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Influencing of the Pile-Up and the Sink-In by the Coefficient of Friction in the Nanoindentation Test
Kovář, J. ; Fuis, Vladimír ; Čtvrtlík, Radim
The influence of the coefficient of friction between an indenter and a specimen on the height of the pile-up or depth of the sink-in during the nanoindentation test is discussed in this paper. When the indenter is pressed into the hard material, the sink-in behavior causes the bending of the specimen’s surface under the indenter. When the indenter is pressed into the soft material, the deformed material accumulates under the sides of the indenter and makes a pile-up region. The pile-up or sink-in behavior influences the contact area. In this paper, the finite element method was used for calculation of the dependency between the depth of the sink-in or height of the pile-up and the coefficient of friction. The results showed that while there is not any dependency between the friction and the depth of the sink-in, there is a strong dependency between the friction and the height of the pile-up until a specific value of the coefficient of friction. When the pile-up behavior occurs, the friction influences the contact area and should be included into the calculation of the contact area.
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Why monitor acoustic emissions during nanomechanical tests?
Čtvrtlík, Radim ; Václavek, L. ; Tomáštík, J.
Acoustic Emissions (AE) monitoring has been proved as an effective non-destructive technique at the macro scale. Nevertheless, it may also be employed at nano/micro scale during nanomechanical and nanotribological testing. Local mechanical properties of surfaces or micro object are routinely explored using nanoindentation, scratch test or dynamic impact tests that are evaluated based on analysis of depth-load-time records or microscopic observation of residual indents, scratch grooves or impact craters, respectively. Although these approaches have been proven to be sufficient in most cases for a variety of materials, there are many situations where they do not provide sufficient information for a complex understanding of the deformation response. On the other hand, analysis of AE signals generated during these tests may provide valuable complementary information and provide some insight into the dynamics of phenomena like cracking, phase transitions, plastic instabilities, etc.\n
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Characterization of titanium laser welds
Chmelíčková, H. ; Hiklová, H. ; Václavek, L. ; Tomáštík, J. ; Čtvrtlík, Radim
Butt welding of commercially pure titanium Grade 1 and Ti6Al4V alloy sheets using a pulsed Nd:YAG laser KLS 246 - 102 LASAG were carried out to determine optimal values of pulse energy and pulse length to create completely penetrated weld. Surface peak power density of about 3.105 W.cm−2 was found as an optimal value. Weld dimensions, both face width and penetration depth, are found to be proportional to increasing energy and decreasing pulse length. Gentle sagging and root penetration were revealed by means of contact surface profilometry. The nanohardness tests on transverse cross-sections detected approximately 50% higher hardness in the fusion zone than in the base material.\n
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Měření tvrdosti nehomogenních plazmových nástřiků
Čtvrtlík, Radim ; Stranyánek, Martin ; Boháč, Petr ; Jastrabík, Lubomír ; Hrabovský, Milan ; Ctibor, Pavel
Článek pojednává o mechanických vlastnostech plazmově nastříkaného TiO2 vyhodnocovaných metodou hloubkově citlivé indentace (DSI) na měřicím systému NanoTest 600™. NT600™ je modulární měřicí zařízení originální koncepce, kde je zatěžující síla aplikována horizontálně. Je na něm možno měřit tvrdost, modul pružnosti, přilnavost, opotřebení, lomové a dynamické charakteristiky. V poslední době je věnována vzrůstající pozornost vrstvám připraveným pomocí plazmového nástřiku. Zde studované nástřiky byly připraveny v ÚFP AVČR pomocí plazmatronu WSP. Cílem příspěvku je prohloubit znalosti o lokálním rozdělení mechanických vlastností plazmových nástřiků, zejména tvrdosti a modulu pružnosti.
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