Study of the Monotypic

The emphasis upon publications as a means of diffusing knowledge was expressed by the first Secretary of the Smithsonian Institution. In his formal plan for the Institution, Joseph Henry articulated a program that included the following statement: "It is proposed to publish a series of reports, giving an account of the new discoveries in science, and of the changes made from year to year in all branches of knowledge." This keynote of basic research has been adhered to over the years in the issuance of thousands of titles in serial publications under the Smithsonian imprint, commencing with Smithsonian Contributions to Knowledge in 1848 and continuing with the following active series

Optical Stress Probe: In-Situ Stress Mapping With Raman And Photo-Stimulated Luminescence Spectroscopy

The optical stress probe system, developed in this work, provides a non-invasive method of monitoring and mapping the optical properties of a material during in situ stress tests. The design and construction of such a system was achieved by coupling a fiber optic probe based spectrometer system with an electromechanical loading system. This novel instrumentation integration enables the quantitative study of Raman or Photo-stimulated luminescence peak shifts with stress, known as piezospectroscopy. It further enables mapping of these spectral shifts over a surface of the specimen under load. To achieve this, a focusing method was developed that optimizes the intensity of specific optical bands of interest with the probe position. Individual software programs for the various systems that make up the instrumentation including the spectrometer, load frame and the XYZ stage were integrated and a single user interface was created. The system was calibrated by replicating published linear correlation between compressive stress and spectral peak position, 2.5cm -1/GPa for polycrystalline alumina. © 2010 IOP Publishing Ltd and SISSA

Portable Piezospectroscopy System: Non-Contact In-Situ Stress Sensing Through High Resolution Photo-Luminescent Mapping

Through the piezospectroscopic effect, certain photo-luminescent materials, once excited with a laser, produce spectral emissions which are sensitive to the stress or strain that the material experiences. A system that utilizes the piezospectroscopic effect for non-contact stress detection over a material\u27s surface can capture important information on the evolution of mechanical response under various conditions. Therefore, the components necessary for piezospectroscopic mapping and analysis have now been integrated into a versatile and transportable system that can be used with photo-luminescent materials in any load frame or on a variety of structures. This system combines compact hardware components such as a portable laser source, fiber optics, spectrograph, charge-coupled device (CCD), and an X-Y-Z stage (with focusing capabilities) with a series of data analysis algorithms capable of analyzing and outputting high resolution photo-luminescent (PL) maps on-site. Through a proof of concept experiment using a compressed polycrystalline alumina sample with sharp machined corners, this system successfully captured high resolution PL maps with a step size of 28.86μm/pixel and located high stress concentrations in critical areas, which correlated closely with the results of a finite element model. This work represents an important step in advancing the portability of piezospectroscopy for in-situ and non-contact stress detection. The instrumentation developed here has strong implications for the future of non-destructive evaluation and non-invasive structural health monitoring

Prediction of piezospectroscopic properties with nanoparticle load transfer theories

Embedded alumina nanoparticles acting as stress sensors enable a wide array of applications for non destructive evaluation and materials testing. This work aims to predict the stress sensitive properties of these nanocomposites through theoretical models and finite element simulations. The Eshelby model is accurate in representing the piezospectroscopic (PS) properties for low volume fractions, but modifications were needed to predict higher volume fractions. An iterative technique which uses the framework of the Eshelby model is able to predict the PS properties for intermediate volume fractions. Finite element models were developed to investigate the effects of various microstructural features on the PS properties. The introduction of isotropic interfaces and neighbouring interacting particles in the model improved correlation with experimental data for higher volume fractions. Microcracks included in the model were capable of creating correlation with experimental data for lower volume fractions. These qualitative results give insight into the direction for future nanoparticle load transfer theories

Prediction of piezospectroscopic properties with nanoparticle load transfer theories

Embedded alumina nanoparticles acting as stress sensors enable a wide array of applications for non destructive evaluation and materials testing. This work aims to predict the stress sensitive properties of these nanocomposites through theoretical models and finite element simulations. The Eshelby model is accurate in representing the piezospectroscopic (PS) properties for low volume fractions, but modifications were needed to predict higher volume fractions. An iterative technique which uses the framework of the Eshelby model is able to predict the PS properties for intermediate volume fractions. Finite element models were developed to investigate the effects of various microstructural features on the PS properties. The introduction of isotropic interfaces and neighbouring interacting particles in the model improved correlation with experimental data for higher volume fractions. Microcracks included in the model were capable of creating correlation with experimental data for lower volume fractions. These qualitative results give insight into the direction for future nanoparticle load transfer theories

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. Here, for the first time, the evolution of stresses within air plasma spray (APS) coatings under increasing substrate loads were captured using piezospectroscopy. With mechanical cycling of the substrate, the PS properties revealed anelastic and inelastic behavior and a relaxation of residual tensile stress within the APS coatings. With decreasing substrate thickness, the coating was observed to sustain more stress, as the substrate\u27s influence on the mechanical behavior decreased. The findings provide an insight into the microstructural response that can serve as the basis for model validation and subsequently drive the design process for these coatings