Kink Deformation Research Articles

A Deformation Mechanism for Ridge-Shaped Kink Structure in Layered Solids

A deformation mechanism for ridge-shaped kink structure (RSKS), a type of localized deformation, is studied with a discussion focusing on the kink deformation of a monocrystal with a single-slip system under a plane-strain condition. From a geometrical study of displacement continuity it is found that, to satisfy displacement continuity, the kink boundary formed by the deformation from an initially homogeneous structure must have symmetry. We propose a simple model of the RSKS deformation mode to accomplish plastic deformation from a compressive force parallel to the slip direction. First, important geometrical knowledge related to the RSKS formation mechanism is formulated analytically. Then, a simulation of a spring–mass model is performed to clarify the RSKS formation mechanism. The intensity of the angle-dependent force field is found to affect the deformation mode.

OS0121-236 CRSSの寸法依存性を考慮したMg基LPSO相単結晶のマイクロピラーに対する転位-結晶塑性FEM解析

In this study, a finite element analysis based on a dislocation-based crystal plasticity model considering a size dependence of a critical resolved shear stress (CRSS) is performed to reproduce a size dependence of yield stress in a micropillar composed of single crystal of Mg-based LPSO phase. The CRSS model in which a size-dependent term is proportional to the inverse of a pillar diameter is applied and a numerical parameter is identified from experimental results. We consider four initial crystal orientations where a basal slip, prismatic slip, pyramidal slip and kink deformation are likely to occur. The results show that the applied model reproduces the size dependence of the yield stress. In addition, in the initial orientation where a kink deformation is tend to occur, the deformation mode changes according to the specimen size.

Deformation Analysis of the Long-Period Stacking-Ordered Phase by Using Molecular Dynamics Simulations: Kink Deformation under Compression and Kink Boundary Migration under Tensile Strain

Deformation Analysis of the Long-Period Stacking-Ordered Phase by Using Molecular Dynamics Simulations: Kink Deformation under Compression and Kink Boundary Migration under Tensile Strain

Mg基LPSO相単結晶におけるキンク帯形成の転位-結晶塑性シミュレーション

In this study, two-dimensional FE simulations for a single crystal of a Mg-based LPSO phase are performed to computationally reproduce a deformation kink in the LPSO phase using a dislocation-based crystal plasticity model for HCP crystals developed in our previous work. We take account of activities of only basal slip systems of which CRSSes are set to be consistent with the experimental results on the LPSO phase. In addition, the characteristic shape of the LPSO crystal caused by preferential growth along the a-axis is introduced into the specimen. Since we need to consider some initial imperfection to numerically express a buckling phenomenon such as the deformation kink, we assume a small inclination of the basal plane for the loading direction as the initial crystal orientation. Moreover, we apply rmin method for the slip increment to the analysis for stability of calculation. As a result of this simulation, we predict the kink band formation computationally through the accumulation of GN dislocation, disclination and the crystal lattice rotation. The validity of the present model is discussed by comparing obtained results with a well-known explanation for kink formation based on dislocation behaviors qualitatively. Then we conclude that the kink band is rapidly formed by localized basal slips.

G0100201 回位双極子を用いたキンク変形理論と応力解析

Kink deformation bands appearing in compressed specimens of Mg alloy with long-period stacking ordered structure (LPSO) are thought to contribute to improving their mechanical properties. Accordion kink (AK) is considered as the main body of ridge-shaped kink structure (RSKS) which has been observed in layered solids such as metal alloy, muscovite aggregate, geological strata and so on. In this work, we will build mechanical analysis model of AK in finite body based on disclination dipoles in simply-supported boundary condition, and solve the boundary value problem using the approach. The influence of the interval of AK to the stress field in finite body will be discussed in details. The relationship between energy (including strain energy and boundary energy) and intervals of AK will be calculated. The simulation results show that with the extending of intervals of AK, the strain energy increases monotonically. Meanwhile the total area of kink boundary decreases, which effect the variety of boundary energy obviously.

In-Situ Observation on the Formation Behavior of the Deformation Kink Bands in Zn Single Crystal and LPSO Phase

In-Situ Observation on the Formation Behavior of the Deformation Kink Bands in Zn Single Crystal and LPSO Phase

Crystallographic nature of deformation bands shown in Zn and Mg-based long-period stacking ordered (LPSO) phase

Formation of curious deformation bands has been reported as one of the deformation mechanisms occurring in an Mg-based long-period stacking ordered (LPSO) phase. The origin of the deformation band is still unknown, and the possibility of the deformation kink band and/or the deformation twin has been discussed. To clarify this, the crystallographic nature of deformation bands formed in the LPSO phase was examined by scanning electron microscope–electron backscatter diffraction (SEM-EBSD) pattern analysis. The results were compared to those of the deformation kink bands formed in hcp-Zn and deformation twins formed in hcp-Mg polycrystals. The deformation bands in the LPSO phase was confirmed not to exhibit a fixed crystal orientation relationship with respect to the matrix, different from the case shown in the deformation twin. Instead, the deformation band in the LPSO phase showed three arbitrariness on its crystallographic nature: an ambiguous crystal rotation axis that varied on the [0 0 0 1] zone axis from band to band; an arbitral crystal rotation angle that was not fixed and showed relatively wide distributions; and a variation in crystal rotation angle depending on the position even within a deformation band boundary itself. These features were coincident with those observed in the deformation bands formed in Zn polycrystals, suggesting that the formed deformation bands in LPSO phase crystals are predominantly deformation kink bands.

INTERACTING TILT AND KINK INSTABILITIES IN REPELLING CURRENT CHANNELS

We present a numerical study in resistive magnetohydrodynamics where the initial equilibrium configuration contains adjacent, oppositely directed, parallel current channels. Since oppositely directed current channels repel, the equilibrium is liable to an ideal magnetohydrodynamic tilt instability. This tilt evolution, previously studied in planar settings, involves two magnetic islands or fluxropes, which on Alfvenic timescales undergo a combined rotation and separation. This in turn leads to the creation of (near) singular current layers, posing severe challenges to numerical approaches. Using our open-source grid-adaptive MPI-AMRVAC software, we revisit the planar evolution case in compressible MHD, as well as its extension to 2.5D and full 3D scenarios. As long as the third dimension remains ignorable, pure tilt evolutions result which are hardly affected by out of plane magnetic field components. In all 2.5D runs, our simulations do show secondary tearing type disruptions throughout the near singular current sheets in the far nonlinear saturation regime. In full 3D, both current channels can be liable to additional ideal kink deformations. We discuss the effects of having both tilt and kink instabilities acting simultaneously in the violent, reconnection dominated evolution. In 3D, both the tilt and the kink instabilities can be stabilized by tension forces. As a concrete space plasma application, we argue that interacting tilt-kink instabilities in repelling current channels provide a novel route to initiate solar coronal mass ejections, distinctly different from currently favored pure kink or torus instability routes.

THE DYNAMICS OF FUNNEL PROMINENCES

We present numerical simulations in 2.5D settings where large scale prominences form in situ out of coronal condensation in magnetic dips, in close agreement with early as well as recent reporting of `funnel prominences'. Our simulation uses full thermodynamic MHD with anisotropic thermal conduction, optically thin radiative losses, and parametrized heating as main ingredients to establish a realistic arcade configuration from chromosphere to corona. The chromospheric evaporation from especially transition region heights ultimately causes thermal instability and we witness the growth of a prominence suspended well above the transition region, continuously gaining mass and cross-sectional area. Several hours later, the condensation has grown into a structure connecting the prominence-corona transition region with the underlying transition region, and a continuous downward motion from the accumulated mass represents a drainage that matches observational findings. A more dynamic phase is found as well, with coronal rain, induced wave trains, and even a reconnection event when the core prominence plasma weighs down the fieldlines until a fluxrope gets formed. The upper part of the prominence is then trapped in a fluxrope structure, and we argue for its violent kink-unstable eruption as soon as the (ignored) length dimension would allow for ideal kink deformations.

141 金属微視組織中に形成されるキンク変形の回位多重極子と連続分布転位モデルによる検討(材料力学・機械材料)

141 金属微視組織中に形成されるキンク変形の回位多重極子と連続分布転位モデルによる検討(材料力学・機械材料)

Variable-Length Link-Spring Model of Wire-Bonding Looping Process

Looping is a key technology in modern thermosonic wire bonding. To provide insight into the loop formation mechanism, a variable-length link-spring (VLLS) model is proposed. In this model, the wire segments and moment balance equations at the opening end of the wire are dynamically added during the capillary upward movement stage, to simulate the wire feeding and kink formation process. The complete looping process is analyzed by solving nonlinear equations iteratively and using Newton's method. Using this model, the wire profile evolution process and kink number, position, and deformation during looping are obtained and verified by experimental results. The effects of the upward loop trace parameters (reverse motion and kink height parameters) on the final loop profile are studied. The results show that the VLLS model, which considers the upward loop trace, is more suitable for looping process analysis.

Crystallographic classification of kink bands in an extruded Mg–Zn–Y alloy using intragranular misorientation axis analysis

Within extruded Mg89Zn4Y7 (at.%) alloys containing a long period stacking ordered (LPSO) phase a unique deformation mode referred to as “kink deformation” is found to occur within the LPSO phase grains, forming kink bands that are each represented by an array of geometrically necessary dislocations. Intragranular misorientation axis (IGMA) analysis suggests that this kink deformation results in lattice rotation predominately about the 〈11¯00〉,〈01¯10〉,〈0001〉, and 〈12¯10〉 axes of the 18R-type LPSO structure. IGMA analysis is based on slip-induced lattice rotation and determination of its rotation axis (Taylor axis). Therefore, it is possible to determine the dominant slip mode in a grain that is deformed by matching the Taylor axis for a given slip system to its experimentally obtained IGMA distribution. In this study the strong preference of 〈11¯00〉and〈01¯10〉 Taylor axes suggests that kinking occurs through a basal 〈a〉 slip mode. The 〈0001〉 Taylor axes suggest that kink bands form through a prismatic 〈a〉 slip mode. These axes are categorized as “principal rotation” axes, which result from one Burgers vector of dislocations. Kink bands with a 〈12¯10〉 Taylor axis are produced through combination of basal 〈a〉 slip variants. This axis is categorized as a “combination-type rotation” axis, which results from more than one Burgers vector of dislocations. It is concluded that IGMA analysis can be effectively used to study and geometrically classify kink bands.

Plastic strain heterogeneities in an Mg–1Zn–0.5Nd alloy

The distribution of plastic strain, both intergranular and intragranular, has been evaluated using digital image correlation on a tensile-deformed Mg–1Zn–0.5Nd alloy. The intergranular strain distribution is sensitive to both the orientation of the grains and the orientations of neighbouring grains. Large intragranular strain gradients were observed close to some grain boundaries. These high levels of local strain were seen to correlate to the operation of additional slip and/or twin systems close to grain boundaries, deformation kinking and/or grain boundary sliding.

Micro-Kinking of the Long-Period Stacking/Order (LPSO) Phase in a Hot-Extruded Mg<sub>97</sub>Zn<sub>1</sub>Y<sub>2</sub> Alloy

Microstructures of a hot-extruded Mg97Zn1Y2 alloy containing the long-period stacking/order (LPSO) phase have been investigated by transmission electron microscopy (TEM), particularly focusing on kink-deformed LPSO crystals. It is found that kink-deformation in the LPSO phase grains are mostly characterized by singular straight interfaces across which the host crystals are sharply bended, as being similar to those reported previously. In addition to these common LPSO phase kink-bands, we occasionally find unique microscopic traces at the kink-boundaries, which are composed of multiply segmented kink-interfaces that are sequentially rotated with small angles in a same direction, accomplishing a macroscopic large crystalline bend; i.e., a micro-kinking feature. Occurrence of such micro-kinking may hardly be explained by generation of dipole-pair dislocations in the early stage of kinking, which have been successfully used for phenomenological understanding of kink deformation.

Activation Free Energy of Nucleation of a Dislocation Pair in Magnesium

Kink deformation is one of the possible principal deformation modes of alloys with a long-period stacking ordered structure under compression parallel to the basal plane. In this deformation, dislocation pairs are massively nucleated, and these dislocations align in a line to form kink bands. In this study, we investigated the nucleation of a dislocation pair in a pure magnesium single crystal by molecular dynamics simulations. We also evaluated the activation free energy of nucleation of a dislocation pair and investigated the dependence of the activation free energy on the applied shear stress and temperature. [doi:10.2320/matertrans.MI201213]

OS0418 LPSO型Mg多結晶合金のキング変形に関する転位-結晶塑性FEM解析

OS0418 LPSO型Mg多結晶合金のキング変形に関する転位-結晶塑性FEM解析

W012001 シンクロ型LPSO相におけるキンク変形帯の結晶学的特徴(【W01200】シンクロ型LPSO構造の力学特性と高強度Mg合金の変形機構(その2),計算力学部門企画,ワークショップ)

W012001 シンクロ型LPSO相におけるキンク変形帯の結晶学的特徴(【W01200】シンクロ型LPSO構造の力学特性と高強度Mg合金の変形機構(その2),計算力学部門企画,ワークショップ)

OS0413 LPSO相, HCP結晶におけるキンク変形の実験的考察

The deformation behavior accompanied by the formation of deformation kink in synchronized LPSO-phase was examined by comparing the behavior in the hcp-Zn single crystal. Deformation process of the LPSO phase DS crystal accompanied by the formation of deformation kink was investigated by dynamical observation and the features were compared to that in Zn single crystal. In both crystals the formation of deformation kink bands were confirmed in specimens that were compressed along the direction parallel to the basal plane. The characteristic features of the deformation kink band showed many similarities in them.

Effect of final rolling reduction on the microstructure and mechanical properties of Mg–Gd–Y–Zn–Zr alloy sheets

The Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt.%) alloy was hot rolled with different final rolling reductions at 400°C. The microstructure evolution and texture of the sheets were analyzed, and their effect on the mechanical properties was discussed. All of the rolled sheets consist of fine dynamically recrystallized grains with almost random orientation, large deformed grains with strong basal texture. In addition, bent lamellar-shaped long period stacking ordered (LPSO) phases due to kink deformation were observed in the deformed grains. The volume fraction of the dynamic recrystallization increased with increasing final rolling reduction and the basal texture weakened gradually. The strength of the alloy sheets changed a little with increasing final rolling reduction, while the yield anisotropy and the ductility were significantly improved. The sheet final-rolled with thickness reduction of 60% exhibits tensile yield strength of 306MPa, ultimate tensile strength of 393MPa and elongation to failure of 14.6% at ambient temperature, and tensile yield strength of 264MPa, ultimate tensile strength of 345MPa and elongation to failure of 19.4% at 250°C.

Effect of Capillary Trace on Dynamic Loop Profile Evolution in Thermosonic Wire Bonding

Thermosonic wire bonding remains the most commonly used interconnection technology in microelectronic packaging, and looping is an important aspect in modern wire bonders. To identify the loop formation mechanism, the effect of capillary trace on the standard wire looping process was studied. Dynamic looping processes with different capillary trace parameters and reverse motions of 4, 8, and 16 mil were recorded by a high-speed camera. The capillary trace and wire profile evolution were obtained from the looping videos using a digital image processing program, and the relationship between capillary trace and loop profiles was analyzed. A finite-element model was established to study the strain distribution on wire during looping. Experimental and simulation results show that the wire profile of the standard loop is mainly affected by capillary position and is not sensitive to capillary velocity. The upward capillary trace mainly affects the loop configuration, including the number, position, and deformation of kinks and the loop length. The downward capillary trace affects the stress states, loop height, kink deformation, and loop profiles. A kink is the wire with the largest local curvature, and it is a plastically deformed wire segment with little elastic core. The kink has two functions: 1) shaping the loop and 2) isolating the pulling force on the first bond and neck caused by capillary movement. This paper can be of great help in loop profile optimization in the industry and in academic research of loop dynamics.