Structures
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This catalog contains training modules developed by the NESC Structures Technical Discipline Team (TDT). Aerospace structures are lightweight, they house all flight systems and payloads, and they must withstand all mission loads and environments. The structures discipline strives to meet often contradictory mission requirements by performing trade and sensitivity studies using various sub-disciplines - structural mechanics, structural design and sizing, structural testing, computational mechanics, damage and failure prediction, and interdisciplinary analyses. The modules in this catalog capture lessons learned, perspectives, advice, and experiences of the various members of the structures TDT.
Upcoming Webcasts
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Buckling, Shells, Knockdown Factors, and Validation Testing
| Presenter | Dr. Mark Hilburger |
|---|---|
| Published | November 2012 |
| Recorded | November 2012 |
| Duration | 01:46:14 |
| Tags | #Advanced, .Analysis / Modeling and Simulation, .Testing, ~Structural Analysis, ~Stress Analysis, ~Failure Modes, ~Structural Response, ~Buckling, ~Digital Image Correlation |
Discipline: Structures<br>NASA’s Shell Buckling Knockdown Factor Project (SBKF), was established in the spring of 2007 by the NASA Engineering and Safety Center (NESC) in collaboration with NASA’s Constellation Program and Exploration Systems Mission Directorate. The SBKF project has the goal of developing improved (i.e., less-conservative, robust), shell buckling design factors (a.k.a. knockdown factors) and design and analysis technologies for launch vehicle (LV) structures. Preliminary design studies indicate that implementation of these new knockdown factors can enable significant reductions in mass and control mass-growth in these vehicles and can help mitigate some of the typical LV development and performance risks. In particular, the new design technologies are expected to reduce the reliance on testing, provide high-fidelity estimates of structural performance, reliability, robustness, and enable increased payload capability. <br><br>The lecture will provide a brief summary of SBKF objectives and approach towards developing and validating these new technologies and provide a look towards the future of design, analysis and testing of the next generation of buckling-critical launch vehicle structures. In particular, a historical review of the current design recommendations for buckling-critical thin-walled cylindrical shell structures will be presented, and their limitations relative to the design of modern launch vehicle structures will be discussed. Next, the lecture will identify some key technologies that are enabling the development of updated design factors including advancements in computational tools for structural analysis, testing and measurement technologies, and manufacturing and materials, and suggest other areas of R&D investment. Finally, results from a recent (and exciting!) full-scale structural test of a 27.5-ft-diameter orthogrid-stiffened Space Shuttle External Tank barrel section, ETTA1, will be presented.
Damage Arresting Composites, Part 1: Building Blocks
| Presenter | Dawn Jegley |
|---|---|
| Published | October 2016 |
| Recorded | September 2016 |
| Duration | 01:56:00 |
| Tags | #Advanced, .Design, .Testing, .Materials, .Lessons Learned, ~Pressure Vessels, ~Material Properties, ~Failure Models, ~Damage Tolerance |
Discipline: Structures<br>Webcast Air Date: October 5, 2016<br><br>NASA conducted the Environmentally Responsible Aviation Project to explore and document the feasibility, benefits, and technical risk of advanced vehicle configurations and enabling technologies that will reduce the impact of aviation on the environment. A critical aspect of this pursuit is the development of a lighter, more robust airframe that will enable the introduction of unconventional aircraft configurations that have higher lift to drag ratios, reduced drag, and lower community noise. Although such novel configurations like the Hybrid Wing Body (HWB) offer better aerodynamic performance as compared to traditional tube-and-wing aircraft, the blended wing shape with its almost-flat sided pressure vessel poses significant design challenges.<br><br>Developing an improved structural concept for a non circular pressurized cabin is the primary obstacle in implementing large lifting body designs. To address this challenge, researchers at NASA and The Boeing Company worked together to advance new structural concepts like the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS), which is an integrally stiffened panel design that is stitched together and designed to maintain residual load carrying capabilities under a variety of damage scenarios. A building block approach was used in this technology development effort.<br><br>This topic will be addressed in two parts. Part one will focus on the structural building blocks from small elements through large panels designed to demonstrate that the concept of out-of-autoclave cured, stitched composite structure with no mechanical fasteners in the acreage of flat and curved panels would efficiently support the axial, bending internal cabin pressure loads representative of the passenger compartment of a HWB vehicle. Part two, to be covered in a separate webcast, will focus on the design, analysis and testing of the complex pressurized structures of a PRSEUS “cube” and a 30-foot-long, 80%-scale, multi-bay box. All building blocks and the built-up structures were analyzed and tested and the results documented to demonstrate the feasibility of the concept for application to commercial transport aircraft.
Damage Arresting Composites, Part 2: Large-Scale Multi-Bay Box
| Presenter | Dr. Adam Przekop |
|---|---|
| Published | December 2016 |
| Recorded | October 2016 |
| Duration | 01:19:40 |
| Tags | #Advanced, .Analysis / Modeling and Simulation, .Materials, .Lessons Learned, ~Impact Damage, ~Structural Analysis |
Webcast Air Date: 12/09/2016<br>Discipline: Structures<br>NASA conducted the Environmentally Responsible Aviation Project to explore and document the feasibility, benefits, and technical risk of advanced vehicle configurations and enabling technologies that will reduce the impact of aviation on the environment. A critical aspect of this pursuit is the development of a lighter, more robust airframe that will enable the introduction of unconventional aircraft configurations that have higher lift to drag ratios, reduced drag, and lower community noise. Although such novel configurations like the Hybrid Wing Body (HWB) offer better aerodynamic performance as compared to traditional tube-and-wing aircraft, the blended wing shape with its almost-flat sided pressure vessel poses significant design challenges.<br><br>Developing an improved structural concept for a non circular pressurized cabin is the primary obstacle in implementing large lifting body designs. To address this challenge, researchers at NASA and The Boeing Company worked together to advance new structural concepts like the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS), which is an integrally stiffened panel design that is stitched together and designed to maintain residual load carrying capabilities under a variety of damage scenarios. A building block approach was used in this technology development effort.<br><br>This topic is being addressed in two parts. Part one, presented by Dawn Jegley on 10/05/2016, was focused on the structural building blocks from small elements through large panels designed to demonstrate that the concept of out-of-autoclave cured, stitched composite structure with no mechanical fasteners in the acreage of flat and curved panels would efficiently support the axial, bending internal cabin pressure loads representative of the passenger compartment of a HWB vehicle. In part two, Adam Przekop will focus on the design, analysis and testing of the complex pressurized structures of a PRSEUS “cube” and a 30-foot-long, 80%-scale, multi-bay box. All building blocks and the built-up structures were analyzed and tested and the results documented to demonstrate the feasibility of the concept for application to commercial transport aircraft.
Engineering of Space Systems (Lessons Learned)
| Presenter | Robert "Bob" Ryan |
|---|---|
| Published | September 2011 |
| Recorded | October 2011 |
| Duration | 35:22 |
| Tags | #Intermediate, .Lessons Learned, .Systems / Subsystems, ~Designing for Systems Engineering |
Discipline: Structures
Metal Fatigue Part 1
| Presenter | Raymond Patin |
|---|---|
| Published | May 2013 |
| Recorded | March 2013 |
| Duration | 01:44:37 |
| Tags | #Fundamental, .Materials, ~Material Properties, ~Fracture Mechanics, ~Fracture Control, ~Structural Analysis, ~Crack Growth |
Structural integrity is assured via static strength and service life (fracture control) requirements. The mitigation of catastrophic failures in metallic materials resulting from fatigue damage accumulation during the useful life of a structure is one of the primary functions of fracture control. This Webcast provides a cursory overview of metal fatigue which includes the basic elements of stress-life (S-N) fatigue, strain-life, and linear elastic fracture mechanics. Details regarding the micro and macro mechanics associated with metal fatigue crack nucleation, initiation, and propagation are also addressed.
Metal Fatigue Part 2
| Presenter | Raymond Patin |
|---|---|
| Published | June 2013 |
| Recorded | March 2013 |
| Duration | 01:46:00 |
| Tags | #Intermediate, .Materials, ~Material Properties, ~Fracture Mechanics, ~Fracture Control, ~Structural Analysis, ~Crack Growth |
Structural integrity is assured via static strength and service life (fracture control) requirements. The mitigation of catastrophic failures in metallic materials resulting from fatigue damage accumulation during the useful life of a structure is one of the primary functions of fracture control. This Webcast provides a cursory overview of metal fatigue which includes the basic elements of stress-life (S-N) fatigue, strain-life, and linear elastic fracture mechanics. Details regarding the micro and macro mechanics associated with metal fatigue crack nucleation, initiation, and propagation are also addressed.
Residual Stress and Effect on Crack Growth and Fracture
| Presenter | Dr. Frederick W. (Bud) Brust |
|---|---|
| Published | February 2019 |
| Recorded | October 2018 |
| Duration | 01:33:15 |
| Tags | #Advanced, .Materials, ~Pressure Vessels, ~Material Properties, ~Fracture Mechanics, ~Fracture Control, ~Structural Analysis, ~Crack Growth |
Sandwich Structures Failure Modes and Their Prevention
| Presenter | Dr. Ronald Krueger |
|---|---|
| Published | October 2016 |
| Recorded | September 2016 |
| Duration | 01:13:14 |
| Tags | #Intermediate, .Analysis / Modeling and Simulation, .Materials, ~Fracture Mechanics, ~Failure Models |
Discipline: Structures<br>Webcast Air Date: September 28, 2016<br><br>Typical damage modes in light honeycomb sandwich structures include face sheet/core disbonding and core fracture, both of which can pose a threat to the structural integrity of a component. These damage modes are of particular interest to aviation certification authorities since several in-service occurrences, such as rudder structural failure and other control surface malfunctions, have been attributed to face sheet/core disbonding. Extensive studies have shown that face sheet/core disbonding and core fracture can lead to damage propagation caused by internal pressure changes in the core. <br><br>In order to identify, describe and address the phenomenon associated with facesheet/core disbonding, a reliable means of characterizing facesheet/core disbonding must be developed. In addition to the characterization tests, analysis tools are required, to help assess the likelihood of a structure exhibiting critical disbonding. These analysis tools need to be verified and validated.<br><br>In this webcast, sandwich structures are introduced and their failure modes are discussed. Actual in-service occurrences are presented and a road map to standardization for facesheet/core disbonding in sandwich composite components is described. An overview is given on the development of test methods that yield a critical strain energy release rate associated with disbonding, with a focus on mode-I dominated loading conditions. Further, an analysis approach is discussed to compute energy release rates along an arbitrarily shaped disbond front. Finally, a brief summary of observations is presented and recommendations for improvements are provided.
Structural Analysis Part 1
| Presenter | Dr. Ivatury Raju |
|---|---|
| Published | July 2013 |
| Recorded | February 2012 |
| Duration | 39:59 |
| Tags | #Fundamental, .Analysis / Modeling and Simulation, .Lessons Learned, ~Structural Analysis, ~Stress Analysis, ~Boundary Conditions, ~Building Blocks Approach |
Discipline - Structures
Structural Analysis Part 2
| Presenter | Dr. Ivatury Raju |
|---|---|
| Published | July 2013 |
| Recorded | February 2012 |
| Duration | 56:18 |
| Tags | #Fundamental, .Analysis / Modeling and Simulation, .Lessons Learned, ~Structural Analysis, ~Stress Analysis, ~Boundary Conditions, ~Building Blocks Approach |
Discipline - Structures
Testing and Analysis of Advanced Composite Tow-Steered Shells
| Presenter | Dr. Chauncey Wu |
|---|---|
| Published | January 2017 |
| Recorded | December 2016 |
| Duration | 01:14:52 |
| Tags | #Advanced, .Analysis / Modeling and Simulation, .Design, .Testing, .Materials, ~Material Properties, ~Structural Analysis |
The structural performance of two advanced composite tow-steered shells, manufactured using a fiber placement system, is assessed using both experimental and analytical methods. The fiber orientation angles vary continuously around the shell circumference from 10 degrees on the shell crown and keel, to 45 degrees on the shell sides. The two shells differ in that one shell has the full 24-tow course applied during each pass of the fiber placement system, while the second shell uses the fiber placement system s tow drop/add capability to achieve a more uniform shell wall thickness. The shells are tested in axial compression, and estimates of their prebuckling axial stiffnesses and bifurcation buckling loads are generated using linear finite element analyses.<br> <br>Cutouts, scaled to represent commercial aircraft passenger and cargo doors, are then machined into one side of each shell. The prebuckling axial stiffnesses and bifurcation buckling loads of the shells with cutouts are then computed using linear finite element analyses. When retested, large deflections were observed around the cutouts, but the shells carried an average of over 90 percent of the axial stiffness, and 85 percent of the buckling loads, of the shells without cutouts. These relatively small reductions in performance demonstrate the potential for using tow steering to mitigate the adverse effects of typical design features on the overall structural performance.<br><br>Previous studies have typically shown poor correlation between experimental buckling loads and supporting linear bifurcation buckling analyses. The good correlation noted for these tow-steered shells may result from their circumferential axial stiffness variation, which may reduce sensitivity to geometric imperfections. A numerical investigation was performed using measured geometric imperfections from both shells. Finite element models of both shells were analyzed first without, and then, with the measured imperfections, superposed in different orientations around the shell longitudinal axis. Small variations in both the axial prebuckling stiffness and global buckling load of the shells were noted for the range of orientations studied.
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