Analysis of changes in the rat cardiovascular system under the action of lead intoxication and muscular exercise

Introduction. One of the risk factors for cardiovascular diseases is the toxic metal pollution of the industrial area and the environment. Lead is the most critical of toxic metals. In industrial conditions, the body’s exposure to harmful substances is often combined with muscular work of varying severity. It has not been studied enough how these combinations influence the development of pathological processes associated with harmful exposure. Materials and methods. The subchronic experiment was carried out on white outbred male rats for six weeks. Intoxication was simulated by repeated intraperitoneal injections of lead acetate three times a week. Running was chosen to model the muscle exercise at a 25 m/min speed for 10 minutes 5 days a week. We performed biochemical and electrocardiographic studies. Blood pressure parameters were recorded. Muscle contractility was studied on isolated multicellular preparations of the right ventricular myocardium in isometric and physiological contraction modes. The ratio of myosin heavy chains was determined by the polyacrylamide gel electrophoresis. The sliding velocity of reconstituted thin filaments on myosin using an in vitro motility assay. Results. Physical exercise under lead intoxication normalized the level of calcium and the angiotensin-converting enzyme activity in the blood serum, the voltage of the isoelectric line and the amplitude of the T wave on the electrocardiogram. The combined action of lead and physical exercise showed an increase in the creatinine kinase-MB level. We found that the effect of exercise under lead intoxication on myocardial contractility was ambiguous. The maximum isotonic shortening velocity in trabeculae was normalized, but the maximum rate of strength development in the isometric mode in the papillary muscles decreased to a greater extent than under lead intoxication. The maximum sliding velocity of reconstituted thin filaments and myosin and the heavy chain ratio was partly normalized. Conclusion. In general, muscle exercise attenuated the lead cardiotoxic effects.

Physical, mechanical and dry sliding wear properties of non-woven viscose fabric epoxy-based polymer composites: An optimization study

Polymer-based composites have been widely used in the enhanced tribological technologies of various automobile, aerospace industry, sports, etc. The epoxy-based polymer composites reinforced with glass fiber have significantly improved the wear inhibitors and ultimate strength along with ultra-low density than other available materials. This current research aims to fabricate a variation of such non-woven viscose-based polymer composites for various weight fractions (100–400 GSM) with a constant fiber loading of 30 wt% and subsequently analyze its physical, mechanical, and tribological properties under various operating parameters. The density of the fabricated composite exhibits an increase of magnitude with an increase in weight fraction. The composites consist of 400 GSM fabric showing a higher tensile, impact, flexural strength, hardness, and inter lamina shear strength (ILSS). A pin-on-disc wear set-up held dry sliding wear tests of various nonwoven viscose fabric-based composites under various operating parameters like sliding velocity, sliding distance, area density, and normal load. A Taguchi-based L16 orthogonal array design was utilized to estimate the optimal behavior for maximum wear resistance for operating conditions. The result reveals that the normal load over the composite contributes the highest towards wear on a composite compared to area density, sliding velocity, and distance. The wear phenomena have been verified with SEM micrographs to characterize various wear phenomena like fiber rapture, ploughing, micro-cracks, and wear lines.

Tribological studies of different bioimplant materials for orthopedic application using Taguchi experimental design

In this research ball on disc wear tests have been carried out with ASTM G-99 standard at room temperature in simulated body fluid. The tribological property such as the coefficient of friction and wear weight loss was studied by using the Taguchi design of experiments. The design of the experiment was done using L8 orthogonal array to determine the collective contribution of the wear parameters. An analysis of variance demonstrated that the individual contribution of type of material factor was 97.15% and 66.66% for the coefficient of friction and wear weight loss respectively, which is the highest individual contribution as compared to other factors. It was concluded that the coefficient of friction and wear weight loss is mainly influenced by type of material factor. The analysis of the signal-to-noise ratio shows that the optimal coefficient of friction and wear weight loss was obtained with CoCrMo material at an applied normal load of 5 N with a sliding velocity of 0.05 m/s for a track diameter of 30 mm. To check the accuracy of results a confirmation test was carried out which indicates that predicted values are very close to the experimental values and the model is significant to predict the coefficient of friction. The results showed that the coefficient of friction and wear weight loss increases with increasing the applied load and sliding velocity. The microstructure of all substrates materials was analyzed using a scanning electron microscope. Wear track study showed that adhesive dominant wear mechanism for all four different substrate materials.

Experimental studying the effect of water temperature on friction properties of marine propeller sliding bearing

This paper presents the effect of water’s temperature on the friction properties of materials used in marine propeller sliding bearing. Copper-Rubber and Copper-Capron, two common pairs of material in the shaft water-lubricated polymer bearing were chosen to conduct experiments with the pin-on-disc model. Various conditions including water temperature, stress, and sliding velocity were examined, their results showed that in the range 30 °C to 100 °C of water temperature, the frictional coefficient of both friction pairs were unchanged under the small stress and low sliding velocity (0.3 MPa and 0.9 m/s). While in the case of stress and sliding velocity were both high (0.6 MPa and 1.5 m/s), it increased significantly in a certain transition temperature range. This temperature range of the pair Copper-Rubber and Copper-Capron is 50 °C to 60 °C and 80 °C to 90 °C, respectively. The experiment’s results also pointed out that in these transition temperature ranges, the friction coefficient of two pairs was slightly influenced by the change in sliding velocity, whereas the stress change has an important impact on its values. Nonetheless, when the water temperature was below the transition range, the effect of the stress change on the friction coefficient was not significant. Thus, high water temperature is the main reason for the friction coefficient’s increase rather than the increase of the stress. This work is expected to broaden the understanding of the friction behavior of the water-lubricated polymer bearing.

Wear analysis of natural-inorganic fiber reinforced automotive brake composites

Brake friction composite materials comprising varying proportions of natural (banana) and inorganic (lapinus) fibers were designed, fabricated by compression molding, and characterized for sliding wear performance. The sliding wear properties of the manufactured friction composites have been studied by the Taguchi method. An orthogonal array (L 16) was used to investigate the influence of sliding wear parameters. A series of tests were conducted on a pin-on-disc machine by considering four control parameters: composition, normal load, sliding velocity, and sliding distance, each having four levels. The results showed that the wear in terms of weight loss decreases with increasing banana fiber and increases with increasing lapinus fiber, normal load, sliding velocity, and sliding distance. The results indicate that the normal load emerges as the most significant control parameter affecting wear performance, followed by sliding distance and sliding velocity.

Investigation of the wear of rolls in asymmetric rolling

In the present work, both symmetric and asymmetric rolling processes were investigated by means of numerical approaches. From the algorithm presented, the values of rolling pressure and sliding velocity in the roll gap were determined. These variables allow the estimation of tribological parameters of a given material. To determine the wear of the rolls and rolled materials the Archard's law has been employed. Results of numerical simulations show that the quantitative characteristics of the wear reveal a slight change for slower roll. Whereas the wear value for the faster roll increases with an increase of roll velocity ratio. It was found that for a given roll velocity ratio, rise of friction coefficient causes insignificant change in the wear value for the slower roll, while this value tends to decrease rapidly for the faster roll.

Tensile and wear properties of repetitive corrugation and straightened Al 2024 alloy: an experimental and RSM approach

Repetitive Corrugation and Straightening (RCS) on sheet geometries causes Cyclic Plastic Deformation, resulting in potential improvements of mechanical characteristics in metals and alloys. In this study, sample sheets of Al 2024 are subjected to severe plastic deformation with specially designed corrugated rollers to generate heterogeneous repeated plastic deformation at room temperature. The material shows enhanced properties under severe plastic deformation, with 5.07% increase in tensile strength, compared to unprocessed material. Maximum tensile strength was observed at annealed temperature of 150 °C is of about 3.49% increase in tensile strength over other temperature conditions. A wear study was carried out by considering the processed sheet that yields high tensile strength (annealed at 150 °C) by varying process parameters like sliding distance, load and sliding velocity as per design of experiments. In comparison to all other combinations, the wear resistance was shown to be better with a sliding distance of 6000 m, a load of 9.81 N, and a sliding velocity of 1.45 m s−1. The Response Surface Methodology (RSM) approach was adopted for comparing purpose, the experimental findings are found to be more similar to the RSM approach’s outcomes.

Friction and wear of polyetheretherketone (PEEK) samples with different melt flow indices

Polyetheretherketone (PEEK) is a promising polymer material for tribological applications. Friction and wear tests of PEEK samples vs. steel with different melt flow indexes (MFI) were studied. The results showed dependencies of the friction force on the sliding velocity, either decreasing or increasing depending on whether the normal load exceeds the yield strength of the polymer. The data can be well fitted with the assumption of the two-component friction law involving the Amontons component and an adhesional component. With a decrease in MFI, i.e. with an increase in viscosity of polymer. The adhesive component of friction increases with increasing viscosity while the abrasive wear decreases. At high loads, the plastic displacement increases with an increase in the viscosity and plasticity of the polymer. The wear does not show a clear correlation with the viscosity.

Coupled Strengthening Effects by Lattice Distortion, Local Chemical Ordering, and Nanoprecipitates in Medium-Entropy Alloys

Extraordinary mechanical properties can be achieved in high-entropy alloys (HEAs) or medium-entropy alloys (MEAs) with nanoprecipitates. In the present study, the extra coupled strengthening effects by lattice distortion, local chemical ordering, and nanoprecipitates in the HEAs and MEAs with nanoprecipitates have been systematically investigated by large-scale molecular dynamics simulations. The moving of the dislocation can be slowed down, and the dislocation line shows a wavy configuration due to lattice distortion and local chemical ordering, resulting in strengthening. The degree of the wavy configuration increases and the sliding velocity of the dislocation decreases with increasing degrees of local chemical ordering. It is clearly indicated that the dislocation moves via nanoscale segment detrapping mechanism due to the effects of lattice distortion and local chemical ordering, resulting in roughened dislocation pathways for strengthening. The activated nanoscale segments are observed to be easier to detrap from the regions with stronger Co-Cr local chemical ordering and then propagate into the regions without such chemical ordering. These moving characteristics of the dislocation can delay the unpinning process from nanoprecipitates; thus, extra coupled strengthening effect has been revealed in the HEAs and MEAs with nanoprecipitates compared to pure Orowan’s strengthening.