Mechanical characterization of natural building stones: observation of the fracture process zone by ESPI

Francesco Calvetti; Giuliana Cardani; Alberto Meda

doi:10.1117/12.360999

9 September 1999 Mechanical characterization of natural building stones: observation of the fracture process zone by ESPI

Francesco Calvetti, Giuliana Cardani, Alberto Meda

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Proceedings Volume 3823, Laser Metrology and Inspection; (1999) https://doi.org/10.1117/12.360999
Event: Industrial Lasers and Inspection (EUROPTO Series), 1999, Munich, Germany

Abstract

The cultural heritage of many nations consist of a great variety of structures of high intrinsic value, which are often composed of natural building stones (NBS), as granite, limestone, marble and sandstone. The use of accurate inspection devices, such as laser interferometry, allows us to acquire information regarding the mechanical properties and damage (tensile cracks) of NBS, which represents the first step in the restoration process. In this paper, the potential application of an electronic speckle pattern interferometry (ESPI) is shown, with particular attention to the observed displacement field and the crack penetration during laboratory testing. In ESPI, by superimposing a reflected light to a reference digitized image, an interference phenomenon is produced. By comparing two recorded interference patterns (before and after loading), the corresponding deformation can be evaluated. The application of ESPI in several laboratory tests on NBS is presented in this paper. In particular, during bending tests performed on geometrically similar NBS specimens, it was observed that the size and shape of the localized damage zone do not depend on the specimen size. These results allow for an interpretation of the 'size- effect,' which consists of a reduction of nominal strength as the specimen size increases.

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Francesco Calvetti, Giuliana Cardani, and Alberto Meda "Mechanical characterization of natural building stones: observation of the fracture process zone by ESPI", Proc. SPIE 3823, Laser Metrology and Inspection, (9 September 1999); https://doi.org/10.1117/12.360999

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