A scheme for finite element analysis of mode I and mixed mode stable crack growth and a case study with AISI 4340 steel

A new scheme for elastic–plastic finite element analysis has been proposed for the study of stable crack growth (SCG) from initiation to instability in both mode I and mixed modes (I and II). The scheme is based on node-release technique and helps to determine the variation of fracture load with crack extension without requiring much computer storage and time. The scheme permits predictions of load variation with load line displacement (LLD), maximum fracture load, crack tip current plastic zone and crack edge profile. In the analysis the condition for crack extension at every stage of the SCG is considered to be governed by CTOA/COD reaching a critical value. The scheme of analysis is different from the ones proposed by earlier investigators. The whole SCG is analysed in a few stages using the ANSYS software and a single discretization. Element arrangement in the discretization is decided from the very beginning; it has a capability of accommodating changes in boundary conditions arising out of crack extension in the later stages. Each stage is analysed afresh ignoring state of stress–strain reached at a material point at the end of the previous stage. Case studies on both mode I and mixed mode presented considering AISI 4340 steel, which is widely used in nuclear power industry, indicate that the SCG through it can be characterized in terms of a single COD or CTOA. Predictions for the initiation and maximum fracture loads in both the cases compare very closely with the experimental data reported. The results presented also include the value of critical COD/CTOA (0.035 mm/0.0875 rad) characterizing the SCG through the steel and show that the initiation load is not significantly affected by crack tip radius up to 0.05 mm.     

Effect of CsBr–MnCl2 mixed fillers on the crystal structure and optical and electrical properties of poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA) films filled with (x)CsBr(15 ? x)MnCl₂, where 0.0 ≤ x ≤ 15%, were prepared by a casting technique. The crystal structure properties of the prepared films were examined by XRD, DTA, and FTIR. A correlation between XRD, DTA, and FTIR of the filled polymer was discussed. Optical absorption measurements revealed two optical band gaps (E_g1 and E_g2). The electrical properties were studied using dc electrical conductivity. The filling level (FL) dependency of E_g1 and E_g2, thermal activation energy (ΔE), and hopping distance (R₀) are given to illustrate the behavior of the filled polymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2178–2186, 2004     

Coupled Eulerian Lagrangian finite element modeling of friction stir welding processes

A 3-dimensional localized finite element model (FEM) is developed to predict likely conditions that result in defect generation during friction stir welding (FSW). The workpiece is modeled using Eulerian formulation, while the tool is modeled using Lagrangian. Coulomb's frictional contact model is adopted to define the tool workpiece interaction, while the welding speed is defined by material inflow and outflow velocities. The numerical results show that the coefficient of friction has a major effect on void formation; the lower the friction coefficient is applied, the larger the void is formed. Furthermore, welding using force control (FC) at lower welding speed results in smaller void size and wider plastic zone, leading to higher quality weld.     

Performance of Low Earth Orbit Satellite Systems with Coding

The effect of block, convolutional and Turbo coding on the probability of error and the capacity are investigated for CDMA Low Earth Orbit (LEO) Satellite systems. The model employed assumes a contaminated Gaussian traffic model to be more compatible with different population areas. The conventional Gaussian distribution can be considered as a special case.     

A framework for the characterization and verification of embedded phase-locked loops

With the increasing use of phase-locked loops (PLLs) embedded in FPGAs, ASICs, and system-on-chip (SOC), there is a growing need for methods to verify their operation. This paper describes a general and organized list that includes tests for lock, jitter, stability, and modulation response. The list is offered as a guide to the verification and testing of an embedded PLL. For that reason, it is presented in such a way as to allow the reader to determine the extent to which the verification will be carried out. The tests are covered from the easiest to the most complicated to perform, with the amount of information gathered increasing along with the complexity of the test.     

A new alternative method to evaluate the J-integral in the case of elastomers

This study concerns the fracture of rubbers. The objective is to verify the validity of the J-integral expression we proposed for such materials (Aït Hocine et al., 2002). In this expression, the parameter J is represented as a multiplicative form of a geometrical η^* (or η) factor and elastic work per unit area as it has been already done in the Linear Elastic Fracture Mechanics (LEFM) (Turner, 1973). The whole problem rests in the fact that the factor η^* (or η) is unknown whereas in LEFM, expressions of η_el factors are available for several kinds of specimen geometry. Thus, in this work, an experimental and a numerical analysis have been achieved and we have shown, for both the studied materials and the considered specimens, that these unknown factors could be replaced by those issued from the LEFM or from the work of Kim and Joe (1989) on rubber-like materials. The results obtained confirm the validity of our model representing a single specimen method of an experimental evaluation of the elastomers fracture energy.     

Stability and calibration of platinum/palladium thermocouples following heat treatment

In this paper we describe the changes in the thermo EMF of Pt/Pd thermocouples in the temperature range from 0 to 1100 °C following a series of heat treatment at 960 °C. The magnitudes of the changes in EMF, the short and long term stability of the thermocouple were estimated, experimental results are presented. For the calibration of the thermocouple we have employed a reference polynomial function given in the literature [Metrologia 35 (1998) 761] for Pt/Pd thermocouples based on the International Temperature Scale of 1990 (ITS-90).     

Influence of state of stress on mixed mode stable crack growth through D16AT aluminium alloy

The stable crack growth through three-point bend (TPB) and stiffened and unstiffened compact tension (CT) specimens of D16AT aluminium alloy has been studied both theoretically and experimentally. The specimen thickness is 8 mm. The variation of load with crack opening displacement, the extent of stable crack growth, the cumulative plastically deformed zone and crack edge profiles have been obtained experimentally. These are also predicted theoretically under the assumption of either a state of plane stress or plane strain using a finite element scheme and the COA criterion. Generally, the experimental results agree well with the predictions based on the plane stress condition. There appears to be no significant variation in size of the experimental cumulative plastic zone across the specimen thickness, thereby indicating that the constraint on the plastic zone does not develop near the mid-thickness region.     

Synthesis and characterization of cellulose triacetate and poly(ethylene imine) membranes containing a polyether macrobicyclic: Their application to the separation of copper(II) and silver(I) ions

A cellulose triacetate (CTA)–poly(ethylene imine) (PEI) membrane containing a polyether macrobicyclic (cryptand) as a carrier and 2‐nitrophenyloctyl ether (NPOE) as a plasticizer was prepared. The CTA–PEI–cryptand–NPOE membrane was characterized with chemical techniques as well as Fourier transform infrared, X‐ray diffraction, differential scanning calorimetry, and scanning electron microscopy. The permeation of silver and copper ions through the CTA–PEI–cryptand–NPOE membrane was comparable to that through a supported liquid membrane. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1401–1410, 2004     

A Dempster–Shafer Based Tit-for-Tat Strategy to Regulate the Cooperation in VANET Using QoS-OLSR Protocol

In this paper, we address the problem of cooperation among vehicles in VANET using QoS-OLSR protocol in the presence of selfish nodes. QoS-OLSR is a proactive protocol that considers the Quality of Service (QoS) of the nodes while electing the cluster-heads and selecting the Multi-Point Relay (MPRs) nodes. Cluster-heads and MPRs might misbehave on the roads by over-speeding or under-speeding. Classical and generous Tit-for-Tats are proposed to analyze the interaction among vehicles. However, both strategies are not able to enforce the cooperation due the fact that they (1) count on individual watchdogs monitoring, (2) rely on the node-to-node cooperation decision, (3) and ignore the high mobility and packet collisions. Therefore, we propose a Dempster–Shafer based Tit-for-Tat strategy that is able to improve the decision and regulate the cooperation in the vehicular network. This is done by (1) launching a cooperative watchdogs monitoring, (2) correlating the observations of the different watchdogs using Dempster–Shafer theory, and (3) propagating the decisions among clusters. Thereafter, we compare the Dempster–Shafer based strategy with several strategies derived from the original Tit-for-Tat. Simulation results prove that the Dempster–Shafer based strategy is able to maintain the survivability of the vehicular network in the presence of high mobility and packet collisions with minimal time and overhead.