Aristia-Ioana Popovici

When used to analyze the wear of rough surfaces, Archard’s law implicitly assumes that the surface subjected to wear is homogeneous and that its hardness is equal to that of the bulk material, an assumption that does not apply to asphalt mixtures, where, in the case of road pavements, the wearing surface is a mosaic of aggregate particles and binder (bitumen). This study examines this assumption by comparing two models of the wheel–asphalt pavement contact for four BA16 asphalt mixtures: a reference specimen (M0), a modified specimen (M1, characterized by high porosity), a specimen with aggregate replacement in its composition (M2, containing 3% plastic material in flake form), and a specimen with aggregate replacement in its composition (M3, containing 3% cellulosic material in pellet form). The macro-equivalent model treats the specimens as homogeneous media, whereas the meso-structural model explicitly incorporates 93 polyhedral aggregate particles within a representative volume element of 30 mm × 30 mm × 30 mm, under three loading scenarios: severe dry, wet, and thermal conditions, with extreme temperatures of 5 and 40 °C, respectively. The results were assessed using two independent indicators: a composite tribological degradation indicator and an indicator derived from Archard’s law. The explicit modeling shows that the wearing surface contains 16.2% mineral aggregate, compared with 25.2% in the bulk asphalt mixture, while the effective elastic modulus at the wearing surface is 10.5% lower than that of the bulk asphalt mixture. This ratio remains nearly constant (0.894–0.897) for all mixtures and loading scenarios. Both analyses yield the same ranking of wear susceptibility—M0 < M3 < M2 < M1—in all scenarios, with deviations below 4.3%. Tangential loading at the wearing surface triples the stress in the binder and has a predominant effect on wear compared with the normal tire pressure, while the maximum stress occurs precisely at the aggregate–binder interface.

The flights of rotary dryers used for drying mineral aggregates face significant erosive-abrasive wear, affecting efficiency and maintenance costs. This study explores—by way of example—the possibility of using experimental measurements and statistical modeling to evaluate the wear mechanisms and the effect of covering the active surface of the flights with hard materials (welding deposits). The in situ thickness loss was measured on the active surface of the flights, in areas with and without deposits, after different periods of industrial operation (720 and 1118 h). The statistical analysis (Wilcoxon and Mann-Whitney U tests) aimed to assess the relevance of the measurements in a situation affected by a multitude of influencing factors, such as the situation of the wear of the rotary dryer flights. Finnie and Hutchings erosion models were used to predict wear behavior based on the impact velocity of mineral aggregates, incidence angles, and drum filling degree. The proposed methodology provides a predictive approach for optimizing rotary dryer maintenance and extending component life.

In the cement concrete manufacturing industry, mixers are critical pieces of equipment that play an essential role. Mixers ensure, by mechanically mixing the materials that make up the concrete, the homogeneity of the mixture. Since the active elements of the mixer in the concrete industry—the mixing blades—come into permanent contact with the mineral aggregates in the mixture formed by water and cement, they are permanently subjected to a strong abrasive–erosive wear process. The authors of this article were concerned with the establishment of tribological models for studying the wear of mixing blades, in order to identify the influence of their constructive parameters on the wear intensity. A complex model (Kraghelsky–Nepomnyashchi model) was adopted for the study. The modeling results revealed that the wear intensity decreases with an increasing blade angle of attack and increases linearly with increasing speed, as well as with an increasing friction coefficient. The modeling results confirm that the wear intensity is lowest when the mixing blade is inclined at a 60° angle, while the highest value is recorded for 30°. By identifying the angle at which the greatest wear of blades occurs, interventions can be made in the design of a more durable mixer (with the optimal installation angle of the mixer blades), thus requiring fewer corrective maintenance interventions. Based on these findings, we conclude that the complex model used in the experiment can provide a convenient and efficient tool for the study of erosive–abrasive phenomena.

Progressive cavitation pumps are designed to work in aggressive environments thus their wear is inevitable. The specific tribological coupling of these pumps is composed of a helical rotor with a single outward helix and a stator with a double inside helix. These elements are in relative motion and direct contact to each other and also in direct contact with the pumped oil. Therefore the main forms of wear of rotor-stator coupling elements are the abrasive wear and the erosion wear. In this paper is presented the analysis of erosion with Bitter and Hutchings models. The results are useful for estimation of progressive cavity pumps specific abrasive-erosive wear.

Progressive cavitation pumps are designed to work in aggressive environments thus their wear is inevitable. The specific tribological coupling of these pumps is composed of a helical rotor with a single outward helix and a stator with a double inside helix. These elements are in relative motion and direct contact to each other and also in direct contact with the pumped oil. Therefore the main forms of wear of rotor-stator coupling elements are the abrasive wear and the erosion wear. In this paper is presented the analysis of erosion with Finnie models. The results are useful for estimation of progressive cavity pumps specific abrasive-erosive wear.