Thermomechanical modelling of laser surface glazing for H13 tool steel

A two-dimensional thermomechanical finite element (FE) model of laser surface glazing (LSG) has been developed for H13 tool steel. The direct coupling technique of ANSYS 17.2 (APDL) has been utilised to solve the transient thermomechanical process. A H13 tool steel cylindrical cross-section has been modelled for laser power 200 W and 300 W at constant 0.2 mm beam width and 0.15 ms residence time. The model can predict temperature distribution, stress–strain increments in elastic and plastic region with time and space. The crack formation tendency also can be assumed by analysing the von Mises stress in the heat-concentrated zone. Isotropic and kinematic hardening models have been applied separately to predict the after-yield phenomena. At 200 W laser power, the peak surface temperature achieved is 1520 K which is below the melting point (1727 K) of H13 tool steel. For laser power 300 W, the peak surface temperature is 2523 K. Tensile residual stresses on surface have been found after cooling, which are in agreement with literature. Isotropic model shows higher residual stress that increases with laser power. Conversely, kinematic model gives lower residual stress which decreases with laser power. Therefore, both plasticity models could work in LSG for H13 tool steel

Quantum Smoluchowski equation: Escape from a metastable state

We develop a quantum Smoluchowski equation in terms of a true probability distribution function to describe quantum Brownian motion in configuration space in large friction limit at arbitrary temperature and derive the rate of barrier crossing and tunneling within an unified scheme. The present treatment is independent of path integral formalism and is based on canonical quantization procedure.Comment: 10 pages, To appear in the Proceedings of Statphys - Kolkata I

Finite element modelling of creep deformation in fibre-reinforced ceramic composites

The tensile creep and creep-recovery behaviour of a unidirectional SiC fibre-Si 3 N 4 matrix composite was analysed using finite element techniques. The analysis, based on the elastic and creep properties of each constituent, considered the influence of fibre-matrix bonding and processing-related residual stresses on creep and creep-recovery behaviour. Both two- and three-dimensional finite element models were used. Although both analyses predicted similar overall creep rates, three-dimensional stress analysis was required to obtain detailed information about the stress state in the vicinity of the fibre-matrix interface. The results of the analysis indicate that the tensile radial stress, which develops in the vicinity of the fibre-matrix interface after processing, rapidly decreases during the initial stages of creep. Both the predicted and experimental results for the composite show that 50% of the total creep strain which accumulated after 200 h at a stress of 200 MPa and temperature of 1200°C is recovered within 25 h of unloading.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44717/1/10853_2004_Article_BF00576283.pd

Am J Prev Med

CC999999/Intramural CDC HHS/United States2017-02-19T00:00:00Z26456878PMC531651

A new efficient catalytic system for the chemoselective cobalt-catalyzed cross-coupling of aryl Grignard reagents with primary and secondary alkyl bromides

1 - ArticleThe cobalt-catalyzed alkylation of aromatic Grignard reagents is performed in good yields by using a new simple and efficient catalytic system: CoCl2/TMEDA (1:1). Primary and secondary cyclic or acyclic alkyl bromides were used successfully. The reaction is highly chemoselective since ester, amide, and keto groups are tolerated. The procedure is inexpensive and very easy to carry out on a larger scale

Multiscale modelling of plastic deformation

In order to describe the plastic behavior of crystalline materials containing structural heterogeneities and/or under complex loadings, a new non local method that incorporates both dislocation properties and a rigorous treatment of boundary value problems is proposed. This new computer model makes use of a coupling between two different types of three-dimensional simulations : a Finite Elements code and a simulation of dislocation dynamics at the mesoscopic scale. The simulation technique is briefly presented and is illustrated by preliminary tests on the plastic deformation of copper single crystals at small strains

Cobalt-catalyzed cross-coupling reaction between functionalized primary and secondary alkyl halides and aliphatic Grignard reagents

1 - ArticleThe coupling of primary and secondary unactivated alkyl bromides with alkyl-Grignard reagents was performed in good yields under mild conditions by using a new catalytic system: consisting of cobalt chloride and tetramethylethylenediarnine (COCl(2 center dot)2LiI, 4TMEDA). The reaction is very chemoselective since ketone, ester and nitrile functions are tolerated