带裂纹的椭圆孔口问题的应力分析

断裂现象与材料和结构中的孔洞、缺口或裂纹等缺陷密切相关,这是因为缺陷附近的应力集中明显.该文利用复变方法,通过保角映射研究了带裂纹的椭圆孔洞的平面弹性问题,给出了应力强度因子的解析解.并由此计算了两互相垂直的裂纹问题.     

计算应力强度因子的离散分离变量法

提出一种用于数值求解带有一条边界裂纹的多角形区域上的Navier's方程组边值问题的半离散方法。做一个适当的坐标变换后,将原边值问题化为半无限长条上的不连续系数问题。将其半离散化以后,等价于一个常系数常微分方程组的边值问题。进一步,用直接法来求解这个边值问题,便得到原问题的半离散近似解。值得指出的是,这个用分离变量形式给出的半离散近似解自然地具有原问题的奇性。数值例子显示,用该方法可以很方便地计算出在裂纹顶端的应力强度因子的近似值。     

星形裂纹的应力分析

利用复变函数的方法, 通过构造适当的保角映射研究了星形裂纹的平面弹性问题,给出了裂纹尖端I型与II型问题应力强度因子的解析解.并由此模拟出了经典的Griffith裂纹,共点均匀分布三裂纹,十字裂纹,对称八裂纹问题.      

Moiré-numerical hybrid analysis of cracks in orthotropic media

The effectiveness of a new photomechanical-numerical hybrid method for evaluating stress intensity factors (SIFs) in orthotropic composites is demonstrated. Reliable results are obtained from few moiré-measured displacements and they originate well away from the crak tip. The method is illustrated for the case of a uniaxially loaded orthotropic glass/epoxy composite containing a central, transverse crack.     

Comparison of the Wetting Properties of Three Commonly Used Simulated Intestinal Fluids Used as Dissolution Media in the Characterization of Drugs

Simulated intestinal fluids (SIFs) are described in the United States Pharmacopoeia (USP) and the International Pharmacopoeia (IntPh) as recommended dissolution media for the characterization of solid drugs. This study was carried out to compare their wettability properties. Six different model substrates were used as surrogates for solid drugs. These surrogate solid substrates were characterized by the Lifshitz-van der Waals, electron donor and electron acceptor terms, which are the three components of the total surface energy obtained by the van Oss model, which is based upon Young’s equation. Contact angles of the SIFs on the surrogate solid-substrates were determined dynamically by image analysis up to five minutes after applying a drop of the fluid on the solid surface. Observed time-dependent spreading behavior was accounted for by a linear extrapolation of the experimental data to zero contact time to obtain the apparent equilibrium contact angle at zero time. Additionally, the pH, osmolality and buffer capacity of the SIFs were experimentally determined. Although some differences in osmolality and buffer capacity were observed, no statistically significant differences in the wetting properties of the three SIFs were detected. This confirms recent findings that there are no observed differences in dissolution behavior among these simulated intestinal fluids. Harmonization of these SIFs is thus recommended.     

Stress intensity factors for the Brazilian disc with a short central crack: Opening versus closing cracks

Closed form expressions are obtained for the stress intensity factors (SIFs) in case of a Brazilian disc with a short central crack, the length of which does not exceed one fifth of the disc radius. The disc is loaded by uniform radial pressure along two finite symmetric arcs of its periphery. The solution is achieved using the method of complex potentials introduced by Kolosov and Muskhelishvili. The advantage of the expressions obtained is that they are valid both for cracks under opening mode as well as for closing cracks. For the first case (opening cracks) the results of the present study are compared with existing approximate solutions and it is concluded that the agreement is excellent as long as the length of the crack remains relatively small compared to the radius of the disc. Regarding the case of a closing mode crack the procedure proposed here (based on a recent alternative approach of the cracked Brazilian disc) leads to a physically acceptable deformed crack shape instead to an unnatural crack with overlapped lips. At the same moment the dependence of the SIFs on the properties of the material is eliminated.     

带k条径向边裂纹的圆形孔口问题的应力分析

利用复变函数方法,通过构造保角映射研究了带k条径向边裂纹的圆形孔口的平面弹性问题,给出了裂纹尖端Ⅰ型与Ⅱ型问题应力强度因子的精确分析解.在极限情况下,不仅可以还原出星形裂纹,Griffith裂纹,十字裂纹等经典的裂纹问题的结果,而且当k取任意正整数值时,可以模拟出更多的、复杂的带裂纹的圆形孔口问题.     

幂函数型曲线裂纹平面问题的一般解

通过构造一个新的、精确的和通用的保角映射,利用Muskhelishvili复势法研究了任意自然数次幂的幂函数型曲线裂纹的平面弹性问题,给出了远处受单向拉伸载荷下裂纹尖端Ⅰ型和Ⅱ型应力强度因子的一般解．当幂次取不同的自然数时,可以退化为若干已有的结果．通过数值算例,讨论了幂函数型曲线裂纹的系数、幂次及在x轴上的投影长度对Ⅰ型和Ⅱ型应力强度因子的影响规律．     

一维六方准晶中具有不对称裂纹的圆形孔口问题的解析解

利用复变函数方法,通过构造保角映射,研究了一维六方准晶中具有不对称裂纹的圆形孔口的反平面剪切问题,给出了Ⅲ型裂纹问题的应力强度因子的解析解,在极限情形下,不仅可以还原为已有的结果,而且求得一维六方准晶中具有对称裂纹的圆形孔口问题,带裂纹的圆形孔口问题在裂纹尖端的应力强度因子解析解.仅声子场而言,所得结果与经典弹性的结果完全一致.     

海洋平台K型管节点的疲劳裂纹扩展分析 II:数值分析

对于已含初始裂纹平台管节点的寿命预测很大程度上依靠应力强度因子的精确值,而复杂载荷条件下的节点应力强度因子的计算尚无参数方程直接确定。本文提出了一种含表面裂纹的K节点的有限元网格产生方法,即把整个K节点划分为几个子区域,每个子区域的网格具有不同类型的单元和不同的密度。这种方法在控制网格密度,尤其是控制沿着裂纹边缘单元的边长比方面有其独特的优越性,当所有子区域的网格自动产生后,容易得到整个结构的有限元模型。同时用J积分和位移外推插值法分别计算了一个K型节点沿着裂纹前缘的应力强度因子值,发现:试验得到的应力强度因子值和提出的模型计算结果非常吻合,证明了所提有限元模型的准确性。