New improvements in shearography techniques

Shearography is a non-contact full field technique used in the assessment of spatial gradient of displacements through a preset direction, Hung and Taylor [1]. The optical set-up can be based on a Michelson interferometer scheme, for static or quasi-static measurements, and on the Mach- Zehnder interferometer if dynamic measurements have to be performed, Santos et al [2]. In both set-ups a speckle pattern, obtained from a rough surface, is laterally shifted to create the interference and the light used for the interferometer arms have a common path between the object and the set-up. So, this interferometric technique can be used with low coherence lasers and is almost insensitive to rigid body motion. The fringe patterns obtained with shearography result from the interference between two speckled wave fronts and have lower contrast that the ones obtained with specular reference interferometers

The dynamic analysis of piping systems using pseudo-dynamic techniques

This paper describes an application of pseudo-dynamic techniques to the dynamic analysis of piping structures. Essentially it consists in coupling a direct time integration algorithm, such as the Newmark method, to an experimental step. At each time step the integration algorithm generates a displacement vector of the structure, which is prescribed for the test specimen. This is mounted in a rigid test rig fitted with a set of displacement actuators and load cells at the level of the structure degrees of freedom. The load cells allow the reading of the internal restoring force vector, which is fed back to the direct time integration algorithm in an actual time step. Further calculations for the velocity and acceleration vectors will define a new structure configuration by evaluating a new displacement vector referred to the next time step. This procedure makes it possible to assess experimentally a realistic stress distribution at sections of complex shape piping parts. The method is a precise tool in dynamic analysis and, on being carried out in a quasi-static procedure, it operates with less expensive equipment than is necessary in real dynamic test

Short communication: brood production and mortality rate of young saúva queens (atta sexdens linnaeus, 1758) (hymenoptera: formicidae) reared in artificial colonies with mixed substratum

The use of plaster as a substratum for colonies of leaf-cutting ants in laboratory is widespread. Because Atta Fabricius, 1804 species excavate the soil in order to found new colonies in nature, we wanted to test whether mixing plaster with soil (Latossolo Vermelho) would influence the number of eggs, larvae, pupae and workers in A. sexdens Linnaeus, 1758 colonies. Here we report results that possibly indicate the plaster substratum as the most suitable for rearing young A. sexdens colonies in laboratory.É comum o uso de gesso estuque como substrato em colônias artificiais de formigas cortadeiras (Forti et al., 1994). Devido ao fato de espécies de Atta Fabricius, 1804 escavarem o solo para fundar novas colônias na natureza, deseja-se testar se o uso de solo de terra de barranco (Latossolo Vermelho) misturado ao pó de gesso como substrato teria influência sobre o número de ovos, larvas, pupas e operárias em colônias de A. sexdens Linnaeus, 1758. Reportamos aqui os resultados preliminares que possivelmente indicam o substrato feito unicamente de pó de gesso como o mais adequado para criar colônias de A. sexdens em laboratório

Unwrapping techniques for speckle phase maps: study and comparison of the performance of principal methods

Holographic interferometry (HI) techniques are powerful tools for experimental mechanics which can be used to assess displacement fields on a loaded object surface. Used with no contact and high resolution HI can be combined with image methods for data analysis. Nevertheless, the speckle should be fully resolved by the image detector to digitally record an interferogram. This leads to a noisy recording which difficult it’s post-processing. Each measurement with HI ends normally in a phase map computation representing the object displacement. Phase calculation algorithms are based on spatial or temporal phase modulation and lead to wrapped phase maps. To obtain the continuous phase distribution several solutions have been implemented. This paper describes the main filtering and unwrapping algorithms available and compares it´s performance to solve discontinuities in noisy phase maps

Numerical simulation of wall deformation in an aneurysm model

This work presents the numerical assessment of the deformation of an artery wall with and without an aneurism. The simulations consider the hyper-elastic behaviour of the artery tissues, taken in consideration the properties of polydimethylsiloxane (PDMS), which are more similar to the biological tissues. The numerical simulations were performed using the commercial finite element routines ANSYS®, by considering the inner the artery fluid flow and the consequent pressure is used to simulate the wall deformation.info:eu-repo/semantics/publishedVersio

Damage identification using real time rotating field analysis

This paper proposes a real time damage identification method based on the perturbation analysis of the rotation field, which are measured using shearography technique. A particular case of phase modulation method is applied to the interference pattern in order to improve the spatial resolution of the rotation field. A program was developed in Matlab® platform for digital recording the information capture by CCD camera and post-processing the data using dedicated image techniques. The phase filter and unwrapping algorithms were optimized to allow the visualization at video rate the full-field rotations fields. For small internal damages in laminated composite plates, the results show a superior performance of the proposed technique in relation to the classical raw fringe analysis

Damage identification using real time rotating field analysis

This paper proposes a real time damage identification method based on the perturbation analysis of the rotation field, which are measured using shearography technique. A particular case of phase modulation method is applied to the interference pattern in order to improve the spatial resolution of the rotation field. A program was developed in Matlab® platform for digital recording the information capture by CCD camera and post-processing the data using dedicated image techniques. The phase filter and unwrapping algorithms were optimized to allow the visualization at video rate the full-field rotations fields. For small internal damages in laminated composite plates, the results show a superior performance of the proposed technique in relation to the classical raw fringe analysis

Displacement and strain field assessment of PDMS using digital image correlation

The main goal of this work is to characterize the hyper-elastic mechanical behaviour of PDMS. For that, were made-up special specimens of PDMS (Sylgard® 184) for test them in bi-axial tensile machine. During the tensile test was used a commercial digital image correlation system (ARAMIS of GOM) to obtain de displacement and strain fields. These measurements are compared with numerical simulations which uses the more popular algorithms of constitutive models