Sinuous flow in metals

Abstract

Annealed metals are surprisingly difficult to cut, involving high forces and an unusually thick "chip." This anomaly has long been explained, based on ex situ observations, using a model of smooth plastic flow with uniform shear to describe material removal by chip formation. Here we show that this phenomenon is actually the result of a fundamentally different collective deformation mode-sinuous flow. Using in situ imaging, we find that chip formation occurs via large-amplitude folding, triggered by surface undulations of a characteristic size. The resulting fold patterns resemble those observed in geophysics and complex fluids. Our observations establish sinuous flow as another mesoscopic deformation mode, alongside mechanisms such as kinking and shear banding. Additionally, by suppressing the triggering surface undulations, sinuous flow can be eliminated, resulting in a drastic reduction of cutting forces. We demonstrate this suppression quite simply by the application of common marking ink on the free surface of the workpiece material before the cutting. Alternatively, prehardening a thin surface layer of the workpiece material shows similar results. Besides obvious implications to industrial machining and surface generation processes, our results also help unify a number of disparate observations in the cutting of metals, including the so-called Rehbinder effect.folding | plasticity | metal cutting | instability | deformation

Comment on ‘The cutting of metals by plastic buckling’ by Udupa et al .

“…tool. It gives a deterministic explanation of bulging, alternative to buckling, that is not considered in [1] despite split and oscillating shear zones having been previously reported in machining brass, albeit on a finer scale, in figure 12 of [5] and the ghost of a similar field having been reported for sinuous flow in figure 2 of [6]. Publication of the strain rate fields from the streak lines in [1] would be valuable.…”

Geometric flow control of shear bands by suppression of viscous sliding

“…Mesoscale flow modes in plasticity, such as shear banding [1,2], kinking [3] and sinuous flow [4,5], have a marked effect on the mechanical response of metals. In particular, shear bands have long been recognized as a common mode of non-homogeneous flow in condensed matter systems, ranging from metals [1, 2,6] to geomaterials (rocks, soils) [7] and complex fluids [8].…”

Dynamic Covalent Self‐Assembly Based on Oxime Condensation

“…Imine (‐C=N‐) condensation has been considered as one of the most promising reaction motifs in dynamic covalent chemistry (DCC) . Its reversible nature allows the systems to perform error‐checking and self‐correcting during searching for their thermodynamic minimum.…”