Predicting delayed instabilities in viscoelastic solids

Urbach, Erez Y.; Efrati, Efi

doi:10.1126/sciadv.abb2948

Cited by 22 publications

(15 citation statements)

References 24 publications

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“…Early works modelled viscoelasticity via an evolving stiffness, achieving qualitative agreement with experiments [66,67]. A recently proposed metric framework introduces viscoelasticity as a temporally evolving (fictitious) reference length instead, and among its merits is the ability to predict delayed snap-back instability [38,68]. Observing this instability in our setting would require maintaining the pressure load for a sufficiently long time while the shell is fully buckled before unloading.…”

Section: Discussionmentioning

confidence: 67%

“…Devoid of any plausible geometric explanation for this strange buckling behaviour, our results require a closer examination of the materials. Although silicone elastomers are selected precisely because they behave elastically in most settings, they are in fact prone to time-dependent molecular rearrangement, and hence are viscoelastic [36][37][38]. Thus, they behave differently depending on how fast they are loaded, and exhibit both stress-relaxation (softening when subjected to a constant strain) and creep (deformation over time under constant stress).…”

Section: Introductionmentioning

confidence: 99%

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Delayed buckling of spherical shells due to viscoelastic knockdown of the critical load

Stein-Montalvo

Coupier

2021

Proc. R. Soc. A.

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We performed dynamic pressure buckling experiments on defect-seeded spherical shells made of a common silicone elastomer. Unlike in quasi-static experiments, shells buckled at ostensibly subcritical pressures, i.e. below the experimentally determined critical load at which buckling occurs elastically, often following a significant delay period from the time of load application. While emphasizing the close connections to elastic shell buckling, we rely on viscoelasticity to explain our observations. In particular, we demonstrate that the lower critical load may be determined from the material properties, which is rationalized by a simple analogy to elastic spherical shell buckling. We then introduce a model centred on empirical quantities to show that viscoelastic creep deformation lowers the critical load in the same predictable, quantifiable way that a growing defect would in an elastic shell. This allows us to capture how both the deflection at instability and the time delay depend on the applied pressure, material properties and defect geometry. These quantities are straightforward to measure in experiments. Thus, our work not only provides intuition for viscoelastic behaviour from an elastic shell buckling perspective but also offers an accessible pathway to introduce tunable, time-controlled actuation to existing mechanical actuators, e.g. pneumatic grippers.

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Section: Discussionmentioning

confidence: 67%

Section: Introductionmentioning

confidence: 99%

Delayed buckling of spherical shells due to viscoelastic knockdown of the critical load

Stein-Montalvo

Coupier

2021

Proc. R. Soc. A.

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show abstract

“…The compatibility conditions allow to identify the set of admissible states, which in turn greatly reduces the dimensionality of the problem. This dimensional reduction paves the way to better understanding frustrated assemblies, and may guide the engineering of their response [19,20].…”

Section: Discussionmentioning

confidence: 99%

Cumulative geometric frustration in physical assemblies

Meiri,

Efrati

2021

Preprint

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Geometric frustration arises whenever the constituents of a physical assembly locally favor an arrangement that cannot be realized globally. Recently, such frustrated assemblies were shown to exhibit filamentation [1], size limitation [2], large morphological variations [3,4] and exotic response properties [5,6]. These unique characteristics can be shown to be a direct outcome of the geometric frustration. There are, however, geometrically frustrated systems that do not exhibit any of the above characteristics. The epitome of frustration in condensed matter physics, the Ising anti-ferromagnet on a triangular lattice, is one such system. In this work we provide a framework for directly addressing the frustration in physical assemblies and their expected energy scaling exponents. We also present a new spin model that exhibits cumulative geometric frustration, and use the newly devised framework to analyze it.

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“…Devoid of any plausible geometric explanation for this strange buckling behavior, our results require a closer examination of the materials. Although silicone elastomers are selected precisely because they behave elastically in most settings, they are in fact prone to time-dependent molecular rearrangement, and hence are viscoelastic [36][37][38]. Thus, they behave differently depending on how fast they are loaded, and exhibit both stress-relaxation (softening when subjected to a constant strain) and creep (deformation over time under constant stress).…”

Section: Introductionmentioning

confidence: 99%

Delayed buckling of spherical shells due to viscoelastic knockdown of the critical load

Stein-Montalvo,

Holmes,

Coupier

2021

Preprint

View full text Add to dashboard Cite

We performed dynamic pressure buckling experiments on defect-seeded spherical shells made of a common silicone elastomer. Unlike in quasi-static experiments, shells buckled at ostensibly subcritical pressures (i.e. below the experimentally-determined load at which buckling occurs elastically), often following a significant time delay. While emphasizing the close connections to elastic shell buckling, we rely on viscoelasticity to explain our observations. In particular, we demonstrate that the lower critical load may be determined from the material properties, which is rationalized by a simple analogy to elastic spherical shell buckling. We then introduce a model centered on empirical quantities to show that viscoelastic creep deformation lowers the critical load in the same predictable, quantifiable way that a growing defect would in an elastic shell. This allows us to capture how both the critical deflection and the delay time depend on the applied pressure, material properties, and defect geometry. These quantities are straightforward to measure in experiments. Thus, our work not only provides intuition for viscoelastic behavior from an elastic shell buckling perspective, but also offers an accessible pathway to introduce tunable, time-controlled actuation to existing mechanical actuators, e.g. pneumatic grippers.

show abstract

Predicting delayed instabilities in viscoelastic solids

Cited by 22 publications

References 24 publications

Delayed buckling of spherical shells due to viscoelastic knockdown of the critical load

Delayed buckling of spherical shells due to viscoelastic knockdown of the critical load

Cumulative geometric frustration in physical assemblies

Delayed buckling of spherical shells due to viscoelastic knockdown of the critical load

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