John Willian Branch Bedoya

Computational reduction of the image sets required in conventional phase shifting methods applied to digital photoelasticity

Phase shifting techniques are often limited in digital photoelasticity by the quantity of acquisitions they require, and the process to perform them. This work simplifies such process by developing only a part of the acquisitions, and the rest are generated computationally. Our proposal was validated for a six-acquisition method by generating synthetic images from the analytical model of a disk under diametric compression. The results show that although our method uses less acquisitions, it is capable to recover the stress field with similar performance than conventional methods. This proposal could be useful for evaluating dynamic cases because the reduction of the exposure time expended during the acquisition stage.

High stress concentration analysis using RGB intensity changes in dynamic photoelasticity videos

Photoelasticity images and videos contain information about the stress distribution in birefringent materials. Yet, its processing has difficulties in regions with high-stress concentrations. Making the material fail under load application. This paper identifies such regions by analyzing the intensity changes contained in photoelasticity videos. The evaluation is by the summa of each Euclidean distance between a frame, and the previous. The summa produces a grayscale image. Which is segmented using a thresholding process based on the range of intensity changes. It allowed separating regions with higher summa of color changes. That in this case, it corresponds to the zones with high-stress concentrations reported for a disc under compression. This technique allowed identifying high-stress concentration avoiding the sub-processes used in traditional photoelasticity.

Computational analysis of stress map variations by industrial light sources and load additions in digital photoelasticity

In digital photoelasticity, evaluating the stress map is often affected in regions with critical values. This phenomenon is associated to color degradation effect and high fringe densities. It is a consequence of different experimental conditions, such as: type of birefringent material, relative spectral content of light source, relative spectral response of camera sensor, polarization optical elements, load application, etc. In this study field, the main goal accounts for evaluating the stress values, as better as possible, from photoelasticity images. Which turns the view towards the process that allow to acquire photoelasticity images with more complete information. This makes necessary to analyze the possible effects that each element could introduce into the photoelasticity image generation. This paper presents a computational analysis on the effect that different industrial light sources introduces for recovering the stress maps. Hence, four common industrial light sources are considered for generating the photoelasticity images. In this case, results reveal that there are light sources which represent stronger limitations for evaluating the stress, and that Such effect varies with the load increments. This approach is useful for predicting the possible effect that a light source selection could introduce into the stress evaluation process.

Análisis de resolución en imágenes de fotoelasticidad: caso carga dinámica

En imagenes de fotoelasticidad, los patrones de franjas envuelven el campo de esfuerzos de un cuerpo birrefringente bajo cargas mecanicas. En estos casos, zonas con concentraciones de esfuerzos producen altas densidades de franjas, dificultando la recuperacion, y en ocasiones la perdida, de la informacion envuelta en la imagen. Este articulo evalua el crecimiento de tales regiones y su efecto en el campo de esfuerzos para un caso donde el cuerpo es sometido a cargas dinamicas. Aqui, una secuencia sintetica de imagenes de fotoelasticidad es generada partiendo del modelo analitico de la distribucion de esfuerzos en un disco bajo compresion diametral. El tamano de las regiones con perdida de informacion es estimado mediante la implementacion de transformadas de Fourier y filtros paso alto. Los resultados muestran que el incremento de la carga introduce aumentos en las regiones con perdida de informacion. En estos casos, los esfuerzos maximos recuperados a partir de las imagenes se alejan de los valores en el modelo analitico. Esto permite identificar regiones en las imagenes de fotoelasticidad, donde el campo de esfuerzos debe ser corregido

Análisis de campos de esfuerzos utilizando fotoelasticidad visible e infrarroja

Analisis de campos de esfuerzos en imagenes de fotoelasticidad son llevados a cabo mediante descriptores de textura en este articulo. En este caso, los descriptores considerados permiten identificar zonas con altas concentraciones de esfuerzo, incluso en casos con perdida de contraste, los cuales son por lo general atribuidos a la baja resolucion espacial de las franjas. De manera adicional, en este trabajo se analiza la variacion en la densidad de franjas en terminos de la longitud de onda. Esto ultimo se hace extendiendo la generacion de imagenes de fotoelasticidad en el infrarrojo lejano.

Texture analysis integrated to infrared light sources for identifying high fringe concentrations in digital photoelasticity

In digital photoelasticity images, regions with high fringe densities represent a limitation for unwrapping the phase in specific zones of the stress map. In this work, we recognize such regions by varying the light source wavelength from visible to far infrared, in a simulated experiment based on a circular polariscope observing a birefringent disk under diametral compression. The recognition process involves evaluating the relevance of texture descriptors applied to data sets extracted from regions of interest of the synthetic images, in the visible electromagnetic spectrum and different sub-bands of the infrared. Our results show that extending photoelasticity assemblies to the far infrared, the stress fields could be resolved in regions with high fringe concentrations. Moreover, we show that texture descriptors could overcome limitations associated to the identification of high-stress values in regions in which the fringes are concentrated in the visible spectrum, but not in the infrared.