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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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Influencing the Indentation Curves by the Bluntness of the Berkovich Indenter at the Fem Modelling
Kovář, J. ; Fuis, Vladimír ; Tomaštík, Jan
The influence of the Berkovich indenter bluntness on the indentation curves at nanoindentation test of fused silica is determined by the FEM (finite element method) in this paper. The Berkovich indenter, which is mostly used for the nanoindentation test, was assumed for calculations. The indenter is always blunted in real tests. The bluntness of the indenter has an influence on the results of the nanoindentation test. The combination of the nanoindentation test and the FE modelling can be used for the calculation of the parameters of fused silica plasticity and estimation of the bluntness of the indenter. In this paper, the FEM was used for calculating of the indentation curves. Two cases of bluntness were assumed. The curves for ideally sharp or blunted indenter were determined. The results of these calculations showed that the indentation curves are dependent on the bluntness of the Berkovich indenter. The greatest relative influence of the nanoindentation curves by the bluntness is in the area of small values of the indenter displacement. The impact of assuming blunted indenter to calculated parameters of plasticity was assessed. It is often difficult to measure the bluntness of the indenter but it has an influence on the results of the nanoindentation test and should be included into calculations to make it more precise.
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Využití akustické emise k vyhodnocování mechanické odolnosti tenkých vrstev
Boháč, Petr ; Tomáštík, Jan ; Koula, V. ; Dráb, M. ; Jastrabík, Lubomír
Tenké vrstvy se deponují jako funkční povlak na součástky. Omezujícím faktorem jejich aplikace je jejich adheze k podložce. Scratch test je laboratorní metoda k vyšetřování jejich adheze a mechanické odolnosti. Tato metoda do určité míry simuluje mechanizmus abrazivního opotřebení. Výsledky testu se vyhodnocují především mikroskopickým zkoumáním deformací a mikrotrhlin v rýze na povrchu materiálu. Nevratné deformace, které vznikají během scratch testu generují akustickou emisi(AE). Simultánním snímáním a záznamem vzrůstající hloubky penetrace se vzrůstající zátěžnou silou na nanotesteru a tím generované AE (zaznamenané pomocí analyzátoru) se pro každý test obdrží soubory dat, v nichž je uložen celý průběh experimentu a příslušná AE. Pomocí vhodného software se pak může libovolněkrát (tzn. nezávisle na době, místě a prostředí experimentu) zpracovávat soubor AE za účelem izolovat jednotlivé akustické události, resp. hity, odpovídající vzniku trhlinky ve zkoumaném vzorku.
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