Self-healing of cracks during ductile regime machining of silicon: Insights from molecular dynamics simulation

During nanoindentation and ductile-regime machining of silicon, a phenomenon known as “self-healing” takes place in that the microcracks, microfractures, and small spallings generated during the machining are filled by the plastically flowing ductile phase of silicon. However, this phenomenon has not been observed in simulation studies. In this work, using a long-range potential function, molecular dynamics simulation was used to provide an improved explanation of this mechanism. A unique phenomenon of brittle cracking was discovered, typically inclined at an angle of 45° to 55° to the cut surface, leading to the formation of periodic arrays of nanogrooves being filled by plastically flowing silicon during cutting. This observation is supported by the direct imaging. The simulated X-ray diffraction analysis proves that in contrast to experiments, Si-I to Si-II (beta tin) transformation during ductile-regime cutting is highly unlikely and solid-state amorphisation of silicon caused solely by the machining stress rather than the cutting temperature is the key to its brittle-ductile transition observed during the MD simulations

Self-perceptions of the role of the planner

The role of the planning practitioner has received considerable attention in a diverse range of theoretical and empirical debates within the broad spectrum of planning scholarship from normative debates surrounding the planner's role in society, to more empirical investigations into the skills, attributes, and evolving nature of planning practitioners. Fundamental questions surrounding the role and purpose of planners have also entered into more mainstream discussions as the democratic nature of the planning system has been consistently undermined by allegations of misconduct, corruption, and incompetence. Despite the broad range of literature and debate which centres on the role of the planner, relatively few studies have explored the views of planning practitioners themselves, making it difficult to judge whether the ideas of planning academics are actually shared by those in the field. In this paper we seek to address this particular gap and argue that such insights are critical in determining the extent to which planning practitioners serve to challenge, maintain, or reinforce existing power imbalances in the planning system. The methodology consists of a series of qualitative interviews with twenty local authority planners working throughout the Greater Dublin Area, Ireland. The results suggest that planners' self-perceptions of their role tend to reflect traditional pluralist and managerialist perspectives. More broadly, the results suggest that the role orientations of contemporary planners are being shaped by dominant discourses in current planning ideology — namely, collaborative and participatory approaches