The present invention provides meta-materials with an actively controllable mechanical property. The meta-material includes a deformable structure and a set of activation elements. The activation elements are controllable between multiple states. The meta-material includes a first value for a mechanical property when one or more of the activation elements is in the first activation state and includes a second value for the mechanical property when the activation elements have been activated to the second activation state. In one aspect, the meta-material resembles a composite material where the connectivity between the component materials or shape and arrangement of the component materials is dynamically controllable so as to affect a mechanical property of the meta-material.

Mechanical meta-materials

As a relatively non-regenerative tissue, articular cartilage has been targeted for cryopreservation as a method of mitigating a lack of donor tissue availability for transplant surgeries In addition, subzero storage of articular cartilage has long been used in biomedical studies using various storage temperatures The current investigation studies the potential for freeze-thaw to affect the mechanical properties of articular cartilage through direct comparison of various subzero storage temperatures Both subzero storage temperature as well as freezing rate were compared using control samples (4°C) and samples stored at either -20°C or -80°C as well as samples first snap frozen in liquid nitrogen (-196°C) prior to storage at -80°C All samples were thawed at 375°C to testing temperature (22°C) Complex stiffness and hysteresis characterized load resistance and damping properties using a non-destructive, low force magnitude, dynamic indentation protocol spanning a broad loading rate range to identify the dynamic viscoelastic properties of cartilage Stiffness levels remained unchanged with exposure to the various subzero temperatures Hysteresis increased in samples snap frozen at -196°C and stored at -80°C, though remained unchanged with exposure to the other storage temperatures Mechanical changes shown are likely due to ice lens creation, where frost heave effects may have caused collagen damage That storage to -20°C and -80°C did not alter the mechanical properties of articular cartilage shows that when combined with a rapid thawing protocol to 375°C, the tissue may successfully be stored at subzero temperatures

/pdf/freeze-thaw-treatment-effects-on-the-dynamic-mechanical-8f86p6atyw.pdf

Freeze-thaw treatment effects on the dynamic mechanical properties of articular cartilage

Dynamic stiffness and loss factor measurement of engine rubber mount by impact test

This paper explores the influence of linear hysteretic damping on the performance of passive tunedinerter devices An inerter is a device that produces a force proportional to the relative acceleration across its two terminals; devices incorporating inerters have received widespread attention in the earthquake engineering community, because they offer the ability to improve the seismic response of structures However, the majority of this research has assumed that the damping components within the tuned-inerter device exhibit viscous, rather than hysteretic, damping This restriction imposes an essential question on how the hysteretic damping model will change the performance of the device compared to the viscous damping model It is shown that the response of viscous
and hysteretic inerter systems have significant differences in displacement amplitude due to the frequency-dependency of the damping Therefore, a new formulation for obtaining the optimum loss factor of the hysteretic damping in the inerter system is proposed Next, the challenges associated with accurately predicting the time-response of a hysteretically damped system are discussed A numerical time-integration method is extended to address these challenges, using
a new formulation that has the benefit of being broadly applicable to multi-degree-of-freedom hysteretic linear systems and nonstationary random signals The results show that the earthquake responses from the hysteretic damping model can differ significantly from the ones obtained via the viscous model

https://onlinelibrary.wiley.com/doi/pdf/10.1002/eqe.3287

Tuned inerter dampers with linear hysteretic damping

Descriπbed herein is electroadhesion technology that permits controllable adherence between two objects Electroadhesion uses electrostatic forces of attraction produced by an electrostatic adhesion voltage, which is applied using electrodes (18) in an electroadhesive device The electrostatic adhesion voltage produces an electric field and electrostatic adherence forces When the electroadhesive device and electrodes are positioned near a surface of an object such as a vertical wall (16), the electrostatic adherence forces hold the electroadhesive device in position relative to the surface and object This can be used to increase traction or maintain the position of the electroadhesive device relative to a surface Electric control of the electrostatic adhesion voltage permits the adhesion to be controllably and readily turned on and off.

Wall crawling devices

As vibration suppression technology has matured, the application of viscoelastic materials in passive damping mechanisms has proven to be a reliable means toward improved structural dynamics This paper discusses general steps required in characterization of viscoelastic damping elements and presents several successful passive damping devices as examples of the approach Sample devices include a damper for the Hubble Space Telescope Solar Array 3, a damped strut built for the FORTE satellite, a viscoelastic isolator, and a cocured viscoelastic/composite strut When damping is built into a structure with a damped element, it is necessary to measure the element stiffness to understand its effect on the system dynamics The stiffness measurement is complex because of the level of damping The complex stiffness function, with both real and imaginary components, characterizes the behavior of a damping device, a damped structural element, or a sample of viscoelastic material Stiffness characterization of structural elements with viscoelastic damping is presented in terms of real stiffness and loss (imaginary stiffness/real stiffness)

Complex stiffness measurement of vibration-damped structural elements

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Complex stiffness measurement of vibration-damped structural elements