Foreign object impact resistance of GFRP plates and polyurea reinforcement characteristics

In response to the demand for improving the impact resistance performance of glass fiber reinforced plastic (GFRP) shell structures of high-speed trains against foreign object impacts, the mechanical characteristics and impact damage mechanisms of polyurea-reinforced GFRP composites were researched. The mechanical performance parameters of polyurea and GFRP materials were determined through quasi-static tensile tests. Based on an air cannon impact test apparatus, impact tests were performed on 3 mm-thick GFRP plates and GFRP plates coated with different polyurea layers of varying thicknesses (2.5, 3.0, 4.5, and 5.0 mm), using ice balls with a diameter of 30 mm (simulating hail) and aluminum balls with a diameter of 24.5 mm (simulating gravel) as impactors. During the test process, high-speed photography was employed to record the impact process. The impact deformation sequences, damage evolution patterns, and failure modes were analyzed. Scanning electron microscopy was utilized to characterize the microscopic morphology of severely damaged specimens to reveal their damage mechanisms. Research results indicate that polyurea material exhibits high ductility (fracture strain of 2.35), while GFRP demonstrates high strength properties (tensile strength of 141.4 MPa). For 3 mm-thick GFRP plates, the critical velocity for slight damage under ice ball impact is 145.3 m·s^-1, which is increased to above 162.6 m·s^-1 after coating with 2.5 mm polyurea, representing an improvement of at least 11.9%. Under aluminum ball impact, the critical velocities for slight damage and severe damage of uncoated GFRP plates are 73.2 m·s^-1 and 88.8 m·s^-1, respectively, which are increased to 88.7 m·s^-1 and 119.2 m·s^-1 after coating with 4.5 mm polyurea, representing improvements of 21.3% and 34.4%. When the polyurea coating thickness is increased from 2.5 mm to 4.5 mm, the aluminum ball rebound velocity is reduced from 13.15 m·s^-1 to 11.92 m·s^-1, and the residual velocity after aluminum ball penetration is decreased from 21.1 m·s^-1 to 16.9 m·s^-1. Scanning electron microscopy analysis reveals that the polyurea coating effectively maintains the structural integrity of glass fibers in the damage zone. When the coating thickness increases to 3 mm, the improvement in critical velocity for slight damage tends toward a plateau, but the critical velocity for severe damage can still be further improved. The findings provide a basis for optimizing coating thickness in the impact-resistant design of lightweight structures for high-speed trains.