Optical Methods for Solid Mechanics

Solid mechanics is fundamental for civil, aerospace, nuclear, and mechanical engineering, for geology, and for many branches of physics such as materials science. It has specific applications in many other areas, such as understanding the anatomy of living beings, and the design of dental prostheses and surgical implants. One of the most common practical applications of solid mechanics is the Euler-Bernoulli beam equation. Solid mechanics extensively uses tensors to describe stresses, strains, and the relationship between them. Fundamental problems in engineering are now being solved by optical methods. Stress on materials, thermodynamic properties, elasticity are some of the factors that can be measured or estimated by using optical techniques. The physics behind all these powerful methods is very rich, goes from spectroscopy to photoelasticity. The research in this field aims to understand full scale objects using two and three dimensional models, the strain fields at the surface of materials or constructions, and also on transparent materials such as organic and inorganic glasses and monocrystals. The ability to measure in real time and non-invasively variations of certain physical quantities brought into the solids mechanics some of the measurements needed to compute with speed and accuracy some of the hallmark features. This book takes some examples that covers the most relevant methods in specific applications to some materials and giving a little inside into the physics of the techniques involved. Optical methods in experimental solid mechanics, yielding field information, combined with digital image processing and on-line evaluation of the experimentally obtained data by means of numerical procedures enable the stress-strain analysis of many problems, which couldn’t be analysed satisfactorily as yet. Thus the effects of non-linear elastic, of viscoelastic material response and of any combination of such materials on the stress-strain state can be considered. Hybrid techniques, i.e. the combination of measurement techniques with numerical methods for data evaluation based on advanced mathematical algorithms yield reliable knowledge on the actual state and the real reactions of any kind of structures. The possibilities of direct measure are nowadays extremely rare and to measure implies besides manipulation of complex measuring systems, understanding of measurand and limit of application of measurement method. Stress analysis has been considered for some time as a distinct professional branch of engineering, the main objective to determine and improve the mechanical strength of elements, structures and machines. Experimental stress analysis strives to achieve these aims by experimental means. In the investigation of problems of mechanical strength, many factors make the experimental approach indispensable, and often the only means of access. In addition to this, theoretical considerations are usually based on simplifying assumptions which imply certain deviations from reality, and it can be established only by experimentation whether such idealization do not produce an undue distortion of the problem. Using experimental stress analysis is required especially if the analysis is done under real service conditions, where thre are all the influential factors such properties of the employed materials, the methods of manufacture and the operation conditions. A special place among the experimental techniques is occupied by optical methods. Among their numerous possible applications, they can help the researcher to characterize the materials’ behaviour, to give access to the time-evolution of fields of data at different scales and maybe, the most important advantage, they are non-contact and provide full-field data that are naturally suitable for direct comparison with numerical solutions.