Polymer gels: Investigation of the swelling induced deformations with a thermodynamically consistent chemo-mechanical model

An increasing demand for adaptive structures using smart materials has emerged in the last decades. These innovative materials are able to meet the required performance of the up-to-date devices improving current systems, especially in the fields of medicine and aerospace. Among adaptive structures, polymer gels are gaining a particular interest due to their similar behavior to that of biological systems. Polymer gels are elastic materials soaked in a fluid that undergo swelling or shrinking when triggered by an external stimulus such as electric field, pH, humidity, temperature. During the swelling or shrinking of the gel, the fluid is absorbed or released, respectively, while large deformations (40-80%) occur. The main applications involving polymer gels are bioinspired microstructures, biological tissues, but also fuel cells and actuators. The effectiveness of polymer gels for adaptive structure applications critically depends on the capability of the gel to achieve both prescribed changes in shape and size within the range of requested performance. Currently, several approaches to perform the shape control of swellable materials are pursued for materials in the form of thin sheets (~10-4m). Furthermore, frequent swelling-deswelling cycles of the gel may generate critical stresses, fracture, and eventually fatigue issues. It is worth noting that fatigue is still a big challenge for polymers

Considerations on higher-order finite elements for multilayered plates based on a unified formulation

International audienceIn this work, a numerical assessment of a series of multilayered finite plate elements is proposed. The finite elements are derived within the ‘‘Unified Formulation’’, a technique developed by Carrera for an accurate modeling of laminates. The Unified Formulation affords an implementation-friendly possibility to derive a large number of two-dimensional, axiomatic models for plates and shells. An accurate model for multilayered components naturally involves transverse shear and normal stresses, as well as higher-order displacement assumptions in thickness direction. The aim of this work is to give a first insight of the numerical properties of finite elements relying on these formulations. Some considerations concerning the numerical difficulties associated to thickness locking phenomena are presented. A detailed numerical analysis is performed to study the shear locking phenomenon. For the selected case study, once the latter spurious stiffening effect is suppressed with classical or advanced numerical techniques, the resulting elements are shown to behave robustly and accurately

Multiwalled carbon-nanotubes-sheet actuators: Theoretical and experimental investigations

In this paper we present experimental measurements as well as a theoretical model for the chemo-electro-mechanical behavior of multi walled (MWNT) carbon nanotubes sheet actuators. Investigations of MWNT paper as an actuator and the analysis of the experimental and theoretical characteristics are special features of the presented work. The influencing parameters of the actuation behavior such as thickness of sheet materials and electrolyte concentration have been investigated. We report the experimentally measured active displacement varying quadratically with the applied electric field and non-linearly with the electrolyte concentration. In the theoretical part, we present a macroscopic actuation model for the global displacement behavior of MWNT materials. Finally, a comparison between the theoretical and the experimental investigations has been conducted

Actuation and buckling effects in IPMCs

In the last decade, ionic polymer–metal composites are emerged as viable intelligent materials working both as bending actuators and energy harvesting systems. Recently, the feasibility of actuation from mechanical buckling has been investigated. In the present research, we present relevant numerical experiments concerning the possible electromechanical transduction when different patterned electrodes are considered. The focus of this research is theoretical, numerical, and experimental. In particular, with reference to almost one–dimensional IPMC strips, we take into account the large influence of electrodes’ bending stiffness on the IPMC behavior. We consider an original continuous metal strip covering the ionic polymer, and the patterned electrodes with one or more gaps. The actuation response of the system to low and to high voltages is studied; a strong difference is evidenced in the two situations as, in presence of high voltage, the system shows a buckling in opposite direction which needs further investigations

Simulationsgestützte Optimierung von Partiell Gehärteten Automobilteilen aus Mehrphasen-Stahl

In the automotive industry, increasing demands for weight reduction as well a safety requirements have motivated the use of locally optimized components. This study shows how crashrelevant side rails made of multi-phase steels can be improved in terms of local rigidity by local hardening, thus avoiding an increase of the cross section. Based on the experiments, the improvement of crash simulations by simulation of the entire production chain is investigated. A dedicated software tool was developed to enable the coupling of a wide range of commercially available FEM software products for forming, heat treatment, and crash simulations. One central aspect to be solved is the transfer of tensor-like properties such as stress or strain states