Sinuous plastic flow: Mechanics, microstructural basis, and control

Experimental investigations of large strain deformation processes such as cutting and sliding have primarily involved analysis of process-level variables such as deformation forces and surface finish. Using high speed in situ imaging coupled with finite element simulations, we show that these processes exhibit a rich variety of complex plastic flows. Detailed investigations of one such flow mode, termed sinuous flow and widely prevalent in ductile metals, are presented. Sinuous flow involves unsteady local deformation in the form of repeated material folding arising from grain-level heterogeneity. The microstructural basis of this flow, along with quantitative replication of its kinematics, is demonstrated using finite element simulations. Sinuous flow is ubiquitous in that it occurs in different deformation configurations and in other ductile material systems, like some polymers, which are devoid of any grain-structure. Being associated with a range of deleterious effects, methods for disrupting sinuous flow using surface coatings and kinematic constraints are demonstrated. Implications for our general understanding of machining processes are discussed. [Display omitted] •Machinability of soft, annealed metals is poor due to high forces and poor finish.•Cutting phenomena is investigated using high-speed in situ imaging and FE simulations.•Plastic flow is found to occur via energy intensive, complex sinuous flow.•Microstructural heterogeneity and plastic buckling cause sinuous flow.•Sinuous flow can be avoided by mechanochemical techniques or external constraints.