Autoprogressive training of neural network constitutive models

A new method, termed autoprogressive training, for training neural networks to learn complex stress–strain behaviour of materials using global load–deflection response measured in a structural test is described. The richness of the constitutive information that is generally implicitly contained in the results of structural tests may in many cases make it possible to train a neural network material model from only a small number of such tests, thus overcoming one of the perceived limitations of a neural network approach to modelling of material behaviour; namely, that a voluminous amount of material test data is required. The method uses the partially-trained neural network in a central way in an iterative non-linear finite element analysis of the test specimen in order to extract approximate, but gradually improving, stress–strain information with which to train the neural network. An example is presented in which a simple neural network constitutive model of a T300/976 graphite/epoxy unidirectional lamina is trained, using the load–deflection response recorded during a destructive compressive test of a [(±45)₆]_S laminated structural plate containing an open hole. The results of a subsequent forward analysis are also presented, in which the trained material model is used to simulate the response of a compressively loaded [(±30)₆]_S structural laminate containing an open hole. Avenues for further improvement of the neural network model are also suggested. The proposed autoprogressive algorithm appears to have wide application in the general area of Non-Destructive Evaluation (NDE) and damage detection. Most NDE experiments can be viewed as structural tests and the proposed methodology can be used to determine certain damage indices, similar to the way in which constitutive models are determined. © 1998 John Wiley & Sons, Ltd.     

Chemical contribution of oxygen to silicon carbide plasma etching kinetics in a distributed electron cyclotron resonance (DECR) reactor

This paper deals with the influence of the oxygen additive on the fluorinated plasma etch rate of silicon carbide. The assumption according to which the oxygen has a direct contribution to silicon carbide etching, by chemical reaction with carbon atoms, is generally reported in the literature. Our etching experiments are performed in a distributed electron cyclotron resonance reactor, on both 3C- and 6H-SiC. An SF₆/O₂ gas mixture (avoiding the presence of C species in the plasma), fluorine saturation conditions and constant ion bombardment energy and flux are used, allowing the study of O₂ contribution exclusively. In these conditions, our results demonstrate the neutrality of O₂ on SiC etching mechanisms. These results will be discussed reinfored both by several other experimental observations.     

ANALYSIS OF HEAT AND MASS TRANSFER DURING COMBINED MICROWAVE CONVECTIVE SPOUTED-BED DRYING

Heat and mass transfer phenomena during the combined microwave-convective batch spouted bed drying are analyzed. Wheat was chosen as a test material. The governing equations, including consideration of internal heat generation and thermodiffusion are formulated and solved using the numerical method of lines. The model allowed variable material transport and dielectric properties. The parameters investigated include electric field strength, electromagnetic field frequency, inlet air temperature, and superficial air velocity. Representative drying and temperature curves as well as moisture and temperature profiles are presented and discussed.     

Aromatic polyamide–imides as materials for membranes. I. Synthesis and characterization

Diamine amic acids were synthesized by reacting aromatic diamines with pyromellitic dianhydride in dimethylacetamide/dioxane. High molecular weight polyamide-amic acids were prepared by low-temperature solution polymerization of diamine amic acids with isophthaloyl chloride in dimethylacetamide. The cyclodehydration of polyamide-amic acids to the corresponding polyamide–imides was accomplished by heating the cast films at 175°C for 3 h. The polyamide–imides were soluble in polar aprotic solvents like dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone and could be cast into tough and flexible films. They were characterized by elemental analyses, inherent viscosities, IR, and ¹H-NMR spectra. The glass transition temperatures of polyamide–imides were determined by differential scanning calorimetry. The thermal stabilities of the polymers were measured by thermogravimetric analyses in air. © 1995 John Wiley & Sons, Inc.     

Electronic and electrochemical properties of cationic complexes [Fe(R-Sal)2Trien] in solution: Evidence of formation of phenoxyl radicals upon oxidation

Electronic and electrochemical properties of four ferric [Fe(R-Sal)₂Trien]⁺ complexes with R = 5-OMe, 5-Cl, 5-Br and 3,5-Cl₂ were studied. The occurrence of thermally-induced spin equilibria in solution was demonstrated by optical spectroscopy. Electrochemical properties of these complexes revealed interesting behaviour in oxidation, and the formation of phenoxyl radicals within these compounds was evidenced by spectro-electrolysis.     

Degradation of Interfacial Chemistry of Epoxy/Silane/Aluminium Interfaces as a Result of Aqueous Attack

The degradation of a thin layer of adhesive on a grit-blasted aluminium substrate, as a result of aqueous attack, was investigated and compared with the behavior of the adhesive on a grit-blasted aluminium substrate treated with γ-glycidoxypropyl trimethoxy silane (GPS). The degradation study was achieved by examining aluminium coupons treated with adhesive that had been immersed in water at 25°C and an elevated temperature (50°C) for various treatment times ranging between 10 min and 1 day. All samples were characterized using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS and ToF-SIMS data indicated that the adhesive layer on both types of substrate was readily displaced by water. This is shown to be a two-stage process with bond rupture being identified by ToF-SIMS analysis and the displacement of the organic phase occurring at a later stage, as indicated by the XPS analysis, which showed a reduction in surface carbon concentration. When the substrates were directly in contact with water, a hydration process occurred and hydrated oxide species were formed on the surfaces. The results indicated that the hydration process was a postfailure event.     

Mechanical Behavior of a Triaxial Woven Fabric Composite

The results of an experimental and finite-element investigation on a single-ply triaxial woven fabric composite loaded in tension are presented. The fabric is made of graphite yarns oriented in the 0 degrees and plus/minus 60 degrees directions and a thermoset resin. It is used by EMS Technologies Canada Ltd. for the manufacturing of super-lightweight spaceborne antenna reflectors. Two types of tensile test specimens were evaluated, straight and dog-bone, as well as three methods for bonding the strain gauges to the specimen. The effects of the specimen shape and bonding methods were evaluated. A finite-element model was developed to predict the behavior of the specimen under tensile conditions. The measured data provide information on the elastic properties and ultimate strength of the composite when subjected to loads acting either along the axial yarns or perpendicular to them.     

Attachment styles and fear of personal death: A case study of affect regulation.

The relation between attachment styles and fear of personal death was assessed. We classified a sample of Israeli undergraduate students into secure, ambivalent, and avoidant attachment groups and assessed the extent of, and the meaning attached to, overt fear of personal death as well as the extent of fear at a low level of awareness. Ambivalent subjects exhibited stronger overt fear of death than did secure and avoidant subjects, and both ambivalent and avoidant subjects showed stronger fear of death at a low level of awareness than secure subjects. Ambivalent subjects were also more likely to fear the loss of their social identity in death, and avoidant subjects were more likely to fear the unknown nature of their death. Results are discussed in terms of the effects of attachment styles on affect regulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)