Deformation and fracture of a particle-reinforced aluminum alloy composite: Part II. Modeling

In this article, the tensile and fracture properties of a discontinuously reinforced aluminum (DRA) alloy composite are modeled to determine the influence of constituent parameters on material behavior. Comparison of the elastic-modulus calculations to the experimental data suggest that the angular particles are more effective in load transfer than spherical particles, and that a unit cylinder geometry is a good representation of the particles under elastic conditions. This same geometry is used in the finite element-based elastic-plastic model of Bao et al., and reasonably good agreement is obtained between the experimental and predicted yield strengths. A fracture-mechanics model is proposed for predicting the elongation to failure. The model assumes the existence of particle cracks, and criticality is based on the strain required for matrix rupture between cracked particles. The damage criterion of Cockcroft and Latham is utilized, and model predictions are compared to data from different investigations. It is shown that the volume fraction of particles and the work-hardening coefficient of the matrix have a strong influence on the strain to failure. Fracture toughness modeling once again exposes the limitations of existing zero-degree crack-propagation models, such as that of Hahn and Rosenfield, which predict increased toughness with yield strength rather than a decrease, which is observed experimentally. A shear-failure model along a 45-deg direction is proposed for the higher-strength conditions, where concentrated slip bands were observed. The model exhibits the inverse toughness dependence on strength and better correlation to peak-aged (PA) data, but shows poorer agreement with underaged (UA) data. Thus, a transition from zero-degree propagation to 45-deg propagation with increasing strength is suggested. A simplified method for extracting particle stresses is illustrated and is used to estimate a Weibull modulus of 4.9 and a Weibull strength of 2450 MPa for the SiC particles of an average diameter of 10 μm. This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October 11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials Committee.     

Effect of manganese and cobalt doping on conductivity of ZnO based varistors: a study by complex plane modulus

Effect of manganese and cobalt doping (0.50 mole%) on electrical properties of ZnO based varistors has been studied using complex plane modulus analysis. It is found that total resistivity of Mn doped sample is more as compared to that of Co doped sample. This has been ascribed to existence of Mn in variable valence states viz. Mn²⁺, Mn³⁺ and Mn⁴⁺ which promotes hopping conduction leading to increase in the conductivity as compared to Co doped sample, in which Co exists predominantly in +3 state with traces of Co²⁺ or Co⁺⁴ states. This accounts for its less conductivity. Mechanism of conduction is the same for grains and grainboundaries.     

Influence of incident beam divergence on the intensity of diffuse streaks

The influence of incident beam divergence on the length of the streak intercepted by the Ewald sphere is considered, as a relpHK·L of a faulted hexagonal crystal, mounted about itsc-axis on the goniometer head attached to the ø-circle, is brought into diffracting condition for the bisecting setting of a 4-circle diffractometer. For the special crystal mounting correction factors required to convert the measured intensities corresponding to a fixed length of the streak are derived. A procedure for experimentally verifying the mathematical approach employed in these derivations is also presented.     

Implementation and Optimization of CNTFET Based Ultra-Low Energy Delay Flip Flop Designs

Silicon - Energy conservation and delay minimization are the two major goals while designing ultra-low-power digital integrated circuits at lower technology nodes. Here, silicon based carbon...     

Reaction of wood with inorganic salts

Wood samples and veneers of Hevea brasiliensis (Rubber wood) and Acacia auriculaeformis treated with aqueous solutions of chromium trioxide, ferric chloride and ferric nitrate were studied for water repellency and their reaction with wood constituents. FTIR spectra obtained from wood surface treated with chromium trioxide indicate the formation of a water insoluble complex between chromium trioxide and aromatic ring of lignin, whereas no reaction takes place with ferric salts. Treatment of wood by chromium trioxide was found to be effective in imparting water repellency in wood.     

Identification of FOPDT and SOPDT process dynamics using closed loop test

In this paper, identification of stable and unstable first order, second order overdamped and underdamped process dynamics with time delay is presented. Relay with hysteresis is used to induce a limit cycle output and using this information, unknown process model parameters are estimated. State space based generalized analytical expressions are derived to achieve accurate results. To show the performance of the proposed method expressions are also derived for systems with a zero. In real time systems, measurement noise is an important issue during identification of process dynamics. A relay with hysteresis reduces the effect of measurement noise, in addition a new multiloop control strategy is proposed to recover the original limit cycle. Simulation results are included to validate the effectiveness of the proposed method.     

Effect of Ultrasonic Shot Peening on Microstructure and Mechanical Properties of High-Nitrogen Austenitic Stainless Steel

The effect of ultrasonic shot peening (USSP) was studied on microstructural modification and mechanical properties such as microhardness, yield strength, tensile strength, and low cycle fatigue (LCF) life of a nitrogen stabilized austenitic stainless steel, at room temperature. There was grain refinement up to nano scale in surface region of the shot peened specimens and the microhardness was increased markedly up to the depth of approximately 100 µm. There was insignificant increase in yield and tensile strength, but drastic reduction in LCF life, particularly at low strain amplitude, from USSP. The nominal increase in yield and tensile strength was due to grain refinement in the surface region and drastic fall in LCF life was due to surface cracking resulting from USSP.     

Metabolic fingerprint of patients showing responsiveness to treatment of septic shock in intensive care unit

Magnetic Resonance Materials in Physics, Biology and Medicine - An early metabolic signature associated with the responsiveness to treatment can be useful in the better management of septic shock...