Destructive and nondestructive evaluations of the effect of moisture absorption on the mechanical properties of polyester-based composites
Introduction
The mechanical properties of a material determine its manufacturability, performance, and longevity. This means that a knowledge of the mechanical properties is essential for making good design decisions. Polymers are exceptionally complex materials – their mechanical properties depend on chemistry, processing, and the thermo-mechanical history, as well as on volume constraints. Thus, in order to gain useful information for making sound decisions when designing with polymer composites, mechanical property measurements should be made on a relevant sample in a relevant context [1], [2], [3], [4], [5], [6], [7]. Glass-fiber-reinforced polyester (GFRP) is the most “popular” composite, with a matrix based on cured, thermosetting resin. Its first main civilian application was for boat building. Other uses of GFRPs include hot tubs, pipes for drinking water and sewers, office plant-display containers and flat-roof systems. Mayer [1] showed that the mechanical performance of GFRP composites depends on the fibers’ strength and modulus, the strength of the matrix and the chemical stability. In addition to this, Erden et al. [2] showed that matrix modifications can enhance the mechanical properties of glass-polyester composites. Rowell [3] demonstrated fiber-reinforced composite materials that offer a combination of strength and modulus that are either comparable to, or better than, many pure materials. But thermoplastics exhibit a hydrophobic nature, as was demonstrated by Kim et al. [8]. When glass–polyester composites are immersed in water, uptake of the water can occur. This is the result of the capillarity of the materials and the water absorption of the hydrophilic groups in the glass fiber and the unsaturated polyester. Huang and Sun [9] and Visco et al. [10] concluded that a reaction between the water molecules and the matrix could deteriorate the interface, resulting in a weaker material. Kouba et al. showed a simple modelling of impregnation in pultrusion process of thermoplastic composites [11].
The performance of GFRP pipes is critical in many engineering applications when they are subjected to a combination of high-temperature/high-humidity environments. The diffusion of water or an aqueous fluid into GFRP pipes may lead to changes in the thermo-physical, mechanical, and chemical characteristics. Many of these changes can result in a degradation of the material’s performance. In order to properly predict the service life of a GFRP pipe, we need to understand the mechanisms that govern these changes.
Water absorption by the resin may cause both reversible and irreversible changes to the resin, including hydrolysis, plasticization, micro-cracking, and even the glass-transition temperature [12], [13], [14], [15]. For a reversible process, the mechanical properties can usually be recovered by drying; however, for the irreversible case, the mechanical properties are permanently altered. Deniz et al. [16] described the effect of seawater on failure pressure and its impact on the behaviors of polymer–matrix composites.
Huang [17] used a common method to evaluate the failure behavior of materials with a dynamic mechanical analysis (DMA). Many studies have shown that temperature and the environment are the most critical factors in reducing the strength of GFRP materials. Ray [18] has demonstrated that the higher the temperature of the environment and the longer is the exposure time, the larger will be the decrease in the strength and modulus of the GFRP. In those applications in which GFRP composites are subject to heat and a mechanical load, it is essential to determinate the elastic properties using nondestructive methods. A non-destructive evaluation offers advantages compared to conventional polymer-characterization methods, and without extracting test specimens. Schmerr [19], Krautkramer and Krautkramer [20] and Rojek et al. [21] found that the best methods for elastic-properties determinations are the ultrasound methods. El-Sabbagh et al. [22] studied the feasibility of using an ultrasonic longitudinal sound wave in the definition of the fiber content and the distribution in natural fiber composites.
Grimberg et al. [23] proposed the use of measuring of propagation speed of longitudinal and transversal waves, as well as Lamb waves for characterization overheated zones in fiber reinforced plastics composites. Santos et al. [24] have used guided waves (Lamb waves) to characterize the effect of multiple impacts in laminate composites. The analysis of the impact has been made by two parameters; amplitude response and time shift. PZT sensors have been bonded to the samples in a pitch-and-catch configuration and the Lamb wave symmetrical mode (S0) signal was used. Fahim et al. [25] have designed and developed a non-destructive monitoring technique based on ultrasonic transmission through thickness. A sensible analysis has shown that the Young modulus can be reasonably well identified.
Section snippets
Sample preparation
Samples of GFRP plates having as their reinforcement six sheets of ravings with 250 ± 50 gm−2 density and a matrix made from different types of unsaturated Orthophthalic polyester resins, made by Helios, Slovenia, were used in this study. The characteristics of the studied GFRP samples are presented in Table 1.
Water-absorption test
The effect of water absorption on the GFRP composites was investigated. Initially, DMA measurements on non-immersed samples and immersed samples were conducted on unconditioned samples. The
DMA measurements
The measurements of the elastic modulus along the three directions were made with a Dynamic Mechanical Analyzer DMA 242C from Netzsch, Germany with a three-point bending fixture and using the analysis software Proteus v.4.8.5. The measurements were carried out at a frequency of 1 Hz.
Polymers are often employed in products because of their ability to both store and damp energy. The complex modulus E∗ is a phase vector that incorporates both capacities:where .
The real part (E′) of the
Conclusions
The water-absorption behaviors of three types of GFRP composite were recorded, and from these results we can conclude the following:
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The destructive tests showed good mechanical results for the composite 7524, where the polyester is produced in-situ. In-situ production means a cheaper process in comparison with the similar composite 7201. The glass-transition temperature is 10 °C higher in the case of the 7524 composite, compared to the 7201 composite.
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For a more effective use of the composite
Acknowledgements
This paper is partially supported by The National Authority for Scientific Research of Romania (ANCS) as part of the Romanian–Slovenian Bilateral Cooperation Program-Contract No. 371/2009 – RO-SI and Slovenian Research Agency for the Republic of Slovenia (SRA) under Romanian Slovenian Bilateral Cooperation Program-Contract No.: BI-RO/10-11-002.
References (36)
- et al.
The effect of types of maleic anhydride-grafted poly-propylene (MAPP) on the interfacial adhesion properties of bio-flour-filled polypropylene composites
Composites Part A
(2007) - et al.
Effect of water absorption on the mechanical properties of glass/polyester composites
Mater Des
(2007) - et al.
Modification of polyester resin based composites induced by seawater absorption
Composites Part A
(2008) - et al.
The water ageing of unsaturated polyester-based composites: influence of resin chemical structure
Composites
(1983) - et al.
Failure pressure and impact response of glass-epoxy pipes exposed to seawater
Composites Part B
(2013) Temperature effect during humid ageing on interfaces of glass and carbon fibers reinforced epoxy composites
J Colloid Interface Sci
(2006)- et al.
Ultrasonic methods in diagnostics of epoxy-glass composites
J Mater Process Technol
(2005) - et al.
Characterization of flax polypropylene composites using ultrasonic longitudinal sound wave technique
Composites Part B
(2013) - et al.
Low velocity impact damage evaluation in fiber glass composite plates using PZT sensors
Composites Part B
(2013) - et al.
Model-based damage reconstruction in composites from ultrasound transmission
Composites Part B
(2013)
Ultrasonic and vibration methods for the characterization of pultruded composites
Compos Eng
Design with reinforced plastics
Enhancement of the mechanical properties of glass/polyester composite via matrix modification
Fibers Polym
Utilization of natural fibers in plastic composites, problems and opportunities
J Thermoplast Compos Mater
Stress redistributions in unit cells of fibre-reinforced polymer composites with interface degradation
Int J Microstruct Mater Prop
Processing and characterization of two- and three-phase polymer-based nanocomposites for energy storage applications
Int J Microstruct Mater Prop
Effect of sonication applied during production of carbon fiber/epoxy resin composites evaluated by differential scanning calorimetry and thermo-gravimetric analysis
Macedonian J Chem Chem Eng
Analysis of the material and the actuator influence on the characteristics of a pneumatic valve
Mater Technol
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