Strength Degradation of Soda-Lime-Silica Glass During Dynamic Loading

The strength degradation of soda-lime-silica glass during dynamic loading was studied by using a fracture-mechanics approach. The theoretical and experimental results indicate that subcritical flaw growth during loading causes the strength degradation.     

THE ROLE OF PRIOR AUSTENITE GRAINS IN FATIGUE CRACK INITIATION AND PROPAGATION IN LOW CARBON MARTENSITE

Abstract— A study has been made of the role of Prior Austenite Grains (PAG) in fatigue crack initiation and propagation in low carbon martensite. The occurrence of ferrite precipitation along prior austenite grain boundaries during rapid cooling will lead to the formation of intergranular cracking. This intergranular cracking has a close relationship with the reduction of the endurance limit for fine grained low carbon martensite.     

Controllability and the theory of economic policy: a structural approach

Tinbergen's policy rule states that we must have at least as many policy instruments as the number of target variables if we wish to realize an arbitrarily fixed set of policy targets. We explore the structural characterization of the controllability of economic systems described by a set of static or dynamic equations. First, an economic system is represented as a directed graph, where the nodes stand for economic variables, while the arcs indicate the relations among these variables. Then, the main result is as follows: a static economic system is structurally controllable if and only if there exists a set of disjoint paths on the graph representation or the system which connect the set of instruments to each target. Similar graph-theoretic characterization of structural controllability is obtained for dynamic systems. Conditions for structural output controllability and structural perfect controllability are also discussed.     

Performance evaluation of marked graphs by linear programming

Performance evaluation is an important issue for discrete event dynamic systems, which in many cases can be described in terms of the language of Petri nets. In particular, for marked graphs, a subclass of Petri nets, a formula for performance evaluation is widely known. That is, the ratio of the total execution time to the number of tokens in a cycle gives a lower bound for the cycle time of the system, and the maximum of these ratios over all cycles determines the overall system performance. However, we need to enumerate all directed cycles in a graph to apply this formula of performance evaluation. Carrying out this enumeration for an actual system is often impractical, since the number of cycles in a graph usually grows exponentially with the size of a system. We give a linear algebraic characterization for directed cycles, and based on this result, transform the problem of performance evaluation into a simple linear programming problem. A few explanatory examples are also given.     

DISPERSION STATE OF PROTEIN-STABILIZED EMULSIONS Dependence of Globule Size and Size Distribution upon pH in Concentrated Oil-in-Water Systems

Concentrated benzene-in-water emulsions were prepared with various proteins such as lysozyme, bovine serum albumin, ovalbumin, casein and gluten. The emulsions consisted of coarse globules whose size distribution could be approximated to the log-normal distribution function, while the adsorbed film of protein molecules seemed to contribute to the stabilization of the globules. These properties were influenced by the pH of the aqueous phase. The mean globule size increased progressively up to the isoelectric point of the proteins. Both the interfacial tension and the rate of coalescence between the globules were minimized as the isoelectric point of the proteins was approached.     

STRESS-RATIO EFFECT OF FATIGUE CRACK PROPAGATION IN A BIAXIAL STRESS FIELD

Fatigue crack propagation tests were conducted under conditions of equibiaxial, uniaxial and shear loading by using a cruciform specimen in a servo hydraulic testing machine. The effect of non-singular stress cycling on the fatigue crack propagation rate was examined based on the observation of crack opening behavior. The crack propagation rate was significantly influenced by the non-singular stress parallel to the crack when it was correlated to the stress intensity range. The crack closure behavior was greatly affected by the non-singular stress. The crack propagation rate was uniquely correlated to the effective range of the stress intensity factor except for the case of completely reversed shear loading where significant plasticity was detected. The crack opening displacement range was concluded to be a parameter controlling the crack propagation rate for all the stress conditions examined in the present experiments. Some discussion is made on the effect of material anisotropy on fatigue crack propagation in a biaxial stress field.     

Preparation of Submicrometer A12O3 Powder by Gas-Phase Oxidation of Tris (acetylacetonato) aluminum (111)

Fine A1₂O₃ powder was prepared by the gas-phase oxidation of aluminum acetyl-acetonate. The reaction products were amorphous material at 600° and 800°C, γ-Al₂O₃ at 1000° and 1200°C, and δ-Al₂O₃ at 1400°C. The powders consisted of spherical particles from 10 to 80 nm in diameter; particle size increased with increasing reaction temperature and concentration of chelate in the gas.