Effect of Cold Deformation on Phase Evolution and Mechanical Properties in an Austenitic Stainless Steel for Structural and Safety Applications

The effects of cold deformation on the formation of strain induced α’ martensite and mechanical properties of an austenitic stainless steel have been examined.X-ray diffraction analysis has revealed that 30% and 40% cold rolling have resulted in the formation of 24% and 31.5% martensite respectively.Microstructural investigation has demonstrated that the formation of martensite is enhanced with increase in the percent deformation at 0 ℃.Investigation of mechanical properties reveals that hardness,yield strength and tensile strength values increase where as percent elongation drops with increasing deformation.The fractographic observation corroborates the tensile results.Examination of sub-surface at the fractured end of the tensile sample manifests that void/microcrack nucleation occurs in the interfacial regions of the martensite phase as well as at the austenite-martensite interface     

Optimization of nitrilase production from a new thermophilic isolate

A new thermostable nitrilase‐producing isolate identified as Streptomyces sp. MTCC 7546 has been studied extensively for the optimization of enzyme production operating in batch mode. The benzonitrile was observed as inducer of nitrilase production. The isolate showed maximum nitrilase production after 24 h of incubation at optimal conditions. The strain grows well on a variety of carbon sources and produces the nitrilase that catalyses the hydrolysis of nitriles to acids without formation of amides. The enzyme is mostly active against mono‐ and di‐aliphatic nitriles (10 mmol L^?1) at pH of 7.4 and at a temperature of 50 °C. Copyright © 2007 Society of Chemical Industry     

Secondary and tertiary structural changes in gamma delta resolvase: comparison of the wild-type enzyme, the I110R mutant, and the C-terminal DNA binding domain in solution

gamma delta Resolvase is a site-specific DNA recombinase (M(r) 20.5 kDa) in Escherichia coli that shares homology with a family of bacterial resolvases and invertases. We have characterized the secondary and tertiary structural behavior of the cloned DNA binding domain (DBD) and a dimerization defective mutant in solution. Low-salt conditions were found to destabilize the tertiary structure of the DBD dramatically, with concomitant changes in the secondary structure that were localized near the hinge regions between the helices. The molten tertiary fold appears to contribute significantly to productive DNA interactions and supports a mechanism of DNA-induced folding of the tertiary structure, a process that enables the DBD to adapt in conformation for each of the three imperfect palindromic sites. At high salt concentrations, the monomeric I110R resolvase shows a minimal perturbation to the three helices of the DBD structure and changes in the linker segment in comparison to the cloned DBD containing the linker. Comparative analysis of the NMR spectra suggest that the I110R mutant contains a folded catalytic core of approximately 60 residues and that the segment from residues 100 to 149 are devoid of regular structure in the I110R resolvase. No increase in the helicity of the linker region of I110R resolvase occurs on binding DNA. These results support a subunit rotation model of strand exchange that involves the partial unfolding of the catalytic domains.     

AN INVESTIGATION OF 3-D CURLED CHIP IN MACHINING-PART 1: A MECHANICS-BASED ANALYTICAL MODEL

This paper presents an analytical model of the 3-D curled chip that is commonly produced in oblique machining. The chip model is based on a 3-D spiral with continuously varying center and curl radius. Stresses in the chip are analyzed by an energy-based approach. Bending and torsional shear stresses in the chip are generated based on input reaction forces. A case study with typical input values of reaction forces is analyzed for finding the magnitude and location of the maximum stresses. Also, the octahedral shear stress is proposed as a comprehensive 3-D chip failure criterion, because it combines the individual effects of the bending and shear stresses.     

Investigation of fatigue crack growth characteristics of NR/BR blend based tyre tread compounds

Tyre tread directly comes in contact with various road surfaces and is prone to damage due to cuts from sharp objects during service. As tyres undergo millions of fatigue cycles, these cuts propagate continuously and lead to catastrophic failure. Therefore fatigue crack growth (FCG) characteristics should be an essential criterion for tread compound selection. The present study investigates FCG behavior of blends comprising of Natural Rubber (NR) and Polybutadiene Rubber (BR) over a wide range of tearing energy. Pure shear specimens with a notch on both edges were tested in a Tear Analyser. Rapid increase in FCG rate after a certain strain level was observed. This transition point appeared in a strain range of 20–35 %, depending on the blend composition. The higher BR containing compounds exhibited better FCG characteristics below the transition point but reversal of ranking was seen above this point. The influence of temperature, R ratio, waveforms and cure system on FCG characteristics was also investigated in NR and 60–40 NR/BR blend compounds. Higher FCG rate was achieved under pulse loading compared to the sine waveform. The relaxation time between pulse cycles played an important role. With an increase in relaxation time, FCG rate decreases significantly. The higher sensitivity towards R ratio was observed in NR compound. The 60–40 NR/BR blend showed higher FCG rate with increase in temperature compared to the NR compound. The NR compound with high Sulfur/Accelerator (S/Ac) ratio showed better FCG characteristics whereas for 60–40 NR/BR blend with low S/Ac ratio achieved superior FCG characteristics.     

Design and realization of high-performance wave-pipelined 8×8b multiplier in CMOS technology

Wave pipelining is a design technique for increasing the throughput of a digital circuit or system without introducing pipelining registers between adjacent combinational logic blocks in the circuit/system. However, this requires balancing of the delays along all the paths from the input to the output which comes the way of its implementation. Static CMOS is inherently susceptible to delay variation with input data, and hence, receives a low priority for wave pipelined digital design. On the other hand, ECL and CML, which are amenable to wave pipelining, lack the compactness and low power attributes of CMOS. In this paper we attempt to exploit wave pipelining in CMOS technology. We use a single generic building block in Normal Process Complementary Pass Transistor Logic (NPCPL), modeled after CPL, to achieve equal delay along all the propagation paths in the logic structure. An 8×8 b multiplier is designed using this logic in a 0.8 μm technology. The carry-save multiplier architecture is modified suitably to support wave pipelining, viz., the logic depth of all the paths are made identical. The 1 mm×0.6 mm multiplier core supports a throughput of 400 MHz and dissipates a total power of 0.6 W. We develop simple enhancements to the NPCPL building blocks that allow the multiplier to sustain throughputs in excess of 600 MHz. The methodology can be extended to introduce wave pipelining in other circuits as well