Spallation fracture of cement paste cylinder by SHPB experiment and peridynamic simulation incorporating axisymmetry, strain-rate dependency and damage softening

The spallation fracture of cement mortar cylinders is experimentally investigated using a Split Hopkinson pressure bar (SHPB) system, which is a crucial technique for analyzing the dynamic mechanical properties and dynamic fracture behavior of materials at medium and high strain rates. The spallation simulation of cement-based materials requires further supplementation and modeling using improved peridynamics (PD), which possesses unique advantages in simulating spontaneous discontinuity evolution. Specifically, the peridynamic differential operator (PDDO) is employed to establish an integral nonlocal model for spatial axisymmetric problems, which can be categorized as a non-ordinary state-based peridynamic (NOSB PD) model; then, the non-spherical influence function (NSIF) is further incorporated to enhance its numerical accuracy and stability, particularly in wave propagation analysis. Both static and dynamic axisymmetric deformation examples, i.e., a thick-walled cylinder subjected to inner pressure and the wave propagation in a slender cylinder, are numerically simulated with high accuracy and stability. Additionally, an improved bond-based peridynamics (BB PD), replacing the prototype micro-elastic brittle (PMB) constitutive model with a bilinear constitutive model, is introduced. On this basis, an accurate and robust peridynamic approach for simulating the SHPB impact test is established and validated by the wave propagation in the SHPB system without a specimen. Subsequently, both bond-based and axisymmetric formulations of peridynamics are adopted to simulate the SHPB impact spallation of cement mortar cylinders under different striker velocities. The length and flying velocity of the spalling flyer and the strain history curve obtained from experiments and simulations are compared and analyzed, demonstrating that peridynamics can effectively model the impact spallation phenomenon.