Thermomechanical stress fields in high-temperature fibrous composites. I: Unidirectional laminates

This two-part paper presents a closed-form procedure for evaluation of estimates of local thermomechanical stress fields in two-phase fibrous composites and laminates. The first part is concerned with a unidirectional elastic laminate subjected to uniform mechanical loads and to uniform changes in temperature. Both phases are assumed to be elastic, with temperature-dependent moduli and expansion coefficients; the solution reflects the influence of thermomechanical interactions. Exact solutions are not possible for any real system, because the local geometry is not known in detail. Instead, estimates of the fields are found from a modified Mori-Tanaka approximation. Examples are presented for two SiC/Ti---Al---Nb composites. Local stresses of interest are found after cooling from fabrication to room temperature. The presence of local yielding, and the influence of coupling terms on the local stress magnitudes are examined. Extension of the results to laminated plates is presented in Part II (Dvorak, G.J., Chen, T. & Teply, J., Composites Science and Technology, 43 (1992) 359–368, this issue).     

聚吡咯导电材料合成方法的进展

本文对聚吡咯及聚吡咯导电复合物的合成方法进行了综述。     

Use of inverse gas chromatography to quantify interactions in amine cured epoxy resins

Flory–Huggins interaction parameters, λ, were determined for a series of probes in an amine cured epoxy resin matrix (433–493 K) and its precursors (324–363 K) by inverse gas chromatography (IGC). Hildebrand–Scatchard theory was combined with Flory–Huggins theory in order to estimate infinte dilution solubility parameters (δ₂) for the matrix and its precursors at 298 K. It was shown that the value of the solubility parameter for the cured resin matrix lies between those of its precursors. Compared to the majority of published work, an unusual aspect of this application of IGC is that solubility parameters have been determined when the stationery phases are (i) small molecules and (ii) a highly crosslinked polymer. Moreover, all possible attempts have been made to ensure equilibrium conditions between probe and stationary phase, and compensation for asymmetry of peak profile has been applied in determining δ₂. The solubility parameters estimated by IGC are in good agreement with those calculated by other methods.     

Development of sealing compositions with nanostructure iron-based fillers

The possibility of utilizing nanopowders of iron and Fe-Co-Ni produced bu a thermochemical method in the fabrication of sealing composition materials is investigated. It is established that such hermetic sealing composition materials function reliably under extremal conditions and guarantee elevated strength of adhesion to the surface of the metal and high corrosion and temperature stability. __________ Translated from Poroshkaya Metallurgiya, Nos. 3–4(448), pp. 112–117, March–April, 2006.     

Effects of temperature, ammonium and glucose concentrations on yeast growth in a model wine system

In enology, alcoholic fermentation is a complex process involving several mechanisms. Slow and incomplete alcoholic fermentation is a chronic problem for the wine industry and factors leading to sluggish and stuck fermentations have been extensively studied and reviewed. The most studied cause of sluggish and stuck fermentation is the nitrogen content limitation. Nevertheless, other factors, such as temperature of fermentation and sugar concentration can affect the growth of yeasts. In this study we modelled the yeast growth‐cycle in wine model system as a function of temperature, sugar and ammonium concentrations; the individual effects and the interaction of these factors were analysed by means of a quadratic response surface methodology. Cell concentrations and weight loss were monitored in the whole wine fermentation process. The results of central composite design show that lower is the availability of nitrogen, higher is the cell growth rate; moreover, initial nitrogen concentration also influences survival time of Saccharomyces cerevisiae.     

Ermüdungsverhalten und Dauerfestigkeit von Graphit und Aluminium – infiltriertem Graphit

Fatigue behaviour and endurance limit of graphite and of aluminium‐infiltrated graphite Fatigue properties of polycrystalline, isotropic graphite FU2590 and of FU2590 infiltrated with AlSi7Mg (FU2590/AlSi7Mg) were investigated in reversed bending tests at 25 Hz at numbers of cycles below 10⁷ and in tension‐compression tests at 20 kHz below 10⁹ cycles. The open porosity of Graphite (10‐11 Vol.‐%) was infiltrated with the aluminium alloy using the squeeze casting infiltration method, which led to an increase of the bending strength by 50 %, increase of tensile strength by 30 % and increase of stiffness by 15 %. Fully reversed tension‐compression loading of FU2590 delivers a mean endurance limit at 10⁹ cycles at the normalized maximum stresses (i.e. maximum tension stress of a cycle divided by the static strength) of 0,65±0,03. Mean numbers of cycles to failure of 10⁴ were found in fully reversed bending tests at the normalized maximum stress of 0,78. The infiltrated material shows approximately 30 % higher cyclic strength in reversed bending tests, and the mean endurance limit under tension compression loading increases by 15 %. The increased endurance limit of the infiltrated material is caused by the increased stiffness. The increased toughness of graphite due to the infiltration with aluminium is of additional beneficial influence at the higher cyclic stresses investigated in reversed bending tests and in static tests.     

Neutron Stress Measurement of W‐Fiber Reinforced Cu Composite

Stress measurement methods using neutron and X‐ray diffraction were examined by comparing the surface stresses with internal stresses in the continuous tungsten‐fiber reinforced copper‐matrix composite. Surface stresses were measured by X‐ray stress measurement with the sin²ψ method. Furthermore, the sin²ψ method and the most common triaxal measurement method using Hooke's equation were employed for internal stress measurement by neutron diffraction. On the other hand, microstress distributions developed by the difference in the thermal expansion coefficients between these two phases were calculated by FEM. The weighted average strains and stresses were compared with the experimental results. The FEM results agreed with the experimental results qualitatively and confirmed the importance of the triaxial stress analysis in the neutron stress measurement.     

Development of cable fault location method using fiber optic distributed temperature sensor

When ground-fault problems occur on a cable line, immediate fault location and restoration are required. Therefore, various new methods to locate the fault point instantaneously have been investigated to replace such conventional methods as the Murray loop method and the pulse radar method [1]. These methods require a long time to locate the fault point. One possible fault location method is to sense the temperature rise following a ground fault using a fiber optic distributed temperature sensor. Application of this method was found feasible through sensing the temperature rise at a ground-fault test using a thermocouple as a temperature sensor with test cables [4]. A power/optical composite cable was prepared experimentally and after verifying its thermal mechanical performance, the temperature rise at an incidence of a fault was determined and the anticipated performance was demonstrated in a ground-fault test. This article describes the outline of the test.     

New nanocomposite materials based on polymerization of [oligo(oxyethylene) methacrylates] in the presence of montmorillonite clay

Intercalation of poly[oligo(oxyethylene) methacrylates] onto sodium montmorillonite (MMT) clay has been investigated. A polymer–clay hybrid has been synthesized through intercalation of the monomer followed by its solution free‐radical polymerization. Eight polymer–clay hybrids were prepared using different weight ratios of clay, different oligo(oxyethylene) lengths and different proportions of crosslinker. Evidence of the development of nanostructures is obtained from scanning electron microscopy, and wide‐angle X‐ray diffraction studies support these results which show disappearance of the peak characteristic to d₀₀₁ spacing. In this hybrid MMT is dispersed homogeneously in the polymer matrix. © 2003 Society of Chemical Industry