Multiphysical Dislocation Dynamics Models for High Strain Rate Plastic Deformation PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Multiphysical Dislocation Dynamics Models for High Strain Rate Plastic Deformation PDF full book. Access full book title Multiphysical Dislocation Dynamics Models for High Strain Rate Plastic Deformation by Oxana Skiba. Download full books in PDF and EPUB format.
Author: Oxana Skiba Publisher: ISBN: Category : Languages : en Pages : 151
Book Description
Discrete Dislocation Dynamics (DD) models provide a framework to advance the understanding of plasticity. However, existing DD models currently do not account for multiphysical effects. Multiphysical phenomena are often present during plastic deformation. Two particular examples are the electromechanical behavior of plastically deformed piezoelectric materials and the thermomechanical behavior of metals under high strain rate plastic deformation. Thus, I present two new DD models, that take these behaviors into account. The basic carriers of plastic deformation are dislocations, which are crystallographic defects. Therefore, in the two new DD models, dislocations are directly modeled as crystallographic line defects in an elastic continuum. These models are based on the Extended Finite Element Method (XFEM), which is a versatile tool used to analyze discontinuities, singularities, localized deformations, and complex geometries. The XFEM captures the slip from edge dislocations by way of Heaviside step enrichment function.
Author: Oxana Skiba Publisher: ISBN: Category : Languages : en Pages : 151
Book Description
Discrete Dislocation Dynamics (DD) models provide a framework to advance the understanding of plasticity. However, existing DD models currently do not account for multiphysical effects. Multiphysical phenomena are often present during plastic deformation. Two particular examples are the electromechanical behavior of plastically deformed piezoelectric materials and the thermomechanical behavior of metals under high strain rate plastic deformation. Thus, I present two new DD models, that take these behaviors into account. The basic carriers of plastic deformation are dislocations, which are crystallographic defects. Therefore, in the two new DD models, dislocations are directly modeled as crystallographic line defects in an elastic continuum. These models are based on the Extended Finite Element Method (XFEM), which is a versatile tool used to analyze discontinuities, singularities, localized deformations, and complex geometries. The XFEM captures the slip from edge dislocations by way of Heaviside step enrichment function.
Author: Eleanor Yi Kei Mak Publisher: ISBN: Category : Deformations (Mechanics) Languages : en Pages : 92
Book Description
There has been a trend of miniaturization in recent technological advances, particularly through the development of microelectromechanical systems (MEMS). To cope with the demand for increasing performance from ever smaller components, alternatives to traditional scaling techniques is required, for example, by exploiting scale-dependent material properties. The investigation of material behaviour through computer simulations is an attractive alternative to experimental techniques which are limited by scale and cost. Metallic crystalline solids are commonly the material of choice for MEMS components. The majority of a metal's capacity for deformation is irreversible, otherwise known as plasticity. The dislocation -- a defect in the crystal structure at the atomic level -- acts as the microscopic carrier of plasticity. The Discrete Dislocation Dynamics (DD) family of numerical models serves as a bridge between an atomistic and a continuum description of plasticity at the mesoscale. In continuum models, plasticity is captured through the homogenization of localized effects induced by dislocation activity. With DD models, the activity of discrete dislocations is instead explicitly simulated. Conventional DD models are purely mechanical and are based on a quasi-static formulation. For the purpose of high strain-rate loading scenarios, they fail to capture the localized thermal effects which emerge, as well as the inertial effects which are particularly relevant. As such, the fully Dynamic and coupled Thermo-Mechanical Dislocation Dynamics model (DTM-DD) was developed in this thesis to address the limitations of existing DD models in the context of high strain-rate plasticity. Inertia was included via an elastodynamic description of material behaviour and the consideration of dislocation mass; and thermal influences, through thermo-mechanical coupling and the temperature dependence of dislocation parameters. Using the DTM-DD, the high strain-rate plastic behaviour of metals was investigated. The interaction and interference of elastic waves was observed; and the implications and convergence of dynamic dislocation motion was determined. The framework of extension load testing was presented to investigate the influence and strain-rate sensitivity of system and dislocation parameters to inertial and thermal effects. The selection of the thermal boundary condition was identified to significantly influence the simulated material response. The nature of temperature dependence, as investigated through parameter studies of dislocation drag and nucleation strength, was shown to be a competition between influences causing material softening and hardening. The DTM-DD was extended to investigate the effect of loading rate on the nano-indentation of a thin film sample. Loading rate-dependent propagation of dislocation nucleation and slip as a plastic front was observed. Ultimately, the investigations using the DTM-DD demonstrate that the interplay between inertial and thermal effects are highly complex in a fully dynamic and thermo-coupled system.
Author: Taira Suzuki Publisher: Springer Science & Business Media ISBN: 364275774X Category : Science Languages : en Pages : 237
Book Description
In the 1950s the direct observation of dislocations became possible, stimulat ing the interest of many research workers in the dynamics of dislocations. This led to major contributions to the understanding of the plasticity of various crys talline materials. During this time the study of metals and alloys of fcc and hcp structures developed remarkably. In particular, the discovery of the so-called in ertial effect caused by the electron and phonon frictional forces greatly influenced the quantitative understanding of the strength of these metallic materials. Statis tical studies of dislocations moving through random arrays of point obstacles played an important role in the above advances. These topics are described in Chaps. 2-4. Metals and alloys with bcc structure have large Peierls forces compared to those with fcc structure. The reasons for the delay in studying substances with bcc structure were mostly difficulties connected with the purification techniques and with microscopic studies of the dislocation core. In the 1970s, these difficulties were largely overcome by developments in experimental techniques and computer physics. Studies of dislocations in ionic and covalent bonding materials with large Peierls forces provided infonnation about the core structures of dislocations and their electronic interactions with charged particles. These are the main subjects in Chaps. 5-7.
Author: Ulrich Messerschmidt Publisher: Springer Science & Business Media ISBN: 3642031773 Category : Science Languages : en Pages : 509
Book Description
Along with numerous illustrative examples, this text provides an overview of the dynamic behavior of dislocations and its relation to plastic deformation. It introduces the general properties of dislocations and treats the dislocation dynamics in some detail.
Author: Publisher: ISBN: Category : Languages : en Pages : 10
Book Description
Time-resolved plastic waves in plate-impact experiments give information on relation between applied shear stress and plastic strain rate at low plastic strain. This information is different from that obtained at intermediate strain rates using Hopkinson bar techniques, because the material deformation state is driven briefly into the regime dominated by dislocation drag. Two VISAR records of particle velocity at the tantalum/sapphire (window) interface are obtained for symmetric impact producing peak in-situ longitudinal stresses of 75 and 111 kbar. Rise-times of plastic waves are about l00 and 50 ns, respectively, with peak strain rates of about 2 x l05 and 8.5 x l05/s, respectively, as determined by weak-shock analysis. These data show a much stronger dependence of plastic strain rate on applied shear stress than predicted by linear viscous drag models in combination with thermal activation through a large Peierls barrier. The data also show complex evolution of the mobile dislocation density during early stages of high-rate plastic flow. This measurement and corresponding analysis aid significantly in establishing the fundamental picture of dynamic deformation of metals and the evolution of the internal material state at early times following shock compression.
Author: P.O. Kettunen Publisher: Trans Tech Publications Ltd ISBN: 3035705976 Category : Technology & Engineering Languages : en Pages : 420
Book Description
This publication is based upon lectures given during a well-received course on physical metallurgy and originally intended for students specializing in fields related to metallic materials. But, as the author points out, metallic materials are the most widely investigated group of materials and their study therefore gives a good basis for understanding how other materials can be made to reveal interrelationships between their structures and properties; especially with regard to those properties associated with strain. Similar types of rule can then be applied to other materials, in spite of their apparent differences.
Author: Shamseddin Akhondzadeh Publisher: ISBN: Category : Languages : en Pages :
Book Description
Most metals are crystalline materials that can undergo significant plastic (permanent) deformation when subjected to applied loading. Plastic deformation is usually accompanied by an increase in the flow stress of the material. This phenomenon is called strain hardening and is of vital importance in many engineering applications, including aerospace, automotive, and power generation industries. Developing accurate material models to predict the plastic response and hardening behavior of metals during deformation is a prerequisite to the engineering design processes, which requires a physical understanding of the underlying deformation mechanisms. In single crystals, plastic deformation of the crystal is governed by the evolution of dislocations--line defects inside the crystalline materials which marks the boundary between the slipped and unslipped regions--moving and interacting in response to the applied loading. Dislocation dynamics (DD) simulations, which track the time-space trajectories of individual dislocation lines, provide a promising tool to establish a physical link between the dislocation microstructure evolution and the strain hardening phenomenon. However, the high computational cost of DD simulations renders the accessible length and time scales to well below those which are relevant to most engineering applications. Due to this challenge, instead of directly using DD simulations for engineering applications, we have utilized DD simulations to delineate how constitutive relations of crystal plasticity (CP) can be constructed for FCC copper, based on coarse-graining of high-throughput DD simulations. This thesis consists of three main components, and we show how they fit together into a complete, physical model like three pieces of a puzzle. The first piece is a massive DD simulation database that we were able to generate thanks to recent computational advances in DD, including the subcycling time-integration algorithm and its implementation on Graphics Processing Units (GPUs). By systematically coarse-graining the database we present a strain hardening model which consists of two components: 1) a dislocation multiplication model, which accounts for slip-free multiplication, and 2) an exponential flow-rule connecting slip system shear rate to the resolved shear stress through an exponential function. These components can be thought of as the second and third puzzle pieces. By analyzing the data, it was discovered that dislocation multiplication frequently occurs on slip systems which experience zero applied shear stress (i.e., zero Schmid factor) and have a plastic strain rate of zero; we termed such multiplication slip-free multiplication and it serves as the second puzzle piece. This finding questions the assumption of the existing phenomenological expression that multiplication is proportional to the shear rate. We propose to add a correction term to the generalized Kocks-Mecking expression to account for slip-free multiplication, whose mechanistic explanation is provided. A major finding of this thesis is that DD results suggest an exponential flow-rule, in contrast to the commonly used power-law flow-rule, even in the cases where thermal fluctuations are not present. The exponential flow-rule is the third piece in the puzzle of the presented strain hardening model. We demonstrate that the observed exponential flow-rule, despite the common notion that thermal fluctuations are the responsible mechanism, can be explained by statistical properties of the dislocation links. Hence, by statistically analyzing the number density and plastic activity of links in terms of their length, we formulate a physically justified link length based flow rule which can numerically capture the exponential dependence of shear rate on shear stress. The proposed link length based flow-rule has two key components: 1) the number density of links on each slip system, which was observed to follow the sum of two exponentials distribution, and 2) an average velocity of links as a function of resolved shear stress and link length, whose fitting coefficients are independent of the loading orientation. The exponential dependence of on resolved shear stress is traced to the spatial fluctuation of the internal stress field, which can be approximated by a Laplace distribution. The proposed average velocity function incorporates the Laplace distribution in its form. This thesis shows that discrete dislocation dynamics simulations can be used to inform higher length scale models of non-phenomenological constitutive relations. The presented model captures the strain hardening as a result of slip system interactions in FCC single crystals. It works as an example for developing similar coarse-grained models based on DDD which includes additional strain hardening mechanisms such as cross-slip, or precipitate hardening. We hope that the present thesis motivates more researchers to use DDD simulations for constructing constitutive relations.
Author: Oxana Skiba
Author: Oxana Skiba
Author: Eleanor Yi Kei Mak
Author: Taira Suzuki
Author: Dale Henry Klahn
Author: Alan R. Rosenfield
Author: Ulrich Messerschmidt
Author: 
Author: P.O. Kettunen
Author: Harold E. Read
Author: Shamseddin Akhondzadeh