Gray Disks Research Articles

Properties of Laser-Alloyed Stainless Steel Coatings on the Surface of Gray Cast Iron Discs

The influence of laser-alloyed stainless steel coatings on the properties of the surfaces of cast iron discs, such as friction-induced vibration and noise, friction coefficient, residual stress, hardness, and corrosion resistance, was investigated in this study. The experimental results show that after laser alloying, the surface hardness of the cast iron discs increased significantly. The residual stresses on the surfaces of the laser-alloyed discs changed from tensile to compressive residual stresses, while any compressive residual stresses increased by more than six times. Most of the laser-alloyed discs demonstrated better performance in friction-induced vibration and noise damping and friction reduction. Metallographic observation and XRD (X-ray diffraction) analysis results show that the laser-alloyed layer is mainly a mixture of acicular martensite and dendritic material, while the phase composition of laser-treated discs is mainly martensitic, [Fe, Ni], Fe3Si, Cr23C6, and austenite, which plays a significant role in the improvement of the properties of the laser-alloyed cast iron in physics, tribology and corrosion resistance. This research has significance for the laser surface treatment of various cast irons and steels, which is an increasingly important manufacturing technology in the vehicle friction brake industry.

The effect of solid lubricants in the brake friction composite on brake emissions: A case study with graphite, Sb2S3, and MoS2

Particulate matter produced during brake application was investigated, focusing on the effect of the solid lubricants in the brake friction composite, such as graphite, antimony trisulfide, and molybdenum disulfide. Results showed that the brake emission was significantly affected by the solid lubricant type and braking temperatures. Antimony trisulfide caused high brake emissions at moderate temperatures, whereas graphite produced high emissions at elevated temperatures. The brake emission at moderate temperatures was affected by the aggressiveness of the composites and the presence of friction films on the gray iron disc surface. In contrast, the brake emissions at elevated temperatures were determined by the thermal decomposition of the composite and the oxidation of solid lubricants.

Microstructure evolution and tribo-oxidation induced by friction and wear of cast iron brake discs

Braking discs play an important role for the safety of vehicles whereas severe frictional contacts in repeated braking operations result in thermal and tribological failures. This paper reports comprehensive surface and subsurface analyses of a used grey cast iron braking disc to investigate its failure mechanisms as well as related microstructure evolution. Thermal cracking, spalling wear and tribo-oxidation have been found to contribute to the wear failure. The flake-type graphite of the grey cast iron triggered propagation and internal oxidation of the metallic matrix. In a depth of 3 mm beneath the rubbing surface, extensive microstructure evolution occurred by severe plastic deformation of the ferritic matrix, nodularisation and partial dissolution of the lamellar carbides, and internal oxidation. The microstructure evolution resulted in decreased surface hardness to HV0.3 247 as compared to HV0.3 284 of the bulk cast iron.

Poster Session: Towards Understanding Retinal Processing of Single-Cone Scale Stimulation.

The magnocellular (M) visual pathway can be distinguished from its finer-grained parvocellular (P) counterpart by its stronger response gain to contrasts near human detection threshold. This distinction is found when stimulus size is matched to the relatively large receptive field size of M cells, but it is less clear if preserved at smaller spatial scales. We examined foveal detection thresholds in tandem with a masking paradigm known to desensitize the M pathway. We used a custom DLP display in Maxwellian view to present either 3 or 23 arcmin spots for 100 ms against a uniform gray disk (1° VA) surrounded by a 0.5 cpd, 100% contrast, square wave grating flickered at 7 frequencies ranging from 0 to 30 Hz. Detection data were fit with psychometric functions to estimate threshold and thresholds were normalized to the static (0 Hz) condition. Relative sensitivity was fit with a modified impulse response function and compared to a constant model with ANOVA. With masking we found a significant reduction in sensitivity for large (23arcmin) increments (mean=0.39 log units; n=4; p<0.01) and decrements (0.31 log units; n=4; p=0.02)at 8.3Hz. By contrast, no significant masking effect was observed for small spot increments or decrements (p>0.05). These data suggest that the M pathway is not the primary determinant of small spot thresholds under the conditions studied. Further investigation with adaptive optics may be necessary to fully elaborate single-cone processing in the fovea.

EXPERIMENTAL STUDY OF RADIATION HEAT TRANSFER OVER VERTICALLY PLACED CIRCULAR DISKS

The radiation heat transfer over vertically placed circular disks under vacuum and air medium were experimentally investigated. Two type’s disks black and grey were considered for the study, which were placed vertically inside a heated chamber called an oven. A constant temperature was imposed inside the chamber. The chamber was partially vacuumed to prepare vacuum medium by controlling the air pressure with -0.8 to 0.6 bar. To understand the heat transfer, time requirement to obtain certain temperatures and heat transfer coefficient were calculated. Correlation between temperature and heat transfer coefficient were also analyzed. The findings highlighted that black disk provided the highest heat transfer coefficient and the lowest time requirement to achieve a certain temperature. Polynomial relationships between temperature and heat transfer coefficient for black and grey disks with R2 less than 1 were obtained through the trendlines.

Corrosion Stiction in Automotive Braking Systems.

This review paper targets the corrosion-stiction phenomenon that can occur in automotive braking systems under static conditions in aggressive environments. The corrosion of gray cast iron discs can lead to a strong adhesion of the brake pad at the pad/disc interface that can impair the reliability and performance of the braking system. The main constituents of friction materials are initially reviewed in order to highlight the complexity of a brake pad. Corrosion-related phenomena, including stiction and stick-slip, are considered in detail to discuss the complex effect of the chemical and physical properties of friction materials on these phenomena. In addition, testing methods to evaluate the susceptibility to corrosion stiction are reviewed in this work. Electrochemical methods, including potentiodynamic polarization and electrochemical impedance spectroscopy, are useful tools for a better understanding of corrosion stiction. The development of friction materials with low susceptibility to stiction should follow a complementary approach targeting an accurate selection of the constituents, control of local conditions at the pad-disc interface, and the use of specific additives or surface treatments to reduce the corrosion susceptibility of gray cast-iron rotors.

Perception of self-generated and externally-generated visual stimuli: Evidence from EEG and behavior.

Efference copy-based forward model mechanisms may help us to distinguish between self-generated and externally-generated sensory consequences. Previous studies have shown that self-initiation modulates neural and perceptual responses to identical stimulation. For example, event-related potentials (ERPs) elicited by tones that follow a button press are reduced in amplitude relative to ERPs elicited by passively attended tones. However, previous EEG studies investigating visual stimuli in this context are rare, provide inconclusive results, and lack adequate control conditions with passive movements. Furthermore, although self-initiation is known to modulate behavioral responses, it is not known whether differences in the amplitude of ERPs also reflect differences in perception of sensory outcomes. In this study, we presented to participants visual stimuli consisting of gray discs following either active button presses, or passive button presses, in which an electromagnet moved the participant's finger. Two discs presented visually 500-1250 ms apart followed each button press, and participants judged which of the two was more intense. Early components of the primary visual response (N1 and P2) over the occipital electrodes were suppressed in the active condition. Interestingly, suppression in the intensity judgment task was only correlated with suppression of the visual P2 component. These data support the notion of efference copy-based forward model predictions in the visual sensory modality, but especially later processes (P2) seem to be perceptually relevant. Taken together, the results challenge the assumption that N1 differences reflect perceptual suppression and emphasize the relevance of the P2 ERP component.

Quench hardening effect of gray iron brake discs on particulate matter emission

In this study, particulate matter produced during the braking of motor vehicles was investigated. In particular, this study focused on the effect of quench hardening of gray iron discs on brake emissions. The disc hardening effect was evaluated with commercial low-steel and non-steel brake pads using a 1/5 scale inertial brake dynamometer equipped with a particle counter. The results indicate that the disc hardening effect was significantly affected by the type of friction material due to different wear mechanisms. The low-steel brake pads produced more brake emissions when using the quench-hardened disc due to the increased aggressiveness of the hardened disc against the brake pad. In contrast, the hardened disc substantially reduced particulate matter emission when using the non-steel brake pads because the pad's surface became more wear-resistant due to the smaller amount of iron transferred from the hardened disc compared to conventional gray iron discs. These results suggest that the iron transfer from the disc to the pad's surface plays a crucial role in brake emissions.

Contextual drive of neuronal responses in mouse V1 in the absence of feedforward input.

Neurons in the primary visual cortex (V1) respond to stimuli in their receptive field (RF), which is defined by the feedforward input from the retina. However, V1 neurons are also sensitive to contextual information outside their RF, even if the RF itself is unstimulated. Here, we examined the cortical circuits for V1 contextual responses to gray disks superimposed on different backgrounds. Contextual responses began late and were strongest in the feedback-recipient layers of V1. They differed between the three main classes of inhibitory neurons, with particularly strong contextual drive of VIP neurons, indicating a contribution of disinhibitory circuits to contextual drive. Contextual drive was strongest when the gray disk was perceived as figure, occluding its background, rather than a hole. Our results link contextual drive in V1 to perceptual organization and provide previously unknown insight into how recurrent processing shapes the response of sensory neurons to facilitate figure perception.

Cover Feature: Improvement of Solid Photoluminescence of Tridentate Schiff Base Pt(II) Foldamer by Hybridizing Poly (4‐Vinylpyridine) (Eur. J. Inorg. Chem. 36/2022)

The Cover Feature shows the bis(tridentate Schiff base Pt(II)) complex containing dimethyl sulfoxide (Pt2L2DMSO) as a combination of yellow disks, gray disks, orange cones, and a black curved line. Pt2L2DMSO is unfolding due to the steric repulsion of the bulky ligand. The blue hexagons connected to the branched black lines stand for poly(4-vinylpyridine) (P4VP). The green curved figure in the background indicates hybridization. The top image shows the hybridization of Pt2L2DMSO and P4VP, which causes a ligand exchange reaction for Pt2L2DMSO, forming a folding network structure in the yellow membrane. The yellow membrane exhibits red photoluminescence under ultraviolet irradiation (green wavy arrow). The reddish thunder expresses phosphorescence. The bottom image in the cover shows hybridization of Pt2L2DMSO and 4-vinylpyridine (4VP), which causes a ligand exchange reaction for Pt2L2DMSO, forming the folding columnar packing structure in the brown block crystal. The black wavy arrow indicates non-radiative deactivation. The metallofoldamer crystal does not exhibit solid photoluminescence under ultraviolet irradiation, while the metallofoldamer membrane is luminescent, thanks to the hybridization with P4VP. The background color changes gradually from orange to gray at the bottom to orange at the top, showing the improvement of photoluminescence from bottom to top. More information can be found in the Research Article by H. Achira and co-workers.

Lightness Contrast Spatially Propagates on Perceptually Unified Elements

Abstract In 1993, Agostini and Proffitt showed that perceptual belongingness (the subsumption of some sets of elements into a perceived whole) causes simultaneous lightness contrast to be seen in configurations in which the inducing elements are not adjacent to the target. The aim of the present research was to measure the strength of belongingness in determining the contrast phenomenon when the numbers of the inducing and induced elements and their relative positions are manipulated in Agostini-and-Proffitt-type configurations. In the first experiment, by using a forced choice paradigm, naïve observers indicated which gray disks arranged to form the letter T in two rows (organized with black/white inducers) appeared lighter/darker. In the second experiment, expert observers performed two nulling tasks: 1) the lightness of gray disk(s) was adjusted until it was perceived equal to that of gray target(s) aligned with white/black inducers; 2) the lightness of target(s) organized with white/black inducers was adjusted to match the target(s) organized with black/ white inducers. We found that also when there are few inducers, perceptual belongingness causes the contrast effect to propagate spatially on all the induced elements. Spatial position does not influence the induction effect. Low-level theories cannot account for these phenomena, but higher-level processes must be factored in to explain them.

Effects of abrasive particles on the particulate matter emission of brake friction composites

The correlation between the type of abrasive in the brake friction composite and the braking induced emission was studied. Brake pads with four different abrasives; silicon carbide, alumina, zircon, and magnesia, were evaluated using a reduced scale dynamometer with an airborne particle counter. The results indicated that the particle abrasivity, comprising aspects such as hardness, fracture toughness, and angularity, strongly affected the disc wear and airborne particle emission, whereas the pad wear was more influenced by the strength of the friction film that was changed by the iron moved from the grey iron disc. The fracture toughness of the abrasives had a significant effect on the disc wear rate and mass concentration of airborne wear particles emitted during brake application. In contrast, the number concentration was considerably influenced by the wear mode of the abrasives against the grey iron disc.

Characterization, wear and emission properties of MnS containing laser cladded brake disc

In this study, the laser cladding of gray cast iron brake discs using a Fe-based coating material was investigated. A 5 wt% MnS was added as a solid lubricant to the coating formulation to track the improvement of wear and emissions. Microstructural and tribological characteristics of the coated discs (with and without MnS) were studied comparatively. Three different friction materials, that are typically used for commercial brake pads, were adopted to evaluate the performance of the coatings. The pin on disc results indicated that, with the addition of MnS, both friction coefficient and wear rate have been reduced to levels comparable with those obtained in case of uncoated gray cast iron discs. The tribological behavior of MnS containing coating showed the best results when sliding against a Cu full friction material.

Familiarity with an Object's Size Influences the Perceived Size of Its Image.

It is known that judgments about objects’ distances are influenced by familiar size: a soccer ball looks farther away than a tennis ball if their images are equally large on the retina. We here investigate whether familiar size also influences judgments about the size of images of objects that are presented side-by-side on a computer screen. Sixty-three participants indicated which of two images appeared larger on the screen in a 2-alternative forced-choice discrimination task. The objects were either two different types of balls, two different types of coins, or a ball and a grey disk. We found that the type of ball biased the comparison between their image sizes: the size of the image of the soccer ball was over-estimated by about 5% (assimilation). The bias in the comparison between the two balls was equal to the sum of the biases in the comparisons with the grey disk. The bias for the coins was smaller and in the opposite direction (contrast). The average precision of the size comparison was 3.5%, irrespective of the type of object. We conclude that knowing a depicted object’s real size can influence the perceived size of its image, but the perceived size is not always attracted towards the familiar size.

Effect of space fillers in brake friction composites on airborne particle emission: A case study with BaSO4, Ca(OH)2, and CaCO3

This study investigated particulate matter (PM) produced during brake application, focusing on the effect of space fillers in low-steel friction composites. The composites ranked in terms of brake emissions in a descending order were BaSO4, Ca(OH)2, and CaCO3. CaCO3 produced thicker friction films on the steel fibres than Ca(OH)2, whereas bare steel fibres were found with BaSO4, indicating strong effects of the filler-dependent coverup layers, which was confirmed by microhardness tests. The filler effect on PM suggests that proper selection of space fillers can reduce brake emissions from grey iron discs by preventing direct adhesion with steel fibres.

ImageNet-trained deep neural networks exhibit illusion-like response to the Scintillating grid.

Deep neural network (DNN) models for computer vision are capable of human-level object recognition. Consequently, similarities between DNN and human vision are of interest. Here, we characterize DNN representations of Scintillating grid visual illusion images in which white disks are perceived to be partially black. Specifically, we use VGG-19 and ResNet-101 DNN models that were trained for image classification and consider the representational dissimilarity ( distance in the penultimate layer) between pairs of images: one with white Scintillating grid disks and the other with disks of decreasing luminance levels. Results showed a nonmonotonic relation, such that decreasing disk luminance led to an increase and subsequently a decrease in representational dissimilarity. That is, the Scintillating grid image with white disks was closer, in terms of the representation, to images with black disks than images with gray disks. In control nonillusion images, such nonmonotonicity was rare. These results suggest that nonmonotonicity in a deep computational representation is a potential test for illusion-like response geometry in DNN models.

Effect of disc materials on brake emission during moderate-temperature braking

Disc material effects on particle emission were investigated under moderate braking conditions using grey iron discs with different microstructures and a ceramic disc. The results demonstrate that brake emissions are strongly affected by disc hardness and the iron transferred to the pad surface. The transferred iron increased brake emissions due to the reduced cohesive strength of the plateaus on the pad surface. The grey iron microstructure also affected the ultrafine particle concentration owing to the graphite flakes. Conversely, the ceramic disc exhibited significantly lower brake emissions due to high wear resistance and no iron transfer to the pad surface.

Root cause study of corrosion stiction by brake pads on the grey iron disc

Corrosion stiction at the sliding interface of a brake system was investigated to identify its leading cause and countermeasure. Porosity, acidity, hydrophobicity, strength, contact stiffness, and contact area of commercial brake pads were examined to find the correlation with corrosion stiction. Results showed that the compliant brake pads with low cohesive strength showed high stiction forces owing to the larger contact area after brake applications than stiff pads. Electrochemical analysis of the corroded interface supports the contact area dependency of the stiction force, suggesting that corrosion stiction can be reduced by minimizing the contacts on the brake pad surface.

Pin-on-disc study of dry sliding behavior of Co-free HVOF-coated disc tested against different friction materials

The dry sliding behavior of three commercial friction materials (codenamed FM1, FM2, and FM3) tested against a Co-free cermet coating produced by high-velocity oxy-fuel (HVOF) on gray cast-iron discs is investigated. FM1 is a conventional low-metallic friction material, FM2 is developed for using against HVOF-coated discs, and FM3 is a Cu-free friction material with a low content of abrasives and a relatively high concentration of steel fibers. For the tribological evaluation, they are tested on a pin-on-disc (PoD) test rig against Co-free HVOF-coated discs, with particular attention to the running-in stage, which is fundamental for the establishment of a friction layer between the two mating surfaces, i.e., the pin and disc. The PoD tests are performed at room temperature (RT) and a high temperature (HT) of 300 °C. At RT, all materials exhibit a long running-in stage. At HT, no running-in is observed in FM1 and FM2, whereas a shorter running-in period, with respect to the RT case, is observed in FM3 followed by the attainment of a comparatively high coefficient of friction. At RT, the pin wear is mild in all cases but severe at HT. FM3 shows the lowest wear rate at both temperatures. Moreover, the coated disc shows no wear when sliding against the FM3 friction material. All the results are interpreted considering the microstructural characteristics of the friction layers formed on the sliding surfaces. The findings of the present study provide insights into reducing wear in braking system components and hence reducing environmental particulate matter emissions from their wear, through the use of disc coatings.

Effect of disc material on particulate matter emissions during high-temperature braking

Brake emissions during high-temperature brake applications were investigated using four different brake discs—FC170 and FC250 Gy iron discs, oxynitride-coated gray iron discs, and ceramic discs. The brake emission tests were performed with a low-steel brake pad using a 1/5 scale brake dynamometer with a high resolution electrical low-pressure impactor. The highest number concentration was observed using ceramic discs, whereas the gray iron discs produced higher mass concentrations than others. The effect of the disc material on brake emissions at elevated temperatures was primarily determined by the thermal conductivity of the disc and the time- and temperature-dependent variations of contact plateaus on the pad surface.