DEM analysis of the dynamic characteristics of QH-E lunar soil simulant under cyclic triaxial tests

In this paper, cyclic triaxial tests are performed by using discrete element method (DEM) to investigate the dynamic behaviors of QH-E lunar soil simulant. The influences of number of cycles, loading frequency, waveform, cyclic stress ratio (CSR) and confining pressure on the dynamic behaviors of lunar soil simulant are discussed. The results indicate that the axial strain and dynamic modulus first increase and then tend to be stable with increasing number of cycles. The dynamic modulus increases with increasing the loading frequency, while the axial strain decreases. The damping ratio is not particularly sensitive to the confining pressure and CSR, it only decreases slightly with increasing confining pressure or decreasing CSR. Under the same conditions, rectangular wave dynamic load can produce a larger axial strain and a smaller dynamic modulus than those of sine and triangular waves, and a higher loading frequency will lead to a higher dynamic modulus and a lower axial strain, these characteristics are consistent with other lunar soil simulants and sandy soils tested in the experiment. However, the effect of confining pressure on the dynamic modulus depends on the magnitude of the CSR. For the lower CSR (CSR<0.6), the dynamic modulus increases with increasing confining pressure. While for the higher CSR(CSR>0.6), the dynamic modulus decreases significantly with increasing confining pressure, which demonstrates the unique dynamic characteristics that differs from other lunar soil simulants and sandy soils, and shows the importance of considering the magnitude of the CSR under cyclic triaxial tests.