Stress-induced ordering due heavy interstitial atoms in Nb-0.3 wt.% Ti alloys

The mechanical properties of metals with bee structure, such as niobium and their alloys, are changed of a significant way by the introduction of heavy interstitial elements. These interstitial elements (oxygen, for example) present in the metallic matrix occupy octahedral sites and constitute an elastic dipole of tetragonal symmetry and might produce anelastic relaxation. Polycrystalline samples of Nb-0.3 wt.% Ti (Nb-Ti) alloy with oxygen in solid solution were analysed. The anelastic spectroscopy measurements had been made in a torsion pendulum, with frequencies in the Hz range, in a temperature range between 300 and 700 K. The results showed thermally activated relaxation structures were identified four relaxation process attributed to stress-induced ordering of single oxygen, nitrogen and carbon atoms around niobium and stress-induced ordering of single oxygen atoms around titanium atoms. (c) 2005 Elsevier B.V. All rights reserved.

Modification of surface properties of Ti-16Si-4B powder alloy by plasma immersion ion implantation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Controlled fluorination of a-C:F:H films by PECVD of ethylene-hexafluorobenzene mixtures

Highly fluorinated plasma polymers are chemically inert,acid resistant and have low friction coefficients, thereby being useful in chemical laboratories and for tribological applications. Here we report the plasma polymerization of ethylene-hexafluorobenzene mixtures by PECVD. The principal parameter of interest is the proportion of C(6)F(6) in the feed, R(F). Films were analyzed using near-normal and grazing-angle Infrared Reflection Absorption Spectroscopy (IRRAS), the latter being particularly useful for detecting modes not usually observed at near-normal incidence. The presence of CH and CF(x) (x=1 to 2) groups was thus confirmed in films deposited with R(F)>= 40%. Depending on R(F) IRRAS also revealed the presence of -CH(x) (x=1 to 3) -C=C, -C=O and phenyl rings. Deconvolution of C is spectra obtained by X-ray Photoelectron Spectroscopy (XPS) confirmed the presence of CH, CF and CF(2) groups in films deposited with R(F)>= 40%. Atomic ratios of F:C calculated from the XPS spectral data show that the degree of fluorination rises with increasing RF Some unbound fluorine is present in the films. Post-deposition reactions account for the presence of oxygen (similar to 5%) in the films. Surface energies, determined from contact angle measurements, fall with increasing R(F). (C) 2008 Elsevier B.V. All rights reserved.

Rheological Analysis of Water Clay Compositions in Order to Investigate Mudflows Developing in Canals

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Hydrogenated amorphous carbon as protective coating for a forming tool

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Lubricating coating prepared by PIIID on a forming tool

In this work, the performance of a-C: H films produced by the hybrid Plasma Immersion Ion Implantation and Deposition technique as lubricating layers for a steel forming tool has been investigated. Hardened steel (AISI M2, 64 HRC) plates coated with a commercial TiN layer were used as substrates and the films were deposited in a vacuum chamber fitted with two parallel-plate electrodes. The discharges were generated in atmospheres composed of 91% C2H2 and 9% Ar by the application of radiofrequency power (13.56 MHz, 100 W) to the upper electrode while the lower one, also used as the sample holder, was biased with high voltage negative pulses (3.6 kV, 30 mu s, 300 Hz). A deposition time of 840 s was used. The effects of the gas pressure, p, on thickness, molecular structure, wettability, surface morphology and topography, hardness and friction coefficient of the films lwere investigated. Film thickness increased from 0.3 to 0.5 mu m when p was increased from 2.7 to 16.5 Pa. Generally, the films were slightly hydrophilic, with contact angles of around 84 degrees, and the deposition decreased the roughness of the steel. A polymer-like structure was detected in high pressure depositions and an amorphous carbon structure derived from the low pressure procedures. Hardness decreased from 8.2 to 7.0 GPa with increasing p. Improvement in tribological performance was indicated by the fall in the friction coefficient from 0.5 to 0.2 as the deposition pressure was reduced. Operating at the latter value (of mu) would lead to a significant reduction in wear and hence to significant economy in diverse industrial applications.

ADJUSTED F FACTOR FOR MULTIPLE-OUTLET PIPES.

An adjusted F factor to compute pressure head loss in pipes having multiple, equally spaced outlets is derived for any given distance from the first outlet to the beginning of the pipe. The proposed factor is dependent on the number of outlets and is expressed as a function of the J. E. Christiansen's F factor. It may be useful to irrigation engineers to estimate friction in sprinkle and trickle irrigation laterals and manifolds, as well as gated pipes.

Anelastic relaxation due to OH pairs in NbZr alloys

In the last 30 years several studies have been made to understand the relaxation mechanisms of the hydrogen atoms present in transition metals and their alloys. In this work, we observed the stress-induced ordering of hydrogen atoms around the interstitial oxygen atoms near the niobium matrix atoms. We studied this relaxation process by measuring the attenuation of longitudinal ultrasonic waves. These measurements were made in Nb1.0%Zr polycrystalline alloys at 10 and 30 MHz, pure and doped with 0.7 and 4.2 at.% hydrogen. The results revealed a thermally activated relaxation structure around 202 K and 235 K for 10 MHz and 30 MHz respectively. This relaxation structure increases with increasing hydrogen concentration. © 1994.

Performance of low/correct pressure radial ply tires

Extensive field testes were conducted using the UCD single wheel tester employing three large radial ply tractor tires in two different soils, four different soil conditions, two axle load levels, and three levels of tire inflation pressures in order to quantify the benefits of using low/correct inflation pressures. During these tests slip, net traction, gross traction, and dynamic axle load were recorded. Furthermore, soil moisture content, cone index, and dry bulk density data were obtained at test locations. The results of the analysis showed a significant increase in net traction and traction efficiency when low/correct inflation was used. Benefits of using low/correct pressure was higher in tilled soil conditions.

Coeficientes de perda de carga em valvulas e acessorios no escoamento laminar de fluidos nao-Newtonianos

Friction loss coefficients for laminar flow of xantan gum solutions (concentrations in the range of 0.1-0.5% by weight) through valves and fittings were experimentally determined. The rheological behavior, studied by means of a concentric cylinder rheometer, was pseudoplastic, being well described by the Ostwald-De Waele model with non-linear correlation coefficients (r) between 0.998 and 0.999. In the pressure drop measurements the following fittings were employed: completely open and half way open ball valve, completely open and half way open angle valve, tee used like coupling, tee used like a 90° elbow, short radius 90° elbow and coupling. The results showed that the friction loss coefficients increased with decreasing generalized Reynolds number. The friction loss coefficients could be well adjusted by a potential model, suggested by Kittredge & Rowley (1957) for Newtonian fluids, K f = A(Re g) -B, with correlation coefficients between 0.837 and 0.999.

Water waves generated by local disturbance: Serre's model validity

Water waves generated by landslides were long menace in certain localities and the study of this phenomenon were carried out at an accelerated rate in the last decades. Nevertheless, the phase of wave creation was found to be very complex. As such, a numerical model based on Boussinesq equations was used to describe water waves generated by local disturbance. This numerical model takes in account the vertical acceleration of the particles and considers higher orders derivate terms previously neglected by Boussinesq, so that in the generation zone, this model can support high relative amplitude of waves.

Stick-slip chaos in a non-ideal self-excited system

In engineering practical systems the excitation source is generally dependent on the system dynamic structure. In this paper we analyze a self-excited oscillating system due to dry friction which interacts with an energy source of limited power supply (non ideal problem). The mechanical system consists of an oscillating system sliding on a moving belt driven by a limited power supply. In the oscillating system considered here, dry friction acts as an excitation mechanism for stick-slip oscillations. The stick-slip chaotic oscillations are investigated because the knowledge of their dynamic characteristics is an important step in system design and control. Many engineering systems present stick-slip chaotic oscillations such as machine tools, oil well drillstrings, car brakes and others.

Resistência ao Cisalhamento de um Latossolo sob Diferentes uso e Manejo

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The influence of vinegars on exposure of dentinal tubules: a SEM evaluation.

Dentin hypersensitivity is a common painful condition observed in clinics. Dietary habits have been much associated with its development and persistence during and following periodontal treatment. The aim of this in vitro study was to evaluate the influence of vinegars on the removal of smear layer and exposure of dentinal tubules. Extracted human teeth were submitted to manual scaling with Gracey curettes in order to remove the cementum as well as to form a smear layer. Dentin samples with 3 mm(2) were obtained and distributed into six experimental groups: one control and five types of vinegars (alcohol, apple, rice, white wine and balsamic). Each group included two methods of vinegar application: topical and friction. After routine preparation for SEM analysis, photomicrographs were assessed by a calibrated and blind examiner using an appropriate index system. Kruskal-Wallis test indicated a significant influence of vinegars on smear layer removal. There was a statistically significant difference between groups treated with apple, white and rice vinegars and the control group (p < 0.05). Nevertheless, Mann-Whitney test indicated that removal of smear layer did not vary with the method of application (topical versus friction) for any of the tested substances. We can conclude that the contact of vinegar may remove smear layer and expose dentinal tubules, regardless of the type of application. However, balsamic vinegar was associated with less removal of smear layer after both methods of application.

Influence of natural fruit juices in removing the smear layer from root surfaces - An in vitro study

Certain elements of a patient's diet may be associated with dentin hypersensitivity. The intent of this study was to evaluate the degree of removal of the smear layer from dentin surfaces by various fruit juices. A smear layer was created on extracted human teeth by manual scaling. The roots were reduced and distributed into 8 experimental groups. Distilled water was the negative control. The juices were applied by 2 methods: topical application and topical application with friction. Specimens were photomicrographed and graded according to an index of smear layer removal. With topical application, all but 2 of the tested substances resulted in significantly greater removal of the smear layer and opening of dentinal tubules than was the case with the negative control (p = 0.05); the exceptions were Gala apple and Italian grape juices, which were no different from the control. For the active application (with friction), most substances removed more smear layer than the control (p < 0.05); Gala apple, Italian grape and orange juices were similar to the control. For each of the tested substances, removal of the smear layer did not differ with the method of application (topical vs. friction; p > 0.05). It is concluded that natural fruit juices can remove the smear layer from dentin surfaces, and the efficacy of this removal varies with the type of juice. © J Can Dent Assoc 2004.