Formation of Plastic Creases in Thin Polyimide Films

Dharmadasa, B. Yasara; McCallum, Matthew W.; Mierunalan, Seyon; Dassanayake, Sahangi P.; Mallikarachchi, Chinthaka; Jiménez, Francisco López

doi:10.1115/1.4046002

Cited by 28 publications

(11 citation statements)

References 24 publications

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“…In origami structures, creases have been modeled as discrete hinges ( 18 , 20 – 24 ), smooth folds with C 1 continuity ( 25 – 27 ), and as thinner ( 28 , 29 ) or narrower ( 30 ) structural elements, which either need a careful specification of matching conditions between the creases and the joining facets or require a detailed definition of the crease region. Recently, Jules et al used the Heaviside feature of a hyperbolic tangent function to describe the local geometry of creases as C ∞ continuity and studied the mechanics of creased elastica ( 31 ).…”

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confidence: 99%

Continuous modeling of creased annuli with tunable bistable and looping behaviors

Marmo

Cesarano

et al. 2023

Proc. Natl. Acad. Sci. U.S.A.

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Creases are purposely introduced to thin structures for designing deployable origami, artistic geometries, and functional structures with tunable nonlinear mechanics. Modeling the mechanics of creased structures is challenging because creases introduce geometric discontinuity and often have complex mechanical responses due to local material damage. In this work, we propose a continuous description of the sharp geometry of creases and apply it to the study of creased annuli, made by introducing radial creases to annular strips with the creases annealed to behave elastically. We find that creased annuli have generic bistability and can be folded into various compact shapes, depending on the crease pattern and the overcurvature of the flat annulus. We use a regularized Dirac delta function (RDDF) to describe the geometry of a crease, with the finite spike of the RDDF capturing the localized curvature. Together with anisotropic rod theory, we solve the nonlinear mechanics of creased annuli, with its stability determined by the standard conjugate point test. We find excellent agreement between precision tabletop models, numerical predictions from our analytical framework, and modeling results from finite element simulations. We further show that by varying the rest curvature of the thin strip, dynamic switches between different states of creased annuli can be achieved, which could inspire the design of deployable and morphable structures. We believe that our smooth description of discontinuous geometries will benefit the mechanical modeling and design of a wide spectrum of engineering structures that embrace geometric and material discontinuities.

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confidence: 99%

Continuous modeling of creased annuli with tunable bistable and looping behaviors

Marmo

Cesarano

et al. 2023

Proc. Natl. Acad. Sci. U.S.A.

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“…Accurate modeling of the mechanics of creased thin sheets requires a precise description of the mechanics of the crease, which usually have complex relaxation phenomena and complicated mechanical responses under external loading [50,74,75]. We have adopted only an elastic response for the crease in this study.…”

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confidence: 99%

Bistability and equilibria of creased annular sheets and strips

2021

Preprint

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A creased thin disk is generally bistable since the crease could be pushed through to form a stable cone-like inverted state with an elastic singularity corresponding to the vertex of the conical surface. In a recent study, we found that this bistability could be destroyed by removing the singularity through cutting a hole around the vertex, depending on the size and shape of the hole. Particularly, to maintain the bistability, a circular hole normally cannot exceed 20% of the disk size. This paper extends our recent work and is based on the following observations in tabletop models with circular holes: (i) reducing the circumference of the creased disk by removing an annular sector could increase the hole size to be as large as the disk without destroying the bistability, (ii) with a single crease, the circular hole could be as large as the disk without loss of the bistability, and (iii) a family of stable inverted states can be obtained by inverting the disk almost anywhere along the crease. An inextensible strip model is implemented to investigate these phenomena. We formulate a minimal facet of the creased disk as a two-point boundary value problem with the creases modeled as nonlinear hinges, and use numerical continuation to conduct parametric studies. Specifically, we focus on geometric parameters which include an angle deficit that determines the circumference of the disk, the rest crease angle, the number of evenly distributed creases, and an eccentricity that determines the position of the hole on the crease. Our numerical results confirm the qualitative observations in (i)-(iii) and further reveal unexpected results caused by the coupling between these geometric parameters. Our results demonstrate that by varying the geometry of a simply creased disk, surprisingly rich nonlinear behaviors can be obtained, which shed new light on the mechanics and design of origami, kirigami, and morphable structures.

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“…Furthermore, the nonwoven fabrics formed by rotary pleating are soft sheet materials for which there is little knowledge about bending behavior at high curvatures. The mechanics of crease formation and recovery, and particularly of networks of facets and creases, govern the dynamic behavior of folded deployable structures [6][7][8] and pleated fabrics [9,10], as well as the assembly of packaging or other folded structures [11]. Naturally occurring pleated structures include insect wings and plant leaves [12,13].…”

Section: Introductionmentioning

confidence: 99%

Avoiding localization instabilities in rotary pleating

Tian¹,

Hanna²

2022

Preprint

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Rotary pleating is a widely used process for making filters out of nonwoven fabric sheets. This involves indirect elastic-plastic bending of pre-weakened creases by continuously injecting material into an accordion-shaped pack. This step can fail through a localization instability that creates a kink in a pleat facet instead of in the desired crease location. In the present work, we consider the effects of geometric and material parameters on the rotary pleating process. We formulate the process as a multi-point variable-arc-length boundary value problem for planar inextensible rods, with hinge connections. Both the facets (rods) and creases (hinges) obey nonlinear momentcurvature or moment-angle constitutive laws. Some unexpected aspects of the sleeve boundary condition at the point of material injection, common to many continuous sheet processes, are noted. The process, modeled as quasistatic, features multiple equilibria which we explore by numerical continuation. The presence of, presumably stable, kinked equilibria is taken as a conservative sign of potential pleating failure. Failure may also occur due to localization at the injection point. We may thus obtain "pleatability surfaces" that separate the parameter space into regions where mechanical pleating will succeed or fail. Successful pleating depends primarily on the distance between the injection point and the pleated pack. Other factors, such as the crease stiffness and strength relative to that of the facets, also have an influence. Our approach can be adapted to study other pleating and forming processes, the deployment and collapse of folded structures, or multi-stability in compliant structures.

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Formation of Plastic Creases in Thin Polyimide Films

Cited by 28 publications

References 24 publications

Continuous modeling of creased annuli with tunable bistable and looping behaviors

Continuous modeling of creased annuli with tunable bistable and looping behaviors

Bistability and equilibria of creased annular sheets and strips

Avoiding localization instabilities in rotary pleating

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