Elastic Memory Composite Material: An Enabling Technology for Future Furlable Space Structures

Elastic Memory Composite (EMC) materials exhibit many favorable qualities for deployable space structures and have piqued a broad interest within America's deployable space structures industry. EMC materials are similar to traditional fiber-reinforced composites except for the use of a thermoset shape memory resin that enables EMC materials to achieve much higher failure strains than traditional composites when exercised through a very specific thermomechanical load cycle. This unique behavior is exploited in the development of EMC structural components that exhibit very high packaging-strain capability while guaranteeing predictable postdeployment structural performance. This paper presents a review of the current state of development of EMC technologies and EMC deployable space structure components. The paper is intended primarily to help potential users of EMC materials develop a better understanding of the special capabilities of EMC materials and considerations that must be applied while engineering with EMC materials.

Elastic memory composite (EMC) materials exhibit many favorable qualities for deployable structures and have piqued a broad interest within America's deployable space structures industry. EMC materials are similar to traditional fiber-reinforced composites except for the use of a thermoset shape memory resin that enables much higher packaging strains than traditional composites without damage to the fibers or the resin. This unique capability is being exploited in the development of very efficient EMC structural components for deployable spacecraft systems. The present paper is intended primarily to help deployable system designers develop a better understanding of the special capabilities of EMC materials, and the unique considerations that must be applied when engineering structural components with these materials. Specifically, the paper discusses: 1) the impacts of incorporating EMC materials on deployable system design, 2) analyses for packaging strain, deployment time, and deployment energy; and 3) requirements and concepts for heating systems.

Near-term and future spacecraft and satellites will require large ultra-lightweight structures and components that must be efficiently packaged for launch and reliably deployed on orbit. A new material technology called Elastic Memory Composite (EMC) materials, shows promise in meeting these needs. The EMC polymer matrix materials enable a fully cured composite structure or component to be deformed or folded for efficient packaging into a spacecraft or launch vehicle, then regain its original shape with no degradation or loss in mechanical or physical properties. A component using EMC materials is fabricated in its deployed, on orbit shape using conventional composite manufacturing processes. Then by heating the material and applying force this fully cued composite material can be folded or deformed for packaging. When cooled, it will retain the packaged shape indefinitely. When reheated the structure will regain its original shape with little or no external force. This packaging/deployment cycle is reversible. This paper reviews new developments in EMC materials technology including material properties, analytical and designs tools, testing and evaluation protocols, and new applications.

The growing application of TEMBO Elastic Memory Composite (EMC) materials for deployable space structures has highlighted the need for an improved understanding of the material’s mechanical behavior. Recent mechanical testing has revealed significant nonlinearity in the stress-strain response of highly-aligned, unidirectional EMC materials. It is hypothesized that the nonlinearity in the material’s longitudinal modulus is due to a combination of nonlinear behavior inherent in the carbon fiber reinforcement and processinduced wavy fiber imperfections in EMC laminates. A model is developed accounting for fiber nonlinearity and process-induced wavy fibers and using this model, a data-analysis protocol is developed that allows the relative contribution of these effects to be separated out of the observed global nonlinear stress-strain response. In essence, this protocol provides an indirect method of measuring the effective magnitude of the wavy fiber imperfections, given an accurate knowledge of the nonlinear elastic response of the fibers, or vice-versa. The results for the test laminates considered indicate that the nonlinearity in the fiber reinforcement is predominately responsible for the nonlinear behavior of the composite material. However, effects due to process-induced wavy fibers on the longitudinal modulus can become significant at relatively high compression strains.

A technique is introduced for the kinematic synthesis of deployable cable-stiffened truss structures. This technique, which is an extension of a prior procedure [l-21 for generating deployable truss structures, can be applied to generate all concepts of cable-stiffened truss structures as well as all their deployable derivatives. Examples illustrating the implementation of this new technique, along with a discussion of the results achieved. are included in this article. The primary function of a deployable structure is to maintain a stable configuration in its deployed state. This is reflected in current design practices of trading off decreased deployment or retraction performance for increased structural performance. As a result, various designs of deployable truss structures (with, and without cables) have been introduced that are over-constrained during deployment/retraction, i.e. deployment/retraction of these structures can only be achieved through the deformation of individual links or by exploiting symmetric features of the structure. The number of different conceptual designs of deployable structures that are based on a given structural configuration is unlimited, if deployable structures are permitted to be overconstrained during deploymenthetraction. For this reason, researchers in the area of deployable structures have given little attention to the systematic design of deployable truss structures and have instead devoted much of their attention to the introduction and discussion of novel concepts of deployable truss structures [3-171. If, on the other hand, it is assumed that the primary function of a deployable structure is to serve as a mechanism with a minimum number (i.e. at least one) of degrees-of-freedom, then the number of different conceptual designs that are based on a given structural configuration is finite. Hence, it is then possible to generate all possible designs for a given structural configuration. The assumption that a deployable structure is not constrained during deployment/retraction has enabled the development of a technique for the generation of all conceptual designs of deployable truss structures that can be used as building blocks (modules) of much larger structures [I-21. It should be noted that this technique, referred to as kinematic synthesis of * Sr. Mechanical Engineer, Member AIAA deployable structures, does not assume that the structural configuration is known but instead uses the characteristics of a given class of structures (i.e. truss modules) to generate all possible configurations of structures in this class. The limitation of this technique to truss modules has been avoided in the Explosion-Implosion technique [19], developed by the same authors, for the generation of allconceptual designs of deployable truss structures of which the locations of the nodes are known. Both techniques have been shown to result in the generation of an enormous, yet finite, number of novel conceptual designs as well as those that have been reported in the literature. Furthermore, by limiting the degrees-of-freedom available at individual joints, conceptual designs can be generated of deployable structures that are overconstrained during deployment/retraction. Although the kinematic synthesis technique and the explosionimplosion technique result in the generation of an enormous number of conceptual designs of deployable truss structures, they are not applicable to truss structures with cables. Yet, cable-stiffened truss structures have important advantages such as the reduction in mass and/or reduction in joints that can be achieved by replacing links in truss structures with cables. The objective of this article is to modify the technique introduced in [I-21 such that the new technique is also applicable to cablestiffened truss structures. This new approach can then be applied to generate novel concepts of deployablecable-stiffened truss structures as well as those that have been reported in the literature.

Elastic-memory composites (EMCs) is a class of polymeric composites that can be folded into a very compact shape and later deployed to the original shape upon reheating. They have significant potential in developing large deployable structures greater than 10m in size that can be stowed in a small launch vehicle and deployed in space to predetermined levels of precision. Generally, the composite is folded by heating it above the glass transition temperature of the resin. The primary deformation mode that allows EMCs to achieve significantly higher effective strains than traditional composites is microbuckling of the compressed fibers. The magnitude of this microbuckling dictates whether the laminate behaves elastically or if the laminate exhibits material failure such as fiber breakage, or fiber kinking. This paper explores the micromechanics of both types of fiber-deformation modes associated with the bending of such soft-resin composites. An analysis method is developed and correlated with experimental data to provide an estimate for the level of folding strain that a soft-resin laminate can achieve based on microbuckling-induced material failure. Additionally, insight is provided into the effects of fiber and matrix material properties on the formation and magnitude of the kink mode. Tests were also conducted to determine the deployment accuracy after a number of folding/deployment cycles to help design deployable sensor structures with these materials.

An experimental investigation on the Half Scissor-Like Elements (H-SLEs) mechanism deployable structure under compression axial load is presented. Two prefab cylindrical shape H-SLEs mechanism deployable steel structures namely M1 (Bolted base column) and model M2 (Unbolted base column) were tested on their performance in term of strength and stability performance. The model prototype consists coldformed and hot roll steel with bolted connection and tested at deployed vertical configuration. Compression axial load was applied at the middle top of loading platform, transferred equally to the six H-SLEs deployable mechanism through supporting beams. The experimental results obtained indicated that three types of failure modes, i.e. excessive bearing capacity failure at lipped C-section flange around bolt hole perimeter, instability due to horizontal displacement at mid-height of H-SLEs deployable mechanism (Bolted joint area) and member buckling. Among these failures, horizontal displacement nominated the overall structure stability while section thickness impacts member bucking and bearing capacity. The experimental ultimate load was 1.63% greater than BS EN 1993 design load resistance for M1 condition while 30% less for M2 condition. The applied load difference between these two model prototypes was 31.15%. Thus, M1 ultimate loads capacity was satisfactory since less than 15% acceptable level while M2 not satisfactory. Beside, horizontal displacement was identify highly impacted scissor mechanism deployable structure instability and suitable member thickness may avoid section premature failure.

Design and analysis of scissor-like hoop truss deployable antenna mechanism with arbitrary curvature support ribs

This paper aims at investigating precisely the dynamic performance of deployable structure constituted by scissor unit mechanisms with clearance joint. Based on the motion law in real joints, the contact model is established using an improved Gonthier nonlinear continuous contact force model, and the friction effect is considered using LuGre model. Moreover, the resulting contact force is suitable to be included into the generalized force of the equations of motion of a multibody system and contributes to replace motion constraints. In the sequel of this process, the effect of joint clearance is successfully introduced into the dynamical model of scissor deployable structure and the dynamic characteristics of deployable structure with joint clearance are obtained using a direct default correction method, which can directly modify the coordinates and speed of the system to avoid the numerical results divergence. Also, the new hybrid contact force model of revolute joint clearance is verified through comparing with the original model. The numerical simulation results show that the improved contact model proposed here has the great merit that predicts the dynamic behavior of scissor deployable structure with joint clearance.

Structure and genetic engineering of antigens and antibodies: Applications in immunoassays

The overall, macroscopic constitutive behavior of most materials of technological importance such as fiber-reinforced composites or polycrystals is very much influenced by the underlying microstructure. The latter is usually complex and heterogeneous in nature, where each phase constituent is governed by non-linear constitutive relations. In order to capture such micro-structural characteristics, numerical two-scale methods are often used. The purpose of the current work is to provide an overview of state-of-the-art finite element (FE) and FFT-based two-scale computational modeling of microstructure evolution and macroscopic material behavior. Spahn et al. (Comput Methods Appl Mech Eng 268:871–883, 2014) were the first to introduce this kind of FE-FFT-based methodology, which has emerged as an efficient and accurate tool to model complex materials across the scales in the recent years.

A series of out-of-pile quench tests is currently performed at the QUENCH facility of the Karlsruhe Research Center. Due to some non-prototypical features in the fuel rod and bundle design and in the whole test set-up, the results of these tests cannot directly be extrapolated and applied to reactor conditions. Therefore simulations of these quench tests with the help of computer codes are needed to achieve this aim. This led to the development of the bundle code CALUMO. The simulation of the test conditions in the CALUMO code is based on the solution of balance equations for the fuel rod simulators, the shroud, and the coolant. The code calculates also the oxidation of the bundle, the hydrogen production and the steam consumption. Models for the behavior of boron carbide absorber rods have also been implemented, as well as a simple quench model. The main aim of the code was to have a simple tool for the investigation of the oxidation of the claddings and the shroud and the mechanisms leading to temperature escalations in the transient and re-flooding phase. The CALUMO code has been validated in post test calculations for most of the QUENCH tests done so far. In this report results of the triplet of the tests QUENCH-07, QUENCH-08, and QUENCH-09 are presented and compared to results of the test instrumentation and to findings of post test examinations (PTE). The results of the code are in the overall encouraging, although still some improvement of the modeling is needed, especially with regard to relocation of liquid material. One big advantage of the code is the possibility to implement new models for material behavior rather easily and to test different oxidation correlations.

Tetrahedral and strut-reinforced tetrahedral microlattices: Selectively laser melted high-strength and high-stiffness cellular metamaterials

In a regular extrusion process for thermoplastic specimen, the material behavior in dies and its rheological properties have a major influence on the mechanical properties and the quality of the extruded product. This study outlines the multiphysical model, which has been adapted to address the specific issues associated with polyamide 12 polymer extrusion. A series of numerical simulations, based on the modeling of material behavior, have been conducted using the computational code Comsol Multiphysics®. These simulations have been applied to the study of polymer melt flows through an industrial extrusion die. The objective of this study is to analyze the influence of the imposed extrusion parameters on the physical field distribution and the material displacement within the die. The die swell at the exit of the extrusion die has been investigated as a function of the imposed pressure. The progression of the polymer flow front inside the extrusion tool and the swelling rates have been analyzed. In particular, the phenomenon of delayed swelling at high pressure has been highlighted at high pressure. Highlights Polymer swelling at industrial extrusion die exit is investigated. Polymer melt extrusion within industrial extrusion tool is numerically simulated. Flow front progression and extrudate swell are analyzed. Effect of extrusion pressure on instabilities and die swell is highlighted.

Various models of polymer behavior during thermoplastic injection molding are considered. A computer simulation is described for injection mold filling and cooling in complex shaped cavities. Both fountain flow and coupling of crystallization kinetics within the equation of transport have a profound influence on the predictions of the thermo-mechanical history experienced by the material. A summary of some polymer crystallization kinetics models is included. Comparisons are made between the Avrami and Tobin models. Some practical relationships are outlined for evaluating the effects of induction time, pressure, and stress on crystallization kinetics. Direct and inverse models are outlined to estimate thermal stresses and the optimal temperature or pressure conditions during injection molding required to obtain a prescribed distribution of the thermal stresses.