Flexible composite structures with controlled physical and mechanical characteristics
Authors: Likhachev Alexey N. 
Published: April 2023

The article presents the results of theoretical and experimental studies that are the basis for the development of a new class of aerospace engineering structures that allow implementing approaches to create structures with variable morphological and functional characteristics of products. Condensed soft substances, such as elastomers, gels, gradually become functional elements on the basis of which the creation of soft machines and electronics develops [1-3]. Research in this direction has led to the creation of structures with a special architecture that are mechanically compatible, deformable and capable, with a certain combination, of perceiving and transmitting a signal, changing their shapes and physical characteristics (thermal conductivity, electrical conductivity, etc.). The use of such structures in a certain sense models the multifunctionality observed in biological objects and structures (skin, muscles, nervous tissue) [4-7]. The creation of structures that change their shape, structure and change their functional and operational characteristics in the process of work, taking into account changing external and internal conditions, is an urgent task for many systems of aerospace technology. In this paper, morphologically changeable structures are considered, which include reconfigurable antennas, aircraft wings with variable shape and geometry, flexible robotic systems [8]. The use of such systems with flexible structural elements makes it possible to create structures capable of overcoming unpredictable obstacles due to their adaptive geometry, fit into limited spaces and withstand significant loads and vibrations. One of the most important tasks in the development of such systems is the organization of a distributed actuation system associated with the problem of creating an internal structure of actuators integrated into a flexible composite design of actuators made of elastic materials. In a number of works for the operation of thermoactive actuators, the use of rigid nanoparticles as surface heating elements or as fillers for composites that are electrically sensitive, magnetically sensitive and/or photoreactive has been investigated [9-13]. However, surface heating elements are limited in use beyond a thickness of several hundred micrometers due to their low intrinsic thermal conductivity [14]. In addition, rigid components significantly change the mechanical properties of the structure being created, which limits the morphological capabilities of the structures being created. For example, in [15], it is shown that reducing the electrical resistance for a thermal heater to acceptable values requires an increase in the filler to 15% of the mass of the structure, while the deformation of the actuation of the structure is reduced by 35.0%. In this paper, overcoming the above limitations is carried out by creating a material architecture that dramatically expands the range of properties and dynamic functions of the heating element being developed for the actuator. Multifunctionality is achieved by embedding metal fibers of a certain configuration into an elastic medium based on polydimethylsiloxane elastomer, which provide mobility and conformality of the deformable structure of the actuator during its operation. It is shown that the inclusion of metal fibers of a certain configuration in the structure of the actuator does not interfere with its ability to change shape and perform mechanical work in response to external stimuli. Shape morphing in the absence of an external load can be programmed in the composite structure by including fibers with certain stiffness and thermal characteristics in it so that it can reversibly switch between programmed morphologies using electrical or thermal stimulation. Together, these properties allow the composite to demonstrate a rich variety of functionality, which allows it to simultaneously realize sensory and dynamic characteristics.