An investigation into the effect of isothermal aging on the development of transverse cracks in cross‐ply laminates of two high temperature composite systems was performed. The composite materials investigated were BASF X5260/640–800 and DuPont Avimid K/IM6. Changes in the glass transition temperature, composite weight loss, crack density, and mode I intralaminar fracture toughness were monitored during isothermal aging in air at 177°C for up to 2232 h. The two laminate configurations used in this study include two variations of the generic cross‐ply configuration [02/90n]s, in which n equals 1 and 2. The results of this investigation show that a layer of degraded material forms at the surface of the X5260/640–800 bismaleimide laminates and that the thickness of the degraded layer increases with aging time. After 744 h of aging, transverse cracks form in the surface plies and an increasing crack density evolves as aging time is increased; however, transverse cracks do not form in the inner 90° ply groups with aging during the time period investigated. The Avimid K/IM6 thermoplastic polyimide laminates, which show evidence of cracking prior to aging, do not exhibit any significant change in crack density with aging. The results of the aging experiments also show that the bismaleimide system exhibits a weight loss of 1.5% and an increase in glass transition temperature from 250°C to 300°C after 2232 h of aging at 177°C, while the thermoplastic polyimide system shows a weight loss of only 0.05% and an increase in glass transition temperature from 280 to 285°C after 2232 h. Changes in the resistance to crack formation are also seen in these materials during aging. The mode I intralaminar fracture toughness, a measure of resistance to transverse crack formation, shows a 50% decrease after aging for 2232 h for the bismaleimide system, while the behavior exhibited by the thermoplastic polyimide shows little evidence of a reduction.
The paper deals with laboratory research and development of alkali activated system with thermal insulation properties, where, such as additive, low density materials are used. The experiment is focused on strength and heat conductivity of prepared substances.In research five kinds of mixtures were prepared. The values of compressive strength and thermal conductivity of tested admixtures qualitatively correspond to commercially available building material. Results are foundations for next lightweight alkali activated system development and research focused on practical application in building.
KeywordsLightweight alkali activated system, thermal insulating materials, blast furnace slag, activated water glass, expanded perlite, ekostyren, Liapor, expanded vermiculite.
AbstraktPříspěvek se zabývá laboratorním výzkumem a vývojem alkalicky aktivovaných systémů s tepelně izolačními vlastnostmi, ve kterých je jako plnivo použit materiál s nízkou objemovou hmotností. Experiment je zaměřen na pevnosti a tepelnou vodivost vytvořených hmot.V rámci výzkumu bylo připraveno pět druhů záměsí. Hodnoty pevnosti v tlaku a součinitele tepelné vodivosti u zkoumaných receptur kvalitativně korespondují s komerčně dostupnými stavebninami. Výsledky jsou základem pro další výzkum a vývoj lehčených alkalicky aktivovaných systémů se zaměřením na praktické využití ve výstavbě.
Klíčová slovaLehčené alkalicky aktivované systémy, tepelně izolační materiály, vysokopecní granulovaná struska, aktivované vodní sklo, expandovaný perlit, ekostyren, Liapor, expandovaný vermikulit.
Metakaolin, fly ashes and other secondary raw materials serves as suitable input in preparation of alkali-activated binders. This work deals with preparation of alkali-activated materials based on metakaoline and fly ash. Mixtures were prepared with a minimum of mixture water, ready for pressing. Prepared specimens were tested for tensile strength and pressure strength, resistance to high temperatures, frost resistance and resistance to water and salt.
Mechanical properties of alkali-activated materials are intensively studied nowadays. Great attention is paid to the economic problems and the effort to reduce the price of the finished product. This paper deals with usage of secondary raw materials from building industry used as aggregate for alkali-activated material. The mechanical and durability properties are tested and compared with porosity determined by mercury porosimetry.
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