Epoxy resin is a versatile material, most widespread as a matrix material in the production of fibrous composites, and is also often used as an adhesive. It has excellent casting properties, relatively small shrinkage, high static strength and low absorptivity of moisture in comparison to competing resins. Main disadvantage is low impact toughness and high notch sensitivity. Toughness can be improved with addition of flexibilizer, which is being linked in the molecular structure of epoxy resin as elastic links between rigid pre-polymers, increasing toughness, but simultaneously it can significantly reduce strength. In the thesis we were varying volume percentage of reactive flexibilizer in epoxy resin and then evaluating its effect on mechanical characteristics. We have prepared four different blends with 0, 20, 40 and 60 % of flexibilizer content. We measured changes of static strength and elongation with tensile, pressure and three-point flexural tests. Impact toughness was tested by Charpy test and hardness by Shore D test. The results showed, that with increasing share of flexibilizer, the toughness and elasticity of epoxy resin rise, but strength and hardness decrease. Up to 40 % of the flexibilizer content, the ratio between the drop in strength and the increase in ductility is still appropriate for use, but at 60 % material becomes rubberlike and useless in applications where certain strength is necessary.
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