Method for conducting in situ high-temperature digital image correlation with simultaneous synchrotron measurements under thermomechanical conditions.

This work presents a novel method of obtaining in situ strain measurements at high temperature by simultaneous digital image correlation (DIC), which provides the total strain on the specimen surface, and synchrotron x-ray diffraction (XRD), which provides lattice strains of crystalline materials. DIC at high temperature requires specialized techniques to overcome the effects of increased blackbody radiation that would otherwise overexpose the images. The technique presented herein is unique in that it can be used with a sample enclosed in an infrared heater, remotely and simultaneously with synchrotron XRD measurements.

Modeling luminescence behavior for phosphor thermometry applied to doped thermal barrier coating configurations.

Phosphor thermometry is a promising non-destructive method for accurate temperature measurement using phosphor elements that emit temperature-dependent luminescence. The method relies on the intensity and decay of luminescence arising from the phosphor elements upon excitation by an incident laser. In this work, the classical Kubelka-Munk model has been utilized and modified to model the luminescence emitted from phosphor elements that are added into thermal barrier coatings (TBCs) to enable temperature sensing using phosphor thermometry.

Silane functionalization effects on dispersion of alumina nanoparticles in hybrid carbon fiber composites.

Hybrid carbon fiber reinforced polymer composites are a new breed of materials currently being explored and characterized for next-generation aerospace applications. Through the introduction of secondary reinforcements, such as alumina nanoparticles, hybrid properties including improved mechanical properties-fracture toughness, for example-and stress-sensing capabilities can be achieved. However, problems with manufacturing can arise resulting from the inherent variability of the manufacturing techniques along with the tendency for the nanoparticles to agglomerate.

Quantifying Alumina Nanoparticle Dispersion in Hybrid Carbon Fiber Composites Using Photoluminescent Spectroscopy.

Composites modified with nanoparticles are of interest to many researchers due to the large surface-area-to-volume ratio of nano-scale fillers. One challenge with nanoscale materials that has received significant attention is the dispersion of nanoparticles in a matrix material. A random distribution of particles often ensures good material properties, especially as it relates to the thermal and mechanical performance of composites.

Strain response of thermal barrier coatings captured under extreme engine environments through synchrotron X-ray diffraction.

The mechanical behaviour of thermal barrier coatings in operation holds the key to understanding durability of jet engine turbine blades. Here we report the results from experiments that monitor strains in the layers of a coating subjected to thermal gradients and mechanical loads representing extreme engine environments. Hollow cylindrical specimens, with electron beam physical vapour deposited coatings, were tested with internal cooling and external heating under various controlled conditions.

Piezospectroscopic measurements capturing the evolution of plasma spray-coating stresses with substrate loads.

Plasma-spray coatings have a unique microstructure composed of various types of microcracks and weakly bonded interfaces which dictate their nonlinear mechanical properties. The intrinsic photo-luminescence (PL) characteristics of alpha-alumina (α-Al2O3) within these coatings offer a diagnostic functionality, enabling these properties to be probed experimentally at the microscale, under substrate loading. The piezospectroscopic (PS) measurements from the coatings are capable of revealing microstructural stress at high spatial resolution.

Synchrotron X-ray measurement techniques for thermal barrier coated cylindrical samples under thermal gradients.

Measurement techniques to obtain accurate in situ synchrotron strain measurements of thermal barrier coating systems (TBCs) applied to hollow cylindrical specimens are presented in this work. The Electron Beam Physical Vapor Deposition coated specimens with internal cooling were designed to achieve realistic temperature gradients over the TBC coated material such as that occurring in the turbine blades of aeroengines. Effects of the circular cross section on the x-ray diffraction (XRD) measurements in the various layers, including the thermally grown oxide, are investigated using high-energy synchrotron x-rays.

Investigation of temperature dependent multi-walled nanotube G and D doublet using pseudo-Voigt functions.

A pseudo-Voigt (PV) function is used as a representation of the Stoke's phonon frequency distributions for a multi-walled nanotube (MWNT) composite G and D doublet. Variable peak assignments with the PV function have been shown to enhance the resolution of these bands commonly used for characterization of carbon nanotube (CNT) composites. The peak assignment study was applied to an in-situ temperature experiment where the addition of new sub-bands in the G and D doublet was determined to reduce the uncertainty of the Raman characteristics.

Stress-sensing nanomaterial calibrated with photostimulated luminescence emission.

Calibration of high spatial resolution stress-sensing alumina-epoxy nanomaterials is presented. The piezospectroscopic property of luminescent chromium-doped alumina nanoparticles embedded as "nano-sensors" in epoxy-based materials is the basis for the stress sensing capabilities. The stress-optical properties are determined as piezopectroscopic coefficients in compression experiments for nanomaterials containing varying volume fractions of alumina nanoparticles.

High-resolution stress mapping of polycrystalline alumina compression using synchrotron X-ray diffraction.

The ability to achieve uniform stress in uniaxial compression tests of polycrystalline alumina is of significance for the calibration of piezospectroscopic coefficients as well as strength studies in ceramics. In this study high-energy X-rays were used to capture powder diffraction profiles over a half-section of a polycrystalline alumina parallelepiped sample under an increasing uniaxial compressive load. The data were converted to strain and results were used for stress mapping of the sample.

Spectral analysis of R-lines and vibronic sidebands in the emission spectrum of ruby using genetic algorithms.

The advancement in spectral analysis methods for the emission spectrum of ruby has been driven by the characterization of R-line peak shifts with stress in order to establish piezospectroscopic relationships. These relationships form the basis for the development of photo-stimulated luminescence spectroscopy (PSLS) as a nondestructive method to determine the integrity of the thermally grown oxide (TGO) layer on jet engine turbine blades. Besides the measurement technique, the accuracy of PSLS in stress measurements is influenced by the spectral analysis methodology, which is the focus of this paper.