Cyclic Fatigue of Ce-TZP/AI2O3 Composites: Role of the Degradation of Transformation Zone Shielding

The origin of cyclic fatigue in two Ce-TZP/Al₂O₃ composites was investigated by (a) measurements of residual stresses in the transformation zones and crack-tip stress intensities in in situ loaded compact specimens using microprobe Raman spectroscopy, (b) examination of the crack-tip transformation zones by transmission electron microscopy, and (c) measurements of crack-growth rates in cyclic fatigue and in sustained loading at 400°C, a temperature at which stress-induced transformation of the tetragonal zirconia to the monoclinic polymorph was suppressed. Transformation zones formed during cyclic fatigue consistently showed lower compressive residual stresses and higher crack-tip stress intensities than the zones formed in sustained loading. Transmission electron microscopy revealed monoclinic laths of smaller average twin spacing and of multiple types of lattice correspondence in the transformation zones of the fatigue specimens as compared to the sustained-load specimens. Crack-growth measurements at 400°C indicated a significant suppression of the cyclic fatigue effect in the absence of transformation plasticity. These results in combination pointed to degradation of transformation-zone shielding as an important contributing cause of cyclic fatigue in Ce-TZP/Al₂O, composites. A more efficient accommodation of the transformation strains within the zones appears to be the underlying mechanism of the degradation of zone shielding in cyclic fatigue.     

Application of the method of caustics to the centre-cracked diametral compression test specimen

Normalized Mode I stress intensity factors,N ₁(a/R), for symmetrical radial cracks in diametral compression test specimens were experimentally evaluated using disc specimens of polymethyl methacrylate and the method of caustics. The method of caustics was first employed with precracked three-point bend specimens to assess the optical constant for the test material. This material property and the diameters of the caustics as a function of the applied load at different relative crack lengths (a/R) yielded the non-dimensional stress intensity factors using equations presented by Theocaris. These experimental values agreed closely with the theoretical solutions reported in the literature. Disc specimens of a polycrystalline alumina were also tested in diametral compression at temperatures up to 1000° C and the measured fracture toughness values were compared to those measured with chevron-notched bend specimens. It is shown that the centre-cracked diametral compression specimens give very reproducible fracture toughness measurements, and the specimen and the test technique can be usefully employed to assess the fracture toughness of structural ceramics at both ambient and elevated temperatures.     

Fire safety assessment and optimal design of passive fire protection for offshore structures

The article presents a unified probabilistic approach to fire safety assessment and optimal design of passive fire protection on offshore topside structures. The methodology was developed by integrating quantitative risk analysis (QRA) techniques with the modem methods of structural system reliability analysis (SRA) and reliability based design optimisation (RBDO). Reliability analysis methodologies are presented for both plated (e.g. fire and blast walls) and skeletal structures (deck framing), which take into account uncertainties in fire and blast loading, thermal and mechanical properties of the steel and insulation. Probability of component and system failure are evaluated using first- and second-order reliability methods (FORM/SORM). The optimisation of passive fire protection is performed such that the total expected cost of the protection system is minimised while satisfying reliability constraints.     

A survey of 4478 biopsy specimens of oral lesions

A surgery of 4478 biopsy specimens in dental institute in India was carried out to compare and correlate results obtained from such studies carried out elsewhere. The study revealed that there are more than 150 common and rare oral diseases which are diagnosed and treated by dentists. 13 common diseases comprised majority (60.37%) of the biopsy specimens studied. Of these, tumors (25.53%) and Cysts (14.38%) constituted the majority of the bulk. The study also shows that most of the benign tumors were mesenchymal in origin (almost 5.5:1) while malignant tumors were epithelial (almost 20:1) in origin. Cystic lesions included the most common radicular cyst (7.12%) and the rare hydatid cyst (one case reported). Gingival hyperplasia mainly due to local aetiology, constituted the 3rd largest group. The purpose of this report is to provide some information about the type and frequency of oral lesions usually diagnosed, with the help of histopathological examination in India.     

Design and Development of a Mobile Wireless Video Streaming Mote

Video streaming is considered as one of the best compelling sources of information for several applications ranging from vehicular technology, security systems, biomedical systems to aerospace applications. Video streaming using wireless network is quite challenging and a lot of research is in progress. In this paper, design and development of a low-cost real-time wireless video streaming mote is proposed which is an outcome of a funded project. Three different variants of the proposed system are designed, tested and their performances are evaluated. The first prototype uses an Arduino YUN board, second prototype uses a Raspberry PI board and the third prototype uses an Arducam ESP8266 Uno Module. The proposed wireless video streaming mote is aimed at moving around an area under surveillance, gathering images and transferring the same to control station. The proposed system has potential applications including assistance to vehicle drivers during reversing, parking, autonomous driving of the vehicles, driving vehicles using mobile application etc. The proposed system designed has a myriad of real-time applications for domestic requirements with social cause too.     

Design of complex adaptive multiresolution directional filter bank and application to pansharpening

This paper proposes a new 2-D transform design, namely complex adaptive multiresolution directional filter bank, to represent the spatial orientation features of an input image adaptively. The proposed design is completely shift invariant and represents the input image by one low-pass and multiscale N directional band-pass subbands. Here, N represents estimated number of dominant directions present in the input image. Our design consists of two main filter bank stages. A fix partitioned complex-valued directional filter bank (CDFB) is at the core of the design followed by a novel partition filter bank stage. Fine partitioning of the CDFB subbands is used to get the adaptive nature of the proposed transform. The partitioning decision is made based on the directional significance of range of CDFB subband angle selectivity in the input image. Partition filter bank stage which nonuniformly partitions the CDFB subbands provides total N dominant direction selective subbands. Local orientation map of the input image is used to determine the dominant directions and hence N. For better sparsity properties, we design the multiresolution stage with filters having high vanishing moments and better frequency selectivity. Applicability of the proposed adaptive design is shown for pansharpening of multispectral images. Our proposed pansharpening approach is evaluated on images captured using QuickBird and IKONOS-2 satellites. Results obtained using the proposed approach on these datasets show considerable improvements in qualitative as well as quantitative evaluations when compared to state-of-the-art pansharpening approaches including transform-based methods.     

LIQUID PHASE BACKMIXING IN BUBBLE COLUMN REACTORS—A NEW CORRELATION

Bubble column reactors are widely used in many industrial applications due to their simplicity of operation. Although simple to operate, bubble columns are difficult to scale-up due to the uncertainties in the estimation of some non-adjustable design parameters. One of these design parameters is the liquid phase backmixing.

The present work proposes a new correlation to estimate the liquid phase backmixing in bubble column reactors. The correlation is based on principles originally developed for flow through porous media and uses experimental data obtained over a wide range of operating conditions. This correlation is simple to use and requires parameters which are easily available or can be measured on a small scale apparatus. The proposed correlation shows a significant improvement over available literature correlations and is applicable to three phase systems as well.     

Interfacial Sliding Friction in Silicon Carbide–Borosilicate Glass Composites: A Comparison of Pullout and Pushout Tests

Interfacial sliding friction stress (τ_f) was assessed using both pushout and pullout tests on SiC-borosilicate glass composite specimens. Single-filament composite specimens were fabricated by heating to 950°C in argon borosilicate glass rods with fine-diameter (250-μm) capillary in which SiC filaments were inserted. The composite specimens prepared in this manner showed only frictional bonding. The maximum frictional sliding loads for pushout and the initial frictional sliding loads in pullout were measured as functions of the embedded length of the filament in the glass rods. The nonlinear variations of the frictional loads were analyzed using shear-lag models that include corrections for the effects of Poisson expansion or contraction on the sliding friction stress. It is shown that under identical conditions of composite fabrication the two tests give nearly identical properties for the interfaces. Pushout tests on hotpressed bulk composite specimens, however, showed both chemical bonding and a higher sliding friction stress relative to the single-filament capillary specimens. The presence of compressive residual stress on the filaments was independently confirmed by evidence of stress-induced birefringence.     

Role of Autocatalytic Transformation in Zone Shape and Toughening of Ceria–Tetragonal-Zirconia–Alumina (Ce-TZP/Al2O3) Composites

Stress–strain behaviors in three-point bending, transformation zones in single-edge-notch-bend specimens, and transformation toughening were studied in two types of Ce-TZP/Al₂O₃ composites. A commercial grade exhibited yield-point behavior triggered by autocatalytic transformation and elongated zones. A new grade of Ce-TZP/Al₂O₃ composite showed monotonic stress–strain behavior and a zone shape close to theoretical prediction based on a shear–dilatation yield criterion. The effects of zone sizes and shapes on fracture toughness of the two ceramic composites are shown to be qualitatively consistent with the predictions of transformation-zone shielding theories.