Spiral microstructures

Fig. 8.13 Cross-sectional views of microstructures produced by (a) linear raster and (b) rectangular spiral raster patterns. Process- ing used the tool shown in Fig. 8.9. The distinct uplift pattern in (a) reflects the switching between advancing and...

A1, 3.0-5.0Fe, 0.6-3.5Mn, 4.5 Ni, bal Cu, with typical elongation of 23%. A typical fusion weld defect is shown on the left side (arrow), which appears to be associated with the interface between passes. The microstructure in the fusion zone is a fine Widmanstatten (Fig. 14.44). This fusion weld was friction stir processed without removing the weld crown. The FSP parameters included a step-spiral 12.7 mm (0.5 in.) deep Densimet tool at 1000 rpm and 102 mm/min (4 in./min), with 6.4 mm (0.25 in.) translation between passes. 

Fibers with a radial transverse microstructure can exhibit a crack, which Volk [54] reports will tend to spiral around the fiber axis. The crack is able to transform into a true radial structure along a single filament and vice versa (Figure 7.13). White et al [55] believe that this is due to the annihilation of disclinations, as depicted in Figure 7.14. Yoon et al [56,57] have investigated crack formation in mesophase pitch based carbon fibers. 

The first reported real 3D microstructure [10] is a 7 m-diameter and 50 /tm-long spiral coil with a line cross-section of 1.3 mx2.2 m (Fig. 11). Due to the use of a relatively low NA (0.85) objective, the feature size is larger than the potential limit provided by the technology. However, it confirmed the feasibility of two-photon photopolymerization in three dimen-... 

Our previous works with the open spiral flow and the square plate injection molding indicated that quite similar on the hierarchical microstructure development. However the difference in shape, size and the layer thickness affect on the impact properly. With a specific mold, the open spiral flow, with much longer flow length than typical injection mold, which is not restricted since the flow length to mold thickness ratio is over 400 [3], hence hold pressure was not apphed. 

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