Abstract Recent reports in the literature identified pre-yield stress-strain nonlinearity and hysteresis (anelasticity) as occurring in metals at virtually all stresses. These observations raise foundational questions about metal deformation. Does a critical stress exist below which dislocations are immobile? Is there a critical stress for which permanent deformation occurs? Is anelasticity distinct from elasticity and plasticity? To answer such questions, special tensile tests with loading-unloading cycles after various prestrains were performed for 11 commercial sheet alloys: 9 AHSS (advanced high strength steels) and two Mg alloys. A dissipative dislocation bow-out model of anelasticity was derived that closely reproduces the experimental results and is consistent with the evolving experimental picture of anelasticity. Following prestrain, a finite yield stress was found to exist, below which no permanent deformation or hardening occurs. Anelasticity is distinct from elasticity and plasticity: it is recoverable and dissipative; mechanically reversible and thermodynamically irreversible. Corresponding tests of initial loading suggest radically different conclusions. Without prestrain, i.e. without a developed internal stress pattern, plastic deformation occurs near zero stress. A postulate of local and nonlocal interactions accounting for elastic, plastic and anelastic deformation was proposed.
ABSTRACT A general meso-scale (“GM”) crystal plasticity (CP) model was developed that accounts for lower-order (strain hardening) and higher-order (internal stress) effects of geometrically necessary dislocations (GNDs). It is predictive: no arbitrary parameters or length scales were invoked and no ad hoc numerical techniques were employed. It uses general stress field equations for GND content and a novel harmonization technique to enforce consistency of elastic long-range singular defect field...
#1Soon Kim(UNIST: Ulsan National Institute of Science and Technology)H-Index: 4
#2Hokun Kim(UNIST: Ulsan National Institute of Science and Technology)H-Index: 2
Last. Sung Youb Kim(UNIST: Ulsan National Institute of Science and Technology)H-Index: 26
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Abstract Phonon scattering, a dominant source of drag, is one of key issues to understand the dynamic behaviors of a dislocation. In this paper, it is found that a relativistic effect causes additional drag that is not ignorable when the dislocation's speed is comparable to the transverse shear wave speed. By considering the emission of lattice waves from the dislocation core, we theoretically derive an equation of dislocation motion wherein the relativistic effect is well considered in the fram...
Last. Hyuk Jong Bong(OSU: Ohio State University)H-Index: 12
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Abstract This study explores the evolution of GNDs and their effects on back stress through experimental and computational methods. Four large-grained tantalum tensile specimens were strained in uniaxial tension, electron backscatter diffraction (EBSD) data were collected, and geometrically necessary dislocation (GND) maps of the four specimens in the unloaded state were produced. EBSD-based GND maps revealed several types of features with high GND content which caused back stress in the specime...
#1Ashutosh Rajput(IITP: Indian Institute of Technology Patna)H-Index: 3
#2Surajit Kumar Paul(IITP: Indian Institute of Technology Patna)H-Index: 23
Abstract The present analysis focus on the mechanism of deformation in different tensile deformation modes. Uniaxial, plane strain and equi-biaxial tensile deformation modes play a significant role in determining the yield stress of the material. Yielding of the material begins with nucleation of 1/6 Shockley partial dislocation and subsequent deformation cause an increase in dislocation line length in the material. Consequently, strain hardening is observed in the RVE of nanocrystalline copper....
Abstract: A new mathematical modelling framework for simulation of metal cyclic plasticity is proposed and experimental validation based on tension-compression cyclic testing of S355J2 low carbon structural steel presented over the two parts of this paper. The advantages and limitations of the stress-strain curve shape modelling given by “Armstrong and Frederick” type hardening rules are discussed and a new formulation for kinematic hardening is proposed for more accurate representation of the s...
Last. Matthias Weiss(Cats: Geelong Football Club)H-Index: 20
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Abstract The paper presents the first experimental verification of dislocation repulsion during springback of Dual Phase (DP) steel, a mechanism which is suggested to cause non-linear unloading due to micro-plastic strain generation. In-situ loading-unloading tests are conducted within a Scanning Electron Microscope (SEM). It is shown that strain partitioning between ferrite grains as well as within a single ferrite grain occurs. It was observed that dislocations pile up during loading and repel...
Abstract Martensite volume fraction, composition and grain size are the known primary factors controlling the mechanical behavior of ferrite-martensite dual-phase steels. Recently, excellent performances of dual-phase steels with a fibrous microstructure have been reported. However, the precise role of martensite morphology and orientation has not been thoroughly elucidated yet. This study develops a two-scale micromechanical modeling strategy in order to investigate the effect of particle morph...
Last. Sam Nakhla(MUN: Memorial University of Newfoundland)H-Index: 6
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ABSTRACTMolecular dynamics simulations, which take place on the atomistic scale, are now being used to predict the influence of atomistic processes on macro-scale mechanical properties. However, th...
#2Xiaohua Hu(ORNL: Oak Ridge National Laboratory)H-Index: 14
Last. Yang Ren(Argonne National Laboratory)H-Index: 85
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Abstract The constitutive behavior of a hexagonal close-packed (HCP) polycrystalline ZEK100 magnesium alloy was investigated using combined high energy X-ray diffraction (HEXRD) from a synchrotron source and crystal plasticity modeling approach. The in-situ tensile test data coupled with the HEXRD enabled the tracking of the lattice strain evolution during deformation. The microscopic behavior represented by lattice strain and the macroscopic behavior represented by stress-strain curves were the...
Last. Myoung-Gyu Lee(SNU: Seoul National University)H-Index: 44
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Abstract Oscillating cold forming (OCF) has gained attentions in automotive and aerospace industries owing to force reduction and enhanced precision. However, the mechanism of force reduction and material flow in the OCF compared to those of conventional cold forming (CCF) was not clear. Therefore, the implementation of realistic elastic response under loading–unloading–loading (LUL) cyclic condition, which is the one of main deformation mechanism of current application, was studied through expe...
Last. Myoung-Gyu Lee(SNU: Seoul National University)H-Index: 44
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Abstract In this study, the strengths of a steel pipe in different material orientations are predicted using a distortional anisotropic hardening model, namely, the HAH model, implemented in a finite element simulation. The investigated hardening can capture the transient flow behavior under bending and reverse bending strain paths. In addition, the model reproduces the material behavior under orthogonally applied tension from the prior deformation path. To improve the predictive accuracy of the...
Last. Mingwang Fu(PolyU: Hong Kong Polytechnic University)H-Index: 40
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Abstract Bending is widely usedfor manufacturing of lightweight tubular parts and structuresin many industrial clusters. Intube bending, springback is an important deformation behavior since it causes crucial problemsrelated to the accuracy, quality, and properties of the bent tubular parts. This research presents a generalized analytical solution for springback in tube bending, enablingaccurate and efficient analysis of springbackfor bending of general tubular materials, in particular, for the ...
#3S.E. Offerman(TU Delft: Delft University of Technology)H-Index: 16
Abstract null null Intricate knowledge of dislocation networks in metals has proven paramount in understanding the constitutive behaviour of these materials but current experimental methods yield limited information on the characteristics of these networks. Recently, the isotropic anelastic response of metals has been used to investigate complex dislocation networks through the well-known phenomenon that the observed elastic constants are influenced by dislocations. Considering the dependence of...
ABSTRACT A general meso-scale (“GM”) crystal plasticity (CP) model was developed that accounts for lower-order (strain hardening) and higher-order (internal stress) effects of geometrically necessary dislocations (GNDs). It is predictive: no arbitrary parameters or length scales were invoked and no ad hoc numerical techniques were employed. It uses general stress field equations for GND content and a novel harmonization technique to enforce consistency of elastic long-range singular defect field...
