Mechanical properties of ferrous alloys after fast neutron-irradiation at high temperature

The results are given of an international “round-robin” experiment to study the nature of the damage structure in neutron irradiated zirconium and zircaloy-2 using transmission electron microscopy. The damage structure consists entirely of $\text{1}\text{3}\text{α<11}\text{2}\text{?}\text{0>}$ dislocation loops and no evidence has been found for c-component loops. Both vacancy and interstitial loops were found in specimens irradiated at 400 °C, with an excess of vacancy loops. Quantitative measurements of loop size distributions and loop concentrations are reported. All specimens exhibited “corduroy” contrast to varying degrees. The importance of choice of imaging conditions to minimize the contrast from thin foil artefacts such as oxide films and surface hydrides is stressed. The significance of the results is briefly discussed with reference to current theories of irradiation growth.     

Introduction of a biochemical allosteric property for creating a new electronic signal transmission system under the time-minimum optimization

We introduce and allosteric property of enzymes on biological membranes to create a new electronic signal transmission system. In the allosteric enzymes, sequential binding of substrates, activators, and inhibitors induces molecular conformational changes in subunits of the inactive allosteric enzymes. By this binding, the enzyme is partially activated. Successive binding of the substrates accelerates the structural change in the subunits and activates the enzyme progressively. Based on reported biological experimental data, we expressed the complicated activation and inactivation processes of the allosteric enzyme reaction system by 20 rate equations. We proposed a time-minimum optimal control strategy for the allosteric reaction system as a dominating principle. This is because the biochemical, signals have to be transmitted as quickly as possible to achieve their purpose, particularly for life-saving defense, reactions to harmful exogenous disturbances. The present mathematical model describes the complicated sequential, information transmission processes of the biochemical reactions. We can show that the allosteric effect had a marked influence on species conversion. With the increases in allosteric parameters, the concentrations of all species changed more rapidly and in larger amounts than they did at the standard allosteric parameter values. This meant that increasing the allosteric activity of the subunit accelerates the reactions and enhances the reactive production. Hence, the allosteric property is important for high-speed, extensive signal transmission among the components that constitute a complicated network circuit. This property, when it is linked with the time-optimal controller, will create a new signal transmission device. This work was presented, in part, at the Fourth International Symposium on Artificial Life and Robotics, Oita, Japan, January 19–22, 1999.     

Study of local oxidative degradation in polypropylene impact copolymer by energy dispersive X-ray system

Summary In this study, the thermal oxidative degradation of a polypropylene (PP) impact copolymer was examined using a transmission electron microscope equipped with an energy dispersive X-ray system (TEM/EDX). The oxidative behavior was visually captured by oxygen line analysis. The oxidation resistance of the ethylene-propylene rubber (EPR) phase was considerably higher than that of the PP matrix, indicating that the degradation behavior of the PP impact copolymer was heterogeneous. It was found that the higher resistance of the EPR phase originated from its primary structure by ¹³C-NMR measurement.     

Proposal of a method to analyze 3D deformation/fracture characteristics inside materials based on a stratified matching approach

In the past, deformation/fracture (D/F) characteristics, defined as load-deformation relationships until the materials are fractured, have been analyzed and evaluated on the surface. The D/F characteristics are affected by more than 10,000 micro-scale internal structures like air bubbles (pores), dispersed particles and cracks in 1 mm³; therefore, it is required to analyze nano-scale D/F characteristics inside materials. In this paper, we propose an analysis method by obtaining displacement vectors of dispersed particles from nano-order 3D-CT images. A problem of matching over 10,000 dispersed particles between deformation is solved by a stratified matching.     

Cavitation during high-temperature deformation in Al–Mg alloys

It has recently been revealed that high-density pre-existing hydrogen micropores, formed during production processes, exhibit premature growth and coalescence under external loading at room temperature, thereby inducing ductile fracture. This process is incidentally supplemented by the well-established ductile fracture mechanism based on particle damage. It is reasonable to assume that the pre-existing hydrogen micropores may also contribute to damage evolution at high temperatures. In the present study, synchrotron X-ray microtomography was applied to the in situ observation of deformation and fracture in Al–Mg alloys at a high temperature. High-density hydrogen micropores were observed in the alloys. Flow localization controlled deformation through the mechanism of solute drag creep. A combined effect of grain boundary sliding and heterogeneous nucleation on particles was also confirmed to accelerate the growth of pre-existing hydrogen micropores and cavities. Although continuous nucleation occurred together with the growth of pre-existing hydrogen micropores, the effects of the pre-existing hydrogen micropores, especially those located on grain boundaries, were predominant in the overall damage evolution. It seemed likely that supersaturated hydrogen in the aluminum alloys might also make an appreciable contribution to cavitation during high-temperature loading.     

Study on the Application of Kenaf Core as a Composite Reinforcement: Injection Molding of Kenaf Core/Poly(l-lactide) Compounds

Injection molding was performed using poly(l-lactide) (PLLA) as a matrix and by varying the reinforcements, i.e., dry-distilled kenaf core (D-core) or untreated kenaf bast fibers, and the physical properties for these composites were subsequently compared. The dry-distillation was able to reduce the moisture content of D-core by a maximum of 4.2% as compared with untreated control core. As a result, the hydrophobicity was increased, which contributed to favorable Charpy impact strength and tensile properties of the D-core/PLLA composite relative to the kenaf bast fiber/PLLA composite. Moreover, the puffing phenomenon, which arises when heating with a microwave oven due to the vaporization of water dispersed within the interfacial regions and associated softening of the PLLA matrix by the heated vapor, was completely suppressed for the D-core/PLLA composite, whereas a large puffing ratio was observed for the kenaf bast fiber/PLLA composite. Reducing the moisture content also effectively suppressed the occurrence of transesterification reactions, leading to a decrease in the molecular weight of PLLA. However, the apparent nucleation effect of the D-core remains slightly inferior to that for the hydrophilic bast fibers due to its stronger affinity for PLLA molecules.     

Electron microscopy study on a new phase in beta-titanium alloys aged at a high temperature

In a Ti-20mass%Mo alloys aged by two steps aging at 623 and 823K, a new phase has been observed. In the first step aging, [Formula: see text] -phase crystals appear and at the second step aging, these crystals disappear and are replaced with the newly discovered phase crystals. Observations in the dark field image and analysis of composition of the new phase crystals have shown that the formation is closely related to the [Formula: see text] -phase structure. The new phase crystals have been also observed in four kinds of [Formula: see text] -type Ti alloys and a ( [Formula: see text] ) type Ti alloy aged at high elevated temperatures. Based on high-resolution electron microscope observations, the atomic structure of the new phase is assumed.     

Inorganic microballoon production from shinju-gan using an entrained bed reactor

Hollow inorganic microparticles were produced continuously from a volcanic glass (shinju-gan or per-lite) using an entrained bed reactor. The microparticles are called expanded perlite. The raw material was a sieved fraction (104 μm in volume average diameter) of crushed perlite, which is from China. The effects of temperature and residence time on expanded perlite yield were investigated.