Research on the Tensile Mechanical Properties and Fracture Characteristics of GFRP Mortar Tubes under Impact Loads

To investigate the protective effect of glass fiber-reinforced plastic (GFRP) pipes on cement mortar, dynamic splitting tests were carried out on cement mortar and GFRP-mortar pipe specimens by using a 74 mm diameter Hopkinson pressure bar (SHPB) test device combined with a high-speed video camera device to obtain the crack expansion process and rupture and fragmentation morphology of the specimens. The results show that the tensile strength of cement mortar rings is lower and that the stress?strain curve is single-peaked. Compared with cement mortar rings, the tensile strength of GFRP-mortar ring specimens increases significantly, and the stress-strain curve is bimodal. For 0.5 MPa air pressure and wall thicknesses of 0, 2, 3, and 4 mm, the hollow rate of the 0.187 specimen peak stress is 3.21, 1.02, 1.05, and 1.26 times that of the 0.292 specimen. For 0.5 MPa air pressure and a hollow rate of 0.187, the wall thickness of the 2, 3, and 4 mm specimen peak stress is 1.06, 1.31, and 1.69 times that of the 0 mm specimen. The increase in the wall thickness, the decrease in the hollow rate and the increase in the strain rate make the dynamic tensile strength of the specimens increase. The dynamic modulus of elasticity of the GFRP-mortar pipe specimens was lower than that of the mortar specimens, and the increase in strain rate and the thickness of the GFRP pipe wall resulted in an increase in the dynamic modulus of elasticity of the specimens. The cement mortar specimen under impact load was split and tensile damage occurred; the GFRP-mortar specimen suffered tensile damage at the two ends of the applied force, and the upper and lower ends were crushed. With the increase in the strain rate, the GFRP-mortar specimens transitioned from cracks to the formation of “V” area damage, and the specimen crushing degree increased, but the existence of GFRP pipe can have a protective effect on the mortar, reducing the degree of specimen rupture and crushing. The increase in the hollow ratio reduces the ability of the specimen to resist the external load, and the degree of specimen rupture and fragmentation increases.