Composite Tape Springs Research Articles

Kinematics-driven design of reconfigurable bistable hinges with high stiffness and stability

Composite tape springs are curved shells with the ability to assume two energetically stable states. By carefully selecting layup and mold during manufacturing, these structures can store significant strain energy, making them ideal for deployable systems. Yet, their potential as reversible reconfigurable structures, particularly as adaptive hinges, remains largely unexplored. In structural applications, both stable states of these hinges must exhibit high stiffness to support loads while retaining the capacity for reversible reconfiguration. This paper introduces kinematics-based stacking concepts aimed at enhancing the stiffness of bistable hinges in both states, allowing for specific fold angles without compromising compliance. These designs leverage snap-through kinematics, resulting in unique architectures with customizable stiffness and stability. Additionally, the paper presents a novel energy-based semi-analytical approach for analyzing the stacking concepts. This approach involves constrained exploration of the energy landscape to assess the design space in terms of stiffness and energy barriers. Through comprehensive parametric studies, the research demonstrates significantly increased stiffness and reduced peak stresses compared to single tape spring designs. This research highlights the potential of employing tape springs as reconfigurable load-bearing structures in diverse applications, including precise adjustments of low-mass payloads like solar panels or antennas on space structures.

High-cycle folding fatigue mechanics of a bistable composite tape-spring

A bistable composite tape-spring (CTS) is a thin-walled open slit tube, which can be coiled or folded into two stable configurations. The CTS has been applied to roll-out-solar-array and successfully launched to space station and micro-satellites based on their one-time deployment performance. There is growing interest on CTS to be applied in reversible deployable structures and foldable mechanical hinges; however, its high-cycle fatigue under large shape folding is still unknown. Here, we device a novel folding fatigue setup to investigate the folding-unfolding cyclic behaviour of the CTS. This is achieved by using a bespoke folding fatigue rig, where both the tape ends of the CTS were clamped separately on rotatable shafts to enable folding under cyclic axial displacements. Since stress concentration is more significant in the snapping fold region, analysis is focused on the peak fatigue stress. It is found that the folding peak stress decreases with the folding cycle: although progressive local damage is observed during 3000 to 100,000 cycles, the CTS is still functional and tends to be stablised after 300,000 folding cycles. The Basquin’s law is applied to predict the fatigue life of the CTS, indicating a fatigue life of 1.4E11 folding cycles with a 40% decrease in peak folding stress. These findings are expected to facilitate the structural designs and applications of the CTS to flexible composite hinges.

Folding mechanics of a bistable composite tape-spring for flexible mechanical hinge

A bistable composite tape-spring (CTS) structure is stable in both extended and coiled configurations, which can be fully coiled or folded. Its bistable coiling feature has been employed in a Roll-Out Solar Array and successfully deployed in space; its foldable characteristics is analogous to a flexible mechanical hinge, showing great potential to be applied in an aircraft landing gear. Both the structural coiling and folding mechanics are dependent on tape geometry; whilst the correlated scale effect has not been investigated, which significantly constrains its foldable mechanical hinge designs and smart driving analysis in order to further reduce weight and complexity for conventional mechanical hinges. Here, we studied the folding stability mechanics of the CTS structure towards its full tape-length range, where novel stress and shape transitional mechanisms are revealed. This is achieved by investigating the quasi-static folding process of the CTS, where new stable shape features in terms of critical transitional length and stable folded angle are observed and identified through experimental observations, finite element model, as well as theoretical analysis. Theoretical criteria were then determined from the strain energy analysis in comparison to the predefined folded tape shape features. The folding stability mechanisms towards its full tape-length range were proposed in order to facilitate customized flexible hinge design and in-situ smart driving analysis in order to replace conventional mechanical hinges.

Optimizing deployment dynamics of composite tape-spring hinges

The composite tape-spring hinge (CTSH) is a lightweight structural connector widely employed in space structures, including spacecraft and satellites, due to its high specific strength and stiffness. Introducing cutouts enables CTSH to possess folding and deployment capability, while optimizing the cutouts finely to optimize the performance of CTSH. However, the interaction between cutout size and the dynamic deployment of CTSH is a novel topic. To address this, a multi-objective optimization problem is formulated, aiming to minimize both the maximum overshoot angle and deployment time while considering mass constraints. An accelerated size optimization is achieved by integrating data-driven surrogate modeling and size optimization. The optimized CTSH design exhibits a significant improvement in performance, with a 26.3% reduction in the maximum overshoot angle and a 12.6% reduction in the deployment time compared to the initial design. The proposed optimization strategy is highly adaptable and can be applied to various optimization problems, offering valuable insights for future designing space deployable structures with desirable performance.

A multistable composite hinge structure

A composite tape-spring (CTS) structure is a thin-walled open slit tube with fibres oriented at ±45°, which is stable in both extended and coiled configurations. The governing factors of its bistability include composite constitutive behaviour, initial geometrical proportions, and geometrically non-linear structural behaviour. Its bistable principle can be employed to produce a flexible multistable hinge structure with tailorable stability. This is achieved by introducing variable stiffness design within a cylindrical shell structure, where folding stability is dependent on central functional patch region, and then connected to linking ploy regions. Thus, a novel multistable composite hinge structure can be designed with positive Gaussian curvature deformation, and its multistability is highly tailorable: a lengthy one-dimensional mechanical arm can be designed to coil and fold multiple times to enable large folding ratio. An analytical model was established based on the strain energy principle, in order to determine effects from functional tape length; the typical structural stability and stable configurations were then predicted with respect to regional length of the functional layer. It is found that the stability of a multistable composite hinge structure is dependent on geometry and combination of both the functional patch region, and connecting ploy region; the stable criteria are then proposed and show good agreement with experimental observations and FE analysis. These enrich the diversities of functional deployable structures to benefit novel requirements for various deployable mechanisms, and enable customised design, as well as smart driving for flexible and multifunctional mechanical composite hinge applications.

A bistable helical structure based on composite tape-springs

Conventional twistable structures use discrete parts articulated around a number of linkages. These allow only a limited degree of twisting angle, are low in storage ratio, heavy and complex in morphing mechanisms. Double-helix structures are commonly applied to induce twistable shape-changing capability for deployable structures, these being capable of large axial deformations where prestressed thin-shell composite flanges or strips are employed; however, their structural stabilities are susceptible to thermal effects, and suffer from non-zero Gaussian curvature deformation induced by prestressing of the precured flat strips. Here, we propose a novel bistable helical structure, where zero Gaussian curvature deformation applies, and shows more stable and reliable morphing mechanics for a twistable structure to be engineered. This is achieved by exploiting bistable composite tape-spring (CTS) structures, where two CTS samples are pin-joined through spokes to formulate a helical structure. It is capable of large axial morphing, and stable in both the fully extended and twisted configurations, with adjustable storage ratio. A theoretical model was established to predict its bistability and a bespoke axial displacement rig was developed to investigate its non-linear morphing mechanisms in order to reveal the underlying fundamentals. These will facilitate torsional structural design for aerospace deployable structures.

Effect of different material on the folding of composite ultrathin tape spring hinges via unifed 2D shell models

The aim of this work is to analyze the effect of different materials on the folding of ultrathin tape spring hinges. This mechanism is modeled using the Finite Element Method (FEM) combined with the Carrera Unified Formulation (CUF) for the development of refined 2D shell models. These models can deal with different materials and different theoretical approximations can be introduced in an automatic way thanks to the hierarchical capability of the CUF formalism, according to which the degree of refinement of the mathematical model is an input to the analysis. The nonlinear governing equations are developed using a Total Lagrangian formulation and solved via a Newton-Raphson linearization technique with arc-length type constraints. A validation of the proposed model is carried out by comparing the results with those available in the literature involving a cured T300-1k/913 tow and HexPly 913 resin. After a convergence analysis, the mathematical model proves to ensure a good fit. This model is used for the final analysis with different materials, i.e. isotropic metallic with hardened steel tape spring and unidirectional T300 graphite fibre/epoxy prepreg with 34% resin content by weight. The results, in the form of moment angle curves, are reported for two different values of the thickness of the structure.

Roll-Out Deployment Process Analysis of a Fiber Reinforced Polymer (FRP) Composite Tape-Spring Boom.

Deployable extendable booms are widely used in aerospace technology due to many advantages they have, such as high folded-ratio, lightweight and self-deployable properties. A bistable FRP composite boom can not only extend its tip outwards with a corresponding rotation speed on the hub, but can also drive the hub rolling outwards with a fixed boom tip, which is commonly called roll-out deployment. In a bistable boom's roll-out deployment process, the second stability can keep the coiled section from chaos without introducing a controlling mechanism. Because of this, the boom's roll-out deployment velocity is not under control, and a high moving speed at the end will give the structure a big impact. Therefore, predicting the velocity in this whole deployment process is necessary to be researched. This paper aims to analyze the roll-out deployment process of a bistable FRP composite tape-spring boom. First, based on the Classical Laminate Theory, a dynamic analytical model of a bistable boom is established through the energy method. Afterwards, an experiment is introduced to produce some practical verification for comparison with the analytical results. According to the comparison with the experiment, the analytical model is verified for predicting the deployment velocity when the boom is relatively short, which can cover most booms using CubeSats. Finally, a parametric study reveals the relationship between the boom properties and the deployment behaviors. The research of this paper will give some guidance to the design of a composite roll-out deployable boom.

Analysis of the Mechanical Properties and Study of Influential Factors of Different Materials in Tape Spring

This paper analyzes and calculates the mechanical properties of composite tape spring structures during folding and bending and establishes a non-linear control equation for the folding and bending of composite laminate tape spring structures. Accurate expressions for folding and bending displacements are obtained. The influence of the cross-section’s central angle and the composite tape spring’s ply thickness on their mechanical properties are analyzed. Finite element numerical analysis is performed on [−45 45]s laminated composite tape springs, and the correctness of the theoretical derivation is proved by comparing the curvature radius-bending moment curve. Based on previous research, the mechanical properties of different tape spring materials and structures are compared, further studying the lightweight design of space deployment mechanisms. The results show that the steady-state bending moment performance of composite tape springs is excellent, with a 162.1% improvement in steady-state bending moment performance per unit mass compared to traditional metallic tape springs. Additionally, the critical bending moment performance of negative Poisson ratio honeycomb structure tape springs is also excellent, with a 62.3% improvement in steady-state bending moment performance per unit mass compared to traditional metallic tape springs.

Smart driving of a bilayered composite tape-spring structure

Composite tape-springs (CTS) structure has been applied to spatial developable structures due to its bistability. There is growing interest in smart driving of the CTS-based structures because of the limitations on the working environment. Here, we propose a detailed analysis of the smart driving of the CTS structure. This is achieved by using smart materials to develop a bilayered CTS intelligent structure: the smart material forms the active layer to generate stress/strain to drive the structure; the CTS layer acts as a passive layer where its intrinsic bistability, designability further enriches the diversity of intelligent morphing structures. A theoretical analytical model is developed to anticipate the bistability; the stability criteria are then determined to guide the intelligent morphing design. These will facilitate the future smart driving design of aerospace deployable structures.

Parabolic deployable mesh antenna with a hingeless system of superelastic SMA ribs and composite tape springs

This paper describes an experimental and numerical investigation of a compact parabolic deployable mesh antenna with a hingeless deployment system of superelastic SMA ribs and composite tape springs. One of the key features of the proposed antenna is the primary reflector with SMA ribs. The SMA's superelasticity allows the stowed reflector to deploy without plastic deformation with high damping and fatigue resistance. Thus, the antenna can be folded compactly like lotus flowers. Furthermore, composite tape springs with inherent hysteresis make the mast structure folded. Due to these hingeless deployment mechanisms, high reliability is achieved with a moderate level of packaging efficiency, lightweight, and low deployment shock.The effectiveness of the mechanism design was demonstrated by validation tests such as a basic characteristic test of superplastic SMA ribs, a deployment test of the antenna, and surface error measurement, as well as a deployment simulation with the aid of the finite element method.

Surrogate Modeling Accelerated Shape Optimization of Deployable Composite Tape-Spring Hinges

Composite tape-spring hinge (CTSH) is a simple yet elegant mechanical component for various deployable space structures. This paper formulates and addresses cut-out shape optimization of a CTSH, which is seldom touched upon in literature. Both the maximum strain energy stored during the folding process as well as the maximum bending moment during deployment were maximized in a concurrent way, and the multi-objective optimization problem was realized by merging data-driven surrogate modeling and shape optimization. Four different surrogate modeling techniques (radial basis function, kriging, Gaussian process regression, and artificial neural network) are evaluated and compared. The maximum stored strain energy at the fully folded state and the maximum bending moment during deployment for the optimal CTSH are increased by 50 and 35%, respectively, compared to the initial design under a previously developed composite failure criterion as constraint. To ensure reproducibility and foster future research, we publicly share our full implementation with the source codes and trained models with the community.

Dynamic interferometric measurements of thermally-induced deformations on telescope based on high-strain composite tape-springs

Thin carbon fibre reinforced polymer (CFRP) tape-springs are attractive structures for use in space-based optical instruments because of their compact stowed form, and their high dimensional stability when deployed. In this paper we present, with examples, two inexpensive methods to assess the thermal expansion properties of tape-spring structures: one based on strain gauges to obtain coupon level values, and another based on laser interferometry for structure level measurements. The strain gauge technique is a versatile approach that exploits the thermal output characteristics of the sensors. The thermal expansion characterisation of thin-composite samples measured a longitudinal expansion of 4.44 ppm/∘C and transverse expansion 5.95 of ppm/∘C. The interferometry system is designed with a view to capturing the displacements and tilts that occur when a structure with a low thermal mass, like a tape-spring, experiences a rapid change in flux, as occurs in the space environment. The homodyne interferometer is developed for three degree-of-freedom (DoF) measurements with a resolution of 10−8 m for distances and 10−6 rad for angles. The interferometric setup is based on the classical Michelson architecture and consists of few inexpensive commercial optical components. The source is a 0.8 mW Helium–Neon laser with a wavelength of 632.8 nm. The other elements include two spherical singlets, a right-angle prism, a cubic beamsplitter and a CMOS camera. The recorded interference fringes are analysed by using an algorithm based on Discrete Fourier Transform (DFT). Spectral information on the light intensity signals can be used to determine relative displacements and tilts. The dimensional stability of an optical payload based on high-strain composites was tested. The telescope has a deployable Cassegrain design, which uses six extendable members for the separation of its secondary mirror. Axial deformations between 20–30μm along with angle variations of the order of 0.1 mrad were recorded with good repeatability.

Multiscale modeling of viscoelastic behavior of unidirectional composite laminates and deployable structures

Due to the inherent viscoelasticity of constituent matrix and the possibility of long-term storage, space deployable structures made of composites are likely to exhibit relaxation in the stored strain energy, which may degrade their deployment performance. This paper presents a bottom-up finite element based multiscale computational strategy that bridges the experimentally measurable properties of constituent fibers and matrix to numerical predictions of viscoelastic behavior of composite laminates and general shell structures. A user-friendly RVE analysis plug-in tool is developed in Abaqus/CAE to rapidly estimate the effective orthotropic viscoelastic properties of unidirectional composites by taking as input the microstructure geometry as well as the known properties of fibers and matrix. Some benchmark problems were solved, and the accuracy and efficiency of the proposed plug-in tool were verified. Next, the strategy is shown to be applicable to model the viscoelastic behavior of macroscale composite laminates and deployable shell structures, by utilizing built-in functions in Abaqus to define the stacking sequence and accordingly update the material properties. In particular, the proposed multiscale strategy was employed to simulate the influence of modulus relaxation on the deployment dynamics of a composite tape-spring hinge, and good agreement was achieved as compared to reported experimental results.

On tailoring deployable mechanism of a bistable composite tape-spring structure

A bistable composite tape-spring (CTS) structure is a thin-walled open slit tube with fibres oriented at ±45°, which is stable at both its extended and coiled configurations. The traditionally manufactured CTS is effectively self-deploying. Here, we devise a novel manufacturing method to tailor the deployable mechanism of a CTS. This is achieved through adjusting the internal stress levels by subjecting the fully coiled as-manufactured CTS samples to additional heat treatment process. Their deploying performance were then characterised through a bespoke axial load monitoring rig, in order to reveal the underlying mechanics. It is demonstrated three different deployable mechanisms can be manufactured based on the same CTS, namely self-deploying, neutrally stable and self-coiling CTS structures. The processed CTS samples also show specialised stabilities, varying from mono-stability to multi-stability. The tailoring mechanism is then proposed. Since the CTS sample is in a highly strained state when coiled, the polymeric composite material would slowly deform due to viscoelasticity. According to the time-temperature superposition principle, the custom heat treatment of a fully coiled tape is equivalent to acceleration of the viscoelastic deformation, where local stress relaxation occurs on both the outer and inner tape surfaces, which in turn altering the internal stress levels. Thereby, the heat treatment processing is able to tailor the deployable mechanism of the CTS structure. These enrich the deployment diversity of the CTS to better fit the requirements for various deployable mechanisms in order to further promote the applications of CTS structures to aerospace explorations.

Folded strains of a bistable composite tape-spring

The bistable composite tape-spring (CTS) structure has received increasing interest in industrial applications, especially in aerospace engineering. Its ability to fold under large displacements makes it attractive as a hinge-safety assembly, with reduced weight, complexity and maintenance compared to the conventional lock-link connections. The shape of a CTS during folding has been studied; but research on its folded strain levels is limited. We devise a novel method to evaluate the strain evolution in a folded CTS. This is achieved by embedding strain gauges in a CTS sample before ‘‘rolling’’ the fold through them at constant fold angle: the rolling shape thus provides an exact profile of the strain along the CTS centreline. The strain has maximum levels at the centre of the folded CTS, as expected, whilst a new shoulder-like local peak feature is observed. A finite element (FE) analysis is performed to reveal expected levels of strain: the experimental strain profile is then compared to reveal fundamental correlations. Further insight therefore can be drawn from the FE model, which is beneficial in maintaining structural integrity, and ensure the composite is not over-confined and liable to damage during and after folding.

Viscoelastic bistable tape spring behavior modeled by a two-dimensional system with rigid links, springs and dashpots

Bistable composite tape springs are often used as deployable structures in aerospace applications because of their ability to be tailored for compact size, deployed lengths and stiffness. Analytical studies of the coupling between stress-strain and moment-curvature of thin curved shells have been used to estimate the total stored strain energy in different tape spring configurations. The strain energy as function of the curvatures reveals the fundamental stability behavior of the tape springs in the different configurations. The present study investigates the minimum strain energy path between two stable equilibrium points and the passage through the unstable saddle point along this path. For a coiled fiber-reinforced composite tape spring, the strain energy level for the local minimum and the saddle points will change with respect to time due to viscoelastic effects. To explain the fundamental mechanical behavior of viscoelastic bistable tape springs, a two-dimensional (2D) model composed of rigid links, elastic springs and viscous dampers was proposed. It was shown how the 2D model can be made strain energy-equivalent to a shell model with respect to the minimum strain energy paths. The 2D model was able to capture the fundamental behavior of viscoelastic tape springs during both snap-through and snap-back paths.

In-situ multiscale shear failure of a bistable composite tape-spring

A bistable composite tape-spring (CTS) is stable in both the extended and coiled configurations, with fibres oriented at ±45°. It is light weight and multifunctional, and has attracted growing interest in shape-adaptive and energy harvesting systems in defence-, civil- and, especially aerospace engineering. The factors governing its bistability have been well-understood, but there is limited research concerning the mechanics of structural failure: here, we investigate the shear failure mechanisms in particular. We perform in-situ neutron diffraction on composite specimens using the ENGIN-X neutron diffractometer at Rutherford Appleton Laboratory (STFC, UK), and shear failure is characterised at both macroscopic and microscopic scales. Elastic and viscoelastic strain evolutions at different strain levels reveal the fundamentals of micromechanical shear failure, and their temperature dependency. Multiscale shear failure mechanisms are then proposed, which will benefit the optimisation of structural design to maintain structural integrity of CTS in aerospace applications.

Rotational stiffness of drum deployed thin-walled open tubular booms

Abstract Tape springs are a type of thin-walled deployable boom that are used extensively in the space industry to deploy sensors, drag sails and antennas. When a tape spring is stowed it coils into a cylindrical shape and so deployment drums are manufactured as cylinders to match. The consequence of this is that when the tape spring is deployed a portion of the cross section remains flat against the cylindrical drum. This has the effect of reducing the stiffness of the tape spring. In this paper a Finite Element (FE) model is presented to capture this reduction. An experimental method for validating the FE model is also presented on which Beryullium-Copper (BeCu) and glass fibre polypropylene (PP) composite tape springs were tested. The FE model is able to predict the rotational stiffness of the BeCu tape springs more accurately than the composite tape springs. The disagreement in the case of the composite tape springs is attributed to inaccuracies in the available data for the mechanical properties, and the assumption that the tape spring does not compress through the thickness. Increasing the drum length has been shown to decrease the rotational stiffness due to increased flattening at the root. BeCu tape springs show an increase of 82% in the rotational stiffness when the flattened drum region reduces from 90% to 30% of the tape springs’ width. Glass fibre PP tape springs with a layup of [ ± 34 ∘ f/0°/ ± 34 ∘ f] show an increase of 65% when the drum length percentage reduces from 82% to 27%. A parametric study showed that the rotational stiffness can be significantly improved with the introduction of local root reinforcing plies.

Stowage and Deployment of a Viscoelastic Orthotropic Carbon-Fiber Composite Tape Spring

Strain energy deployable composite structures offer spacecraft designs reduced payload and compact volume. One of the greatest advantages presented by deployable composite structures arises from their ability to maintain high-strain configurations for extended periods of stowage. Because of the viscoelastic nature of the polymer matrix, the stowed composite structure undergoes stress relaxation that results in a decrease of the energy available for deployment. This paper focuses on a three-layered carbon-fiber-reinforced polymer composite deployable structure, known as a tape spring. Stress relaxation testing was used to define the viscoelastic behavior of the epoxy matrix. Experimental long-term stowage and deployment testing was performed on the tape spring specimens. Finite element simulations considering viscoelastic, orthotropic stress relaxation were developed to predict the effects of stress relaxation on the deployment of a tape spring.