Rolling friction plays an important role in the heap formation of granular materials. In this paper, three rolling friction models, which are incorporated into the discrete element method, are compared with simulation of sandpile formation in detail. The experiments were first implemented for cement particles to verify the reliability of simulated results. An approximate approach, which can be used to determine the friction coefficient between particles and between particles and a boundary, is also proposed. Then, numerical simulations parallel to the experiments were carried out by using the three rolling friction models. The simulated results are detailed and discussed compared with the experimental results. In addition, the rolling friction between the particles and boundaries was also studied through an example of a sphere moving on a horizontal plate with an initial translational velocity. The numerical results suggest that the rolling friction model described by the relative angular velocity...

Reinforced concrete (RC) slab is an important component in civil construction and protection engineering, and its dynamic response under impact loading is a complex mechanical problem, especially for two or multiple continuous impact loads. In this paper, a series of drop hammer impact tests were carried out to investigate the dynamic response of RC slabs with two successive impacts. The time history of impact force and the failure characteristic of the slab surface were recorded. Moreover, four influence factors, including slab thickness, reinforcement ratio, impact location, and drop hammer height have been discussed. Besides, a 3D numerical model based on the finite element method (FEM) was established to expand the research of constrained force, deflection, and vertical stress of an RC slab. The results show that increasing the slab thickness and reinforcement ratio can improve the impact resistance of an RC slab. The impact point location and drop hammer height have a great influence on the dynamic response of the RC slab. In addition, the RC slab will have more obvious damage under the second impact, but the dynamic response becomes weaker. It may be because of the local damage in the concrete caused by the first impact that would weaken the propagation of vibration.

In blasting operation, some undesirable impacts, such as fly-rock, fragmentation, and back break, are induced. If the blasting design is not optimized, these mentioned impacts would reduce the blasting efficiency. To improve and optimize the blast design, blasting effect evaluation is essential. Due to the complexity of interactions among blasting parameters, empirical methods may not be appropriate for blast design optimization. A two-level mathematical model based on fuzzy mathematics, is proposed in this work. In total, 11 typical parameters were chosen and classified into three groups. The blasting effect is evaluated from three aspects, and then the comprehensive evaluation is given. A blasting effect evaluation system was developed based on the mentioned method on the platform of VC++. Some other techniques, such as image processing, were integrated into the system, which allowed for obtaining all of the parameters rapidly and conveniently. The system was applied in practical bench blast engineering. The results obtained from the system can provide effective information for the optimization of the next blast design.