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Additive manufacturing (AM) is an emerging and promising technology. In this manuscript, an attempt is made to simulate an AM process via molecular dynamics simulations. Amorphous Cu pillars are built by bundling melting Cu wires parallelly one by one, with a particular temperature-controlling procedure through the use of ‘mediate temperature’. Thus, the volume fraction of the amorphous phase becomes adjustable. Uniaxial tests are conducted on the pillars after free relaxation. The mediate temperature is found to play a profound role in atomic arrangement, which governs the volume fractions of amorphous and crystalline phases. The results obtained also show that crystallization prevails when the pillar is subjected to an external tension. Furthermore, such a stress-induced crystallization serves as the dominant plastic mechanism instead of dislocation, and a vibrating uniaxial loading is found to accelerate the transformation from an amorphous to a crystalline phase, compared with a monotonic tension.

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In recent decades, size effects caused by grain size, strain gradient, typical defects etc., have been widely investigated. Nevertheless, the dependence of tensile strength on the specimen length, addressed by Da Vinci around 500 hundred years ago, has received rather limited attention, even though it is one unavoidable question to answer if people attempt to bring materials’ amazing nano-scale strengths up to macro-level. Therefore, we make efforts to study tensile behaviors of copper nanowires with a common cross-section and various lengths by employing the molecular dynamics simulations. Surprisingly, a strong size effect of Da Vinci type indeed arises. We have shown the influences of lattice orientation, temperature and prescribed notch on such a Da Vinci size effect. Two different theoretical explanations are briefly proposed for a qualitative understanding. Finally, a simple scaling rule is summarized to cover the tendencies observed.

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