ALBERT

Description: With the increasing challenges of climate change and scarce resources, the development of sustainable and energy-efficient technical systems is becoming increasingly important. In many applications, the friction losses occurring in contacts have a decisive influence on the overall efficiency. At this point, tribological contact optimization can make an important contribution to increasing the efficiency of technical systems. However, improvements are often associated with a considerable experimental effort. To reduce the development time, additional simulation models can be applied to predict the tribological behavior. This requires the closest possible approximation of the real contact within a numerical model. This paper presents a simulation approach for the time-dependent simulation of a cam–tappet contact. The simulation uses realistic operating conditions as they arise in the valve train of internal combustion engines. The influence of edge effects on the friction behavior is considered by a scaled calculation area and the influence of the surface roughness is investigated using stochastic asperity models. It is shown that the tribological behavior within the contact strongly depends on the surface properties and the load spectrum used. In addition, edge effects on the sides of the contact area have a clear influence on the pressure and film thickness distribution.

Description: The last decade has experienced a tremendous development of several technologies that are likely to shape our future [...]

Description: Convolutional Neural Network (CNN) has been widely used in bearing fault diagnosis in recent years, and many satisfying results have been reported. However, when the training dataset provided is unbalanced, such as the samples in some fault labels are very limited, the CNN’s performance reduces inevitably. To solve the dataset imbalance problem, a Generative Adversarial Network (GAN) has been preferably adopted for the data generation. In published research studies, GAN only focuses on the overall similarity of generated data to the original measurement. The similarity in the fault characteristics is ignored, which carries more information for the fault diagnosis. To bridge this gap, this paper proposes two modifications for the general GAN. Firstly, a CNN, together with a GAN, and two networks are optimized collaboratively. The GAN provides a more balanced dataset for the CNN, and the CNN outputs the fault diagnosis result as a correction term in the GAN generator’s loss function to improve the GAN’s performance. Secondly, the similarity of the envelope spectrum between the generated data and the original measurement is considered. The envelope spectrum error from the 1st to 5th order of the Fault Characteristic Frequencies (FCF) is taken as another correction in the GAN generator’s loss function. Experimental results show that the bearing fault samples generated by the optimized GAN contain more fault information than the samples produced by the general GAN. Furthermore, after the data augmentation for the unbalanced training sets, the CNN’s accuracy in the fault classification has been significantly improved.

Description: The coefficient of friction between a wheel tread and the top of the rail should be maintained at intermediate levels to limit frictional tangential contact forces. This can be achieved by applying top-of-rail products. Reducing the coefficient of friction to intermediate levels reduces energy consumption and fuel costs, as well as damage to the wheel and rail surfaces, such as, e.g., wear, rolling contact fatigue, and corrugation. This work describes a simulation model that predicts the evolution of the coefficient of friction as a function of the number of wheel passes and the distance from the application site for wayside application of top-of-rail products. The model considers the interplay of three mechanisms, namely the pick-up of product by the wheel at the application site, the repeated transfer of the product between the wheel and rail surfaces, and the product consumption. The model has been parameterized with data from small-scale twin disc rig experiments and full-scale wheel–rail rig experiments. Systematic investigations of the model behaviour for a railway operating scenario show that all three mechanisms may limit the achievable carry-on distance of the product. The developed simulation model assists in understanding the interplay of the mechanisms that govern the evolution of the coefficient of friction in the field. It may aid in finding optimal product application strategies with respect to application position, application amount, and application pattern depending on specific railway operating conditions.

Description: According to the ASTM D97, the pour point is the temperature below which petroleum products cease to flow. To evaluate the relevance of pour point measurements for synthetic lubricating oils, we investigated the crystallization, melting temperature and low-temperature flow behavior of one mineral and five synthetic lubricating oils. The classification of three groups emerged from this process. The formation of paraffin crystals in mineral oils (I) below the crystallization temperature causes shear-thinning behavior and a yield point. The crystallization temperature determined in the thermal analysis and rheology correlates well with the pour point. Synthetic lubricating oils, which solidify glass-like (II), exhibit a steady viscosity increase with falling temperature. The temperature at which viscosity reaches 1000 Pas corresponds well to the pour point. Synthetic oils, especially esters, with complex crystallization behavior (III), exhibit supercooling depending on the shear rate and cooling conditions. For these lubricating oils, the pour point provides no information for low-temperature applicability.

Description: The oil film generation of a U-cup rod seal and the oil film thickness on the rod after outstroke were analyzed analytically, numerically, and experimentally. The analyzed sealing system consists of an unmodified, commercially available U-cup, a polished rod, and mineral oil. The inverse theory of hydrodynamic lubrication (IHL) and an elastohydrodynamic lubrication (EHL) model—both based on the Reynolds equation for thin lubricating films—were utilized to simulate the oil film generation. In the EHL analysis, physical parameters and numerical EHL parameters were varied. Both the analytical and numerical results for the varied parameters show that the film thickness follows a square-root function (i.e., with a function exponent of 0.5) with respect to the product of dynamic viscosity and rod speed, also referred to as the duty parameter. In comparison to the analytical and numerical results, the film thickness obtained via ellipsometry measurements is a function of the duty parameter with an exponent of approximately 0.85. Possible causes for the discrepancy between theory and experiments are discussed. A potential remedy for the modeling gap is proposed.

Description: The augmentation of lubricant oil properties is key to protecting engines, bearings, and machine parts from damage due to friction and wear and minimizing energy lost in countering friction. The tribological and rheological properties of the lubricants are of utmost importance to prevent wear under unembellished conditions. The marginal addition of particulate and filamentous nanofillers enhances these properties, making the lubricant oil stable under severe operating conditions. This research explores the improvement in SAE 5w-30 base oil performance after the addition of multiwalled carbon nanotubes (MWCNTs) in six marginal compositions, namely, Base, 0.02, 0.04, 0.06, 0.08, and 0.10 weight percentage. The effect of the addition of MWCNTs on flash and pour points, thermal conductivity, kinematic viscosity, friction coefficients, and wear are investigated and reported. X-ray diffraction and transmission electron microscopy are used to characterize the MWCNTs. The purity, crystallinity, size, shape, and orientation of the MWCNTs are confirmed by XRD and TEM characterization. Pour points and flash points increase by adding MWCNTs but inconsistency is observed after the 0.06 wt.% composition. The thermal conductivity and kinematic viscosity increase significantly and consistently. The friction coefficient and wear scar diameter reduce to 0.06 wt.% MWCNTs and then the trend is reversed due to agglomeration and inhomogeneity. A composition of 0.06 wt.% is identified as the optimum considering all the investigated properties. This composition ensures the stability of the tribo-film and hydrodynamic lubrication.

Description: Gravimetric measurements were applied to study the inhibitory effect of 4-benzyl-1-(4-oxo-4-phenylbutanoyl)thiosemicarbazide (BOT) on the corrosion of mild steel in 1.0 M HCl. BOT has a good inhibitory efficacy of 92.5 percent at 500 ppm, according to weight loss results. The effect of inhibitor concentration on the mild corrosion behavior of steel was investigated and it was discovered that the higher the inhibitor concentration, the higher the damping efficiency. The results confirm that BOT is an effective corrosion inhibitor for mild steel in the presence of 1.0 M HCl. Furthermore, the higher protection efficiency with increasing temperature and the free energy value showed that BOT molecules participate in both chemisorption (coordination bonds between the active sites of BOT molecules and d-orbital of iron atoms) and physisorption (through the physical interactions on the mild steel surface). The adsorption mechanism on the mild steel surface obeys the Langmuir adsorption isotherm model. Quantum chemical calculations based on the DFT calculations were conducted on BOT. DFT calculations indicated that the protective efficacy of the tested inhibitor increased with the increase in energy of HOMO. The theoretical findings revealed that the broadly stretched linked functional groups (carbonyl and thionyl) and heteroatoms (sulfur, nitrogen and oxygen) in the structure of tested inhibitor molecules are responsible for the significant inhibitive performance, due to possible bonding with Fe atoms on the mild steel surface by donating electrons to the d-orbitals of Fe atoms. Both experimental and theoretical findings in the current investigation are in excellent harmony.

Description: Technical thermoplastic materials (e.g., PEEK, PPA and POM) are widely used for tribological applications combined with different filler systems (e.g., glass- or carbon fibres) because of their excellent mechanical properties. The friction and wear behaviour of thermoplastics can be specifically improved by solid lubrication systems such as graphite, PTFE and MoS2. Besides these systems, others such as WoS2 and MnS are becoming scientifically interesting. This work investigates the influence of different solid lubricants—alternative metal sulphides and polymer-based—in combination with different glass fibre contents on the tribological behaviour of unfilled PEEK and glass fibre-filled PPA. For this purpose, compounds were produced and injection-moulded into tribological test specimens that were subsequently tested. It is particularly evident for both matrix materials that the solid lubricant SLS 22 shows a 25% wear rate reduction when compared to MoS2 and, in addition, the proportion of fibre content in PPA shows an additional wear rate reduction by a factor of 10. The friction level could be kept at a similar level compared to the usually utilised solid lubricants. The investigations showed the potential use of metal sulphide filler systems in high-performance thermoplastic with enhanced tribological properties as alternatives to the well-established solid lubricants.

Description: Using the molecular dynamics (MD) simulations with ReaxFF potential, two different types of PFPE lubricants (Ztetraol and ZTMD) are prepared on a-C film, and SiO2 particles are adsorbed onto the lubricants at room temperature. From the simulation results, it is observed that the adsorbed SiO2 particles increase the stiffness of PFPE lubricants leading to less airshear displacement. Since Ztetraol has higher mobility with lower viscosity than ZTMD, the adsorbed SiO2 particles penetrate deeper into the Ztetraol lubricants. Accordingly, the effect of SiO2 on the airshear displacement is more obvious to Ztetraol than ZTMD. In addition, the adsorbed SiO2 particles increase the friction force and the amount of lubricant pick-up during the sliding contact with a nanosized a-C tip.