Origami, the ancient art of paper folding, has inspired the design of engineering devices and structures for decades. The underlying principles of origami are very general, which has led to applications ranging from cardboard containers to deployable space structures. More recently, researchers have become interested in the use of active materials (i.e., those that convert various forms of energy into mechanical work) to effect the desired folding behavior. When used in a suitable geometry, active materials allow engineers to create self-folding structures. Such structures are capable of performing folding and/or unfolding operations without being kinematically manipulated by external forces or moments. This is advantageous for many applications including space systems, underwater robotics, small scale devices, and self-assembling systems. This article is a survey and analysis of prior work on active self-folding structures as well as methods and tools available for the design of folding structures in general and self-folding structures in particular. The goal is to provide researchers and practitioners with a systematic view of the state-of-the-art in this important and evolving area. Unifying structural principles for active self-folding structures are identified and used as a basis for a quantitative and qualitative comparison of numerous classes of active materials. Design considerations specific to folded structures are examined, including the issues of crease pattern identification and fold kinematics. Although few tools have been created with active materials in mind, many of them are useful in the overall design process for active self-folding structures. Finally, the article concludes with a discussion of open questions for the field of origami-inspired engineering.

No abstract

Origami engineering—the practice of creating useful three-dimensional structures through folding and fold-like operations on two-dimensional building-blocks—has the potential to impact several areas of design and manufacturing. In this article, we study a new concept for a self-folding system. It consists of an active, self-morphing laminate that includes two meshes of thermally-actuated shape memory alloy (SMA) wire separated by a compliant passive layer. The goal of this article is to analyze the folding behavior and examine key engineering tradeoffs associated with the proposed system. We consider the impact of several design variables including mesh wire thickness, mesh wire spacing, thickness of the insulating elastomer layer, and heating power. Response parameters of interest include effective folding angle, maximum von Mises stress in the SMA, maximum temperature in the SMA, maximum temperature in the elastomer, and radius of curvature at the fold line. We identify an optimized physical realization for maximizing folding capability under mechanical and thermal failure constraints. Furthermore, we conclude that the proposed self-folding system is capable of achieving folds of significant magnitude (as measured by the effective folding angle) as required to create useful 3D structures.

Origami engineering, which is the practice of creating useful three-dimensional structures through folding and fold-like operations applied to initially two-dimensional entities, has the potential to impact several areas of design and manufacturing. In some instances, however, it may be impractical to apply external manipulations to produce the desired folds (e.g., as in remote applications such as space systems). In such cases, self-folding capabilities are valuable. A self-folding material or material system is one that can perform folding operations without manipulations from external forces. This work considers a concept for a self-folding material system. The system extends the ‘programmable matter’ concept and consists of an active, self-morphing sheet composed of two meshes of thermally actuated shape memory alloy (SMA) wire separated by a compliant passive layer. The geometric and power input parameters of the self-folding sheet are optimized to achieve the tightest local fold possible subject to stress and temperature constraints. The sheet folding performance considering folds at different angles relative to the orientation of the wire mesh is also analyzed. The optimization results show that a relatively low elastomer thickness is preferable to generate the tightest fold possible. The results also show that the self-folding sheet does not require large power inputs to achieve an optimal folding performance. It was shown that the self-folding sheet is capable of creating similar quality folds at different orientations.

Background: subclinical hypothyroidism (sh), defined as mild thyroid-stimulating hormone (Tsh) elevation with normal free thyroxine (FT4) levels and no symptoms, is common during the first few years of life in Down syndrome (Ds) and can be self-limiting. Our objective was to confirm that sh is usually a transitory disorder and to identify the factors associated with spontaneous remission. Methods: We reviewed clinical histories of patients from the catalan Down syndrome Foundation (cDsF) with Ds and sh diagnosed before 5 y of age. sh was defined as Tsh 5.5-25 µU/ml (6 mo-4 y) or 4.13-25 µU/ml (4-7 y), with FT4 0.89-1.87 ng/dl (6 mo-4 y) or 0.96-1.86 ng/dl (4-7 y). results: Fifty-three patients with sh were identified, with an average age of 2.4 ± 1.1 y, median (range) Tsh at diagnosis 7.1 (4.2-23.9 µU/ml), and median (range) FT4 1.1 (0.9-1.7 ng/dl). sh resolved spontaneously in 39 cases (73.6%), with Tsh at the most recent visit (mean age 6.7 ± 1.4 y) 3.9 (1.8-12.7 µU/ml). The rate of remission was significantly higher in patients without goiter (94.9 vs. 28.6%) and in those who were negative for antithyroid antibodies (89.7 vs. 42.9%). conclusion: sh in infants and preschool children with Ds is usually a transitory disorder, with remission in >70% of cases. The absence of goiter and thyroid autoantibodies was associated with a greater rate of spontaneous remission in our study. t he prevalence of medical conditions in individuals withDown syndrome (DS) is greater than in the general population, which has negative implications for their quality of life and life expectancy (1). Among these medical problems, thyroid pathology is a primary area of concern. Both hyper-and hypothyroidism occur more often in patients with DS (1-3), the latter disorder occurring six times more frequently than the former (4,5).In addition to the increased risk of developing autoimmune hypothyroidism with age (2,6), children with DS have a higher chance of displaying a mild, isolated increase in thyroid-stimulating hormone (TSH) in the absence of low free thyroxine (FT4) or overt hypothyroid symptoms (7,8). This phenomenon, of uncertain etiology, can be referred to as subclinical hypothyroidism (SH) and seems usually to be transitory and self-limiting without treatment (9,10). However, there are few systematic studies on SH, and the factors related to its remission are unclear. The possibility that thyroxine replacement may have a beneficial effect on the somatic and psychomotor development of patients with DS and SH has been raised (11). In this context, the results of a randomized, double-blind clinical trial with 196 DS children are important with respect to previous studies. On the basis of the theory that all DS subjects have slight hypothyroidism at birth (12,13), this study evaluated the effect of systematic treatment with levothyroxine initiated in the neonatal period and continued during the first 2 y of life, as compared with that of placebo. Treatment with levothyroxine resulted in a subtle improvement in psychomotor developme...

Origami provides both inspiration and potential solutions to the fabrication, assembly, and functionality of various structures and devices. Kinematic modeling of origamibased objects is essential to their analysis and design. Models for rigid origami, in which all planar faces of the sheet are rigid and folds are limited to straight creases having only zeroth-order geometric continuity, are available in the literature. Many of these models include constraints on the fold angles to ensure that any initially closed strip of faces is not torn during folding. However, these previous models are not intended for structures with non-negligible fold thickness or with maximum curvature at the folds restricted by material or structural limitations. Thus, for general structures, creased folds of merely zeroth-order geometric continuity are not appropriate idealizations of structural response, and a new approach is needed. In this work, a novel model analogous to those for rigid origami with creased folds is presented for sheets having realistic folds of nonzero surface area and exhibiting higher-order geometric continuity, here termed smooth folds. The geometry of smooth folds and constraints on their associated shape variables are presented. A numerical implementation of the model allowing for kinematic simulation of sheets having arbitrary fold patterns is also described. Simulation results are provided showing the capability of the model to capture realistic kinematic response of origami sheets with diverse fold patterns.

No abstract

The purpose of the present work is to survey the effect of pulsed laser ablation on copper substrates (CuZn40) deployed for adhesive bonding. Surface pre-treatment was carried using an Yb-fiber laser beam. Treated surfaces were probed using Scanning Electron Microscopy (SEM) and X-Ray Photoelectron Spectroscopy (XPS). The mechanical performance of CuZn40/epoxy bonded joints was assessed using the T-peel test coupon.In order to resolve the mechanisms of failure and adhesive penetration within surface asperities induced by the laser treatment, fracture surfaces were surveyed using SEM.Finite element simulations, based on the use of the cohesive zone model of fracture, were carried out to evaluate the variation of bond toughness. Results indicated that the laser ablation process effectively modifies surface morphology and chemistry and enables enhanced mechanical interlocking and cohesive failure within the adhesive layer.Remarkable improvements of apparent peel energy and bond toughness were observed with respect to control samples with sanded substrates.