Delson Braz

Computed tomography in the fatigue test analysis of an asphaltic mixture

Abstract This work applies the computerized tomography technique to the study of an asphaltic mixture. It was required to detect and follow the evolution of a crack, when this mixture was submitted to fatigue tests. The fatigue tests to produce stresses were done in a diametral compression equipment of repeated loading. The trajectory of a crack is influenced by original voids in the specimen; it may be noted that troughs exist in all tomographic images at the same positions and, as these could be due to voids, with a sufficient sequence of applied loads they would be transformed into a small crack that would increase in size, causing the collapse of the specimen. It was possible to detect and follow the evolution of a crack as the 900 blows were applied to the phantom. It was also noted that the crack begins to appear in the central region of the specimen and is propagated in the direction of the applied load.

Elemental mapping of teeth using μSRXRF

Human teeth were analysed by X-ray microfluorescence analysis using synchrotron radiation (μSRXRF). The aim of this work was to study the elemental distribution for Ca, Zn and Sr along the dental regions, enamel, dentine and pulp from patterns of relative fluorescence intensities. The measurements were performed in standard geometry of 45° incidence, exciting with a white beam and using a conventional system collimation (orthogonal slits) in the XRF beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). The results show that Ca distribution is quite constant and it is independent of the tooth type and individuals characteristics. An increase of the Zn concentration was found for the pulp region and for untreated carious areas. Ca and Sr distributions show a similar behavior.

3D X-ray tomography to evaluate volumetric objects

The 3D-CT and stereological techniques are used concomitantly. The quantitative stereology yields measurements that reflects areas, volumes, lengths, rates and frequencies of the test body. Two others quantification, connectivity and anisotropy, can be used as well to complete the analysis. In this paper, it is presented the application of 3D-CT and the stereological quantification to analyze a special kind of test body: ceramic filters which have an internal structure similar to cancellous bone. The stereology is adapted to work with the 3D nature of the tomographic data. It is presented too the results of connectivity and anisotropy.

3D histomorphometric quantification of trabecular bones by computed microtomography using synchrotron radiation.

Conventional bone histomorphometry is an important method for quantitative evaluation of bone microstructure. X-ray computed microtomography is a non-invasive technique, which can be used to evaluate histomorphometric indices in trabecular bones (BV/TV, BS/BV, Tb.N, Tb.Th, Tb.Sp). In this technique, 3D images are used to quantify the whole sample, differently from the conventional one, in which the quantification is performed in 2D slices and extrapolated for 3D case. In this work, histomorphometric quantification using synchrotron 3D X-ray computed microtomography was performed to quantify the bone structure at different skeletal sites as well as to investigate the effects of bone diseases on quantitative understanding of bone architecture. The images were obtained at Synchrotron Radiation for MEdical Physics (SYRMEP) beamline, at ELETTRA synchrotron radiation facility, Italy. Concerning the obtained results for normal and pathological bones from same skeletal sites and individuals, from our results, a certain declining bone volume fraction was achieved. The results obtained could be used in forming the basis for comparison of the bone microarchitecture and can be a valuable tool for predicting bone fragility.

Research on fatigue cracking growth parameters in asphaltic mixtures using computed tomography

Abstract Distress of asphalt concrete pavement due to repeated bending from traffic loads has been a well-recognized problem in Brazil. If it is assumed that fatigue cracking growth is governed by the conditions at the crack tip, and that the crack tip conditions can be characterized by the stress intensity factor, then fatigue cracking growth as a function of stress intensity range ΔK can be determined. Computed tomography technique is used to detect crack evolution in asphaltic mixtures which were submitted to fatigue tests. Fatigue tests under conditions of controlled stress were carried out using diametral compression equipment and repeat loading. The aim of this work is imaging several specimens at different stages of the fatigue tests. In preliminary studies it was noted that the trajectory of a crack was influenced by the existence of voids in the originally unloaded specimens. Cracks would first be observed in the central region of a specimen, propagating in the direction of the extremities. Analyzing the graphics, that represent the fatigue cracking growth (dc/dN) as a function of stress intensity factor (ΔK), it is noticed that the curve has practically shown the same behavior for all specimens at the same level of the static tension rupture stress. The experimental values obtained for the constants A and n (of the Paris–Erdogan Law) present good agreement with the results obtained by Liang and Zhou.

X-ray fluorescence with synchrotron radiation to elemental analysis of lead and calcium content of primary teeth.

Primary teeth were analyzed by micro-SRXRF. The aim of this study was to determine the elemental distribution of lead and calcium in different regions of primary incisor of children living in a notoriously contaminated area (Santo Amaro da Purificação, Bahia State, Brazil). The measurements were performed in standard geometry of 45 degrees incidence, exciting with a white beam and using a conventional system collimation (orthogonal slits) in the XRF beamline at the Synchrotron Light National Laboratory (Campinas, Brazil).

Computed tomography: an evaluation of the effect of adding polymer SBS to asphaltic mixtures used in paving

This work applies the Computed Tomography (CT) technique to the study of asphaltic mixtures to which polymer has been added. An evaluation has been made of the effect of adding Brazilian produced polymer SBS (styrene-butadiene-styrene), to the asphaltic mixtures used in paving. Laboratory mechanical tests and non-destructive testing (NDT) of cylindrical specimens have been made. Three mixtures were prepared for the purpose of this study, all containing 5.4% of asphalt RASF (propane deashalting). One of the mixtures contained no polymer, while the other two were made with 7 and 5% of the SBS polymer. Investigations of Brazilian pavements have shown that cracking is the most important defect due to fatigue in the asphaltic contained overlay. Preliminary results of mechanical tests show that the polymer additive favorably enhances performance of the mixtures. It may be noted that adding polymer SBS to the asphaltic mixture used in paving increases the percentage void. Crack growth in specimens of asphaltic mixtures to which polymer has been added displays the same behaviors as that in specimens in which polymer has not been added.

Analysis of the percentage voids of test and field specimens using computerized tomography

Abstract Computerized tomography has been an excellent tool of analysis of asphaltics mixtures, because it allows comparison of the quality and integrity of test and field specimens. It was required to detect and follow the evolution of cracks, when these mixtures were submitted to fatigue tests, and also helping to interpret the distribution of tensions and deformations which occur in the several types of solicitations imposed to the mixtures. Comparing the medium values of percentage voids obtained from tomographic images with the project’s values, it can be observed that the values of test and field specimens for the wearing course are closer to the ones of the project than the ones of the binder. It can be verified that the wearing course specimens always present a distribution of the aggregate, and voids quite homogeneously in the whole profile of the sample, while the binder specimens show an accentuated differentiation of the same factors in the several heights of the sample. Therefore, when choosing a slice for tomography, these considerations should be taken into account.

X-ray transmission microtomography using synchrotron radiation

This work reports the feasibility of a non-destructive synchrotron radiation X-ray transmission imaging technique development at Brazilian synchrotron light source. The quality control image parameters (spatial and density resolution and noise) are given and microtomograms presented. Microtomograms of biomedical samples are presented. The tomography system was mounted into the XRF beamline that uses a high-intensity white beam with 12 keV effective energy, and maximum width and height equals to 11 and 1 mm, respectively. The detector used to collect the data was a 512-pixel Hamamatsu linear array with width of 50 μm (36 μm of sensitivity length) and cooled by a Peltier junction, causing the temperature falling down to 15°C. The samples were placed over a computer controlled table with 0.5° angular resolution and turned around the center covering 360°. To reconstruct the sample a parallel beam filtered back-projection algorithm was used.

Computed tomography: evaluation of stability tests and indirect tensile strength of field asphaltic mixtures

This work applies the computed tomography technique to the study of asphaltic mixtures. After analyzing Marshall stability and indirect tensile strength (IDT) tests, this technique was used for NonDestructive Testing (NDT) structural evaluations of field specimens. By analyzing the tomograms of the asphaltic mixtures it is possible to compare quality and physical conditions of field specimens, and also helps to interpret the distributions of tensions and deformations which occur in several types of solicitations imposed to the mixtures. The performance of asphaltic mixture could be more accurately predicted when all properties are known. The CT results of this work will be grouped with older and earlier data acquisition in order to compose a more complete database beyond years. Then these investigations could be used to increase the asphaltic mixtures quality by improving design and manufacturing procedures.