Local Wrinkling Research Articles

Wrinkled flames and geometrical stretch

Localized wrinkles of thin premixed flames subject to hydrodynamic instability and geometrical stretch of uniform intensity (S) are studied. A stretch-affected nonlinear and nonlocal equation, derived from an inhomogeneous Michelson-Sivashinsky equation, is used as a starting point, and pole decompositions are used as a tool. Analytical and numerical descriptions of isolated (centered or multicrested) wrinkles with steady shapes (in a frame) and various amplitudes are provided; their number increases rapidly with 1/S>0. A large constant S>0 weakens or suppresses all localized wrinkles (the larger the wrinkles, the easier the suppression), whereas S<0 strengthens them; oscillations of S further restrict their existence domain. Self-similar evolutions of unstable many-crested patterns are obtained. A link between stretch, nonlinearity, and instability with the cutoff size of the wrinkles in turbulent flames is suggested. Open problems are evoked.

Formation mechanism of graphene layers on SiC (0001¯) in a high-pressure argon atmosphere

Graphene layers were grown on a C-terminated SiC (000$\overline{1}$) surface in a high-pressure Ar atmosphere. Their growth mechanism was investigated using high-resolution transmission electron microscopy (TEM). First at a low temperature, local areas of SiC surface are decomposed, and several layers of graphene nucleus are formed in the resulting craters. Then graphene layers grow in all directions laterally, keeping their number of layers invariant. These results indicate that control of the number of graphene layers require precise control of the first stage of decomposition. After the graphene layers cover the surface completely, SiC decomposition occurs at a higher temperature along the [0001]${}_{\mathit{SiC}}$ direction, and the number of graphene layers increase. The formation of local wrinkles accompanies the increase of the number of layers. In addition we propose that the formation mechanism strongly affects the rotational stacking, which is characteristic of multilayer graphene on the C-face of SiC.

Hot-Stamping Process Simulation and Optimize Research for Collision Beam of Automobile Door

Hot-stamping molding for ultra-high-strength steel have some similarities with traditional cold-stamping molding in the aspects of molding process and die design. But due to the effect of temperature variation of blank, hot-stamping have some differences in ultra-high-strength products design, material selection and forming process design. Some special forming defects, such as local thinning, cracking and wrinkling, could appear in hot-stamping process due to these differences. In order to obtain uniform phase structure and get high-quality products, it is very important to be able to predict and control the blank temperature and the consistence of blank cooling rate. The thermo-mechanical characteristics of hot-stamping are studied with the material of ADVANCE1500 (22SiMnTiB). Based on the results of simulations and experiments, conclusion are drawn that the complexity of the product and the blank which contacts with die asynchronously causes the uneven distribution of the blank temperature. This is the key factor that leads to the poor mobility of the blank material and local thinning, cracking, wrinkling and other defects in forming process. Proper clearance between punch and die can reduce the probability of defects which could contribute to the improvement of hot-stamping process.

Estimating Posture-Recognition Performance in Sensing Garments Using Geometric Wrinkle Modeling

A fundamental challenge limiting information quality obtained from smart sensing garments is the influence of textile movement relative to limbs. We present and validate a comprehensive modeling and simulation framework to predict recognition performance in casual loose-fitting garments. A statistical posture and wrinkle-modeling approach is introduced to simulate sensor orientation errors pertained to local garment wrinkles. A metric was derived to assess fitting, the body-garment mobility. We validated our approach by analyzing simulations of shoulder and elbow rehabilitation postures with respect to experimental data using actual casual garments. Results confirmed congruent performance trends with estimation errors below 4% for all study participants. Our approach allows to estimate the impact of fitting before implementing a garment and performing evaluation studies with it. These simulations revealed critical design parameters for garment prototyping, related to performed body posture, utilized sensing modalities, and garment fitting. We concluded that our modeling approach can substantially expedite design and development of smart garments through early-stage performance analysis.

Spontaneous Formation of Periodic Nanostructures by Localized Dynamic Wrinkling

Micro/nanoscale periodic structures are widely used in display, optics and bio industries as key functional elements. We present a novel nanopatterning method, localized dynamic wrinkling (LDW), which creates micro/nanoscale metal gratings continuously by simply sliding a flat edge of a hard material over a thin metal surface coated on a polymer layer. The LDW process presented in this paper is an etching- and template-free nanopatterning technology based on nanoscale wrinkling phenomenon. This simple process enables spontaneous formation of large-area metal gratings with controllable periodicity from micrometer down to 120 nm.

A theory for nonlinear soft webs

In this paper, a fundamental theory for deformable webs not resisting any compressive membrane forces is developed through a direct derivation on the deformed configuration. In order to better describe the deformable webs, the classification of deformable webs is presented. A theory for the non-continuum elastic network webs consisting of many deformable cables is presented from the deformable cable theory, and then a theory for fabric deformable webs without relative sliding is developed as well. Finally, a nonlinear theory for continuous deformable webs is presented on the deformed configuration. The local criteria for the existence of such deformable webs are presented through the definitions, and such criteria are very significant for the wrinkling stability of the deformable webs. A deformable web possessing the local wrinkling is an unsolved problem in numerical computations. The theory for fabric webs with relative motions needs to be further developed. Herein the fundamental theory for deformable webs is presented only, and numerical examples will be presented in sequel. Such a theory of deformable webs can be applied to textile or other soft materials and bio-membranes.

접힌자국이 있는 멤브레인에서 두께에 따른 주름거동의 변화

본 논문에서는 코너에서 대각선방향으로 인장하중을 받고 있는 접힌자국이 있는 사각형 멤브레인에서 두께가 주름 거동에 미치는 영향을 기하학적 비선형 후좌굴 유한요소해석을 통하여 연구하였다. 멤브레인은 쉘 요소로 모델링 하였고 좌굴을 발생시키기 위하여 면외방향으로 미소의 무작위성 기하학적 결함을 메쉬에 가하였다. 해석은 접히지 않은 원멤브레인과 수직방향으로 접힌 멤브레인에 대해 수행하였고 그 결과를 비교하였다. 해석결과 멤브레인의 두께가 감소함에 따라 주름의 발생과 성장을 크게 촉진함을 알 수 있었다. 또한 접힌 자국의 초기 전개각이 증가할수록 국부주름의 낮은 하중에서 발생하였으나 전역주름으로의 성장은 지연되는 경향을 보였다. In this paper, the thickness effect on the wrinkle-crease interaction behavior of corner-loaded creased square membranes was studied using geometrically nonlinear post-buckling analysis. The membranes were modeled using shell elements, and the meshes were seeded with semi-random geometrical imperfection to instigate the buckling deformation. Results indicated that the wrinkle-crease interaction behavior was significantly dependent on the membrane thickness. Both the global and local wrinkles developed earlier as the thickness decreased. It was also found that the wrinkling behavior depended on the initial deployment angle in which the local wrinkle initiation occurred earlier, while the global wrinkle formation was delayed as the angle increased.

Formulas for Rupture, Necking, and Wrinkling of Oil Country Tubular Goods Under Combined Loads

SummaryAdvanced well-design methods based on risk assessment of actual failure mechanisms require accurate formulas for burst, collapse, yield, and fracture. Moreover, these strength formulas should be generalized to account for the combined internal pressure, external pressure, and axial load that well tubulars experience.This paper describes the development of a set of formulas for burst strength [i.e., the failure envelope and the design limit for oil country tubular goods (OCTG) under internal overpressure and any axial tension or axial compression]. Phenomena covered are ductile rupture, pipe necking, and local pipe-wall wrinkling, thus spanning the first and second quadrant in the effective-axial-load/pressure-differential-load space.This set of formulas is based on a large-strain, elastic/plastic, &amp;lt;3D&amp;gt; formulation of pipe equilibrium, deformation, and buckling that has been solved analytically in closed form for the situation of combined loads. The formulas describe features such as a maximum internal-pressure load (rupture), a maximum axial-tension load (necking), and local buckling of a pipe under axial compression (wrinkling).Approximate burst-strength formulas are presented that together span the entire axial-load range and closely match the more complex, exact model predictions.The joint American Petroleum Institute/International Organization for Standardization SC5 Work Group 2B (API/ISO SC5 WG2B) tasked with modernizing the API 5C3 property equations has incorporated the approximate burst-strength formulas presented in this paper into the new ISO TR 10400/API TR 5C3 document (API 2008; ISO 2007).

Orientational ordering of buckling-induced microwrinkles on soft substrates

Orientational order in buckling-induced microwrinkles of elastic membranes on soft substrates is investigated both theoretically and experimentally. Anisotropic orientational correlation in wrinkles induced by isotropic compression is characterized using an orientational order parameter, and is explained by an effective elastic free energy that suppresses Gaussian curvature. We find that orientationally correlated domains tend to extend in ± 45° directions from the local wrinkle orientation. Excellent agreement is obtained between numerical, theoretical, and experimental results.

Numerical Investigation of Tearing Fracture of Wrinkled Pipe

Steel pipelines, buried in cold regions, often respond to thermal strains and/or geotechnical movement caused by factors such as thaw settlement, frost heave, and slope instability. These complex field conditions can impose large displacements on these pipelines, resulting in localized wrinkles well into the plastic range of the pipe material. Eventually, there is a possibility of a fracture occurring at a wrinkled location under continuous deformation. A recent field fracture and a failed laboratory specimen have been observed within a telescopic wrinkle under tearing action and the loading histories have been found to be monotonic, without significant strain reversals. These incidents underscore the need for a detailed investigation, which seeks to answer fundamental questions regarding this unique mode of failure. In this study, a finite element model has been developed, which is capable of accounting for material nonlinearity effects, large displacements, large rotations, initial imperfections, and possible complex contact surfaces. Based on limited test data, the comparison of the numerical and the experimental results demonstrates the ability of the present model to predict the local buckling behavior of pipes when deformed well into the postwrinkling range. The results of this analytical work include the global and local deformation patterns and a detailed assessment of the stress-strain relations at the region of the telescopic wrinkle. The results obtained from this study have recognized the occurrence of strain reversal at the sharp fold of the wrinkle on the compression side of the pipe, a phenomenon that could be considered to be the key factor for triggering this unique failure mechanism.

접힌 자국이 있는 멤브레인의 주름 거동 해석

본 논문에서는 수직방향으로 접은 사각형 멤브레인의 주름 거동을 기하학적 비선형 후좌굴 해석을 사용하여 연구하였다. 멤브레인은 쉘 요소로 모델링 하였고 하중은 멤브레인의 코너에서 대각선 방향으로 가하였다. 해석에는 다양한 각도의 초기 전개각을 가지는 멤브레인을 고려하였고 접힌 자국이 없는 경우에 대해서도 해석을 수행하여 그 결과를 비교하였다. 해석결과 주름은 큰 코너하중이 가해진 지역에서 국부적으로 발생하였는데, 이 국부 주름은 하중 비의 증가에 따라 점차 성장하여 전역 주름으로 발전하였다. 또한 주름의 발생 및 성장 거동은 접힌 자국의 초기 전개각에 좌우되는 경향을 보였다. In this paper, the wrinkling behavior of vertically creased corner-loaded square membranes was studied using geometrically nonlinear post-buckling analysis. The membranes were modeled using shell elements, and the meshes were seeded with semi-random geometrical imperfection to instigate the buckling deformation. A pristine and creased membranes with various initial deployment angles were considered in the analyses and the results were compared. Results showed that local wrinkles initiated near the corner where the higher load was applied, which grew to form a single diagonal global wrinkle as the load ratio increased. It was also found that the local wrinkle initiation and the global wrinkle formation were significantly dependent on the initial deployment angles.

A study on the thermomechanical behavior of semiconductor chips on thin silicon substrate

This study is concerned with the deformation or warping behavior of thin layered semiconductor structure comprising a silicon substrate, a pattern layer and a polyimide coating layer with its thickness varying from 100um to 50 um. In contrast with the conventional thick semiconductor structure, today’s semiconductor structure is increasingly thin and therefore the warping is extremely conspicuous, being among the major concerns in the structural design of a chip. In the view of thermomechanical analysis of an extremely thin layer structure considered in the present paper, a few parameters on the deformation should be taken into consideration such as the pattern layer and intrinsic stress. To account for the effect of the pattern layer, we make a well educated guess for the mechanical properties, employing the test results and the CBA (Composite Beam Analysis) theory. In addition, we take into consideration the effect of the intrinsic stress due to moisture absorption on deformation. We show that the chip warpage is accurately predicted when all these are properly considered. Furthermore, we have found that the local instability or wrinkling, associated with the nonuniformity or the inhomogeneity in material properties and bonding quality between any two neighboring layers, appears as one important mode of energy relaxation in addition to the overall warpage when the chip thickness becomes very small.

Finite-element analysis of tubular fabric beams including pressure effects and local fabric wrinkling

Pressurized beams made from synthetic fibers that are woven or braided into a circular cross-section are used as main load-carrying members in a variety of terrestrial and space structures. This paper focuses on the development of a Timoshenko beam finite element for the nonlinear load–deflection analysis of pressurized fabric beams, and the numerical examination of the effect of pressure on beam load–deflection behavior. The basis of the element formulation is an incremental virtual work expression that explicitly includes the work done by pressure under deformation-induced volume changes. The inability of the fabric to carry significant compressive stress is accommodated with a nonlinear moment–curvature relationship. Details of the element development and solution methodology are provided. Parametric studies that demonstrate the importance of including work done by pressure and wrinkling-induced moment–curvature nonlinearity in the formulation are described. These studies indicate that not only does beam stiffness increase with inflation pressure, but work done by pressure increases the beam bending capacity well beyond the theoretical limiting value. Further, accurate prediction of the nonlinear load–displacement response requires the inclusion of work done by pressure due to both shear and bending deformations.

Implication of Nonclassical Effects on Dynamic Response of Sandwich Structures Exposed to Underwater and In-Air Explosions

A study devoted to the dynamic response of sandwich panels to underwater and in-air explosions is presented. The study is carried out in the context of a geometrically nonlinear model of sandwich structures featuring anisotropic laminated face sheets and a transversely compressible orthotropic core. The unsteady pressure generated by the explosion and acting on the face of the sandwich panel includes the effect of the pressure wave transmission through the core. Its implications on the structural time-histories as corresponding to the underwater and in-air explosions are put into evidence. The effects of the transverse core compressibility on dynamic response are highlighted. In this sense, one of its major implications is the possibility to capture interactively the global and local (wrinkling) dynamic response of the panel. It is shown that implementation of the structural tailoring technique in the face sheets can constitute an important mechanism for enhancing the dynamic load-carrying capacity of sandwich panels when exposed to blast pulses. Effects of the core, the composite architecture of face sheets, orthotropy of the material of the core, geometrical non-linearities, initial geometric imperfection, and the damping ratio are investigated, and their implications for the dynamic response are highlighted. The comprehensive structural model considered in conjunction with the time-dependent loads generated by the underwater and in-air explosions, and the results obtained in this context, are expected to contribute to a better understanding of the response behavior and to be instrumental toward a better design of these structures.

A simulation-based design parameter study in the stamping process of an automotive member

Abstract This paper is concerned with the quantitative effect of design parameters on a stamped part of the autobody. The considered parameters in this paper are the blank holding force, the draw-bead force and the blank size, which greatly affect the metal flow during stamping. The indicators of formability selected in this paper are failures such as tearing, wrinkling and the amount of springback. The stamping process of the front side inner member is simulated using the finite element analysis changing the design parameters. The numerical results demonstrate that the blank holding force cannot control the local metal flow during forming although it controls the overall metal flow. The modification of the initial blank size considering the punch opening line ensures the local wrinkling and reduces the amount of springback after forming. The restraining force of draw-bead controls the metal flow in the local area and reduces the amount of excess metal. It is noted that the parametric study of design parameters such as blank holding force, the blank size and the draw-bead are very important in the process design of the complicated member.

A real-time cloth draping simulation algorithm using conjugate harmonic functions

This paper describes a simplified mathematical model and the relevant numerical algorithm that simulates a draped cloth over a virtual human body. The proposed algorithm incorporates an elliptical, or non-consecutive, method to simulate the cloth wrinkles on moving bodies without having to reference the results of past drape simulation time steps. A global-local analysis technique was employed to decompose the drape of a cloth into large-scale deformation and local wrinkles. The large-scale deformation is determined directly by the rotation and translation of body parts to generate a wrinkle-free yet globally deformed shape of the cloth. The local wrinkles are calculated by solving simple elliptical equations based on the orthogonality between conjugate harmonic functions. The large-scale deformation and the local wrinkles are then superposed to simulate the draped cloth. The elliptical equations used to simulate the local wrinkles require no interpolative time frames, even for rapidly moving virtual bodies. Avoiding the incremental approach of time integration used in conventional methods, the proposed method yields markedly enhanced computational efficiency as well as enhanced simulation stability.

Multiscale dynamics of an interacting sheet by a bond‐fluctuating Monte Carlo simulation

AbstractThe conformation and dynamics of sheets with attractive and repulsive node–node interactions (nn) are examined in an effective solvent medium using Monte Carlo simulations. A bond‐fluctuating coarse grained description is used to model the sheet by a set of nodes (N) tethered together by flexible bonds in a planar structure with linear scale Ls = 16–64, N = L on a cubic lattice with characteristic dimensions of L3 = 643–2003. Variations of the mean square displacement of the center of mass of the sheet (R) and that of its center node (R) and radius of gyration (Rg) of the sheet with the time step (t) are analyzed to characterize the nature of its global motion, segmental dynamics, and conformational relaxation at a low (T = 2) and a high (T = 10) temperature with the range (r = √8) of interaction nn = 1, –1. We find that sheets achieve their global diffusive motion, that is, R ∝ t, in the long‐time (asymptotic) regime while their segmental dynamics exhibits a range of power‐law behavior R ∝ tν with ν = 1/4−1 from short to long‐time regimes. The magnitude of the exponent ν and their crossover (and relaxation) from one power‐law to the next depend on temperature, interaction, and molecular weight N of the sheet. The radius of gyration of the sheet relaxes well to its equilibrium with its distinct patterns of expansion (swelling with relatively stiffer bonds (nn = 1)) and contraction (crumpling with nn = −1). Both the relaxation time and the rate of change of Rg depends on N, Ls, and T. Data for the equilibrium value of the gyration radius scale with its size Rg ∝ N1/2 suggesting that sheets remain nearly flat with localized wrinkles and crumpling.© 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2512–2523, 2006

Formability of tube hydroforming under various loading paths

Finite-element simulations of the tube hydroforming process with rectangular dies are carried out for various loading paths, and the reasons why the loading paths of the so-called pressure advanced type, in which the hydraulic pressure is raised to a certain magnitude in advance of the axial pushing, are effective to obtain good formability are investigated in detail. It is clarified that, in the early stage of the deformation process by the pressure advanced type, the growth of local wrinkling is prevented and the effect of axial pushing from the tube ends is attained at the whole part in the axial direction. Consequently the desirable biaxial stress condition of the circumferential tensile and longitudinal compressive stresses is obtained in the subsequent stages, thus achieving large expansion without the occurrence of local wrinkling and local thinning.

Analytical Study of Bifurcation and Nonlinear Behavior of Sandwich Columns

Buckling behavior of axially compressed sandwich columns exhibits a variety of interesting phenomena. The column can buckle in a long wave “overall mode” or a short-wave “wrinkling mode,” the latter involving severe bending of the facings and transverse deformation of the core. The full-range nonlinear behavior of these structures is investigated in the elastic range taking typical examples. Columns can be, though not always, imperfection sensitive when wrinkling is the principal mode of buckling. The columns buckling in the overall mode collapse by the formation of localized wrinkles in the postbuckling range. An interesting new finding of this study is that, for certain combinations of core compliance and facing thickness, there can be a bifurcation from the prebuckling path at a load smaller than that predicted by the linear stability analysis. In this scenario, if wrinkling is the dominant mode of buckling, the column turns out to be imperfection sensitive.

해석적인 방법을 이용한 복잡한 형상의 자동차 부재 스탬핑 공정에서의 주요 설계인자 연구

This paper is concerned with the quantitative effect of design parameters on a stamped part of the auto-body. The considered parameters in this paper are the blank holding force, the draw-bead force, the blank size which greatly affect the metal flow during stamping. The indicators of formability selected in this paper are failures such as tearing, wrinkling and the amount of springback. The stamping process of the front side inner member is simulated using the finite element analysis changing the design parameters. The numerical results demonstrate that the blank holding force cannot control the local metal flow during forming although it controls the overall metal flow. The modification of the initial blank size considering the punch opening line ensures the local wrinkling and reduces the amount of springback after forming. The restraining force of draw-bead controls the metal flow in the local area and reduces the amount of excess metal. It is noted that the parametric study of design parameters such as blank holding force, the blank size and the draw-bead are very important in the process design of the complicated member.