金属裂纹板复合材料修补结构的超奇异积分方程方法

根据应力强度因子在线弹性范围内具有可叠加性,将金属裂纹板复合材料修补结构进行简化,在表面裂纹线弹簧模型的基础上,建立了基于超奇异积分方程的Line-Spring模型。利用第二类Chebyshev多项式展开的方法,将超奇异积分方程转化为线性方程组,推导出以裂纹面位移表示的应力强度因子表达式,得到了裂纹尖端应力强度因子的数值解,并利用虚拟裂纹闭合法加以验证。参数分析确定了影响对称修补裂纹板应力强度因子的两个主要参数:胶层界面刚度和补片与金属板刚度比,为胶接修补结构的承载能力分析以及改进设计提供理论依据。     

穿过界面的刚性线夹杂对SH波的散射

利用两个联结半平面中简谐集中力的格林函数,得出了穿过界面刚性线的散射场。刚性线的散射场可分解为有界部分和奇异部分。利用散射场的有界部分和奇异部分得出了刚性线的在SH波作用下的Cauchy型奇异积分方程。根据所得奇异积分方程和Cauchy型积分的端点性质,得出了确定刚性线和界面交点处奇异性阶数的特征方程。根据刚性线和界面交点处的奇性应力定义了交点处的应力奇异因子。对所得Cauchy型奇异积分方程的数值求解,可得刚性线端点和交点处的应力奇异因子。     

压电介质夹杂功能梯度压电带界面双裂纹反平面问题

利用积分方程方法,本文研究了夹在两个均匀压电半空间的功能梯度压电带界面共线双裂纹的反平面问题。在电渗透型边界条件下,通过Fourier余弦变换将所考虑的问题化为一对偶积分方程,再用Copson方法将该对偶积分方程转化为Fredholm方程进行数值求解,从而给出了裂纹尖端的应力强度因子,电位移强度因子的表达式。分析了裂纹长度,功能梯度非均匀参数以及材料的几何尺寸等对应力强度因子的影响。     

联合载荷下无裂纹DLC薄膜的内应力有限元分析

本文用有限元分析的方法,对受法向和切向联合载荷作用下的无裂纹类金刚石(DLC)薄膜系统内部应力进行了模拟计算,分析了不同摩擦系数和膜厚比对于内部应力的影响,数值模拟结果表明:较大的摩擦系数可以使得界面处剪切应力和Mises等效应力以及y轴Mises等效应力显著增大,而对于界面处的y向压应力影响不是很大。在一定的范围内(0相似文献   

无限长条板中弹性与粘弹性界面裂纹尖端场

研究无限长条板中粘弹性-弹性界面Griffith裂纹在 Ⅰ 型突加载荷作用下,裂纹尖端动态应力强度因子的时间响应。利用积分变换方法、Fourier和Laplace变换,分别推导出了弹性和粘弹性问题的控制方程组;引入位错密度函数,并结合边界条件,导出了反映裂纹尖端奇异性的Cauchy型奇异积分方程组,运用Chebyshev正交多项式化奇异积分方程组为代数方程组,用配点法进行求解;最后用Laplace积分变换数值反演方法,将拉氏域内的解反演到时间域内,求得动态应力强度因子的时间响应,并对材料参数的影响进行了分析。结果表明,剪切松弛参量对 Ⅰ 型动应力强度因子的影响小于对 Ⅱ 型的影响,而膨胀松弛参量对 Ⅰ 型动应力强度因子的影响大于对 Ⅱ 型的影响。      

应力强度因子计算的边界元法

本文利用非连续元离散边界的积分方程，推导了奇异积分的具体表达式，将非连续边界元和多域缩聚法用于二维弹性断裂应力强度因子计算，得到了合理的计算结果。     

梯度涂层材料中裂纹问题的非均匀元分析

本文采用非均匀等参有限元的方法研究了薄膜梯度涂层/均匀基材中的界面裂纹问题,并与双材料界面裂纹情况进行了对比计算。研究表明:在均匀基材上采用梯度涂层,与双材料相比可以有效地降低裂尖场应力强度因子;同时还分析了涂层厚度与梯度参数对界面应力强度因子的影响。结果表明:当薄膜厚度大于或等于裂纹长度时,应力强度因子(KI、KII)对其尺度的变化显得不敏感;对梯度参数的影响而言,当材料性能曲线的幂指数m大于1时,裂尖场的应力强度因子KII相对KI很小且基本不随m变化,因此裂尖场与均匀材料情况类似;当m小于1时,应力强度因子KII随m减小而急剧增大,裂尖场由KI及KII控制,断裂趋于混合型。     

与土体部分脱离的刚性半圆形基础的出平面动力响应

本文利用波函数法结合奇异积分方程技术分析了刚性半圆形基础与土体部分脱离时的出平面动力响应问题.将界面脱离区模拟为界面裂纹,根据问题的混合边值条件获得一组奇异积分方程,通过数值求解给出了基础和土体的位移场,并借助断裂力学中动应力强度因子的概念讨论了界面剪应力强度.     

奇异薄层单元及其在双材料界面断裂分析中的应用

构造了一种平面应力奇异薄层单元并证明了其具有-1/2阶奇异性。用此单元研究了双材料界面层的刚度对界面裂纹尖端场的影响。研究发现:对于I 型界面断裂, 减小界面法向刚度对K_Ⅰ、K_Ⅱ的影响远大于减小界面切向刚度, 且法向和切向刚度的减小对K_Ⅱ的影响均大于对K_Ⅰ的影响, 降低法向刚度会显著改变裂尖正应力和剪应力的分布, 而降低切向刚度只明显改变剪应力的分布, 对正应力的分布影响不大;对于界面II 型断裂, 则减小切向刚度对K_Ⅰ、K_Ⅱ的影响远大于减小法向刚度, 且切向、法向刚度的减小对K_Ⅰ影响均大于对K_Ⅱ影响, 降低切向刚度会显著改变裂尖正应力和剪应力的分布, 而降低法向刚度只明显改变裂尖正应力的分布, 对剪应力的分布影响不大。随着界面刚度增大, 应力强度因子和裂尖应力分布均趋近无厚度理想界面情况。     

液氮薄膜在切应力作用下的降膜流动和传热模型

以钎焊板式换热器当中液氮薄膜为研究对象,通过建立在切应力作用下层流饱和蒸发液氮薄膜的传热特性的物理模型,推导出了无量纲液膜厚度和表面传热系数与气液界面切应力、界面对流换热强度、初始雷诺数和流动长度之间的非线性关系式.     

基于应力功恒等法的振动时效研究

振动时效主要用于消减构件的残余应力,本质上类似于应力松弛,应变变程恒定的情况下峰值应力随周期减小。材料发生应力松弛的部分为应力集中区,振动时效过程中产生局部塑性应变。针对如7075高强铝合金幂次硬化材料,可以采用基于等效线弹性模型的应力功恒等法近似计算材料的局部应力和应变变程,以弥补实验过程需要测量但不易获得的重要数据。计算得到的应力-应变曲线与流变塑性理论公式推导的结果及其它研究者通过模型仿真得到的结果相似,表明应力功恒等法应用于振动时效分析具有计算简单,准确实用的特点,对工程实践有一定的参考价值和指导作用。     

工艺因素对TC4合金应力松弛行为的影响

研究了TC4合金应力松弛行为的特征和工艺因素的影响.结果表明,TC4合金应力松弛行为可以分为两个阶段:第一阶段,应力松弛非常快,第二阶段应力松弛缓慢,但长时间应力松弛后剩余应力趋向于一极限值;应力松弛行为可以用应力松弛极限和应力松弛速率两个参量进行表征;温度升高时,松弛速率加快,应力松弛极限降低;同一温度不同初应力作用的应力松弛,应力松弛极限相同.     

基于振动时效仿真的流变塑性模型

振动时效是一种局部循环塑性现象,当循环载荷与材料内部残余应力叠加超过材料的局部屈服强度时就会发生残余应力释放。采用流变塑性模型对振动时效进行仿真,分析了振动时效过程中应力幅、应变幅、振动频率、振动周期和材料屈服应力等对振动时效的影响。结果表明,振动时效中应力释放很大程度上取决于应力幅或应变幅,振动频率和材料参数也是关键因素,而振动周期或时间对振动时效没有很大影响。将此振动时效模型应用于7075铝合金试样机械载荷下的应力松弛实验,所得结果与仿真较一致。     

Study on elastic-plastic component in indentation fatigue of sodalime glass

Fracture mechanics studies on glass by indentation has become predominant in recent times. Interest in it has become more prominent due to a large application of such materials in areas of engineering applications encountering fluctuating stresses induced thermally, mechanically or physically. However, glass subjected to repeated indentation at a point prior to crack initiation with subcritical loads phenomenological to metal fatigue has not been systematically investigated. Repeated indentation at a single point with different subcritical loads (0·1N, 0·15N, 0·25N, 0·50N, 1·0N) was performed till radial cracks occurred. The length of the diagonal was measured after each indentation, which was found to increase with indentation cycle eventually leading to crack initiation. This observation was analysed considering the elastic plastic component and the residual stress developed during each cycle. A mathematical model has been postulated to correlate the contribution of cumulative residual stress for crack initiation. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995.     

磁流变胶的沉降和力学性能研究

研制了一种新型的磁流变胶（magnetorheological gels），它具有良好的沉降稳定性和优良的磁流变效应。在2500r/min的离心实验中，离心20min之后才完全沉降：其剪切应力与剪切速率的关系可用Herschel-Bukley模型进行很好的描述；剪切屈服应力在小磁场下剪切屈服应力与磁场成线性关系，当磁场为70kA/m时，剪切屈服应力达到了53．9kPa。     

Effect of surface/interface on the dynamic stress of two interacting cylindrical nano-inhomogeneities under compressional waves

Based on the surface/interface elasticity theory, the effect of surface/interface on the dynamic stress of two interacting cylindrical nano-inhomogeneities under compressional waves is considered. The analytical solutions of displacement potentials are expressed by employing wave function expansion method and the expanded mode coefficients are determined by satisfying the boundary conditions at the interfaces. The addition theorem for cylindrical wave function is used to accomplish the superposition of wave fields in different coordinate systems. Analyses show that the effect of the interface properties on the dynamic stress is significantly related to the wave frequency of incident waves, the shear modulus ratio of the nano-inhomogeneities to matrix, and the relative position and distance between the two nano-inhomogeneities.     

磁性应力测量条件对应力感度的影响

磁性应力测量具有测量速度高,探测深度大(可达数毫米),无辐射危险,携带方便等优点.可以对使用中的构件进行实时实地且安全的测量.但磁性应力测量法只能用于铁磁材料并且对铁磁材料结构等因素也敏感.因此,在磁性应力测量中影响测量精度的原因很多,其中一个最主要的参数就是应力感度.本文主要研究了两种材料的应力感度与材料测定条件的关系,以及测定环境对应力感度的影响,从而在磁性测量的过程中能排除不利条件,正确地确定磁性应力的感度,提高磁性应力测量技术的准确度.     

More on the effects of thermal residual and hydrostatic stresses on yielding behavior of unidirectional composites

The influence of manufacturing process thermal residual stresses and hydrostatic stresses on yielding behavior of unidirectional fiber reinforced composites has been investigated when subsequently subjected to various mechanical loadings. Three-dimensional finite element micro-mechanical models have been used. The results of this study reveal that the size of the initial yield surface is highly affected by the thermal residual and hydrostatic stresses. It was also found that effects of a uniform temperature change on the initial yield surface in the composite stress space is not equivalent to a solid translation of the surface in the direction of the hydrostatic stress axis. At the micro-level, magnitudes of various stress components within the matrix due to the thermal residual and hydrostatic stresses are different. However, at a macro-level, both temperature change and hydrostatic loading of composites show similar effects on the initial yield surface in the composite stress space. In an agreement with experimental data, results also show that residual stresses are responsible for asymmetric behavior of composites in uniaxial tension/compression in the fiber direction. This asymmetric behavior suggests that the existing quadratic yield criteria need modification to include thermal residual stress effects.     

Disappearance Conditions of Thermal Stress Singularities Based on Stress Intensity in Two and Three-Phase Bonded Structures

The characteristics of stress singularities near the free edge of the interface of bonded dissimilar materials subjected to change in temperature are investigated. The thermal stresses are represented by the sum of the singular terms of types r^-1 and log r, no singular ones and the particular ones. The functions, K × F (j=1,2,3), associated with the terms except the particular terms contributing to the thermal stresses are described as new stress intensity factors. The K is obtained from the technique of the Mellin transform and the F is calculated by numerical analysis such as finite element analysis. The emphasis here is placed on clarifying material combinations with arbitrary wedge angles and elastic properties yielding K = 0. The results can be used to determine material/geometry which ensures that interface residual stresses will be in compressive. This revised version was published online in July 2006 with corrections to the Cover Date.     

单侧有U形槽弯曲平板应力集中的研究

本文根据折线形截面假设，计算了单侧有U形槽的弯曲平板的应力集中和极限载荷问题．文中分析了槽宽系放和槽深系数对局部应力的影响，导出了弹塑性局部应力的表达式及极限载荷和弹塑性交界面的关系．