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

The application of digital techniques for data acquisition in 2-D transmission photoelasticity and reflection photoelasticity is well developed and these were discussed in the earlier chapters. The extension of digital techniques for data acquisition to integrated photoelasticity and scattered light photoelasticity have just made a beginning. In integrated photoelasticity, one has to determine three parameters experimentally and these are known as characteristic parameters. In scattered light photoelasticity, the illumination levels are quite low due to light scattering. This necessitates the use of high-resolution CCD cameras. The ultimate aim of integrated photoelasticity or scattered light photoelasticity is to evaluate the stress field interior to the model. The current developments on tensorial tomography are discussed in this chapter.

Recent Developments and Future Trends

A novel and simple approach to plot fringe contours from finite element results that simulates the fringe thickness variation as observed in experiments is presented. The procedure does not require solution of any non-linear equation. Shape functions are used as interpolation functions to plot fringe contours from the nodal values of fringe orders. The various fringe contours one usually comes across in stress analysis are also reviewed. The program code in Turbo-Pascal employing the new algorithm is given. Stress and displacement contours at the tip of a crack in an SEN (single-edge-notched) specimen are plotted using the code developed. The fringe contours plotted correspond to those observed in experiments such as photoelasticity, holography and Moire.

Plotting of fringe contours from finite element results

Colour adaptation in three fringe photoelasticity using a single image

Thermal nitridation of SiO2 was carried out at 25% and 40% of NH3 for various times and temperatures. Flat‐band voltage and interface‐state densities were studied as a function of processing conditions. Avalanche injection was used to study electron trapping. The density of electron traps in nitrided oxides depended on the nitridation conditions in the same way as the negative flat‐band voltage (positive voltage). A consistent model for negative flat‐band voltage and electron traps is presented to explain the results obtained. Thermal emission of trapped electrons dominates the detrapping mechanism. Energy depths of these traps were found to be 1.3–1.6 eV.

Electron trapping and detrapping in thermally nitrided silicon dioxide

Quantification of residual stresses in glass articles necessitates the knowledge of photoelastic constant of the glass material. The recent developments in digital photoelasticity have increased its applicability in residual stress analysis of glass. In this paper, photoelastic calibration of the glass material has been performed using the carrier fringe method (CFM) and phase shifting technique (PST) in digital photoelasticity. The retardations measured by both of these techniques are used for the calculation of photoelastic constant of the glass material and they were found to be in good agreement with each other. Calibration of glass by CFM is recommended for industrial applications since it requires only a few images as compared to PST.

K. Ramesh

Papers

Recent Developments and Future Trends

Plotting of fringe contours from finite element results

Colour adaptation in three fringe photoelasticity using a single image

Electron trapping and detrapping in thermally nitrided silicon dioxide

A simple approach to photoelastic calibration of glass using digital photoelasticity