Residual stress levels induced during the process are one of the more relevant characteristics of thermal spray coatings. Therefore, there are different techniques, such as the x-ray diffractometry ...or the classical micro hole drilling and milling method, to analyse and optimize the thermal spray coating process in order to obtain a desired level of residual stresses on coatings. The state of the art of the new developed non-contact, quasi non-destructive residual stress analysis method is presented. The material removal is based on laser ablation and complex ablation geometries are possible by using a spatial light modulator (SLM) for beam conditioning. 3D deformations on the specimen surface are measured in the nanoscale range by high-resolution digital holographic interferometry. Numerical procedures using the finite differences method are performed in order to calculate the shape geometry and the calibration curves required for the residual stress calculation from the measured 3D displacements, coating-substrate material combination and the ablation geometry. Experimental results on thermal spray coatings are presented and discussed with comparative measurements by the hole-drilling method. The potentials and difficulties of the method are discussed.
•Residual stress levels induced during the process are one of the more relevant characteristics of thermal spray coatings.•A very interesting and recently developed non-contact, quasi non-destructive residual stress analysis characterization technique for the analysis of residual stresses on coatings is presented.•The greatest attraction of this technique is the smart combination of the machining of complex geometries by a laser ablation process and the optical determination of superficial 3D deformations in the nanoscale range by high-resolution digital holographic interferometry.•Numerical procedures using the finite element method are performed in order to calculate the shape geometry and the calibration curves required for the residual stress calculation from the measured 3D displacements, coating-substrate material combination and the ablation geometry.
Digital shearography is an interferometric technique, which is often used for defect detection on composite structures. The measurement is fast and non‐destructive and thus suitable for the ...application to cultural heritage. However, a major drawback of the technique is the indirect measurement, because surface strain is used to detect subsurface defects. So the determination of depth, size, and type of the defects is rather difficult. To overcome this issue, we use a combination of finite element method simulation and shearographic measurement. Due to the comparison of both data sets, the inverse problem can be solved in a more reliable way. In this paper, we investigate the application of finite element method simulation for an improved defect detection on anisotropic material. We validate the technique on a wooden sample with notches on the backside.
In this paper, a method for residual stress analysis of ceramic coatings by applying a laser for quasi non-destructive material removal and measuring the 3D displacement around the machined area by ...means of high-resolution digital holography is described. The residual stresses are retrieved by numerical calculations using the finite element method (FEM) from the measured 3D displacements, the profile of the machined hole and the material parameters of the coating and substrate. Experimental results on thermal spray coatings together with discussion of the difficulties, work in progress, potential of the method, and comparative measurements by the hole-drilling method are presented.
Optical coherent techniques are well suited for the measurement of microcomponents but give accurate results only when calibrated systems are used. This paper presents a strategy for the calibration ...that involves at first the development of micromechanical reference components deforming in a reproducible retraceable and precise way when submitted to standard loadings. These reference materials are then used for the calibration of the measuring systems. Guidelines for building and measuring reference materials together with methods for evaluating the measurement uncertainty are presented.
A phase retrieval method for microscopy using multiple illumination wavelengths is proposed. A fast algorithm suitable for calculations with high numerical aperture is used for the iterative ...retrieval of the object wavefront. The advantages and limitations of the technique are systematically analyzed and demonstrated by both simulation and experimental results.
: In the first part (section 2) of the paper, a system based on digital holographic interferometry for the measurement of vibrations is presented. A high‐power continuous laser (10 W) and a ...high‐speed charge coupled device camera are used. Hundreds of holograms of an object that was subjected to dynamic deformation are recorded. The phase of the wave front is calculated from the recorded holograms by use of a two‐dimensional digital Fourier‐transform method. The deformation of the object is obtained from the phase. By combination of the deformations recorded at different time it is possible to reconstruct the vibration of the object. In the second part (section 3) of our paper, the holographic method is used for the measurements of the elastic properties of the bone. Samples of bone were loaded and deformed and a large number of interferograms (digital holograms) were recorded over a short period of time. In the third part (section 4) of the paper, we show how the holographic systems are adapted for performing measurements in hidden cavities.
Abstract The following paper aims to analyse the perceptions or images of a good university student and to identify the competences needed to be a good student, according to the implicit theories ...held by first and second year teachers of the University Teacher Training Course in Biology at the Faculty of Exact, Chemical and Natural Sciences of the National University of Misiones. The methodological approach of the research is mixed and of flexible design. The instruments used were the questionnaire and the interview. From the analysis of the data, it can be seen that the teachers consider that a good student should have transversal competences such as teamwork, autonomy and time organisation. They also mentioned study habits which would be related to causal and linear learning linked to direct and interpretative theory. For women and men, students possess instrumental and interpersonal transversal competences; men add systemic competences. The accompaniment strategies mentioned by the teachers coincide with their conception of learning.
: Optical techniques are well suited for the measurement of microcomponents but give accurate results only when calibrated systems are used. This paper presents the development of a standard ...reference device whose in‐plane displacement is precisely reproducible when submitted to standard loadings. The reference device has been manufactured and tested by optical measuring systems. This reference device is to be used for the calibration of optical measuring systems in the future.
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