自紧身管疲劳寿命的可靠性分析

基于概率断裂力学理论和Monte Carlo模拟方法，给出了自紧身管疲劳寿命的可靠性分析方法．自紧残余应力采用了符合身管材料具有强化和包辛格效应性能推导的公式计算，身管工作的应力强度因子通过权函数方法得到．实例分析结果表明，对数正态分布为身管疲劳寿命的最佳分布，同时给出了各种置信度和可靠度下的身管疲劳寿命．另外，还分析了初始裂纹尺寸和材料的断裂韧性对身管疲劳寿命的影响．该研究对保证身管的安全，避免灾难性事故的发生具有重要意义．     

自紧炮管的疲劳寿命分析

本文用有限单元法计算了自紧残余应力对应的炮管的应力强度因子.自紧残余应力采用了符合炮管材料具有强化和包辛格效应性能推导的公式计算,根据工作内压和残余应力共同作用下炮管的总应力强度因子和测定的炮钢断裂韧度及疲劳裂纹扩展性能,分析了自紧炮管的疲劳寿命及自紧度和裂纹构形对疲劳寿命的影响.     

自增强厚壁圆筒疲劳裂纹扩展寿命的可靠性分析

本文提供了自增强厚壁圆筒疲劳裂纹扩展寿命的可靠性分析的方法和公式,自增强残余应力用符合厚壁筒用钢具有强化和包辛格效应实际性能推得的公式进行计算,残余应力对应的应力强度因子的计算采用了有限元法,得到了工作内压与自增强残余应力共同作用下的厚壁筒应力强度因子公式,通过实验测定了厚壁筒用钢的断裂韧度和疲劳裂纹扩展速率等性能。     

用有限单元法计算具有对称轴向双裂纹自增强厚壁圆筒的应力强度因子

本文研究了在自增强残余应力下,具有对称轴向双裂纹的厚壁简的应力强度因子的计算方法。文中采用了符合厚壁筒材料具有强化和包辛格效应实际性能的厚壁简自增强残余应力计算公式,通过叠加和等效载荷处理用有限单元法计算了残余应力对应的强度因子。本文的方法对具有自相平衡的残余应力结构的K1计算都有参考价值。     

等参奇性元在双孔边裂纹平板分析中的应用及其计算精度研究

本文用八节点等参数单元及其相应的奇性元,对两种双孔边裂纹平板的应力强度因子进行了计算。文中首先导出了平面复合型裂纹问题应力强度因子K_1、K_Ⅱ与等参奇性元节点位移间的关系式,作为用等参单元法推算应力强度因子的依据;然后,以单边裂纹板条为数值例子,对于等参奇性元尺寸的选择、裂纹段单元的配置以各种推算应力强度因子的方法与计算精度之间的关系进行了研究;最后,按一定精度的要求选择等参奇性元尺寸和裂纹段单元配置数,并以三种推算方法计算了两种双孔边裂纹平板的应力强度因子值。     

焊接残余应力平板多个共面表面裂纹的应力强度因子

采用线弹簧模型求解含焊接残余应力平板多个共面任意分布表面裂纹的应力强度因子.利用边裂纹权函数给出了裂纹表面上沿厚度非线性分布的残余应力向线性分布的转化公式.基于Reissner板理论和连续分布位错思想,将含多个共面任意分布表面裂纹的无限平板问题归结为一组Cauchy型奇异积分方程,并采用Gauss-Chebyshev方法获得了奇异积分方程的数值解.以三共面表面裂纹为例,计算了表面裂纹的应力强度因子,并讨论了裂纹间距、裂纹几何形状等因素对应力强度因子的影响.     

基于圆弧底试件的动态裂纹扩展及止裂规律研究

为了研究脆性材料的动态裂纹扩展及止裂规律，设计了一种带圆弧形底边的梯形开口边裂纹（trapezoidal opening crack with arc bottom，TOCAB）构型的试件。在落锤冲击设备加载下，对圆心角为0°、60°、90°和120°的TOCAB试件进行了冲击实验，并采用裂纹扩展计(crack propagation gauge，CPG)监测裂纹起裂和扩展时间，从而获得裂纹扩展速度。采用有限差分软件AUTODYN对落锤冲击设备和试件进行数值模拟，研究了裂纹的动态扩展过程及止裂规律。还基于实验和数值方法，计算了裂纹的临界动态应力强度因子。实验和数值结果均表明:3种弧度的TOCAB试件都可以实现运动裂纹止裂，该构型可用于研究动态裂纹止裂问题；数值计算的裂纹扩展路径与实验结果基本一致，验证了数值模型的有效性；裂纹起裂和止裂时刻的临界动态应力强度因子大于裂纹动态扩展过程中的临界动态应力强度因子。     

基于权函数法的核主泵飞轮应力强度因子研究

采用权函数法确定了含裂纹飞轮在离心力和接触压力作用下的应力强度因子,计算了在同步转速工况下裂纹尖端应力强度因子的值,并与解析法和有限元法计算结果进行了对比。结果表明:权函数法与解析法的误差在3%以内,与有限元法的误差在1%以内,验证了权函数法计算应力强度因子的准确性高;在结构不变的情况下,权函数法可以快速求解不同载荷条件、不同长度裂纹的应力强度因子。通过控制变量法研究了不同参数对应力强度因子的影响,结果表明,飞轮裂纹尖端总应力强度因子随着裂纹尺寸、旋转转速、飞轮尺寸外径与内径比值的增大而增大。     

残余应力下厚壁筒表面裂纹的应力强度因子计算

本文首先介绍了边界元法计算裂纹尖端应力强度因子的基本理论,接着利用边界元法计算了在残余应力下不同厚壁筒内表面椭圆裂纹的应力强度因子,研究了其大不随椭圆裂纹不同而变化的规律,为厚壁筒结构的设计,制造以及疲劳寿命分析提供了许多有价值的参考资料。     

共线裂纹体尺寸对应力强度因子的影响

本文在文献[1]的基础之上,用文献[2]中提出的奇异准谐调元,进一步对二维裂纹体几何尺寸对一对共线裂纹应力强度因子的影响进行了大量的数值计算和研究,给出了计算表格、拟合曲线以及经验公式,定量地分析了裂纹体几何尺寸对共线裂纹应力强度因子的影响。为工程中的裂纹体的脆性断裂分析与评定,提供了必要的计算依据。     

Combined analysis of fracture under stresses acting along cracks

A joint approach to the study of two non-classical fracture mechanisms, namely fracture of cracked materials with initial (residual) stresses acting along the crack planes and fracture under compression along parallel cracks, is considered in the framework of three-dimensional linearized solid mechanics. Mathematical statements of problems for pre-stressed solids that contain interacting circular cracks are given. Problems for an infinite solid containing two parallel co-axial cracks and for a space with the periodical set of co-axial parallel cracks as well as for a half-space with near-the-surface crack are solved. Several patterns of loading on the crack faces (normal loading, radial shear and torsion) are considered. The effects of initial stresses on stress intensity factors are analyzed for highly elastic materials with some types of elastic potentials. Formulation of fracture criteria accounting effect of initial (residual) stresses is given. Critical parameters of fracture of solids containing interacting cracks under compression along the cracks are calculated. The influence of geometrical parameters of the problems as well as physical and mechanical properties of materials on these critical parameters is analyzed.     

冲击载荷下自增强身管残余应力变化规律

基于有限元分析方法,建立速射火炮身管截面的有限元模型,采用直接耦合的方法,模拟了承受热应力和火药燃气压力的自紧身管在先50连发、冷却后再连发10发过程中身管的残余应力,得到并分析了残余应力的变化规律,指出内壁薄层的塑性变形和残余应力的反复变化,不利于内壁的稳定,还提出了减小残余应力变化程度的策略.     

THERMAL FRACTURE OF FUNCTIONALLY GRADED PLATE WITH PARALLEL SURFACE CRACKS

This work examines the fracture behavior of a functionally graded material （FGM） plate containing parallel surface cracks with alternating lengths subjected to a thermal shock. The thermal stress intensity factors （TSIFs） at the tips of long and short cracks are calculated using a singular integral equation technique. The critical thermal shock △Tc that causes crack initiation is calculated using a stress intensity factor criterion. Numerical examples of TSIFs and △Tc for an Al2O3/Si3N4 FGM plate are presented to illustrate the effects of thermal property gradation, crack spacing and crack length ratio on the TSIFs and △Tc. It is found that for a given crack length ratio, the TSIFs at the tips of both long and short cracks can be reduced significantly and △Tc can be enhanced by introducing appropriate material gradation. The TSIFs also decrease dramatically with a decrease in crack spacing. The TSIF at the tips of short cracks may be higher than that for the long cracks under certain crack geometry conditions. Hence, the short cracks instead of long cracks may first start to grow under the thermal shock loading.     

Crack kinking in sandwich structures under three-point bending

Sandwich beams under three-point bending containing cracks in the core material very close to the upper skin interface are investigated. The cracks considered parallel or with an imperceptible inclination to the longitudinal beam axis and at different distances from the upper skin interface, are analyzed with static non-linear elastic two and three dimensional finite element analyses. From the proposed analyses stress intensity factors are calculated using linear elastic fracture mechanics. It is demonstrated that the crack propagation on the compression side of the core is mainly subjected in shear. The strain energy density criterion is used in order to determine the angle of kinking of the crack into the core.     

Fatigue crack growth through residual stress fields—theoretical and experimental studies on thick-walled cylinders

Experiments are described which determined the effects of various residual stress distributions on the growth rate of fatigue cracks. For each stress distribution, the contribution (K_RS) to the net stress intensity at the crack tip is determined, and a comparison is then made with the behaviour predicted using a fracture mechanics approach based on a weight function analysis and a simple crack closure model. The example studied is a thickwalled pressure vessel containing a longitudinal crack which grows radially from the inner surface; fatigue cracks were grown under laboratory conditions in ring test specimens. sectioned from vessels which had been cold-expanded by different amounts to increase their pressure limits, and so contained various complex residual stress distributions. The experiments provide direct evidence that the effects of residual stress (and by extension, thermal stress) on the crack tip stress intensity may be modelled conveniently using weight function techniques, and can be incorporated satisfactorily in fatigue crack growth analyses.     

Construction of quasi-brittle and quasi-ductile fracture diagrams based on necessary and sufficient criteria

Materials with a regular structure characterized by quasi-brittle and quasi-ductile fractures are considered in the case where the characteristic linear dimension of the structural element is known. Necessary and sufficient fracture criteria are constructed using the Neuber-Novozhilov approach. A modified Leonov-Panasyuk-Dugdale model for an opening mode crack is proposed where the width of the prefracture zone coincides with the width of the plasticity zone. For the critical parameters of quasi-brittle fracture (tensile stress, length of prefracture zones, stress intensity factors), relations are obtained that allow material fracture to be considered in the case where the crack length is negligible compared to the characteristic linear dimension of the structural element. A fracture diagram obtained using the critical stresses calculated from the necessary and sufficient criteria is considered in a wide range of crack lengths. The elastoplastic problem of extension of a plate with a central crack is solved using the finite-element method. The dimensions and shape of the plastic zone near the crack tip are determined for different levels of loads corresponding to quasi-brittle and quasi-ductile fracture. The obtained results are analyzed to estimate the width of the prefracture zone and the critical crack opening.     

层状磁电复合材料界面共线裂纹平面问题分析

本文研究了面内电磁势载荷作用下双层压电压磁复合材料中共线界面裂纹问题．考虑了压电材料的导磁性质和压磁材料的介电性质,引入了界面电位移和磁感强度的连续性条件．利用Fourier 变换得到一组第二类Cauchy 型奇异积分方程．进一步导出了相应问题的应力强度因子、电位移强度因子和磁感强度强度因子的表达式,给出了应力强度因子的数值结果．结果表明电磁载荷会导致界面裂纹尖端I、II 混合型应力奇异性,同时还伴随着电位移和磁感强度的奇异性．比较了双裂纹左右端的应力强度因子,发现在面内极化方向上施加面内磁势载荷时共线裂纹内侧尖端区域的两个法向应力场发生互相干涉增强．