Wetting behavior and nanotribological properties of silicon nanopatterns combined with diamond-like carbon and perfluoropolyether films.

A large number of silicon (Si) patterns consisting of nanopillars of varying diameter and pitch have been fabricated and further coated with diamond-like carbon (DLC) and perfluoropolyether (Z-DOL) films. The wetting behavior and nano-adhesion/friction of the patterns are investigated experimentally in relation to the nanostructures and the hydrophobicity of the materials. Measurements of water contact angle illustrate that the patterning-enhanced wettability of the Si flat surface, along with two distinct wettings which are in good agreement with the Wenzel and hemi-wicking states, depended on the value of the pitch-over-diameter ratio. In the case of the coated patterns, three wetting states are observed: the Cassie-Baxter, the Wenzel, and a transition from the Cassie-Baxter into the Wenzel, which varies with regard to the hydrophobic properties of the DLC and Z-DOL. In terms of tribological properties, it is demonstrated that a combination of the nanopatterns and the films is effective in reducing adhesive and frictional forces. In addition, the pitch and diameter of the patterns are found to significantly influence their adhesion/friction behaviors.

Applications of nonlinear ultrasonics to the NDE of material degradation.

Nonlinear ultrasonics is suggested as a new approach for the effective evaluation of material degradation. As its quantification, the parameter beta is introduced on the basis of nonlinear elasticity, and a new method to measure the parameter beta using bispectral analysis is proposed. Then, the correlation between beta and material degradation is investigated. From the results for several mild steel (SS41, SS45) specimens that were degraded by stretching and cyclic loads, it was confirmed that the parameter beta has a strong correlation with material degradation. As another practical application, the evaluation of the aging degradation in a high temperature material is tried. For this, Cr-Mo-V specimens that are generally used in turbine rotors in power plants were prepared, and the variation of beta caused by aging time was investigated. For comparison, the fracture appearance transition temperature (FATT) of the specimen was measured, and its behavior showed good agreement with beta. In addition, for all of the experiments, no noticeable change in attenuation and sound velocity in the same specimens with change of degradation were observed. From these results, it may be concluded that nonlinear ultrasonics could be applied to the quantitative evaluation of material degradation.

3-D velocity field measurement using multiple ultrasonic plane detections and high-order correlation analysis.

A method of measuring the three-dimensional velocity field of laminarlike flow noninvasively by combining multiple ultrasonic plane detectors and a corresponding level of high-order cross-correlation analysis is presented. It is assumed that the velocity field consists of a set of straight line streams and that each stream contains random fluctuations that serve to tag the location of each stream as it passes through the detectors. The time delays of each stream between the various pairs of plane detectors are estimated by using high-order cross-correlation analysis of the detected signals. From the estimated time delays the stream velocities and their positions are measured and the three-dimensional velocity field pattern is reconstructed. To confirm the usefulness of this method, an actual measurement system has been constructed in a water tank, and experiments using controlled flow through thin tubes have been carried out. The details of the system and the results are shown.