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In recent years the use of multi-stable components for designing adaptive structures and energy harvesting systems has been broadly investigated. Most of these studies have concentrated on analyzing the equilibrium shapes and the snap-through loads of the bi/multi-stable elements. However, there is minimal work on quantifying the strength of these stable equilibrium shapes. The strength of stable states is a measure of the ease or difficulty of the transition between the different stable states of any multi-stable system. Quantifying the strength of stability becomes paramount while designing adaptive structures which integrate multi-stable elements. Previous studies have argued that snap-through loads represent the goodness of stability; however, the magnitude of the snapthrough load highly depends on the boundary conditions of the structure and the loads’ application point. This work presents a mathematical framework that quantifies the strength of stability of the stable equilibrium shapes of multi-stable elements and identifies the minimum energy path (MEP) between two stable states. The method is based on finding, either with an analytical approach or finite element (FE) models, the stable and transition points of the energy landscape. Results prove that the method provides a quantitative measure of stability, a key parameter when designing adaptive structures. In addition, the minimum energy path between two stable states provides a tool to simplify the design of efficient actuation strategies for multi-stable systems. Four numerical examples are detailed to demonstrate the robustness of the approach., Thin-Walled-Structures, 189, ISSN:0263-8231, ISSN:1879-3223

Shape transformation offers the possibility of realizing devices whose 3D shape can be altered to adapt to different environments. Many applications would profit from reversible and actively controllable shape transformation together with a self-locking capability. Solutions that combine such properties are rare. Here, a novel class of meta-structures that can tackle this challenge is presented thanks to multi-stability. Results demonstrate that the multi-stability of the meta-structure is strictly tied to the use of highly anisotropic materials. The design rules that enable large-shape transformation, programmability, and self-locking are derived, and it is proven that the shapes can be actively controlled and harnessed to realize inchworm-inspired locomotion by strategically actuating the meta-structure. This study provides routes toward novel shape adaptive lightweight structures where a metamaterial-inspired assembly of anisotropic components leads to an unforeseen combination of properties, with potential applications in reconfigurable space structures, building facades, antennas, lenses, and soft robots., Advanced Science, 9 (26), ISSN:2198-3844

Airbus is working on various technologies to make future A/C more sustainable. One of them are disruptive, more efficient, wing designs comprising i.a. adaptive structures inducing the need for new materials & processing technologies. Together with ETH Zurich thin ply CFRTPs are investigated for damage tolerant mechanical hinges. Investigations include interaction of processing and mechanical performance. Novel, highly controlled processing method for the TP-CFRTP are presented.

Fibre-matrix interface performance is essential in fibre reinforced polymer composites, leading to important efforts in quantification and optimization. This is even more relevant for thermoplastics, since interfacial bonding happens only via physical interactions. Standardised mechanical tests provide homogenized composite properties, but fail to isolate the contribution of the interface. Micromechanical ones are designed for this exact purpose, but need complex set-ups and sample preparation. This study adopts a novel multiscale approach to measure mechanical properties of polycarbonate-glass fibre composites, manufactured under different interfacial conditions (sized & desized). This is enabled by use of focused ion beam in precise manufacturing and post-mortem analysis of specimens. The results show an evident difference between tested conditions at the macroscale (mode I), where sized specimens outperform desized ones. At the microscale (mode II), these differences are less pronounced due to the high ductility of the matrix resulting in a cohesive failure of the composite., Proceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability, ISBN:978-2-9701614-0-0

Hybrid fibres combine individual reinforcing filaments with a precise amount of thermoplastic polymer matrix, providing an alternative solution to pre-consolidated blanks in stamp forming of thermoplastic composites. Preforms made from such fibres remain flexible at ambient conditions. This study investigates the consolidation behaviour of unidirectional arrangements made from E-glass monofilaments clad in polycarbonate sheaths (69 vol% glass). It assesses the influence of pre-heating temperature, press temperature, and holding time inside the press on the resulting laminates’ void content. The results prove that preforms made from hybrid fibres can be directly stamp formed while achieving void contents below 0.35 vol% with dwell times inside the press as low as 5 s for 1 mm thick laminates.

One of the greatest challenges facing polymeric cardiovascular devices is the issue of hemocompatibility. Devices such as polymeric heart valves potentially offer improved mechanical properties and quality of life compared to their animal tissue counterparts. However, they are still strongly limited by problematic interactions with blood. The reduction of platelet adhesion, thrombogenicity, and calcification have been addressed in a variety of surface and bulk modification methods, generally by increasing the hydrophilic character of polymers. However, most hydrophilization processes – oxygen plasma in particular – tend to offer limited longevity. The crystallinity of polymers has previously been observed to influence the extent of platelet adhesion, though the underlying mechanisms for this phenomenon are not clear. In this research, we report on the effect of crystallinity on hemolysis, thrombogenicity, and platelet adhesion in PEEK surfaces. By tailoring the bulk crystallinity, we demonstrate changes in the surface chemical composition and propose a potential strategy to achieve longer term surface modification for improved hemocompatibility. Additionally, we explore the influence of crystallinity on the mechanical properties of thin PEEK films, establishing the multi-dimensional impact of polymer crystallinity. The results shown here may have implications for the design of polymeric cardiovascular devices and considerations that should be taken during material selection.