Evaluation of Wear of Disc Brake Friction Linings and the Variability of the Friction Coefficient on the Basis of Vibroacoustic Signals.

The article presents the results of friction and vibroacoustic tests of a railway disc brake carried out on a brake stand. The vibration signal generated by the friction linings provides information on their wear and offers evaluation of the braking process, i.e., changes in the average friction coefficient. The algorithm presents simple regression linear and non-linear models for the thickness of the friction linings and the average coefficient of friction based on the effective value of vibration acceleration. The vibration acceleration signals were analyzed in the amplitude and frequency domains. In both cases, satisfactory values of the dynamics of changes above 6 dB were obtained. In the case of spectral analysis using a mid-band filter, more accurate models of the friction lining thickness and the average coefficient of friction were obtained. However, the spectral analysis does not allow the estimation of the lining thickness and the friction coefficient at low braking speeds, i.e., 50 and 80 km/h. The analysis of amplitudes leads to the determination of models in the entire braking speed range from 50 to 200 km/h, despite the lower accuracy compared to the model, based on the spectral analysis. The vibroacoustic literature presents methods of diagnosis of the wear of various machine elements such as bearings or friction linings, based on amplitude or frequency analysis of vibrations. These signal analysis methods have their limitations with regard to their scope of use and the accuracy of diagnosis. There are no cases of simultaneous use of different methods of analysis. This article presents the simultaneous application of the amplitude and frequency methods in the analysis of vibroacoustic signals generated by brake linings. Moreover, algorithms for assessing the wear of friction linings and the average coefficient of friction were presented. The algorithm enables determination of the time at which the friction linings should be replaced with new ones. The final algorithm analyzes the vibration acceleration signals using both amplitude analysis for low braking speeds, as well as spectral analysis for medium and high braking speeds.

[Tragedy in the Valley Jaworowa: incredible coincidence or perfect murder?]

The paper presents the case of an unexplained and the most mysterious death in the history of Polish Tatra tourism. It concerns three people of different ages and occurred on August 3, 1925 in the Valley of Jaworowa. Kazimierz Kasznica, his son Waclaw Kasznica and a newly discovered mountaineer Ryszard Wasserberger died suddenly for unknown reasons in 15 minutes during a mountain trek. This story is interesting due to the mysterious, simultaneous death of three people of different ages and due to the fact that Waleria Kasznica - the wife of Kazimierz and the mother of Waclaw Kasznica survived the journey. KEY WORDS.

Evaluation of Adhesive Joints Using Ultrasonic Rayleigh Waves.

Adhesive joints are non-separable connections that are used in numerous ways in vehicle construction, particularly in buses. The widespread use of adhesive joints makes it necessary to assess their quality, especially under production conditions. The main goal of this study was to develop a mathematical model to estimate the width of the adhesive path in a plywood-adhesive-closed-profile joint based on selected parameters of the ultrasonic surface wave. A digital ultrasonic flaw detector and Rayleigh wave probes were applied. The test involved evaluating different widths of hybrid adhesive and two-component epoxy adhesive. The tests were conducted on a steel profile from a bus construction. The attenuation of the ultrasonic waves on the steel profile (0.026 db/mm) and the adhesive (0.264 dB/mm) was determined. A one-size-fits-all model for estimating adhesive path width for specific conditions is proposed.

Inspection of Spot Welded Joints with the Use of the Ultrasonic Surface Wave.

Spot welded joints play a crucial role in the construction of modern automobiles, serving as a vital method for enhancing the structural integrity, strength, and durability of the vehicle body. Taking into account spot welding process in automotive bodies, numerous defects can arise, such as insufficient weld nugget diameter. It may have evident influence on vehicle operation or even contribute to accidents on the road. Hence, there is a need for non-invasive methods that allow to assess the quality of the spot welds without compromising their structural integrity and characteristics. Thus, this study describes a novel method for assessing spot welded joints using ultrasound technology. The usage of ultrasonic surface waves is the main component of the proposed advancement. The study employed ultrasonic transducers operating at a frequency of 10 MHz and a specially designed setup for testing various spot welded samples. The parameters of the spot welding procedure and the size of the weld nugget caused differences in the ultrasonic surface waveforms that were recorded during experiments. One of the indicators of weld quality was the amplitude of the ultrasonic pulse. For low quality spot welds, the amplitude amounted to around 25% of the maximum value when using single-sided transducers. Conversely, for high-quality welds an amplitude of 90% was achieved. Depending on the size of the weld nugget, a larger or smaller amount of wave energy is transferred, which results in a smaller or larger amplitude of the ultrasonic pulse. Comparable results were obtained when employing transducers on both sides of the tested joint, as an amplitude ranging from 13% for inferior welds to 97% for superior ones was observed. This research confirmed the feasibility of employing surface waves to assess the diameter of the weld nugget accurately.

Adhesive Joints of Additively Manufactured Adherends: Ultrasonic Evaluation of Adhesion Strength.

Adhesive joints are widely used in the construction of machines and motor vehicles. Manufacturers replace them with the welding and spot-welding methods due to the lack of damage to the material structure in the joint area. Moreover, it is aimed at reducing the weight of vehicles and producing elements with complex shapes. Therefore, additive manufacturing technology has been increasingly used in the production stage. This fact has not only changed the view on the possibilities of further development of the production technology itself, but it has also caused an intense interest among a greater number of companies in the advantages of structural optimization. There is a natural relationship between these two areas in the design and production, allowing for almost unlimited possibilities of designing new products. The main goal of the research described in this article was to determine the correlation between the strength of the adhesive joint of elements produced using additive technology and the parameters of the ultrasonic wave propagating in the area of the adhesive bond. The tests were carried out on samples made of AlSiMg0.6 material and a structural adhesive. Strength tests were performed to determine the shear force which damaged the joint. Furthermore, an ultrasonic echo technique enabling the determination of a nondestructive measure of the quality and strength of the joint was developed. The samples of the adhesive joints had a strength of about 18.75-28.95 MPa, which corresponded to an ultrasonic measure range of 4.6-7.8 dB. The determined regression relationship had a coefficient of determination at the level of 0.94. Additional ultrasonic tests of materials made with the additive technology confirmed its different acoustic properties in relation to aluminum produced with the standard casting or extrusion process. Designated dependence combining the mechanical strength and the decibel difference between the first and second impulses from the bottom of the joint may constitute the basis for the development of a nondestructive technique for testing the strength of adhesive joints.

Tribocorrosion and Abrasive Wear Test of 22MnCrB5 Hot-Formed Steel.

The article presents the results of research on abrasive and tribocorrosion wear of boron steel. This type of steel is used in the automotive and agricultural industries for the production of tools working in soil. The main goal of the article is the evaluation of tribocorrosion and abrasive wear for hot-formed 22MnCrB5 steel and a comparison of the obtained results with test results for steel in a cold-formed state. The spinning bowl method to determine the wear of samples working in the abrasive mass was used. Furthermore, a stand developed based on the ball-on-plate system allows to determine the wear during the interaction of friction and corrosion. After the hot-forming process, 22MnCrB5 steel was three times more resistant for the abrasive wear than steel without this treatment. The average wear intensity for 22MnCrB5 untreated steel was 0.00046 g per km, while for 22MnCrB5 hot-formed steel it was 0.00014 g per km. The tribocorrosion tests show that the wear trace of hot-formed 22MnCrB5 steel was about 7.03 µm, and for cold-formed 22MnCrB5 steel a 12.11 µm trace was noticed. The hot-forming method allows to obtain the desired shape of the machine element and improves the anti-wear and anti-corrosion properties for boron steel.

Investigation and Modelling of the Weight Wear of Friction Pads of a Railway Disc Brake.

This paper presents the results of tests on the railway disc brake with regard to the weight wear of friction pads. The tests were carried out at a certified brake test bench where the friction-mechanical characteristics of the railway brake were determined. The test stand was additionally equipped with a thermal imaging camera to observe the contact between the brake pads and the brake disc. The scientific goal of the test is to evaluate the relationship between the weight wear of friction pads and the quantities characterizing the braking process. The quantities characterizing the braking process included pad-to-disc contact area, friction pad thickness, pad-to-disc pressure, and braking speed. A regression model to estimate the friction pad wear on the basis of a single braking with the given input quantities was determined. The greatest influence on the increase in weight wear of friction pads has the braking velocity, which was confirmed by the value of the correlation coefficient of the regression model at value 0.81. The pressure of the friction pad to the disc and the friction pad thickness do not have a significant effect on the weight wear described by the regression model, and the obtained correlation coefficient for these parameters was lower than the value of 0.2.

Modeling the Depth of Surface Cracks in Brake Disc.

The article presents the state of knowledge and research in the field of surface cracks occurring in disc braking systems of rail and car vehicles. The craze formed during the operation of vehicles is particularly dangerous and leads to breaking the disc into several pieces. It may lead to a loss of braking force and damage to the entire disc brake caliper. The main aim of the research is to identify surface cracks in brake discs made of cast iron and use experimental methods to estimate their depth. Research were conducted on the disc braking system developed by the authors. In examining the location and depth of cracks, the penetration method, ultrasound, as well as a special probe were used. This device measures the crack depth based on the electrical resistance between two points on the surface of the metallic object. The tests showed that the first microcracks on the brake discs appeared after 309 braking tests on the test stand. In addition, it was observed that the surface cracks length of the disc increased linearly to depth until they reached about 11.5-12 mm with corresponded to crack lengths in the range of 65-70 mm. However, determination of the regression functions presented in the article allows to estimate the depth of surface cracks up to 70 mm long on cast iron brake discs by measuring their length.

Modeling the Average and Instantaneous Friction Coefficient of a Disc Brake on the Basis of Bench Tests.

This article presents the results of tests conducted on the average and instantaneous friction coefficients of railway vehicle disc brakes. The tests were carried out independently of various states of wear on the friction linings and the brake disc. The requirements of the International Union of Railways (UIC) regarding the approval of brake linings for use were taken into account. Based on many years of research using a brake bench to test railway disc brakes, the authors developed multiple regression models for the average friction coefficient and fluctuations (tolerances) in the instantaneous friction coefficient and achieved 870 results. The models proposed three types of variables: the input braking parameters (speed, pressure, and mass to be braked), operational parameters (the wear on the friction linings and the brake disc), and design parameters (perforations in the form of holes on the disc surface). The above two models were validated on the basis of 384 brakes, and in subsequent stages a further evaluation was performed. The coefficients were determined to be, respectively, 0.99 for the model of the average friction coefficient and 0.71 for the model of tolerance (fluctuations) of the instantaneous friction coefficient.

Assessment of Padding Elements Wear of Belt Conveyors Working in Combination of Rubber-Quartz-Metal Condition.

Elements of belt conveyors, like other machine parts, are subject to wear processes. The conveyors transporting the spoil in the quartz sand mine are exposed to accelerated wear due to the effect of quartz on metal elements. Intensive wear of metal parts leads to downtime and the need to replace damage parts which generates additional costs. Therefore, it is important to perform surface treatment of metal elements, which will allow to extend the operation time of belt conveyors by reducing wear. The main objective of the article is to determine the impact of the pad welding process of the surface layer of metal elements on the abrasive wear of elements working in the metal-quartz sand-rubber conditions used in belt conveyors. In this research study, three different types of electrodes were used for pad welding the surface. The wear results obtained on the test stand were compared to wear of the basic element without surface treatment. The average wear value of the samples padded with electrode 3 was about 25% lower than the samples without surface treatment. The main mechanism of sample wear was the abrasion process due to the interaction between the steel surface and hard sand particles. The results presented in the article are important not only for belt conveyor elements but also for other machine parts where it is desirable to reduce abrasive wear.

Reliability Analysis for Unrepairable Automotive Components.

The analysis of the reliability parameters of a technical object and the determination of the change in the reliability of the object over time, requires the knowledge of the functional characteristics and reliability parameters of the elements included in a system. On the basis of the failure data of the selected element of the object, in this case the vehicle, it is possible to determine the average working time to failure of the element and the appropriate form of distribution that characterizes the reliability and durability parameters of the tested element. The main purpose of the research presented in the article was to develop a method of assessing the reliability of an electronic component of a vehicle-a boot lid contactor. This paper also presents three possible methods of repairing the boot lid contactor (sealing the housing with adhesive with better way, replacing the element with a new one or the most time-consuming solution, changing the shape of the boot lid). The authors also decided to determine the reliability and cost parameters that will allow preventive replacement of this element. The tests were carried out on a fleet of 61 vehicles of the same model, but with different body structures. Contactor failures were reported in 41 cases, of which 29 were in the hatchback construction and 12 in the estate type. The analysis of the distribution selection for the tested part of the passenger car-the boot lid contactor-was performed using the Likelihood Value (LKV) test to determine the rank of distributions. Also the maximum likelihood (MLE) method was used to estimate the distribution parameters. The three-parameter Weibull distribution was the best-fitted distribution in both cases. It was clearly defined that one model of car with two different types of body have vastly different reliability characteristic. Based on the reliability characteristic and parameters, the appropriate preventive actions can be taken, minimizing the risk of damage, thus avoiding financial losses and guaranteeing an appropriate level of vehicle safety.

Real-Life Impact on Lipid Profile of a Switch from Tenofovir Disoproxil Fumarate to Tenofovir Alafenamide in HIV-Infected Patients.

BACKGROUND: Tenofovir disoproxil fumarate is a prodrug of tenofovir diphosphate that exposes patients to renal toxicity over the long term. Tenofovir alafenamide, a new prodrug, now makes it possible to reduce toxicity, but at the cost of an alteration in lipid profile. There is currently no recommendation for follow-up of lipid profile when switching from tenofovir disoproxil fumarate to tenofovir alafenamide. OBJECTIVE: Our study aimed to evaluate the effects on renal function and lipid profile of a switch from tenofovir disoproxil fumarate to tenofovir alafenamide, and the consequences for patient management. METHODS: Demographic, clinical and biological data was recorded from a retrospective clinical cohort study in real-life, including patients who switched from tenofovir disoproxil fumarate to tenofovir alafenamide. A descriptive analysis of the study population, with a comparison of biological parameters using the paired Student t test for paired data was performed. RESULTS: From January 2016 to January 2019, a total of 103 patients were included. There was no significant difference in renal function before vs after the switch in therapy (p=0.29 for creatinine, p=0.30 for phosphoremia). We observed a change in lipid profile, with a significant increase in total cholesterol (p=0.0006), HDL cholesterol (p=0.0055) and triglycerides (p=0.0242). Four patients received lipid-lowering therapy after switching. CONCLUSION: In patients who switch from tenofovir disoproxil fumarate to tenofovir alafenamide, lipid profile is altered, and may require initiation of lipid-lowering therapy. It seems necessary to monitor lipid parameters after this switch, despite the absence of an official recommendation.

Glass-Adhesive-Steel Joint Inspection Using Mechanic and High Frequency Electromagnetic Waves.

The utilization of a glass-adhesive-steel joint in modern machine and vehicle production is constantly growing. Despite the technological regime during the production process, various defects in the adhesive joints may occur. One of the major problems is lack of adhesive between joined materials. Due to the widespread use of non-transparent layers increasing adhesion, it is frequently not possible to conduct simple visual inspections. Hence, it is important to develop a non-destructive adhesive path continuity examination procedure. In that process, the different physical properties of the joint materials must be taken into account. Therefore, in this paper various testing methods were used, including ultrasound, thermographic and electromagnetic methods operating in the microwave and terahertz frequency range. Different physical phenomena of the methods allowed for examination of the joint in a wide context. In order to verify the information brought by each method, the results were transferred into common coordinate space, compared and finally integrated. Various opinion pooling strategies were conducted to fuse data, which allowed us to emphasize convergent and complementary information on adhesive continuity. The obtained results are promising and constitute the basis for further work on an integrated system for automatic evaluation of a wide range of possible defects in glass-adhesive-steel joints.

Experimental Study of Abrasive, Mechanical and Corrosion Effects in Ring-on-Ring Sliding Contact.

This article presents the application of the ring-on-ring test to investigate some of the important factors affecting the abrasive and corrosion wear of a face seal used in the sugar industry. The test involves the sliding contact between two steel rings working in different conditions such as mechanic, abrasive, corrosive extortions and its combination. Rings were made of the C45 steel and the surface layers were modified by heat and thermochemical treatment such as normalizing, flame hardening, nitriding and chrome diffusion. Maximum wear of the sample after tests under mechanic, abrasive and corrosion extortion were obtained. For C45 steel without surface modification the biggest wear was obtained for mechanical, abrasive and corrosive extortion and equals 0.0138 g. This value was three times bigger than the result for the mechanical extortion and ten times than for the corrosive conditions. For individual research options the percentage increase or decrease in wear resistance in relation to the normalized surface layer was determined. In the corrosive extortion the highest increase (90%) of wear resistance was recorded for the chrome layer relative to normalizing sample. The main conclusion of the paper is that the wear effect caused by all factors-mechanical, abrasive and corrosive-is not a straight sum of values of wear.

An evaluation of antisocial behaviour in children after traumatic brain injury: the prospect of improving the quality of life in rehabilitation.

INTRODUCTION AND OBJECTIVE: The aim of the article is to present the consequences of traumatic brain injury in children, associated with general cognition and behavioural disorders, mainly of the antisocial type. MATERIAL AND METHODS: A total of 20 school-age children took part in the study, including six girls and 14 boys. The average age of the children was 13.35 years (standard deviation SD = 1.95). The research instruments included an analysis of documentation, a structured clinical interview, MMSE and Frontal Behavioral Inventory (FBInv) with additional set of five supplementary questions directed for detection of antisocial behavior. The research was conducted from the beginning of January 2009 until the end of May 2009. RESULTS: As hypothesized, the functioning of the children with traumatic brain injury is severely disrupted, because of the presence of cognitive impairment, however, dementia is not manifested. In a significant number of the children with traumatic brain injury we found not only the frontal syndrome, but also the occurrence of antisocial behaviour. The most commonly reported behavioural problems were: disorganization commonly referred to as laziness, hypersensitivity, and anxiety. The most common types of anti-social behaviour were: impulsivity, physical and verbal aggression, and also an outburst of anger. CONCLUSIONS: The children with traumatic brain injury suffer from a cognitive disorders and behavioural problems, especially impulsivity, physical and verbal aggression, increased anxiety, and disorganization. The occurrence of frontal syndrome is related to the development of antisocial behaviour.