Experimental and Computational Method for Determining Parameters of Stress-Strain State from the Data Obtainable by Interference Optical Techniques

Abstract

Experimental and computational method for determining parameters of stress-strain state is proposed which is based on estimation of compliance between the data sets obtained experimentally and the results of numerical calculations of the boundary problems in formulation of which all distinctive features of area geometry, character of the loads being considered and deformation characteristics of materials are taken into account. The procedure proposed was checked at a number of practically important problems. The methods for investigation into stress-strain state (SSS) of structures based on interference optical techniques for registration of strain or displacement fields (photoelastic techniques, holographic interferometry, speckle photography, electronic digital speckle pattern interferometry techniques) provide the acquisition of uninterrupted information at the surface of the object being studied (1,2). These methods being commonly used to solve the problems of mechanics of deformed solids, fracture mechanics, vibration-based diagnostics, structural dynamics etc., have distinct advantages over traditional measuring tools that allows only averaged (accumulated over known time base) values of strains or displacements in one direction and at the point given to be registered. The adequacy of the results of such measurements requires, as a rule, additional substantiation. In modern practice the photoelastic coatings technique and, in recent years, electronic digital speckle pattern interferometry (EDSI) became the most common among these methods; significant advantage of these techniques is the capability of creating compact and reliable measurement instrumentation which can be used effectively under full-scale conditions. Besides, the evolvement of modern computer technologies offers a considerable increase in accuracy of measurement results as well as development of conceptually new methodological approaches to solving mechanics problems. The determination of SSS parameters for the object being studied on the basis of processing of the experimental data obtainable by interference optical techniques includes three main stages: • registration of baseline information on the basis of one or another effect of interference optics (photoregistration of interference patterns, hologram recording, registration of images with speckle pattern etc.); • presentation of obtainable information on electronic media in digital format in terms of phase differences of light waves or (after primary processing) directly through components of three- dimensional vector of body surface point displacements;