Alineación Láser para Experimentación con Fotografía Digital de Speckle (DSP)

Non-contact techniques have returned to optical metrology one of the most booming branches of science, making digital speckle photography (DSP) one of the most used in the measurement of structural changes in surfaces. This technique uses a laser as a measurement system and compares the changes in the speckle pattern obtained by irradiating the surface that is subjected to deformations; however, the alignment of these systems plays an important role in the results obtained. In this work, the alignment errors of an optical system are estimated based on the analysis of the Fraunhofer diffraction pattern, as well as the statistical properties of the speckle pattern for field near and far. The results indicate that the alignment of the light beam can be determine by a fringes quantification system when passing through a pinhole and that the highly developed speckle pattern is more similar to the intensity distribution shown in the literature.

Effect of noise on measurements of diffusivity in transparent liquid mixtures by digital speckle photography

Interfacing two liquid mixtures in a diffusion cell induces noise in the initial state of the diffusing system, which produces a gap between the diffusion boundary and the ideally boundary assumed in the theory. Measured diffusivity values systematically drift with time and they are often corrected by using a linear shift of the zero-time of the process after sufficiently long time when the system reaches the free one-dimensional diffusion regime. In data analysis methods which involve optical correlation between pairs of successive digital images of the cell, it is not easy to establish how long the transient lasts. We show that when the initial perturbation between solution and solvent relaxes slowly toward the diffusive regime no simple zero-time correction can be applied.

Monitoring of jute/hemp fiber hybrid laminates by nondestructive testing techniques

Damage following static indentation of jute/hemp (50 wt.% total fiber content) hybrid laminates was detected by a number of nondestructive testing (NDT) techniques, in particular, near (NIR) and short-wave (SWIR) infrared reflectography and transmittography, infrared thermography (IRT), digital speckle photography (DSP), and holographic interferometry (HI), to discover and evaluate real defects in a laminate with a complex structure. A comparative study between thermographic data acquired in the mid- (MWIR) and long-wave infrared (LWIR) spectrum bands, by pulsed (PT) and square pulse (SPT) thermography, is reported and analyzed. A thermal simulation by COMSOL® Multiphysics (COMSOL Inc., Burlington, MA, USA) to validate the heating provided is also added. The robust SOBI (SOBI-RO) algorithm, available into the ICALAB Toolbox (BSI RIKEN ABSP Lab, Hirosawa, Japan) and operating in the MATLAB® (The MathWorks, Inc., Natick, MA, USA) environment, was applied on SPT data with results comparable to the ones acquired by several thermographic techniques. Finally, segmentation operators were applied both to the NIR/SWIR transmittography images and to a characteristic principal component thermography (PCT) image (EOFs) to visualize damage in the area surrounding indentation.