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The objective of the study was to analyze the influence of coating treatments on sound propagation speeds in thin boards, along the longitudinal and radial directions of resonance wood. The samples studied were thin boards made of spruce and maple wood with dimensions of 240 mm × 80 mm × 4 mm (length × width × thickness) subjected to different coating treatments (oil-based varnish and alcohol varnish) as well as unvarnished samples, exposed to radiation UV, and specimens treated in the saline fog. The test method consisted of evaluating the propagation speeds of Lamb waves applied to thin plates, according to a semicircular test model, so that the results highlighted both the acoustic response in the longitudinal and radial directions as well as the variation in the anisotropy of the samples with the change in the sound propagation direction relative to wood fibers. Based on the statistical analysis, sound propagation speed profiles were obtained in each of the 38 directions analyzed for all wood samples. The results highlighted that the oil-based varnish led to a decrease in the speed of propagation in the radial direction, compared to the alcoholic varnish, whose major effect was in the longitudinal direction, on the spruce wood. On maple wood, increasing the number of varnish layers, regardless of the type of varnish, led to a decrease in the anisotropy ratio between the longitudinal and radial directions. [ABSTRACT FROM AUTHOR]

Experiments with changes in motion geometry can provide valuable data for engineering and development purposes, allowing a better understanding of the influence of tribological factors on the performance and service life of joints. The presented subject article focused on the experimental investigation of the influence of the geometry of the movement of the friction process on the change in the tribological properties of 30CrNiMo8 steel. The friction process was carried out without the use of a lubricant in contact with a steel ball of G40 material with a diameter of 4.76 mm. The steel ball performed two types of movement on the surface of the experimental material. The first method used was ball on disc, in which the ball moved reciprocally in an oval direction at an angle of 180° on a circumferential length of 35 mm at a speed of 5 mm/s. The second method consists of the same input parameters of the measurement, with the difference that the path along which the ball moved had a linear character. The load during the experiment was set at a constant value of 50 N with 1000 repetitions. The results show that with the ball on disc method, there was an increase in wear by 147% compared to the linear test method, which was approximately a coefficient of increase in wear of 2.468. EDS analysis pointed to the occurrence of oxidative wear that affected the resulting COF values, which were lower by 8% when using the ball on disc method due to a more uniform distribution of O and C on the surface of the friction groove where these elements acted as solid microlubricants. With the ball on disc method, defects in the form of microcracks occurred, which affected the reduction in the values of the depth of the affected area of microhardness. [ABSTRACT FROM AUTHOR]

Tool steels are used in stamping, shearing processes, and as cutting tools due to their good mechanical properties. During their working cycle, steels are subject to aggressive conditions such as heat stress, fatigue, and wear. In this paper, three tool steels, namely X153CrMoV12, X37CrMoV5-1, and X45NiCrMo4 were selected against two types of bearing balls, ZrO 2 and X46Cr1. All measurements were performed on a UMT TriboLab universal tribometric instrument under dry conditions. The main objective of the experiment was to analyze and compare tool steel wear in contact with two kinds of bearing balls with a diameter of 4.76 mm. This evaluation is focused on the hardness, surface roughness, and microstructure of all samples and on the impact of the input parameters on the resulting wear. All three types of tool steels were measured in the basic annealed state and, subsequently, in the state after hardening and tempering. Experimental results show that tool steels, belonging to high strength steels, can successfully represent wear resistant steels. The content of carbide elements, their size, and shape in the microstructure play an important role in the friction process and subsequent wear. Three types of loads were used and compared in the experiments 30, 60, and 90 N. Increasing the load results in significant degradation of the material on the sample surface. Lastly, the impact of hardness and roughness of materials on wear has also been proven. If abrasive wear occurs in the friction process, there is a greater degree of wear than that of adhesive wear. This is due to less abrasive particles, which behave like a cutting wedge and are subject to subsequent deformation strengthening due to the load increase, which adversely affects the further friction process. Analysis of the results showed that the ZrO 2 ceramic ball showed significantly better wear values when compared to the X46Cr13 stainless steel ball. It also improves the values of the coefficient of friction with respect to the type of wear that occurs when the experimental materials and counterparts are in contact.