Dense networks of deformation twins endow metals and alloys with unprecedented mechanical properties. However, the formation mechanism of these hierarchical twin structures remains under debate, especially their relations with the imperfect nature of twin boundaries (TBs). Here, we investigate the intrinsic deformability of defective TBs in face-centered cubic metallic materials, where the inherent kinks on a set of primary TBs are demonstrated to facilitate the formation of secondary and hierarchical nanotwins. This defect-driven hierarchical twinning propensity is critically dependent on the kink height, which proves to be generally applicable in a variety of metals and alloys with low stacking fault energies. As a geometric extreme, a fivefold twin can be constructed via this self-activated hierarchical twinning mechanism. These findings differ from the conventional twinning mechanisms, enriching our understanding of twinning-mediated plasticity in metallic materials.

The mechanism of bending electrostriction in polyurethane films is discussed and elucidated through a numerical calculation. The simulations are carried out on a model in which charge carriers are assumed to be electrons injected from the cathode by the Schottky effect, and the positive charges are immobile. Under a dc field, our simulation results show that the electrons go out of the anode, leaving behind a large quantity of positive charge around the anode. As a result, the electric field near the anode eventually becomes much larger than that near the cathode. The asymmetrical electric field distribution leads to an asymmetrical stress distribution through the electrostriction effect and thus to bending of the polyurethane film under the application of a dc electric field. The results can also explain the gradual change in bending direction after reversing the polarity of the electric field.

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In underground metal mines, goaf brings huge safety risks. It is an important part of mine to evaluate goaf stability and determine the best goaf handling measures. However, the evaluation and decision are often separated; they need to be unified. Meanwhile, stability evaluation and decision for goaf are a complex system engineering of rock masses in underground mining, and subjectivity exists in the evaluation and decision process. Under these conditions, it is necessary to minimize subjectivity, and the results of stability evaluation also need to be considered comprehensively in determining handling measures. In this paper, the fuzzy theory was adopted based on the fact that the goaf stability evaluation and handling measure decision were fuzziness. Firstly, the goaf stability model was established by a two-layer fuzzy comprehensive evaluation. It took into account 12-factor indexes of goaf with engineering empirical approaches and divided them into 3 categories according to their engineering categories. The model improved the applicability of the goaf stability evaluation results, and the results were the basis for goaf handling measures as well. Secondly, a decision model of the goaf handling measures was established by multiobjective fuzzy optimization. It consisted of five goaf handling measures and five evaluation indexes. The model provided a comprehensive decision and optimal scheme for goaf handling. Two models were also applied to the Paishanlou gold mine and achieved a good handling result. The practical application showed that the two models were feasible.

Critical medium column theory has typically been used to predict the scope of caved rock zone (CRZ) caused by caving mining method. It is essential to understand the distribution laws of lateral pressure induced by caving mining method with different dipping angles. In this study, a self-designed scaled physical model was used to investigate the distribution laws with angles ranging from 80° to 90°, and ore drawing was employed in experiments to simulate caving mining method. The experimental results indicated that the distribution laws were divided into the reductive region and the extensive region during ore drawing. The reductive region was close to the drawing hole, and its scope was smaller than the other part. Moreover, decreasing the dipping angle was an effective way of controlling the maximum reduction rates and the scope of reductive region. By varying laws of lateral pressure, the predictive model of CRZs’ scope was established. Additionally, the rock mass located outside the predictive CRZs’ scope did not rupture based on the monitoring of Digital Optical Televiewing (OPTV), which was verified by the field test in Dabeishan Iron Mine, China. The results of the field test demonstrated that the prediction method used in this study was valid and could be used in practice.