The wavelike structure is observed on both sides of the deformed area but not at the base region. Moreover, the wave structures at opposite positions on the deformed surface appear to be identical in shape, except that they are mirror images. A cross section of the target system shows that the crest of the waves to the right of the bottom region are turned to the right, whereas those on the left of the bottom are turned to the left, as indicated in Fig. 5a. Figure 5b shows a close-up view of the wave form in the right weld region (see Fig. 2 for wave structure in the left weld region). This behavior of the crest indicates that the velocity of the base plate was somewhat higher than that of the second plate. It is not yet possible to provide an unequivocal solution to this problem nor to establish the value of the critcial contact angle, since the results of the flow are not well known. However, the results in the figures are in qualitative agreement with a plausible extension of the considerations of the references to the present case. Concluding Remarks Melting is the usual commercial method for bonding of metals. In this process, the surface films (principally oxides) dissolve in the melt and/or float to the liquid surface and ultimately are segregated in and removed with the slag. A mechanical method such as hot or cold rolling frequently is employed to disrupt these surface films in order to bring bare metal into contact and provide bonding. We believe this is the first evidence that multiplate metallic structures may be spot-welded as a result of hypervelocity particle impact. It is evident from this work that meteoroid impact may cause seizure between surfaces (e.g., bearing surfaces) that are intended to slide freely on each other, even without penetration to the bearing interface.
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