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Kenneth N Segal

Publications and source records attributed to Kenneth N Segal.

11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2025

Structural Sizing of a 50-m-Tall Thermoplastic Composite Truss Tower Structure for the Lunar South Pole

At the lunar south pole, solar arrays elevated by truss towers are exposed to near continuous sunlight since the sun remains near the horizon. Recent studies suggest that tower heights on the order of 50 m are needed to meet the power requirements to support a sustained lunar presence. While eventually towers may be constructed using materials sourced in-situ, initially structural elements will likely be brought from the Earth, deployed, and assembled. Thermoplastic composites offer the benefit of high specific stiffness and strength properties along with welding for assembly joints, and therefore represent a promising material system for this application. The focus of this paper is on the structural sizing of such towers. A set of expressions based on beam theory are presented for preliminary sizing of the truss tower structure for strength and buckling. The loading condition that drives sizing is base excitation resulting from moonquakes. A point design, developed through finite element analysis, verifies the analytical sizing routine and shows the importance of joints. The results show a viable point design and highlight the factors most significant in the structural sizing.

Thermoplastic composites↗
NASA NTRSDate not supplied

Testing and Analysis Correlation of a Large-Scale Composite Sandwich Longitudinal Bonded Joint for Space Launch Vehicle Structures

The NASA Composite Technology for Exploration (CTE) Project is developing and demonstrating critical composite technologies with a focus on composite bonded joints; incorporating materials, design/analysis, manufacturing, and tests that utilize NASA’s expertise and capabilities. The project has goals of advancing composite technologies and providing lightweight structures to support future NASA exploration missions. In particular, the CTE project will demonstrate weight-saving, performance-enhancing composite bonded joint technology for Space Launch System (SLS)-scale composite hardware. Advancements from the CTE project may be incorporated as future block upgrades for SLS structural components. This paper discusses the details of the development of a composite sandwich bonded longitudinal joint for a generic space launch vehicle structure called the CTE Point Design. This paper reports on the large-scale longitudinal bonded joint test articles that were fabricated and tested under axial compressive loading conditions to test the capability of the bonded joint design for buckling and joint failure. Test and analysis correlation of an as-manufactured undamaged longitudinal bonded joint panel are presented in the paper for tests to the onset of buckling and panel failure. Analysis predictions for buckling initiation and panel failure were both within 10% of the longitudinal bonded joint panel test results. This testing and analysis provide confidence in the potential use of composite bonded joints for future launch vehicle structures.

David W Sleight↗
NASA NTRSDate not supplied

Experimental Observations of Damage States in Unnotched and Notched 3D Orthogonal Woven Coupons Loaded in Tension

This paper describes a series of unnotched and notched tensile tests on two 3D orthogonal woven architectures. Dog bone specimens were used for the unnotched tests, and open-hole specimens were used for the notched tests. For each architecture and test type, two specimens were loaded under monotonic displacement control to failure and two specimens were incrementally loaded to failure in five steps. X-ray computed tomography (CT) was used to characterize the woven architecture and defects on each specimen prior to testing. Digital image correlation (DIC) images were obtained from both sides of the specimen throughout the loading and unloading. Acoustic emission (AE) data were also continuously acquired throughout the loading. For the incremental tests, X-ray CT was used to document the damage progression after each load increment. The damage progression was analyzed based on the results from these three techniques. The results for both architectures and test specimens followed a pattern where matrix cracks formed at the surface perpendicular to the tensile load direction. New surface cracks formed continuously throughout the loading and cracks extended in depth and width. In general, fiber failure was not detected until specimen failure.

Wade C Jackson↗
NASA NTRSDate not supplied

3D Woven Composite End Ring Structure: Design Development and Verification Testing

The National Aeronautics and Space Administration (NASA) Space Technology and Mission Directorate (STMD) is advancing composite technologies for exploration missions. The Composite Technology for Exploration (CTE) project goal is to advance lightweight joint concepts for Space Launch System (SLS) class structures. To this end CTE is developing and demonstrating a 3D woven carbon /epoxy composite joint design co-bonded in a circumferential end ring configuration, applied to a SLS sized conceptual payload attachment structure. This joint is a lightweight alternative to heavy and costly metallic joints. The 3D woven joint development advances lightweight joint technologies through material and structural design, material and joint analyses, and fabrication, as well as demonstration through building block testing. Prior limited building block tests are mentioned. In this paper, new sub-element-scale test results are described that demonstrate the structural capability well beyond design limit load. Then, results for a sub-component test article with a 889 mm joint subjected to combined loads are presented.

Kenneth N Segal↗
NASA NTRSDate not supplied

Challenges in Scaling Analysis from Coupons to Elements in 3D Woven Composites for a Launch Vehicle End-Ring Structure

The limitations of structural design with 3D woven composites based on homogenized material models characterized using coupon test data, representative unit cell analysis, or a combination of the two are discussed in the context of a space launch system (SLS)-scale end ring. Selected building block test configurations at the coupon, element, and subcomponent scales are described in detail. Highly instrumented tests and X-ray computed tomography inspections are used to characterize the structural behavior and associated damage progression with increasing load. It is shown that a single homogenized material constitutive relationship, applied at coupon and element scale, is not sufficient to model the structural response observed in both tests. In fact, substantially different stress-strain laws are required to predict the response of the coupon and element scale specimens, despite similar loading conditions. A model with discrete representation of the binder tows and cohesive interfaces to model matrix cracking shows much better agreement with the test data at the two length scales. Thus, evidence is provided showing that predictive structural analysis of 3D woven composites requires discrete representation of the tows, matrix cracking morphology, and their interactions in the structural configuration. With accurate knowledge of the element scale behavior, engineering approximations readily enable analysis scale-up to the subcomponent level.

Andrew C Bergan↗
NASA NTRSDate not supplied

Experimental Observations of Damage States in Unnotched and Notched 3D Orthogonal Woven Coupons Loaded in Tension

This paper describes a series of unnotched and notched tensile tests on two 3D orthogonal woven architectures loaded in the warp direction. Dogbone specimens were used for the unnotched tests, and open-hole specimens were used for the notched tests. For each architecture and test type, two specimens were loaded under monotonic displacement control to failure, and two specimens were incrementally loaded to failure in five steps. X-ray computed tomography (CT) was used to characterize the woven architecture and defects on each specimen prior to testing. Digital image correlation (DIC) images were obtained from both sides of the specimen throughout the loading and unloading. For the incremental tests, X-ray CT was used to document the damage progression after each load increment. The results for both architectures and test specimens followed a similar pattern where matrix cracks formed perpendicular to the load direction and were primarily located between the stacks of warp tows. Two-piece failure path always occurred perpendicular to the loading direction, along the through-thickness segments of the Z-tows. The combination of stress concentrations due to the specimen geometry, weave geometry, and cut tows created stress concentrations that appear to initiate failure.

Woven materials↗
NASA NTRSDate not supplied

Estimation of 3D Woven Design Sensitivities Using a Rapid Multiscale Analysis Technique

Highly-refined finite element models of three-dimension (3D) woven composite systems currently require excessive computational demands that limit their use in sensitivity analysis, uncertainty quantification, and optimization. An alternative analysis methodology was developed using the NASA Multiscale Analysis Tool (NASMAT) where multiscale models of a 3D woven composite (including inter-tow matrix voids and constituent failure) can be completed on a single central processing unit (CPU) on the order of ~30s. To develop inputs and validation data for the NASMAT model, coupon and acid-digesting testing and x-ray computed tomography were performed. The NASMAT inputs were parameterized using a set of 25 input variables and distributions. These inputs were randomly sampled to generate a total of 100,000 NASMAT analyses that could be used to understand the influence of different material and geometric properties on the warp and weft-direction stiffness and strength. These analyses (including pre/post-processing) were performed in less than eight hours on a 120 CPU cluster. The computational efficiency of the NASMAT model enabled a sensitivity analysis to be performed, and dominant input variables were able to be identified. Key results were consistent with theoretical and experimental observations for the specific 3D woven system studied in this work.

NASMAT↗
NASA NTRSDate not supplied

Structural Sizing of a 50-m-Tall Thermoplastic Composite Solar Array Truss Tower Structure for the Lunar South Pole

At the lunar south pole, solar arrays elevated by truss towers are exposed to near continuous sunlight since the sun remains near the horizon. Recent studies suggest that tower heights on the order of 50 m are needed to meet the power requirements to support a sustained lunar presence. While eventually towers may be constructed using materials sourced in-situ, initially structural elements will likely be brought from the Earth, deployed, and assembled. Thermoplastic composites offer the benefit of high specific stiffness and strength properties along with welding for assembly joints, and therefore represent a promising material system for this application. The focus of this paper is on the structural sizing of such towers. A set of expressions based on beam theory are presented for preliminary sizing of the truss tower structure for strength and buckling. The loading condition that drives sizing is base excitation resulting from moonquakes. A point design, developed through finite element analysis, verifies the analytical sizing routine and shows the importance of joints. The results show a viable point design and highlight the factors most significant in the structural sizing.

Thermoplastic composites↗
NASA NTRSDate not supplied

P-band Antenna Array for NASA's Space Exploration Synthetic Aperture Radar (SESAR) Instrument

A dual-polarized, wideband, lightweight P-band (435 MHz) antenna element and array for spaceborne radar applications has been developed for NASA’s SESAR (Space Exploration Synthetic Aperture Radar) instrument for planetary synthetic aperture radar (SAR) applications. The antenna array is based on lightweight, low-profile antenna elements that form the building blocks of configurable “array panels” that can in turn be used to build larger arrays consisting of multiple panels. The element design combines a novel, mostly planar conductor antenna element geometry with a robust lightweight composite material construction.

Synthetic Aperture Radar↗