Self-healing polymers composed of microencapsulated healing agents exhibit remarkable mechanical performance and regenerative ability, but are limited to autonomic repair of a single damage event in a given location. Self-healing is triggered by crack-induced rupture of the embedded capsules; thus, once a localized region is depleted of healing agent, further repair is precluded. Re-mendable polymers can achieve multiple healing cycles, but require external intervention in the form of heat treatment and applied pressure. Here, we report a self-healing system capable of autonomously repairing repeated damage events. Our bio-inspired coating-substrate design delivers healing agent to cracks in a polymer coating via a three-dimensional microvascular network embedded in the substrate. Crack damage in the epoxy coating is healed repeatedly. This approach opens new avenues for continuous delivery of healing agents for self-repair as well as other active species for additional functionality.

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Self-healing materials with microvascular networks

Polyurethanes have many properties that qualify them as high-performance polymeric materials, but they still suffer from mechanical damage. We report the development of polyurethane networks that exhibit self-repairing characteristics upon exposure to ultraviolet light. The network consists of an oxetane-substituted chitosan precursor incorporated into a two-component polyurethane. Upon mechanical damage of the network, four-member oxetane rings open to create two reactive ends. When exposed to ultraviolet light, chitosan chain scission occurs, which forms crosslinks with the reactive oxetane ends, thus repairing the network. These materials are capable of repairing themselves in less than an hour and can be used in many coatings applications, ranging from transportation to packaging or fashion and biomedical industries.

https://science.sciencemag.org/content/sci/323/5920/1458.full.pdf

Self-Repairing Oxetane-Substituted Chitosan Polyurethane Networks

This paper presents an active–adaptive tuned vibration absorber (AATVA) which is based on magnetorheological elastomer (MRE). A voice coil motor is attached to a conventional MRE adaptive tuned vibration absorber (ATVA) to improve its performance. In this study, two feedback types of the activation force were analyzed and the stability condition was obtained. In order to eliminate the time delay effect during the signal processing, a phase-lead compensator was incorporated. Based on the analysis, an MRE AATVA prototype was designed and its dynamic properties were experimentally investigated. The experimental results demonstrated that its resonant frequency could vary from 11 to 18 Hz and its damping ratio decreased to roughly 0.05 from 0.19 by adding the activation force. Besides, its vibration reduction abilities at the first two resonant frequencies of the experimental platform could reach 5.9 dB and 7.9 dB respectively. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0964-1726/20/7/075015/pdf

The design of an active–adaptive tuned vibration absorber based on magnetorheological elastomer and its vibration attenuation performance

This article presents the development of an active-damping-compensated magnetorheological elastomer (MRE) adaptive tuned vibration absorber (ATVA). The principle and the vibration attenuation performance of the proposed active-damping-compensated ATVA were theoretically analyzed. Based on the analysis, a prototype was designed and manufactured. Its dynamic properties and vibration attenuation performances were experimentally investigated. The experimental results demonstrated that the damping ratio of the prototype was significantly reduced by the active force. Consequently, its vibration attenuation capability was significantly improved compared with a conventional MRE ATVA.

An Active-damping-compensated Magnetorheological Elastomer Adaptive Tuned Vibration Absorber

In the past, adaptive tuned vibration absorbers (ATVAs) based on magnetorheological elastomers (MREs) have mainly been developed in a shear working mode. The enhancing effect of MREs in squeeze mode has already been investigated, but ATVAs in squeeze mode have rarely been studied. This paper reports the development of a compact squeeze MRE absorber and its subsequent performance in various magnetic fields characterized under various frequencies by a vibration testing system. The results revealed that the natural frequency of the MRE absorber working in squeeze mode can be tuned from 37 Hz to 67 Hz. Following this, a theoretical model based on magnetic dipole theory was developed to investigate the dynamic performance of the squeeze MRE absorber, and the vibration attenuation of the squeeze MRE absorber was then verified by mounting it on a beam with supports under both ends. The results revealed that the squeeze MRE absorber extended its vibration attenuation range from 37 Hz to 67 Hz while the passive absorber was only effective around 53 Hz.

/pdf/the-development-of-an-adaptive-tuned-magnetorheological-5fqoez7lgi.pdf

The development of an adaptive tuned magnetorheological elastomer absorber working in squeeze mode

Vibration control of a structure by using a tunable absorber and an optimal vibration absorber under auto-tuning control

A new type of tire is presented, in which there is no air leakage when nails puncture the tire. The broken part is repaired automatically by a self-repairing mechanism. The self-repairing unit consists of two rubber sheets with internal lattices. Polymer particles, which expand their volume on adding water, are inserted into the lattices. The unit is adhered to the inside wall of the tire. Coolant fluid diluted with water is introduced to the polymers uniformly. In this system, the polymer particles expand with water-diluted coolant fluid, and become gel. Hence, they stop air leakages in the tire. Fundamental experiments are performed, and optimum conditions are found. This technique is also applied to real tires, and it is ascertained that there is no air leakage when the tire is punctured by nails.

Sigeo Ikai

Papers

Vibration control of a structure by using a tunable absorber and an optimal vibration absorber under auto-tuning control

Tire with Self-Repairing Mechanism

Electromagnetic Actuator and Stacked Piezoelectric Sensors for Controlling Vibrations of a Motor on a Flexible Structure