Jaime Monteiro

NDI of Interfaces in Coating Systems Using Digital Interferometry

Abstract This paper describes a new application of two laser interferometry techniques to the non-destructive inspection (NDI) of coated surfaces. The purpose is to detect interfacial disbond between the coating and the substrate. Debonding is detected by properly exciting the surface of the object under inspection in such a way that the interference fringe pattern is modified rendering the disbond readily visible. The fringe patterns resulting from the associated images were captured using electronic speckle pattern interferometry (ESPI) and shearography. Image processing techniques are applied to enhance the detection and better definition of the debonded layer. Some results and discussions are presented to illustrate the applicability of these two optical techniques to thermal barrier coatings.

Numerical–Experimental Method for the Validation of a Controlled Stiffness Femoral Prosthesis

The aim of this paper is to describe a new numerical-experimental method to determine the stiffness of a conceptual proximal femoral prototype. The methodology consists of the comparison of the numerical and experimental displacement distributions of the prosthesis loaded as a cantilever beam to validate a design concept: controlled stiffness prosthesis. The manufactured prototype used to test the applicability of the numerical-experimental procedure integrates a stiff metal core bonded to a composite material made of an epoxy resin reinforced with carbon-glass braided pre-forms. The prosthesis with an embedded controlled stiffness concept was obtained by varying the geometry of the core with the composite layer thickness.

Use of interferometric techniques for measuring the displacement field in the plane of a part-through crack existing in a plate

An experimental procedure based on holographic interferometry coupled with computer-aided image processing techniques was used to estimate the stress intensity factor (SIF) of a part-through crack in a plate. The loading consisted of a uniform remote tensile stress, leading to an opening and edge rotation displacement field along the crack plane. The evaluation of the crack opening displacements and edge rotations, carried out after the numerical interpretation of the fringe pattern, made possible an estimation of the SIF along the crack line, following the theoretical basis of the Line-Spring Model developed by Rice and Levy.

Assessment of the Displacement Field Along a Surface Crack in a Flat Plate Using Optical Techniques

Structural components may contain cracks, and for these components a crack tip represents a highly singular stress. The evaluation of the associated strain gradient is difficult to achieve with experimental discrete methods. An efficient alternative are the optical techniques which are non-contact, and so delivering continuous information of the displacement fields and associated derivatives for strain evaluation. This paper describes some experimental methods to fully characterize the displacement field near a crack tip existing in flat plates. Three optical field techniques based on image analysis were used in the present work; respectively, Electronic Speckle Pattern Interferometry, Moiré Interferometry, and Digital Image Correlation. These methods allow different resolutions which can be adjusted according to the expected strain gradient. While the first method depends on the laser wavelength and position of the illumination sources, the second depends on the grating pitch and the last on the surface texture or painted speckle. Algorithms to derivate and filtering the displacement field are developed to compute the strain field and will be used for further works.

Analysis of mechanical behavior of implant-supported prostheses in the anterior maxilla: analysis by speckle pattern interferometry

The use of implants to rehabilitation of total edentulous, partial edentulous or single tooth is increasing, it is due to the high rate of success that this type of treatment present. The objective of this study was to analyze the mechanical behavior of different positions of two dental implants in a rehabilitation of 4 teeth in the region of maxilla anterior. The groups studied were divided according the positioning of the implants. The Group 1: Internal Hexagonal implant in position of lateral incisors and pontic in region of central incisors; Group 2: Internal Hexagonal implant in position of central incisors and cantilever of the lateral incisors and Group3 - : Internal Hexagonal implants alternate with suspended elements. The Electronic Speckle Pattern Interferometry (ESPI) technique was selected for the mechanical evaluation of the 3 groups performance. The results are shown in interferometric phase maps representing the displacement field of the prosthetic structure.