This study presented the details of multi-wall carbon nanotubes (MWCNTs)-modified resin injection repair aiming to enhance the mechanical properties, considering the flexural and compression behavior. The resin injection of epoxy resin dispersed with MWCNTs (0.1, 0.3, and 0.5 wt.%) as low viscosity resin that delaminated composite structure repair was conducted using a developed vacuum-based resin injection system at 80°C with constant injection pressure. The quasi-static indentation (QSI) method with a circular window was applied to create the barely visible impact damage (BVID) in the laminate specimen and thus obtain the delamination damage with reproducibility. The flexural strength and compression after impact (CAI) test were conducted on repaired carbon fiber reinforced laminates to assess the effect of the dispersion of the MWCNTs in the epoxy resin injection approach compared to neat epoxy resin. The mechanical test results exhibited that the recovery rate was better improved in the case of the modified resin infiltration approach in laminate composites dispersed with nanoparticles. It was attributed to their more enhanced strengthening mechanisms under effective interaction in mixed interface of fiber-matrix-MWCNTs, mainly attributing to bridge connection and stronger interfacial adhesion properties.
Nickel coating of reinforcing fibers via electroless plating can provide superior properties to polymer composites, particularly for radar stealth, although its effect on thermomechanical properties and thermal cycling response are relatively unverified. Thermal cycling of strained nickel‐coated glass fiber epoxy laminates was performed to evaluate its effect through in‐plane shear mechanical testing and fiber‐matrix interface region microscopic observations. Laminates were subjected to 4000 cycles of thermal conditioning (regular and strained). Subsequent in‐plane shear tensile tests revealed a ~10% increase in their ultimate shear strength, which was credited to polymer relaxation and increased plastic energy storage capacity. Atomic force microscopy in force modulation mode showed the most significant fiber‐matrix interface region changes for strained thermal cycled specimens, which we attribute to their higher stress during conditioning and plastic deformation. A relatively short fiber‐matrix interface region length was observed, which we attribute to the lower surface energy of Ni‐glass fiber. Thermomechanical analysis (TMA) revealed a glass‐transition temperature range of 71–110°C, and coefficients of thermal expansion (CTE) were evaluated for several laminate configurations.
This paper presents an electromagnetic-mechanical repair patch (EMRP) to restore the mechanical and electromagnetic (EM) wave absorption performance of a radar-absorbing structure (RAS) damaged by lightning strike. Several researchers have primarily focused on ensuring high repair efficiency, particularly in terms of the primary load-bearing properties of repaired fiber-reinforced plastics. However, no study has proposed a practical repair approach that considers the multi-functionality of the radar-absorbing structure. The EMRP method can be used to repair lightning strike damage in a radar-absorbing structure with electroless nickel-plated glass fabric, considering the need to maintain structural integrity and electrical continuity to achieve a high repair efficiency. Damage due to an artificial lightning strike was assessed in terms of area and depth of the damage using image processing, ultrasonic C-scan, and micro X-ray inspection. The EM characteristics of one-dimensional return loss scanning and the echo radar-cross-section level were measured to verify the stealth performance of the repaired radar absorber in the X-band. In addition, the tensile test results demonstrated that the repaired radar absorber had a high recovery rate of 93% compared to the pristine radar absorber. The experimental results obtained in this study validate the use of the proposed EMRP method in repairing radar-absorbing structures.
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