*Editorial* **Crystal Strengths at Micro- and Nano-Scale Dimensions**

**Ronald W. Armstrong 1,\* and Wayne L. Elban <sup>2</sup>**


Received: 3 February 2020; Accepted: 3 February 2020; Published: 5 February 2020

**Abstract:** Higher strength levels, achieved for dimensionally-smaller micro- and nano-scale materials or material components, such as MEMS devices, are an important enabler of a broad range of present-day engineering devices and structures. Beyond such applications, there is an important effort to understand the dislocation mechanics basis for obtaining such improved strength properties. Four particular examples related to these issues are described in the present report: (1) a compilation of nano-indentation hardness measurements made on silicon crystals spanning nano- to micro-scale testing; (2) stress–strain measurements made on iron and steel materials at micro- to nano-crystal (grain size) dimensions; (3) assessment of small dislocation pile-ups relating to Griffith-type fracture stress vs. crack-size calculations for cleavage fracturing of α-iron; and (4) description of thermally-dependent strain rate sensitivities for grain size strengthening and weakening for macroto micro- to nano-polycrystalline copper and nickel materials.

**Keywords:** crystal strength; micro-crystals; nano-crystals; nano-polycrystals; nano-wires; whiskers; pillars; dislocations; hardness; crystal size dependencies; fracture; strain rate sensitivity
