Formation Of Creases Research Articles

Mechanical positional information guides the self-organized development of a polygonal network of creases in the skin of mammalian noses.

The glabrous skin of the rhinarium (naked nose) of many mammalian species exhibits a polygonal pattern of grooves that retain physiological fluid, thereby keeping their nose wet and, among other effects, facilitating the collection of chemosensory molecules. Here, we perform volumetric imaging of whole-mount rhinaria from sequences of embryonic and juvenile cows, dogs, and ferrets. We demonstrate that rhinarial polygonal domains are not placode-derived skin appendages but arise through a self-organized mechanical process consisting of the constrained growth and buckling of the epidermal basal layer, followed by the formation of sharp epidermal creases exactly facing an underlying network of stiff blood vessels. Our numerical simulations show that the mechanical stress generated by excessive epidermal growth concentrates at the positions of vessels that form rigid base points, causing the epidermal layers to move outward and shape domes-akin to arches rising against stiff pillars. Remarkably, this gives rise to a larger length scale (the distance between the vessels) in the surface folding pattern than would otherwise occur in the absence of vessels. These results hint at a concept of "mechanical positional information" by which material properties of anatomical elements can impose local constraints on an otherwise globally self-organized mechanical pattern. In addition, our analyses of the rhinarial patterns in cow clones highlight a substantial level of stochasticity in the pre-pattern of vessels, while our numerical simulations also recapitulate the disruption of the folding pattern in cows affected by a hereditary disorder that causes hyperextensibility of the skin.

Thin-Film Buckling Theory and Clinical Application of the Mechanism of Double Eyelid Formation.

The mechanism underlying the formation of upper eyelid creases has been the subject of extensive study and ongoing debate. This research aims to elucidate the principles of upper eyelid creases formation, leveraging the membrane bending theory from engineering mechanics. We developed an anatomical model of the eyelid and implemented the finite element analysis. Preprocessing and mesh division were conducted using HyperMesh, followed by computational analysis with Abaqus. This approach enabled the observation of dynamic changes in the upper eyelid during eye opening and closing. The study reveals that natural upper eyelid crease formation is influenced by multiple factors. These include the softer texture of the upper eyelid skin and the suborbicularis oculi fat, reduced rigidity at the eyelid crease, optimal contraction force of the upper eyelid, and the strategic placement of the pre-tarsal fat pad just above the eyelid crease. Ultimately, our findings demonstrate the effectiveness of finite element analysis, grounded in membrane bending theory, in elucidating the dynamics of upper eyelid crease formation. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Computational Fluid Dynamics Modeling of Concrete Flows in Drilled Shafts

Drilled shafts are cylindrical, cast-in-place concrete deep foundation elements. During construction, anomalies in drilled shafts can occur due to the kinematics of concrete, flowing radially from the center of the shaft to the concrete cover region at the peripheral edge. This radial component of concrete flow develops veins or creases of poorly cemented or high water-cement ratio material, as the concrete flows around the reinforcement cage of rebars and ties, jeopardizing the shaft integrity. This manuscript presents a three-dimensional computational fluid dynamics (CFD) model of the non-Newtonian concrete flow in drilled shaft construction developed using the finite volume method with interface tracking based on the volume of fluid (VOF) method. The non-Newtonian behavior of the concrete is represented via the Carreau constitutive model. The model results are encouraging as the flow obtained from the simulations shows patterns of both horizontal and vertical creases in the concrete cover region, consistent with previously reported field and laboratory experiments. Moreover, the flow exhibits the concrete head differential developed between the inside and the outside of the reinforcement cage, as exhibited in the physical experiments. This head differential induces the radial component of the concrete flow responsible for the creases that develop in the concrete cover region. Results show that the head differential depends on the flowability of the concrete, consistent with field observations. Less viscous concrete tends to reduce the head differential and the formation of creases of poorly cemented material. The model is unique, making use of state-of-the-art numerical techniques and demonstrating the capability of CFD to model industrially relevant concrete flows.

On the effect of the poisson’s ratio on samples subjected to shearing

The effect of shearing on finite-sized auxetic and non-auxetic samples was examined through finite element simulations. It was shown that when shear was applied in a manner representative of a common shear-testing setup, which is not dissimilar to the situation encountered in sports applications, auxetics manifested very different characteristics compared to their non-auxetic counterparts; with very pronounced edge effects. These included extensive lateral expansion of the samples and the formation of non-insignificant concave creases on their exposed lateral faces. It was shown that these creases became even more pronounced when the samples were subjected to combined shear and compressive loads and need to be taken into consideration when assessing the suitability, or otherwise, of auxetics for practical applications where shear loading may be present to a certain extent.

Formation of surface wrinkles and creases in constrained dielectric elastomers subject to electromechanical loading

This paper investigates issues that have arisen in experimental and theoretical studies of the stability of a dielectric elastomeric layer bonded to a stiff substrate and subject to a voltage difference across the top and bottom conducting surfaces of the layer. The role of equi-biaxial pre-stretch of the layer prior to bonding to the substrate is a central factor in the investigation. The focus is the competition between wrinkling and creasing and how this competition is affected by pre-stretch. A finite element model of the system is employed to generate wrinkling bifurcation and advanced post-bifurcation solutions in the form of localized modes, either crease-like or groove-like depending on the pre-stretch. The constitutive model includes elastic compressibility, but the formulation produces accurate solutions for nearly incompressible materials which coincide with the neo-Hookean solid in the incompressible limit. The numerical simulations reveal that localized crease solutions exist at voltages below the critical voltage for wrinkling bifurcation for equi-biaxial pre- stretches below about 2.4. In this range, the wrinkling bifurcation is highly unstable, creasing rather than wrinkling can be expected, and a discontinuous transition is predicted with a finite energy barrier that may be overcome due to the presence of surface defects. With an equi-biaxial pre-stretch greater than 2.4, a continuous transition is predicted with no energy barrier, forming a localized groove due to nonlinear interactions among the unstable wrinkling modes.

The Mobius Strip’s Shape

The Möbius strip, obtained by taking a rectangular strip of plastic or paper, twisting one end through 180∘ , and then joining the ends, is the canonical example of a one-sided surface. Finding its characteristic developable shape has been an open problem ever since its first formulation. Here we use the invariant variational bicomplex formalism to derive the first equilibrium equations for a wide developable strip undergoing large deformations, thereby giving the first non-trivial demonstration of the potential of this approach. We then formulate the boundary-value problem for the Möbius strip and solve it numerically. Solutions for increasing width show the formation of creases bounding nearly flat triangular regions, a feature also familiar from fabric draping and paper crumpling. This could give new insight into energy localization phenomena in unstretchable sheets, which might help to predict points of onset of tearing. It could also aid our understanding of the relationship between geometry and physical properties of nano- and microscopic Möbius strip structures

Laboratory testing of film-forming substances for the manufacture of ophthalmic medicinal films

In the manufacture of ophthalmic medicinal films, special attention should be paid to the choice of a film-forming substance, since both the shape of the future film and its medicinal properties as a whole depend on it. This article provides a laboratory analysis with a comparative assessment of the optimal concentrations of two film-forming substances, polyvinyl alcohol and gelatin. Most of the presented film formers have a number of disadvantages, such as thickness, insufficient strength and elasticity, heterogeneity, formation of cracks and creases. One of the requirements for ophthalmic medicinal films is the smoothness of the surface and the absence of sharp corners. Based on the foregoing, we set the goal of the study - to conduct a laboratory test of film-forming substances for the manufacture of ophthalmic medicinal films. An analysis of domestic and foreign works gave reason to use polyvinyl alcohol and gelatin as the basis for ophthalmic medicinal films. As a result of the study, we have established the optimal concentrations of film-forming substances (polyvinyl alcohol and gelatin) that meet the existing requirements. The optimal concentration of the gelatin solution was the ratio of 1:7. The addition of the plasticizer glycerol to gelatinin the manufacture of ophthalmic medicinal films is mandatory. The optimal concentration of the solution of polyvinyl alcohol was the ratio of 1:15. Films from both film formers did not lose their shape, did not form cracks or breaks when introduced into the conjunctival sac. No irritant effect was observed. Laying the films did not cause difficulties. Forms of gelatin completely dissolved in the eye in 40 minutes, of polyvinyl alcohol - in 90 minutes.

Erratum: “Formation of Plastic Creases in Thin Polyimide Films” [ASME J. Appl. Mech., May 2020, Vol. 87; DOI: 10.1115/1.4046002

Abstract In the original publication, the finite element model (Sec 3.2) had a width W of 20 mm while it should have been 25 mm. Based on the corrected analysis, Fig.10 (page 7) and Fig.13 (page 8) should be updated as follows.

A perturbation force based approach to creasing instability in soft materials under general loading conditions

The formation and control of surface creases in soft materials under compression have intrigued the mechanics community for decades and recently found many applications in tissue biomechanics, soft robotics and tunable devices. In spite of a rapidly growing literature in this field, existing methods of analysis often rely on a presumed crease configuration and consequently there is still a lack of profound theoretical understanding on crease nucleation. In this study, we propose a force based perturbation approach to predicting the occurrence of crease nucleation without assuming a post-instability configuration. In a set of carefully controlled FEM simulations, by considering the relative magnitudes among the element size, perturbation displacement and sample size, we find that beyond a critical strain around −0.36, a flat surface under uniform deformation becomes metastable, while the creased configuration becomes stable, with energy barrier for creasing proportional to the square of the FEM element size and therefore vanishing in the continuum limit. Beyond the Biot critical strain of−0.46, the uniformly deformed configuration of a flat surface becomes unstable. Our force-based instability criterion also enabled us to determine the critical conditions of crease formation for different materials under general loading conditions, leading to a set of crease diagrams. Interestingly, it is shown theoretically and validated experimentally that some highly compressible soft materials do not undergo creasing under loading conditions close to equibiaxial compression.

Swelling-Induced Interface Crease Instabilities at Hydrogel Bilayers

Two dissimilar hydrogel layers bonded together become unstable when the compressive stresses due to diffusion-driven swelling of the layers reach a critical point and creases form at the interface. Although creasing instabilities observed on surfaces of soft solids subjected to large compressions are well studied, the transient nature and critical conditions for the emergence of interface creases as a result of swelling behavior of hydrogels remain elusive. Here, we investigate the formation and transient growth of interface creases in bilayer hydrogels through experimental and computational approaches. Equipped with a mixed isogeometric analysis that accounts for large swelling deformations along with dissipative fluid transport phenomena, we show that both the equilibrium and the transient characteristics of interface creases can be tuned by controlling the material properties, in contrast to the reported material-independent behavior of creases in elastomers. The effects of material parameters on the onset and growth of interface creases are quantified in terms of the critical swelling ratio and critical chemical potential, and these values are compared to the critical conditions for the emergence of wrinkling instabilities. In agreement with our experimental observations of swelling bilayer hydrogels, our computational results demonstrate that the formation of creases is energetically more favorable than wrinkle formation at the interface.

Formation of Plastic Creases in Thin Polyimide Films

Abstract We present a combined experimental and analytical approach to study the formation of creases in tightly folded Kapton polyimide films. In the experiments, we have developed a robust procedure to create creases with repeatable residual fold angle by compressing initially bent coupons. We then use it to explore the influence of different control parameters, such as the force applied, and the time the film is being pressed. The experimental results are compared with a simplified one-dimensional elastica model, as well as a high fidelity finite element model; both models take into account the elasto-plastic behavior of the film. The models are able to predict the force required to create the crease, as well as the trend in the residual angle of the fold once the force is removed. We non-dimensionalize our results to rationalize the effect of plasticity, and we find robust scalings that extend our findings to other geometries and material properties.

Harnessing Multiple Surface Deformation Modes for Switchable Conductivity Surfaces.

Surface deformation modes, such as wrinkling, creasing, and cracking, enable a plethora of surface morphologies under mechanical loading, which have been widely exploited to provide flexibility and stretchability to electronic devices. As each phenomenon offers a distinct set of potential advantages, controlling the types and spatial locations of deformation modes is key for their successful application. In this study, we demonstrate a method to simultaneously harness multiple surface deformation modes-wrinkles, creases, and cracks-in patterned multilayer films. The wrinkling of metal-coated stiff patterned films provides flexibility and stretchability, while the reversible formation of creases in the intervening regions of the bare elastomer is used to template the formation of patterned cracks in the metal. While conventional cracks can be difficult to precisely control, the patterned cracks demonstrated here remain straight over long distances and show tunable lateral spacings from hundreds of micrometers to centimeters. Finally, the reversible opening and closing of these cracks under mechanical loading provides mechanically gated electrical switches with small and tunable critical switching strains of 0.05-0.18 and high on/off ratios of >107, enabling the preparation of mechanical NAND and NOR logic gates each composed of multiple patterned switches on a single elastomer surface.

Wrinkling to crinkling transitions and curvature localization in a magnetoelastic film bonded to a non-magnetic substrate

This work studies experimentally and numerically the post-bifurcation response of a magnetorheological elastomer (MRE) film bonded to a soft non-magnetic (passive) substrate. The film-substrate system is subjected to a combination of an axial mechanical pre-compression and a transverse magnetic field. The non-trivial interaction of the two fields leads to a decrease of the critical magnetic field with applied pre-compression, while the observed wrinkling patterns evolve into crinkles, a bifurcation mode that is defined by the accompanied curvature localization and strong shearing of the side faces of the wrinkled geometry. Using a magneto-elastic variational formulation in a two-dimensional finite element numerical setting, we find that the crinkling is an intrinsic feature of magnetoelasticity and its presence is directly associated with the repulsive magnetic forces of the neighboring wrinkled-crinkled faces. As a result, the presence of the magnetic field prohibits the formation of creases and folds. In an effort to obtain a good quantitative agreement between the numerical and the experimental results, we also introduce an approximate way to model the friction of the lateral film-substrate faces. This analysis reveals the strong effects of friction upon the magneto-mechanical wrinkling modes.

Plasticity retards the formation of creases

When an elastomer is compressed, its surface forms creases at a critical strain about 0.35. When a plastically deformable material is compressed, however, its surface remains smooth at much larger strains. As the smooth surface folds locally into a crease, the material around the crease loads and unloads. We show that the hysteresis of plasticity retards the formation of the crease. For a crease growing in an infinite body, the stress field is self-similar as the crease grows, and the critical strain ec is the applied strain needed to maintain the self-similar growth. We simulate the formation of creases using an elastic-plastic model with linear hardening, and characterize the degree of plasticity of the model by the ratio of the tangent modulus to elastic modulus, Et/E. A small value of Et/E leads to a large critical strain for the onset of creases. We further show experimentally that creases can form at a strain of 0.49 for high-density polyethylene (HDPE) with Et/E ∼ 0.025, but cannot form for metals (aluminum, copper, and stainless steel) with Et/E ∼ 0.001.

Effects of Stiff Film Pattern Geometry on Surface Buckling Instabilities of Elastic Bilayers.

Buckling instabilities-such as wrinkling and creasing-of micropatterned elastic surfaces play important roles in applications, including flexible electronics and microfluidics. In many cases, the spatial dimensions associated with the imposed pattern can compete with the natural length scale of the surface instabilities (e.g., the wrinkle wavelength), leading to a rich array of surface buckling behaviors. In this paper, we consider elastic bilayers consisting of a spatially patterned stiff film supported on a continuous and planar soft substrate. Through a combination of experimental and computational analyses, we find that three surface instability modes-wrinkling, Euler buckling, and rigid rotation-are observed for the stiff material patterns, depending on the in-plane dimensions of the film compared to the natural wrinkle wavelength, while the intervening soft regions undergo a creasing instability. The interplay between these instabilities leads to a variety of surface structures as a function of the pattern geometry and applied compressive strain, in many cases yielding contact between neighboring stiff material elements because of the formation of creases in the gaps between them.

Assessment of durable press performance of cotton finished with modified DMDHEU and citric acid

Cotton apparels possess inherent tendency to form wrinkles under external stress. Conventionally selective cross-linking agents in presence of specific catalyst are applied on cotton to supress formation of creases or wrinkles via pad-dry-cure technique at high curing temperature under acidic conditions imparting stability and elasticity to the fabric. Extensive research carried out in this field identifies invariable deterioration in mechanical properties of finished cotton. In this study, two different cross-linking agents, i.e. modified DMDHEU and citric acid working on etherification and esterification crosslinking reaction with cellulose respectively were applied on cotton through selection of factors using Box Behnken experimental design in conjunction with response surface analysis and regression methods to study their DP ratings as well as other mechanical properties. Significant factors were further drastically narrowed down to reach to most specific concentrations of cross-linker, catalyst as well as other chemicals along with finishing parameters. It was found that modified DMDHEU performed better in terms of DP rating as well as overall physical properties as compared to those obtained with citric acid.

Grain‐ to multiple‐grain‐scale deformation processes during diffusion creep of forsterite + diopside aggregate: 1. Direct observations

AbstractWe uniaxially deformed fine‐grained (~ 1 μm) forsterite + diopside (5 and 20 vol %) aggregates in the diffusion creep regime. Prior to deformation, line markers were milled on a lateral surface of a cylindrical sample to detect single‐ to multiple‐grain‐scale deformation. We performed deformation experiments and observations of the marker‐etched surface after sample cooling multiple times on the same specimens. The strain measured at the scale of several tens of grains from macroscopic shortening of the markers parallel to the compression axis is consistent with the total strain of the sample. However, microscopically, the markers are intensely segmented and rotated at the grain scale increasing with the sample strain. Meanwhile, essentially, no deformation is observed within the grains in most of the samples. The surface microstructures, including the deformation of the markers, reveal the serial operations of grain boundary migration, grain boundary sliding, rigid body grain rotation, and grain neighbor switching, which correspond well to processes expected in diffusion‐controlled superplasticity. This sequence is commonly observed in both samples consisting of forsterite grains of tabular and equiaxed grain shapes, which have been shown to develop notable crystallographic preferred orientation (CPO) and random (or weak) CPO, respectively, during diffusion creep. Intragranular regions of relatively larger forsterite grains in the specimens deformed at stresses near the transition between deformation mechanisms from diffusion creep to dislocation creep reveal marker deformation and formation of surface creases and subgrain boundaries, which indicate intragranular dislocation processes. Overall, the surface microstructures reflect the deformation state of the materials well.

Plasticity-induced origami for assembly of three dimensional metallic structures guided by compressive buckling

Development of origami-inspired routes to assembly of three dimensional structures is an area of growing activity in scientific and engineering research communities due to fundamental interest in mathematical topics in topology and to the potential for practical applications in areas ranging from advanced surgical tools to systems for space exploration. Recently reported approaches that exploit the controlled, compressive buckling of 2D precursors induced by dimensional change in an underlying elastomer support offer broad versatility in material selection (from polymers to device grade semiconductors), feature sizes (from centimeters to nanometers), topological forms (open frameworks to closed form polyhedra) and shape controllability (dynamic tuning of shape), thereby establishing a promising avenue to autonomic assembly of complex 3D systems. Localization of origami-like folding deformations at targeted regions can be achieved through the use of engineered, spatial variations in the thicknesses of the 2D precursors. While this approach offers high levels of control in the targeted formation of creases, creating the necessary thickness variations requires a set of additional processing steps in the fabrication. This paper presents an alternative, and complementary, approach that exploits controlled plastic deformation in the precursors, as validated in a comprehensive set of experimental and theoretical studies. Specifically, plasticity and strain localization can be used to dramatically reduce the bending stiffness at targeted regions, to form well-defined creases as mountain or valley folds during the 2D to 3D geometrical transformation process. The content begins with studies of a model system that consists of a 2D precursor in the form of a straight ribbon with reduced widths at certain sections. The results illustrate the important role of plasticity in the course of folding, in such a manner that dictates the final 3D layouts. A broad range of complex 3D shapes, achieved in both the millimeter-scale and the mesoscale structures (i.e. micron to sub-millimeter), demonstrate the power of these ideas.

“The magic finger technique” a simplified approach for more symmetric results in alar base resection

Alar base surgery is one of the most important and challenging steps of aesthetic rhinoplasty. While an ideally shaped alar base is the goal in a desired nose, nearly all patients have asymmetric nostrils preoperatively. Ethnicity, trauma, cocaine use, or previous rhinoplasties are some factors affecting the width and shape of the nasal base. After the conclusion of all planned rhinoplasty sequences and closure of the mid-columellarincision, we mark the midline inferior to the columella at the nasolabial junction and use acaliper to measure an equal distance from the mid-columellar point to the alar creases on eachside, and mark the medial points of the alar creases. Next we draw on the natural creasesbilaterally extending to 3 o’clock on the right side and 9 o‘clock on the left side as the limit ofthe lateral excisions to avoid scarring. We then gently depress the alae and alar-facial grooveswith the index finger and allow the formation of new creases superior to the original alarcreases in order to detect excess skin to remove. After marking, the resection was performed with a no. 15 blade. The excision was closed using 6-0 Prolene sutures. We aimed to describe a simple technique for making asymmetric resections in which theapplication of pressure by a finger reveals excess skin in both nostril sill and nostril flareindependently for each alar base. With these asymmetric excisions from the right and left alar bases, a more symmetric nostrils and nasal base can be achieved. Level of Evidence: Level IV, therapeutic study.

Surface and interfacial creases in a bilayer tubular soft tissue.

Surface and interfacial creases induced by biological growth are common types of instability in soft biological tissues. This study focuses on the criteria for the onset of surface and interfacial creases as well as their morphological evolution in a growing bilayer soft tube within a confined environment. Critical growth ratios for triggering surface and interfacial creases are investigated both analytically and numerically. Analytical interpretations provide preliminary insights into critical stretches and growth ratios for the onset of instability and formation of both surface and interfacial creases. However, the analytical approach cannot predict the evolution pattern of the model after instability; therefore nonlinear finite element simulations are carried out to replicate the poststability morphological patterns of the structure. Analytical and computational simulation results demonstrate that the initial geometry, growth ratio, and shear modulus ratio of the layers are the most influential factors to control surface and interfacial crease formation in this soft tubular bilayer. The competition between the stretch ratios in the free and interfacial surfaces is one of the key driving factors to determine the location of the first crease initiation. These findings may provide some fundamental understanding in the growth modeling of tubular biological tissues such as esophagi and airways as well as offering useful clues into normal and pathological functions of these tissues.