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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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135 records · Page 8

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NASA NTRS2018

Real Time Detection of Damage During Quasi-Static Loading of a Single Stringer Panel Using Passive Thermography

Real time nondestructive evaluation is required for composites load testing. The early detection and measurement of damage progression is important to understand failure modes. A single stringer panel was subjected to quasi-static loading to induce deformation which can result in the formation of delamination damage between the stiffener flange and skin. Passive thermography was used to detect damage in real time as a function of the applied load. The loading was stopped when damage growth was detected. Of particular interest was the early detection of damage formation which can be challenging, as compared to cyclic fatigue loading. Passive thermography data were acquired and processed in real time and revealed damaged areas due to heating from fiber breakage and delamination formation. The processed thermal imagery was also compared to acoustic emission and ultrasound data.

Zalameda, Joseph N.↗

NASA NTRS1993

TAB interconnects for space concentrator solar cell arrays

The Boeing Company has evaluated the use of Tape Automated Bonding (TAB) and Surface Mount Technology (SMT) for a highly reliable, low cost interconnect for concentrator solar cell arrays. TAB and SMT are currently used in the electronics industry for chip interconnects and printed circuit board assembly. TAB tape consists of sixty-four 3-mil/1-oz tin-plated copper leads on 8-mil centers. The leads are thermocompression gang bonded to GaAs concentrator solar cell with silver contacts. This bond, known as an Inner Lead Bond (ILB), allows for pretesting and sorting capability via nondestruct wire bond pull and flash testing. Destructive wire pull tests resulted in preferred mid-span failures. Improvements in fill factor were attributed to decreased contact resistance on TAB bonded cells. Preliminary thermal cycling and aging tests were shown excellent bond strength and metallurgical results. Auger scans of bond sites reveals an Ag-Cu-Tin composition. Improper bonds are identified through flash testing as a performance degradation. On going testing of cells are underway at Lewis Research Center. SMT techniques are utilized to excise and form TAB leads post ILB. The formed leads' shape isolates thermal mismatches between the cells and the flex circuit they are mounted on. TABed cells are picked and placed with a gantry x-y-z positioning system with pattern recognition. Adhesives are selected to avoid thermal expansion mismatch and promote thermal transfer to the flex circuit. TAB outer lead bonds are parallel gap welded (PGW) to the flex circuit to finish the concentrator solar cell subassembly.

Avery, J.↗

NASA NTRSDate not supplied

Comparison of In-situ Near Infrared Melt Pool Imagery to Optical Microscopy Measurements

Additive manufacturing (AM) is a rapidly growing technology. An area of major importance is the integrity and repeatability of AM parts. The goal is to reduce obstacles to certify AM built parts to allow for use in critical aerospace applications. In-situ nondestructive evaluation sensors can be used for build assessment and can potentially play a key role in certifying AM parts. For example, melt pool features are understood to have a strong correlation to microstructural defects and the use of a near infrared (NIR) camera can be used to record the melt pool, cooling areas, and temperature gradients during the build. This work explores the use of a low cost NIR camera to obtain single line track imagery of the Ti-6Al-4V melt pools for various processing parameters. The NIR camera is radiometrically calibrated and configured in-line with the laser source to obtain high resolution imagery of the melt pool shape and dynamics. The challenge to measure melt pool shapes is to identify the transition points between the metal solid to liquid phase. Factors for melt pool measurements such as thermal camera pixel resolution, surface emissivity, and blurring due to the laser beam movement are discussed. Lastly, the melt pool imagery are compared to optical microscopy measurements for validation.

additive manufacturing↗

NASA NTRS1988

Investigation of a SiC/Ti-24Al-11Nb composite

A summary of ongoing research on the characterization of a continuous fiber reinforced SiC/Ti-24Al-11Nb (at percent) composite is presented. The powder metallurgy fabrication technique is described as are the nondestructive evaluation results of the as-fabricated composite plates. Tensile properties of the SiC fiber, the matrix material, and the 0-deg SiC/Ti-24Al-11Nb composite (fibers oriented unidirectionally, parallel to the loading axis) from room temperature to 1100 C are presented and discussed with regard to the resultant fractography. The as-fabricated fiber-matrix interface has been examined by scanning transmission electron microscopy and the compounds present in the reaction zone have been identified. Fiber-matrix interaction and stability of the matrix near the fiber is characterized at 815, 985, and 1200 C from 1 to 500 hr. Measurements of the fiber-matrix reaction, the loss of C-rich coating from the surface of the SiC fiber, and the growth of the Beta depleted zone in the matrix adjacent to the fiber are presented. These data and the difference in coefficient of thermal expansion between the fiber and the matrix are discussed in terms of their likely effects on mechanical properties.

Brindley, P. K.↗

NASA NTRS1972

Assessment of and standardization for quantitative nondestructive test

Present capabilities and limitations of nondestructive testing (NDT) as applied to aerospace structures during design, development, production, and operational phases are assessed. It will help determine what useful structural quantitative and qualitative data may be provided from raw materials to vehicle refurbishment. This assessment considers metal alloys systems and bonded composites presently applied in active NASA programs or strong contenders for future use. Quantitative and qualitative data has been summarized from recent literature, and in-house information, and presented along with a description of those structures or standards where the information was obtained. Examples, in tabular form, of NDT technique capabilities and limitations have been provided. NDT techniques discussed and assessed were radiography, ultrasonics, penetrants, thermal, acoustic, and electromagnetic. Quantitative data is sparse; therefore, obtaining statistically reliable flaw detection data must be strongly emphasized. The new requirements for reusable space vehicles have resulted in highly efficient design concepts operating in severe environments. This increases the need for quantitative NDT evaluation of selected structural components, the end item structure, and during refurbishment operations.

Neuschaefer, R. W.↗

NASA NTRS2008

Monitoring Damage Accumulation in Ceramic Matrix Composites Using Electrical Resistivity

The electric resistance of woven SiC fiber reinforced SiC matrix composites were measured under tensile loading conditions. The results show that the electrical resistance is closely related to damage and that real-time information about the damage state can be obtained through monitoring of the resistance. Such self-sensing capability provides the possibility of on-board/in-situ damage detection and accurate life prediction for high-temperature ceramic matrix composites. Woven silicon carbide fiber-reinforced silicon carbide (SiC/SiC) ceramic matrix composites (CMC) possess unique properties such as high thermal conductivity, excellent creep resistance, improved toughness, and good environmental stability (oxidation resistance), making them particularly suitable for hot structure applications. In specific, CMCs could be applied to hot section components of gas turbines [1], aerojet engines [2], thermal protection systems [3], and hot control surfaces [4]. The benefits of implementing these materials include reduced cooling air requirements, lower weight, simpler component design, longer service life, and higher thrust [5]. It has been identified in NASA High Speed Research (HSR) program that the SiC/SiC CMC has the most promise for high temperature, high oxidation applications [6]. One of the critical issues in the successful application of CMCs is on-board or insitu assessment of the damage state and an accurate prediction of the remaining service life of a particular component. This is of great concern, since most CMC components envisioned for aerospace applications will be exposed to harsh environments and play a key role in the vehicle s safety. On-line health monitoring can enable prediction of remaining life; thus resulting in improved safety and reliability of structural components. Monitoring can also allow for appropriate corrections to be made in real time, therefore leading to the prevention of catastrophic failures. Most conventional nondestructive evaluation (NDE) techniques such as ultrasonic C-scan, x-ray, thermography, and eddy current are limited since they require structural components of complex geometry to be taken out of service for a substantial length of time for post-damage inspection and assessment. Furthermore, the typical NDE techniques are useful for identifying large interlaminar flaws, but insensitive to CMC materials flaws developed perpendicular to the surface under tensile creep conditions. There are techniques such as piezoelectric sensor [7,8], and optical fiber [9,10] that could be used for on-line health monitoring of CMC structures. However, these systems involve attaching an external sensor or putting special fibers in CMC composites, which would be problematic at high temperature applications.

Smith, Craig E.↗

NASA NTRSDate not supplied

Realistic Thermographic Simulation of Impact Damage with Quadrupole Method

Flash thermography has been shown to be an effective method for detection of delaminations in carbon fiber reinforced polymer (CFRP) composite structures. Improved understanding of the limitations of the technique can be obtained by simulating the inspection process. Time domain finite difference and finite element methods are well suited for such simulations but can be computationally intensive. An alternate method is to solve the Laplace transform of the heat equation, then invert the Laplace transform to produce a time domain response. Often this is referred to as the thermal quadrupole method and is well suited for simulating flash thermography. The quadrupole method has been used extensively for simulating one-dimensional heat flow in multilayer systems with contact resistances at the interfaces. It is also applicable for three dimensional configurations, in particular for simulation of changes in thermographic response due to delaminations in composites. This presentation discusses three-dimensional simulations with realistic shapes and contact resistances at the interfaces between layers. The results of these simulations are compared to thermography measurements on composites specimens with impact induced delaminations.

thermography↗

NASA NTRS1999

Technologies for Nondestructive Evaluation of Surfaces and Thin Coatings

The effort included in this project included several related activities encompassing basic understanding, technological development, customer identification and commercial transfer of several methodologies for nondestructive evaluation of surfaces and thin surface coatings. Consistent with the academic environment, students were involved in the effort working with established investigators to further their training, provide a nucleus of experienced practitioners in the new technologies during their industrial introduction, and utilize their talents for project goals. As will be seen in various portions of the report, some of the effort has led to commercialization. This process has spawned other efforts related to this project which are supported from outside sources. These activities are occupying the efforts of some of the people who were previously supported within this grant and its predecessors. The most advanced of the supported technologies is thermography, for which the previous joint efforts of the investigators and NASA researchers have developed several techniques for extending the utility of straight thermographic inspection by producing methods of interpretation and analysis accessible to automatic image processing with computer data analysis. The effort reported for this technology has been to introduce the techniques to new user communities, who are then be able to add to the effective uses of existing products with only slight development work. In a related development, analysis of a thermal measurement situation in past efforts led to a new insight into the behavior of simple temperature probes. This insight, previously reported to the narrow community in which the particular measurement was made, was reported to the community of generic temperature measurement experts this year. In addition to the propagation of mature thermographic techniques, the development of a thermoelastic imaging system has been an important related development. Part of the work carried out in the effort reported here has been to prepare reports introducing the newly commercially available thermoelastic measurements to the appropriate user communities.

Source record↗

NASA NTRS2021

Thermal Inspection of a Composite Fuselage Section Using theMethod of Proper Generalized Decomposition

Proper Generalized Decomposition (PGD) is a reduced order modeling technique for the simulation of physical systems whose governing equations depend on boundary conditions, initial conditions, material properties, and geometric parameters. It uses separated representations of system covariates combined with an iterative approximation method known as successive enrichment in order to compute an accurate parameter-dependent approximation to the full governing equations. PGD can also be used as an alternative to the Singular Value Decomposition (SVD) of a matrix and therefore as an alternative to PCA thermography. In this paper PGD was used to analyze data derived from the inspection of a composite fuselage forward section using flash thermography, and the results were compared against the standard PCA approach.

Nondestructive Evaluation↗