Shape memory polymer composites (SMPCs) are being evaluated for aerospace applications due to their lightweight and ease of self-deployment. For such applications, the mechanical properties of SMPCs, including long-term behavior, need to be determined in the particularly harsh environments that are likely to be encountered. In this study, the storage modulus of carbon fiber-reinforced SMPCs (CF-SMPCs) was investigated under high vacuum condition and ultraviolet (UV) irradiation. The storage modulus of CF-SMPCs generally degrades as a function of time and temperature. However, the opposite behavior was observed under vacuum and UV exposure due to induced crosslinking. These two phenomena were characterized separately using acceleration tests at various temperatures under UV irradiation in a vacuum chamber and were modeled as two time-temperature superposition laws. The long-term mechanical behavior of CF-SMPCs in vacuum and UV environment is predicted by a linear product of shift factors obtained from the two acceleration tests.

Four-dimensional (4D) printing is used to describe three-dimensional (3D)-printed objects with properties that change over time. Shape memory polymers (SMPs) are representative materials for 4D printing technologies. The ability to print geometrically complex, free-standing forms with SMPs is crucial for successful 4D printing. In this study, an SMP capable of frontal polymerization featuring exothermic self-propagation was synthesized by adding cyclooctene to a poly(dicyclopentadiene) network, resulting in switching segments. The rheological properties of this SMP were controlled by adjusting incubation time. A nozzle system was designed such that the SMP could be printed with simultaneous polymerization to yield a free-standing structure. The printing speed was set to 3 cm/min according to the frontal polymerization speed. A free-standing, hexagonal spiral was successfully printed and printed spiral structure showed excellent shape memory performance with a fixity ratio of about 98% and a recovery ratio of 100%, thereby demonstrating the 3D printability and shape memory performance of frontally polymerizable SMPs.

The mechanical modeling and simulation of woven fabric-reinforced shape-memory polymer composites (wf-SMPCs) are quite complex tasks because a temperature change introduces thermal stress that dramatically affects the interaction between the matrix and fiber. This study aimed to develop a new homogenized constitutive model for wf-SMPCs considering the thermally induced residual stress. The orthotropic properties of the wf-SMPC due to the woven fabric reinforcement were modeled using classical anisotropic hyperelasticity theorems. The stress generated in the hyperelastic model was then complemented by combining with the stress generated in the SMP constitutive equation and the thermal residual stress according to Eshelby's inclusion theorem. The prediction capability of the proposed model was verified by three-point bending tests of the wf-SMPC having various fiber volume fractions. Finally, the unique features of the proposed constitutive model were investigated by experiments and simulation of a self-deployable antenna made of a wf-SMPC.

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Carbon fiber-reinforced shape memory polymer composites (CF-SMPCs) have been researched as a potential next-generation material for aerospace application, due to their lightweight and self-deployable properties. To this end, the mechanical properties of CF-SMPCs, including long-term durability, must be characterized in aerospace environments. In this study, the storage modulus of CF-SMPCs was investigated in a simulation of a low Earth orbit (LEO) environment involving three harsh conditions: high vacuum, and atomic oxygen (AO) and ultraviolet (UV) light exposure. CF-SMPCs in a LEO environment degrade over time due to temperature extremes and matrix erosion by AO. The opposite behavior was observed in our experiments, due to crosslinking induced by AO and UV light exposure in the LEO environment. The effects of the three harsh conditions on the properties of CF-SMPCs were characterized individually, using accelerated tests conducted at various temperatures in a space environment chamber, and were then combined using the time–temperature superposition principle. The long-term mechanical behavior of CF-SMPCs in the LEO environment was then predicted by the linear product of the shift factors obtained from the three accelerated tests. The results also indicated only a slight change in the shape memory performance of the CF-SMPCs.