Ionic polymer metal composites (IPMCs) consist of an ionomeric membrane, including mobile counterions, sandwiched between two thin noble metal electrodes. IPMCs find application as sensors and actuators, where an imposed mechanical loading generates a voltage across the electrodes, and, vice versa, an imposed electric field causes deformation. Here, we present a predictive modelling approach to elucidate the dynamic sensing response of IPMCs subject to a time-varying through-the-thickness compression (‘compression sensing’). The model relies on the continuum theory recently developed by Porfiri and co-workers, which couples finite deformations to the modified Poisson–Nernst–Planck (PNP) system governing the IPMC electrochemistry. For the ‘compression sensing’ problem we establish a perturbative closed-form solution along with a finite element (FE) solution. The systematic comparison between these two solutions is a central contribution of this study, offering insight on accuracy and mathematical complexity. The method of matched asymptotic expansions is employed to find the analytical solution. To this end, we uncouple the force balance from the modified PNP system and separately linearise the PNP equations in the ionomer bulk and in the boundary layers at the ionomer–electrode interfaces. Comparison with FE results for the fully coupled nonlinear system demonstrates the accuracy of the analytical solution to describe IPMC sensing for moderate deformation levels. We finally demonstrate the potential of the modelling scheme to accurately reproduce experimental results from the literature. The proposed model is expected to aid in the design of IPMC sensors, contribute to an improved understanding of IPMC electrochemomechanical response, and offer insight into the role of nonlinear phenomena across mechanics and electrochemistry.

The use of virgin and recycled plastic macro fibers as reinforcing elements in construction materials has recently gained increasing attention from researchers. Specifically, recycled fibers have become more attractive owing to their large-scale availability, negligible cost, and low environmental footprint. In this work, we investigate the benefits related to the use of fully-recycled synthetic fibers as dispersed reinforcement in Fiber Reinforced Cement Composites (FRCCs). In light of the reference performance of FRCCs including virgin polypropylene (PP) fibers only, the mechanical response of composites reinforced with polyolefin filaments treated with a sol-gel silica coating and polyethylene terephthalate (PET)/polyethylene (PE) cylindrical draw-wire fibers is here assessed through three-point bending tests. Remarkably, recycled polyolefins lead to a notable enhancement in terms of peak strength and post-crack energy dissipation capability. This improvement is ascribed to both the flattened shape of fibers and the surface coating, which turns out to be very effective at strengthening the fiber-to-matrix bond. On the other hand, PET/PE fibrous reinforcement generally leads to a lower toughness, if compared to the virgin fibers. However, no reduction in terms of peak stress is evidenced. Balancing the significance of mechanical performance and environmental sustainability in the framework of a circular economy approach, both fully-recycled fibers at hand can be regarded as promising candidates for innovative structural applications.

We investigate antiplane Stoneley waves, localized at the discontinuity surface between two half-spaces in perfect contact. Both half-spaces are elastic linear isotropic and possess a microstructure that is described within the theory of couple stress materials with micro-inertia. In contrast to classical elasticity, where antiplane Stoneley waves are never supported and in-plane Stoneley waves exist only inasmuch as the ratio of the shear velocity of the half-spaces is small enough, we find that propagation is possible under broad conditions. However, Stoneley waves only propagate beyond a cuton frequency, for which an explicit expression is provided. For a given frequency above cuton, this expression lends the admissible range of material parameters that allows propagation. In particular, significant contrast between the adjoining materials is possible, provided that Stoneley waves propagate at high-enough frequency. Therefore, micro-inertia plays an important role in determining the features of propagation. Considerations concerning existence and uniqueness of antiplane Stoneley waves are given: it is found that evanescent and decaying/exploding modes are also admitted. Results may be especially useful when accounting for microstructure in Non-Destructive Testing (NDT) and near-surface prospection.

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We characterize poly(3-hydroxybutyrate- co -3-hydroxyhexanoate) (PHBH) scaffolds for tissue repair and regeneration, manufactured by three-dimensional fused filament fabrication (FFF). PHBH belongs to the class of polyhydroxyalkanoates with interesting biodegradable and biocompatible capabilities, especially attractive for tissue engineering. Equally, FFF stands as a promising manufacturing technology for the production of custom-designed scaffolds. We address thermal, rheological and cytotoxicity properties of PHBH, placing special emphasis on the mechanical response of the printed material in a wide deformation range. Indeed, effective mechanical properties are assessed in both the linear and nonlinear regime. To warrant uniqueness of the material parameters, these are measured directly through digital image correlation, both in tension and compression, while experimental data fitting of finite-element analyses is only adopted for the determination of the second invariant coefficient in the nonlinear regime. Mechanical data are clearly porosity dependent, and they are given for both the cubic and the honeycomb infill pattern. Local strain spikes due to the presence of defects are observed and measured: those falling in the range 70–100% lead to macro-crack development and, ultimately, to failure. Results suggest the significant potential attached to FFF printing of PHBH for customizable medical devices which are biocompatible and mechanically resilient.

Recent research has shown that hierarchical laminated composites can be profitably employed to improve the actuation performance of electricallyactivated soft dielectric transducers. This note focuses on two types of rank-two layouts composed of ideal dielectric phases which follow nonlinear hyper-elastic mechanical behaviour and aims at providing a simplified set of solving equations for voltage-controlled actuation. We obtain such equations by analytical manipulations allowing to partly uncouple the set of equations usually employed within this theoretical framework. By focusing on neo-Hookean hyperelasticity, we validate the proposed methodology with the results available in literature for one layout. For the other layout, we obtain new configurations by maximising the axial stretch. In both cases, we study the sensitivity of the optimal actuation stretch to changes of the parameters characterising the rank-two mesoand micro-structures. In average, the computational time required to reach a convergent solution with the new methodology is one order of magnitude lower than that necessary to solve the whole set of nonlinear coupled equations.

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