Ultra-high-performance fiber reinforced concrete (UHPFRC) exhibits strain hardening and multiple cracking behaviors when subjected to tension load. There are limited studies on the effect of steel fiber aspect ratios on the tensile performance of UHPFRC. Also, tensile testing of cementitious materials and composites is challenging due to the lack of a standardized direct tensile testing method with wide variation. This study experimentally investigated the effect of hooked end and straight steel fiber aspect ratios on the tensile behavior of UHPFRC with a 2% fiber volume fraction. A direct tensile test setup was first developed to obtain good alignment and desirable experimental data in an attempt to overcome some of the difficulties with other tensile tests. UHPFRC failure modes, stress-strain relationships, initial cracking strength, and peak strength, as well as stress–crack width relationships, were characterized and analyzed. The developed tensile test results showed that, as the aspect ratio of the hooked end fiber increased, the ductility ratio and the characteristic stress increased. However, the effect of the straight fiber aspect ratio on tensile behavior was not more significant than that of the hooked end fiber aspect ratio. Over-large straight fiber aspect ratios led to a reduction in characteristic stress and ductility ratio and an acceleration of crack propagation in the early softening phase. In comparisons of the developed direct tensile test and other test methods in terms of peak strength, the small-scale briquette tensile test showed the potential to become an alternative to conservatively evaluate UHPFRC composition strength of.

In this paper, series of full-scale cutting tests and cutting simulations are carried out to investigate the influence of installation parameter and geometry of the pick on cutting performance. The discrete element method is used to simulate the rock cutting process. A general process to calibrate macro properties of rock including uniaxial compressive strength (UCS), elastic modulus, Poisson’s ratio, cohesion and internal friction angle is proposed and used to complete the calibration of coal model. The cutting simulations are performed using picks with different tip angles and rake angles. The results show that the peak cutting force (PCF) decreases with the increase of rake angle following an inverse proportional function when the rake angle is positive, while it varies following a parabolic curve in the condition of negative rake angle. Moreover, the crack mode changes from primarily shear failure to primarily tensile failure with the increase of rake angle. Finally, a multiple-attribute index is proposed to evaluate the cutting performance and select the optimum cutting parameters.

This article investigates the fragmentation of rock during the indentation process with a conical pick. The study explores the impact of indentation dip angle, indentation spacing, and confining pressure on rock fragmentation through simulation using the discrete element method. Rock models of coal and red sandstone are created and calibrated for the simulation. The findings indicate that the indentation force increases exponentially with the increase of indentation dip angle for both coal and red sandstone. The specific energy increases first and then decreases with the increase of indentation dip angle. The maximum specific energy is found in the condition of indentation dip angle of 25° for red sandstone, while it is 20° for coal. The indentation force increases logarithmically with the increase of indentation spacing tending to be an unrelieved indentation condition. The optimal indentation spacing with the lowest specific energy is determined to be 50 mm for breaking coal and 34 mm for breaking red sandstone. Additionally, the indentation force increases exponentially for coal while it increases linearly for red sandstone with the increase of the confining pressure. For both coal and red sandstone, specific energy increases with the increase of the confining pressure.

This study investigates the effects of kinematic parameters and rock properties on the cutting performance of an oscillation disc cutter (ODC) based on the discrete element method. The cutting model with ODC is established using the particle flow code in three dimensions (PFC3D) and validated by experiments. Through simulation analysis, the influence of geometric parameter (eccentric ratio, R_E), motion parameters (velocity ratio, R_V) and rock characteristics on cutting crushing characteristics, cutting force and cutting efficiency is analyzed. The simulation results reveal that mean cutting force, mean torque, and specific energy (SE) increase with R_E and R_V. The mean cutting force and mean torque are positively correlated with the cutting depth and have a good linear relationship, while SE is negatively correlated with the cutting depth. Furthermore, the study demonstrates that as the cutting depth increases, the fracture mode of the rock transitions from plastic to brittle. Meanwhile, the peak cutting force occurs during the crack initiation stage and subsequently decreases during crack propagation. Finally, the multivariate regression equations of rock mechanical properties, cutting depth and SE are obtained. These findings enhance the understanding of the cutting mechanism of ODC, and provide a theoretical foundation for ODC parameter design in practical applications.

Prediction of rock fracturing capacity demands particular requirements for the exploitation of mineral resources, especially for the parameter design of conical pick performance for hard rock fragmentation, which must take into account differences in rock mechanical properties. Among these parameters, the peak cutting force (PCF) is important in designing, selecting, and optimizing the cutting head of mining equipment and a cutability index of rocks. Taking high lithological tolerance as demand traction, this study proposes a theoretical model for estimating the peak cutting force of conical picks based on the improved projection profile method for which the influence of alloy head, pick body structure, and installation parameters are taken into consideration. Besides, experimental results corresponding to different numbers of rock samples are used to verify the accuracy and stability of the theoretical model. Meanwhile, the comparison of performance in cutting force estimation between this model and four other existing theoretical models is conducted. The results found that the new method has the highest correlation coefficient with the experimental results and the lowest root mean square error comparing with other models, i.e., the estimation performance of this method has high lithological tolerance when the rock type increases and the lithology changes. Consequently, the proposed peak cutting force estimation of improved projection profile method will provide a more valid and accurate prediction for rock fracturing capacity with large differences in rock mechanical properties.