crack location and size.     

Vibration analysis of non-uniform beams having multiple edge cracks along the beam's height

Bending vibration of non-uniform rectangular beams with multiple edge cracks along the beam's height is investigated. These cracks are called height-edge cracks in this paper. The energy based method is used for defining the vibration of height-edge cracked beams. The opening form of the height-edge crack is determined when the external moment is assumed to be applied for stretching the beam's width. Strain energy increase is obtained by calculating the strain change at the stretched surface by taking into account the effect of angular displacement of the beam due to the bending. The Rayleigh-Ritz approximation method is used in the analysis. The cases of multiple cracks are analysed in the method by using the approach based on the definition of strain disturbance variation along the beam. Examples are presented on a fixed-fixed beam and several cantilever beams having different taper factors. When the results are compared with the results of a commercial finite element program, good agreement is obtained. The effects of taper factors, boundaries and positions of cracks on the natural frequency ratios are presented in graphics.     

受弯梁中开裂纹的位置识别与分析

利用有限元计算判定受弯梁中开裂纹的位置 ,从中得出 :同正常梁相比 ,裂纹梁的固有频率与振型的变化不但与裂纹深度而且与裂纹位置有关 ,因而 ,通过裂纹梁低阶固有频率及振型的变化情况可以判定裂纹的位置。对于裂纹较浅的情况 ,直接利用振型与固有频率的变化很难判定裂纹的位置 ,必须借用一些特征参数来提高识别的敏感性 ,这样 ,裂纹梁中早期裂纹的识别也是可行的     

Numerical and experimental method for the prediction of the propagation life of fatigue crack on metallic materials

A prediction method for the propagation life of fatigue crack for cracked components was provided and verified in this study to predict the propagation life of fatigue cracks on components in engineering applications conveniently and directly. In the simulation aspect, a finite element (FE) model of cracked specimen was created to obtain the stress intensity factor range ΔK. The FE model was verified by comparing simulated ΔK to a formulary calculated one. The simulated ΔK could be used for studying the relationship with crack size. In the experimental aspect, the fatigue crack propagation test was conducted on three specimens. The material coefficients C and m were fitted according to Paris’ law. The load cycles with different crack depths were recorded in the testing process. The propagation life of fatigue cracks of specimen was predicted via the relationship between ΔK and crack size a according to Paris’ law. The comparison between predicted life and experimental life of specimens indicated the feasibility of the method. The proposed prediction method in this study for the propagation life of fatigue cracks can be used in engineering applications.     

梁类结构多裂纹微弱损伤的小波有限元定量检测方法

提出了一种定量检测梁类结构多裂纹参数的方法。利用适宜求解奇异性问题的小波有限元法,从动力学正问题入手,对裂纹梁进行有限元建模,获得裂纹故障在结构固有频率上反映的本质征兆,并利用曲面拟合技术绘制出以裂纹位置和深度作为变量的固有频率变化率曲面,然后对整个裂纹梁进行剖分,迭代求解出每个剖分单元上的结构损伤系数。损伤系数为正的单元诊断为裂纹单元,在每个裂纹单元上求出裂纹对应的前三阶固有频率变化率,并分别将其作为输入参数代入固有频率变化率曲面,做出前三阶模态的频率变化率等高线,最后通过三条等高线的交点预测出裂纹存在的位置和深度,算例分析验证了该算法的有效性。     

Free vibration analysis of Euler-Bernoulli beam with double cracks

In this paper, the influence of two open cracks on the dynamic behavior of a double cracked simply supported beam is investigated both analytically and experimentally. The equation of motion is derived by using the Hamilton’s principle and analyzed by numerical method. The simply supported beam is modeled by the Euler-Bemoulli beam theory. The crack sections are represented by a local flexibility matrix connecting three undamaged beam segments. The influences of the crack depth and the position of each crack on the vibration mode and the natural frequencies of a simply supported beam are analytically clarified for the single and double cracked simply supported beam. The theoretical results are also validated by a comparison with experimental measurements.     

Residual fatigue life prediction of ball bearings based on Paris law and RMS

Paris law can reflect the failure mechanism of materials and is usually used to be a method to predict fatigue life or residual fatigue life.But the variable which can represent the health of machine i...     

基于固有频率的呼吸式裂纹梁损伤识别方法

将呼吸裂纹梁简化为由扭转弹簧连接的两段弹性梁,在假定振动响应随振幅变化的基础上推导出呼吸裂纹梁的固有频率方程;考虑振动过程中呼吸裂纹的开合情况,假定裂纹梁的刚度是振幅的非线性函数,建立了呼吸裂纹梁的多项式刚度模型;结合等高线裂纹识别理论和方法,提出了一种基于固有频率的呼吸裂纹梁损伤识别方法,算例验证了方法的可行性与有效性。研究表明,该方法的识别精度取决于实验固有频率的精度。     

Examining the trend in loss of flexural stiffness of simply supported RC beams with various crack severity using model updating

The flexural stiffness of simply supported cracked reinforced concrete beams was determined by model updating. The beams were 150 mm wide, 250 mm deep and 2200 mm long. Different FE models were created which include a datum and models with a single crack at three different locations along the length of the beam. The mode shape equation was obtained by using non-linear regression. The equation used in the regression was the generalized solution of transverse vibration of a prismatic beam. Local flexural stiffness, EI, at each coordinate point was derived by substituting the regressed data by using the centered-finite-divided-difference formula. Experimental modal analysis was performed on a control beam and beams with load-induced cracks at predetermined loading. Results from FE analyses showed the trend in the loss of stiffness was similar to the results obtained on the experimental beams. The more severe the damage, the higher the loss of stiffness and the loss patterns are similar for damage at different locations along the beam. The updating technique is able to indicate the trend in the loss of stiffness as a result of cracks of varying severity in the RC beams showing good agreement with experimental results.