断裂过程区D—B模型的叠加原理和截荷修正法

提出分析中心裂纹板剪切断裂的断裂过程区D－B模型的叠加原理，考虑了压剪断裂的摩擦阻力和体现有限权宽影响的载荷修正，以非常简便的方法推导出计算断裂过程区长度和位移的公式。     

砂岩方梁断裂过程区范围的实验确定方法

裂纹前端的断裂过程区是引起岩石非线性断裂及尺寸效应的主要原因。利用数字图像相关技术对砂岩开展了三点弯曲梁实验,获得观测区域高精度的全场位移和应变数据,根据断裂韧带区域水平位移和水平应变的分布特征,结合裂尖岩石颗粒变化的微观分析,提出采用裂纹尖端水平位移波动性和水平应变突变性所得到的波动系数和水平应变突变值,确定断裂过程区形状和临界尺寸的方法。结果表明:砂岩断裂过程区的形状为不规则的狭长带状区域,断裂过程区的临界长度为11~13mm,临界宽度为1.58~2.36mm。断裂过程区区域内形变在趋向裂尖时呈指数增加,但其单位区域内的形变增量呈波动状态。该方法能够更加准确判断岩石断裂过程区的范围,有助于分析岩石的非线性断裂特性。     

板试样Ⅲ型裂纹长度的计算

本文设计Ⅲ型裂纹断裂及扩展速率的试验装置，测量了Ⅲ型裂纹试样在不同裂纹长度下的裂纹边缘滑开位移，给出了裂纹滑开位移与裂纹长度的显式柔度公式．     

基于数字图像相关方法的鲁灰花岗岩断裂特性研究

采用单边直裂纹三点弯曲梁(SC3PB)对鲁灰花岗岩I型裂纹的断裂特性进行了实验研究,得到其断裂韧度为0.9~1.4MN/m1.5。基于数字图像相关方法(DIC)分析了峰值载荷前试件断裂位移场及应变场的演化过程,根据位移场的不连续性给出过程区的扩展轨迹,由应变场得到了高应变区域的变化规律。当局部水平位移梯度发生剧烈变化时,鲁灰花岗岩I型断裂进入过程区;且以水平方向应变达到0.11%~0.20%时作为进入过程区的门槛值;并进一步给出了过程区尖端沿竖直方向的扩展速率与过程区长度呈三次多项式递增关系。     

一维六方准晶有限板孔边对称反平面双裂纹问题的边界配置法

从断裂力学的观点出发,采用边界配置法研究了一维六方准晶中带双裂纹的圆孔口反平面问题.通过选取恰当的位移函数,求得声子场与相位子场的应力和应力强度因子.而板的边界条件由边界配置法近似满足.通过数值算例,讨论了裂纹长度、板的宽度、幂级数项数以及圆孔半径等对应力强度因子的影响.结果表明圆孔半径对应力强度因子的影响非常明显.在有限大板与无限大板两种情况下,裂纹长度与幂级数项数对应力强度因子的影响恰好相反.     

梁在纯弯曲力矩作用下的动态塑性断裂

本文采用刚塑性分析方法,研究了带裂纹有限长韧性材料梁在纯弯曲力矩作用下的动态塑性断裂过程,本文考虑了由于断裂引起的附加轴向力对断裂过程的影响,并在分析中考虑了应变率对断裂过程的影响。文章给出了断裂过程中断裂截面上弯曲力矩和轴向力随时间的变化规律,以及裂纹长度,裂纹扩展速度和加速度随时间的变化规律。     

含裂纹有限结构的局部—整体分析

基于局部－整体分析法用限元研究了有限结构内含穿透裂纹的Ｉ型断裂问题,作为局部分人出了有限结构内穿透直裂纹尖端区域应力场的渐近表达式,并以此为位移模式构造了高阶奇异元,代替通常有限元分析中裂纹尖端的稠密网格。文中以中心穿透裂纹板结构为例细致地讨论了有限结构有限尺寸效应,讨论了结构厚度结构长度对应力强度因子的影响。     

压缩双裂纹和单裂纹圆孔板应力强度因子公式

从理论模型和数值分析上澄清了国外文献关于压缩双裂纹圆孔板(double cleavage drilled compression,DCDC) 的应力强度因子不同的公式引起的混淆. 证明Plaisted 等用修正压缩无限大板中圆孔双边裂纹的解和欧拉-伯努利梁理论得到的DCDC 应力强度因子公式都存在推导和原理性的失误. 指出Jenne 等推导的公式形式过于复杂不便使用, 而He 等的公式适用范围偏小. 通过拟合有限元法宽范围数值计算结果导出DCDC 的应力强度因子的新公式, 该公式形式简单, 对无量纲裂纹长度和无量纲板宽度适用范围较大, 最大误差是7%. 此外, 还对新提出的压缩单裂纹圆孔板(single cleavage drilled compression, SCDC)做了分析, 首次得到的SCDC应力强度因子公式的最大误差是5%. 给出的2 个公式可分别用于脆性材料DCDC 或SCDC 试样的断裂韧度测试.     

含界面裂纹Reissner板弯曲问题分析的奇异单元

首先,采用特征函数渐近展开法,推导了Reissner板弯曲界面裂纹尖端附近位移场渐近展开的前两阶显式表达式,并利用所获得的位移场渐近表达式构造了一种可用于Reissner板弯曲界面裂纹分析的奇异单元。然后,将该奇异单元与外部的常规有限单元相结合,开展了含界面裂纹Reissner板弯曲断裂问题的数值分析。奇异单元可以较好地描述裂纹尖端附近的内力场与位移场,其优势是它与常规单元进行连接时不需要使用过渡单元,并且可以直接给出应力强度因子等断裂参数的高精度数值结果。最后,通过两个数值算例验证了本文方法的有效性。     

基于数值模拟的混凝土系列有效断裂判据

基于ANSYS平台,对某系列混凝土断裂破坏试验的加载过程进行有限元数值模拟,获得了荷载-加力 点位移曲线.利用获得的曲线,在线性渐进叠加假定的基础上,确定了试件在失稳断裂时的临界有效裂缝长度.将模拟峰值荷载和临界有效裂缝长度代入由LEFM推导出的公式计算了考虑断裂过程区影响的有效断裂韧度.最后,通过对系列试验有效断裂韧...     

Fatigue crack growth under anti-plane shear mode deformation

In this paper, the theory of the steady growth of fatigue crack in an infinite medium under the periodic anti-plane remote shear loading has been examined. The criterion of accumulative plastic work for material failure associated with the slip displacement in the fracture process zone of Dugdale type ahead of the crack tip is employed in the analysis. The effect of the locked dislocation in the fracture process zone is considered. Under the assumption that the speed of fatigue crack propagation remains uniform through the fracture process zone, the steady speed of fatigue crack can be expressed as a function of the range of the applied shearing stress and the maximum shearing stress. The effect of the crack size on the fatigue crack speed is discussed. The effect of the finite width of specimen on the speed of fatigue crack speed is investigated. The differences between the present work and the previous studies on fatigue crack speed are discussed.     

铁路车轴过盈配合面微动损伤分析及有限元仿真

基于全尺寸铁路车轴疲劳试验，观察并分析了微动区损伤形貌及损伤机理. 基于测量的磨损轮廓建立有限元模型，计算分析了微动磨损对过盈配合面微动参量及轴向应力的影响. 结果表明:轮座近加载侧存在1个宽度约为20 mm的微动损伤区，根据形貌特征可以分为3个区域. 仿真得到的微动滑移区宽度与损伤区宽度基本一致，张开区宽度略小于磨损区. 未磨损时，接触压应力、摩擦剪应力及轴向应力峰值均出现在接触最边缘；在微动磨损作用下，接触压应力、摩擦剪应力、轴向应力峰值出现在磨损-未磨损边界，且轴向应力数值在磨损区由负变正. 磨屑的存在为接触面提供承载平台，在一定程度上抑制应力集中向内部转移.      

基于弹性-塑性内聚力模型的纤维拔出界面宏观行为分析

用解析法分析了单纤维从聚合物基体中的拔出过程,采用弹性—塑性内聚力模型模拟裂纹的扩展和界面失效,确定了临界纤维埋入长度,该值区分两种不同长度的纤维拔出过程. 在纤维拔出过程,界面经历不同的阶段. 纤维埋长小于临界长度时,界面的脱粘载荷与纤维的埋长成正比;超过临界长度后,界面的脱粘载荷近似为常数. 分析了界面参数对脱粘载荷的影响:增加界面的剪切强度和界面的断裂韧性,或减小界面裂纹萌生位移,均能提高界面的脱粘载荷;界面脱粘后无界面摩擦应力时,拔出载荷—位移曲线的峰值载荷等于界面的脱粘载荷;界面摩擦应力存在时,使峰值载荷大于脱粘载荷,需要较长的纤维埋入长度和较大的界面摩擦应力.      

Sufficient criterion of fracture in the case with a complex stress state and non-proportional deformation of the material in the pre-fracture zone

A general case of proportional loading with a complex stress state of the material in the pre-fracture zone, which is typical for polycrystalline solids with plastic deformation, is considered. A sufficient criterion of fracture is proposed for the case of a complex stress state with non-proportional deformation of the material in the pre-fracture zone. Critical parameters of fracture (pre-fracture zone length and load) for cracks propagating in quasi-brittle materials are obtained with the use of a modified Leonov-Panasyuk-Dugdale model. The pre-fracture zone width is determined by solving the problem of the plasticity theory in the vicinity of the crack tip. The proposed modification of the Leonov-Panasyuk-Dugdale model makes it possible to estimate the critical opening of the crack and the critical displacement of the crack flanks. Inequalities that describe different mechanisms of material fracture under proportional loading (predominantly shear fracture mechanism and fracture mechanism through cleavage) are derived.     

Slip, stick, and reverse slip characteristics during dynamic fibre pullout

Inertial effects in the mechanism of fibre pullout (or push-in) are examined, with emphasis on how the rate of propagation of stress waves along the fibre, and thence the pullout dynamics, are governed by friction and the propagation of companion waves excited in the matrix. With a simple shear lag model (assuming zero debond energy at the fibre/matrix interface), the effect of uniform frictional coupling between the fibre and the matrix is accounted for in a straightforward way. Analytical solutions are derived when the pullout load increases linearly in time. The process zone of activated material is generally divided into two or three domains along the axis of the fibre. Within these domains, slip in the sense implied by the load, slip in the opposite sense (reverse slip), and stick may be observed. The attainable combinations define three regimes of behavior, which are realized for different material parameter values. The elastodynamic problem is also solved more accurately using a plane stress finite element method, with friction represented by an interfacial cohesive zone. The predictions of the shear lag theory are broadly confirmed.     

岩质高边坡卸荷带形成及其工程性状研究

首先针对边坡开挖或河谷下切的卸荷过程, 讨论了边坡应力场的分布, 提出了边坡二次应力的“驼峰应力分布”规律。在此基础上, 分析了伴随边坡二次应力场的形成, 岩质高边坡卸荷带的形成机理。进-步, 结合三峡船闸高边坡的开挖和监测实践, 讨论了卸荷带的工程地质意义及其力学性状表现。最后, 利用本文的基本观点, 对三峡船闸高边坡卸荷带进行了合理的数值模拟研究。     

A variational approach to analyze a natural fault with hydraulic fracture based on the strain energy density criterion

A simplified analytical model of the interaction between a hydraulic fracture and an existing natural fault is developed. The mechanical activation of the natural fault as a result of contact with a pressurized fracture is described for plane strain conditions and quasi-static fracture propagation approximation. Using a variational approach, the normal and shear stresses, as well as the boundaries of the open and sliding zones along the fault, are predicted for three stages of the fracturing process (fracture approaching, coalescence, and fluid penetration). An accumulated concentration of shear stress at the tip of the fault’s sliding zone is shown to create sufficient tensile stress to initiate a new tensile crack on the opposite side of the fault, provided either the differential in situ stress is low or the friction coefficient is sufficiently large. The results of direct numerical simulation of the fracture interaction fit the model predictions made from the strain energy density fracture criterion.     

求解I型裂纹构元J积分的半解析方法

表征裂纹尖端应力应变场程度的J积分是一个定义明确、理论严密的弹塑性断裂力学基础参量. 目前J积分的计算主要是依靠塑性因子法和有限元法,但对各类裂纹构元获得J积分以及载荷-位移关系的解析公式以实现材料断裂韧性理论预测和材料测试是断裂力学的重要和困难的任务. 以J积分为参量的材料断裂测试中应用最广的是I型裂纹试样的断裂韧性测试. 本文在平面应变条件下,针对断裂韧性测试中使用的6种I型裂纹构元,基于能量等效假设,提出了J积分-载荷和载荷-位移的工程半解析统一表征方法,进而结合有限元分析的少量计算获得J积分-载荷和载荷-位移关系的半解析公式待定参数. 分析表明,6种I型裂纹构元的J积分-载荷和载荷-位移统一公式的预测结果与有限元结果吻合良好. 新提出的J积分-载荷工程半解析公式包含了材料的弹性模量、应力强度系数和应变硬化指数,能够广泛适应不同的材料,且运用该公式能够方便获取任意载荷点对应的J积分值. 应用新方法可便于获得各类I型裂纹构元的J积分-载荷和载荷-位移工程半解析公式.      

Partial sliding along a planar crack weakened by the presence of fluid

Partial sliding along a infinite planar crack that is locally weakened by the presence of fluid is analyzed. Under uniformly applied normal and shear loads the crack surface generates non-uniform frictional resistance that has a local minimum within a penny-shaped fluid-filled domain. After the applied shear load reaches the resistance minimum a circular sliding zone initiates and then spreads around as the applied shear load is gradually increased. The primary focus of this work is to analyze sliding evolution as a function of the applied loads and the induced fluid pressure. The growth of the sliding zone is studied based on the criterion that shear stress intensity factors are zero along the zone boundary. An analytical relation between the radius of the sliding zone and the applied shear load is determined.