Terahertz Computed Tomography studies at NASA's Glenn Research Center using Advanced Photonix T-4000

Image via Wikipedia

 MY NOTE: Thanks once again to bucktailjig on sharing this informative piece.




Glenn Research Center

Title: X-ray & Terahertz studies (including 3D Computed Tomography) for Complex Aerospace Structures (Flexible Path Vehicle TPS, Stirling Engine Heater Heads)

Center Point of Contact:  Don J. Roth, 216-433-6017, Donald.J.Roth@nasa.gov.   Other participants include Mr. Richard Rauser (Univ. of Toledo), Dr. Ali Abdul-Azia (Cleveland State University, and Ms. Solimar Reyes (Michigan State University).

Objectives:  Baseline and apply X-ray and Terahertz methods to aerospace structures of interest in NASA Exploration and Aeronautics programs for quality assessments. This will include 3D computed tomography (CT) for both X-ray and terahertz.  NASA GRC will have the only terahertz computed tomography capability at the Agency.  Additionally, further develop the ability to create 3D solid and finite element models from CT volume renderings utilizing state-of-the-art tools, and use the models for further engineering analyses of samples with true damage

Background: The Terahertz pulse-echo NDE method has proven very useful in the inspection of external tank foam, shuttle underbelly tiles, ceramic materials and certain composite materials.  In the proposed work, we intend to fully characterize the capabilities of first-generation terahertz computed tomography that was developed by Picometrix, Inc. under an SBIR development program. Of particular interest is the application of this technology to new thermal protection system materials being developed for the Flexible Path Vehicle Crew Module, and possibly non-conducting (e.g. thermoplastic) structural foams and seals.  

Although Terahertz CT is not expected to compete resolution-wise with state-of-the-art X-ray computed tomography, it can potentially be more applicable as an inspection tool for very low density materials such as the TPS materials (unless the TPS materials are treated with contrast-enhancing substances that contaminate them). Also terahertz CT can be applied to complex-shaped structures such as tubes where reflection-mode terahertz is not applicable. It is necessary to baseline terahertz CT capabilities in order to determine how it can be used, and whether it can be used post-test for reuse assessment of TPS materials.   Because of its non-ionizing radiation character, it is possible to consider the use of Terahertz CT in field/depot applications with no safety implications.  Additionally, the use of Terahertz CT to virtually slice structures, create 3d volume renderings, and develop solid and FE models that allow further modeling is desirable to explore.  Further work in this effort will involve 1) X-ray CT for super high resolution aerospace structure characterization with direct application to Stirling Engine Heater Head being developed at GRC for future space missions, and for characterization of composite materials being developed under the ACT program 2) X-ray CT comparison with Terahertz CT, 3) upgrading the NDEWIP software to 64-bit to handle gigabyte-sized data sets and 4) modeling the X-ray CT process using SimCT software or an extension of the CIVA X-ray module.

This work addresses IMMEDIATE needs in the Stirling Engine and Flexible Path Vehicle Thermal Protection System development program, and tackles inspection issues with novel methods related to future space components including thermal protection systems (TPS), composite materials, and nickel-based superalloy materials for the next-generation space nuclear power systems

Technical Methodology/Approach:  A 3-year effort includes the following tasks:

1. Baseline basic capabilities of Terahertz CT against X-ray CT for the same phantoms, standards, or other samples including assessing MMOD damage for actual thermal protection system materials and other aerospace structure materials.
2. Apply X-ray CT to ACT composites, Stirline Engine Heater Heads and other aerospace structures for assessment of cracks, inclusions, ply waviness and other flaw conditions.  Up to 200 heater heads will be examined and hundreds of composite samples will be examined during this period.
3. Develop 3d Volume Renderings and, subsequently, develop solid models and finite element models from such renderings.
4. Perform thermal and/or mechanical load modeling utilizing the solid and FE models developed from the volume renderings, and utilize for NDE modeling (SimCT - see task 6), in a demonstration project to show how Terahertz CT and X-ray CT can be used in engineering capacity.
5. Upgrade NDEWIP software to 64-bit cpability for batch pre-processing, visualization, and analysis of gigabyte-sized data sets.
6. Model the X-ray CT process and compare with experimental results for model validation, inspection optimization, and better understanding of experimental results using SimCT or extension of CIVA X-ray module.
7. Complete reports including final report for NNWG secure website.

Customers:  This work will support initiatives in the Exploration and Aero programs at NASA.  Flexible Path Crew Vehicle and Stirling Engine are the primary customers with Stirling engine providing significant co-funding (200K).

Metrics: Progress on samples tested, slice images and volume renderings computed, models developed, NDEWIP software upgrade process, thermal and/or mechanical load modeling results from the volume renderings.  Reports written.

Products: Reports on testing and simulation.  Software upgrades.  System upgrades.

Schedule/Milestones:

• Years 1-3:  Baseline basic capabilities of Terahertz CT against X-ray CT for the same phantoms, standards, or other samples including thermal protection system materials and non-conducting aerospace structure materials such as forms.  Apply X-ray CT to aerospace structures (Flexible Path Vehicle TPS, Stirline Engine Heater Head, ACT composites) for characterization.  Upgrade NDEWIP software to 64-bit capability and debug/test.  Model X-ray CT process and compare with experimental results. (10/10 - 9/13)
• Year 2:  For test cases, create 3d Solid and Finite element models from 3d Volume Renderings for both Terahertz and X-ray CT.  Perform thermal/mechanical load modeling utilizing the actual models developed from the methods' renderings. (10/11 - 9/12)
• Year 3:  Complete reports (e.g. NASA TMs and/or journal articles) from the above tasks.  Complete final report for NNWG secure website posting. (10/12 - 9/13)

Status & Accomplishments as of October 30, 2010:  

• Terahertz tomography system has been received in-house and extensive experiments were performed this summer by a Ph.D. candidate from Michigan State, Ms. Solimar Reyes.  A NASA TM and journal article
• Extensive X-ray CT ensued on many different components from many different NASA programs and departments.  Primarily ACT (Advanced Composites Technology) and ASC (Advanced Stirling Converter) programs.
• Initial phase of using X-ray CT data in engineering capacity has been started.  X-ray CT slice data for NASA thermal protection system material was segmented using multiple methods in order to form finite element models that could be used for further physical modeling.  A NASA TM is in preparation detailing this effort.
• Alpha version of 64-bit NDEWIP has been developed using LabVIEW 2009.  99% of the code works but various features do not port to 64-bit.  We are developing workarounds for these.
• A procurement has been placed for X-ray CT software simulation development with the CEA.  This software will build upon the CIVA X-ray Simulation program.

Key Facilities:                                                                                         

·         Xray CT facility, bldg. 6 – Rm. 11
·         THz CT facility, bldg. 6 – Rm. 6 (new facility)
·         Finite Element Modeling Station, bldg. 6, Rm. 118