Friction coefficient and abrasive wear modes in ball-cratering tests conducted at constant normal force and constant pressure-Preliminary results

The micro-scale abrasive wear test by rotative ball has gained large acceptance in universities and research centers, being widely used in studies on the abrasive wear of materials. Two wear modes are usually observed in this type of test: ""rolling abrasion"" results when the abrasive particles roll on the surface of the tested specimen, while ""grooving abrasion"" is observed when the abrasive particles slide; the type of wear mode has a significant effect on the overall behaviour of a tribological system. Several works on the friction coefficient during abrasive wear tests are available in the literature, but only a few were dedicated to the friction coefficient in micro-abrasive wear tests conducted with rotating ball. Additionally, recent works have identified that results may also be affected by the change in contact pressure that occurs when tests are conducted with constant applied force. Thus, the purpose of this work is to study the relationship between friction coefficient and abrasive wear modes in ball-cratering wear tests conducted at ""constant normal force"" and ""constant pressure"". Micro-scale abrasive wear tests were conducted with a ball of AISI52100 steel and a specimen of AISIH10 tool steel. The abrasive slurry was prepared with black silicon carbide (SiC) particles (average particle size of 3 mu m) and distilled water. Two constant normal force values and two constant pressure values were selected for the tests. The tangential and normal loads were monitored throughout the tests and their ratio was calculated to provide an indication of the friction coefficient. In all cases, optical microscopy analysis of the worn craters revelated only the presence of grooving abrasion. However, a more detailed analysis conducted by SEM has indicated that different degrees of rolling abrasion have also occurred along the grooves. The results have also shown that: (i) for the selected values of constant normal force and constant pressure, the friction coefficient presents, approximately, the same range of values and (ii) loading conditions play an important role on the occurrence of rolling abrasion or grooving abrasion and, consequently, on the average value and scatter of the friction coefficient in micro-abrasive wear tests. (C) 2009 Elsevier B.V. All rights reserved.

Scope of chemical explosive cratering experiment /

"Issued: Aug.,1963"--Cover : "May 15, 1963"--Title page.

Seismic effects from a high yield nuclear cratering experiment in desert alluvium /

"Final report "--Cover.

Influence of a cratering device on close-in populations of lizards /

"PNE-224F."

Operator's and organizational maintenance manual (including repair parts and special tools list) : demolition materials, demolition kit, cratering, M180, NSN 1375-00-148-7159 and demolition kit, cratering, training, M270 (inert), NSN 6920-01-0038.

Shipping list no.: 89-268-P.

Er : YAG laser, ultrasonic system, and curette produce different profiles on dentine root surfaces: An in vitro study

Objective: The aim of the present study was to compare the in vitro effects of the Er:YAG laser, an ultrasonic system, and manual curette on dentine root surface by roughness and micro-morphological analysis. Materials and Methods: Thirty-six flattened bovine roots were randomly assigned to one of the following groups: group 1 (n = 12): Er: YAG laser ( 2940 nm), 120 mJ/pulse, 10 Hz, 8.4 J/cm(2); group 2 ( n = 12): ultrasonic system; and group 3 ( n = 12): manual curette. The mean surface roughness (Ra) of each sample was measured using a profilometer before and after the treatments. The micro-morphology of the treated and untreated ( control) root surfaces was evaluated with scanning electron microscopy (SEM) at 50 x and 1000 x magnification. Results: Analysis with the profilometer showed that for equal times of instrumentation, the smoothest surfaces were produced by the Er: YAG laser and the ultrasonic system, followed by the curette ( p < 0.05). Morphological analyses demonstrated that treatment with the Er: YAG laser produced some areas with an irregular surface, craters, and ablation of the intertubular dentin. The smear layer was removed and dentine tubules were opened by both curettes and the ultrasonic system. The micro-morphology of the dentine root surface after ultrasonic treatment, however, demonstrated randomly distributed areas cratering. Conclusion: All instruments increased the roughness of the dentine root surface after treatment; however, the curette produced rougher surfaces than the other devices. SEM analysis revealed distinct root surface profiles produced by the three devices.

Mechanical and tribological characterization of TiB2 thin films

Titanium Diboride (TiB2) presents high mechanical and physical properties. Some wear studies were also carried out in order to evaluate its tribological properties. One of the most popular wear tests for thin films is the ball-cratering configuration. This work was focused on the study of the tribological properties of TiB2 thin films using micro-abrasion tests and following the BS EN 1071-6: 2007 standard. Due to high hardness usually patented by these films, diamond was selected as abrasive on micro-abrasion tests. Micro-abrasion wear tests were performed under five different durations, using the same normal load, speed rotation and ball. Films were deposited by unbalanced magnetron sputtering Physical Vapour Deposition (PVD) technique using TiB2 targets. TiB2 films were characterized using different methods as Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Electron Probe Micro-Analyser (EPMA), Ultra Micro Hardness and Scratch-test Analysis, allowing to confirm that TiB2 presents adequate mechanical and physical properties. Ratio between hardness (coating and abrasive particles), wear resistance and wear coefficient were studied, showing that TiB2 films shows excellent properties for tribological applications.

TiB2 nanostructured coating for GFRP injection moulds

In the injection moulding of polypropylene reinforced with hard glass fibres, die materials are commonly subjected to severe abrasive wear. In order to improve its wear resistance, an unbalanced magnetron sputtering PVD compositional monolayered coating has been produced. The film was composed by a nanostructured TiB2 monolayer. Microstructure characterization and thickness evaluation were conducted by scanning electron microscopy (SEM). Film topography and roughness were accessed by SEM and Atomic Force Microscopy (AFM). The phase analyse was investigated by X-ray diffraction (XRD), using Cu Kalpha radiation. Scratch tests were conducted in order to study the film adhesion to the substrate. Load-Displacement curves (nanoindentation analysis) allowed measuring the film hardness and Young's modulus. A ball-cratering tribometer was used to determine the micro-abrasion laboratorial wear resistance, under different tests conditions, using SiC particles in distilled water slurry. At the end of these tests, the worn surfaces were analyzed by SEM and Energy Dispersive X-ray Spectroscopy (EDS) in order to compare these results with some other coatings already tested in the same conditions. To test the practical wear resistance, 135000 injection cycles were done in a plastic injection industrial mould. Coated samples were put on the plastic feed canal, after a turbulent zone. In these tests, a 30% (wt) glass fibres reinforced polypropylene was used. Worn sample surfaces were analyzed by SEM after 45.000 and 90.000 cycles. Image analyses were made in order to evaluate the damage increases and to observe the wear mechanisms involved.

Role of abrasive material on micro-abrasion wear tests

Micro-abrasion wear tests with ball-cratering configuration are widely used. Sources of variability are already studied by different authors and conditions for testing are parameterized by BS EN 1071-6: 2007 standard which refers silicon carbide as abrasive. However, the use of other abrasives is possible and allowed. In this work, ball-cratering wear tests were performed using four different abrasive particles of three dissimilar materials: diamond, alumina and silicon carbide. Tests were carried out under the same conditions on a steel plate provided with TiB2 hard coating. For each abrasive, five different test durations were used allowing understanding the initial wear phenomena. Composition and shape of abrasive particles were investigated by SEM and EDS. Scar areas were observed by optical and electronic microscopy in order to understand the wear effects caused by each of them. Scar geometry and grooves were analyzed and compared. Wear coefficient was calculated for each situation. It was observed that diamond particles produce well-defined and circular wear scars. Different silicon carbide particles presented dissimilar results as consequence of distinct particle shape and size distribution.

Geoelectric evidence for centripetal resurge of impact melt and breccias over central uplift of Araguainha impact structure

We present five profiles from electrical resistivity tomography (ERT), with surface constraints and gravity data, in the central uplift of the Araguainha impact structure in central Brazil. The central uplift, the overlying polymict breccias, and decameter-scale impact melt rocks are characterized by contrasting ranges of electrical resistivity. Our resistivity model provides empirical evidence that supports the existing model in which impact melt and breccias resurged toward the crater center in the final stages of the cratering process. On the basis of our results from the first use of ERT in impact cratering studies, we conclude that the deposition and flow of impact melt and breccias over the central uplift were influenced by the geometry of the lithologic boundaries in the central uplift.

Avaliação do comportamento ao desgaste de compósitos poliméricos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Avaliação da resistência ao desgaste de uma resina composta odontológica nanoparticulada empregando diferentes tempos de fotopolimerização

Pós-graduação em Engenharia Mecânica - FEG

Insights into the morphology of the Serra da Cangalha impact structure from geophysical modeling

Forward modeling is commonly applied to gravity field data of impact structures to determine the main gravity anomaly sources. In this context, we have developed 2.5-D gravity models of the Serra da Cangalha impact structure for the purpose of investigating geological bodies/structures underneath the crater. Interpretation of the models was supported by ground magnetic data acquired along profiles, as well as by high resolution aeromagnetic data. Ground magnetic data reveal the presence of short-wavelength anomalies probably related to shallow magnetic sources that could have been emplaced during the cratering process. Aeromagnetic data show that the basement underneath the crater occurs at an average depth of about 1.9 km, whereas in the region beneath the central uplift it is raised to 0.51 km below the current surface. These depths are also supported by 2.5-D gravity models showing a gentle relief for the basement beneath the central uplift area. Geophysical data were used to provide further constraints for numeral modeling of crater formation that provided important information on the structural modification that affected the rocks underneath the crater, as well as on shock-induced modifications of target rocks. The results showed that the morphology is consistent with the current observations of the crater and that Serra da Cangalha was formed by a meteorite of approximately 1.4 km diameter striking at 12 km s-1.

Geochronological constraints on the age of a Permo-Triassic impact event: U-Pb and Ar-40/Ar-39 results for the 40 km Araguainha structure of central Brazil

Impact cratering has been a fundamental geological process in Earth history with major ramifications for the biosphere. The complexity of shocked and melted rocks within impact structures presents difficulties for accurate and precise radiogenic isotope age determination, hampering the assessment of the effects of an individual event in the geological record. We demonstrate the utility of a multi-chronometer approach in our study of samples from the 40 km diameter Araguainha impact structure of central Brazil. Samples of uplifted basement granite display abundant evidence of shock deformation, but U/Pb ages of shocked zircons and the Ar-40/Ar-39 ages of feldspar from the granite largely preserve the igneous crystallization and cooling history. Mixed results are obtained from in situ Ar-40/Ar-39 spot analyses of shocked igneous biotites in the granite, with deformation along kink-bands resulting in highly localized, partial resetting in these grains. Likewise, spot analyses of perlitic glass from pseudotachylitic breccia samples reflect a combination of argon inheritance from wall rock material, the age of the glass itself, and post-impact devitrification. The timing of crater formation is better assessed using samples of impact-generated melt rock where isotopic resetting is associated with textural evidence of melting and in situ crystallization. Granular aggregates of neocrystallized zircon form a cluster of ten U-Pb ages that yield a "Concordia" age of 247.8 +/- 3.8 Ma. The possibility of Pb loss from this population suggests that this is a minimum age for the impact event. The best evidence for the age of the impact comes from the U-Th-Pb dating of neocrystallized monazite and Ar-40/Ar-39 step heating of three separate populations of post-impact, inclusion-rich quartz grains that are derived from the infill of miarolitic cavities. The Pb-206/U-238 age of 254.5 +/- 3.2 Ma (2 sigma error) and Pb-208/Th-232 age of 255.2 +/- 4.8 Ma (2 sigma error) of monazite, together with the inverse, 18 point isochron age of 254 +/- 10 Ma (MSWD = 0.52) for the inclusion-rich quartz grains yield a weighted mean age of 254.7 +/- 2.5 Ma (0.99%, 2 sigma error) for the impact event. The age of the Araguainha crater overlaps with the timing of the Permo-Triassic boundary, within error, but the calculated energy released by the Araguainha impact is insufficient to be a direct cause of the global mass extinction. However, the regional effects of the Araguainha impact event in the Parana-Karoo Basin may have been substantial. (C) 2012 Elsevier Ltd. All rights reserved.

The Sedan event /

"April 1965"--Title page ; "Issued August 6, 1965"--Cover.