On the investigation of singular stress field around radial cracks in annulii subjected to diametrical tension

Results of photoelastic investigation conducted on annulii containing a radial crack at inner edge and subjected to diametrical tension are reported. The cracks are oriented at 90°, 60° and 45° to the loading direction. The Stress-Intensity Factors (SIFs) were determined by analysing the crack-tip stress fields. Smith and Smith's method [Engng Fracture Mech.4, 357–366 (1972)] and a modified method developed earlier by the authors (to be published) were adopted in the evaluation of SIFs.

Mixed-mode stress intensity factors for arbitrarily oriented cracks in cylindrical shells under axial pull and torsion

Results of photoelastic investigations conducted on cylindrical tubes (made of Araldite material) containing cracks oriented at 0°, 30°, 45°, 60° and 90° to the axis of the tube and subjected to axial and torsional loads are reported. The stress-intensity factors (SIFs) were determined by analysing the crack-tip stress fields. Smith and Smith's method [Engng Fracture Mech.4, 357–366 (1972)] and a new method developed by the authors by modifying Rakesh et al.'s method [Proc. 26th Congress of ISTAM, India (1981)] were employed to evaluate the mixed-mode SIFs.

Theoretical and experimental investigation of framed structure-layered soil interaction problems

The plane stress solution for the interaction analysis of a framed structure, with a foundation beam, resting on a layered soil has been studied using both theoretical and photoelastic methods. The theoretical analysis has been done by using a combined analytical and finite element method. In this, the analytical solution has been used for the semi-infinite layered medium and finite element method for the framed structure. The experimental investigation has been carried out using two-dimensional photoelasticity in which modelling of the layered semi-infinite plane and a method to obtain contact pressure distribution have been discussed. The theoretical and experimental results in respect of contact pressure distribution between the foundation beam and layered soil medium, the fibre stresses in the foundation beam and framed structure have been compared. These results have also been compared with theoretical results obtained by idealizing the layered semi-infinite plane as (a) a Winkler model and (b) an equivalent homogeneous semi-infinite medium

An experimental investigation into pile group-layered soil interaction

An interaction analysis of an axially loaded single pile and pile group with and without a pile cap in a layered soil medium has been investigated using the two-dimensional photoelastic method. A study of the pile or pile group behaviour has been made, varying the pile cap thickness as well as the embedded length of the pile in the hard stratum. The shear stress distribution along the pile-soil interface, non-dimensionalized settlement values of the single pile and the interaction factor for the pile group have been presented. Wherever possible, the results of the present analysis have been compared with available numerical solutions.

Interaction analysis of strip footing resting on a non-homogeneous elastic medium

In this paper, a plane stress solution for the interaction analysis of strip footing resting on (i) a non-homogeneous elastic half-plane and (ii) a non-homogeneous elastic layer resting on a rigid stratum has been presented. The analysis has been done using a combined analytical and FEM method in which the discretization of the half-plane is not required and thereby minimizes the computational efforts considerably. The contact pressure distribution and the settlement profile for the selected cases of varying modulus half-plane, which has more relevance to foundation engineering, have been given. Experimental verification through a photoelastic method of stress analysis has been carried out for the case of footing on Gibson elastic half-plane, and the contact pressure distribution thus obtained has been compared with the theoretical results. Copyright (C) 1996 Elsevier Science Ltd

Design and analysis of novel compression fracture specimen with constant form factor: Edge cracked semicircular disk (ECSD)

Inspired by the Brazilian disk geometry we examine the utility of an edge cracked semicircular disk (ECSD) specimen for rapid assessment of fracture toughness of brittle materials using compressive loading. It is desirable to optimize the geometry towards a constant form factor F for evaluating K-I. In this investigation photoelastic and finite element results for K-I evaluation highlight the effect of loading modeled using a Hertzian. A Hertzian loading subtending 4 degrees at the center leads to a surprisingly constant form factor of 1.36. This special case is further analyzed by applying uniform pressure over a chord for facilitating testing.

Characterizing Frictional Contact Loading via Isochromatics

Isochromatic patterns in the vicinity of frictional contacts furnish vital clues for characterizing friction. Though friction effects are evident in a diametrally loaded circular disk, three-point loading provides better results towards highlighting friction. In this paper, a new method of characterizing friction at loading contacts using photoelastic isochromatics patterns is presented. Location of isotropic points (IPs) formed in three-point and four-point loadings of circular disk is used as a main tool to quantify the friction component using theoretical analysis. Bifurcation of isochromatic fringe loops near the distributed loads is explained by the presence of anti-symmetric Hertzian shear traction in addition to Hertzian normal traction. The classical solution by Flamant for point load at the edge of half plane is used to derive stresses in circular disk for all required loading configurations. A semicircualr ring under three-point loading is examined using photoelasticity to understand the isochromatics pattern theoretically by considering normal and shear traction components at loaded regions.

Mixed Mode Analysis of Obliquely Oriented Edge Cracked Semicircular Disk Under Compression

A new mixed-mode compression fracture specimen, obliquely oriented edge cracked semicircular disk (OECSD) is analyzed by extending pure opening mode configuration of edge cracked semicircular disk (ECSD) under Hertzian compression. Photoelastic experiments are conducted on two different specimens of OECSD of same size and different crack lengths and inclinations. Finite element method (FEM) is used to solve a number of cases of the problem varying crack length and crack inclination. FE results show a good match with experiments. Inclination of edge crack in OECSD can be so made as to obtain any mode-mixity ratio between zero and one and beyond for any crack length. The new specimen can be used for fracture testing under compression more conveniently than the existing ones in several ways.

基于光栅成像投影的微位移检测方法

提出了一种基于光栅成像投影的微位移检测方法，利用光学傅里叶变换原理给出了具体的理论分析。准直激光束照明的光栅通过一个4f系统成像投影在被测物体表面上，光栅投影经过被测物体表面反射后由另一个4f系统成像在探测光栅上。探测光栅由一个透镜组成像在光电探测器上，其中采用由起偏器、光弹调制器和检偏器组成的偏振调制单元对探测光强进行调制。通过在4f系统的频谱面上设置滤波光阑，在光电探测器上获得了与被测物体的微位移成正弦关系的光强变化，检测出光电探测器上的光强变化即可以获得被测物体的位移量。实验验证了该检测方法的可行性

精确标定光弹调制器的新方法

针对现有光弹调制器标定方法的不足，提出了一种精确标定光弹调制器的新方法。首先利用起偏器、波片、光弹调制器和检偏器构成标定光路．通过寻找探测信号基频分量的极大值进行粗略标定，使光弹调制器的峰值延迟量处在1．841rad附近。然后撤走波片形成光弹凋制器的精确标定光路．在检偏器旋转90°前后获得探测信号的直流分量和二次谐波分量。最后利用这两种探测信号的直流分量和二次谐波分量精确地计算出光弹调制器的峰值延迟量。实验验让了此光掸调制器标定方法，实验结果表明其标定误差仅为0．7％。在此光掸凋制器标定方法中．光弹调制器

光弹调制器在偏振方向调制中的应用

提出了一种将光弹调制器应用于偏振方向调制的方法．介绍了它的两种基本使用模式，利用琼斯矩阵对其偏振方向调制原理及其两种基本使用模式进行了分析。光弹调制器和1／4波片形成偏振方向调制器件时，光弹调制器处于两块透光轴相互垂直的1／4波片之间．且光弹调制器的振动轴分别和两块1／4波片的透光轴成±45°角，线偏振光通过此器件其偏振方向被调制。实验验证了光弹调制器组合1／4波片调制偏振方向的原理。将光弹调制器应用在偏振方向的调制中．使现有偏振方向调制技术的光谱范围扩展到了紫外波段。

基于光弹调制技术的波片相位延迟量测量方法

提出了一种基于光弹调制技术的波片相位延迟量测量方法，利用米勒矩阵对其进行了理论推导和误差分析。测量光路包括激光器、起偏器、光弹调制器、被测波片、检偏器和光电探测器，利用探测信号的归一化基频分量和二次谐波分量精确计算出被测波片的相位延迟量。该方法能测量紫外到红外光谱范围内任意相位延迟量的波片，误差分析表明其误差小于0．05°。实验验证了该测量方法的有效性，波片相位延迟量的重复测量精度为0．0048°．

Silicon optical phase shifter based on strain induced by a piezoelectric PZT thin film

We demonstrate a silicon optical phase shifter based on photoelastic effect controlled by a piezoelectric thin film. The hysteresis behavior of the piezoelectric response shows potential application as bistable device independent of the optical intensity. © 2012 OSA.

Silicon optical phase shifter based on strain induced by a piezoelectric PZT thin film

We demonstrate a silicon optical phase shifter based on photoelastic effect controlled by a piezoelectric thin film. The hysteresis behavior of the piezoelectric response shows potential application as bistable device independent of the optical intensity. © OSA 2012.

Bistability in silicon microring resonator based on strain induced by a piezoelectric lead zirconate titanate thin film

We demonstrate bistability in a submicron silicon optical phase shifter based on the photoelastic effect. The strain magnitude is electrically controlled by a piezoelectric thin film placed on top of the device. The hysteresis behavior of the piezoelectric response shows potential application as bistable device independent of the optical intensity. © 2012 American Institute of Physics.