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

Digital photoelasticity is a whole field experimental technique which can analyze both 2-D and 3-D models. In this paper, stress frozen 3-D models are sliced mechanically and the whole field principal stress differences (Isochromatics) and principal stress directions (Isoclinics) are evaluated by capturing only five images using the standard optical arrangements of a conventional polariscope. The wrapped isoclinic values obtained by processing the first four colour polarization stepped images in the range -π/4 to +π/4 are unwrapped using adaptive quality guided phase unwrapping algorithm to get isoclinics in the range of -π/2 to +π/2. The total fringe order is evaluated by three fringe photoelasticity or RGB photoelasticity with its latest developments like colour adaptation combined with refined three fringe photoelasticity. The methodology is validated for two slices cut from aero-structural components.

Photoelastic analysis of stress frozen slices using five-step method

We have studied the dependence of breakdown field in nitrided oxides on nitridation conditions. Nitridation improves the breakdown field of the oxides. In an attempt to explore the cause of the improved breakdown, the breakdown field was related with electron‐trap density and refractive index (which increases with nitrogen concentration in the oxide). Our results suggest that the enhanced breakdown field of nitrided oxides is mainly due to incorporation of nitrogen, which results in structural changes in the nitrided oxide.

Process dependence of breakdown field in thermally nitrided silicon dioxide

Transient thermal stresses of a bimaterial specimen with interface cracks, under uniform cooling by convection, are analyzed by photothermoelasticity and a coupled temperature-displacement, finite element scheme. The stress intensity factors of the interface crack are determined by a multiparameter overdeterministic system of equations in a least-squares sense using the experimental data and by J-integral, numerically. The study showed that a normal temperature variation can lead to significant stresses due to the mismatch of thermal expansion coefficients.

Digital Photothermoelastic and Numerical Analysis of Transient Thermal Stresses in Cracked Bimaterial Interfaces

The stresses and its distribution in complex shape chain plate geometry play a critical role in the fatigue life performance of a chain assembly. However, it is difficult to identify the stress distribution and stress concentration zones precisely using only the conventional industrial friendly tools such as routine quality control test, breaking load test and numerical computations. In this context the transmission photoelastic technique has made it possible to identify the stress distribution, its concentration and also to quantify the stress and strain at any point in the chain plate. This paper explains how transmission photoelastic technique is used to estimate the stress distribution and its concentration zones in a complex chain plate when it is loaded.

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Analysis of a Complex Shape Chain Plate Using Transmission Photoelasticity

Photoelasticity directly provides the information of principal stress difference and the orientation of the principal stress direction at the point of interest. Using these, one can find the normal stress difference and in-plane shear stress by invoking equations in mechanics of solids or Mohr’s circle.

K. Ramesh

Papers

Photoelastic analysis of stress frozen slices using five-step method

Process dependence of breakdown field in thermally nitrided silicon dioxide

Digital Photothermoelastic and Numerical Analysis of Transient Thermal Stresses in Cracked Bimaterial Interfaces

Analysis of a Complex Shape Chain Plate Using Transmission Photoelasticity

Stress Separation Techniques