Shape Control for Experimental Continuation

Neville, Robin; Groh, Rainer; Pirrera, Alberto; Schenk, Mark

doi:10.1103/physrevlett.120.254101

Cited by 37 publications

(33 citation statements)

References 8 publications

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“…An unstable equilibrium was found when the reaction force on the probe vanished, as this condition is equivalent to the 'unprobed' cylinder. Neville et al [18] introduced the ability to both push and pull on 'probes' to control the deformed shape of a shallow arch, and was thus able to identify multiple unstable equilibria.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper, we embed the concept of shape control [18] in a continuous control algorithm that allows for experimental path-following of stable and unstable equilibrium branches, and the traversal of limit points. This will (i) enable the validation of structures that exploit nonlinearities for engineering applications; (ii) expand the design space for shape-adaptive structures by enabling access to 'islands of stability'; and (iii) allow several longstanding numerical benchmarks found in the literature to be validated experimentally [26].…”

Section: Introductionmentioning

confidence: 99%

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Beyond the fold: experimentally traversing limit points in nonlinear structures

et al. 2020

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Recent years have seen a paradigm shift regarding the role of nonlinearities and elastic instabilities in engineering science and applied physics. Traditionally viewed as unwanted aberrations, when controlled to be reversible and well behaved, nonlinearity can enable novel functionalities, such as shape adaptation and energy harvesting. The analysis and design of novel structures that exploit nonlinearities and instabilities have, in part, been facilitated by advances in numerical continuation techniques. An experimental analogue of numerical continuation, on the other hand, has remained elusive. Traditional quasi-static experimental methods control the displacement or force at one or more load-introduction points over the test specimen. This approach fails at limit points in the control parameter, as the immediate equilibrium beyond limit points is statically unstable, causing the structure to snap to a different equilibrium. Here, we propose a quasi-static experimental path-following method that can continue along stable and unstable equilibria, and traverse limit points. In addition to controlling the displacement at the main load-introduction point, the technique relies on overall shape control of the structure using additional actuators and sensors. The proposed experimental method enables extended testing of the emerging class of structures that exploit nonlinearities and instabilities for novel functionality.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Beyond the fold: experimentally traversing limit points in nonlinear structures

et al. 2020

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“…Quantitatively, the enclosed area below the force–displacement curve is the total absorbed energy under displacement control. Based on the measurement under displacement control, we can further estimate the behavior under force control: once a peak force is reached, a sudden increase of displacement will occur, resulting in the enclosed area by the force–displacement curve nearly two times of that under displacement control. Therefore, the absorbed energy under force control is expected nearly doubled compared with displacement control.…”

Section: Resultsmentioning

confidence: 99%

Programmable Granular Metamaterials for Reusable Energy Absorption

Zhao

Jin

2019

Adv Funct Materials

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Designing metamaterials with programmable features has emerged as a promising pathway for reusable energy absorption. While the current designs of reusable energy absorbers mainly exploit mechanical instability of flexible beams, here is created a new kind of metamaterial for reusable and programmable energy absorption by integrating rigid granular materials and compliant stretchable components. In each unit cell of the metamaterial, the stretchable components connect the granular particles to maintain the integrity and control the deformation pattern of the material. When the metamaterial is subjected to an external load, the input energy is partially trapped as elastic energy in the stretchable components, and partially dissipated by friction between the granular particles, forming hysteresis between the loading and unloading force-displacement curves. Through tuning the structural design of the metamaterial, the pretension and stiffness of the stretchable components, and the size of and friction between the particles, a vast design space is achieved to program the mechanical behavior of the metamaterial, such as the load-displacement curve, the multistability, and the amount of energy dissipation. Experimental impact tests on a thin glass panel confirm energy-absorbing capability of the proposed metamaterial. This design strategy opens a new avenue for creating reusable energy-absorbing metamaterials.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201901258. and a long working distance. Most commercial energy-absorbing products adopt plastic deformation or fragmentation of foams, [3] metals, [4] and ceramics, [5] to gain the desired hysteresis behavior, and introduce artificial defects, such as prefolding of origami, [6][7][8] to control the deformation mode. In the products with plastic deformation or fragmentation, dislocations and bond breakage occur at the molecule level, and a large amount of energy can be absorbed. However, they are only for one-time usage, since the materials are permanently damaged.In order to overcome the shortcoming of one-time usage, reusable energyabsorbing materials have been proposed by developing damage-tolerant micro [9] or nano lattices, [5] architectured composite materials, [10,11] and mechanical metamaterials. [12][13][14][15] Mechanical metamaterials are materials with microstructures, which give rise to unique mechanical properties that are otherwise hard to achieve. [12][13][14] By designing the microstructures, researchers have developed energy-absorbing metamaterials mainly through exploiting mechanical instability of the deformable microstructures. [16][17][18][19][20] A well-utilized strategy to achieve reusability is making use of bistability of curved beams and tilted straight beams under buckling, [21][22][23] since during the working process, deformation of these constituent structures is elastic. Although the energyabsorbing capability of these metamaterials is currently not comparable to those...

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“…For instance, the analyst has very limited control over the equilibrium path that is being traced, such that unwanted path-jumping typically occurs. As a viable alternative, the in-house MATLAB-based FE code [3] has been employed as it has been validated on various occasions against commercial FE packages (as much as these allow given the lack of comparable capabilities), other results in literature, and also experimental results-the interested reader is encouraged to study these selected examples [31,32,33].…”

Section: Model Definitionmentioning

confidence: 99%

Nudging Axially Compressed Cylindrical Panels Toward Imperfection Insensitivity

Cox

Groh

Pirrera

2019

Journal of Applied Mechanics

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Curved shell structures are known for their excellent load-carrying capability and are commonly used in thin-walled constructions. Although theoretically able to withstand greater buckling loads than flat structures, shell structures are notoriously sensitive to imperfections owing to their postbuckling behavior often being governed by subcritical bifurcations. Thus, shell structures often buckle at significantly lower loads than those predicted numerically and the ensuing dynamic snap to another equilibrium can lead to permanent damage. Furthermore, the strong sensitivity to initial imperfections, as well as their stochastic nature, limits the predictive capability of current stability analyses. Our objective here is to convert the subcritical nature of the buckling event to a supercritical one, thereby improving the reliability of numerical predictions and mitigating the possibility of catastrophic failure. We explore the elastically nonlinear postbuckling response of axially compressed cylindrical panels using numerical continuation techniques. These analyses show that axially compressed panels exhibit a highly nonlinear and complex postbuckling behavior with many entangled postbuckled equilibrium curves. We unveil isolated regions of stable equilibria in otherwise unstable postbuckled regimes, which often possess greater load-carrying capacity. By modifying the initial geometry of the panel in a targeted—rather than stochastic—and imperceptible manner, the postbuckling behavior of these shells can be tailored without a significant increase in mass. These findings provide new insight into the buckling and postbuckling behavior of shell structures and opportunities for modifying and controlling their postbuckling response for enhanced efficiency and functionality.

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Shape Control for Experimental Continuation

Cited by 37 publications

References 8 publications

Beyond the fold: experimentally traversing limit points in nonlinear structures

Beyond the fold: experimentally traversing limit points in nonlinear structures

Programmable Granular Metamaterials for Reusable Energy Absorption

Nudging Axially Compressed Cylindrical Panels Toward Imperfection Insensitivity

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