Increasing the imaging rate of atomic force microscopy (AFM) without impairing of the imaging quality is a challenging task, since the increase in the scanning speed leads to a number of artifacts related to the limited mechanical bandwidth of the AFM components. One of these artifacts is the loss of contact between the probe tip and the sample. We propose to apply an additional nonlinear force on the upper surface of a cantilever, which will help to keep the tip and surface in contact. In practice, this force can be produced by the precisely regulated airflow. Such an improvement affects the AFM system dynamics, which were evaluated using a mathematical model that is presented in this paper. The model defines the relationships between the additional nonlinear force, the pressure of the applied air stream, and the initial air gap between the upper surface of the cantilever and the end of the air duct. It was found that the nonlinear force created by the stream of compressed air (aerodynamic force) prevents the contact loss caused by the high scanning speed or the higher surface roughness, thus maintaining stable contact between the probe and the surface. This improvement allows us to effectively increase the scanning speed by at least 10 times using a soft (spring constant of 0.2 N/m) cantilever by applying the air pressure of 40 Pa. If a stiff cantilever (spring constant of 40 N/m) is used, the potential of vertical deviation improvement is twice is large. This method is suitable for use with different types of AFM sensors and it can be implemented practically without essential changes in AFM sensor design.

In this study, the effect of shot peening intensity of the structural steel specimens on the bending fatigue strength was investigated. Three structural steels S235JRG2, S355J2+N, P460NH were shot-peened with three levels of intensity. The results of fatigue tests were compared with non-peening processed samples. S-N curves in fatigue were determined in cyclic bending fatigue. The novel attempt to evaluate the bending fatigue, which relies on the 3D optical profiler measurement of the side-area of fractures, was proposed. All investigated steels present ferritic-pearlitic structure. Moreover, due to the peening process, refinement of the grains size was observed. Also, fractures were analysed with the 3D profiler. In the presented results of research, the highest level of peening gave the greater increase in fatigue life. For all types of investigated steels, shot-peening gave superior results of fatigue bending performance compared with unpeened specimens.

Termiškai purkšTų dangų Tyrimas ulTragarsiniais meTodaisJustinas gargasas 1 , irmantas gedzevičius 2 , saulius nagurnas 3 Vilniaus Gedimino technikos universitetas El. paštas: 1 justinas.gargasas@vgtu.lt; 2 irmantas@vgtu.lt; 3 saulius.nagurnas@vgtu.lt santrauka. Straipsnyje pateikiami elektrolankiniu terminio purškimo būdu užpurkštų dangų tyrimai taikant ultragarsinius tyrimų metodus. Purkšta skenuojant besisukančius bandinius 30 cm/s greičiu. Atlikti dangos mikrostruktūros, ultragarsiniai storio, porėtumo, mikrokietumo ir dangos tamprumo modulio tyrimai. reikšminiai žodžiai: terminis purškimas, ultragarsiniai tyrimų metodai, mikrostruktūros, dangos mikrokietumas. research inTo Thermal sprayed coaTings wiTh ulTrasonic meThods J. gargasas, i. gedzevičius, s. nagurnas AbstractResearch on thermal sprayed coatings with ultrasonic methods is the main object of this thesis. Metal surface coating was applied to modify its mechanical and physical-chemical properties and resistance to external impact and improve aesthetics. Spraying was carried out by scanning the rotating sample of 30 cm/s speed. Surface microstructure, ultrasonic thickness, porosity, micro hardness and surface modulus tests performed. Conclusions were formulated. keywords: thermal spray, ultrasound testing, microstructure, micro hardness of coatings.

This paper present the result obtained from new experimental STEIN-MESYFIL 953 V; STEIN-MESYFIL 954 V coatings. The surfacing material was wires of 1.6 mm diameter. The tests aimed at determining wear resistance of coatings sprayed on steel substrate. The investigation shows that the tribological behaviour of new experimental thermal arc sprayed coatings is greatly affected by its microstructural constituents such as porosity, oxide inclusions, and microhardness of coatings. Results show that increasing porosity of coatings twice, it doubles the mass loss. Results for thermal sprayed coatings of all experiments showed their high wear resistance and are discussed.

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