An Analytical Shape Memory Polymer Composite Beam Model for Space Applications

Shape memory polymers (SMPs) are evolving intensively in smart materials research. SMPs can undergo large deformations, hold a temporary shape and then recover their original shape upon exposure to a particular external stimulus. The emerging development of fibre reinforced shape memory polymer composites (SMPCs) has improved SMPs’ mechanical properties to be comparable to modern fibre reinforced composites. Moreover, the inclusion of nanoparticles has enhanced the diversity in activation mechanisms and improved structural properties and durability.
\n
\nToday, the SMPCs are generally viewed as promising substances for engineered applications that have raised intensive interest among the scientists and engineers. Interestingly, stimulation by light enables unique and advanced shape memory effects (SMEs) in SMPCs that can fulfill the sophisticated demands of engineering. The ability to vary the light wavelength, intensity, periodicity, polarization and the irradiated position on the SMP component enables wavelength selective, reversible, sequential and multiple SMEs. Furthermore, light travel long distances in a vacuum, can be focussed onto a certain area, is safe to humans and, can be a control signal carrier and most notably, can be sent through optical fibres to extremely inaccessible areas.
\n
\nIncorporation of metallic, carbon and organic based photothermal fillers into a SMP matrix is a convenient proven method to prepare light activated shape memory polymer composites (LASMPCs). These photothermal fillers convert electromagnetic radiation into thermal energy that triggers the SMP matrix. The current study comprehensively reviewed the performances, mechanisms, challenges and limitations of the existing LASMPC systems and associated optical technologies. Predominantly this research was intended to develop reinforced LASMPC systems and allied optical technologies applicable for large scale structural engineering applications.
\n
\nIn this study, styrene and bisphenol A epoxy based thermosets and polylactic acid (PLA) based thermoplastic SMPs were used as polymer matrix materials. Carbon fibre, glass fibre, multiwalled carbon nanotube (MWCNT) and rare earth organic complexes of Nd(TTA)3Phen and Yb(TTA)3Phen were used as reinforcement and photothermal fillers. The samples were produced by means of vacuum bagging, mould casting and 4D printing. Morphological investigations were conducted to identify the microstructure and manufacturability of the LASMPCs. The samples’ mechanical and physical properties were tested by standard test methods for polymer matrix composites. Dynamic mechanical analysis was carried out to determine the thermomechanical characteristics. The photothermal effect was investigated through thermal imaging and associated shape memory behaviours were studied through shape fixing and recovery experiments. A finite element analysis was performed with ABAQUS to simulate the photothermal heating behaviour.
\n
\nThe current study established a material development framework for LASMPC materials and presented apt manufacturing methods for structural and large scale engineering applications. Different modes of light diffusion such as scattered low intensity light, focussed laser beams and light delivery through fibre optics were proved for structural LASMPCs. Sequential and selective wavelength activation of structural LASMPCs are presented. The FEA simulation provided additional understanding on light exposed LASMPCs’ 3-dimensional heating behaviour. Embedding a D-shaped optical fibre in an LASMPC created a single unit smart actuator, which was remotely activated by light. It was proven that flexible radiation shields can reduce the unanticipated shape recovery of LASMPCs components and protect the LASMPCs from polymer degradation due to radiation.
\n
\nThe improvements to their structural properties and innovative remote activation methodologies have justified LASMPCs’ aptness for space engineering applications. This study has proven its successful completion by three selected case studies of space applications. An LASMPC solar panel array model was sequentially deployed in four recovery steps. In a vacuum, a space habitat structure model was compressed to a third of its volume and then recovered its original shape. A 4D printed boom structure model was tested, proving customized LASMPC structures for sophisticated space equipment fabrication. The deployable LASMPC structures can reduce the occupied room in spacecraft. The improvements to the structural properties of LASMPCs while keeping the SME, understanding on thermomechanical and photothermal behaviours, remote actuation through optical fibres, radiation shields and the insight to space applications are the most significant novel outcomes of this study. This thesis opens up windows of opportunity for the scientific and engineering communities to provide innovative solutions to realize the sophisticated large scale engineering demands in aerospace and space applications and beyond.

Shape memory polymers (SMPs) are a new type of smart material, they perform large reversible deformation with a certain external stimulus (e.g., heat and electricity). The properties (e.g., stiffness, strength and other mechanically static or quasi-static load-bearing capacity) are primarily considered for conventional resin-based composite materials which are mainly used for structural materials. By contrast, the mechanical actuating performance with finite deformation is considered for the shape memory polymers and their composites which can be used for both structural materials and functional materials. For shape memory polymers and their composites, the performance of active deformation is expected to further promote the development in smart active deformation structures, such as deployable space structures and morphing wing aircraft. The shape memory polymer composites (SMPCs) are also one type of High Strain Composite (HSC). The space deployable structures based on carbon fiber reinforced shape memory polymer composites (SMPCs) show great prospects. Considering the problems that SMPCs are difficult to meet the practical applications in space deployable structures in the recent ten years, this paper aims to research the mechanics of deformation, and failure of SMPCs. In the overall view of the shape memory polymer material’s nonlinearity (nonlinearity and stress softening in the process of pre-deformation and recovery, relaxation in storage process, irreversible deformation), by the multiple verifications among theory, finite element and experiments, one obtains the deformation and mechanism for the process of “pre-deformation, energy storage and actuation and its non-fracture constraint domain. Then, the parameters of SMPCs will be optimized. Theoretical analysis is realized by the strain energy function, additionally considering the interaction strain energy between the fiber and the matrix. For the common resin-based or soft-material-based composites under pure bending deformation, we expect to uniformly explain the whole process of buckling occurrence, evolution and finally failure, especially for the early evolution characteristics of fiber microbuckling inside the microstructures. The research results are meaningful for the practical applications for SMPC deployable structures in space. Considering the deformation mechanisms of SMPCs, the local post-microbuckling is required for the unidirectional fiber reinforced composite materials, at the conditions of its large geometrical deflection. The cross section of SMPC is divided into three areas: non-buckling stretching area, non-buckling compressive area, and buckling compressive area. Three variables are considered: critical buckling position, and neutral plane, the fiber buckling half-wavelength. Considering the condition of the small strain and large displacement, the strain energy expression of the SMP/fiber system was derived, which contains two types, e.g., strain energy of SMP and fiber. According to the minimum energy principle, the expression for all key parameters were derived, including the critical buckling curvature, neutral plane position, the buckling half-wavelength, fiber buckling amplitude, and strain.

Shape memory property and mechanism of the knitting-fabric reinforced epoxy composites subjected to tensile loading

Typical techniques for creating synthetic morphing structures suffer from a compromise between quick shape change and geometric complexity. A novel approach is proposed for encoding numerous shapes and forms by magneto-electroactive shape memory polymer composite (SMPC) structures and integrating sustainability with 4D printing (4DP) technology. Electrically driven, remote controllability, and quick reaction are the features of these sustainable composite structures. Low-cost 4D-printed SMPC structures can be programmed remotely at high temperatures to achieve multi-stable shapes and can snap repeatedly between all programmed temporary and permanent configurations. This allows for multiple designs in a single structure without wasting material. The strategy is based on a knowledge of SMPC mechanics, magnetic response, and the manufacturing idea underlying fused deposition modelling (FDM). Iron-filled magnetic polylactic acid (MPLA) and carbon black-filled conductive PLA (CPLA) composite materials are investigated in terms of microstructure properties, composite interface, and mechanical properties. Characterisation studies are carried out to identify how to control the structure with a low magnetic field. The shape morphing of magneto-electroactive SMPC structures is studied. FDM is used to 4D print MPLA and CPLA adaptive structures with 1D/2D-to-2D/3D shapeshifting by the magnetic field. The benefits of switchable multi-stable structures are reducing material waste and effort/energy and increasing efficiency in sectors such as packaging.Graphical

A novel shape memory polymer composite was fabricated by introducing various amounts of silicon carbide whiskers (SiCws) into a shape memory epoxy. The relationship between the thermomechanical properties of the system and structural changes were investigated via dynamic mechanical analysis, scanning electron microscopy, and bending tests. The results show that the bend strength of composites can improve by 64.1% when SiCw content reaches 12 wt %. The shape transition temperatures of SiCw/epoxy composites decreased slightly with the increase in SiCw content, but it was noted that all of the composites showed excellent shape memory properties. The shape fixity ratio increased as SiCw content increased (>99%), and the shape recovery ratio slightly decreased as SiCw content increased (>95%). All of the composites nearly recovered to their original shape within 2 min (not 100%), and the shape recovery speed significantly improved at a higher temperature. It is anticipated that tagging products will be used in the aerospace industry.

Shape memory polymers (SMPs) are employed in a wide range of fields because to their appealing properties, which include low density, low production costs, and ease of processing. In the present work, SMP composites were developed using ultrasonic mixing of carbon fiber (CF) and amorphous epoxy to enhance the properties of epoxy and shape memory effect. The prepared composites were tested for mechanical and shape memory properties. Flexural strength and tensile strength of pristine epoxy enhanced after dispersing 1% CF which are about 12.7% and 16.2%, respectively, higher than pristine epoxy. Fracture toughness of epoxy improves after adding 1% CF which is about 94.05% higher compared to pristine epoxy. UV–vis-NIR showed reduction in energy bandgap. Shape fixity and shape recovery ratios for pristine epoxy was 98.49% and 93.40%, respectively. These ratios decrease to 90.52% and 87.86%, respectively with addition of 1.5 wt.% CF. However, recovery time improves from 57 s to 33 s with addition of 1.5 wt.% CF in epoxy. Shape recovery rate enhances with CF reinforcement in epoxy composite.

Shape memory polymers (SMPs) possess the remarkable ability to recover their original shape after being severely deformed, triggered by the right stimulus. This chapter reviews recent progress in shape memory materials, focusing on traditional types like shape memory alloys (SMAs) and SMPs, as well as emerging shape memory hybrids, which enable customizable properties for specific applications in a “do-it-yourself” manner. SMPs, in particular, show great promise for morphing aircraft applications due to their temperature- and time-dependent mechanical properties. Tests on SMPs under monotonic loading in high shear demonstrate their ability to recover original shapes while resisting large loads. Advances in SMP composites (SMPCs), which incorporate functional materials and nanostructures, further enhance their deformation recovery, mechanical properties, and controllable actuation. SMPs have broad applications across aerospace, biomedical devices, flexible electronics, and more. This chapter also provides an in-depth analysis of the shape recovery mechanisms, multifunctionality, and potential future directions for SMP development.

A shape memory polymer is capable of multifunctional performance, be it structural or non-structural. Several actuation mechanisms can be employed to trigger shape memory behaviour. Among these, thermal actuation is most comprehensively studied and applied due to its ease of understanding and utility. However, from the point of view of some niche applications, electrical actuation also needs to be examined. This is all the more relevant for modern aircraft where actuation is amenable to remote computer controls and advanced instrumentation. This in turn paves the way for realizing lightweight and adaptive aircraft structures. In this work, shape memory performance via electrical actuation of unidirectional carbon ply–epoxy shape memory polymer composites has been investigated using an in-house designed test set-up in the manual and automated modes. The synergistic role of carbon plies and the epoxy shape memory polymer matrix for realizing faster shape recovery has been observed. The effect of number of carbon plies on the cyclic shape memory performance of the shape memory polymer composite has also been evaluated. This work demonstrates the feasibility of developing efficient electrically actuated shape memory composites and their potential for different applications.

Functional polymer composite is expected to be applied to the potential material for space deployable structures. Especially, thermally-activated shape-memory polymer (SMP) composites are increasingly investigated due to their excellent shape fixity and shape recovery; the thermomechanical properties of these materials greatly change around their glass transition temperature Tg. To enhance the ability of space deployable structures, the microstructural design at the fiber-matrix level in the material is required to pursuit the better performance of SMP composite. The present study focused on a micromechanics consideration of shape-memory polymer (SMP) composite with slits in the fiber mat, and attempted to discuss the effect of microstructural heterogeneities (slit positions) on the shape-fixity and shape-recovery performance. Analysis of the shape-recovery performance of SMP composites was conducted using the micromechanical model based on a viscoelastic thermomechanical constitutive model. According to the numerical results, only when the slits gather at the same location, the best shape-fixity property and shape-recovery performance is achieved, while sacrificing its bending stiffness. This is because the slits act as a hinge in the material under a bending loading.

Abstract. A novel architecture of shape memory polymer composite (SMPC) sandwich actuator has been designed and prototyped. Epoxy foams obtained by a solid-state process without the use of foaming agent were placed in the center of the device. High performance Carbon Fiber Reinforced (CFR) prepreg was used for the external skins and at the edges of the device to increase the stiffness of the actuator. Thermal activation was obtained through a flexible heater powered with a maximum tension of 26 V. Moreover, SM thin layer (interlayer) obtained by the same resin used for the foam were deposited to insulate the heater from the CFR plies and to allow adhesion of the foam to the bottom CFR skin. Two more actuators in the forms of a 2-ply laminate and of a 2-ply sandwich with two epoxy foams placed in the center of the device were also manufactured for comparison. All the actuators were manufactured by a hot press moulding process. At the end of manufacturing, optical images revealed the soundness of the manufacturing procedure. Memory, constrained recovery and free recovery tests in three point bending configuration were performed to evaluate the shape memory performances and the actuation loads. The developed actuator exhibited the highest value of shape fixity (97 %) and high shape recovery ratio (95 %) with also interesting actuation load of about 2.3 N.

The applications of the elastocaloric cooling effect (eCE) of shape memory poly(cyclooctene) (PCO) to portable cold-storage devices at high temperatures have been demonstrated. These applications arise due to its good shape fixation properties upon cold-drawing. In this paper, we report that carbon fabric-reinforced PCO composites exhibit enhanced eCE compared to pure PCO due to the increased elasticity and Clausius–Clapeyron factor by carbon fabric reinforcement. The elastocaloric heating and cooling effects of PCO-based shape memory polymer composites (PCO-SMPCs) were characterized and predicted using a constitutive equation of woven fabric-reinforced SMPC and their eCE was analyzed in terms of thermodynamic parameters. Good agreement between experiments and simulations was obtained, showing that 3D finite element analysis can facilitates the design of surface adaptable solid-state coolers fabricated from PCO-SMPC with good efficiency and portability properties.

Shape memory polymers (SMPs) is a type of smart polymers. Shape-memory polymers (SMPs) allow for the development of stimuli-responsive polymer-based materials that can undergo substantial recoverable deformation in response to an external stimulus. Shape-memory effects (SMEs) of these SMP-based materials for task-specific applications are picking the interest of academic and industrial researchers. Significant progress has been gained in the field of shape memory polymers (SMPs) in recent years, with the discovery of new compositions for property tweaking, the discovery of new processes for shape fixing and recovery, and the initiation of phenomenological modelling. The current review will provide a brief account of the history of SMPs, their qualities, their structure and mechanism, classification, biodegradable SMPs and use of SMPs in various fields. Recent advancements in shape memory polymer composites (SMPCs) and shape-memory polymer blends (SMPBs) are also emphasized. This review explains distinct classification criteria of SMPs with a view of polymer type and structure and external stimulation.

Shape memory polymer (SMP) is one of the most highly researched branches of polymer materials in the recent past. It is often called as a smart material due to its unique capability to memorize original shape. Up to now, shape memory polymer composites (SMPCs) are widely being used for developing light weight and low thickness components for space missions. Increasing thickness and fibre layers will improve mechanical properties, but can adversely affect shape memory effect (SME) and increase the possibility of delamination when programming. To study this phenomenon, a 3 × 3 Taguchi array for material thicknesses of 3, 4 and 5 mm was developed. Carbon, glass and basalt fibres were used to reinforce SMPs in various mass fractions. Shape programming was carried out at the onset of storage modulus (TS) and peak of Tan (δ) (Tδ). SME was analysed in terms of fixity ratio (Rf), recovery ratio (Rr) and areal damage percentage (ADP) due to programming. Samples deformed at Tδ showed high ADP (> 16%) while at TS minimal ADP was 0.7 %. Moreover, addition of a unidirectional fibre layer in the compressing side of the specimen (with fibres parallel to the width) has minimized local fibre buckling when programming.

4D printing of tracheal scaffold using shape-memory polymer composite

A fiber reinforced thermosetting styrene-based shape-memory polymer composite (SMPC) is developed, and the main objective is to investigate the deployment performances for SMPC. Firstly, the fundamental material properties, such as mechanical properties and shape recovery properties, are evaluated. It indicates that the SMPC shows nonlinear viscoelasticity at a temperature range between T g -20°C and T g +20°C. At/above T g , the shape recovery ratio of SMPC upon bending is above 90%. The shape recovery properties of SMPC become relatively stable after some packaging/deployment cycles. Then, the micro-deformation mechanism is characterized by optical microscopy and SEM. The fiber microbuckling is the primary deformation mechanism in bending of SMPC, and it ensures that the SMPC can achieve high packaging strain and avoid fiber failure. With the microbuckling, SMPC materials are suitable to be used in deployable structure components because of their high strain-to-failure capability. For the analytical research, the relationship between deployment moment and angle is derived by using dynamic theory. It shows that the SMPC shell shows a linear bending stiffness when recovering, and meanwhile performs a self-locking function at the final state because of sharply increase in moment. It implies that SMPC is a good candidate material for deployable structures.