Characterization of the elastic-plastic region in AISI/SAE 1070 steel by the magnetic barkhausen noise

The magnetic Barkhausen energy in the rolling and transversal directions of AISI/SAE 1070 annealed surfaces is studied. The measurements were made in the samples under applied tension in the elastic-plastic region for different angular directions. The outcomes evidence that the magnetic anisotropy coefficient can be used to characterize the linear and nonlinear elastic limits of the material tinder tensile tresses. The results also show that the area of the curve corresponding to the angular dependence of the number of Barkhausen jumps with average energy presents a maximum value that corresponds to the elastic limit of the sample. (C) 2008 Elsevier Ltd. All rights reserved.

Registration of temporal sequences of coronal and sagittal MR images through respiratory patterns

This work discusses the determination of the breathing patterns in time sequence of images obtained from magnetic resonance (MR) and their use in the temporal registration of coronal and sagittal images. The registration is made without the use of any triggering information and any special gas to enhance the contrast. The temporal sequences of images are acquired in free breathing. The real movement of the lung has never been seen directly, as it is totally dependent on its surrounding muscles and collapses without them. The visualization of the lung in motion is an actual topic of research in medicine. The lung movement is not periodic and it is susceptible to variations in the degree of respiration. Compared to computerized tomography (CT), MR imaging involves longer acquisition times and it is preferable because it does not involve radiation. As coronal and sagittal sequences of images are orthogonal to each other, their intersection corresponds to a segment in the three-dimensional space. The registration is based on the analysis of this intersection segment. A time sequence of this intersection segment can be stacked, defining a two-dimension spatio-temporal (2DST) image. The algorithm proposed in this work can detect asynchronous movements of the internal lung structures and lung surrounding organs. It is assumed that the diaphragmatic movement is the principal movement and all the lung structures move almost synchronously. The synchronization is performed through a pattern named respiratory function. This pattern is obtained by processing a 2DST image. An interval Hough transform algorithm searches for synchronized movements with the respiratory function. A greedy active contour algorithm adjusts small discrepancies originated by asynchronous movements in the respiratory patterns. The output is a set of respiratory patterns. Finally, the composition of coronal and sagittal image pairs that are in the same breathing phase is realized by comparing of respiratory patterns originated from diaphragmatic and upper boundary surfaces. When available, the respiratory patterns associated to lung internal structures are also used. The results of the proposed method are compared with the pixel-by-pixel comparison method. The proposed method increases the number of registered pairs representing composed images and allows an easy check of the breathing phase. (C) 2010 Elsevier Ltd. All rights reserved.

Comparison of adsorbent films obtained by plasma polymerization of oxygenated organic compounds

Thin films obtained by plasma polymerization of ethyl ether, methyl or ethyl acetate, acetaldehyde, acetone and 2-propanol were compared. Infrared spectroscopy (FFIR), resistance to chemicals, contact angle measurements, X-ray photoelectron spectroscopy (XPS), optical and scanning electron microscopy (SEM), and quartz crystal microbalance (QCM) were carried out. For all films FTIR showed high intensity for polar bonds yet the films are not resistant to polar solvents. Contact angle measurements revealed hydrophilic and organophilic surfaces and XPS pointed out a high proportion of oxygenated bonds. All films showed good step coverage and peeling was significant only with acetone and 2-propanol. All films are adsorbent for organic compounds in a large scale of polarity but acetaldehyde and 2-propanol act like a selective membrane. Also, deposition of these films on hydrophobic substrates leads to island formation. A possible model to explain the results must consider the hydrogen bridge formation on 2-propanol and acetaldehyde films. Ethyl ether, ethyl and methyl acetate showed good characteristics for development of sensor and sample pretreatment using miniaturized devices. (C) 2007 Elsevier B.V. All rights reserved.

Synthesis, characterization, and bactericidal properties of composites based on crosslinked resins containing silver

Two different commercial crosslinked resins (Amberlite GT73 and Amberlite IRC748) were employed for anchoring silver. The -SH and -N(CH2COOH)2 groups, respectively, present on these resins were used for Ag+ chelation from an aqueous solution. The Ag+ ions were reduced with three different reductants: hydrazine, hydroxylamine, and formaldehyde (under an alkaline pH). The produced composites were characterized with thermogravimetry/differential thermogravimetry and scanning electron microscopy combined with a backscattered scanning electron detector. Energy-dispersive X-ray spectroscopy coupled to scanning electron microscopy allowed the observation of submicrometer particles of silver, and chemical microanalysis of emitted X-rays revealed the presence of metal on the internal and external surfaces of the composite microspheres. The amount of incorporated silver was determined by titration. The antibacterial activity of the silver/resin composites was determined toward 10(3)-10(7) cells/mL dilutions of the auxotrophic AB1157 Escherichia coli strain; the networks containing anchored submicrometer silver particles were completely bactericidal within a few minutes because of the combined action of silver and functional groups of the resins. (c) 2007 Wiley Periodicals, Inc.

Effect of alpha prime due to 475 degrees C aging on fracture behavior and corrosion resistance of DIN 1.4575 and MA 956 high performance ferritic stainless steels

The 475 degrees C embrittlement in stainless steels is a well-known phenomenon associated to alpha prime (alpha`) formed by precipitation or spinodal decomposition. Many doubts still remain on the mechanism of alpha` formation and its consequence on deformation and fracture mechanisms and corrosion resistance. In this investigation, the fracture behavior and corrosion resistance of two high performance ferritic stainless steels were investigated: a superferritic DIN 1.4575 and MA 956 superalloy were evaluated. Samples of both stainless steels (SS) were aged at 475 degrees C for periods varying from 1 to 1,080 h. Their fracture surfaces were observed using scanning electron microscopy (SEM) and the cleavage planes were determined by electron backscattering diffraction (EBSD). Some samples were tested for corrosion resistance using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Brittle and ductile fractures were observed in both ferritic stainless steels after aging at 475 degrees C. For aging periods longer than 500 h, the ductile fracture regions completely disappeared. The cleavage plane in the DIN 1.4575 samples aged at 475 degrees C for 1,080 h was mainly {110}, however the {102}, {314}, and {131} families of planes were also detected. The pitting corrosion resistance decreased with aging at 475 degrees C. The effect of alpha prime on the corrosion resistance was more significant in the DIN 1.4575 SS comparatively to the Incoloy MA 956.

Failure analysis of belt/roll tribological pair used for the production of eucalypt fiber panels

The premature failure of a large agglomeration machine used for the annual production of 360,000 m(3) of eucalypt fiber panels was investigated to identify the nucleation and growth mechanisms of cracking in PH stainless steel belts (126 m x 2.9 m x 3.0 mm). These belts are used to compress a cushion composed of eucalyptus fibers and glue, being the pressure transmitted from the pistons by the action of numerous case-hardening steel rolls. Examination of the belt working interfaces (belt/rolls and belt/eucalypt fibers) indicated that the main cracking was nucleated on the belt/roll interface and that there is a clear relationship between the crack nucleation and the presence of superficial irregularities, which were observed on the belt/roll working surface. Used rolls showed the presence of perimetric wear marks and 2 mu m silicon-rich encrusted particles (identified as silicon carbide). Lubricant residues contained the presence of helicoidal wires, which were originated by the release of the stainless steel cleaning brush bristles, and 15 mu m diameter metallic particles, which were generated by material detachment of the belt. The presence of foreign particles on the tribological interface contributed to an increase of the shear stresses at the surfaces and, consequently, the number of the contact fatigue crack nucleation sites in the belt/roll tribo-interface. The cracking was originated on the belt/roll interface of the stainless steel belt by a mixed rolling/slip contact fatigue mechanism, which promoted spalling and further nucleation and growth of conventional fatigue cracks. Finally, the system lubrication efficiency and the cleaning procedure should be optimised in order to increase the life expectancy of the belt. (c) 2006 Elsevier Ltd. All rights reserved.

Effect of nitrogen on the corrosion-erosion synergism in an austenitic stainless steel

High temperature gas nitrided AISI 304L austenitic stainless steel containing 0.55 wt% N in solid solution, was corrosion, erosion and corrosion-erosion tested in a jet-like device, using slurry composed of 3.5% NaCl and quartz particles. Scanning electron microscopy analysis of the damaged surfaces, mass loss measurements and electrochemical test results were used to understand the effect of nitrogen on the degradation mechanisms. Increasing the nitrogen content improved the corrosion, erosion and corrosion-erosion resistance of the AISI 304L austenitic stainless steel. Smoother wear mark contours observed on the nitrided surfaces indicate a positive effect of nitrogen on the reduction of the corrosion-erosion synergism. (C) 2011 Elsevier Ltd. All rights reserved.

Corrosion behavior of Eurofer 97 and ODS-Eurofer alloys compared to traditional stainless steels

In the present work, the corrosion resistance of ferritic-martensitic EUROFER 97 and ODS-EUROFER steels was tested in solutions containing NaCl or H(2)SO(4) and KSCN, both at 25 degrees C. The results were compared to those of AISI 430 ferritic and AISI 410 martensitic conventional stainless steels. The as-received samples were tested by electrochemical techniques, specifically, electrochemical impedance spectroscopy, potentiodynamic polarization curves, and double-loop electrochemical potentiokinetic reactivation tests. The surfaces were observed by scanning electron microscopy after exposure to corrosive media. The results showed that EUROFER 97 and ODS-EUROFER alloys present similar corrosion resistance but lower than ferritic AISI 430 and martensitic 410 stainless steels.

Embrittlement of case hardened steel chain link

Various steel chain links presented cracking during their manufacturing process, which includes induction case hardening and electrogalvanizing steps. Fractographic examination of the exposed crack surfaces revealed intergranular cracking with some areas featuring a thin layer of iron oxide, indicating that the cracking took place after the electrogalvanizing step. The location of the cracks coincided with the position of the deepest case hardened layer, suggesting the occurrence of localized overheating during the induction case hardening step. Inductive heating finite element analysis (COSMOS Designstar Software) confirmed that during the case hardening the austenitising temperature reached in the crack region values of approximately 1050 degrees C. The results indicated that intergranular cracking was caused by hydrogen embrittlement. (C) 2009 Elsevier Ltd. All rights reserved.

EROSION-CORROSION SYNERGISM OF AN AISI 410 MARTENSITIC STAINLESS STEEL

In this work, the behavior of an AISI 410 martensitic stainless steel under corrosion-erosion conditions is evaluated. Quenched and tempered samples were used for the wear test, using a low velocity jet-like device connected to a potentiostat. Potentiodynamic polarization curves were obtained with the electrolyte in static state, with flow conditions and under corrosion-erosion, adding quartz particles to the electrolyte. In addition, mass loss measurements under erosion and corrosion-erosion conditions were carried out. The topography of the surfaces was examined after the wear tests, using optical and scanning electron microscopy. This information, together with the results of mass losses and the electrochemical tests were used to establish the degradation mechanisms of the stainless steels under different testing conditions. The results showed that synergism is a significant part of the degradation process of this steel (66.5%) and that the mass removal process of steel was controlled by corrosion assisted by erosion.

Electrophoretic deposition of ZrO(2)-Y(2)O(3): a bi-component study concerning self-assemblies

There are many industrial advantages of using mechanical multi-oxides mixtures to obtain ceramic parts by electrophoretic deposition (EPD). This is mainly because one could avoid complex chemical synthesis routes to achieve a desirable composition. However, EPD of these suspensions is not an easy task as well since many different surfaces are present, leading to unexpected suspension behavior. The particles surface potentials and interactions can, however, be predicted by an extension of the DLVO theory. Using this theory, one can control the suspension properties and particles distribution. The objective of this work was to apply the colloidal chemistry theories to promote the formation of a heterocoagulation between ZrO(2) and Y(2)O(3) particles in ethanol suspension to achieve a suitable condition for EPD. After identifying a condition where those particles had opposite surface charges and adequate relative sizes, heterocoagulation was observed at operational pH 7.5, generating an organized agglomerate with ZrO(2) particles surrounding Y(2)O(3), with a net zeta potential of -16.6 mV. Since the agglomerates were stable, EPD could be carried out and homogeneous deposits were obtained. The deposited bodies were sintered at 1600 A degrees C for 4 h and partially stabilized ZrO(2) could be obtained without traces of Y(2)O(3) second phases.

Fretting fatigue in overhead conductors: Rig design and failure analysis of a Grosbeak aluminium cable steel reinforced conductor

The performance optimisation of overhead conductors depends on the systematic investigation of the fretting fatigue mechanisms in the conductor/clamping system. As a consequence, a fretting fatigue rig was designed and a limited range of fatigue tests was carried out at the middle high cycle fatigue regime in order to access an exploratory S-N curve for a Grosbeak conductor, which was mounted on a mono-articulated aluminium clamping system. Subsequent to these preliminary fatigue tests, the components of the conductor/clamping system, such as ACSR conductor, upper and lower clamps, bolt and nuts, were subjected to a failure analysis procedure in order to investigate the metallurgical free variables interfering on the fatigue test results, aiming at the optimisation of the testing reproducibility. The results indicated that the rupture of the planar fracture surfaces observed in the external At strands of the conductor tested under lower bending amplitude (0.9 mm) occurred by fatigue cracking (I mm deep), followed by shear overload. The V-type fracture surfaces observed in some At strands of the conductor tested under higher bending amplitude (1.3 mm) were also produced by fatigue cracking (approximately 400 mu m deep), followed by shear overload. Shear overload fracture (45 degrees fracture surface) was also observed on the remaining At wires of the conductor tested under higher bending amplitude (1.3 mm). Additionally, the upper and lower Al-cast clamps presented microstructure-sensitive cracking, which was folowed by particle detachment and formation of abrasive debris on the clamp/conductor tribo-interface, promoting even further the fretting mechanism. The detrimental formation of abrasive debris might be inhibited by the selection of a more suitable class of as-cast At alloy for the production of clamps. Finally, the bolt/nut system showed intense degradation of the carbon steel nut (fabricated in ferritic-pearlitic carbon steel, featuring machined threads with 190 HV), with intense plastic deformation and loss of material. Proper selection of both the bolt and nut materials and the finishing processing might prevent the loss in the clamping pressure during the fretting testing. It is important to control the specification of these components (clamps, bolt and nuts) prior to the start of large scale fretting fatigue testing of the overhead conductors in order to increase the reproducibility of this assessment. (c) 2008 Elsevier Ltd. All rights reserved.

Photooxidative behavior of polystyrene-montmorillonite nanocomposites

The weathering behavior of polystyrene and polystyrene-montmorillonite composites containing 2.5, 5.0, and 7.5 wt% of montmorillonite (MMT) was investigated. Samples were exposed to UV radiation for periods of up to similar to 12 weeks and their molecular weight, chemical changes, and mechanical properties were monitored as a function of time. The addition of MMT was shown to improve the photostability of all composites investigated, probably because of a screen effect against UV radiation and barrier effect against diffusion of oxygen promoted by the silicate layers of MMT. Scanning electron microscopy of fracture surfaces of degraded samples showed that there is a degraded layer near the surface that provided a recovery of tensile strength of the samples.

Electrochemical study of modified non-functional bis-silane layers on Al alloy 2024-T3

In the last few years great efforts have been made in order to find and to develop environmentally friendly substitutes for Cr6+ pre-treatments applied on aluminium alloys used in the aircraft industry. Among the potential substitutes, silane layers have attracted considerable interest from researchers and from the industry. The present work investigates the anti-corrosion behaviour of (bis-1, 2-(triethoxysilyl) ethane (BTSE)) silane layers modified with Ce ions and/or silica nanoparticles applied on Al alloy 2024-T3 substrates. The corrosion behaviour was investigated in 0.1 M NaCl solution via d.c. polarization and electrochemical impedance spectroscopy (EIS). Contact angle measurements and XPS were used to assess information on the chemistry of the silane pre-treated surfaces. The results have shown that the introduction of additives improves the corrosion protection properties of the silane layer. (c) 2008 Elsevier Ltd. All rights reserved.

Vibratory noise to the fingertip enhances balance improvement associated with light touch

Light touch of a fingertip on an external stable surface greatly improves the postural stability of standing subjects. The hypothesis of the present work was that a vibrating surface could increase the effectiveness of fingertip signaling to the central nervous system (e.g., by a stochastic resonance mechanism) and hence improve postural stability beyond that achieved by light touch. Subjects stood quietly over a force plate while touching with their right index fingertip a surface that could be either quiescent or randomly vibrated at two low-level noise intensities. The vibratory noise of the contact surface caused a significant decrease in postural sway, as assessed by center of pressure measures in both time and frequency domains. Complementary experiments were designed to test whether postural control improvements were associated with a stochastic resonance mechanism or whether attentional mechanisms could be contributing. A full curve relating body sway parameters and different levels of vibratory noise resulted in a U-like function, suggesting that the improvement in sway relied on a stochastic resonance mechanism. Additionally, no decrease in postural sway was observed when the vibrating contact surface was attached to the subject`s body, suggesting that no attentional mechanisms were involved. These results indicate that sensory cues obtained from the fingertip need not necessarily be associated with static contact surfaces to cause improvement in postural stability. A low-level noisy vibration applied to the contact surface could lead to a better performance of the postural control system.