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openAccessArticle: Falsecover date: 2015-09-08pii: S0266-3538(15)00194-3Harvest Date: 2016-01-06 13:07:53issueName:Page Range: 41-41href scidir: http://www.sciencedirect.com/science/article/pii/S0266353815001943pubType

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's 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.

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.

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