Effect Of Moisture Absorption Research Articles

Moisture absorption effect on the stress distribution of the cross-ply laminates with transverse matrix cracks

The purpose of this paper is to investigate the moisture absorption effect on the stress distribution of the cross-ply laminates with transverse matrix cracks. Two analytical models were used to evaluate the stress distribution, Shear Lag and the variational approach. The results show that a complete parabolic variation of displacement gives a good approximation of the stress distribution compared to the finite element analysis. Furthermore, the cracked cross ply laminate is submitted different temperature and moisture concentration distribution. The predicted model shows that moisture absorption has a significant effect on the stress distribution especially at the higher crack density.

Modelling and monitoring of out-time and moisture absorption effects on cure kinetics and viscosity for an out-of-autoclave (OoA) prepreg

Out-time and moisture absorption during out-of-autoclave (OoA) prepreg preparation are generally unavoidable. The resulting cross-linking and increase in resin viscosity can prevent sufficient flow into the fiber tows during processing and cause porosity. In this study, efficient modelling and in situ methods to monitor cure kinetics and viscosity were developed to account for the effects of out-time and absorbed moisture. First, a commercial OoA prepreg was conditioned to specific levels of out-time and relative humidity (RH). Property data were obtained from differential scanning calorimetry (DSC) and rheometry and used to develop cure kinetics and viscosity models for a wide range of process conditions, initial out-times, and humidity conditions. The dielectric signals were correlated to the measured data and used to demonstrate real-time monitoring of resin state during cure. The predictive models were then used to understand the influence of out-time and absorbed moisture on resin viscosity during consolidation of OoA prepreg.

Moisture Effects on Patch Bonded Composite Repairs

The present work investigated the effects of moisture absorption on the residual tensile strength of unnotched, notched and double-patch repaired carbon/epoxy composites. Patches were bonded to the parent plate using Araldite2015 adhesive. Specimens were aged in demineralised water at 70°C and tested at moisture content of 0% (dry), 3%, 6% and 7%. Results showed that upon ageing, a maximum of 11% and 17% of strength reduction was found in unnotched and repaired specimens, respectively. On the contrary, a maximum of 15% increment in strength was observed in notched specimens. In addition, good fits to the experimental data were found using the proposed residual strength model, with the maximum difference of less than 6%.

Effect of moisture on elastic and viscoelastic properties of epoxy and epoxy-based carbon fibre reinforced plastic filled with multiwall carbon nanotubes

In this study, we investigated the peculiarities of moisture absorption and moisture-induced effects on the elastic and viscoelastic flexural properties of epoxy resin and carbon fibre reinforced plastic (CFRP) filled with multiwall carbon nanotubes (MWCNTs). Short-term cyclic creep-recovery tests of moistened epoxy and CFRP filled with MWCNTs revealed improvements in creep resistance for both materials. The addition of MWCNTs to the epoxy resin suppressed the moisture absorption by the material, causing a reduction in the diffusion coefficient by 31% and equilibrium moisture content by 15%. The addition of MWCNTs reduced the flexural strength of moistened epoxy and CFRP samples by approximately half, and also lowered the flexural modulus by ∼1.4 and ∼3 times, elastic strain by 1.25 and 1.04 times, viscoelastic strain by 1.39 and 1.03 times, and plastic strain by 2.68 and 1.60 times, respectively.

Influence of Nano‐Calcium Carbonate Particles on the Moisture Absorption and Mechanical Properties of Epoxy Nanocomposite

AbstractThe moisture absorption and diffusion characteristics of epoxy‐based nanocomposites containing nano‐calcium carbonate (nano‐CaCO3) are investigated. Although the moisture absorption decreased with increasing nano‐CaCO3 content except for 8 wt%, the moisture absorption and diffusion behaviors were different from each other. It was found that the incorporation of 2 wt% and 4 wt% nano‐CaCO3 decreased moisture absorption capacity effectively. This is due to the more uniform distribution of nano‐CaCO3 particles, which created a longer diffusion path of moisture molecules in the nanocomposites. For the diffusion rate of moisture, there is no significant change observed on adding nano‐CaCO3. The effect of moisture absorption on the mechanical properties of nano‐CaCO3‐filled epoxy nanocomposites were investigated as a functional property of nano‐CaCO3 content. Due to moisture absorption, the flexural strength of epoxy/nano‐CaCO3 composites significantly impaired when compared to dry nanocomposites. However, the effect of nano‐CaCO3 on these mechanical properties was found to be positive, which allows the application of modified epoxy resin in high‐humidity environments.

Effect of Moisture Absorption on High Temperature Thermal Insulation Performance of Fiber Insulation Materials

In this paper, effect of moisture absorption on high temperature thermal insulation performance of fiber insulation material is studied. Fiber material is stored in 40°C through a long period of time, then spontaneous moisture absorption of fiber material is measured. According this test result, 20% and 40% moisture absorption content gradient are determined. Pore distribution and high temperature thermal insulation property of samples of 20% and 40% moisture absorption and the dry samples are all tested in this study. The internal pore size distribution of fiber insulation material after moisture absorbing has a certain coarsening. Fiber material after moisture absorbing will make its pore size become large. And oxygen acetylene test results showed that: the larger moisture absorption, the more slowly the initial temperature rises. Fiber material after moisture absorbing will make its low temperature thermal insulation performance reduce, but it has little impact of its high temperature thermal insulation performance.

Effects of water absorption on Napier grass fibre/polyester composites

The effect of moisture absorption on untreated and alkaline-treated Napier grass fibre-reinforced polyester composites was evaluated. Under room-temperature immersion, the water absorption behaviour of the Napier grass fibre composites conformed to the Fickian diffusion mechanism. Compared with the untreated fibres, the treated fibres absorbed less water due to the removal of lignin and hemicelluloses. The tensile and flexural strength of the Napier grass composites decreased with increased water absorption. SEM analysis showed that the treated Napier grass fibre composites contained fewer fibre pull-outs and splits compared with the untreated composites, which supports the improved performance.

Moisture absorption and mechanical degradation of hybrid Pennisetum purpureum/glass–epoxy composites

The effect of moisture absorption on the mechanical degradation of hybrid Pennisetum purpureum/glass–epoxy composites was investigated. The hybrid P. purpureum/glass–epoxy composites plates were manufactured by the vacuum infusion method using epoxy resin as a matrix. Following 50h of water immersion, the hybrid composite specimens were tested. The moisture content reduced as the glass fibre content increased. The wet and dry hybrid composite specimens were subjected to tensile and flexural tests. The incorporation of the glass fibre into the P. purpureum–epoxy composites enhanced their tensile and flexural strength, as well as their modulus. The tensile and flexural strengths of the hybrid P. purpureum/glass–epoxy composites (24/6–70vol%) were 43 and 60MPa, respectively. However, the tensile and flexural properties significantly degraded under wet conditions. Using field emission scanning electron microscopy (FESEM), morphological analysis was performed to observe the fracture behaviour of the specimens and the effect of water molecules.

Effect of sea and distilled water conditioning on the overall mechanical properties of carbon nanotube/epoxy composites

The study of mechanical properties of carbon nanotube reinforced polymeric materials under different environmental conditions are very much essential as this material possesses potential for using it in structural parts, automobiles, marine field and so on. This study deals with the effect of moisture absorption on the mechanical and thermal properties of carbon nanotube/epoxy composites by immersing it in sea and distilled water at 30℃ temperature and at 75% Relative Humidity (RH) humidity. Composite specimens containing different wt.% of carbon nanotubes were prepared, tested and subjected to water immersion test. The flexural properties, hardness and glass transition temperature ( Tg) of water-immersed specimens were evaluated and compared with unexposed specimens as per the American Society for Testing and Material (ASTM) standard. It is concluded that the water absorption brought certain loss in the mechanical properties and reduction in Tg of the composites. It was also found that moisture uptake affected both sea and distilled water samples in different ways.

Characterisation of Moisture Absorption Effects on the Strength of Composite Materials

In the present work, the variation of the tensile strengths of various polymers and polymer composites due to moisture ageing is investigated. The stacking sequences of the composites include 0o, 90o, ±45o and quasi-isotropic laminates. The variation in the strength of material is then fitted using a residual property model. Results show that the proposed model characterises well the variation in the strengths that exhibits a typical trend, where there is no obvious scattered data. In fibre dominated laminates (0o), the degradation parameter seems to be influenced by the type of material, whereas for matrix dominated laminates (90o), ageing temperature appears to be the dominant factor that affects the degradation trend. As for [±45]2S and adhesives, exponential decay trend is observed. This model could be further improved to include the material and temperature factors.

Studies of the moisture absorption of thin carbon fiber reinforced plastic substrates for x-ray mirrors

We study a lightweight x-ray mirror with a carbon fiber reinforced plastic (CFRP) substrate for next-generation x-ray satellites. For tightly nested x-ray mirrors, such as those on the Suzaku and ASTRO-H telescopes, CFRP is the suitable substrate material because it has a higher strength-to-weight ratio and forming flexibility than those of metals. In flat CFRP substrate fabrication, the surface waviness has a root mean square (RMS) of ∼1 μm in the best products. The RMS approximately reaches a value consistent with the RMS of the mold used for the forming. We study the effect of moisture absorption using accelerated aging tests in three environments. The diffusivity of the CFRP substrate at 60°C and at relative humidity of 100% is ∼9.7×10−4 mm2·h−1, and the acceleration rate to the laboratory environment was 180 times higher. We also develop co-curing functional sheets with low water-vapor transmissivity on the CFRP substrate. Co-curing the sheets successfully reduced the moisture absorption rate by 440 times compared to the un-co-cured substrate. Details of the CFRP substrate fabrication and moisture absorption tests are also reported.

The effect of moisture on the modulus of elasticity of several representative individual cellulosic fibers

Understanding the effect of moisture absorption on the mechanical properties of fibers at cellular level is key important to the application of natural fibers in reinforcement composites. This study focused on the variation of the modulus of elasticity (MOE) of several representative individual cellulosic fibers (bamboo, Chinese fir, ramie and Kevlar) under different relative humidity condition (RH: 40 %, 70 %, 90 %), dedicating for the screening of appropriate candidates of fibers used in outdoors. A special custom-designed microtester (SF-I) with the micro humidity control box was devised in order to observe stress-strain behavior of fibers under different humidity condition. Among the fibers investigated, ramie fiber presented the most sensitive to the humidity, Chinese fir and bamboo fiber was followed, and Kevlar fiber showed the bluntest to moisture variation since it belonged to artificial fiber. Compared with the fibers tested at RH of 40 %, the MOE of Bamboo, Chinese fir, Ramie fibers increased at RH 70 %, and decreased at RH 90 %, respectively. The optimal tensile properties were observed for the bamboo fiber among tested single plant fibers, with a MOE value of 26.3-30.7 GPa, and RH of 70-80 % was deduced for obtaining the highest value of MOE under various humidity testing condition.

Strength of Adhesive T-Joint under Moisture Condition

In this study, an experimental investigation was conducted in order to determine the effect of moisture absorption at different adhesive thickness (i.e., 0.5, 1.0, 1.5 and 2.0 mm) on strength of adhesive T-joint in urea granulator fluidization bed. In particular, T-joint specimens were exposed to three humidity conditions, namely, 80°C, 90°C, and 100°C at a constant time immersion of 15 minutes in water. Stainless steel plate and stainless steel perforated plate were joined by using a specific adhesive jig according to desired thickness. Tensile test was conducted by using universal tensile machine (UTM) at room temperature. The result obtained has enabled to explain the failure mechanisms and characteristics of adhesive T-joint with respect to moisture condition and bonding thickness. Epoxy adhesive with several weight percent of water absorption will degrade the physical properties of the adhesive. Moisture condition has some effect on the strength of the adhesive bonding. 1.0 mm of adhesive thickness provides the highest value of failure load. Experimental results indicated that failure load of adhesive T-joint at room and 90°C water temperature give higher value of strength if compared to water temperature at 80°C and 100°C.

The influence of accelerated weathering on the mechanical and physical properties of wood-plastic composites

This research concentrates on the effect of moisture absorption and UV radiation on the mechanical and physical properties of wood-plastic composites (WPC). The goal is also to evaluate the importance of wood flour fraction size on the mechanical properties of WPC and their influence on the accelerated weathering results. Wood flour reinforced composites with three different fractions of wood flour made from birch (Betula) chips were prepared. Additionally, Bleached-Chemi-Thermo- Mechanical aspen (Populus tremula) pulp (Aspen BCTMP) was used. Thermoplastics (LLDPE-g-MAH, PP) were used to prepare composites. Wood flour and BCTMP surface were treated with two different coupling agents: 3-aminopropyltriethoxysilane (APTES) and polyvinyalcohol (PVA). The WPC specimens were prepared by injection molding. Accelerated weathering tests were carried out to evaluate the influence of weathering on the mechanical and physical properties of composites. Three-point bending test and Charpy impact test were used to test mechanical properties. The test results showed that using wood flour as a filler material in composites made the WPC material more rigid and brittle. Due to the water absorption and swelling of WPC, the flexural modulus (MOE) and strength decreased and impact strength increased by making the material weaker with increasing the deflection of the WPC. The UV radiation decreased the composites flexural strength and MOE, while impact strength was increased. After the accelerated weathering cycles, cracks and voids were found on the surface of the WPC materials. After the UV radiation treatment, also the WPC colour was lightened.

Destructive and nondestructive evaluations of the effect of moisture absorption on the mechanical properties of polyester-based composites

In this study the effect of moisture absorption on the mechanical properties of glass-reinforced polyester composites is evaluated using both destructive and nondestructive tests. The composite resins were produced with two different production processes, while the mechanical properties of the composite materials were measured using DMA destruction tests. According to the DMA tests, the dependency in terms of temperature for the real component of the complex elastic modulus (E′), the imaginary component of the complex elastic modulus (E″), as well as tan(δ) can be traced. For a more efficient use of the composite materials, the compliance tensor was obtained with nondestructive tests based on ultrasound. A method for the generation and reception of Lamb waves in plates of composite materials is described, based on using air-coupling, low-frequency, ultrasound transducers in a pitch–catch configuration. The results of the nondestructive measurements made in this study are in good agreement with those obtained when using the DMA destructive tests.

A Novel Evaluation Tool for Enhancing the Selection of Natural Fibers for Polymeric Composites Based on Fiber Moisture Content Criterion

A systematic evaluation tool for natural fibers’ capabilities based on moisture content criterion (MCC) was developed and introduced as a new evaluation method. This MCC evaluation tool is designed to predict the behavior of the available natural fibers regarding distinctive desirable characteristics under the effect of the moisture absorption phenomenon. Here, the capabilities of different natural fiber types commonly used in industry, in addition to date palm fibers, were systematically investigated based on MCC. The results demonstrated that MCC is capable of predicting the relative reduction of fiber performance regarding a particular beneficial property because of the effect of moisture absorption. The strong agreements between the predicted values of MCC and results reported in the literature verify its usefulness as an evaluation tool and demonstrate its added value steps in predicting the relative behavior of fibers with a minimal range of errors compared with experimental measurements. Therefore, MCC is capable of better evaluating natural fibers regarding distinctive criteria in a systematic manner, leading to more realistic decisions about their capabilities and therefore enhancing the selection process for both better sustainable design possibilities and industrial product development.

Aging by moisture and/or temperature of epoxy/SiC composites: Thermal and mechanical properties

The present work focuses on investigating the effects of moisture absorption on the mechanical and thermal properties of epoxy reinforced with percentage (by wt.) silicon carbide (nano and micro-metric) composites. In order to quantify the effect of moisture and temperature on aging, the specimens were exposed to three aging conditions for 30 days. Variations of Tg (glass transition temperature), water absorption, and mechanical properties were determined as a function of exposure time. In composite materials, aging depends on the exposure conditions, such as amount of absorbed water, temperature, and oxygen concentration. All these factors affect the thermal and mechanical properties. At room temperature and 95% relative humidity, plasticizing and swelling occur, with mechanical properties loss. At 60℃ and 5% relative humidity, polymeric chains crosslink resulting in mechanical properties improvement; Tg and thermal conductivity increase. At 60℃ and 95% relative humidity, the time required to reach saturation decreases when compared to room temperature evaluated condition, as the exposure temperature increases.

Influence of process and formulation parameters on dissolution and stability characteristics of Kollidon® VA 64 hot-melt extrudates.

The objective of the present study was to investigate the effects of processing variables and formulation factors on the characteristics of hot-melt extrudates containing a copolymer (Kollidon® VA 64). Nifedipine was used as a model drug in all of the extrudates. Differential scanning calorimetry (DSC) was utilized on the physical mixtures and melts of varying drug-polymer concentrations to study their miscibility. The drug-polymer binary mixtures were studied for powder flow, drug release, and physical and chemical stabilities. The effects of moisture absorption on the content uniformity of the extrudates were also studied. Processing the materials at lower barrel temperatures (115-135°C) and higher screw speeds (50-100 rpm) exhibited higher post-processing drug content (~99-100%). DSC and X-ray diffraction studies confirmed that melt extrusion of drug-polymer mixtures led to the formation of solid dispersions. Interestingly, the extrusion process also enhanced the powder flow characteristics, which occurred irrespective of the drug load (up to 40% w/w). Moreover, the content uniformity of the extrudates, unlike the physical mixtures, was not sensitive to the amount of moisture absorbed. The extrusion conditions did not influence drug release from the extrudates; however, release was greatly affected by the drug loading. Additionally, the drug release from the physical mixture of nifedipine-Kollidon® VA 64 was significantly different when compared to the corresponding extrudates (f2 = 36.70). The extrudates exhibited both physical and chemical stabilities throughout the period of study. Overall, hot-melt extrusion technology in combination with Kollidon® VA 64 produced extrudates capable of higher drug loading, with enhanced flow characteristics, and excellent stability.

Moisture-uptake induced internal stresses in balsa core sandwich composite plate: Modeling and experimental

The present work investigates the internal stresses induced by moisture absorption in sandwich composite material. Moisture absorption effect was analyzed for balsa core specimens and sandwich structures composed of E-glass/polyester face sheets bonded to a balsa core. These materials were immersed in distilled water at 40°C and the kinetic of moisture content absorption was identified. The hygroscopic strains were also determined and a new analytical model for the calculation of the effective diffusivities was proposed by solving the homogeneous problem.

Comparison between methods for measuring wear in brake friction materials

Three different techniques for measuring wear in brake pads are compared: a gravimetric method (electronic balance), a linear measuring touch probe method, and a three-dimensional laser scanning method. Laboratory-scale wear tests were performed on two different types of brake friction materials: a semi-metallic (SM) and a non-asbestos organic (NAO). All three techniques were able to show clear differences in the wear rates of the materials selected for study. It was observed that choosing only a few points of measurement in the thickness determination using a touch probe can lead to significant errors. These errors were higher than those caused by moisture absorption effects when using the gravimetric method. The laser scanning method proved adequate for investigating the wear profiles produced by braking tests. Results from the tests showed that SM material exhibits a higher coefficient of friction and wear rate than the NAO material. An increase of the contact pressure resulted in increased wear rates for both SM and NAO materials. The ratio between volume loss and mass loss also increased when contact pressure was higher indicating that samples had suffered from compressive deformation.