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Microindentation assessment of climatic loading impacts on polymer sealants
Minster, Jiří ; Šašek, Petr
Sun light, especially the short-wave ultra-violet part of the sun spectrum, together with influence of moisture, are the most enlarged and the most effective sources of climatic damage of polymers. The effects of the both influences became stronger with enhanced temperature. Sun light on the one hand supports the forming of transverse chemical bonds between macromolecules and on the other hand results in their breakdown. This causes a strengthening or softening of polymers. The amount of changes and the dominant process depends on the radiation dose and on the influencing wave length. Every kind of chemical bond has its own critical wave length, which, with sufficient amount of energy, brings a reaction. Ageing, as a result of climatic loading, is therefore very closely connected with a structure of a real material. Microindentation is one of possible methods for assessing influences of a climatic loading on mechanical properties of polymers. Indentation test is checked by the history either of a power or an indent depth. The information about the hardness, Young modulus and viscoelastic properties of the investigated material can be received afterwards from measured data. The investigated materials were tested in their native standard form and also after four model types of physical-chemical ageing. Time-dependent properties of the sealants were assessed by the method of indentation creep. One hundred indentation creep tests were conducted for each sealant and type of ageing. A motivation for this work was a requirement to assess an influence of a climatic loading on the basic mechanical properties of sealants, used for a creation and a repair of mosaics.
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Hodnocení mechanických vlastností částicových polymerních kompozitů pomocí měření mikrotvrdosti
Minster, Jiří ; Berka, L. ; Hristova, J.
The applicability of Vickers microhardness measurements for mechanical assessment of heterogeneous polymer composites (filled polymer composites and polymer concretes) is discussed. Two types of composites based on epoxy and polyester matrices were investigated and two types of finely dispersed fillers were used with the 20% volumetric concentration of the individual fillers. The reinforcing effect of the hard filler and changes in the microhardness (i.e. in the yield strengths and moduli) in the neighbourhood of filler micrograins have been substantiated.
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