D.V.V. Satyanarayana

First order reaction kinetics for transient creep in NiAl hardened austenitic steel

Abstract Transient creep of an NiAl hardened austenitic steel was analysed in the temperature range of 823 to 923 K at stresses ranging from 150 to 450 MPa in the frame work of first order reaction kinetics. The present analysis is aimed: to correlate various transient creep parameters with steady state creep rate following first order reaction rate theory to obtain correlation constants; and to arrive at a unified equation to describe primary and steady state regimes of the creep curves in terms of correlation coefficients thus derived. Good correlation of transient creep parameters with steady state creep rate has been obtained over the test conditions studied indicating that the basic mechanism of deformation is the same for all the three stages of creep. Unified equation that fits the experimental creep strain time data for different test conditions over transient and steady state regimes has been obtained in terms of correlation coefficients.

Strain hardening behaviour of an Fe–Ni–Cr–Al alloy

Abstract Strain hardening behaviour of Fe–Ni–Cr–Al alloys, in both solution treated and aged conditions, has been investigated at ambient temperature. The alloy in both solution treated and aged conditions exhibits three fairly distinct stages of strain hardening. The strain hardening rate decreases in regime I, remains constant in regime II and begins to fall again in regime III. The three regimes shift to lower strain levels upon ageing and then shift to higher strain levels with over-ageing. While interaction of slip and deformation twinning is responsible for the constant strain hardening rate in solution treated specimens, dislocation–dislocation interaction (forest interaction) leading to the formation of dislocation tangled networks contributes to such a behaviour in aged specimens. Although the precipitate size effects on work hardening behaviour are clearly discernible for both θ versus σ and θ d σ d versus σ d plots, as compared to θ versus ϵ plots, the hybrid model (θ d σ d versus σ d plots) provides a quantitative description of precipitate size effects on the work hardening behaviour of the alloy in aged conditions.

Quality Assessment of Efficient LP Analysis Methods

The performance of the autocorrelation method of LP analysis has always been limited when the speech signal is corrupted by noise. In order to overcome these limitations number of efficient LP analysis techniques have been developed such as Moving Average(MA), Moving Maximum (MM) and Average threshold Method(AT). All these methods here compared with conventional Auto correlation Method(AM). The quality of speech will be measured quantitatively by various parameters such as Overall SNR, Segmental SNR, Likelihood Ratio (LLR), Log Area ratio (LAR), Itakura Saito Distortion (ISD), Weighted Spectral Slope Measure (WSS). In this paper an attempt has been made to compare the efficient LP analysis methods based on above parameters. After care full analysis it is found that the Average Threshold (AT) Method of speech processing gives better results compare to other methods.