云纹干涉法研究复合材料构件的应力强度因子

本文采用贴片云纹干涉法，测试并研究了正交异性板纯弯试件及拉伸试件的应力强度因子。文中给出了复合材料纤维加强方向不同时位移与应力强度因子的关系式，通过测试得出受力模型的全场位移，给出云纹图，进而由裂纹尖端位移场推算出应力强度因子Ｋ１及Ｋ值。试验结果与有限元计算结果吻合良好。     

组件裂尖变形场的云纹显微倍增研究

将云纹干涉法与显微、倍增技术相结合，发展了一种位移场云纹条纹显微倍增方法．对该方法进行了严格的理论推导和精确的实验验证，并用该方法对热载下微电子模拟组件的层间裂纹尖端位移场和奇异性进行了实验研究     

云纹干涉反转倍增法及其在微电子组件变形场测量中应用

本文提出并介绍了云纹干涉反转倍增法，该方法将光学载波、反转剪切、富立叶变换倍增技术巧妙地结合于云纹干涉光路中。利用载波频率，把带载波的云纹干涉变形图在富立叶变换系统中进行条纹倍增，而试样变形信息也倍增了相同倍数，将云纹干涉的测量灵敏度又提高了一个数量级。在实验中实现了１６倍倍增，即位移测量灵敏度由０．４μｍ提高到０．０２５μｍ（虚栅频率１／２４００）。将这一方法用于测量热载下金属Ｎｉ膜／ＺｒＯ２陶瓷基界面裂纹尖端面内位移场，分析裂尖位移奇异性。实验表明：热载作用下，膜／基组件界面裂纹尖端的位移奇异性具有指数奇异特性，其奇异性指数与膜／基材料，界面层特性等有关     

云纹干涉条纹倍增方法研究

本文将云纹干涉法与载波法、倍增技术相结合,提出一种位移场和应变场云纹干涉条纹倍增方法,该方法使得云纹干涉法测量灵敏度提高四倍以上。文中对该方法给出了严格的理论推导和实验验证。     

贴片云纹干涉法及其应用

本文采用特种粘结剂和所研究的工艺,将全息胶片粘贴到测试对象的测试表面上,记录用全息干涉形成的高频光栅,以及由高频栅的二次干涉得到的等位移线——云纹条纹,然后使胶片与测试对象分离,再进行各种后处理;这一方法把云纹干涉法的高灵敏度和可分离贴片技术的简易性及低成本结合起来,并获得了有良好对比度和足够精度的云纹条纹。     

复合型裂纹位移场的分析

本文分析了复合型裂纹尖端v向位移场的特点,即v=0的位移线和切点连线(等位移线斜率为零的切点的连线)均为直线,它们的斜率与K_Ⅱ∶K_Ⅰ有关.在裂纹两岸的v向位移大小相等符号相反.当纹尖有刚性转动时,裂纹两岸同x处的v向位移不同.利用它们的代数和可消除变形位移,而得到两倍的刚性转角位移,从而求出刚性转角,并找到无刚性转角时的v=0位移线和切点连线. 作者利用上述特点,由贴片云纹干涉法得到有刚性转角的条纹图中求出转角、纹尖精确位置、和应力强度因子K_Ⅰ、K_Ⅱ.与文[4]的计算值一致,实验与计算的条纹图吻合得很好,结果令人满意.     

贴片云纹干涉法测量离面振动

本文介绍了用贴片云纹干涉法测量一维横向(离面)振动,并就测量原理、定量公式及灵敏度等问题进行了讨论,给出了实验结果。     

部分相干光云纹干涉法测三维位移场

本文提出了一种用部分相干光可同时获得面内位移和离面位移场的云纹干涉法。该法具有装置简单,无需防震,可用于观场测量等特点。文中论述了此法的基本原理,应用波前干涉理论和付里叶光学理论对变形前后波前的干涉、记录和再观进行了分析,导出了计算公式。实现了透射物体和反射物体表面的面内位移分量(U_0,V_(45),U_(90))和离面位移(w)的全场同时测量,典型实验证明,实验值与计算结果符合较好。     

单光束楔形镜云纹干涉法

本文利用单光束楔形镜云纹干涉法代替传统的双光束云纹干涉法进行位移场和应变场的测量.单光束云纹干涉法具有光路简单,不受环境干扰等特点.本文将云纹干涉法的波前理论与近代光学信息技术有机地结合起来,对单光束干涉系统进行了分析,得到了记录的光强和再现的位移应变公式.利用该系统,得到了三点弯矩形梁的全场位移条纹图和应变条纹图.     

压电材料V型切口端电弹场奇异性的实验研究

考虑了由电场和应力集中而引发的压电材料切口端的奇异性问题。通过云纹干涉法测量机电耦合载荷作用下三点弯试验中V形切口尖端的变形场,并利用该结果近似确定切口尖端的占主导地位的奇异性指数。结果表明:正电场使切口张开,切口端的奇异性指数随着切口角度的增大而下降。该结果与有限元法的计算结果定性相符,说明云纹干涉法能够用于判断切口端奇异性状况。     

An experimental analysis of displacement field of mixed mode crack

In this paper, the characteristic properties ofv (y-direction displacement) field surrounding the tip of a mixed mode crack are studied. These properties can be used to evaluate the rigid body rotation of the crack tip, theK _I SIF and the ratio ofK _II SIF toK _I.The authors employ a film to record the displacement information based on the technique of moire interferometry with sticking films. By using the data taken from the moire pattern and treating them with the damping least square method, all of the parameters of the crack can be obtained accurately.     

试验确定自增强圆筒的表面裂纹K1因子和疲劳扩展规律

本文提供了一种可以进行自增强处理的圆筒试样,通过实验用柔度法确定了该试样的表面裂纹的应力强度因子,介绍了含表面裂纹试样的柔度测试技术,导出了柔度与表面裂纹尖端前缘各点的应力强度因子的关系式,该式可作为各种含表面裂纹试样柔度法测表面裂纹 K_1因子的参考,本文还测定了不同自增强程度下,自增强圆筒的表面裂纹疲劳扩展规律。     

A mode III crack crossing the magnetoelectroelastic bimaterial interface under concentrated magnetoelectromechanical loads

A mode III crack cutting perpendicularly across the interface between two dissimilar semi-infinite magnetoelectroelastic solid is studied under the combined loads of a line force, a line electric charge and a line magnetic charge at an arbitrary location. The impermeable conditions are implied on the crack faces. The technique developed in literature for the elastic bimaterial with a crack cutting interface is exploited to treat the magnetoelectroelastic bimaterial. The Riemann-Hilbert problem can be formulated and solved based on complex variable method. Analytical solutions can be obtained for the entire plane. The intensity factors around crack tips can be defined for the elastic, electric and magnetic fields. It shows that, no matter where the load position is, the electric displacement intensity factors (EDIFs), as well as the magnetic induction intensity factors (MIIFs), are identical in magnitude but opposite in sign for both crack tips, on condition that a line force is solely applied. Alternatively, if only a line electric charge is considered, then the stress intensity factors (SIFs) and the MIIFs exhibit the behavior. Likewise, if only a line magnetic charge is applied, it turns to the SIFs and the EDIFs instead. In addition, the dependence of the intensity factors is graphically shown with respect to the location of a line force. It is found that the SIF for a crack tip tends to be infinite if the applied force is approaching the tip itself, but the EDIF, with the complete opposite trend, tends to be vanishing. Finally, focusing on the more practical case of piezoelectric/piezomagnetic bimaterial, variation of the SIF along with the moduli as well as the piezo constitutive coefficients is explored. These analyses may provide some guidance for material selection by minimizing the SIF. It is also believed that the results obtained in this paper can serve as the Green’s function for the dissimilar magnetoelectroelastic semi-infinite bimaterial with a crack cutting the interface under general magnetoelectromechanical loads.     

Edge-cracked stiffened panels analyzed by caustics

Externally bonded composite patches have been proven to be an effective method for repairing damaged aircraft structural components. They are ease in application and provide excellent in-service performance. The major function of a repair is to reduce the stress intensity factor at the crack tip. Calculation of stress intensity factor of a repaired crack has been performed by analytical and numerical methods. However, these methods are based on simplifying assumptions regarding material behavior and repair conditions. In the present paper an experimental determination of mode-I stress intensity factor (SIF), K_I, at the tip of an edge-crack or a V-notch reinforced with double bonded strips or with compression pre-stresses applied along the crack surfaces is undertaken by using the optical method of caustics. This method is simple in its application and has successfully been used for the solution of a host of crack problems of engineering importance.     

A Zener–Stroh crack interacting with a coated inclusion with generalized Irwin plastic zone correction

The elastic–plastic fracture behavior of a Zener–Stroh crack interacting with a coated inclusion in composite materials has been investigated with crack tip plastic zone corrections. With the distributed dislocation method, the crack problem is formulated into a set of singular integral equations which are solved numerically. The plastic zone sizes at the both crack tips are determined by a generalized Irwin model where Von Mises stress yielding criterion is used. The stress intensity factor (SIF), the plastic zone size (PZS), the crack tip opening displacement (CTOD) and the effective stress intensity factor have been evaluated. In the numerical examples, the influence of the inclusion shear modulus, the coating-layer thickness and shear modulus, as well as the distance between the crack and inclusion, on the SIF, the PZS and the CTOD are discussed in detail. Numerical examples show that increasing the shear modulus or the thickness of the coating phase, the influence of the inclusion on the normalized SIF and the normalized PZS will be shielded.     

应用云纹干涉法测量力电耦合作用下铁电陶瓷的破坏行为

本文采用云纹干涉系统对的电陶瓷在力电耦合载荷作用下裂纹尖端的力学行为进行全场实时非接触动态细观测量,采用三点弯实验获取裂纹尖端区域在力电耦合作用下与电场集中有关的电致伸缩位移场,应变场,通过分析实验取得的云纹图得到了裂尖区域的位移场,应变场,发现裂尖区域就变随着与裂尖距离的增加衰减的速率比没有电场作用下的理论计算结果要快。     

Mechanics and fracture of crack tip deformable bi-material interface

Novel interface deformable bi-layer beam theory is developed to account for local effects at crack tip of bi-material interface by modeling a bi-layer composite beam as two separate shear deformable sub-layers with consideration of crack tip deformation. Unlike the sub-layer model in the literature in which the crack tip deformations under the interface peel and shear stresses are ignored and thus a “rigid” joint is used, the present study introduces two interface compliances to account for the effect of interface stresses on the crack tip deformation which is referred to as the elastic foundation effect; thus a flexible condition along the interface is considered. Closed-form solutions of resultant forces, deformations, and interface stresses are obtained for each sub-layer in the bi-layer beam, of which the local effects at the crack tip are demonstrated. In this study, an elastic deformable crack tip model is presented for the first time which can improve the split beam solution. The present model is in excellent agreements with analytical 2-D continuum solutions and finite element analyses. The resulting crack tip rotation is then used to calculate the energy release rate (ERR) and stress intensity factor (SIF) of interface fracture in bi-layer materials. Explicit closed-form solutions for ERR and SIF are obtained for which both the transverse shear and crack tip deformation effects are accounted. Compared to the full continuum elasticity analysis, such as finite element analysis, the present solutions are much explicit, more applicable, while comparable in accuracy. Further, the concept of deformable crack tip model can be applied to other bi-layer beam analyses (e.g., delamination buckling and vibration, etc.).     

胶补加筋板应力强度因子及胶层剪应力计算

在铆钉力法的基础上，提出计算胶接修补加筋板结构应力强度因子及胶层剪应力的解析法，对分析胶接修补的加筋板强度具有现实意义．利用影响系数，可以得到筋条、补片及蒙皮位移的表达式，根据位移协调条件，建立联立方程，从而得到胶层剪应力及铆钉力．通过解析式，计算裂纹尖端的应力强度因子，分析补片对结构修补的效果，综合考虑了筋条及补片对应力强度因子的影响．     

Measurement of the strain field near a crack tip in polymethylmethacrylate by holographic interferometry

An experimental method has been developed for the detailed, real-time study of the strain field near a crack tip in any transparent material. This method combines holography and interferometry to measure the field of averaged transverse strain in a sheet specimen under inplane loading. It is shown that the solution for an edge crack in a semi-infinite sheet based on two-dimensional linear elastic theory can be applied to the finite-width polymethylmethacrylate specimen. This solution is observed to become less valid as the crack tip is approached due to the breakdown of the plane-stress assumption. This effect is evaluated for a range of thicknesses from much less to much more than the crack length.     

Analytic solutions to problem of elliptic hole with two straight cracks in one-dimensional hexagonal quasicrystals

By means of the complex variable function method and the technique of conformal mapping, the anti-plane shear problem of an elliptic hole with two straight cracks in one-dimensional hexagonal quasicrystals is investigated. The solution of the stress intensity factor （SIF） for mode III problem has been found. Under the condition of limitation, both the known results and the SIF solution at the crack tip of a circular hole with two straight cracks and cross crack in one-dimensional hexagonal quasicrystals can be obtained.