A.J. López

Modelling of temperature evolution on metals during laser hardening process

Abstract To achieve a precise and controlled laser process, an exhaustive analysis of the thermal behaviour of the material is necessary. In the present paper, a numerical simulation of the laser hardening process has been developed using both analytical solutions and the finite element code ANSYS™ to solve the heat transfer equation inside the treated material. The knowledge of the thermal cycles has enabled suitable processing parameters to be ascertained thus improving surface properties when metallic alloys have been irradiated. A simpler analytical method is also used to determine the mentioned parameters more quickly. This general purpose method has been applied to a specific experimental situation, namely the treatment of cylindrical pieces used in a multistage pump rotary jacket.

Effectiveness of granite cleaning procedures in cultural heritage: A review.

Most of the Cultural Heritage built in NW Iberian Peninsula is made of granite which exposition to the environment leads to the formation of deposits and coatings, mainly two types: biological colonization and sulphated black crusts. Nowadays, another form of alteration derives from graffiti paints when these are applied as an act of vandalism. A deep revision needs to be addressed considering the severity of these deterioration forms on granite and the different cleaning effectiveness achieved by cleaning procedures used to remove them. The scientific literature about these topics on granite is scarcer than on sedimentary carbonate stones and marbles, but the importance of the granite in NW Iberian Peninsula Cultural Heritage claims this review centred on biological colonization, sulphated black crusts and graffiti on granite and their effectiveness of the common cleaning procedures. Furthermore, this paper carried out a review of the knowledge about those three alteration forms on granite, as well as bringing together all the major studies in the field of the granite cleaning with traditional procedures (chemical and mechanical) and with the recent developed technique based on the laser ablation. Findings concerning the effectiveness evaluation of these cleaning procedures, considering the coating extraction ability and the damage induced on the granite surface, are described. Finally, some futures research lines are pointed out.

Monitoring the laser cleaning of granites by means of multispectral image analysis

In this work it is presented a study about the ability of multispectral techniques for evaluating in situ, nondestructively, the progress of laser removal of crusts and paints in granitic rocks. For this purpose, granites with different characteristics were cleaned by the third harmonic of a Nd:YVO4 laser, and a multispectral camera was used to monitor the process by recording images of the rock surface during the cleaning. Although preliminary, the results are promising and show that the comparative analysis of the spectra could be used for successfully monitoring the cleaning process. Furthermore, it has been possible to discriminate between black crusts of different nature, biogenic and anthropogenic, by analyzing specific spectral bands.

Characterization of drying paint coatings by dynamic speckle and holographic interferometry measurements

In this work we implemented dynamic speckle and holographic interferometry techniques to characterize the drying process of solvent-based paint coatings. We propose a simple way to estimate drying time by measuring speckle activity and incrementally fitting experimental data through standard regression algorithms. This allowed us to predict drying time after about 20-30 min of paint application, which is fast compared to usual times required to reach the so-called tack-free state (≈2  h). In turn, we used holographic interferometry to map small thickness variations in the coating surface during drying. We also demonstrate that results obtained from both techniques correlate with each other, which allows us to improve the accuracy of the drying time estimation.

Biospeckle Activity Evolution of Strawberries

Fil: Mulone, Cecilia. Universidad Tecnologica Nacional. Facultad Regional Parana; Argentina

Laser Hardening of XC42 Steel: Numerical Analysis of Quenched Area

In contrast with conventional tools, laser processing allows hardening of a restricted zone while keeping the structural properties of the steel bulk. This last quality indicates that, in order to verify a laser hardening, only some specific information of the quenched area is required. The aim of this article is to analyse the reliability of finite element numerical simulation by comparing numerical and experimental outcomes. To do that, we define some magnitudes: the maximum width, the real depth of the laser penetration, the maximum hardness and the hardness versus depth profiles (Jominy’s curves). The tests show the good behaviour of the model and how this contributes important information to the choice of the laser parameters.

Compositional Analysis of Polychromes by Laser-Induced Breakdown Spectroscopy

This study deals with the analysis and characterization of wood polychromes by means of Laser-Induced Breakdown Spectroscopy (LIBS). Specimens from a Baroque altarpiece have been analyzed by using a Q-switched Nd:YAG laser source at the wavelength of 355 nm. Previously, a library of characteristic LIBS spectra of the most commonly used pigments and other materials involved was obtained. The knowledge of these spectra allowed us to identify the main constituents of the different layers in polychromes and to obtain compositional depth profiles.

NDT testing by holographic interferometry applied to the structural diagnostic of artwork conservations by means of sound wave excitation

Techniques based on holographic interferometry have achieved a mature state of non destructive testing applications in industry and nowadays they are rising as interesting and promising tools in the field of conservation practices; giving information about the condition of structural integration of artworks. In the practice of these techniques it is necessary to generate a relative deformation in the object under study. Depending of the characteristics of the artwork, different methods may be used to achieve the desired displacement; being thermal excitation by means of filament lamps and wave sounds generated by speakers the most common. By applying these methods the deformation process usually involves a large area of the object, which limits the information obtained of a finite region. However, the use of a wave sound emitter of small dimensions, like a low power monotone buzzer, allows to decrease the affected area and to obtain information about the structural integrity of localized points of the surface. In the present study conventional double exposure double way holographic technique based on holographic films was used to obtain an out of plain deformation pattern caused by a sound emitter in an oil painting which has suffered heavy structural damage. Optimization of the excitation sound wave characteristics (frequency and amplitude) and the adjustment and calibration of the experimental set up, in order to obtain precise information about the physical and mechanical integrity of localized points of the painting are reported.

Provenance Characterization of Archaeological Ceramics by Laser Induced Plasma Spectroscopy

Archaeological ceramics Terra Sigillata manufactured in different production centres have been studied by “laser induced plasma spectroscopy” (LIPS). The aim of this work is to demonstrate the capability of LIPS for the classification of pottery shreds in function of their provenance. Characteristic emission spectra of different pottery groups were obtained and simple linear correlation methods were used for grouping samples. In addition, complementary scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDX) analysis were performed to obtain morphological features and to confirm chemical results

Analysis of small deflections by double-exposure digital holographic interferometry

We analyzed small deflections (~1 μm) of an opaque object by means of the double-exposure digital holographic interferometry technique, using an off-axis lensless Fourier holographic arrangement. The deflections were caused by heating the object with a flowing dc current. In our holographic arrangement, out-of-plane displacements of around 300 nm can be precisely detected by using a He-Ne laser as the coherent illumination source. However, this resolution could be improved by modifying the experimental setup or even choosing an appropriate object reference state. We briefly show the theoretical description of the technique and conduct experiments and simulations to test the results. Since the object we have studied in this work is a bimetallic strip, the obtained results point towards further research concerning precise temperature sensing devices.