金属材料疲劳裂纹扩展速率估计的分层模型

裂纹扩展速率与应力强度因子幅值的关系曲线,是金属构件损伤容限设计及寿命预测的重要疲劳性能数据．为了充分、合理地运用在不同测试条件下获得的试验数据,分层随机样本模型,将总体样本分为若干层,每一层样本都是在相同的测试条件下获得的试验数据,结合压力容器的实际工作状况,对每一层样本赋予适当的权重,从而对疲劳裂纹扩展速率方程做出更符合实际要求的估计．实际计算表明,对不同炉号试样提供的Q235A级钢材的裂纹扩展速率数据,运用分层随机样本模型得到的结果,明显地优于运用简单随机样本模型分别处理每个炉号试样提供的数据所得的结果．     

LZ50车轴钢疲劳长裂纹扩展的概率模型

试验研究了随机疲劳长裂纹扩展率概率模型．首先发展了考虑平均应力影响和低应力强度因子范围趋于门槛值现象的扩展率方程．进而提出了同时考虑试验数据分散性规律与样本数量对概率评价影响的概率模型,模型参量由线性回归法结合极大似然统计分析原理测定．LZ50钢的试验数据分析,验证了方法的有效性与实用性．     

结构疲劳长裂纹扩展速率新模型研究

比较现有疲劳长裂纹扩展速率模型的特点和不足,基于裂纹扩展钝化复锐理论推导,提出了广义钝化复锐疲劳长裂纹扩展速率模型(GPLFCPRM),并推导获得了疲劳长裂纹扩展速率模型通项.该模型克服了现有疲劳长裂纹扩展速率模型的缺点,能有效地描述自门槛值到断裂点全过程的裂纹扩展规律,具有明确的物理含义,且可反映材料的强度特性、断裂特性和热处理状态等因素对疲劳裂纹扩展速率的影响.通过LZ 50钢、A533-B、AlZnMgCu 0.5和0.5Cr 0.5Mo 0.25V钢疲劳裂纹扩展速率试验,结果反映该模型与试验结果十分吻合,且具有更广的通用性和应用推广价值.     

测定概率疲劳长裂纹扩展门槛值的新方法

提出了合理测定随机疲劳长裂纹扩展门槛值的“局部概率Paris关系法”．揭示了常规法不能保证各试样门槛值数据处于相同扩展率水平,测定结果不尽合理的缺陷．以Paris-Erdogan方程描述门槛值附近局部试验数据,考虑数据分散性规律和试样数量两方面的影响,在应力强度因子服从对数正态分布下建立了包含存活概率和置信度的局部概率关系模型,以可接受临界扩展率对应概率因子为依据测定概率门槛值．LZ50钢车轴试验数据分析验证了方法的合理性和有效性．     

描述低周疲劳裂纹扩展速率的循环J积分新参量

探讨了低周疲劳加载条件下的应力增量．应变增量关系，提出了模拟裂纹疲劳扩展的二维模型以建立新的循环．积分参量，详细阐述了该积分参量的定义、主要特点、物理意义以及数值计算方法，并通过紧凑拉伸试样的疲劳试验检验该积分参量的有效性．结果表明：该积分参量能够较好描述恒幅低周疲劳裂纹的扩展速率．此外，基于积分参量体系，从能量的角度解释了疲劳迟滞现象．     

裂纹长度对钢轨裂纹扩展的影响

采用有限元分析软件ANSYS,在纯滚动运行状态下,对实际钢轨裂纹的扩展情况进行了模拟。结果表明:轮轨接触的疲劳裂纹为张开型和滑开型同时存在的复合型裂纹;随裂纹长度的逐渐增加,裂尖有效应力强度因子先减小后增大,裂纹扩展速率会出现先变慢后变快的现象。     

圆形杂质对裂纹扩展的影响

在单轴拉伸载荷作用下，运用分布位错方法对无限大平面内含有一个裂纹和一个任意方向的杂质问题进行求解，得到了裂纹尖端的应力强度因子、应力场以及应变能密度.利用最小应变能密度因子准则来判断裂纹扩展方向.结果显示:软杂质对裂纹尖端应力强度因子、应变能密度和应力场有增强作用，而硬杂质则具有屏蔽作用.在 -30°<θ<30°范围内，杂质对裂纹扩展方向的影响较小，而在 -90°<θ<-30°或30°<θ<90°范围内，杂质对裂纹扩展方向的影响较大.软杂质对裂纹扩展有吸引作用，而硬杂质具有排斥作用.     

扩展裂纹尖端弹塑性场的仿真模拟

通过对紧凑拉伸试样裂纹扩展实验的有限元仿真模拟以及对中心裂纹试样和三点弯曲试样的精细有限元计算和分析,证实了稳态扩展裂纹尖端附近环形区内应力场三参数J-k₂-Q表征的有效性。研究结果进一步表明:在扩展裂纹尖端附近的环形区域内,因试样几何类型的不同,存在着不同类型的双参数主导区。对紧凑拉伸试样和弯曲裂纹试样,在裂关附近环形区内存在着J-k₂主导区;而对中心裂纹试样,在裂尖附近环形区内则存在着J-Q主导区。在一般情况下,应由J-k₂-Q三参数表征。     

高速扩展裂纹尖端的各向异性塑性场

在裂纹尖端的应力分量都只是θ的函数的条件下,利用定常运动方程,应力应变关系及Hill各向异性屈服条件,我们得到反平面应变和平面应变两者裂纹尖端的各向异性塑性场的一般解.将这些一般解用于具体裂纹,我们就求出了Ⅰ型和Ⅱ型裂纹的高速扩展尖端的各向异性塑性场,     

高速扩展裂纹尖端的各向异性塑性应力场

在理想弹塑性材料中,高速扩展裂纹尖端的应力分量都只是θ的函数.利用这个条件以及定常运动方程、应力应变关系与Hill各向异性屈服条件,我们得到反平面应变和平面应变两者的一般解.将这两个一般解分别用于扩展Ⅲ型裂纹和Ⅰ型裂纹,我们就求出了Ⅱ型裂纹和Ⅰ型裂纹的高速扩展尖端的各向异性塑性应力场.     

Elastodynamic Problem of an Interface Linear Crack under Harmonic Loading

The present work is devoted to application of boundary integral equations to the 2D problem for a linear crack located on the bimaterial interface under harmonic loading. The system of linear algebraic equations is derived to solve the problem numerically. The distribution of the displacements and tractions at the bonding interface and the surface of the crack are obtained for the case of the tension–compression wave which propagates normally to the interface. The results are compared with those obtained for the static case. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Direct FEM Simulation and Replacement Crack Approach for Mixed Mode Crack Growth in a Unit Cell

A whole class of continuum damage models uses microcracks as the main source of reduction of stiffness. For the growth of these cracks mostly only mode I is considered. We want to present a method to describe mixed mode crack growth inside a unit cell with a crack, without the need of a direct FEM simulation of crack growth per integration point. We replace the infinitesimal grown and kinked crack with the help of a replacement crack model. This replacement method is mainly based on the equivalence of the dissipation of the original kinking and the replacement crack. The resulting evolution of the stiffness of the unit cell is compared to a direct FEM simulation of mixed mode crack growth. The crack growth criterion used is the principle of maximum energy release rate, which has shown to be a direct consequence of a variational principle of a body with a crack [1]. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

K型管状接头随机疲劳强度和裂纹扩展规律的研究

分析了K型焊接管状接头受轴向和面外弯曲载荷作用下的随机疲劳问题。通过将焊趾处的表面裂纹的初始尺寸和材料常数作为随机变量处理,并计及焊缝的影响,共产生500个随机样本,最终得到裂纹扩展寿命和裂纹形状变化影响的统计计算结果,并与有关实验数据比较,给予了回归分析。同时,也考察了裂纹扩展规律。     

Contact Interaction of Faces of the Plane Crack under Harmonic Loading

The present work is devoted to the solution of the three-dimensional fracture mechanics problem for a linear elastic, homogeneous and isotropic solid with a stationary plane crack under normal time-harmonic loading. The problem has been solved by the method of boundary integral equations with the allowance for the contact interaction of the opposite faces of the crack. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

正交异性复合材料板复合型裂纹尖端的J积分

本文采用复变函数和微积分理论两种途径探讨线弹性正交异性复合材料板复合型裂纹尖端的Ｊ积分，得到了该Ｊ积分在△＞０和△＜０两种情况下的表示式，证明了它们的路径无关性，推出了它们的计算公式。     

Simulation of Crack Propagation under Small-Scale Yielding by means of a Non-local GTN-Model

Today, the local approach to fracture is widely applied to simulate the failure of specimens. For ductile damage processes the Gurson-Tvergaard-Needleman model is the quasi-standard. In the last time non-local extensions allowed a mesh-size independent simulation of crack growth. However, most publications dealing with this subject focus upon the convergence regarding global quantities such as the load-displacement relation. Minor attention is paid to the fields directly at the crack tip. Correspondingly, the interrelationship between the intrinsic length of the model and relevant microscopic damage processes at the crack tip is only partly established until now. In the present study the crack propagation is simulated for an implicitly gradient enriched GTN-model within a boundary layer in order to overcome influences of the specimen geometry. The different stages of damage evolution are resolved by a fine mesh. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)