Study on dynamic mechanical properties and constitutive model of granite under constant strain rate loading

Abstract

A systemic understanding of the dynamic mechanical properties and dynamic constitutive model of granite is of great significance to the study of natural disaster prevention and protection of granite buildings. In the present study, constant strain rate loading tests of granite specimens under different impact velocities were carried out by using a shop-fabricated cylindrical conical striker and split Hopkinson pressure bar (SHPB) test system. The compressive strength of granite material increases with the strain rate, and therefore, a continuously smooth uniaxial dynamic strength criterion suitable for describing the changes in the dynamic increase factor (DIF) with strain rate was proposed and tested. The granite specimen under impact loading was intact when the strain rate was lower than 80 s−1, cracked when it was 80 to 90 s−1, fractured when it was 90 to 135 s−1, and crushed when it was over 135 s−1. Ultrasonic wave tests were performed to evaluate the damage caused by impact, and the quantitative relationship between the damage value and peak stress was established based on regression analysis. The results showed that the stress threshold causing damage was 50.15 MPa with a corresponding strain rate of 31.7 s−1 and a peak strain of 3670 microstrain. A new constitutive model describing the dynamic mechanical properties of granite was developed based on a nonlinear viscoelastic model (the ZWT model), and the constitutive parameters were then determined. A user-defined material subroutine named VUMAT of ABAQUS finite element software was applied to describe the established constitutive model and simulate the impact process of granite. The results confirmed that the developed constitutive model can well describe the prepeak dynamic mechanical properties of granite under impact compression.