Mark S. Lake

Shape memory polymer nanocomposites

The paper describes the fabrication and characterization of composites with a shape memory polymer matrix and SiC nanoparticulate reinforcements. Composites based on a SMP matrix are active materials capable of recovering relatively large mechanical strains due to the application of heat. The composites were synthesized from a commercial shape memory polymer resin system and particulate SiC with an average diameter of 300 nm. Composites with weight fractions of 10%, 20%, 30%, and 40% nanoparticulate SiC were fabricated by casting samples with sizes ranging from a few hundred microns to several millimeters. The former size scale is consistent with a microcasting process for manufacturing microelectomechanical systems. The micro-hardness and elastic modulus of the nanocomposites increased by approximately a factor of 3 with the addition of 40 wt% SiC into the base resin. Unconstrained strain recoverability of the nanocomposites was found to depend on the fraction of SiC. For 180° bend tests, the recoverability of the nanocomposites was perfect for SiC weight fractions below 40%. For 40 wt% SiC, permanent bend strains were discovered. Constrained bending recovery force in the nanocomposites was shown to increase by 50% with the addition of 20 wt% SiC.

Shape Memory Mechanics of an Elastic Memory Composite Resin

Substantially more attention has been given in the past to shape memory alloys and shape memory ceramics than to shape memory polymers because unreinforced shape memory polymers have much lower stiffness and recovery force potential than shape memory alloys and shape memory ceramics. However, when incorporated into a fiber-reinforced composite, both the stiffness and the recovery force of a shape memory polymer can be dramatically improved. This paper presents recent advances in characterizing the shape memory mechanics of a thermoset shape memory polymer resin for Elastic Memory Composite (EMC) materials. In particular, heretofore undocumented response behavior is characterized through a series of thermo-mechanical tests of a commercially available EMC resin, and a lumped parameter model is adapted to accurately correlate this behavior. Through application of this model, it appears that the molecular transition associated with the shape memory effect occurs at a temperature other than the glass transition temperature of the resin.

The fundamentals of designing deployable structures with elastic memory composites

Elastic memory composite (EMC) materials exhibit many favorable qualities for deployable structures and have piqued a broad interest within Americas 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.

Application of elastic memory composite materials to deployable space structures

Elastic Memory Composite (EMC) materials exhibit many favorable qualities for deployable space structures and have piqued a broad interest within Americas 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.

Rationale for Defining Structural Requirements for Large Space Telescopes

The present paper presents a rationale for defining structural requirements for future large space telescope systems. The rationale is based on bounding analyses for the deformation of telescope mirrors in response to expected on-orbit disturbance loads and consideration of active control systems that partially compensate for these deformations. It is shown that the vibration frequency of the telescope structure, independent of telescope size, determines the passive structural stability and requirements for an active control system. This means that future large telescopes with low vibration frequencies will necessarily allocate increased active control error budget in proportion to the square of the vibration frequency. Parametric analyses are also presented for the vibration response of two representative mirror architectures: a tensioned membrane mirror and a truss-supporte d segmented mirror. These examples demonstrate that meeting a specified frequency requirement will require a trade between structural mass fraction and depth of the primary mirror support structure regardless of the structural architecture.

Elastic memory composites (EMC) for deployable industrial and commercial applications

The use of smart materials and multifunctional components has the potential to provide enhanced performance, improved economics, and reduced safety concerns for applications ranging from outer space to subterranean. Elastic Memory Composite (EMC) materials, based on shape memory polymers and used to produce multifunctional components and structures, are being developed and qualified for commercial use as deployable components and structures. 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 as well as capability enhancing components for use in other industries. The present paper is intended primarily to describe the transition of EMC materials as smart structure technologies into viable industrial and commercial products. Specifically, the paper discusses: 1) TEMBO EMC materials for deployable space/aerospace systems, 2) TEMBO EMC resins for terrestrial applications, 3) future generation EMC materials.

ELASTIC MEMORY COMPOSITE MATERIAL: AN ENABLING TECHNOLOGY FOR FUTURE FURLABLE SPACE STRUCTURES

Furlable structures are a class of deployable structures that utilize distributed material strain as a means for compact packaging. Elastic Memory Composite (EMC) materials are ideally suited for furlable structures because they offer high strength, stiffness, and strain capacity for efficient packaging and deployed structural performance. EMC components are packaged in their soft-resin state, which enables higher packaging strains than traditional hard-resin composites. For example, packaging strains on the order of 2-5% are commonly achieved in carbon-fiber-reinforced EMC materials whereas non-EMC, carbon-fiber composites are limited to less than 1% strain. The present paper summarizes two recent advancements in the state-of-the-art of EMC materials: 1) improvments to the design of EMC longerons, key structural elements in furlable truss booms, and 2) advancements in analytical models for EMC material behavior through the use of a Multicontinuum Theory. Preliminary results are presented that illustrate the significant potential for these advancements to further improve the performance and capability of furlable EMC space structures.

Development of Elastic Memory Composite Stiffeners for a Flexible Precision Reflector

Harris Corpor ation is currently developing a next -generation, large -deployable, solid surface radio frequency reflector, called the Flexible Precision Reflector (FPR). The FPR will significantly advance satellite communication systems by enabling very -large -aperture an tennas to be stowed within existing launch vehicle shrouds at a relatively low cost and part count. Additionally, by replacing traditional mesh surfaces with a furlable composite laminate, the FPR antenna will be capable of operating at radio frequencies a bove 40GHz. To realize the full potential of the FPR design, Harris Corporation is considering the use of Composite Technology Development’s TEMBO ® Elastic Memory Composite materials for critical components within the FPR system. This paper present s the de sign, development, fabrication, and testing of a FPR breadboard model that demonstrates the benefits of incorporating TEMBO ® materials in the design.

A Revolute Joint With Linear Load-Displacement Response for Precision Deployable Structures

A Revolute Joint With Linear Load-Displacement Response for PrecisionDeployable StructuresMark S. LakeNASA Langley Research CenterHampton, VAAndPeter A. Warren and Lee D. PetersonUniversity of ColoradoBoulder, COPresented at the 37th AIAA / ASME/ASCE/AHS / ASCStructures, Structural Dynamics, and Materials Conference

Elastic Memory Composite Microbuckling Mechanics: Closed-Form Model with Empirical Correlation

Elastic memory composite (EMC) materials are space-qualified, high-performance, shape-memory-polymer-based composites for use in constructing deployable space structures. EMC materials can be designed to exhibit significantly higher packaging strains than conventional composites through extensive elastic microbuckling of the fiber reinforcement at elevated-temperatures, when the shape-memory-polymer matrix is sufficiently compliant. Herein, we present a novel set of closed-form post-microbuckled mechanics-based solutions that quantify the wavelength and amplitude of fiber microbuckles within uni-directional EMC materials during elevated-temperature bending when the matrix is very compliant. This effort is unique from previously published fiber- microbuckling work in that it focuses on post-microbuckled behavior whereas the existing literature focuses on the initiation of microbuckling, it accounts for essential kinematic constraints on EMC microbuckling behavior that have not been previously captured, and composite properties that can be measured experimentally are used to formulate the model whereas micromechanics calculations based on constituent level properties are imbedded within the majority of the existing models. Correlation of the model with a set of EMC empirical studies is also done. This model provides a proper foundation for predicting other highly nonlinear mechanical behavior in EMC materials, like the applied-moment versus induced-curvature response, which are beyond the scope of the present study.