Theoretical stress analysis for a non-isotropic body of cylindrical configuration containing a row of cracks

A problem of stress analysis for a long circular cylinder has been dealt with in this paper by analytical methods. The cylinder is assumed to be made of an elastic material which is not isotropic but the elastic properties are considered to be similar in directions perpendicular to the axis of the cylinder. The body under consideration is supposed to contain an infinite row of penny-shaped cracks which are parallel to each other and located periodically along the cylinder-axis. All the cracks are assumed to be opened by the same distribution of internal pressure on their surfaces. By choosing appropriate potential functions the problem is treated mathematically through the use of integral equation approach. Numerical results for the stress-intensity factor, the strain energy and the critical pressure, obtained on the basis of the analysis are also given.     

MODE II STABLE CRACK GROWTH

Abstract Mode II stable crack extension has been examined for an aircraft grade aluminium alloy D16AT. Both theoretical and experimental results are presented. The experimental observations include load displacement diagrams, plastic wake, crack front tunnelling and scanning electron micrographs of the fracture surfaces. The crack shows a tendency for in-plane extension, and the fracture surface is very flat, smooth and free of any dimples. The crack front advances with neghgible tunnelling at all stages of extension. The span of mode II stable crack growth (SCG) is longer than in the case of mode I SCG reported earlier for the same material and there is also more extensive plastic deformation. In the presence of a slight mode I load, the crack grows out-of-plane and the fractured surface facets resemble that of a mode I or mixed-mode dimpled fracture. The theoretical study is based on a finite element analysis using small deformation theory and incremental plasticity. Some of the experimental results have been theoretically predicted using the COA criterion as the governing criterion. The theoretical results include load-displacement diagrams, crack edge displacement curves, plastic zones and the J resistance curves. There is good agreement between the load-displacement diagrams. The initiation and maximum loads differ by less than 15%. The J resistance curve has a constant slope over the whole span of stable crack growth.     

Negative bias temperature instability in strain-engineered p-MOSFETs: a simulation study

Negative Bias Temperature Instability (NBTI) in p-MOSFETs is a serious reliability concern for digital and analog CMOS circuit applications. Strain in the channel region affects negative bias temperature instabilities, low frequency noise, radiation hardness, gate oxide quality and hot carrier performance. The understanding of these phenomena in strain-engineered p-MOSFETs from fundamental physics is essential. In this paper, technology CAD (TCAD) has been used to study the effects of strain on the negative bias temperature instabilities in p-MOSFETs. A quasi two dimensional (quasi-2D) physics-based Coulomb scattering mobility model for strained-Si has been developed and implemented in Synopsys Sentaurus Device tool for device simulation to understand NBTI in strain-engineered p-MOSFETs.     

Active cellular preform derived from stems of jute and sticks of cane and their suitability for bulk porous Si/SiC ceramics

Stems of Jute (Corchorus capsularis L.) and sticks of Cane (Calamus rotang L.), plants of immense economic importance in the Indian subcontinent, were converted into carbonaceous perform (C-preform) maintaining the circular cylindrical shapes in lengths of 0.02–0.05 m by controlled thermal processing. Plant material precursors were characterized by analysis of elemental (C, H, N) and molecular (cellulose, hemicellulose, lignin) compositions, by determination of Bulk Density (BD) and ash content and by optical microscopy and X-ray diffractometry (XRD). C-preforms were also characterized by measurement of BD and by Scanning Electron Microscopy (SEM) and XRD. The C-preforms were further subjected to infiltration with Si-melt (1823–1923 K) under vacuum. Spontaneous infiltration and reaction yielded composite ceramics preserving the morphology of native Jute Stem (JS) and Cane Stick (CS) precursors on macro and micro scale. The materials were found to be duplex composites with Si and β-SiC as crystalline phases. The end ceramics were characterized by measurement of BD, and also by SEM and by XRD. Measured mean BD of the Si/SiC composites derived from JS and CS were 2190 Kg m⁻³ and 2250 Kg m⁻³. The respective volume fractions of large diameter (>100 μm) bulk pores were 0.134 and 0.204, in the composites derived from JS and CS. Taking into account the measured volume fraction internal pores of 0.11 and 0.149, the volume fractions of SiC were calculated to be 0.136 and 0.307 in the composites derived from JS and CS respectively, closely tallying with those calculated from the C-preform bulk densities. The cellular Si/SiC ceramics derived from JS and CS having special morphologies with long and large porous channels and oriented growth of constituent phases are likely to be suitable for devices such as high temperature insulators, catalyst support structures for gas phase reactions at elevated temperatures, molten metal filters and others.     

Induction of chemical and moisture resistance in Saccharum spontaneum L fiber through graft copolymerization with methyl methacrylate and study of morphological changes

In this article, morphological modification of Saccharum spontaneum L, a natural fiber through graft copolymerization with methylmethacrylate using ferrous ammonium sulfate—potassium per sulfate redox initiator has been reported. Different reaction parameters such as reaction temperature, time, initiator molar ratio, monomer concentration, pH and solvent were optimized to get maximum graft yield (144%). The graft copolymers thus formed were characterized by Fourier transform infrared, scanning electron microscopy, X‐ray diffraction and thermogravimetric, differential thermal analysis, and differential thermogravimetric techniques. Graft copolymer has been found to be more moisture resistant and also showed higher chemical and thermal resistance. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanical properties of teak wood flour‐reinforced HDPE composites

Mechanical properties such as tensile and impact strength behavior of teak wood flour (TWF)‐filled high‐density polyethylene (HDPE) composites were evaluated at 0–0.32 volume fraction (Φ_f) of TWF. Tensile modulus and strength initially increased up to Φ_f = 0.09, whereas a decrease is observed with further increase in the Φ_f. Elongation‐at‐break and Izod impact strength decreased significantly with increase in the Φ_f. The crystallinity of HDPE also decreased with increase in the TWF concentration. The initial increase in the tensile modulus and strength was attributed to the mechanical restraint, whereas decrease in the tensile properties at Φ_f > 0.09 was due to the predominant effect of decrease in the crystallinity of HDPE. The mechanical restraint decreased the elongation and Izod impact strength. In the presence of coupling agent, maleic anhydride‐grafted HDPE (HDPE‐g‐MAH), the tensile modulus and strength enhanced significantly because of enhanced interphase adhesion. However, the elongation and Izod impact strength decreased because of enhanced mechanical restraint on account of increased phase interactions. Scanning electron microscopy showed a degree of better dispersion of TWF particles because of enhanced phase adhesion in the presence of HDPE‐g‐MAH. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Single‐walled carbon nanotube/poly(methyl methacrylate) composites for electromagnetic interference shielding

Single‐walled carbon nanotube (SWNT)/poly(methyl methacrylate) (PMMA) composites were prepared using coagulation method. The electrical conductivity and the electromagnetic interference (EMI) shielding of SWNT/PMMA composites over the X‐band (8–12 GHz) and the microwave (200–2000 MHz) frequency range have been investigated. The electrical conductivity of composites increases with SWNT loading by 13 orders of magnitude, from 10^?15 to 10^?2 Ω^?1 cm^?1 with a percolation threshold of about 3 wt% SWNTs. The effect of the sample thickness on the shielding effectiveness has been studied, and correlated to the electrical conductivity of composites. The data suggest that SWNT/PMMA composites containing higher SWNT loading (above 10 wt%) be useful for EMI shielding and those with lower SWNT loading be useful for electrostatic charge dissipation. The dominant shielding mechanism of SWNT/PMMA composites was also discussed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Sonochemical synthesis of LaMnO3 nano-powder

We report the preparation of LaMnO₃ nanosized powder by the sonochemical process. Sodium dodecyl sulphate (SDS) was used as surfactant, to prevent agglomeration. The particle size obtained in this method was 19–55 nm. The phase formation temperature of LaMnO₃ was 700 °C which is lower than other conventional processes. So sonochemical process is cost effective and it is more acceptable considering its ease of preparation in comparison to other conventional processes. Powder synthesized was characterized by measuring crystallite size, specific surface area, morphology and by thermal analysis. The particle sizes of the powders were controlled by calcinations schedule. Narrow size distribution and core and shell structure of the prepared powder was revealed by transmission electron microscopy.     

Studies on dielectric relaxation and defect generation for reliability assessments in ultrathin high-k gate dielectrics on Ge

In this work, we present the results of dielectric relaxation and defect generation kinetics towards reliability assessments for Zr-based high-k gate dielectrics on p-Ge (1 0 0). Zirconium tetratert butoxide (ZTB) was used as an organometallic source for the deposition of ultra thin (∼14 nm) ZrO₂ films on p-Ge (1 0 0) substrates. It is observed that the presence of an ultra thin lossy GeO_x interfacial layer between the deposited high-k film and the substrate, results in frequency dependent capacitance-voltage (C-V) characteristics and a high interface state density (∼10¹² cm⁻² eV⁻¹). Use of nitrogen engineering to convert the lossy GeO_x interfacial layer to its oxynitride is found to improve the electrical properties. Magnetic resonance studies have been performed to study the chemical nature of electrically active defects responsible for trapping and reliability concerns in high-k/Ge systems. The effect of transient response and dielectric relaxation in nitridation processes has been investigated under high voltage pulse stressing. The stress-induced trap charge density and its spatial distribution are reported. Charge trapping/detrapping of stacked layers under dynamic current stresses was studied under different fluences (−10 mA cm⁻² to −50 mA cm⁻²). Charge trapping characteristics of MIS structures (Al/ZrO₂/GeO_x/Ge and Al/ZrO₂/GeO_xN_y/Ge) have been investigated by applying pulsed unipolar (peak value - 10 V) stress having 50% duty-cycle square voltage wave (1 Hz-10 kHz) to the gate electrode.     

CMOS performance enhancement in Hybrid Orientation Technologies

Possible MOSFET performance enhancement by combining the hybrid-orientation technology (HOT) and process-induced local strain engineering is predicted for sub-45-nm CMOS technology nodes via technology CAD (TCAD) simulation. Mobility enhancements are modeled for both the hybrid orientation and process-induced local strain in CMOS technologies and are used in simulation. RF performance is investigated in detail and peak cutoff frequency, f _T of 524 GHz for n-MOSFETs and 239 GHz for p-MOSFETs are predicted from simulation.