Abstract:

Objective Due to impact damage, fatigue, aging, and other factors, composite parts may inevitably experience damage. Interface cracking between the layers of glass fiber reinforced composites (GFRP) can significantly reduce mechanical properties, such as stiffness and compressive strength. To prevent resource wastage and economic loss caused by replacing damaged components, this research focuses on developing cost-effective and simple maintenance procedures for repairing defects.

Method We investigated a simple and convenient GFRP repair technique for the repair of sharp-edge delamination cracks. Pressure was not required, as the resin solution containing acetone penetrated the delamination crack through capillary action. The acetone solution effectively covered and wetted the micro-cracks in the composite laminates during service, allowing the resin to fill the cracks. The prepared resin pre-coating solution was applied to the damaged laminates, followed by the conventional repair solution. Over time, the resin filled the cracks, and the repair effect was evaluated using scanning electron microscopy (SEM) and mechanical property testing.

Results Glass fiber composite laminates were prepared using a hot-press pot forming process, and impact damage was induced by the drop hammer method. Five different mass fractions of pre-coat (RPC) solutions were used for the repair: 10% RPC, 20% RPC, 25% RPC, 35% RPC, and 45% RPC. The repair effects were compared with the method without RPC and evaluated at room temperature and 60 ℃. The curing effect of the repair solution was analyzed using Fourier transform infrared (FT-IR) and differential scanning calorimetry (DSC). CT scanning revealed effective repair of the damaged parts, with filling and recombination of the layered damage under the action of resin. The results of FT-IR and DSC showed high conversion of epoxy groups and low curing temperature, indicating good curing performance of the repair liquid. Increasing the temperature was found to enhance the curing of the repair solution, with better repair effects observed at 60 ℃ compared to room temperature, as shown in Tables 2 and 3. The repair rates for the five RPC solutions with different mass fractions at room temperature were 8%, 10%, 17%, 13%, and 12%, respectively. It was found that normal temperature was not conducive to resin permeation, resulting in lower repair rates. At 60 ℃, the repair rates were 11%, 17%, 26%, 20%, and 16%, respectively, which were significantly higher than at room temperature. Among the different concentrations, 25% RPC demonstrated the best performance. After curing at room temperature for 7 days, the compressibility of the repaired specimens recovered by 17%, and this recovery was more pronounced at 60 ℃, reaching 26%. Compressive load-displacement curves were obtained for the specimens cured at 60 ℃ for seven days. After repair with a 25% RPC solution, the composite exhibited significant fluctuations in compressive load with displacement, reaching a maximum of 11 664.57 N, while the compressive load after repair with a 10% RPC solution was relatively low, possibly due to interlaminar fiber fracture. At the point of maximum load, the curve dropped abruptly, indicating complete damage of the specimen under compression. The strain energy was rapidly released, and the composite specimen was no longer subjected to compression load, resulting in a rapid drop in load.

Conclusion Using NPEL-128 epoxy as a component of the repair solution, combined with D230 curing agent, the repair solution demonstrated effective repair, with the resin showing resistance to hydrolysis and strong adhesion to the material. The six repair methods ranked as follows: 25% RPC > 35% RPC > 45% RPC > 20% RPC > 10% RPC > routine repair (without RPC).

Key words: glass fiber reinforced composite, crack repair, interlaminar fracture, resin pre-coating solution, capillary effect