Abstract
Thin-skinned organic matrix composites within aeronautical structures are subjected to thermooxidative aging during their service life, leading to reductions in their durability. In this paper, a durability evaluation of fiberglass epoxy prepreg is performed on the original composite thickness before and after 800 h isothermal aging at 82°C. The characterization of both aged and unaged composites comprised tensile tests, DMA, FTIR, weight loss measurements, SEM, and DSC. The tensile strength and modulus of the composites increased after being exposed to pronounced aging conditions, whereas a decrease was observed in the toughness. DMA results revealed that the glass transition temperature and rubbery state modulus increased as a result of the thermooxidative aging. FTIR spectroscopy demonstrated the formation of carbonyl compounds due to oxidation of the chemical structure of the resin. SEM observations indicated the existence of minor superficial cracking and poor fiber-matrix adhesion after aging. In addition, a minor mass change was observed from mass loss monitoring methods. The overall findings suggest that postcuring and physical aging enhanced the brittleness of the resin, leading to a significant decline in the useful structural life of the thin-skinned composite.
Highlights
The importance of persistently improving civil aircraft performance and improving fuel consumption has resulted in novel improvement in the designs of aeronautical structures
Various tests are conducted to characterize the deterioration of the material, including tensile testing, dynamic mechanical analysis (DMA), Fouriertransformed infrared spectroscopy (FTIR), weight loss measurements, Scanning Electron Microscopy (SEM), and differential scanning calorimetry (DSC)
This study was designed based on industrial interests to evaluate the effect of thermooxidative aging on the durability of thin-skinned EHG 250-68-37 prepreg over a period of 800 h of isothermal aging at 82∘C
Summary
The importance of persistently improving civil aircraft performance and improving fuel consumption has resulted in novel improvement in the designs of aeronautical structures. During thermal aging at moderate temperatures, for example, below the glass transition temperature, organic matrix composites deteriorate by matrix embrittlement resulting from thermooxidative degradation [11]. Thermal-oxidative aging may irreversibly change the chemical structure of polymer matrix composites [13, 14]. Physical aging is universal, is independent of any chemical change, and is related to the gradual densification of nonequilibrium glassy structures These properties result in a higher modulus and strength, lower toughness, and slower relaxation (creep and stress relaxation). The thermomechanical behavior in organic matrix composites can be changed as a result of postcure reactions and physical aging induced by thermooxidative degradation. The influence of thermooxidative degradation on the durability of glass fiber-reinforced epoxy composite is evaluated from mechanical, chemical, and physical perspectives. Various tests are conducted to characterize the deterioration of the material, including tensile testing, dynamic mechanical analysis (DMA), Fouriertransformed infrared spectroscopy (FTIR), weight loss measurements, Scanning Electron Microscopy (SEM), and differential scanning calorimetry (DSC)
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