RDX and HMX with Reduced Sensitivity Towards Shock Initiation–RS‐RDX and RS‐HMX

Reduced Sensitivity RDX (RS‐RDX) has received a lot of attention and interest from the explosive community in the recent years. There are several producers of RS‐RDX, most of them using a direct nitration (Woolwich process) for the RDX synthesis, while Chemring Nobel uses the Bachmann process. The processes for obtaining the RS properties probably differ between the various producers. Chemring Nobel has also developed an HMX quality that shows Reduced Sensitivity (RS‐HMX) of different particle size distributions. The shock sensitivity is at the same level as for RS‐RDX in comparable compositions. Reduced shock sensitivity has been obtained for RS‐RDX and Reduced Sensitivity (RS‐HMX) in both pressable and cast‐cured compositions. By using a pressable composition, it is possible to get the results from a BICT gap test faster than from a cast‐cured composition that has to go through a curing process. Chemring Nobel in cooperation with FFI have performed an extensive accelerated ageing testing of RS‐RDX produced by the Bachmann process. The samples have been aged at 60 and 70 °C and the shock sensitivity tested by two different gap tests. The results demonstrate that the Chemring Nobel RS‐RDX retain the insensitivity towards shock during ageing and show no degradation at all. Accelerated ageing testing of RS‐HMX has also been performed and shows no degradation in the shock sensitivity.     

Algorithms for the car sequencing and the level scheduling problem

This paper deals with two most important problems arising in sequencing mixed-model assembly lines. One problem is to keep the line's workstations loads as constant as possible (the 'car sequencing problem') while the other is to keep the usage rate of all parts fed into the final assembly as constant as possible (the 'level scheduling problem'). The first problem is a difficult constraint-satisfaction problem while the second requires to optimize a nonlinear objective function. The contribution of this paper is twofold: First, we describe a branching scheme and bounding algorithms for the computation of feasible sequences for the car sequencing problem. Second, we present an algorithm which can optimize a level scheduling objective while taking care of the car sequencing constraints. Computational results are presented which show that feasible sequences can be obtained quickly for large problem instances.     

An effective numerical stress intensity factor calculation with no crack discretization

An effective numerical procedure for calculating stress intensity factors (SIF) in plane problems based on a modified boundary element technique not requiring any crack discretization was proposed by Snyder [1]. Instead of the usual fundamental solution, he used Green's function for the problem of a traction-free central crack in an anisotropic plate.In the first part of the present paper, the corresponding Green's function for the isotropic problem, not explicitly included in [1], is presented. In addition to the central crack, a semi-infinite edge crack is considered. Both Green's functions are given for the case of the anti-plane state of strain as well. In the first step of the proposed procedure, the tractions and displacements along the outer boundary are calculated. In the second step, the SIF for modes I, II and III are derived in terms of simple boundary integrals over quantities known from the previous step. Contrary to Snyder's derivation, the determination of the SIF is based on the asymptotic displacement field at the crack tip. The method can easily be extended to multiple crack problems by using the subregion technique. Some illustrative examples demonstrate the effectiveness of the method.

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Résumé Snyder a proposé une procédure numérique pour le calcul des facteurs et intensité de contraintes dans les problèmes plans, en se basant sur une modification de la technique des éléments aux limites ne requérant pas de discrétisation de la fissure. Au lieu d'une solution fondamentale habituelle, il a utilisé une fonction de Green pour traiter le problème d'une fissure centrale libre de contraintes dans un plaque anisotrope.Dans la première partie de la présente étude, on présente la fonction de Green qui correspond à un problème isotrope, qui n'était pas explicitement couvert par le travail de Snyder. Outre le cas de la fissure centrale, on considère le cas de la fissure de bord dans un milieu semi-infini. Les deux fonctions de Green relatives au cas d'un état de déformation antiplanaire sont également communiquées. Dans une première étape de la procédure proposée, on calcule les sollicitations et déplacements le long du contour extérieur; dans une deuxième étape, on établit les facteurs d'intensité de contraintes relatifs aux modes I, II et III en terms d'intégrals sur un contour simple défini par les valeurs résultant de l'étape précédente. Contraitement à l'approche de Snyder, on détermine le facteur d'intensité des contraintes sur base du champs de déplacement asymptotique à l'extrémité de la fissure. Par la technique des sous-régions, on peut aisément étendre la méthode à des problèmes de fissuration multiples. L'efficacité de la méthode est illustrée par divers exemples.

     

Fourier expansion as an aid in the solution of the diffusion equation for three-dimensional power distributions in water reactors

The problem of predicting axial power peaking factors in water moderated reactors is not adequately solved by so called coarse mesh methods for the solution of the neutron diffusion equation. The Fourier Expansion method, briefly described, gives an essentially continuous representation of axial power shapes and therefor a higher precision in the peaking factors.—It does this with a precision equivalent to fine mesh 3D methods. Yet, it is shown to require a factor 5–10 less numerical work than fine mesh.Applications to 3D core power calculations for different types of water reactor (the HWR, BWR and PWR) are illustrated by a range of measured and calculated axial power distributions. These applications have been collected from 10 years of experience with the method. The comparisons show that the Fourier Expansion method is well suited to LWR applications.     

Correction of validity coefficients for direct restriction in range occasioned by univariate selection.

Frequently, in evaluating a selection instrument, criterion data are available only for those applicants selected. Validities computed on the selectees are reduced by restriction in range and do not reflect the actual utility of the predictors. K. Pearson's (1903) correction for direct restriction in range uses the restricted validity (computed in the selectee group) and the predictor standard deviations in the unrestricted and the restricted groups. Often, the applicant group predictor standard deviation is not available. However, the practitioner may know, or be able to estimate, the selection ratio. An equation and a table for estimating the unrestricted validity from the restricted validity and the selection ratio are provided. (5 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A Neural Approach for the Control of Piezoelectric Micromanipulation Robots

Micromanipulation has become an issue of primary importance in industry and biomedicine, since human manual capabilities are restricted to certain tolerances. The manipulation of biological cells or the assembly of a complete microsystem composed of different microcomponents are examples of the application of piezoelectric-driven microrobots. An automated microrobot-based micromanipulation desktop-station is developed by an interdisciplinary group at the University of Karlsruhe. The process of assembly takes place in the field of view of a light optical microscope. This paper focuses on motion control problems of the microrobots. The ability of an intelligent microsystem to adapt itself to the process requirements is of great importance, especially for assembly robots. The microrobots must be able to operate in a partially defined environment and to ensure reasonable behaviour in unpredicted situations. A neural control concept based on a reference model approach is proposed as a solution. It is shown, that the neural controller is able to learn the desired behaviour. It considerably outperforms an analytically designed linear controller. This is demonstrated both in simulation and in the real environment.