Evaluation of nonmetallic thermal protection materials for the manned space shuttle. Volume 1, task 1: Assessment of technical risks associated with utilization of nonmetallic thermal protection system

Technical problems of design and flight qualification of the proposed classes of surface insulation materials and leading edge materials were reviewed. A screening test plan, a preliminary design data test plan and a design data test plan were outlined. This program defined the apparent critical differences between the surface insulators and the leading edge materials, structuring specialized screening test plans for each of these two classes of materials. Unique testing techniques were shown to be important in evaluating the structural interaction aspects of the surface insulators and a separate task was defined to validate the test plan. In addition, a compilation was made of available information on proposed material (including metallic TPS), previous shuttle programs, pertinent test procedures, and other national programs of merit. This material was collected and summarized in an informally structured workbook

Non-destructive characterisation of structural ceramics using impedance spectroscopy

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The aim of this project was to explore the potential applications of impedance spectroscopy (IS) in the non-destructive characterisation of structural ceramics. A major advantage in the use of the IS technique is its capability in distinguishing the properties of different microstructural origins in materials, e.g., grains and grain boundaries, etc. In this thesis, a review of the theoretical aspects of IS is presented. An analytical approach and numerical analyses are conducted to illustrate how impedance spectra become resolved and why the spectral resolution is dependent on the representation formalism as well as on the difference between the electrical properties of different microstructural features. Three categories of structural ceramics, i. e. A1203/SiC nanocomposites, thermal barrier coatings and clay-based ceramics, were used as the model materials for this IS study. Both sintering and degradation phenomenon have been examined. Conventional analytical techniques, such as SEM, XRD, EDS, TGA and dilatometry, were used to aid in the understanding of IS and to prove the reliability of impedance measurements. The research results indicate: * For A1203/SiC nanocomposites, IS can be used to examine the conducting mechanisms for the materials containing different quantities of SiC particles. The content of SiC can be correlated to the impedance spectral features and dielectric constant of the material. The oxidation scale formed at the surface gives a separate relaxation process. Based on the capacitive effect of this relaxation process, the thickness can be determined non-destructively using IS. * For thermal barrier coatings, three relaxation processes can be found in the impedance spectra, which correspond to the top coating, oxidation layer and microstructural defects in the top coating, respectively. The thickness of the oxidation layer can be quantitatively related to the diameter of the corresponding semicircle in electrical modulus spectrum. In the meantime, the top coating degradation could also be monitored using IS. * For clay-based ceramics, the impedance spectra consist of a high frequency semicircle and a low frequency tail, which correspond to bulk effect and electrode effect, respectively. The variation of the bulk conductivity with sintering time can be quantitatively correlated to the densification of the material during sintering. The electrode effect tail is directly related to the capacitive effect of the electrode/specimen interface, which could be an effective indicator of the electrode temperature. Therefore IS is a useful technique for non-destructive characterisation of structural ceramics

Measurement techniques and instruments suitable for life-prediction testing of photovoltaic arrays

Array failure modes, relevant materials property changes, and primary degradation mechanisms are discussed as a prerequisite to identifying suitable measurement techniques and instruments. Candidate techniques and instruments are identified on the basis of extensive reviews of published and unpublished information. These methods are organized in six measurement categories - chemical, electrical, optical, thermal, mechanical, and other physicals. Using specified evaluation criteria, the most promising techniques and instruments for use in life prediction tests of arrays were selected

Progression in Non-Destructive Spallation Prediction and Elevated Temperature Mechanical Property Evaluation of Thermal Barrier Coating Systems by Use of a Spherical Micro-Indentation Method

The accumulation of carbon dioxide in the atmosphere continues to be an important ecological issue associated with global warming. The demand for improved efficiencies in energy conversion in recent years has led to the introduction of land-based gas turbines with significantly increased inlet temperatures. To accomplish this, nickel-based superalloys with protective thermal barrier coatings (TBC) are widely used as systems capable of extending the life and increasing firing temperatures of combustor and stationary turbine components. However, coating durability, thermal-fatigue and erratic spallation failure currently limit the continuous operation of turbine engines. Of the present ceramic coating materials used, yttria stabilized zirconia (YSZ) is most prevalent; its low thermal conductivity, high thermal expansion coefficient and outstanding mechanical strength make it ideal for use in TBC systems. However, residual stresses caused by coefficients of thermal expansion mismatches within the TBC system and unstable thermally-grown oxides (TGO) are considered the primary causes for its premature and erratic spallation failure. The development of new materials, coating technologies and evaluation techniques is required if enhanced efficiency is to be achieved. As a result, several non-destructive evaluation (NDE) techniques have been developed to address this problem yet few comprehensive studies have resulted in the development of true NDE techniques capable of predicting failure location prior to its occurrence.;In this research, a load-based micro-indentation method for NDE of TBCs exposed to thermal loads in air has been developed. Coating surface stiffness responses obtained through use of this technique have been found capable of assessing damage accumulation and macroscopic debonding failure sites following thermal exposure of TBC systems to elevated temperatures. Furthermore, microstructural analyses correlating these surface stiffness response to overall YSZ/TGO interface conditions indicate that high interfacial rumpling and non-uniform oxide growth leads to the development of both in-plane and out-of-plane residual stresses. As a result, areas displaying relative increases in surface stiffness response enable early detection of initial TBC spallation locations. Additionally, with the evolution of nanotechnologies, indentation testing techniques have become more common, yet their ability to evaluate material mechanical properties in harsh environments remains a challenge. Following a classical Hertzian contact mechanics approach, a micro-indentation technique that does not require system compliance calibration or the use of high precision depth sensors has been developed. The removal of these constraints has led to the development of both a portable and high-temperature micro-indentation system for TBC materials mechanical property evaluation up to 1000°C

Index to NASA tech briefs, 1971

The entries are listed by category, subject, author, originating source, source number/Tech Brief number, and Tech Brief number/source number. There are 528 entries

Terahertz Time-domain Reflectrometry of Multilayered Systems.

Presented in this work are applications of terahertz pulse ranging, spectroscopy and imaging to the nondestructive evaluation of three disparate multilayer systems for the detection and measurement of hidden layers, as well as the extraction of system information that will aid in its maintenance, repair or replacement. Thermal protection systems for turbine engine components were investigated. Thermal barrier coatings (TBC) and thermally-grown oxide (TGO) thicknesses were determined with 10 micron resolution using time-of-flight and refractive index calculations. Two alternative methods of monitoring TGO growth using reflection amplitudes and spectral shifts were proposed for the prediction of TBC failure. Laser-machined defects as narrow as 50 microns were resolved in one- and two-dimensional images. The light and dark rings of trees, which reflect the changes in tree growth density over the course of a year, are measurable using pulsed terahertz beams. Tree-rings of bare and painted wood specimen were laterally and axially tomographically imaged in order to facilitate the dendrochronological cross-dating of artifacts. Comparisons were made between photographs and terahertz images to demonstrate the reliability of the technique. Historically, numerous unique artworks have been lost through the act of being covered over time. Samples of paintings, drawings and mosaics were imaged beneath layers of paint and plaster using pulsed-terahertz techniques to demonstrate the efficacy of the technique for art history and restoration. Sketch materials and pigments were measured, between 0.05 and 1.0 THz, to help identify colors in spectroscopic images. Other computational and processing methods were used to optimize the distinction between color domains. Additional time-domain terahertz applications for the examination of artwork and other artifacts were proposed.Ph.D.Applied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/61752/1/jbjz_1.pd