Paolo Ermanni

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Ermanni

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Paolo

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0000-0003-0158-3845

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Publications1 - 10 of 100

Programmable FRP metamaterials for adaptive hinges with multiple 3D shapes
Risso, Giada; Rogenmoser, Tim J.; Sakovsky, Maria; et al. (2021)
AIAA SCITECH 2022 Forum
In many applications, structures need to reversibly change between different 3D shapes to adapt to different environmental conditions or operational requirements. To date, the majority of reconfigurable structures require continuous actuation to hold a selected configuration. Multi-stable elements could potentially be used for shape reconfiguration because they can maintain different 3D shapes without needing a continuous power supply. However, when integrating multi-stable elements with other components, boundary conditions are negatively affecting the multi-stability. A new concept that combines flat fiber-reinforced polymer (FRP) composite shells with bi-axially pre-stretched membranes to realize highly multi-stable structures was recently presented by the authors. In this study, the concept of FRP metamaterials is adapted to realize a hinge that possesses five stable angular configurations. Thanks to the low influence of the boundary conditions on the multi-stability and the large shape change that the structure undergoes, the proposed hinge design demonstrates that FRP metamaterials enable the realization of highly reconfigurable structures. The hinge can achieve angular positions larger than 180° in both directions. Two parametric studies show that the angular positions of the hinge can be tailored by changing either the bending stiffness of the FRP composite shells or the pre-stretch of the membrane. A reconfigurable array of stiff panels connected by adaptive hinges is presented, showing potentials for the realization of a solar array that can change its shape to track the sun or be reversibly stowed and deployed.
Network of selectively compliant actuators based on shape memory alloys and polymers for a reconfigurable sandwich panel
Testoni, Oleg; Bodkhe, Sampada; Bergamini, Andrea; et al. (2023)
Journal of Intelligent Material Systems and Structures
Shape memory alloys (SMA) allow for the realization of smart actuators capable of achieving large stresses and large strains but highly demanding in terms of power input. This work presents a solution integrating shape memory polymers (SMP) in a novel type of selectively compliant actuator to reduce the power input of SMAs. The thermally induced variation in stiffness of the SMP is used to achieve large deformations by temporarily increasing the compliance of the actuator and to lock the actuator in a deformed state by restoring the initial stiffness. The behavior of the actuator is simulated taking into account the viscoelastic behavior of the SMP and validated through a comparison with experimental results. The latter show that the proposed actuator can achieve a maximum contraction of 3.0% and hold a contraction of about 1.6% multiple times without constantly powering the SMA. Finally, a reconfigurable sandwich panel is considered as possible application. A distributed actuator network is implemented in the face sheets of the panel and a digital image correlation system is used to prove the capability of the proposed structure of undergoing large deformations, holding a deformed shape without consuming energy, and recovering its initial shape. A further development of this panel might find application as support structure for morphing aerodynamic surfaces or reconfigurable antennas.
Manufacturing studies of a polymeric/composite heart valve prosthesis
Chen, Mary Jialu; Pappas, Georgios A.; Smid, Caroline C.; et al. (2024)
Polymer Composites
Current transcathether heart valves rely on metal mesh stents, resulting in discontinuous stent-leaflet interfaces that introduce stress concentrations, reducing valve lifetime. This work aims to investigate non-conventional methods to create a fully polymeric transcatheter heart valve, exhibiting a quasi-continuous interface with hemocompatible leaflets with high durability potential. Polyetheretherketone (PEEK) is of particular interest as a cardiovascular material due to hemocompatibility and mechanical resilience, highly relevant for catheter delivered valves. For increased reproducibility and design freedom, an autoclave process was used to manufacture thin-ply PEEK composite stents. We demonstrated that a suitable membrane material during manufacturing is essential to evenly distribute pressure around the stent. Meanwhile, a modified vacuum forming process was used to simultaneously form and attach PEEK leaflets to the stent using a heated mold. This simple and robust method enables rapid manufacturing of an integral PEEK-based valve design, resulting in improved stent-leaflet bonding, demonstrating an alternative to conventional dip-coating. The customized vacuum forming causes a controlled annealing effect in semicrystalline materials such as PEEK. Processing PEEK leaflets at higher mold temperatures results in higher crystallinity, elastic modulus, and bond strength. These processes enable greater design flexibility and promote composite materials for use in heart valve devices.
A novel computational framework for structural optimization with patched laminates
Kussmaul, Ralph; Jónasson, Jónas; Zogg, Markus; et al. (2019)
Structural and Multidisciplinary Optimization
Fiber patch placement (FPP) is a manufacturing technique for discrete variable stiffness composites. In the FPP approach, a structural component is assembled from a multitude of discrete fiber patches. However, due to the discontinuous fibers at patch edges, complex stress distributions occur. To date, a holistic FPP design framework that combines a tailored patch placement method with a dedicated mechanical model for the analysis of patched laminates does not exist. This article introduces a novel approach for the design of fiber patched laminates. It is based on the sequential placement of patches on a finite element shell mesh, using a critical element and angle selection routine in order to optimally locate and orientate fiber patches. They are added to the 3D mesh by employing a highly efficient kinematic draping algorithm. Strength-critical regions of the resulting fiber patched laminates are identified by state-of-the-art finite element analysis and extracted to a shear-lag–based mechanical submodel dedicated to the detailed analysis of patched laminates. The patch placement routine terminates once all design optimization criteria are met. The efficiency of applying optimized patch reinforcements on a continuous fiber-reinforced base laminate is demonstrated using the example of an individualized biomedical component. The work at hand presents the first patched laminate design framework combining a patch placement strategy coupled with a dedicated mechanical model. As a consequence, a substantial progress in the design of patch laminated structures is achieved.
Stiff Composite Cylinders for Extremely Expandable Structures
Ermanni, Paolo; Schlothauer, Arthur (2019)
Scientific Reports
Instability-driven shape forming of fiber reinforced polymer frames
Risso, Giada; Sakovsky, Maria; Ermanni, Paolo (2021)
Composite Structures
Thin fiber reinforced polymer (FRP) composites are widely implemented in adaptive and morphing structures. However, realization of the necessary complex 3‐dimensional FRP structures requires the use of expensive molds thereby limiting the design space and flexibility. Using the elastic strain energy of pre‐stretched membranes holds potential for addressing this challenge. In this work, a novel manufacturing technique for fabricating 3‐dimensional FRP structures moldlessly is presented where pre‐stretched membranes are used to drive out‐of‐plane buckling instabilities of FRP composite shells. To explore the potential of this approach, a simple square frame design is investigated. An analytical model based on high deformation beam buckling theory is developed for understanding the parameters driving the out‐of‐plane behavior of these structures. Experimental and finite element results are used for model validation and reveal excellent agreement, with errors less than 10% over a large portion of the design space. Analytical and finite element models demonstrate that the out‐of‐plane deformation can be tailored by varying the structure’s geometric and material parameters. A new design space for FRP composite laminates is characterized, enabling highly flexible design. The manufacturing and modeling techniques can be extended to other geometries for the realization and analysis of arbitrarily complex surfaces.
Combined experimental–numerical approach for through-thickness unsaturated permeability characterization of deformable fiber-beds
Kabachi, Mohammed Ayyoub; Sandberg, Michael; Ermanni, Paolo (2025)
Composite Structures
Successful implementation of Liquid Composite Molding processes relies on a thorough knowledge of the flow and fiber-bed behavior, with unsaturated permeability being a key parameter. This paper presents a combined experimental–numerical method for the characterization of unsaturated through-thickness permeability of deformable engineering textiles. The experimental procedure, developed in a previous study, is based on visual tracking, and recording of flow-front advancement and eventual flow-induced fiber-bed deformation. This information, along with material and injection parameters, is fed to a numerical dual-scale flow model implemented using a finite volume scheme. The model considers different aspects of the impregnation, namely macro and micro flows between and inside fiber bundles, capillary flow, and fiber-bed deformation. The macro and micro permeability curves are obtained through an inverse method that considers different experimental parameters. The method is successfully applied on a glass fiber Non-Crimped-Fabric, where permeability results satisfy all the employed processing and material conditions.
Flow induced sample deformations in out-of-plane permeability measurement
Willenbacher, Björn; Kabachi, Ayyoub; May, David; et al. (2020)
A novel concept of modular shape-adaptable sandwich panel with distributed actuation based on shape memory alloys
Testoni, Oleg; Christen, Sandro; Bodkhe, Sampada; et al. (2022)
Journal of Intelligent Material Systems and Structures
This work introduces a novel concept of modular, shape-adaptable sandwich panel with a distributed actuation system based on shape memory alloys (SMA). The panel consists of a modular arrangement of rigid cells connected with compliant active joints. Each joint hosts a SMA wire, which can be controlled independently, enabling the panel to achieve multiple shapes and complex curvatures with a single design. A numerical model of the actuators is developed combining the SMA model proposed by Brinson with a finite element model of the compliant joints, and validated against experimental results. Further, a demonstrator of the panel is manufactured and tested implementing four different actuation patterns and measuring the final shapes with a digital image correlation system. The results prove the capability of the proposed concept to achieve both in plane and out-of-plane deformations in the order of millimeters to centimeters, and to reproduce shapes with double curvatures. With the possibility to integrate sensors and additional components inside the core, the proposed shape-adaptable panel can be used to realize smart structures, which might be used for morphing aerodynamic surfaces or reconfigurable space structures.
AORCEA – An adaptive operator rate controlled evolutionary algorithm
Giger, Mathias; Keller, David; Ermanni, Paolo (2007)
Computers & Structures
When applying evolutionary algorithms to optimization problems many different strategy parameters have to be set to define the behavior of the evolutionary algorithm itself. To a certain extent these strategy parameter values determine whether the algorithm is capable of finding a near-optimum solution or not. In particular the choice of the different genetic operators and their relative rates is most often based on experience. Furthermore, the operator rates are defined before starting the optimization runs and remain unchanged until the stopping criterion is reached. Controlling the parameter values during the run has the potential of adjusting the algorithm to the problem while solving the problem. This paper investigates an adaptive strategy controlling the rates of arbitrary chosen genetic operators. The control mechanism is based on the state of the optimization by evaluating a success and a diversity measure for each operator. More efficient operators are favored in order to find better solutions with less evaluations. The algorithm is tested with constrained and unconstrained numerical examples and a concrete structural optimization problem is treated.

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Paolo Ermanni

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