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NASA NTRS1996

Recent Progress in Adaptive Structures for Space

Within the past 10 years, substantial research in Adaptive Structures is evident and continues its integration into various space experiments and missions. The rapid integration is attributable to solutions Adaptive Structures potentially provides to many anticipated space challenges in large precision space structures and commercial availability of reliable actuator materials. The emphasis of the paper is on space experiments related to Adaptive Structures within the past two years.

Adaptive↗

NASA NTRSDate not supplied

Ceramic Matrix Composite (CMC) Thermal Protection Systems (TPS) and Hot Structures for Hypersonic Vehicles

Thermal protection systems (TPS) and hot structures are required for a range of hypersonic vehicles ranging from ballistic reentry to hypersonic cruise vehicles, both within Earth’s atmosphere and non-Earth atmospheres. The focus of this presentation is on air breathing hypersonic vehicles in the Earth's atmosphere. This includes single-stage to orbit (SSTO), two-stage to orbit (TSTO) accelerators, access to space vehicles, and hypersonic cruise vehicles. The presentation will start with a brief discussion of aerodynamic heating and thermal management techniques to address the high heating, followed by an overview of TPS for rocket-launched and air-breathing vehicles. The argument is presented that as we move from rocket-based vehicles to air-breathing vehicles, we need to move away from the “insulated airplane” approach used on the Space Shuttle Orbiter to a wide range of TPS and hot structure approaches. The primary portion of the presentation will discuss issues and design options for CMC TPS and hot structure components, including leading edges, acreage TPS, and control surfaces. The current state-of-the-art will be briefly discussed for some of the components. The two primary technical challenges impacting the use of CMC TPS and hot structures for hypersonic vehicles are environmental durability and fabrication, and will be discussed briefly.

Thermal Protection Systems↗

NASA NTRSDate not supplied

Fully Coupled Aeroelastic Stability Analysis of Adaptive Shape Memory Alloy Structural Technologies for Airframe Noise Reduction

The objective of this work is the development of computational models and analysis of the coupled fluid-structure response of a slat gap filler (SGF) noise treatment applied to the leading-edge-slat component of a high-lift system typical of modern transport aircraft. The representative airframe chosen for this work is NASA’s High-lift Common Research Model (CRM-HL) in a baseline high-lift configuration. Superelastic shape memory alloys (SMAs) have been identified as enabling materials for these structural treatments. Since the technology elements rely upon having a highly reconfigurable structure, designs must be assessed for static aeroelastic deflection as well as dynamic aeroelastic stability using coupled computational fluid dynamics (CFD) and nonlinear computational structural dynamics (NL CSD) tools. The technical approach consists of solving for the flow field around the entire vehicle using a global CFD model, followed by extraction of relevant local subdomain data for CFD and NL-CSD co-simulations. The SGF design is assessed using both 2D and 3D co-simulations to predict quasi-static aeroelastic deformations and to assess dynamic aeroelastic stability.

Fluid structure interaction↗

NASA NTRSDate not supplied

Ceramic Matrix Composite (CMC) Thermal Protection Systems (TPS) and Hot Structures for Hypersonic Vehicles

Thermal Protection Systems, hot structure↗

NASA NTRSDate not supplied

Origami-based Composite Space Structures

The main objective of my internship was working on developing a new type of deployable composite for space structures and new method of deployment via use of origami, composites, UV curing resins, and shape memory polymers. My role in the project was to collect an initial literature survey on the subject including origami, the history of deployable space structures, previous issues and problems faced in the field, previous and current research being done on the structural aspect as well as the materials aspect of the subject. I presented this information to our team, where we discussed and determined our research focus and project design specs. We have been making or will make decisions on the project’s purpose, material, origami type, manufacturing method, and testing methods. I am now in charge of the protype design as we enter the design stage of our research. I am using PTC Creo software to design the structural aspects of the first protype so that we can begin small scale testing. I will perform data analysis in order to review the results with our team, so we can make the next design decisions regarding changes or iterations of the design. We hope to renew this project in the next fiscal year in order to increase the TRL of the project so that it can eventually be used in multiple functions in space such as the construction of lunar habitats. In just my brief time with NASA, I have gained so much personally and professionally. I developed my ability to search through and narrow down information when doing research. In the weekly meetings I practiced presenting information to my peers and superiors, and, just as importantly, discussing and adapting to what we were learning. I acquired experience in using technology to my advantage including remote work, new software like PTC Creo, NASA archives, and connecting with others beyond my team to gain help. I enjoyed the immense resource of knowledge that my mentors had to offer, and that they gave me a large amount of responsibility in this research. I truly felt like I was contributing to something bigger than myself and understood how directly I was involved in NASA’s work. This internship has further cemented my love for space and desire to continue in the field. I have a better understanding of the research and development process and am now considering joining a research lab with my university next year.

Composite↗

NASA NTRSDate not supplied

Cavitation Effects on the Structural Dynamics of Turbomachinery Components

The structural integrity of inducer and impeller blades in rocket engine turbo machinery must be evaluated in the face of complex excitation mechanisms including fluctuating pressures due to cavitation. Cavitation occurs when the local fluid pressure drops below the vapor pressure, causing the formation of vapor-filled bubbles. Cavitation can exist to various extents within the typical operating range of rocket engine turbo pumps. Despite recent progress towards reducing uncertainties in structural dynamic models of turbo machinery components, the extent to which pump cavitation affects the structural dynamic properties (i.e., natural frequencies, damping, and mode shapes) of inducer and impeller blades remains largely unknown. To study the structural dynamic effects of cavitating flows, experiments are conducted in a high-speed water tunnel. The test article is a low aspect ratio cantilevered plate, thus mimicing a single inducer blade that is unwrapped from its hub. The test article is oriented at zero angle of attack and has a triangular trip at its leading edge to induce cavitation. To change the extent of cavitation, the static pressure of the water tunnel is controlled. A high-speed camera is used to quantify the coverage of the cavitation sheet.

Structural Dynamics↗

NASA NTRSDate not supplied

Bi-axial Strain Measurement of Woven-Webbing Inflatable Structures Using Digital Image Correlation with RGB Filtering

Crewed inflatable softgoods structures can significantly reduce launch volume for habitable pressure vessels. To ensure the operational safety of these structures, NASA has developed an extensive testing program to evaluate the structural capability on ground test articles. This paper will discuss a current challenge faced by test engineers evaluating the strain of large-scale inflatable space structures during ground testing. Namely, the difficulty that arises using monochrome digital image correlation (DIC) to evaluate bi-axial strain for woven-webbing restraint layers. This report provides insight into a novel method of photogrammetry using red-green-blue (RGB) filtering in conjunction with DIC to evaluate the strain in each direction on a test article experiencing bi-directional strain. To evaluate this concept, a uniaxial tensile test was performed that represented a biaxial woven architecture using orthogonally interfaced straps. The resulting analysis demonstrates promise for this novel approach for isolating a specific region and direction of strain, reducing the effects of straps not in the area of interest, while allowing for a larger region of analysis. Moreover, it was shown that the application of a white basecoat prior to applying photogrammetry patterns significantly reduced data loss while performing RGB filtered DIC.

inflatable↗

NASA NTRSDate not supplied

Enhancing In-Flight Structural Health Monitoring of Vertical Lift Vehicles Operating in an Urban Environment

In-situ airframe sensors have long been considered a potential solution for structural health monitoring that could change the design, certification, operation and maintenance paradigms of flight vehicles. In this approach, large networks of sensors covering the entire, or most of, an airframe throughout its operational lifetime would support real-time decisions on airworthiness and obviate the need to overbuild components or perform multiple cycles of structural qualification testing and inspections. This concept would go beyond the current practice of placing select sensors in strategic locations or relying on such sensors only during airframe qualification flights and inspections. For vehicles in the emerging urban air mobility space, reducing weight associated with overbuilds and shortening down-time associated with inspections are critical for improving safety and affordability. In practice, the wide-scale use of in-situ sensors as primary assurance for structural health has not been demonstrated to be feasible or the best solution. A sensor integration testbed was developed as a platform to evaluate the potential of multiple sensor types to enable decision making on airworthiness. We report on the initial runs of this testbed with multiple sensors attached to a common test article. Metal foil strain gauges, eddy current, fiber optic, guided wave (acoustic emission and ultrasonic)and carbon nanotube roving sensors were affixed to the test article. Baseline as well as post damage initiation and fatiguing data are presented and discussed. Despite the relative simplicity of the test article, the interpretation of the as-captured test data was generally not conclusive or did not have wide enough coverage. This result emphasizes the challenges and current limitations both in testing and the practical broad application of embedded sensors as the determinative elements in critical decision making on wide-scale structural health.

Vertical Lift Vehicles↗

NASA NTRSDate not supplied

Enhancing In-Flight Structural Health Monitoring of Vertical Lift Vehicles Operating in an Urban Environment

In-situ airframe sensors have long been considered a potential solution for structural health monitoring that could change the design, certification, operation, and maintenance paradigms of flight vehicles. In this approach, large networks of sensors covering the entire, or most of, an airframe throughout its operational lifetime would support real-time decisions on airworthiness and obviate the need to overbuild components or perform multiple cycles of structural qualification testing and inspections. This concept would go beyond the current practice of placing select sensors in strategic locations or relying on such sensors only during airframe qualification flights and inspections. For vehicles in the emerging urban air mobility space, reducing weight associated with overbuilds and shortening down-time associated with inspections are critical for improving safety and affordability. In practice, the wide-scale use of in-situ sensors as primary assurance for structural health has not been demonstrated to be feasible or the best solution. A sensor integration testbed was developed as a platform to evaluate the potential of multiple sensor types to enable decision making on airworthiness. We report on the initial runs of this testbed with multiple sensors attached to a common test article. Metal foil strain gauges, eddy current, fiber optic, guided wave (acoustic emission and ultrasonic) and carbon nanotube roving sensors were affixed to the test article. Baseline as well as post damage initiation and fatiguing data are presented and discussed. Despite the relative simplicity of the test article, the interpretation of the as-captured test data was generally not conclusive or did not have wide enough coverage. This result emphasizes the challenges and current limitations both in testing and the practical broad application of embedded sensors as the determinative elements in critical decision making on wide-scale structural health.

Vertical Lift Vehicles↗

NASA NTRSDate not supplied

An Evaluation of Composite Primary Structure for Habitat Modules

Boeing studied the use of composite structures in deep space habitats. Compared to metallic modules, composite structures offer increased strength and stiffness with reduced mass. The study evaluated the design considerations and the mass benefits of an all composite primary structure. The composite module design included a continuous pressure shell, composite longerons, and circumferential ring frames. The composite material selected was a high strength carbon fiber and epoxy slit tape prepreg. The manufacturing involved automated fiber placement and utilizing existing facilities and autoclaves. Analysis showed a 33% reduction in primary structure mass and an overall net reduction of nearly 1900 kg compared to metallic modules. The composite module demonstrated improved mass efficiency and opens new possibilities for mission performance in deep space exploration.

Composite↗

NASA NTRS1995

(abstract) Characterization of Structural Response for Systems with Loose Joints

This paper describes a technique to locate and characterize loose joints in a large truss structure to generate an accurate structural model. The joint looseness is modeled as a gap in the member that opens and closes depending on the loading. Arbitrarily placed actuators are used to prestress the structure to first linearize the response. Next the actuator displacements are systematically reduced while monitoring the displacement response. The gap locations are determined by comparing the measured displacements with sets of calculated displacements and the sizes are estimated by monitoring the gap member length changes using the appropriate linear force-displacement relationship for the load level. The effect of measurement error in the truss displacements and the actuator length changes are investigated.

truss structures loose joints displacements actuat↗

NASA NTRS1972

In-space fabrication of thin-film structures

A conceptual study of physical vapor-deposition processes for in-space fabrication of thin-film structures is presented. Potential advantages of in-space fabrication are improved structural integrity and surface reflectivity of free-standing ultra-thin films and coatings. Free-standing thin-film structures can find use as photon propulsion devices (solar sails). Other applications of the concept involve free-standing shadow shields, or thermal control coatings of spacecraft surfaces. Use of expendables (such as booster and interstage structures) as source material for the physical vapor deposition process is considered. The practicability of producing thin, textured, aluminum films by physical vapor deposition and subsequent separation from a revolving substrate is demonstrated by laboratory experiments. Heating power requirement for the evaporation process is estimated for a specific mission.

Lippman, M. E.↗

NASA NTRS1972

Experimental investigation of Mach 3 cruise heating simulations on a representative wing structure for flight loads measurement

Radiant heating experiments were performed in the laboratory on an instrumented multispar wing structure to investigate: (1) how accurately the structural temperatures of a Mach 3 cruise-flight profile could be simulated, (2) what the effects of the heating and heating inaccuracies would be on the responses of strain-gage bridges installed on the structure, and (3) how these responses would affect flight loads measurements. Test temperatures throughout the structure agreed well with temperatures calculated for a Mach 3 profile. In addition, temperatures produced by two identical tests were repeatable to less than + or -6 K deg. Thermally induced strain-gage-bridge responses were large enough to be detrimental to a high-speed flight loads program with a goal of establishing aerodynamic loads (exclusive of thermal loads). It was shown that heating simulation can be used effectively for thermal calibration (that is, to provide corrections for a high-temperature environment), and that thermal calibration may not be needed if the simulation data are used to carefully select bridges and load equations.

Fields, R. A.↗

NASA NTRS1972

Design considerations for fiber composite structures

An overview of the design methodology for designing structural components from fiber composites is presented. In particular, the need for new conceptual structural designs for the future is discussed and the evolution of conceptual design is illustrated. Sources of design data, analysis and design procedures, and the basic components of structural fiber composites are cited and described. Examples of tradeoff studies and optimum designs are discussed and a simple structure is described in some detail.

Chamis, C. C.↗

NASA NTRS1972

Delta launch vehicle isogrid structure NASTRAN analysis

Structural analysis applications of NASTRAN to the isogrid structure of the Delta launch vehicle are discussed. Isogrid is a method employed to stiffen the booster cylindrical shell surface by integrally machining ribs and skin from one piece of metal. The ribs are arranged in a repetitive equilateral triangular pattern; this results in a structural surface whose stiffness is orthogonally isotopic. For that structure, both static and general instability buckling analyses are described and the theoretical results are compared to test data. One of the parameters included in the analysis is the effect of pressure loadings on the buckling allowable load. In addition, a description of a supplementary computer program is presented.

Knighton, D. J.↗

NASA NTRS1972

Adaptation of NASTRAN to an integrated system of structural design analysis

Efforts to integrate NASTRAN into a complete structural analysis system for use by large airframe design projects are discussed. NASTRAN was implemented as a major finite element structural analysis program to determine the static and dynamic behavior of complete airframes, as well as structural components. This requires modifications and additions to NASTRAN, to communicate with an existing system, and to provide facilities needed to work within the integrated structural analysis. For this purpose, several special DMAP modules were developed and introduced into the CALAC version of the NASTRAN system.

Haggenmacher, G. W.↗

NASA NTRS1972

Structural design aspects of reusable surface insulation thermal protection systems.

Low density fiber ceramic materials coated with refractory ceramics meet the requirements of reusable low weight thermal protection systems. The structural characteristics of this class of material impose unique design and analysis requirements on the application to spacecraft structural elements. Finite element type stress analysis techniques are required to adequately predict the structural response of the system. Parametric analyses have been performed to determine the response of the system to variations in geometry, and to thermal and structural load conditions. Sensitivity of coating, insulation and attachment stresses are presented and critical failure modes are identified.

Michalak, R. J.↗

NASA NTRS1972

Structural integrity test and assessment.

The feasibility of using an ultrasonic system on board the Space Shuttle Orbiter to facilitate structural evaluation and assessment was studied. Two factors are considered that could limit the capability of an ultrasonic system: (1) the effect of structure configuration and (2) the noise generated during vehicle launch. Results of the study indicate that although the structural configuration has direct bearing on sound propagation, strategic location of transducers will still permit flaw detection. The ultrasonic response data show that a severe acoustic environment does not interfere significantly with either propagation and reflection of surface waves or detection of crack-like flaws in the structure.

Suggs, F.↗