In-situ micro frequency dependent electric field sensors to verify model predictions of cure and aging

Frequency dependent electric field measurements using in situ micro sensors, FDEMS, is a particularly useful technique for monitoring the changing state of a polymer in a composite (or in an adhesive joint or as a coating) during fabrication and aging during use in the field. Measurements can be made in the laboratory to monitor the polymerization process and to monitor durability and aging in an environmental chamber or other degradative environment. Equally important, the FDEMS in situ micro sensor monitoring technique can be used to monitor cure in production ovens and autoclaves on the plant floor as well as outside, for example, coatings on the surface of a ship in dry dock. Durability and aging can be monitored while the object is in use. Examples are a marine coating on a ship, the protective coating on the liner of an acid containing tank, a rocket propellant, an adhesive in a bond joint, or the polymer in a composite structure.     

Near-field optical taper antennas fabricated with a highly replicable ac electrochemical etching method

This paper describes a novel chemical etching method to fabricate high quality near-field optical antennas-tapered metallic tips-from gold wire in a reproducible way for optically probing a specimen on the nanoscale. A new type of an electrochemical cell is introduced and different dc and ac etching regimes are studied in detail. The formation and dynamics of a meniscus around a gold wire immersed in an electrolyte when supplying a square wave voltage are considered. We show that in situ etching current kinetics allows one to improve a yield of tips with a well-defined geometry up to 95% by filtering these on the basis of a cutoff current and a power spectrum of etching current fluctuations. As a quantitative measure for estimating the yield we introduce a probability to find tips with curvature radii falling in the range of interest. Testing the tips for a plasmonic effect is implemented with tip-enhanced Raman spectroscopy and sub-wavelength imaging of a thin fullerene film.     

Monitoring the reaction progress of a high‐performance phenylethynyl‐terminated poly(etherlmide). Part II: Advancement of glass transition temperature

The cure schedule for carbon fiber‐reinforced, phenylethynyl‐terminated Ultem™ (GE Plastics) composites was studied in an attempt to optimize the resultant glass transition temperature, T_g. Reaction progress and possible matrix degradation were monitored via the T_g. On the basis of previous research, matrix degradation induced T_g reduction was expected for increases in cure time or temperature beyond approximately 70 minutes at 350°C. Using the central composite design (CCD) of experiment technique, composite panels, neat resin, and polymer powder‐coated tow (towpreg) were cured following various cure schedules to allow for the measurement of the glass transition temperatures resulting fronm cure time and temperature variations. The towpreg and neat resin specimens were cured in a differential scanning calorimeter. The glass transition temperatures of all specimens were measured via differential scanning calorimetry; the composite glass transition temperatures were also measured with dynamic mechanical thermal analysis. The composite panels and towpreg specimens showed similar trends in T_g response to cure schedule variations. Composite and towpreg glass transition temperatures increased to a plateau with increasing cure time and temperature, whereas, the neat resin showed an optimal T_g followed by T_g reduction with increasing cure time and temperature. The optimal neat resin T_g occurred within a cure time and temperature significantly below that required to maximize the composite and towpreg glass transition temperatures.     

Viscosity–pressure–temperature behaviour of mineral and synthetic oils

A new high‐pressure viscometer that can measure viscosity at pressures up to 0.8 GPa has been developed in the authors' laboratory. The ‘modulus equation’ has been used to compare the behaviour of mineral and synthetic lubricants. Among the oils investigated there was one ester that biodegraded rapidly both before and after ageing in a long‐term test‐rig operation. To facilitate a comparison or application of the results to other oils, an analysis of the correlation between the viscosity—pressure coefficient and the kinematic viscosity measured at atmospheric pressure has been provided. A prediction of lubricant film thickness based on high‐pressure viscosity data is compared with film thickness measurements in a roller bearing.     

TEM and nanomechanical studies on tribological surface modifications formed on roller bearings under controlled lubrication conditions

The chemical composition and microstructure of reaction layers formed under the presence of lubricants with low wear protection, high wear and fatigue protection, and high wear but low fatigue protection on thrust cylindrical roller bearings made of 100Cr6 steel were analysed by transmission electron microscopy. Thin cross sections prepared by the focused ion beam technique were investigated. The nanomechanical properties of the different tribological layers were analysed by static and dynamic nanoindentation. Our results indicate that wear protection not only relies on the lubricant induced formation of a reaction layer, but also on the properties of the combined system of a reaction layer and an underlying tribomutation layer. The formation and structure of the layer system varies with the chemical nature of the basic oil. Our investigations show that its ability to protect against wear and fatigue strongly depends on the oil viscosity and the additives.