Effect of dynamic loading conditions on the dynamic performance of MP1 energy-absorbing rockbolts:Insight from laboratory drop test

Energy-absorbing rockbolts have been widely adopted in burst-prone excavation support, and their serviceability is closely related to the frequency and magnitude of seismic events. In this research, the splittube drop test with varying impact energy was conducted to reproduce the dynamic performance of MP1rockbolts under a wide range of seismic event magnitudes. The test results showed that the impact process could be subdivided into four distinct stages, i.e. mobilization, strain hardening, plastic flow(ductile), and rebound stage, of which strain hardening and plastic flow are the primary energy absorbing stages. As the impact energy per drop increases from 8.1 to 46.7 k J, the strain rate of the shank varies between 1.20 and 2.70 s^(-1), and the average impact load is between 240 and 270kN, which may be considered as constant. The MP1 rockbolt has a cumulative maximum energy absorption(CMEA) of 31.9–40.0 k J/m, with an average of 35.0 k J/m, and the elongation rate is 11.4%–14.7%, with an average of 12.7%, both of which are negatively correlated with the impact energy per drop. Regression analysis shows that energy absorption and shank elongation, as well as momentum input and impact duration,conform to the linear relationship. The complete dynamic capacity envelope of MP1 rockbolts is proposed, which reflects the dynamic bearing capacity, elongation, and distinct stages. This study is helpful to better understand the dynamic characteristics of energy-absorbing rockbolts and assist design engineers in robust reinforcement systems design to mitigate rockburst damage in seismically active underground excavations.

Experiments and modeling of mechanism analysis of maize picking loss

Maize picking is the main form of maize harvest in China.Maize picking loss accounts for a large proportion of the current maize harvest loss.An experimental study and a theoretical analysis were conducted to explore the influencing factors and rules of maize picking loss.First,the boundary conditions,established by analyzing the mechanism of maize picking,determined the influences of maize picking loss.Then,single-factor experiments and a central composite design(CCD)method were used to determine the influence of various factors and their interactions on maize picking loss.Finally,the models of kernel loss and ear loss were set up to determine the optimal parameter combination of maize picking harvest.Field experiment verification was conducted.The results indicated that the optimal parameters of the maize picking harvest were the rotational speed of pulling rollers of 1120 r/min,operating speed of 1.94 m/s,the inclination of the header of 18°and clearance between the picking plates of 30 mm.By establishing these optimal parameters,the kernel loss rate was 0.065%,and the ear loss rate was 0%.The obtained experimental results and regression models could be used to predict the performance of the maize picking harvest,guide the adjustment of header working parameters,and provide a theoretical basis for reducing the mechanical loss of maize harvesting.