Brittle failure of components weakened by cracks or sharp and blunt V-notches is a topic of active and continuous research. It is attractive for all researchers who face the problem of fracture of materials under different loading conditions and deals with a large number of applications in different engineering fields, not only with the mechanical one. This topic is significant in all the cases where intrinsic defects of the material or geometrical discontinuities give rise to localized stress concentration which, in brittle materials, may generate a crack leading to catastrophic failure or to a shortening of the assessed structural life. Whereas cracks are viewed as unpleasant entities in most engineering materials, U- and V-notches of different acuities are sometimes deliberately introduced in design and manufacturing of structural components. Dealing with brittle failure of notched components and summarizing some recent experimental results reported in the literature, the main aim of the present contribution is to present a review of some local approaches applicable near stress raisers both sharp and blunt. The reviewed criteria allowed the present authors to develop a new approach based on the volume strain energy density (SED), which has been recently applied to assess the brittle failure of a large number of materials. The main features of the SED approach are outlined in the paper and its peculiarities and advantages accurately underlined. Some examples of applications are reported, as well. The present review is based on the authors’ experience over more than 15 years and the contents of their personal library. It is not a dispassionate literature survey.

Recent developments in brittle and quasi-brittle failure assessment of engineering materials by means of local approaches

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Some Basic Problems Of The Mathematical Theory Of Elasticity

In contrast to animal and fungal cells, green plant cells contain one or multiple chloroplasts, the organelle(s) in which photosynthetic reactions take place. Chloroplasts are believed to have originated from an endosymbiotic event and contain DNA that codes for some of their proteins. Most chloroplast proteins are encoded by the nuclear genome and imported with the help of sorting signals that are intrinsic parts of the polypeptides. Here, we show that a chloroplast-located protein in higher plants takes an alternative route through the secretory pathway, and becomes N-glycosylated before entering the chloroplast.

Evidence for a protein transported through the secretory pathway en route to the higher plant chloroplast.

A control studio object system is disclosed which allows a process control environment to be easily and quickly configured or modified. The control studio object system includes a stencil portion having stencil items conforming to algorithms and a diagram portion to which the stencil items may be copied via a drag and drop operation. Because the stencil items are objects which contain all of the information required by a diagram portion to create an object that contains all of the information necessary to program the process control environment, the completed diagram portion reflects the actual configuration of the process control environment. Additionally, providing the stencil items as objects allows the diagrammed environment to be installed directly to nodes without requiring the diagram to be compiled or rewritten in a language conforming to the node.

System for configuring a process control environment

Quality-guided phase unwrapping is a widely used technique with different quality definitions and guiding strategies reported. It is thus necessary to do a detailed comparison of these approaches to choose the optimal quality map and guiding strategy. For quality maps, in the presence of noise, transform-based methods are found to be the best choice. However in the presence of discontinuities, phase unwrapping is itself unresolved and hence quality-guided phase unwrapping is not sufficient. For guiding strategies, classical, two-section, and stack-chain guiding strategies are chosen for comparison. If accuracy is the foremost criterion then the classical guiding strategy with a data structure of indexed interwoven linked list is best. If speed is of essence then the stack-chain guiding strategy is the one to use.

Quality-guided phase unwrapping technique: comparison of quality maps and guiding strategies

A novel approach to plot photoelastic fringe contours from three-dimensional finite element results is presented. Plotting of fringe contours from 3D FE models requires the calculation of secondary principal stresses along the light path. The definition of secondary principal stresses and the calculation of relevant photoelastic data for fringe plotting are discussed. The plotting scheme uses a scanning approach and the evaluation of total fringe order is achieved by combining a file structure and subsequent sorting of these data to enable integration along the light path. The methodology is validated for the problem of a cantilever beam with an edge load. The usefulness of the methodology to verify 3D FE modelling and for experimentalists to design their experiments is indicated. Copyright © 2006 John Wiley & Sons, Ltd.

Development of photoelastic fringe plotting scheme from 3D FE results

The use of single-colour image for determining the fringe orders in digital photoelasticity has gained importance in recent years, and in this, the fringe orders are obtained by comparing the colou

New initiatives in single-colour image-based fringe order estimation in digital photoelasticity:

Experimental studies to exploit photoelastic data of conformal geometries to extract contact parameters are non-existent because closed-form stress field equations were not available until recently. In this paper, the explicit equations recently reported in the literature for a flat punch with rounded edges are generalized so that a single set of equations can be used for a flat punch with rounded edges and Hertzian contacts with arbitrary radii of curvatures. The generality of the governing equations is verified by plotting isochromatics for conformal and non-conformal contact situations. A generic method to evaluate unknown contact parameters from the whole-field isochromatic data for conformal and non-conformal geometries is implemented. The methodology is initially verified using theoretically generated isochromatic data and is then used to experimentally evaluate two contact situations. In view of high-fringe gradient zones, the suitability of various digital photoelastic methods is compared. A novel four-step phase shifting technique is proposed in which isochromatic and isoclinic data can be evaluated using the minimum number of images.

Evaluation of Conformal and Non-Conformal Contact Parameters Using Digital Photoelasticity

In photoelasticity, the method of obtaining the individual values of principal stresses/normal stresses separately is referred to as stress separation. Shear difference method is one of the widely used techniques for stress separation in digital photoelasticity. Normally a simple raster scanning approach is used in shear difference method in which stress separation is carried out for all the lines within the model domain by either row-wise horizontally or column-wise vertically starting from the boundary pixels. This requires the presence of a free boundary to start the integration scheme for every row of interest, which is not always possible in most of the practical problems. In order to overcome this, in this paper, an adaptive scanning scheme is proposed so that stress separation can be carried out even if there is only one free boundary pixel available in the model. The new scanning scheme is validated using the theoretically generated data for the problem of a ring subjected to internal pressure. Later, the applicability of this scheme is demonstrated by using two other example problems.

K. Ramesh

Papers

Development of photoelastic fringe plotting scheme from 3D FE results

New initiatives in single-colour image-based fringe order estimation in digital photoelasticity:

Evaluation of Conformal and Non-Conformal Contact Parameters Using Digital Photoelasticity

An adaptive scanning scheme for effective whole field stress separation in digital photoelasticity

Scanning schemes in white light Photoelasticity – Part I: Critical assessment of existing schemes