两种材料的性质对双材料界面裂纹能量释放率及应力强度因子的影响

在实际工程中,结构往往是由多种材料构成,而裂纹经常在两种材料的界面上扩展.针对双材料界面裂纹,建立相应的计算模型.用能量释放率来描述裂纹的扩展情况,并根据界面裂纹能量释放率解析计算方法对不同的材料性质、外荷载、构件厚度,以及裂纹两侧不同的材料宽度对裂纹扩展时的能量释放率和应力强度因子进行仿真分析,得到了能量释放率和两种材料的弹性模量、外荷载及构件厚度之间的关系变化的曲线,以及裂纹两侧不同的材料宽度和应力强度因子之间的关系.并对界面裂纹和单一材料裂纹的情况进行分析、比较.     

核岛主设备不锈钢带极埋弧堆焊剥离机理分析

对核岛主设备不锈钢带极埋弧堆焊层剥离机理进行研究，结果表明：低合金钢母材上的不锈钢带极埋弧堆焊层过渡区出现平均厚度为25μm的硬化层，硬化层为高硬度、低塑性的板条马氏体组织；过渡区存在Ⅱ型边界，硬化层上存在气孔，Ⅱ型边界和气孔是堆焊层发生剥离的内因；随着堆焊层数的增加，接头界面残余应力增大，堆焊层数达到6层时，残余应力为380 MPa,过渡区的Ⅱ型边界在较大的残余应力作用下作为裂纹源扩展导致不锈钢堆焊层剥离。堆焊层界面较大的残余应力是剥离发生的外因。     

压电双材料反平面问题的界面裂纹分析

文中研究了压电双材料在反平面载荷和平面内电载荷共同作用下的电弹场，运用边界配置法求解xoy平面为各向同性面的压电双材料在2种加载情况下的应力强度因子和能量释放率，并根据界面应力强度因子和能量释放率数值计算方法分析了材料尺寸比例、电位移D0、弹性模量、配点数及幂级数项数对应力强度因子和能量释放率的影响，得到了相应的关系变化曲线图。结果表明：在裂尖处应力具有1/2阶的奇异性；材料厚度越小裂纹长度越长，应力强度因子和能量释放率越大；能量释放率随材料弹性模量的增大而减小；配点数和幂级数项数对应力强度因子和能量释放率的影响不大，但随着配点数和幂级数项数增多数值趋于稳定，且更接近真实值。当配点数在35时，应力强度因子和能量释放率都趋于稳定，而幂级数项数分别在35、22时应力强度因子和能量释放率趋于稳定；当应力强度因子和能量释放率与外加电位移在加载情况不同时，有不同的曲线关系；该方法能够方便地计算多种加载情况下压电双材料裂尖的应力强度因子和能量释放率，能反映压电双材料的界面损伤特性，有利于压电智能结构在各行业应用推广。     

双金属板软化界面的止裂与分层机理

采用带软化界面层的双金属层状板,分析了裂纹垂直于界面扩展过程中的力学行为.带单边裂纹的钢/铝层板的实验表明,裂尖到达界面时裂纹扩展速率降低;载荷增高后,易在界面上产生分层.利用有限元软件分析了裂纹前沿应力和应变的变化.计算结果表明,软铝界面层出现较大塑性应变,增加了裂纹扩展阻力,使裂纹扩展应力降低,而界面分层应力提高,导致了裂纹扩展速率降低和界面分层现象.     

软硬交替多层膜应力应变响应的分析

为了对软硬交替多层表面膜在磨粒作用下的应力应变响应、膜层界面剥离和裂纹的产生及扩展的影响等有一个定量和全面的了解，从而为多层表面膜的结构设计提供理论基础，采用大变形弹塑性有限元法对高速钢基体上的ＴｉＮ／Ｔｉ／ＴｉＮ／Ｔｉ…多层膜在法向压痕作用下的力学行为进行了模拟和分析。为了研究膜层数和膜厚的影响，对从单层到１６层的不同膜层体系进行了计算。通过对膜层的变形、最大应力随膜层数的变化、界面切应力分布和表面张应力分布等的分析得出了这些参数的分布及其随载荷和膜层数的变化规律。这些结果将为多层膜的结构优化设计提供定量的依据。     

喷射沉积SiC_p/Al-20Si复合材料高周疲劳行为研究

采用喷射沉积法制备15%(体积分数)4.5 m SiCp/Al-20Si复合材料及其基体合金,研究该组材料的微观组织、力学性能、高周疲劳性能以及疲劳断口形貌。结果表明:SiC颗粒的加入有利于提高材料的力学性能;复合材料及其基体的高调疲劳寿命随应力幅值的减小而增加,在相同应力幅值下,复合材料的疲劳寿命远远高于基体合金。疲劳裂纹从大颗粒的初晶Si的断裂以及Si相脱离处形核,并开始扩展。对于复合材料而言,SiC颗粒尺寸较小,不容易发生断裂,在形核过程中,当裂纹遇到SiC颗粒时,裂纹或者避开增强体,或者受阻于SiC颗粒,只能在基体合金中扩展,从而扩大了疲劳形核区的面积,提高了材料的疲劳寿命。Si颗粒的脱离、Si相的断裂以及SiC颗粒与基体界面的脱粘是复合材料疲劳断裂失效的主要机制。     

废旧塑封芯片分层裂纹仿真

分析了废旧塑封芯片的分层机理,计算得到了芯片分层界面裂纹断裂能释放率并建立了界面裂纹扩展判断准则。通过仿真分析分别获得了芯片内部应力载荷、裂纹长度与裂纹扩展所需断裂能释放率之间的影响规律。结果表明,塑封芯片存在的内应力及其内部结构上的缺陷,均可导致分层裂纹的产生与扩展。最后基于理论与仿真计算的结果分析了旧芯片回收重用工艺,并提出减小芯片分层损伤的工艺方法。     

弯曲载荷作用下工字形截面梁腹板中心穿透裂纹的应力强度因子

工字形梁是工程中最常见的结构之一。其中的任何裂纹都将成为结构断裂失效的隐患。带有裂纹的工字形梁是典型的三维有限边界问题,用经典方法求解其裂纹的应力强度因子通常是相当困难的。文中利用裂纹非自发扩展的能量释放率建立一个求解弯曲载荷作用下工字形截面梁中心裂纹的应力强度因子的新方法。给出工字形截面梁裂纹非自发扩展能量释放率G^＊ -积分与应力强度因子的关系,同时也给出G^＊ -积分与载荷、几何参量以及力学性能参数的关系,进而得到工字形截面梁腹板中心裂纹的应力强度因子。     

多层界面相对陶瓷基复合材料横向开裂的影响模拟

针对多层界面相对陶瓷基复合材料(CMCs)横向开裂行为的影响进行了细观有限元模拟。在代表体单元模型中,按照界面相各亚层的实际厚度建立多层界面相几何模型,然后赋予各亚层对应的组分材料参数,建立细观有限元模型。在此基础上,分别采用扩展有限单元法(XFEM)和内聚力界面模型来模拟CMCs中的开裂裂纹和脱粘裂纹,实现复合材料横向开裂过程的模拟。对单层BN界面相和(BN/Si C/BN)、(BN/Si C/BN/Si C/BN)两种多层界面相的模拟结果进行了对比。可以看出,所研究的Si C/Si C复合材料在横向载荷作用下,首先在纤维与界面相之间产生脱粘裂纹,脱粘裂纹扩展后引起外侧基体开裂,最终引起复合材料横向失效;与单层界面相相比,多层界面相将引起不同形态的脱粘裂纹,其横向开裂应变高于单层界面相,开裂位置也存在显著差异。     

燃气管道裂纹扩展G判据及分形研究

G判据是根据裂纹体能量平衡来判断裂纹是否起裂的方法,用于材料的起裂扩展判定.城市在用燃气管道为韧性材料,其裂纹扩展用J判据进行判定.通过20钢材料的J积分试验得到裂纹起裂阶段的能量释放率G,论证起裂阶段G判据和J判据是等价的.裂纹扩展的亚临界扩展阶段,引入分形维数描述裂纹断面,计算分形效应能量释放率G,得到可用能量释放率G作为裂纹亚临界扩展判定的结论.     

Modelling of delamination of ultra low-k material during chemical mechanical polishing

Two sets of experiments are performed to examine the delamination mechanism of ultra low-k material during chemical mechanical polishing (CMP): (i) a macro-scale polishing test using a metallographic polisher and (ii) a micro-scale scratch test on a micro-tribometer. Delamination has been observed at higher pressures in both sets of experiments and the relationship between delamination rate and pressure has been established. Contact mechanics models are proposed to correlate results from the two sets of experiments, combining a Weibull model of failure with a statistical asperity contact model. Results confirm the usefulness of the combined testing procedure in predicting safe polishing pressures during CMP.     

The Assessment of Interface Adhesion of Cu/Ta/Black Diamond™/Si Films Stack Structure by Nanoindentation and Nanoscratch Tests

The interface adhesion of the Cu/Ta/Black Diamond? (SiOC:H, BD, low-k)/Si substrate films stack structure was investigated. During the nanoindentation tests, a series of indentations under varied maximum normal loads of 1–120 mN were carried out. Regular triangular marks were formed on the surface, and the material pileup around the marks was clearly observed. The delamination occurred first at the Cu/Ta interface with the critical normal load of about 3.14 mN. As the normal load increased to about 63.71 mN, the BD layer began to delaminate from the Si substrate, resulted from the propagation of the cracking within BD layer along the BD/Si interface. The failure behaviors of the stack structure during the nanoscratch tests were similar to that during the nanoindentation tests. At the scratch velocity of 500 μm/min, the critical normal loads for Cu/Ta and BD/Si interfaces delamination were around 15.55 and 27.44 mN, respectively. Furthermore, the critical normal loads were decreased with the increase of the scratch velocity. Due to the similarity between the nanoscratch test and the chemical mechanical polishing (CMP) process, these results implied that lower polishing speed was preferred to avoid the interface delamination during the CMP of Cu/low-k interconnect structure.     

热障涂层层状裂纹的位置对断裂性能的影响

广泛应用于热能动力的热障涂层在高温工作环境下,由于温度梯度产生的热应力不匹配会导致热障涂层层裂或剥落失效。本文针对热障涂层层裂问题,考虑热应力不匹配因素,建立热障涂层层裂I/II复合型断裂准则,并针对分层裂纹在陶瓷层与粘结层界面上和附近的3种位置存在形式,进行了热障涂层结构单裂纹层裂的算例分析。结果表明界面处层裂纹对应变能释放率影响最大。     

Continuous delamination of sprayed deposits via applied curvature

In this work, the delamination of a bimaterial interface continuously subjected to an applied curvature is considered for direct application to the controlled debonding of sprayed metal deposits. Important to the success of some spraying applications is the ability to systematically remove sprayed deposits from their substrates. A method for doing so is described, in which the deposit is sprayed onto a relatively thin substrate, which is subsequently conveyed along a curved path so that the deposit is continuously delaminated from the substrate. In this work, the continuous delamination of a sprayed metal deposit via an applied curvature is studied as a two-dimensional interfacial fracture mechanics problem. A closed-form solution for the steadystate energy release rate governing interfacial fracture is determined. A finite element model is used to verify the analytical prediction, as well as to extract a measure of mode mix. For the case of a substrate that is both thin and stiff relative to the deposit, the mode-mix admits a simplified approach to measuring interfacial toughness values for prospective deposit/substrate combinations. Straightforward analytical design guidelines are presented and are used to investigate the feasibility of the delamination process.     

Solution of analytical-variational method on bi-material interface crack and its comparison with experiment

An analytical method is developed to describe the fields of stress and displacement in a bi material strip with an edge interfacial crack. All of the basic governing equations, boundary conditions on crack surfaces, and conditions of continuity along the interface are satisfied by the eigen-function expansion method. The other boundary conditions will be satisfied by the generalized variational principle. Good convergence of generalized stress intensity factors is obtained, and the values of crack opening displacement and energy release rate obtained by this method are close to the experimental results. Some problems regarding oscillatory singularity, contact zone and energy release rate are discussed. Finally, the effects of modulus, thickness and crack length to mode mixity are presented.     

橡胶纯剪试件断裂力学分析

在橡胶材料纯剪试件中,当裂纹的长度和试件的高度尺寸接近时,应变能释放率与裂纹尺寸无关,由于存在这个特点,纯剪试件经常被用来研究橡胶材料的断裂属性。文中对橡胶纯剪试件在试件中心线上分别存在中心裂纹和边缘裂纹,以及粘接界面分别存在中心裂纹和边缘裂纹的情况进行非线性有限元分析,并将有限元计算的应变能释放率与已存在的解进行比较。对于长裂纹,有限元解与已存在的解吻合较好;但是对于小裂纹,有限元解与已存在的解之间仍然存在一些差异。     

Energy release rate of postbuckled laminates with a through-width delamination

The strain energy release rate is calculated for buckled one-dimensional delamination (through-width delamination) in composite laminates subjected to in-plane compression. A crack closure method based on plate finite elements is used in this analysis. For some laminates containing a one-dimensional delamination in cylindrical bending, closed form solutions are available. The present finite element solutions show excellent agreement with the analytical solutions. The strain energy release rate for various types of laminates is also calculated using the present finite element method. The results show that the strain energy release rate strongly depends on the type of laminate.     

器件韧性镀膜微划痕破坏机理研究

对硅基体上之韧性镀膜（铝膜）的粘结强度及破坏机理进行微划痕实验及理论研究,从实验中观察出该体系的破坏特征,进而测量出微划前水平驱动力、划痕深度随划前水平位移并伴随着界面脱胶发生的变化规律,针对微刈痕破坏特征,建立了双粘聚力模型,并对由微划痕引起的界面弹塑性脱胶进行了数值模拟,给出界面脱胶时能量释放率随其他材料参数变化的理论预测曲线,并将预测值与文中的铝／硅实验结果及与文献中关于铂／氧化镍的实验结果进行对比,达到基本符合。通过以对韧性薄膜／脆性基体的微划痕实验研究和理论分析,获得如下主要结论：（1）韧性膜的微划痕破坏特征为,当划刀尖端接近界面时,将突然发生薄膜测界面的脱胶现象,并在界面附近脆性基一侧形成界面裂纹并扩展;微划痕的水平驱动力表征了整个薄膜脱胶体系的能量释放率;薄膜或涂层材料的塑性变形对微划痕过程有较强的抑制作用。（2）界面的分离强度和材料的剪切强度对微划痕过程有重要的影响。（3）划痕刀片的几何特征角对刻痕水平驱动力影响不大。