Multi-scale simulation of the nano-metric cutting process

Molecular dynamics (MD) simulation and the finite element (FE) method are two popular numerical techniques for the simulation of machining processes. The two methods have their own strengths and limitations. MD simulation can cover the phenomena occurring at nano-metric scale but is limited by the computational cost and capacity, whilst the FE method is suitable for modelling meso- to macro-scale machining and for simulating macro-parameters, such as the temperature in a cutting zone, the stress/strain distribution and cutting forces, etc. With the successful application of multi-scale simulations in many research fields, the application of simulation to the machining processes is emerging, particularly in relation to machined surface generation and integrity formation, i.e. the machined surface roughness, residual stress, micro-hardness, microstructure and fatigue. Based on the quasi-continuum (QC) method, the multi-scale simulation of nano-metric cutting has been proposed. Cutting simulations are performed on single-crystal aluminium to investigate the chip formation, generation and propagation of the material dislocation during the cutting process. In addition, the effect of the tool rake angle on the cutting force and internal stress under the workpiece surface is investigated: The cutting force and internal stress in the workpiece material decrease with the increase of the rake angle. Finally, to ease multi-scale modelling and its simulation steps and to increase their speed, a computationally efficient MATLAB-based programme has been developed, which facilitates the geometrical modelling of cutting, the simulation conditions, the implementation of simulation and the analysis of results within a unified integrated virtual-simulation environment

Multiscale modeling of ductile crystals at the nanoscale subjected to cyclic indentation

A multiscale method is applied to study the response of an aluminum single-crystal substrate to cyclic indentation at finite temperature. The evolution of contact-induced deformation on the nanoscale is controlled based on defect nucleation beneath the indenter. The method allows for visualization of atomistic deformation during loading and unloading. Although there are inherent limitations to our two-dimensional model, we have found qualitative similarities to the mechanisms of homogeneous defect nucleation and deformation in three-dimensional face-centered cubic crystals. It is shown that the atomistic surface roughening process mostly arises from homogeneous dislocation nucleation during successive loading/unloading processes. These sub-surface defects cause major permanent deformation of the substrate during indentation. The slip steps forming on the surface of the indented substrate contribute their own dislocation activity, sending dislocations directly from the surface into the crystal, but those activities mostly remain localized near the indented surface. Force-displacement curves and the hysteresis which occurs due to inelastic deformation and heating of the substrate are studied for each cycle, and correlated with sub-surface and surface nucleation of defects

Coupled atomistic/discrete dislocation simulations of nanoindentation at finite temperature

Simulations of nanoindentation in single crystals are performed using a finite temperature coupled atomistic/continuum discrete dislocation (CADD) method. This computational method for multiscale modeling of plasticity has the ability of treating dislocations as either atomistic or continuum entities within a single computational framework. The finite-temperature approach here inserts a Nose-Hoover thermostat to control the instantaneous fluctuations of temperature inside the atomistic region during the indentation process. The method of thermostatting the atomistic region has a significant role on mitigating the reflected waves from the atomistic/continuum boundary and preventing the region beneath the indenter from overheating. The method captures, at the same time, the atomistic mechanisms and the long-range dislocation effects without the computational coat of full atomistic simulations. The effects of several process variables are investigated, including system temperature and rate of indentation. Results and the deformation mechanisms that occur during a series of indentation simulations are discussed

Finite temperature multiscale computational modeling of materials at nanoscale

The A multiscale computational method (CADD) is presented for modeling of materials at nanoscale whereby a continuum region containing defects is coupled to a fully atomistic region. The method reduces the degree of freedom in simulations of mechanical behavior of nanomaterials without sacrificing important physics. Applications to nanoindentation are used to validate and demonstrate the capabilities of the model

Behavior of Mathieu equation in stable regions

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Coupled atomistic/discrete dislocation simulations of nanoindentation at finite temperature

Simulations of nanoindentation in single crystals are performed using a finite temperature coupled atomistic/continuum discrete dislocation (CADD) method. This computational method for multiscale modeling of plasticity has the ability of treating dislocations as either atomistic or continuum entities within a single computational framework. The finite-temperature approach here inserts a Nose-Hoover thermostat to control the instantaneous fluctuations of temperature inside the atomistic region during the indentation process. The method of thermostatting the atomistic region has a significant role on mitigating the reflected waves from the atomistic/continuum boundary and preventing the region beneath the indenter from overheating. The method captures, at the same time, the atomistic mechanisms and the long-range dislocation effects without the computational cost of full atomistic simulations. The effects of several process variables are investigated, including system temperature and rate of indentation. Results and the deformation mechanisms that occur during a series of indentation simulations are discussed. Copyrigh

Multiscale modeling of solids at the nanoscale: Dynamic approach

One major class of multiscale models directly couples a region described with full atomistic detail to a surrounding region modeled using continuum concepts and finite element methods. Here, the development of a new dynamic approach to such coupled atomistic-continuum models is discussed with insight into the key ideas and features, with emphasis on fundamental difficulties involved in dynamic multiscale models. Simulations of nanoindentation in single crystals are performed to demonstrate the power of the developed method in capturing both long-range dislocation plasticity and short-range atomistic phenomena during single or cyclic loading without the computational cost of full atomistic simulations. The effects of several process variables are investigated, including system temperature and rate of indentation. The deformation mechanisms and the surface evaluation that occur during a series of single and cyclic indentation simulations are discussed