**5. Summary**

Molecular dynamic simulations of beams of single-crystal Cu of dimensions 100*a*<sup>0</sup> × *s* × *s*, *s* = 6*Na*<sup>0</sup> , *N* = 1, 2, 3, and with *a*<sup>0</sup> denoting the lattice parameter of Cu, have been loaded in displacement controlled tension until rupture. Each beam holds a centrally placed, rectangular through-the-thickness defect of extension along the beam length direction equal to *w* and of height *h* = *s/*3. Aspect ratios *w/h* = 1, 2, 3, 4 were considered and the loading was applied along two crystallographic directions, the [100]- or the [110] direction, cf. **Figure 1**. The deformation development was monitored continuously and the strains at plastic initiation, at void closure and at rupture were recorded. The result is given in **Table 2** and visualized in **Figure 3**.

By studying **Figure 3** and **Table 2**, some general trends about the deformation behavior can be drawn. First in the case of total closure of the beams for *s* = 6*a*<sup>0</sup> for both crystallographic orientations, it is observed that the closure strain *ε<sup>c</sup>* steadily decreases as the void width *w* increases. It is also observed that the strain at rupture is in the same range for both orientations for different values of *s* and, for both orientations, the values increase dramatically in magnitude with increasing *s*. Finally, it can be observed that no general trend regarding the influence of *w/h* on the failure strain can be drawn. In some cases, the strain increases, and in some cases, it decreases with increasing value of *w/h*.

It was concluded that geometrical features such as beam size and crystallographic orientation played a crucial role for the mechanical behavior. Plasticity develops through slip along closed packed {111} planes, and the [110] orientation always initiates plasticity first. Further, the strain at plastic initiation increases with beam cross section size as well as with decreasing ratio *w/h* for both orientations.

Studying the deformation pattern, it was found that the plasticity developed and the void deformed in different ways depending on cross section size, void aspect ratio and crystal orientation. As regards the events that lead to final rupture of the beams, different scenarios were observed.

In some cases, the void elongated and the two beam ligaments, above and below the void, eventually necked and ruptured independently. In such cases, the plasticity, through slip along {111} planes before the last ligament rupture, tended to extend away from the regions near the void and could sometimes reach the beam ends.

In the cases where closure of the voids occurred, the strain at closure decreased with increasing *w/h*. Also, it was observed that the strain at failure was relatively independent of crystallographic orientation and that it increased with increasing cross section size.

Sometimes the void first closes at the center, forming two separate voids. Then, two scenarios are possible. One is that the two voids both eventually close, followed by necking and rupture of the now healed cross section. In these cases, the plasticity localizes to the vicinity of the neck and leaves regions away from the neck elastic. The other possible scenario is that one of the created voids start to elongate and the ligaments above and below this void neck and rupture independently.

There were also cases where failure did not occur in the vicinity of the void; instead rupture occurred near one beam end after that the plasticity had spread over the entire beam.
