This study assesses the effect of porosity in the moisture absorption of polymeric composites. The preparation of composites samples with porosity, control, and measurement of void content, and moisture absorption behavior of carbon/epoxy laminates are discussed. Rheological analyses are used to characterize the viscosity behavior of prepregs either in the presence or absence of moisture. Polymeric composites with different levels of voids were produced and submitted to hygrothermal conditioning to study the moisture absorption behavior. It was found that the rate of water uptake and the maximum level of moisture absorption in carbon/epoxy composites depends on the void content and specimen geometry. The dependence on the void content may be quite significant. The nature of the matrix system was also verified to affect the moisture absorption properties of the composite.

Effect of Void Content on the Moisture Absorption in Polymeric Composites

A new method to characterize three-dimensional, anisotropic moisture absorption in polymeric composites using experimental gravimetric absorption data is presented. This is achieved by using the three-dimensional hindered diffusion model to recover the moisture absorption properties of composites which may exhibit Fickian or non-Fickian behavior. Effectiveness of the recovery of absorption properties is assessed using artificially generated experimental data. Anisotropic diffusivities, equilibrium moisture content ( M ∞ ), and molecular binding ( γ ) and unbinding ( β ) probabilities that govern absorption dynamics are recovered by minimizing the difference between model predictions and experimental data. Using artificial moisture absorption data, diffusivities and M ∞ are recovered with less than 1% error, whereas γ and β are recovered with less than 3% error in the non-Fickian diffusion case. Equilibrium moisture content is shown to be accurately determined much earlier by using partial gravimetric data obtained from the initial phases of absorption, even in the presence of considerable measurement error.

Characterization of anisotropic moisture absorption in polymeric composites using hindered diffusion model

Characterization of moisture vapor diffusion in fine aggregate mixtures using Fickian and non-Fickian models

Moisture diffusion studies were carried out on the carbon/epoxy composite at Vf = 0.7 and have been performed for three different cases viz., 60°C/85%, relative humidity (RH), 60°C/95% RH, and 60°C/100% RH, to find out moisture absorption as a function of relative humidity. The specimens under the above conditions exhibited Fickian diffusion behavior. The effect of moisture absorption on the dynamic mechanical behavior and on the fiber/matrix interface was investigated. The humidity combined with the temperature effects may cause significant changes in the Tg of the matrix, and toughness affecting the laminate strength. Moisture absorption was correlated to the fracture mode of the laminate demonstrating the deleterious effect of moisture on the interface which leads to debonding between fiber and matrix. This behavior was investigated by scanning electron microscopy. The effect of cyclic thermal and humidity fluctuations is also characterized by ILSS.

Moisture Diffusion in Carbon/Epoxy Composite and the Effect of Cyclic Hygrothermal Fluctuations: Characterization by Dynamic Mechanical Analysis (DMA) and Interlaminar Shear Strength (ILSS)

The three-dimensional anisotropic moisture absorption behavior of quartz-fiber-reinforced bismaleimide (BMI) laminates is investigated by collecting 21 months of experimental gravimetric data Laminates of six, twelve, and forty plies and various planar aspect ratios are used to determine the three-dimensional anisotropic diffusion behavior when exposed to full immersion in distilled water at 25°C The long-term moisture absorption behavior deviates from the widely used Fickian model, but can be accurately captured by the three-dimensional, anisotropic hindered diffusion model (3D HDM) Excellent agreement is achieved between experimental gravimetric data and the 3D HDM for all laminate thicknesses Recovered model parameters are shown to slightly vary with laminate thickness due to the small changes in the cured-ply thickness However, model parameters identified for a given laminate thickness are observed to accurately predict the absorption behavior of samples with different planar dimensions Equilibrium moisture content of 172, 169, and 184% and corresponding diffusion hindrance coefficients of 0807, 0844, and 0671 are recovered for six, twelve, and forty-ply laminates, respectively, thus confirming strong non-Fickian behavior Moisture absorption parameters may be determined successfully at 165 months of immersion, before reaching approximately 85% of the equilibrium moisture content at 21 months Subsequent gravimetric measurements up to 21 months are consistent with the predicted long-term behavior POLYM ENG SCI, 54:137–146, 2014 © 2013 Society of Plastics Engineers

Three-dimensional anisotropic moisture absorption in quartz-reinforced bismaleimide laminates

This paper presents the moisture diffusion characteristics of autoclave moulded T300-914C unidirectional composite specimens hygrothermally conditioned at 85% RH and 70'C till saturation to 1.5% moisture content. In all, pin bearing strength test specimens of three different layup sequences viz. [45/03/ A 45/03/90/0],, [0/ 4 45/9012s and [45/02/45/03/45/0], were studied. All the test specimens exhibited Fickian Diffusion behaviour. It was further found that the Diffusion coefficient (D,) value of the composites increased with increase in the cut edge surface area and the values obtained compared well with those reported in literature. The difference in D, values obtained for different layup sequences was attributed to tortuousity caused by fibre orientations.

K. Suresh Raju

Papers

Moisture Diffusion Behaviour of T300-914C Laminates:

Salt spray corrosion study on aluminium metal matrix composites (AMMCs) prepared by powder metallurgy route