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Energetics, electronic structure, and structure stability of the calcium alloying Mg17Al12 phase from first principles calculations

100%

Zhou D. W. , Peng P. , Liu J. S.

Materials Science Poland

2007

tom Vol. 25, No. 1

145--153

The energetics and electronic structure of the Ca alloying Mg 17Al12 phase have been calculated using a first principles pseudopotential plane-wave method based on the density functional theory. According to the calculation results, the negative heat of formation and the cohesive energy of (Mg17-xCax)Al12 (x = 0. 1, 4, 12) gradually increase when the Mg atoms at the I, II, III positions of the Mg17Al12 phase are substituted with Ca, which indicates that the alloying ability of (Mg17-xCax)A,)Al12 with the replacement of Ca for Mg(III) atoms is the strongest among the three substitutions and (Mg5Ca12)Al12 formed in this manner has the highest structural stability. After comparing the densities of states (DOS) for (Mg17-xCax)Al12 (x = 0. 1, 4, 12), it is found that the increase in the structural stability of Mg 17Al12 alloyed by Ca attributes to an increase in the bonding electron numbers at energy levels below the Fermi level, which mainly originates from the contribution of the valence electron numbers of Al (p) and Ca (s) orbitals.

Influence of pick layouts on the performance of bolter miner cutting head

75%

Qiao S. , Wang A. L. , Xia Y. M. , Liu Z. Z. , Liu J. S. , Yang M.

2018

tom Vol. 25

147--160

A bolter miner is a new type of mining machinery with cutting and anchoring functions. In order to study the best pick layout of bolter miner cutting head. Based on the constitutive relation of Holmquist-Johnson-Cook (HJC), three simulation models of different cutting heads were established, and the whole crushing process of coal-rock was simulated by finite element method (FEM). The influence of the cutting head on the cutting performance under the condition of different rotational speeds and pick layouts was intensively studied. The results show that the relationship of load fluctuation coefficient among the three pick layouts is as follows: sequential type > hybrid type I > checkerboard type. The circumferential pick layouts can reduce the load fluctuation coefficient of cutting head. The rotational speed from 20 to 40 r/min, the torque linearly decreases with the increase of rotational speed. The rota-tional speed increases from 40 to 50 r/min, the cutting torque is relatively stable. The specific energy of chessboard type is relatively higher than the other three cutting heads. The difference of specific energy between sequential type and hybrid type I is not more than 5.5%, and the reality of the simulation is verified by cutting experiments. The results were successfully applied to the first shield type bolter miner in China.

Finite element analysis of load characteristic of shield bolter miner cutting head under complex coal seam condition

75%

Qiao S. , Xia Y. M. , Liu Z. Z. , Liu J. S. , Ning B. , Wang A. L.

tom Vol. 24

85--97

Aiming at the complex conditions of the first shielded bolter miner in the actual work, the mechanical model of bolter miner cutting head was established. Based on cutting mechanism of the conical pick and the cutting head, the cutting head load and torque analysis model under complex coal seam were established. The dynamic characteristics of load and torque in the process of cutting head are analyzed under three different working conditions of cutting roof-coal layers, coal-floor layers and coal seam by finite element method. The results show that when the damage variable D=1, the coal-rock completely lacks the bearing capacity, and it forms arc-shaped crushing groove on the coal-rock. The large difference of torque between roof-coal layers and the roof-coal layers in the conical pick is 112 Nm, which indicates that the cutting head has the best performance with cutting the coal seam first and then cutting the rock. In the process of excavation, the load fluctuation coefficient of cutting the coal-floor layers and roof-coal layers is about 1.2 times of that of the coal seam. The results can provide a reference for the efficient cutting and performance evaluation of the bolter miner.