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

With rapid advancements in computer technology, colour image processing systems are now available at affordable prices. A proper understanding of the colour image processing techniques requires an understanding of the various models for colour representation. Apart from this, one needs to know the spectral response of the colour camera and the light source. The type of colour image processing hardware used for transmission or reflection photoelastic analysis has an influence on the quality of data acquisition. Data interpretation and analysis requires the understanding of the intensity of light transmitted, for various polariscope arrangements, in white light

Colour Image Processing Techniques

Colour transfer methodology is used in the field of image processing to transfer colour characteristics between images. In this study, colour transfer employing principal component analysis (PCA) is explored to circumvent the colour mismatch between application and calibration images in twelve fringe photoelasticity. For this, the images are considered as 3-D pixel clouds in RGB colour space.

Colour Transfer in Twelve Fringe Photoelasticity (TFP)

Isochromatics and isoclinics are the two fringe contours obtained in a photoelastic experiment. Isochromatics are contours of constant principal stress difference and isoclinics are the loci of points along which the principal stress orientation (with respect to a reference axis) is a constant. For stress analysis at any point, the photoelastic data required are, 

1.

The isochromatic fringe order and




2.

The isoclinic parameter at that point.

Fringe Multiplication, Fringe Thinning and Fringe Clustering

Classification of crack-tip isochromatics in unidirectional orthotropic composites, when the crack is parallel to the fibre and perpendicular to the fibre direction, is considered for mode I, mode II and mixed-mode type of loadings. The knowledge of the mode of fracture helps in identifying the appropriate governing equation to evaluate the Stress Intensity Factor (SIF) from the experimental fringe patterns. The effect of material orthotropy, change of material and a / w ratio in influencing the geometry of the fringe loops is studied in detail for mode I type of loading. Typical experimental fringe patterns are obtained by photo-orthotropic elasticity for mode I, mode II and mixed-mode loadings. The inclusion of the term σ ox to the σ x stress term introduced by Mojtahed and Zachary is validated. The necessity for developing a higher order theory in evaluating the SIF from experimental fringe loops when the crack tip is closer to a free boundary is emphasised.

K. Ramesh

Papers

Colour Image Processing Techniques

Colour Transfer in Twelve Fringe Photoelasticity (TFP)

Fringe Multiplication, Fringe Thinning and Fringe Clustering

Classification of crack-tip isochromatics in orthotropic composites

Innovative use of transmission and reflection photoelastic techniques to solve complex industrial problems