Andrew Gouldstone

Observations of nanoporous foam arising from impact and rapid solidification of molten Ni droplets

The authors report highly nanoporous surfaces on the underside of impacted, rapidly quenched Ni droplets (splats) removed from substrates. The formation mechanism is interpreted as nucleation of gas bubbles during rapid postimpact depressurization, and subsequent freezing to a porous solid. Good agreement is found between experimental observations and predictions from bubble nucleation theory. Results from experimental variations suggest the potential for control of pore size and distribution.

Anisotropic electrical conduction from heterogeneous oxidation states in plasma sprayed TiO2 coatings

Microstructural and electrical characterizations of air plasma sprayed TiO2 coatings were carried out to investigate the details of deoxidation during the spray process and the changes following air annealing. The coatings were found to behave as an n-type semiconductor indicating the presence of oxygen vacancies. Direct-current resistivity measurements in plane (ρIP) and through thickness (ρTT) of the coatings as a function of annealing time and temperature showed remarkably large anisotropies (=ρTT∕ρIP) of up to 105. Impedance spectroscopy of the specimens coupled with microstructural analysis revealed that the origin of this anisotropy lies in the heterogeneous deoxidation and reoxidation behavior of the coatings. Due to rapid quenching, the high temperature deoxidation state is preserved in the splat boundaries making them more conductive than the bulk of the splat in the as-sprayed coating. Upon annealing in air, the splat boundaries get selectively oxidized due to faster surface diffusion of oxygen ...

Indentation to Probe Atelectasis in Mammalian Lung

Of all the internal organs, mechanical behavior of the lung is arguably most closely related to physiologic function. In inflation and deflation, lung parenchyma may be treated as an elastic material with some viscous damping. However, quasi-plasticity is observed, in the form of atelectasis, which is the localized collapse of alveoli under different conditions. General anesthesia in lung is known to increase tendency for pulmonary atelectasis, and this condition is typically removed by mechanical inflation to high pressures, which can be hazardous. The specific mechanisms of atelectasis are not fully known, one reason for this being the difficulty in developing a direct characterization method to perform causal investigations. In a previous abstract, we described the potential for controlled indentation tests to probe atelectatic tendency in lung. In this talk, we present the first results of ‘hardness testing’ on dog and rabbit lung, using different inflation schemes. Specifically, we indented excised lungs at physiologic pressures, inflated with air, pure oxygen, and 0.2% isoflurane in oxygen. Between these three conditions, we found marked differences in ‘hardness’ of the lung, when indented with tip radii comparable to that of ribs. That is to say, large contrasts in residual impressions, as well as re-inflation behavior, were observed. In addition, effects of different inflation gases occurred within a much shorter time than previously reported in other surgical experiments, indicating perhaps different, faster mechanisms controlling atelectasis than previously considered.

Mechanical, thermal and electrical properties of cold sprayed coatings

Publisher Summary This chapter presents and addresses the results from a series of integrated property measurements on a range of Cold Spray [“CS”] metallic materials, in the as-deposited and heat-treated state. It discusses the results in the context of microstructural formation during high velocity impact of particles and the general characteristics of interparticle bonding. Sprayed materials require a multi-scale consideration, as they contain particles of tens of microns in diameter, micro- and nano-scale interfaces that may or might not be continuous. In addition, the highly directional nature of the process subsequently leads to highly anisotropic behavior in mechanical, thermal, and electrical properties. Consideration of as-sprayed and heat-treated behavior under all tests provides a powerful supplement to stand-alone microstructural characterization. The results for CS coatings were compared with those for HVOF and APS coatings, displaying some effect of thermal input on macroscopic behavior, particularly important for the higher-melting-point materials. All the data were contrasted with bulk material behavior. Further high resolution studies of CS interfaces, as well as in-situ macroscopic properties during heat treatment, provide a complete understanding.

Modeling of Interdigital Capacitive Strain Gauges Fabricated Using Direct Write Technology

In this work, an analytical model is developed for an interdigital capacitive strain gauge fabricated using direct-write thermal spray and/or ultrafast laser micromachining direct write technologies. The model is adapted from the electrical engineering literature for inter- digitated capacitors and expanded to include the effects of strain, i.e., dimensional change, on the gauge. Model results are compared to several interdigital capacitive strain gauges with reasonable agreement between the measured and predicted values of nominal capaci- tance and gauge factor. The model represents a powerful tool for the design and optimiza- tion of direct-write capacitive strain gauges on engineering components.

Characterization of Interdigital Capacitive Strain Gauges by Direct Write Technology

Interdigitated capacitive strain gauges have several distinct advantages over resistive-based strain gauges, particularly for applications in harsh environments, such as high-temperature environments. In this work capacitive strain gauges have been fabricated using thermal spray technology. Gauges are fabricated using both a direct-write approach where the gauge is fabricated using a computer-controlled deposition system and by ultrafast laser micromachining in which blanket coatings sprayed onto a substrate are subsequently laser micrornachined. Silver coatings were sprayed onto plastic, polymer, composites, fiberglass and alumina to form the strain gauges. An ultrafast laser machining technique was used to fabricate capacitive strain gauges on copper coated printed circuit boards as well as NiCr coatings on alumina substrate. The typical capacitance of strain gauge was in the range of 5∼25 pF. Mechanical tests included gauge factor, linearity and zero shift. Temperature-based measurements include the temperature coefficient of capacitance (TCC) measurements and thermal cycling tests. The devices show promise for use in wireless strain monitoring applications.Copyright