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Research Projects
Characterization of E-Beam Processes for Aerospace Composites
Start Date - 06/01/01, End Date - 05/31/02
Problem - Electron beam (E-beam) curing of polymeric matrix fibrous composites (PMFC) offers the potential to fabricate light-weight fuel tanks for NASA's future, reusable space transportation systems.
Proposal - Address the fundamental processing issues that need to be characterized before E-Beam composite processing can fulfill NASA needs.
Results - Both BMI/NVP and BMI/Styrene have good response to E-beam radiation and high cure conversion can be given. However, we cannot get homogeneous products from BMI/Styrene systems. Temperature data show the possibilities to increase dosage and dose rate supplied so that temperature will remain in an acceptable range to achieve full cure. However, the cure conversions after the first several radiation passes need to be measured in order to identify the cure diffusion control mechanism during E-beam treatment.
Roger J. Morgan
Composite Structural Integrity Assessment Via High-Resolution Acoustic Microscopy
Start Date - 06/27/03, End Date - 08/15/06
Problem - To achieve a sound design process of composite materials, is it necessary to understand the mechanisms by which damage accumulates over a period of time. Focused ultrasonics (UT) has been used in this field, including the high-resolution UT imaging (acoustic microscope) at US Naval Academy.
Proposal - Refine the high-resolution UT imagery to be even more predictive of physical properties of the composites. Use parameters from the frequency spectrum of the UT waveforms to create “frequency domain” images in which colored regions in the image are indicative of a particular defect class, such as micro-cracking. Refine the correlation between these colored zones and subsequent results of destructive analysis. Incorporate the acoustic microscope into physical models that identify failure mechanisms. Investigate configuring the microscope as a portable PC-based field instrument.
Sarah Mouring
Cryogenic Microcracks Growth in Polymer Composites
Start Date - 06/01/01
Problem - Future single-stage reusable launch vehicles will require light-weight composite materials that can withstand severe stresses and cryogenic temperatures. Research is needed to characterize, and to monitor development and progression of microcracks under cryogenic temperature and service conditions and to apply fracture mechanics studies to assess the influence of such fracture growths on performance, thereby avoiding premature failure.
Proposal - Evaluate materials suitable for use in tanks in order to determine the existence and growth of microcracks. Develop a predictive model that establishes a microcrack threshold for ultimate failure of these composite materials under various manufacturing situations.
David Hui
Development of Self-Healing Composites for Cryogenic Hydrogen Tank
Start Date - 07/01/02, End Date - 07/01/02
Problem - Verification of the structural integrity of composite devices is hampered by the inability to detect flaws inherent in the laminate based, manufacturing process.
Proposal - Use thermal cycling with self-healing composites during the initial manufacturing process to reduce the occurrence of hydrogen leaking caused by microcracking during cryogenic operation.
Dr. Judy Schneider
Fabrication of Composite Hydrogen Fuel Tank - Mississippi State University
Start Date - 06/01/01, End Date - 05/15/02
Problem - Mississippi State University (MSU) Raspet Flight Research Laboratory (RFRL) conducted research in the area of composite structures manufacturing technology leading to composite structures for cryogenic fuel tanks and structures. They determined a need to research new techniques that may fall outside current industry best practices.
Proposal - As large-scale composite manufacturing and processing is studied further, a list of best practices for fabrication and processing of composites will be developed, which will then be applied to the fabrication of large composite cryogenic fuel tanks.
Results - In summary, large composite liquid hydrogen tank can be fabricated using very mature techniques (hand lay-up prepreg) with computer controlled cutting machines and laser-guided placement machines. If the technology matures, this tank can be fabricated with a self-healing system making liquid hydrogen tank virtually leak-proof and highly fatigue resistant.
Dr. Robert L. King
Minimizing Life Cycle Costs of Composites Through Design
Start Date - 06/01/01, End Date - 03/15/06
Problem - There is not a pre-existing body of cost data that covers the entire life cycle of a product including creation, production, distribution, operation, service, disposal and retirement. One study found that material selection during early design stages of a product influences 70% of the product cost.
Proposal - Provide design engineers with a means of taking a solid model design of a composite structure (cured in an autoclave) and determine the life cycle costs within a 95% confidence level for a set production volume.
Kenneth Currie
NDE Techniques for Applications in Composites Manufacturing
Start Date - 06/01/01, End Date - 02/15/07
Problem - Before completely embracing the technology of composite aerospace structures, two things must be improved:
(1) the manufacturing process of the composites and (2) the ability to detect and monitor flaws in these structures during manufacturing and/or service, particularly the location and size of subsurface flaws.
Proposal - Develop Non-Destructive Evaluation procedures for the analysis of the quality of a composite part on a quantitative scale. These procedures should focus on quality assurance as well as being useful in monitoring the integrity of the structure in field conditions.
Melody Verges
Non-Autoclave Processing and Manufacture of Large Reusable Aerospace Structures
Start Date - 06/01/01, End Date - 03/15/06
Problem - Although composite materials are ideal for aerospace applications, current autoclave methods for manufacturing reusable aerospace structures are expensive and time-consuming.
Proposal - Investigate the use of cost effective, non-autoclave manufacturing techniques for fabricating large, reusable composite structures for aerospace applications.
Alfred Loos
Prediction of Microcracking Induced Permeability of Cryogenic Composite Tanks
Start Date - 06/01/01, End Date - 02/15/07
Problem - Future reusable space vehicles require light-weight composite fuel tanks that can withstand the rigors of multiple launches. Optimal performance can only be achieved when the effects of various fabrication and service conditions are predictable through modeling. Structural integrity and leakage-proof assurance must be verified by nondestructive evaluation during and immediately following manufacturing as well as between missions.
Proposal - Develop the understanding and tools necessary to prevent microcracking induced leakage problems. Develop a computational capability for the prediction of fuel leakage through damage paths induced during manufacturing and subsequent thermomechanical loading from -420°F up to 350°F.
John Whitcomb
Size Effects in Ply- and Sublaminated-level Fiber Composites of Cryogenic Temperatures
Start Date - 06/01/01, End Date - 05/31/02
Problem - To reduce production costs, structures are typically designed using small-scale models and scale model testing. The test results are used to predict the behavior of the full-scale structure. Therefore, it is necessary to know if composite materials show any size effects and to understand the nature of the changes in mechanical behavior as composite laminates are scaled to size.
Proposal - Understand the impact of extreme temperatures on composite materials. Also achieve a better understanding of scaling issues at low temperatures.
Results - Overall, ply-level scaled specimens show a decrease in strength due to increased specimen size. Sublaminate-level scaled specimens on the other hand show a moderate increase in strength and strain to failure. Much more testing and larger scaled sizes need to be incorporated to substantiate the findings.
Rani Warsi Sullivan
Solid-State Friction Stir Welding
Start Date - 06/01/01, End Date - 10/23/01
Problem - Classically, theories of mechanics of materials have been proposed that would include all of the phenomena that occur during the process of friction stir welding, and studies have been initiated to determine the applicability of individual theories. The theories in question have been loosely categorized with such titles as thermoelasticity, thermoplasticity, thermo-viscoelasticity and thermo-viscoplasticity.
Proposal - Undertake a systematic computational study of friction stir welding that will utilize accepted modern theories of continuum mechanics. Create a model that can be used in government and private section industrial laboratories and that will describe and characterize friction stir welding in computer code.
George Buchanan and John Peddieson
Space Launch Initiative/Friction Welding Risk Reduction Program
Start Date - 06/03/02, End Date - 10/01/04
Problem - Traditional torch and arc welding techniques are timely and costly in large structure manufacturing.
Proposal - Advance the state of the art in complex curvature welding. Demonstrate the ability to fabricate large-scale aluminum complex contour panels using Friction Stir Welding. Develop the knowledge and tools to employ Friction Stir Welding on the reusable metallic fuel tanks for the 2nd Generation Reusable Launch Vehicle Risk Reduction Program.
Bruce Brailsford
Understanding the Service Life of Composites
Start Date - 06/01/01, End Date - 03/15/06
Problem - There are differences between a composite structure as modeled and the composite structure as built. A common design assumption is that classical lamination theory can be applied to determine the strain and stress states. Further, commonly used failure theories are based on the concept of no initial defects or imperfections in the composite. Finite element analysis usually entails similar assumptions. Differences between the as-manufactured and the as-analyzed structure are not generally considered until unexpected and unwelcome mechanical behavior is observed. In the worst case, there is no real correlation between actual service life and predicted service life failure. Failure occurs well before expected.
Proposal - Develop analytical and numerical models of representative as-manufactured composite components or sub-components using continuum mechanics and the finite element method. These models will be used in service life predictions to determine the service life with the consideration of initial material quality.
Christopher Wilson
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