Heat-treatment belongs to the most ecological methods of wood preservation methods and increase of its natural stability in exposition to outdoor conditions. Research of mechanical properties opens new possibilities of thermowood usage in general.
Wood appertains to viscoelastic materials and due to long-term loading creeps. There currently rise both elastic deformation, deformation elastic in time and plastic deformation. Partially there are irreversible changes due to stress even after unloading.
This work presents first insight to the matters of thermowood rheology and inspects its behavior under long-term loading in bending. This paper compares ratio of these three types of deformation in untreated wood and thermally modified wood in seven different temperatures (140; 160; 180; 190; 200, 210°C). The samples were exposed to 600 hours applied loading covering 40% of ultimate stress (modulus of rapture). Test were performed under constant conditions in special creep units in conditioning kiln. Increasing deformation under constant load was analyzed by Burger rheological model.
The results show that samples treated under lower temperatures (140 and 160°C) exhibit greater creep than untreated wood. This result is positive for structural usage of wood. On the other hand the samples treated under higher temperatures levels (200 an 210°C) display deterioration of mechanical properties. This is due to changes in wood structures caused by heat-treatment.
The most important impact of this work goes to future research of this field. Next development has to apply for the best quality of samples and also select rather prismatic parallelism than transversal one. Also application of 40% ultimate stress loading appeared as too high and together with wood defects led to destruction of samples.
| Identifer | oai:union.ndltd.org:nusl.cz/oai:invenio.nusl.cz:257725 |
| Date | January 2016 |
| Creators | Berková, Tereza |
| Contributors | Borůvka, Vlastimil, Ruman, Daniel |
| Publisher | Česká zemědělská univerzita v Praze |
| Source Sets | Czech ETDs |
| Language | Czech |
| Detected Language | English |
| Type | info:eu-repo/semantics/masterThesis |
| Rights | info:eu-repo/semantics/restrictedAccess |
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