Flexible batteries are essential for wearable electronic devices. To meet practical applications, they need to be mechanically robust and stable. However, strong or multiple bending may sever the interfacial contact between electrode and electrolyte, causing capacity fading or even battery failure. Herein we present a new cooling-recovery concept for flexible batteries, which involves a temperature-sensitive sol-gel transition behavior of the thermoreversible polymer hydrogel electrolyte. Once a battery has suffered from strong mechanical stresses, a simple cooling process can refresh the electrode-electrolyte interface. The energy-storage capability can be recovered with a healing efficiency higher than 98 %. It is believed that this study not only offers new valuable insights, but also opens up new perspectives to develop functional wearable devices.

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Computational modeling of structures subjected to extreme static and dynamic loads (such as snow, wind, impact, and earthquake) using finite-element software are part of mainstream structural engineering curricula in universities (at least at graduate level), and many experts can be found in industry who routinely undertake such analyses. However, only a handful or institutions around the world teach structural response to fire (at any level) and only a few of the top consulting engineers in the world truly specialize in this niche area. Among the reasons for this are the lack of cheap and easily accessible software to carry out such analyses and the highly tedious nature of modeling the full (often coupled) sequence of a realistic fire scenario, heat transfer to structure and structural response (currently impossible using a single software). The authors in this paper describe how finite-element software can be extended to include the modeling of structures under fire load. The added advantage of extending existing finite-element codes, as opposed to creating fire-specific applications, is due to ability to perform multihazard type analysis, e.g., fire following earthquake. Due to its open source nature and object-oriented design, the OpenSees software framework is used for this purpose. In this work, the OpenSees framework, which was initially designed for the earthquake analysis of structures, is extended by the addition of new concrete classes for thermal loads, temperature distributions across element cross sections, and material laws based on Eurocodes. Through class and sequence diagrams, this paper shows the interaction of these classes with the existing classes in the OpenSees framework. The performance of this development is tested using benchmark solutions of a single beam with finite stiffness boundary conditions and a steel frame test. The results from OpenSees agree well with analytical solutions for the benchmark problem chosen and provide reasonable agreement with the test. The experience with OpenSees so far suggests that it has excellent potential to be the basis of a unified software framework for enabling computational modeling of realistic fires, and further work is continuing towards the achievement of this goal. The extensions made to OpenSees described in this work, in keeping with the open source ideals of the framework, have been included in the current OpenSees code and are available for researchers and practicing engineers to test, develop, and use for their own purposes.

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This paper proposes a new scheme for estimating the actuator and sensor fault for Lipschitz nonlinear systems with unstructured uncertainties using the sliding mode observer (SMO) technique. Initially, a coordinate transformation is introduced to transform the original state vector into two parts such that the actuator faults only appear in the dynamics of the second state vector. The concept of equivalent output error injection is then employed to estimate the actuator fault. The effects of system uncertainties on the estimation errors of states and faults are minimized by integrating an scriptℋ∞ uncertainty attenuation level into the observer. The sufficient conditions for the state estimation error to be bounded and satisfy a prescribed scriptℋ∞ performance are derived and expressed as a linear matrix inequality (LMI) optimization problem. Furthermore, the proposed actuator fault estimation method is extended to sensor fault estimation. Finally, the effectiveness of the proposed scheme in estimating actuator and sensor faults has been illustrated considering an example of a single‐link flexible joint robot system.

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