Influence of hygrothermal environment on thermal and mechanical properties of carbon fiber/fiberglass reinforced matrix composite materials
The absorption and diffusion of water in a carbon fiber/glass fiber hybrid composite was investigated. Water-sorption experiments, mechanical property tests and dynamic mechanical analysis (DMA) were performed after immersion in water at different temperatures for up to 32 weeks. The moisture uptake mechanism exhibited by the hybrid fiber system was determined to be more complex than the single fiber type. Weight-change profiles for the composites fitted the theoretical Fickian diffusion curve during the initial immersion time, but diverged substantially as time progressed. The shear properties and the glass transition temperature (Tg) were sensitive to the effects of hygrothermal environment, and values for both decreased with increasing water uptake. Microscopic inspection of water-soaked samples showed no cracking when the absorption was less than saturation. The thermal and mechanical properties were mostly retained (after drying), provided
Moisture Sorption Effects on and Properties of a Carbon Fiber-reinforced Phenylethynyl-terminated Poly(etherimide)
This paper reports the results of anin vestigationof moisture sorption effects on the properties of a carbon fiber-reinforced high-performance phenylethynyl-terminated poly(etherimide). Due to the relative newness of this material, minimal information regarding its performance under the duress of environmental effects is known. Composite and neat resin specimens were cycled to effective moisture equilibrium during exposure to a 85% relative humidity/90 C environment followed by exposure to a 10% relative humidity/90 C environment. The composite through-the-thickness moisture diffusion coefficients (Dz) ranged from 2.3 × 10 -6 to 6 mm2/s. The value of Dz for moisture absorptionwas measured to be about 67% greater thanthe value of Dz for moisture desorption; residual stress-accelerated diffusion, void-assisted diffusion, and diffusion hindered by moisture–matrix interactions are discussed as possible explanations for this difference. At 85% relative humidity, the effective moisture equilibrium content of the composite and neat resin were 0.52 ± 0.02% and 1.60 ± 0.01%, respectively. The average transverse moisture expansion coefficient of the composite was 1.1 × 10 -3±0.7 × 10-3. The 1.2% retention (85% 7.0% retention (10% relative humidity) of the control 9.5 MPa. No conclusive results were obtained from open-hole compression strength and apparent interlaminar shear strength tests. The majority of the surfaces of the TFS specimens displayed moisture sorption induced damage. The dramatic impact that inadequate matrix cure can have on a composite’s ability to transverse flexural strength (TFS) specimens exhibited 60.7 ± relative humidity) and 83.6 ± value of 135.9 ± endure a single moisture sorption cycle is illustrated by comparison with a previous moisture exposure study of this material.
The effects of moisture on the material properties and behavior of thermoplastic polyimide composites
Thermoplastic polyimides are a relatively new class of polymers that exhibit high-temperature stability and are useful in composite applications. One such material is Avimid® K3B reinforced with Magnamite® IM7 graphite fibers. This composite system exhibits excellent strength and toughness, retains its strength and toughness after prolonged exposure to elevated temperatures, and resists microcracking at extremely low (liquid nitrogen) temperatures. Further characterization of IM7/K3B thermoplastic composites is focused on evaluating hygrothermal effects on the material properties and behavior. The environmental conditioning test matrix includes three temperatures (20, 40, and 80°C) and four relative humidity levels (75, 85, 97, and 100%). Observations and conclusions from these studies include the following: (1) the moisture diffusivity of IM7/K3B has a classic Arrhenius dependence on temperature; (2) the moisture saturation level depends on the relative humidity level to the power of 1.34 with a maximum value of 0.55% by weight; (3) the glass transition temperature T g is lowered with moisture absorption but is recovered when the sample is redried; (4) the intralaminar fracture toughness G 1 c remains constant after extensive hygrothermal conditioning; (5) the diffusion kinetics are Fickian in general, except for a few non-Fickian anomalies that are related to development of transverse microcracks.