OPTICAL EXTENSOMETRY BY GEOMETRIC MOIRE DIGITAL ANALYSIS OF STRESS IN THE PLANE - AN APPLICATION IN TIMBER

摘要

The study of the behaviour of building structures pass through the determination of the strain and stresses to evaluate the level of local and global security against the active actions. In the last years in Brazil, the extensometers have been commonly used to measure the strain at a specific single point. The optical extensometry presents itself as an alternative to this task by providing results for all points of measurement area (full field).The moire techniques are the simplest of the optical extensometry and have the smaller indices relating to noise. In this work, the sensitivity of mechanics (or geometric) interference of moire' technique reached levels that previously could only be obtained using interferometers (moire interferometry). It is worth noting that interferometers are appliances that cost thousands of dollars. This task was made possible through the multiplication of fringes obtained through digital technology with application present in photography and digital image processing and proved able to measure deformations for micrometric from very low frequency cross gratings. This work is presented as digital geometric moire technique (TMGD) because everything from image capture of specimen gratings until the generation of fringes was made by digital means and therefore does not fall within the classification set out in chapter which deals with the classification of moire techniques. The result was something still unheard in civil engineering in Brazil, a low-cost technique, insensitive to vibrations and of the environment, moreover able to make measurements in plane surfaces without major apparatus. Findings show the applicability of the proposed method to measure strain and to analyse stresses in models and civil engineering structures, among others. In this work, the sensitivity of mechanics (or geometric) interference of moire technique reached levels that previously could only be obtained using interferometers {moire interferometry). Its application is showed in timber structures.