Effect of Zonal Laser Texturing on Friction Reduction of Steel Elements in Lubricated Reciprocating Motion.

During co-action between contact elements in reciprocating motion, different working conditions exist in outer and inner zones of stationary elements. Because the tribological effects of surface texturing depend on the operating conditions, various dimple patterns were created in the middle part of the steel disc and near the reversal points. The behaviors of variable dimple patterns were compared with those of uniform texturing and untexturing. It was found that the dimple patterns in the middle disc zone depended on the resistance to motion. The best tribological behavior was obtained for a pit area ratio of 13% and diameter of 0.4 mm in the inner zone, and pit area ratio of 3% and diameter of 0.2 mm in the outer zones. Low resistance to motion and the smallest friction variation of all tested sliding pairs were achieved. For the same pit area ratio of 13% in a disc of 0.4 mm, the dimple diameter behaved better than in the 0.2 mm diameter disc. The greatest decrease in the coefficient of friction of 85% compared to untextured sliding pair was achieved for uniform laser texturing with a pit area ratio of 13% and dimple diameter of 0.4 mm, when the normal load was 40 N and frequency of displacement was 20 Hz.

Predictors of periprocedural myocardial infarction after rotational atherectomy.

Introduction: Rotational atherectomy (RA) presents superior efficacy over traditional balloon angioplasty in managing calcified plaques, albeit being associated with a perceived heightened aggressiveness and increased risk of periprocedural complications. Aim: To assess the frequency and predictive factors of periprocedural myocardial infarction (MI) following RA. Material and methods: This was a retrospective observational study, encompassing 534 patients. The definition of periprocedural MI was consistent with the 4th universal definition of MI. Results: Periprocedural MI occurred in 45 (8%) patients. This subset tended to be older (74.6 ±8.2 vs. 72 ±9.3%; p = 0.04) with SYNTAX Score (SS) > 33 points (p = 0.01), alongside elevated rates of no/slow flow (p = 0.0003). These patients less often fulfilled the indication for RA, which is a non-dilatable lesion. The incidence of traditional risk factors was similar in both groups. Univariable logistic regression models revealed: male gender (OR = 0.54; p = 0.04), non-dilatable lesion (OR = 0.41; p = 0.01), prior coronary artery bypass grafting (CABG) (OR = 0.07; p = 0.01) as negative and SS > 33 (OR = 2.8; p = 0.02), older age (OR = 1.04; p = 0.04), no/slow flow (OR = 7.85; p = 0.002) as positive predictors. The multivariable model showed that occurrence of no/slow flow (OR = 6.7; p = 0.02), SS > 33 (OR = 2.95; p = 0.02), non-dilatable lesion (OR = 0.42; p = 0.02), and prior CABG (OR = 0.08; p = 0.02) were independent predictors of periprocedural MI. Conclusions: Periprocedural MI after RA was not an uncommon complication, occurring in nearly one-twelfth of patients. Our analysis implicated female gender, older age, and more severe coronary disease in its occurrence. As expected, the presence of no/slow flow amplified the risk of periprocedural MI, whereas prior CABG and non-dilatable lesions mitigated this risk.

Characterization of the Maximum Height of a Surface Texture.

Average surface height and maximum amplitude can affect surface functions. In the industry, these parameters can be obtained based on profile measurements. However, variability in maximum profile height is high. A more stable parameter can be obtained from the results of the areal surface topography measurements as the average value of the parallel profiles. The aim of this study is to establish this parameter directly from the result of the areal surface texture by correcting the maximum surface height to material ratios in the range of 0.13-99.87%. This method was tested by measuring 100 surface topographies with a stylus profilometer and a white light interferometer. It can be utilized correctly for deterministic textures and random one- and two-process surfaces for which the correlation between neighboring profile ordinates is not very high. In other cases, the method should be modified. Employing this method, the maximum profile amplitude Pt and parameters characterizing the average profile height Pq, Pa, and the ratios Pq/Pa and Pp/Pt describing the shape of the profile ordinate distribution can be correctly estimated. Pq/Pa and Pp/Pt were more stable than the kurtosis Pku and skewness Psk. The corrected maximum height S±3σ can be adopted as a parameter that characterizes the areal surface texture as more stable than the maximum surface height St. Pq/Pa and Pp/Pt were more steady than kurtosis Pku and skewness Psk.

Effects of the surface layer of steel samples after ball burnishing on friction and wear in dry reciprocating sliding.

The effects of ball burnishing on tribological behaviour in dry reciprocating motion have not yet been studied. This work attempts to fill this gap. The steel disc samples after milling were ball burnished. Due to ball burnishing, the average surface height decreased to 85% and the microhardness increased to 20%. Burnishing also generated the compressive residual stresses that were responsible factor to enhance the hardness of the steel surface. Trbological tests were carried out in reciprocating motion under dry sliding conditions. A 10 mm diameter ceramic ball from WC material contacted the steel disc. Ball burnishing was found to lead to improvements in disc wear and friction of the sliding pair. The maximum decreases in friction coefficient and wear volume compared to the milled sample were 39% and 85%, respectively. Samples of the lowest amplitude and high microhardness led to the highest behaviour.

Impact of smoking on outcomes in patients with ST-segment elevation myocardial infarction treated with primary percutaneous coronary intervention.

INTRODUCTION: Smoking is a well­established risk factor for cardiovascular diseases. However, in patients with ST­segment elevation myocardial infarction (STEMI), smoking has been associated with better clinical outcomes; this phenomenon became known as the "smoker's paradox." OBJECTIVES: The aim of this study was to evaluate the association between smoking and clinical outcomes in STEMI patients treated with primary percutaneous coronary intervention (PCI), using 3 large national registries. PATIENTS AND METHODS: We retrospectively analyzed the data of 82 235 hospitalized STEMI patients treated with primary PCI. Among the analyzed population, 30 966 patients (37.96%) were smokers, and 51 269 (62.36%) were nonsmokers. We evaluated the baseline characteristics, pharmacotherapy, clinical outcomes, and readmission causes in a 36­month follow­up. RESULTS: The smokers were significantly younger (median [interquartile range] age, 58 [52-64] vs 68 [59-77] years; P <0.001) than the nonsmokers, and there were more men in this group. The patients who smoked were less likely to have traditional risk factors, as compared with the nonsmokers. In the unadjusted analysis, in­hospital and 36­month mortality and rehospitalization rates were lower in the smokers group. However, after adjustment for baseline characteristics that differed between the 2 groups, the multivariable analysis showed that tobacco use was one of the independent risk factors for 36­month mortality (hazard ratio, 1.11; 95% CI, 1.06-1.18; P <0.001). CONCLUSIONS: In the present large­scale, registry­based analysis, the observed lower 36­month crude rates of adverse events among the smokers, as compared with the nonsmokers, might be partially explained by a significantly lower burden of traditional risk factors and younger age of the smokers. After accounting for age and other baseline differences, smoking was found to be one of the independent risk factors for 36­month mortality.

Surface Texturing of Cylinder Liners: A Review.

The effect of cylinder liners on engine performance is substantial. Typically, the cylinder surfaces were plateau honed. However, recently additional dimples or grooves were created on them. This work discusses the tribological impacts of textured cylinder liner surfaces based on a review of the literature. The results of the experimental research obtained using test rigs and fired engines were critically reviewed. In addition, the results of the modeling are shown. Circular oil pockets and grooves perpendicular to the sliding direction of piston rings of small depths were typically used. Surface texturing of the cylinder liners governs lubrication between the cylinder liner and the piston ring by an increase in oil film thickness near the reversal points leading to reductions in friction force and wear and in the fired engine to a decrease in fuel consumption and to an increase in power or torque. The correct texturing pattern ensures a decrease in the oil consumption, blow-by, and emissions of the internal combustion engine compared to plateau-honed surfaces. Considerations of future challenges are also addressed. The volume of lubricant reservoir in surface topography, called oil capacity, should be a substantial parameter characterizing textured surfaces.

Effects of Operating Conditions and Pit Area Ratio on the Coefficient of Friction of Textured Assemblies in Lubricated Reciprocating Sliding.

The experiment was carried out in a reciprocating lubricated conformal sliding contact between steel discs of the same hardness. The effects of disc surface texturing on the friction coefficient at various operating conditions (temperature, normal load, and frequency of oscillations) were studied. Under various conditions, surface texturing caused friction reductions of sliding pairs. The largest reduction was 4.6 times at a lower temperature and 2.5 times at a higher temperature. The effect of the pit area ratio on the friction reduction was visible at a higher temperature. The highest dimple density of 25% corresponded to a lower coefficient of friction than the smallest density of 9%. The sliding pair with a dimple density of 17% led to large variation of the friction force. At lower temperatures, the coefficients of friction were lower compared to tests at higher temperatures.

Surface Inspection and Description in Metrology and Tribology-Vol.1.

The primary goal of this Special Issue was to present recent trends in surface inspection and description, from both metrological and tribological points of view [...].

The Effects of Selected Measurement Errors on Surface Texture Parameters.

Surface texture measurement, characterized by areal parameters, is very susceptible to measurement errors. Various types of errors differently affect surface texture parameters. In this paper, two types of measurement errors were investigated. To analyze the impact of the presence of scratches, circular valleys of various diameters were added to surface textures measured by a white light interferometer. Measurement errors were larger for higher scratches. Skewness and kurtosis were mostly affected by the presence in valleys, and changes of spatial parameters were also comparatively high. The difference between the results of measurement of the same surface details two times after a break of three months was also studied. This difference was caused by errors of relocation, spikes and non-measured point presences, high-frequency noise, and surface ageing. Spatial parameters were found to be the most stable.

Parametric Characterization of Machined Textured Surfaces.

Surface topography in general is not easy to characterize due to a great number of different features that appear on it. It is still more challenging for machined textured surfaces that are of high functional significance for tribological purposes. For practical reasons, there is a need to describe such surfaces using only a small number of parameters. Which of them represent surface details the best is still an open issue. To find out which parameters can be the most suitable in that case, three groups of machined textured surfaces were prepared. They were plateau-honed cylinder surfaces made of gray cast iron, steel, and bronze surfaces with isolated dimples and steel surfaces after abrasive blasting followed by lapping. All of them were measured by means of a white light interferometer. Different parameters and relationships were evaluated and based on them correlation and regression analyses were used. The basic description contained statistically independent parameters that can be used in production control, while the wider description in scientific research. In general, parameters of random surfaces were more intercorrelated than those of surfaces with isolated dimples. As was found for the basic description of random two-process surfaces, five parameters were enough while description of textured surfaces with isolated oil pockets needed six. In wider, scientific description, regardless the surface type seven parameters contained the necessary information about the surface. It was also proved that a pair of parameters, the emptiness coefficient Sp/Sz and Sq/Sa, can describe the shape of the ordinate distribution of machined textured surfaces better than, for example, skewness Ssk and kurtosis Sku, commonly used for that purpose.

The Effect of Ball Burnishing on Dry Fretting.

Experiments were conducted under a dry gross fretting regime. Steel discs were put in contact with ceramic balls. Before tribological tests, discs were subjected to ball burnishing with different pressures. Due to ball burnishing, a decrease in surface amplitude and an increase in microhardness occurred. Ball burnishing caused decreases in the friction force and volumetric wear of up to 45% in comparison to sliding pairs containing milled discs. The friction force and volumetric wear were higher for a higher roughness of disc.

Functional Importance of Surface Texture Parameters.

Areal 3D analysis of surface texture gives more opportunities than a study of 2D profiles. Surface topography evaluation, considered as 3D dimensional analysis in micro or nanoscales, plays an important role in many fields of science and life. Among many texture parameters, those connected with height are the most often used. However, there are many other parameters and functions that can provide additional important information regarding functional behaviour of surfaces in different applications. The knowledge about the functional importance of various surface properties is low. This review tries to fill this gap. Surface texture parameters are presented in various groups: height, spatial, hybrid, functional, feature, and others. Based on experiences of the present authors and literature review, the relationships among various surface parameters and functional properties are described. A proposal of a selection of parameters on the basis of their functional significations is provided. Considerations for future challenges are addressed.

Selected Methods and Applications of Anti-Friction and Anti-Wear Surface Texturing.

The constant development of environmental protection causes the necessity to increase the efficiency of machines. By increasing the efficiency of machines, energy losses can be limited, leading to lower energy consumption. Friction reduction leads to an increase in efficiency and a decrease in wear. In this paper, selected surface texturing methods, such as burnishing and abrasive jet machining, with their limitations are presented. Thanks to those processes, various surface textures can be obtained. Examples of applications of these methods for friction and wear reduction are shown.

Two-Process Random Textures: Measurement, Characterization, Modeling and Tribological Impact: A Review.

Two-process random textures seem to present better functional properties than one-process surfaces. There are many random two-process textures. Plateau-honed cylinder surfaces are the most popular example. Two-process surfaces are also created during the initial periods of life of machined elements. However, knowledge about two-process textures measurement, modeling, and behavior is low. Two-process surfaces are very sensitive to measurement errors. It is very difficult to model them. Special methods of their characterization were created. Their functional significance was studied in a small number of publications. In this paper, measurement, characterization, and modeling of two-process textures were presented. The functional impact of them was analyzed, the effects on contact mechanics and friction and wear were mainly studied. Finally, considerations of future challenges were addressed. The nature of two-process random textures should be taken into account during analyses of properties of machined elements. The plateau part decides about the asperity contact, and the valley portion governs the hydrodynamic lubrication.

The Influence of Ball Burnishing on Friction in Lubricated Sliding.

Ball burnishing treatment, using the Ecoroll system, of steel samples was conducted. In the experiment, the burnishing pressure was changed. After the treatments, measurements of the surface topographies of disc samples were conducted using a white light interferometer Talysurf CCI Lite. Tribological tests were carried out in a ball-on-disc configuration. After these tests, measurements of surface topographies of disc samples were repeated. Worn surfaces were also analyzed with a scanning electron microscope. It was found that as the result of burnishing, surface topography height of tested samples decreased. Ball burnishing led to a reduction in the frictional resistance. The highest friction reduction of more than 40% was achieved with a burnishing pressure of 20 MPa.

Prediction of Parameters of Equivalent Sum Rough Surfaces.

In statistical models, the contact of two surfaces is typically replaced by the contact of a smooth, flat, and an equivalent rough sum surface. For the sum surface, the zeroth, second, and fourth moments of the power spectral density m0, m2, and m4 respectively, are the sum of spectral moments of two contacted surfaces. In this work, the selected parameters of the sum surfaces were predicted when the parameters of individual surfaces are known. During parameters selection, it was found that the pair of parameters: Sp/Sz (the emptiness coefficient) and Sq/Sa, better described the shape of the probability ordinate distribution of the analyzed textures than the frequently applied pair: the skewness Ssk and the kurtosis Sku. It was found that the RMS height Sq and the RMS slope Sdq were predicted with very high accuracy. The accuracy of prediction of the average summit curvature Ssc, the areal density of summits Sds, and parameters characterizing the shape of the ordinate distribution Sp/Sz and Sq/Sa was also good (the maximum relative errors were typically smaller than 10%).

The Effect of Surface Texture on Lubricated Fretting.

Experiments were conducted using an Optimol SRV5 tester in lubricated friction conditions. Steel balls from 100Cr6 material of 60 HRC hardness were placed in contact with 42CrMo4 steel discs of 47 HRC hardness and diversified surface textures. Tests were carried out at a 25-40% relative humidity. The ball diameter was 10 mm, the amplitude of oscillations was set to 0.1 mm, and the frequency was set to 80 Hz. Tests were performed at smaller (45 N) and higher (100 N) normal loads and at smaller (30 °C) and higher (90 °C) temperatures. During each test, the normal load and temperature were kept constant. We found that the disc surface texture had significant effects on the friction and wear under lubricated conditions. When a lower normal load was applied, the coefficient of friction and wear volumes were smaller for bigger disc surface heights. However, for a larger normal load a higher roughness corresponded to a larger coefficient of friction.

Conditions of the Presence of Bimodal Amplitude Distribution of Two-Process Surfaces.

Two-process surfaces are functionally important. They contain plateau and valley parts. They are created by superimpositions of two one-process textures of Gaussian probability height distributions. It is expected that the resulting two-process surface would have bimodal height probability distribution. However, typically two-process textures have unimodal ordinate distribution. The present authors developed limiting conditions of presence of bimodal ordinate distribution. These conditions depend on the material ratio at the plateau-to-valley transition (the Smq parameter), and on the ratio of heights of the plateau and valley surface parts (Spq/Svq). Generated stratified textures and measured two-process surfaces of cylinder liners were taken into consideration.

Thermal Sources of Errors in Surface Texture Imaging.

This paper presents the influence of thermal phenomena on areal measurements of surface topography using contact profilometers. The research concerned measurements under controlled and variable environmental conditions. The influence of internal heat sources from profilometer drives and their electronic components was analyzed. For this purpose, a thermal chamber was designed and built. Its task was to maintain and control environmental conditions and, at the same time, separate the profilometer from external disturbances. Heat sources and temperature values for elements and systems were determined. It further enabled for the calculation of the displacements in axes as a function of temperature. The largest displacement in the probe due to internal heat sources for the considered cases occurred in the X-axis direction. Its value reached 16.2 µm. However, the displacement in the probe in the Z-axis direction had the greatest impact on the measured surface topography. These displacements for a thermally unstable profilometer reached 7.9 µm in Z, causing results even 90% greater than in the case of a device without such problems. The time after which a proper topography measurement can be started was also determined basing on obtained data. This time for tested profilometers was between 6 and 12 h. It was found that performing thermal stabilization of the profilometer significantly reduced surface irregularity errors. The stabilization time should be determined individually for a specific type of device.

The Effect of Ball Burnishing on Tribological Performance of 42CrMo4 Steel under Dry Sliding Conditions.

Ball burnishing appears to be a very promising approach for reducing surface height, generating compressive residual stresses and increasing hardness. Ball burnishing treatment was carried out using a Haas CNC Vertical Mill Center VF-1 equipped with the Ecoroll burnishing system. After burnishing, surface topographies of machined samples and hardness were measured. Wear tests were conducted using a ball-on-disc tribotester in dry sliding conditions. During tests, the friction force was monitored as a function of time. After tests, wear volumes were determined on the basis of surface texture measurements. Tests revealed that ball burnishing in most cases resulted in minimizing friction and wear of contacting elements.