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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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Laser-induced surface acoustic waves for thin film characterization
Kudělka, R. ; Václavek, L. ; Tomáštík, Jan ; Malecová, S. ; Čtvrtlík, R.
Knowledge of mechanical properties of thin films is essential for most of their applications.However, their determination can be problematic for very thin films. LAW (Laser-induced acousticwaves) is a combined acousto-optic method capable of measuring films with thickness from fewnanometers. It utilizes ultrasound surface waves which are excited via short laser pulses and detectedby a PVDF foil. Properties such as Young’s modulus, Poisson’s ratio and density of both the film andthe substrate as well as film thickness can be explored.Results from the LAW method are successfullycompared with nanoindentation for Young’s modulus evaluation and with optical method for filmthickness evaluation and also with literature data. Application of LAW for anisotropy mapping ofmaterials with cubic crystallographic lattice is also demonstrated
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Benefits of use of acoustic emission in scratch testing
Václavek, L. ; Tomáštík, Jan ; Chmelíčková, H. ; Čtvrtlík, R.
Scratch test is regularly used for assessment of cohesive and adhesive strength of thin films and coatings. By default, its evaluation is based on analysis of depth-load-time record and microscopic observation of residual scratch groove. The visual analysis of the residual groove provides the most detailed description of the final damage of the surface (crack patterns, extent of plastic deformation, delamination, etc.), but it may be a time demanding approach. Although the continuous recording of indenter penetration depth and applied load offers instantaneous information about the performance of the tested material, it may not provide sufficient description of the sample’s deformation behaviour. Therefore, other complementary techniques for description of the deformation response to scratch loading are desirable.
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Mechanical properties of optical thin films
Tomáštík, J. ; Čtvrtlík, R. ; Šebestová, Hana ; Schovánek, Petr ; Jankůj, J. ; Hrabovský, Miroslav
Mechanical properties of optical thin films and coatings are very important for their reliability, because they are often exposed to rough conditions in service. Mechanical attributes of films, that determine their behavior, are in the center of interest. In this paper, mechanical properties of optical thin films deposited on various types of glass substrates were examined. Assessment of such properties was performed using instrumented nanoindentation (hardness, elastic modulus, elastic and plastic work done by indentation) and scratch test (critical loads corresponding to the onset of specific failure). The failure modes of thin films were discussed.
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