Finite element computation of the strain energy release rate for kinking of a crack

The approximate energy release rate for a crack which extends, or kinks, away from its original direction has been computed by finite element analysis using three different methods: stiffness derivative procedure, J integral method and crack closure integral procedure. A case study is presented to compare the computational accuracies. It suggests that a satisfactory approximation can be obtained provided that the ratio of kink length to original crack length, l(0)/a0.04, despite the interaction of the crack tip and knee stress singularities.

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Résumé En utilisant trois méthodes différentes (dérivation de la raideur, intégrale J et intégrale de fermeture de la fissure), on a calculé par éléments finis la vitesse approchée de relaxation de l'energie dans le cas d'une fissure qui diverge ou qui part en arborescence par rapport à sa direction initiale.On présente une étude de cas de manière à comparer les précisions respectives obtenus dans les calculs.Cette étude suggère qu'une approximation satisfaisante peut être obtenue, pour autant que le rapport de la longueur déviée à la longueur initiale de la fissure soit inférieure ou égale à 0,04, en dépit de l'interaction entre l'extrémité de la fissure et la singularité de la contrainte.

     

Designing linear distributed algorithms with memory for fast convergence

Motivated by both distributed computation and decentralized control applications, we studied the distributed linear iterative algorithms with memory. Specifically, we showed that the system of linear equations G x = b can be solved through a distributed linear iteration for arbitrary invertible G using only a single memory element at each processor. Further, we demonstrated that the memoried distributed algorithm can be designed to achieve much faster convergence than a memoryless distributed algorithm. Two small simulation examples were included to illustrate the results. Copyright © 2011 John Wiley & Sons, Ltd.     

Prediction of mode I fracture toughness of unidirectional fibre composites with arbitrary crack fibre orientation from its lowest or matrix fracture tougness

Corrigendum

Prediction of mode I fracture toughness of unidirectional fibre composites with arbitrary crack fibre orientation from its lowest or matrix fracture tougnessby P.K. Sarkar and S.K. Maiti     

Glass formation region and lithium ion conduction in the oxyfluorophosphate glasses

Oxyfluorophosphate glasses containing about 80 mol% of [LiF+Li₂O] show unusually high lithium ion conductivity at elevated temperatures. A detailed investigation has been carried out on the glasses prepared by both conventional cooling and a rapid quenching technique. Chemical analysis of the glasses reveals fluorine loss during melting and it becomes difficult to make glasses with exact predetermined compositions. Electrical conductivity of the glasses, determined from complex impedance analysis increases with Li₂O content. A glass with nominal composition 70 LiF15 Li₂O15 Al(PO₃)₃ shows the highest conductivity (~ 1.3×10^–3 ohm^–1 cm^–1 around 200° C) among all the compositions studied. An interesting feature of the impedance plot is the near perfect semicircle for bulk relaxation indicating a narrow distribution of relaxation times. This has been explained on the basis of a relatively small proportion of lithium ions which are mobile. The electrical conductivity of the glasses is found to be essentailly independent of dissolved water content. The infrared spectra of these glasses (2 to 50m region) could not produce much useful structural information.     

Cover Feature: Superior Proton-Transfer Catalytic Promiscuity of Cytochrome c in Self-Organized Media (7/2021)

Evolutionarily elderly proteins commonly feature greater catalytic promiscuity. Cytochrome c is among the first set of proteins in evolution to have known prospects in electron transport and peroxidative properties. Here, we report that cyt c is also a proficient proton-transfer catalyst and enhances the Kemp elimination (KE; model reaction to show proton transfer catalytic property) by ∼750-fold on self-organized systems like micelles and vesicles. The self-organized systems mimic the mitochondrial environment in vitro for cyt c. Using an array of biophysical and biochemical mutational assays, both acid–base and redox mechanistic pathways have been explored. The histidine moiety close to hemin group (His18) is mainly responsible for proton abstraction to promote the concerted E2 pathway for KE catalysis when cyt c is in its oxidized form; this has also been confirmed by a H18A mutant of cyt c. However, the redox pathway is predominant under reducing conditions in the presence of dithiothreitol over the pH range 6–7.4. Interestingly, we found almost 750-fold enhanced KE catalysis by cyt c compared to aqueous buffer. Overall, in addition to providing mechanistic insights, the data reveal an unprecedented catalytic property of cyt c that could be of high importance in an evolutionary perspective considering its role in delineating the phylogenic tree and also towards generating programmable designer biocatalysts.     

Cement mortar impregnated with poly(methyl methacrylate-co-styrene)

Polymer-impregnated mortars were prepared by copolymerization of a monomer mixture of methyl methacrylate and styrene in the ratios of 13:87 and 40:60 using Co-60 gamma radiation. The copolymerization characteristics viz. the rate of polymerization, the extent of monomer loss, polymer loading, etc., were studied. The nature and molecular weight of the extractable polymer from the composite were determined. The flexural strength of the copolymer-impregnated composites was found to be better than that of the composites impregnated with component homopolymers.     

New block copolymers II. Synthesis and characterization of an ABA-type block copolymer

A new regular ABA-type triblock copolymer has been synthesized by polycondensation of the acid chloride of carboxy-terminated butadience-acrylonitrile rubber (CTBN) with hydroxyterminated polyethylene isophthalate (PEI) oligomer. This block copolymer was characterized by elemental (nitrogen) analysis, vapor pressure osmometry, viscometry, and IR and NMR spectroscopy. Quantitative estimation of block segments has been carried out by measuring the area under peaks assigned to various protons in the NMR spectrum of the polymer. NMR spectral analysis has been found to agree well with the nitrogen analysis of the polymer. The solubility and solution viscosity behavior of the polymer has also been studied.     

Structural development in cycloolefin copolymers under uniaxial elongational flow

Development of structures in new cycloolefin copolymers (COCs) of ethylene–norbornene (E–NB) and ethylene–tetracyclododecene (E–TD) of different NB/TD compositions were investigated under uniaxial elongational flow. For E–NB copolymer, which has multiblock sequences, a shoulder in WAXD at 0.76 nm was evident besides its amorphous halo, and the relative intensity of the peak increased with increasing comonomer content (NB). The appearance of a new peak for E–TD copolymer, and a relatively higher intense peak for E–NB copolymer at the same position of 0.76 nm, indicated that local ordering of the segments occurred when the COC was subjected to uniaxial flow. A lower comonomer composition of elongated COC, at a constant Hencky strain rate, exhibited two T_g values, whereas a higher composition showed a single T_g. Both local ordering and segmentization occurred in low comonomer content COCs but only local ordering occurred in higher comonomer content COCs. Both the shear viscosity and roll processing experiments exhibited similar phenomena of segregation. A model is proposed to illustrate the structure of COC after uniaxial elongation/deformation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3421–3427, 2004     

Security concepts for the dynamics of autonomous vehicle networks

The secure operation of autonomous vehicle networks in the presence of adversarial observation is examined, in the context of a canonical double-integrator-network (DIN) model. Specifically, we study the ability of a sentient adversary to estimate the full network’s state, from noisy local measurements of vehicle motions. Algebraic, spectral, and graphical characterizations are provided, which indicate the critical role of the inter-vehicle communication topology and control scheme in achieving security.