Notch effects on photoelastic determination of mixed-mode stress intensity factors

An investigation into the notch effect on the photoelastic determination of the mixed mode stress intensity factors is presented. This accomplished by comparing the isochromatic loops generated for a crack and an ellipse in an infinite plate. The generated mathematical loops are based on the exact solutions. A method of analysis is proposed and used to correct the distorted maximum angle $\text{θ}{}_{\mathrm{m}}$ and maximum shear stress $\text{τ}{}_{\max }$ due to the notch effect. The results obtained from the photoelastic measurements based on the proposed method compare favourably with those by an earlier investigation.     

A study of near and far field effects in photoelastic stress intensity determination

A technique known as the Taylor Series Correction Method (TSCM) for extracting the stress intensity factor from photoelastic data is reviewed. The need for ‘artificial’ flaws is identified and an approach due to Savin is used to near field effects of various practical flaw shapes upon the apparent stress intensity factor. Using the Sneddon-Srivastav solution for a line crack in a finite width plate, the constriction of the singular zone is demonstrated as the crack tip approaches the free edge. Results indicate that care must be taken in applying TSCM to obtain photoelastic data at appropriate distances from the crack tip.     

Automated photoelastic analysis

Photoelastic stress analysis can be a long and tedious process. However recent and current developments in the field of automated and computer aided photoelastic analysis mean that it is becoming possible to do more complex analysis and to perform it more quickly. This paper provides a survey of these developments and the advances in polariscope design.     

A theoretical and photoelastic contact stress analysis relevant to orthopaedic knee prostheses

This study is based on a theoretical and photoelastic static contact stress analysis, relevant to the design of the plastic tibial plateau in an orthopaedic knee prosthesis. It involves the review of existing theoretical analyses concerned with the contact mechanics of layered elastic systems and, where possible, the validation of any relevant findings using two dimensional photoelasticity. Significant findings include the identification of a general minimum recommendable design thickness for the plastic tibial plateau, the endorsement of using the Hertzian contact theory to predict contact stress levels in the tibial plateau of certain knee implants and the slight improvement in contact conditions in the plastic when the plateau is perfectly bonded to its supporting metal tray.     

Least squares asymptotic analysis of photoelastic data from stress concentration regions in plane problems

A complete separation of stresses throughout the entire stress concentration region near notches in plane, isotropic, linearly elastic plates is achieved using only conventional, easily obtained photoelastic (difference and directions of principal stresses) data. These data are analysed by a special least squares technique based on previously derived equations which describe the asymptotic character of the rapidly varying stress field near the root of the notch. The paper demonstrates the ability of the technique to predict stress concentrations as well as individual stresses accurately using only a small amount of data of typical experimental accuracy from arbitrary data points within the stress concentration zone.     

An assessment of far field effects on the photoelastic determination of mixed mode stress intensity factors

A limiting approach inquiry into far field effects on local field equations for mixed mode surface flaws is investigated by computer analysis. Curves showing the diminishing effect of the far field stress towards the cracks tip are plotted using fringe radii ratios vs fringe number. The zone used in the experimental determination of K₁ and K₂ is superimposed on these curves to investigate the extent to which K₁ and K₂ determined by the two parameter method are influenced by the far field stress.     

On the photoelastic determination of complex stress intensity factors

An improvement of the one-parameter extrapolation method of photoelastic determination of complex (mixed-mode) stress intensity factors at straight or curvilinear crack tips in a plane isotropic elastic medium due to Smith et al. [12, 13] can be achieved by measuring the absolute value of such a factor on the isochromatic fringes along properly selected polar directions and not at the maxima of the isochromatic fringes. In this way, the unknown value of the constant term of the stress field near the crack tip is taken into account. It is seen that it is always possible to find at least one appropriate polar direction to measure the absolute value of the stress intensity factor. In the case of Mode I stress intensity factors, these polar angles are = ± 120° and not = ± 90° as generally considered previously. Some numerical results are also presented in this special case and show the efficiency of the present method.     

A rapid method for stress separation in two dimensional photoelastic models

Obtaining the individual stress components at internal points in a two dimensional photoelastic model is time consuming and requires considerable expertise. A rapid method has been developed for calculating the stress distribution along an axis of symmetry. An example is given to show that the results are sufficiently accurate for engineerng design purposes.     

Reflection photoelastic tomography for the detection of stress distribution in planar optical waveguides

A novel method for measuring local stress distributions and birefringence of films on substrates and planar optical waveguides, with submicrometric resolution, is presented. The technique relies on a reflective tomographic configuration, applied in conjunction with a polarimetric setup, which processes the stress-induced change of the state of polarization of a laser probe beam reflected at the waveguide-substrate (film-substrate) interface. By this means, theoretically foreseen stress behavior can be experimentally verified and spurious or induced local stress variations in integrated optics components can also be brought into evidence. The feasibility of the proposed method has been verified by reconstructing the two-dimensional axial stress distribution in the 4 x 2 microm(2) core region of a doped silica-on-silicon optical waveguide.     

Determination of the stress intensity factor by methods of photoelastic simulation

Various methods of determination of stress intensity factors from the patterns of the isochromes, the isopachs, and the absolute differences in shape at the tip of a notch are analyzed. The range of extrapolation of the values of K_I within which the theoretically obtained stress distributions coincide with the stresses measured experimentally on a model with a finite radius of the stress raiser tip is established. Determination of the parameter K_I from the patterns of absolute differences of the shape is significantly more complex than from the patterns of the isochromes and isopachs but is justified on models of a high-modulus material when increased accuracy, reliability of the results, and an analysis of the stressed and strained state of a specimen with separation of the main stresses are necessary.Translated from Problemy Prochnosti, No. 1, pp. 33–37, January, 1990.     

Optical stress sensor based on electro-optic compensation for photoelastic birefringence in a single crystal

An optical stress sensor is proposed by using a single crystal with both electro-optic and photoelastic effects. Different from previous crystal-based stress sensors, the proposed sensor is based on electro-optic compensation for stress-induced birefringence and does not need an additional quarter-wave plate or modulator, because the stress-sensing element is simultaneously used as an electro-optic compensator. Candidate sensing materials include electro-optic crystals of the 3?m symmetry group and all glass with large Kerr coefficients. A primary experiment has demonstrated that the stress-induced birefringence in lithium niobate crystal can be compensated by its electro-optic birefringence. The proposed stress sensor is compact and low cost, and it is possible to achieve closed-loop stress measurement.     

Towards full field automated photoelastic analysis of complex components

The design of a automated system for photoelastic analysis of complex components is described, and an outline of the theory used in its operation is given. The potential of the system for providing detailed data over the full field of view is demonstrated by the analysis of a slice from a model of a bolt.     

平面镜多次反射的二维高精度小角度偏转测量

介绍了利用平面镜多次反射系统实现二维高精度小角度偏转测量的光学测量方法,构建了实验系统,针对系统的测量精度和测量范围与激光束在平面镜系统中反射次数的关系进行了研究,最后根据应用实例给出了具体的计算分析,研究结果表明,该方法具有结构简单、测量精度高的特点,当反射次数达到10次以上时,系统的测量精度将达到0.01",为亚角秒级高精度动态测量提供了一种新的研究方法.     

A three dimensional photoelastic study of the stress distributions in double helical epicyclic gears

This paper reports on part of a research programme which was carried out using two- and three-dimensional photoelastic model techniques in order to analyse the stress distributions in a double-helical epicyclic gear design incorporating typical features of production gear units.
The paper describes the testing of two three-dimensional models, one subjected to torque loading, i.e. tooth forces; the other to combined rotational and torque loading. Note is made of some of the problems inherent in the design and loading of complex models such as those used in the tests and of the solutions developed to overcome the difficulties.
Attention is devoted to the analysis of contact loads and load distribution, maximum sub-surface stresses, maximum root fillet bending stresses and the geometry of the lines of contact. General conclusions are drawn and an indication given of the subsequent extensive two-dimensional test programme which was carried out.     

A simple method for the photoelastic determination of mode I stress intensity factors

A new simple method for the photoelastic determination of Mode I stress intensity factors from isochromatics is proposed. This method takes into account the fact that a considerable part of the error committed in the photoelastic determination of Mode I stress intensity factors K_I at crack tips, based on experimentally obtained isochromatic fringe patterns, is due to ignoring the non-singular part of the stress field near the crack tips for the evaluation of these factors. This error can, in most cases, be minimized by an appropriate selection of the polar direction from the crack tip on which the experimental measurements for the subsequent evaluation of the stress intensity factors K_I are made. The suitable polar direction for determining K_I depends in general on the distance of the point where measurements on the isochromatics are made from the crack tip. The method was applied to the problem of a simple crack inside an infinite medium under uniaxial and biaxial loading. A comparison of the present method whith the employed analogous methods shows the superiority of the proposed method.