Despite many studies on the subject, brake squeal remains a major concern for the automotive industry. Much progress was made toward understanding and preventing this issue, focusing on the dynamic ...behavior of the brake. However, the problem is far from fully understood. Among many friction material ingredients, abrasives are extensively used to regulate friction and wear and are recognized as the main contributors to brake noise. This work investigates the correlation between characteristics of abrasives and squeal noise occurrence determined through the SAE J2521 dynamometer test procedure, FESEM, EDS, nanoindentation, and roughness profiling analyses. The particle size, hardness, Young's modulus, and resistance to elastic deformation of 13 different grades of abrasives were measured. The correlation between these characteristics and squeal noise occurrence was determined through statistical analysis. Spearman's rank correlation coefficient (ρ) showed that squeal noise strongly correlated with hardness and resistance to elastic deformation (ρ = 0.61 and ρ = 0.56, respectively) of abrasive materials and exhibited a poor correlation with their particle size (ρ = −0.099). However, considering groups of samples of the abrasive type, particle size is a characteristic that should be regarded in analyzing squeal noise propensity. In the case of SiC, coarser particles (D90 = 196.70 μm) showed a significant reduction in squeal noise compared to finer particles (D90 = 6.30 μm). On the other hand, coarse particles markedly increased the mass loss of the brake pad and brake disk.
•Dynamometer was used to evaluate the squeal noise response of thirteen abrasives.•Abrasives hardness affects squeal noise occurrence, friction, and disk wear.•Squeal noise correlates with elastic deformation parameters of abrasive particles.•Squeal noise and wear of friction materials are influenced by tribofilm nature.
This work presents a tribological study of ceramics parts produced by low-pressure injection molding (LPIM) using factorial design technique. An experimental design of 2k+n0 was used to define the ...experiments and evaluate the influence of three variables on friction coefficient, wear rate and wear mechanisms. The normal load (5N to 15N), tangential velocity (0.05ms−1 to 0.15ms−1) and counterbody type (with three contact pairs, alumina-alumina, alumina-silicon nitride and alumina-steel) were selected as the input variables. Discs of ceramic with ϕ20×3mm composed by 86wt% alumina (99.8 % Al2O3) and 14wt% organic vehicle were produced by LPIM process and sintered at 1600°C, and used as samples in tribological tests. Unidirectional sliding wear tests were conducted in unlubricated conditions at room temperature using a ball-on-disk tribometer. The statistical analysis indicated that the friction coefficient and the specific wear coefficient were strongly sensitive to the individually variations of velocity and the counterface type, and especially to the interaction between these factors. The wear behavior was analyzed as a function of contact parameter that considered the contact Hertz pressure, velocity and hardness of the materials in contact. The hardness and the chemical nature of the counterface were determinant in the reduction of friction coefficient and the severity of LPIM-alumina wear. It was identified also that the transfering of oxide films from the active counterfaces protected the LPIM-alumina from severe wear and reduced the coefficient of friction, wear rate and brittle fracture of the structural ceramic.
•The hardness and chemical nature of the counterface material strongly affect the friction and wear behavior of alumina.•Friction and wear values of alumina are reduced in sliding contacts with dissimilar and chemically active counterfaces.•A contact parameter involving Hertz pressure, tangential velocity and effective hardness is related to wear regimes.•A mild wear regime is related to a lower contact parameter and the formation of transfer oxide layer.•A severe wear regime is related to a higher contact parameter and wear mechanism dominated by the pull-out of alumina grains.
Low-temperature plasma nitriding is a thermochemical surface treatment that promotes surface hardening and wear resistance enhancement without compromising the corrosion resistance of sintered ...austenitic stainless steels. Hollow cathode radiofrequency (RF) plasma nitriding was conducted to evaluate the influence of the working pressure and nitriding time on the microstructure and thickness of the nitrided layers. A group of samples of sintered 316L austenitic stainless steel were plasma-nitrided at 400 °C for 4 h, varying the working pressure from 160 to 25 Pa, and the other group was treated at the same temperature, varying the nitriding time (2 h and 4 h) while keeping the pressure at 25 Pa. A higher pressure resulted in a thinner, non-homogeneous nitrided layer with an edge effect. Regardless of the nitriding duration, the lowest pressure (25 Pa) promoted the formation of a homogenously nitrided layer composed of nitrogen-expanded austenite that was free of iron or chromium nitride and harder and more scratching-wear-resistant than the soft steel substrate.
This work analyzes the application of surface treatment of plasma nitriding with post-oxidation applied to injection mold extractor pins to reduce the injection cycle’s interruptions for mold ...lubrication. For that, a device that simulates the operation of the injection mold extraction system was created. Wear was evaluated by mass loss and dimensional variation of the extraction pins and their bushings. The samples were characterized by microhardness and X-ray diffraction (XRD). The wear mechanisms were identified by scanning electron microscopy (SEM) and the coefficient of friction was analyzed employing a ball-on-plate tribological test. The results showed that the proposed system with plasma nitriding and postoxidation meets the requirements with a lubrication interval twice as long as the current system.
In this work, the applicability of a new algorithm for the estimation of mechanical properties from instrumented indentation data was studied for thin films. The applicability was analyzed with the ...aid of both three-dimensional finite element simulations and experimental indentation tests. The numerical approach allowed studying the effect of the substrate on the estimation of mechanical properties of the film, which was conducted based on the ratio
h
max
/l between maximum indentation depth and film thickness. For the experimental analysis, indentation tests were conducted on AISI H13 tool steel specimens, plasma nitrated and coated with TiN thin films. Results have indicated that, for the conditions analyzed in this work, the elastic deformation of the substrate limited the extraction of mechanical properties of the film/substrate system. This limitation occurred even at low
h
max
/l ratios and especially for the estimation of the values of yield strength and strain hardening exponent. At indentation depths lower than 4% of the film thickness, the proposed algorithm estimated the mechanical properties of the film with accuracy. Particularly for hardness, precise values were estimated at
h
max
/l lower than 0.1, i.e. 10% of film thickness.
RESUMO Neste trabalho é apresentado uma revisão de um conjunto de sistemáticas para a estimativa de propriedades elasto-plásticas de materiais metálicos e cerâmicos pelo método de indentação ...instrumentada. As sistemáticas analisadas contemplam a metodologia de Oliver e Pharr original e com uma modificação da função de profundidade de contato de maneira a torná-la mais próxima das medições experimentais além de diferentes métodos analíticos baseados na energia de deformação (Stilwell e Tabor; Tuck Giannakopoulos e Suresh e Malzbender). Os resultados obtidos para o módulo de elasticidade e a dureza resultantes da aplicação das sistemáticas propostas foram comparados com os valores obtidos da literatura referentes ao aço inoxidável austenítico 316L, alumina e boreto de ferro e cromo. De modo geral os resultados encontrados para a dureza e módulo de elasticidade calculados utilizando as diferentes sistemáticas apresentaram boa coerência com os valores da literatura, entretanto algumas metodologias necessitaram de aplicações de fatores de correção para a caracterização correta das propriedades das amostras.
ABSTRACT This paper presents a review of a different number of systematics for the estimation of elastoplastic properties of metallic and ceramic materials by instrumented indentation testing. The analyzed methodologies include Oliver and Pharr's original methodology and a modification of the contact depth function in order to make it closer to experimental measurements besides different analytical methods based on strain energy (Stilwell e Tabor; Tuck Giannakopoulos and Suresh and Malzbender). The results obtained for the Young’s modulus and hardness resulting from the application of the proposed methodologies were compared with the values obtained in the literature for the austenitic stainless steel 316L, aluminum oxide and iron chromium boride. In general, the results obtained for the hardness and modulus of elasticity calculated using the different systematics presented good coherence with the values of the literature, however some methodologies required the application of correction factors for the correct characterization of the properties of the samples.
Depth sensing indentation study was conducted in a Fischerscope H100V machine, equipped with a Vickers indenter with a tip roundness of approximately 1330 nm. Tests were carried out on soda-lime ...glass, fused silica, sapphire, aluminum (1100 alloy), high alloyed steel, titanium and copper. The widely used iterative method of Oliver and Pharr was unsuccessful in the attempts to analyze machine compliance and indenter area function. Therefore, an alternative procedure was adopted. The alternative procedure is based on the ratio between maximum load and unload stiffness squared, Pm/Su². It was found that this procedure, which is not iterative, gives good results. A careful study of the Pm/Su² ratio, lead us to conclude that the Fischercope machine has a low compliance which depends on the sample mounting. This low compliance in conjunction with the recent discovery of the dependence of beta factor on the tip roundness/maximum depth ratio, which appears in the relation between contact stiffness and contact area, explains why the iterative method does not converge. However, variations in beta and machine compliance produces deviation on the hardness and elastic modulus lower that 6% with respect to expected values for the materials and the machine studied in this work.
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