This study used a single pendulum impulse-cutting device to simulate the shearing conditions of cutting
Napier grass stem in different harvest periods for a forage grass harvester. The test data and analysis results suggested
that the shear strength of Napier grass stem increased with the bevel angle and shear velocity, and the shear impulse per
unit area of Napier grass stem increased with the bevel angle, but decreased as the shear velocity increased. The impact
shearing test was carried out for Napier grass stem when the average moisture content was 82.9% and the harvest period
was 30 days. The multiple regression equation of shear strength τm(MPa), bevel angle θ (°), and shear velocity V (m/s)
was obtained as follows: τm = -2.021 + 0.042θ+ 0.631V, correlation coefficient R=0.850, standard deviation S=0.266
(MPa). The shear strength and shear impulse per unit area of Napier grass stem increased with the harvest period, and
the Napier grass stem epidermis significantly affected the process of shear failure. The cut grass stem had fractures and
uneven sections at the bevel angle of 40°.