Search

Phthalonitrile resins have received growing attention due to their superior thermal stability and good structural properties required for high temperature applications in aerospace industry etc. In this work, a newly developed phthalonitrile blend resin with an appropriate viscosity for autoclave processing is employed for manufacturing of high quality void-free thick composite panels using MT300 carbon fabrics. In particular, the effects of postcure temperature are systematically examined on their 400 °C mechanical properties required for high temperature structural applications. Dynamic mechanical analysis reveals that the composite postcured at the high temperature of 375 °C exhibits a high glass transition temperature over 450 °C. Mechanical testing results show that the flexural and compressive strengths at room temperature are lowered by the high temperature postcure, but their counterparts at 400 °C are obviously enhanced by the postcure. Moreover, the 400 °C interlaminar shear strength initially decreases but then increases with increasing the postcure temperature. The char retention in nitrogen at 1000 °C is 89% of its initial weight. Consequently, the newly developed phthalonitrile resin is highly promising for manufacturing of thermal resistant polymeric composites for high temperature application in aerospace industry etc. that need composites to have high temperature capabilities.

It is always of great practical significance to develop carbon fiber (CF) reinforced polymer composites with high residual mechanical properties at elevated temperatures for aerospace engineering structures, etc. In this work, the CF reinforced composite based on acetylene-functionalized benzoxazine (AFBEN) was manufactured by the resin transfer moulding (RTM) technology. The mechanical properties at elevated temperatures (150–350 °C) are first and systematically examined for the as-prepared CF/AFBEN composite. Differential scanning calorimetry and rheological characteristics are employed to evaluate the adaptability of AFBEN for the RTM process. Dynamic mechanical and thermogravimetric properties of the CF/AFBEN composite are also investigated to evaluate the thermal stability. The results display that the mechanical strengths of the CF/AFBEN composite exhibit the high residual rates of ca. 90% at 250 °C and over 60% at 350 °C compared to the mechanical properties at room temperature. The fracture mechanisms at room and elevated temperatures are studied and the fracture behavior of the CF/AFBEN composite is shown to transform from fiber-matrix interfacial debonding to resin matrix failure as the temperature increases. Consequently, the as-prepared CF/AFBEN composite show great potentials for practical applications in aerospace engineering structures, etc. due to its high residual mechanical properties at elevated temperatures and the ease of the RTM processing.

Graphene oxide (GO) has been well accepted as one novel fiber sizing agent for enhancing the mechanical properties at low temperature or room temperature (RT) of short carbon fiber reinforced polymer composites . But knowledge is still lacking about the mechanical behaviors at elevated temperature of GO-coated short fiber reinforced polymer composites. Here the temperature-dependent tensile properties of GO-sized short carbon fiber (GO@SCF) reinforced polyetherimide (PEI) composites were systematically investigated from −70 °C to 170 °C. The GO@SCF/PEI composites with varied GO sizing contents were prepared via an efficient injection molding technique. The GO@SCF/PEI composite with 0.4 wt% GO content was shown to be optimal for the tensile strength at RT and thus was selected to investigate temperature-dependent tensile behaviors . The results show that the GO sizing treatment plays a positive role in enhancing the tensile strength of SCF/PEI composites at −70 °C and 30 °C whereas a negative role at 100 °C and 170 °C. Morphological observations indicate that the fiber–matrix interfaces are enhanced at −70 °C and 30 °C but deteriorated at 100 °C and 170 °C due to the thermal expansion mismatch between SCF (or GO) and PEI. In addition, appropriate empirical equations were established for elucidating the relationships between their strength/modulus and temperature of PEI, SCF/PEI and GO@SCF/PEI composites.

Herein, epoxy resins for composite liquid oxygen (LOX) fuel tanks are modified with phosphorous flame retardant (DOPO) and brominated epoxy resin (EX48). With the incorporation of DOPO and EX48, the processing properties requirements for the hot-melt prepreg are contented with the significantly enhanced viscosity of the modified epoxy resin. At the same time, the tensile performance, flexural performance and fracture toughness of epoxy resin at room temperature and 90 K are improved with the introduction of DOPO and EX48. In addition, the epoxy resin of EP/P7.7/Br40 offers a highest limited oxygen index of 33.5% and a lowest LOX impact sensitivity of 5% with the eliminated LOX incompatible reactions including explosion and combustion. Consideration of the excellent cryogenic mechanical properties and LOX compatibility, combined with ideal viscosity for hot-melt prepreg preparation, the epoxy resin modified with DOPO and EX48 simultaneously is attractive as the polymer matrix for composite LOX fuel tanks.

Impact damage has been identified as a critical form of the defects that constantly threatened the reliability of composite structures, such as those used in the aerospace structures and systems. Low energy impacts can introduce barely visible damage and cause the degradation of structural stiffness, furthermore, the flaws caused by low-velocity impact are so dangerous that they can give rise to the further extended delaminations. In order to improve the reliability and load carrying capacity of composite laminates under low-velocity impact, in this paper, the numerical simulatings and experimental studies on the woven fiber-reinforced composite laminates under low-velocity impact with impact energy 16.7J were discussed. The low velocity impact experiment was carried out through drop-weight system as the reason of inertia effect. A numerical progressive damage model was provided, in which the damages of fiber, matrix and interlamina were considered by VUMT subroutine in ABAQUS, to determine the damage modes. The Hashin failure criteria were improved to cover the failure modes of fiber failure in the directions of warp/weft and delaminations. The results of Finite Element Analysis (FEA) were compared with the experimental results of nondestructive examination including the results of ultrasonic C-scan, cross-section stereomicroscope and contact force - time history curves. It is found that the response of laminates under low-velocity impact could be divided into stages with different damage. Before the max-deformation of the laminates occurring, the matrix cracking, fiber breakage and delaminations were simulated during the impactor dropping. During the releasing and rebounding period, matrix cracking and delaminations areas kept increasing in the laminates because of the stress releasing of laminates. Finally, the simulating results showed the good agreements with the results of experiment.