Field Optical Methods Research Articles

Investigation of self-assembly and topological changes in the sessile droplets of Klebsiella oxytoca by Chronological study

The infectious droplet from the patient self-assembles into a novel pattern depending on bacterial interaction with substrate and liquid. The spatial location of bacteria inside the droplet fluctuates depending on the non-covalent forces. The deformation and dehydration induced stress on bacteria in evaporating contagious-fluid droplets alters the viability and infectivity. The self-assembly of Klebsiella oxytoca (KO) in contagious sessile droplets was studied by natural evaporation. KO forms novel patterns as the droplets exsiccate, thus revealing the unexplored topological changes that govern its survival and infection strategies. The droplets of both bacterial suspension in Milli-Q and SRF of volume 0.95 ± 0.1 μl were placed on the glass material for assessment of the self-assembly. The bacterial suspension was stained before allowing them to desicate. The bacterial chemotaxis and deposition near the end of evaporation are recorded using the bright and dark field optical method. The random time interval is also measured to track the bacterial movement. The investigation shows that the majority of the bacterial population moves toward the rim of the droplet because of edge closely packing, leading to enhanced viability and pathogenesis on the famously known “coffee ring” and few bacteria are present at the centre of the droplet which represents chemotaxis of bacteria. The mechanistic insight gained via our study can have far-reaching implications for bacterial infection through droplets e.g., through open wounds.

Measuring plate vibration using deflectometry: The advantages and limitations of add-on reflective material

Deflectometry is a full field optical method which utilizes the slope fields on the surface of a planar object to track deformations. The use of a high speed camera gives the ability to measure all points on the surface instantaneously and with high spatial resolution, providing more knowledge on how structures react to transient excitations. Here, the reflected grid method will be used, as it involves geometry that allows for simple calculation of curvature distributions. This method of deflectometry relies on specular reflections to create amplifications of the measured deformations in the test plate. Therefore, this requires the plate under test to have a reflective surface. An experiment was constructed to test the vibration of a flat plate excited by an automatic force hammer. A collection of adhesive tapes, films, and spray were applied to the test object in order to increase the reflectivity of the plate. The advantages and limitations of each type of add-on reflective material will be discussed. Finally, the add-on material was used on a more complex structure to showcase the potential of deflectometry for measuring plate vibration.

Estimating of turbulent velocity fluctuations in boundary layer with pressure gradient by Smoke Image Velocimetry

The results of the experimental estimating of the velocity profiles and turbulent pulsations in the boundary layer for adverse and favorable pressure gradients are presented. The profiles of characteristics based on the dynamics of two-component instantaneous velocity vector fields measured by the field optical method of Smoke Image Velocimetry are estimated. The measurements are performed with a large spatial and temporal resolution, the measurement results are relevant for estimating the terms of the conservation equation of turbulent energy in the boundary layer and for improving semiempirical turbulence models.

Fatigue Testing of Continuous GFRP Composites Using Digital Image Correlation (DIC) Technique a Review

Usage of Glass Fiber Reinforced Polymeric (GFRP) composites is increasing drastically in many fields from Aerospace to Sporting good due to light weight and low cost. An effective design of GFRP composites requires detailed understanding of material and the way of testing. Fatigue is the single largest failure that occurs in composites suddenly without any warning, and this failure is catastrophic in nature. In the past years the composites were tested under fatigue loads so that the fatigue behavior can be identified. But this can’t detect the crack behavior of material at the time of testing which is a very important phenomena in identifying the stress concentration of the material. This paper discusses the application of Digital Image Correlation (DIC) technique for fatigue testing of GFRP material in order to capture anisotropic damage. DIC is a non-contact and non–destructive unique exploring full field optical method used to measure accurate displacement, surface strains usually called as speckle pattern for anisotropic material undergoing motion and deformation. In this paper we explained DIC by using Newton- Rapshon (NR) correlation analysis. DIC technique uses high speed, high resolution and accurate Charge-Coupled device (CCD) cameras for measuring displacement components on the surface of the testing material having speckle patterns. Images were captured at the time of testing at every stress cycle and these deformed patterns were correlated with a reference pattern and determining the displacements of the so called subsets. Because of fast data acquisition this technique is well suited for characterization of material properties.

Validation of non-linear dynamic simulations through full field optical methods

Innovative designs of transport vehicles need to be validated in order to demonstrate reliability and provide confidence. The most common design approach of such structures involve simulations based on Finite Element (FE) analysis, which require reliable validation techniques, especially if anisotropic materials, such as fibre reinforced polymers, or complex designs, such as sandwich panels are to be considered. The present paper aims to integrate sophisticated numerical analysis with full-field optical measurement system data in order to improve the quality of both methods and increase reliability of the design.

Radial metrology application to whole-body measurement on hyperelastic tubular samples

This paper focuses on a one-camera/one-shot procedure able to get the whole deformation map of hyperelastic tubular samples. A challenging application of this approach is the investigation of the highly anisotropic and inhomogeneous arterial tissue mechanical response during inflation/extension tests. To address this issue, full field optical methods based on digital correlation (DIC), fringe projection (FP) and stereo-photogrammetry (SP) have been already proposed in literature to overcome limitations of the most widely adopted 2-D video dimension analyzer (VDA) systems. In this paper, the feasibility of a very straightforward full-field procedure that uses radial metrology concepts has been studied. The rationale behind the proposed method relies on the relation existing between image deformation of a world point reflected by a 45° concave conical mirror and the relative position of this point with respect to the specular surface. Under certain assumptions reasonably true for the application of interest, by using simple relationships, it is possible to retrieve the position of markers applied onto the sample surface with great precision. This procedure has several advantages such as the retrieval of the whole 360° surface map in one shot, the ease of application, the use of one single camera, the real-time measurement capability. Conversely, the proposed approach is suitable only for geometries with smooth transversal sections, needs sample preparation and its spatial resolution is limited by the sparsity of the surface control points. The paper describes first the theoretical basis of the procedure; then results of experimental tests on calibration samples and latex tubular specimens are presented and discussed. Further set-up improvements will allow the present procedure to be implemented for in-vitro inflation/extension tests on vascular segments.

Full field methods and residual stress analysis in orthotropic material. I Linear approach

This work analyzes the problem of residual stress determination in an orthotropic material using the hole drilling technique combined with non-contact, full field optical methods. Due to the complex behavior of the material, first a solution algorithm for the isotropic case is analyzed, then the procedure is extended to solving the more complex problem. In the first part of the work, the simplified Smith–Schajer solution to the through-hole problem for an orthotropic material is analyzed, showing that the same linear least square approach used in the isotropic case applies to a large set of orthotropic materials; based on this analysis a simple residual stress measurement algorithm is developed using either analytical or numerically estimated calibration coefficients. In the second part of the work, the general solution is discussed: since in this case the simplified Smith–Schajer solution cannot be used, the Lekhnitskii’s analysis of the through-hole plate in tension is introduced and extended to handle residual stresses. On this basis a solution algorithm using the nonlinear fit of the theoretical displacement field capable of treating all the orthotropic materials at the cost of a more complex numerical procedure is proposed. The performances of both algorithms are tested against numerically generated noisy fields and experimental ones and show a good reliability and accuracy.

Full field methods and residual stress analysis in orthotropic material. II: Nonlinear approach

This paper is the second part of a work that analyses the problem of residual stress determination in an orthotropic material by the hole drilling technique combined with full field optical methods. Due to the complex behaviour of the material, two theoretical formulations capable of describing the displacement field in an infinite plate in tension with a hole have been proposed: a simplified one, which can treat only a subset of all orthotropic materials, and a general, much more complex one. In the first part of this work, it has been shown that by using the simplified formulation, it is possible to develop a linear least square approach to the residual stress identification problem capable of treating a large class of orthotropic materials. This second part shows that the same approach can be extended to the general case providing that a somewhat more complex, nonlinear algorithm, is acceptable.