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At least 253 records · Page 14

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NASA NTRS1991

Precision Cleaning Verification of Nonvolatile Residues by Using Water, Ultrasonics, and Turbidity Analyses

Chlorofluorocarbons (CFC's) in the atmosphere are believed to present a major environmental problem because they are able to interact with and deplete the ozone layer. NASA has been mandated to replace chlorinated solvents in precision cleaning, cleanliness verification, and degreasing of aerospace fluid systems hardware and ground support equipment. KSC has a CFC phase-out plan which provides for the elimination of over 90 percent of the CFC and halon use by 1995. The Materials Science Laboratory and KSC is evaluating four analytical methods for the determination of nonvolatile residues removal by water: (1) infrared analyses using an attenuated total reflectance; (2) surface tension analyses, (3) total organic content analyses, and (4) turbidity analyses. This research project examined the ultrasonic-turbidity responses for 22 hydrocarbons in an effect to determine: (1) if ultrasonics in heated water (70 C) will clean hydrocarbons (oils, greases, gels, and fluids) from aerospace hardware; (2) if the cleaning process by ultrasonics will simultaneously emulsify the removed hydrocarbons in the water; and (3) if a turbidimeter can be used successfully as an analytical instrument for quantifying the removal of hydrocarbons. Sixteen of the 22 hydrocarbons tested showed that ultrasonics would remove it at least 90 percent of the contaminated hydrocarbon from the hardware in 10 minutes or less giving a good ultrasonic-turbidity response. Six hydrocarbons had a lower percentage removal, a slower removal rate, and a marginal ultrasonic-turbidity response.

Skinner, S. Ballou↗

NASA NTRS1981

A Module Experimental Process System Development Unit (MEPSDU)

Design work for a photovoltaic module, fabricated using single crystal silicon dendritic web sheet material, resulted in the identification of surface treatment to the module glass superstrate which improved module efficiencies. A final solar module environmental test, a simulated hailstone impact test, was conducted on full size module superstrates to verify that the module's tempered glass superstrate can withstand specified hailstone impacts near the corners and edges of the module. Process sequence design work on the metallization process selective, liquid dopant investigation, dry processing, and antireflective/photoresist application technique tasks, and optimum thickness for Ti/Pd are discussed. A noncontact cleaning method for raw web cleaning was identified and antireflective and photoresist coatings for the dendritic webs were selected. The design of a cell string conveyor, an interconnect feed system, rolling ultrasonic spot bonding heat, and the identification of the optimal commercially available programmable control system are also discussed. An economic analysis to assess cost goals of the process sequence is also given.

Source record↗

NASA NTRS2001

Ultrasonic/sonic drilling/coring (USDC) for planetary applications

One of the major limitations of sampling on Mars and other low gravity environments is the need for high axial force when using conventional drilling. To address this limitation an ultrasonic/sonic drilling/coring (USDC) mechanism has been developed that employs an ultrasonic horn driven by a piezoelectric stack. The horn dnves a free mass that resonates between the horn and drill stein. Tests have shown that the USDC addresses some of the key challenges to the NASA sampling objectives. The USDC is lightweight (450 g), requires low preload (<5N) and can be driven at low power (5W), The device has been shown to drill rocks with various levels of hardness including granite, diorite, basalt and limestone. The hammering action involved with the coring process can produce cores of various shapes, which need not necessarily be round. Because it is driven by piezoelectric ceramics, the USDC is highly tolerant to changes in its operating environment. These actuation materials can be designed to operate at a wide range of temperatures including those expected on Mars and Venus. Although the drill is driven electrically at 20 kHz, a substantial sub-harmonic acoustic component is found that is crucial to drilling performance. An analytical model has been developed to explain this low frequency coupling in the horn, free mass, drill stem and rock.

Peterson, Thomas↗

NASA NTRS1999

Ultrasonic Nondestructive Characterization of Adhesive Bonds

Adhesives and adhesive joints are widely used in various industrial applications to reduce weight and costs, and to increase reliability. For example, advances in aerospace technology have been made possible, in part, through the use of lightweight materials and weight-saving structural designs. Joints, in particular, have been and continue to be areas in which weight can be trimmed from an airframe through the use of novel attachment techniques. In order to save weight over traditional riveted designs, to avoid the introduction of stress concentrations associated with rivet holes, and to take full advantage of advanced composite materials, engineers and designers have been specifying an ever-increasing number of adhesively bonded joints for use on airframes. Nondestructive characterization for quality control and remaining life prediction has been a key enabling technology for the effective use of adhesive joints. Conventional linear ultrasonic techniques generally can only detect flaws (delamination, cracks, voids, etc) in the joint assembly. However, more important to structural reliability is the bond strength. Although strength, in principle, cannot be measured nondestructively, a slight change in material nonlinearity may indicate the onset of failure. Furthermore, microstructural variations due to aging or under-curing may also cause changes in the third order elastic constants, which are related to the ultrasonic nonlinear parameter of the polymer adhesive. It is therefore reasonable to anticipate a correlation between changes in the ultrasonic nonlinear acoustic parameter and the remaining bond strength. It has been observed that higher harmonics of the fundamental frequency are generated when an ultrasonic wave passes through a nonlinear material. It seems that such nonlinearity can be effectively used to characterize bond strength. Several theories have been developed to model this nonlinear effect. Based on a microscopic description of the nonlinear interface binding force, a quantitative method was presented. Recently, a comparison between the experimental and simulated results based on a similar theoretical model was presented. A through-transmission setup for water immersion mode-converted shear waves was used to analyze the ultrasonic nonlinear parameter of an adhesive bond. In addition, ultrasonic guided waves have been used to analyze adhesive or diffusion bonded joints. In this paper, the ultrasonic nonlinear parameter is used to characterize the curing state of a polymer/aluminum adhesive joint. Ultrasonic through-transmission tests were conducted on samples cured under various conditions. The magnitude of the second order harmonic was measured and the corresponding ultrasonic nonlinear parameter was evaluated. A fairly good correlation between the curing condition and the nonlinear parameter is observed. The results show that the nonlinear parameter might be used as a good indicator of the cure state for adhesive joints.

Qu, Jianmin↗

NASA NTRS1975

Early detection of fatigue damage in composite materials

Early detection of fatigue damage in composite materials by nondestructive inspection (NDI) techniques has been demonstrated for glass/epoxy, graphite/glass/epoxy, and graphite/epoxy composites. Modulus and temperature were monitored and a correlation between them observed. Axial modulus and torsional modulus changes were a function of the laminate orientation. Torsional modulus measurements and coin tap tests were performed at 0, 1 million, 5 million, and 10 million cycles, on axial fatigue specimens. Three distinct regions were noted. In the primary region a small but rapid change in stiffness was noted in the first few thousand cycles. This was followed by a secondary region of little or no stiffness change. The tertiary region was characterized by an increasing rate of stiffness change leading to fracture. NDI procedures including holographic interferometry, ultrasonics, penetrant, and X-ray radiography were evaluated for fatigue damage detection.

Salkind, M. J.↗

NASA NTRSDate not supplied

Effect of Barely Visible Impact Damage on Thermoplastic Welded Structure

Spirit Aerosystems recently conducted screening tests on thermoplastic skin/stringer panels manufactured with Automated Fiber Placement (AFP) and stamp forming which were joined using Spirit’s Co-Fusion process. Skin and stringer gauge were both set to 0.168 cm. The resulting panel design is 48 cm tall, 49 cm wide, and has 3 stringers welded at a 21.5 cm pitch. Barely Visible Impact Damage (BVID) and Residual Compressive Strength were chosen to conduct a damage tolerance study. Zee stringers, made with IM8/PEKK-FC material, were Co-Fusion welded to a T1100/TC1225 skin. Out of these 5 panels, 1 was chosen to be a BVID survey panel, 1 for pristine compressive strength determination, and 3 to be impacted to create BVID followed by testing for residual compressive strength. On the survey panel, impacts ranged in energy from 40J – 65J and dent depth measurements were conducted at 24 hours, 48 hours, and two weeks after impacting. The residual compressive strength panel failed near the predicted load of 214 MPa. For the residual compressive strength panels, BVID was created at two different mid-bay locations: 1) striking the OML coincident with the stringer and 2) striking the skin IML 2.5 cm away from the stringer flange. Pulse Echo Ultrasonic Testing was used to inspect the panels before and after creating BVID.

HiCAM↗

NASA NTRS1991

Failure prediction of thin beryllium sheets used in spacecraft structures

The primary objective of this study is to develop a method for prediction of failure of thin beryllium sheets that undergo complex states of stress. Major components of the research include experimental evaluation of strength parameters for cross-rolled beryllium sheet, application of the Tsai-Wu failure criterion to plate bending problems, development of a high order failure criterion, application of the new criterion to a variety of structures, and incorporation of both failure criteria into a finite element code. A Tsai-Wu failure model for SR-200 sheet material is developed from available tensile data, experiments carried out by NASA on two circular plates, and compression and off-axis experiments performed in this study. The failure surface obtained from the resulting criterion forms an ellipsoid. By supplementing experimental data used in the the two-dimensional criterion and modifying previously suggested failure criteria, a multi-dimensional failure surface is proposed for thin beryllium structures. The new criterion for orthotropic material is represented by a failure surface in six-dimensional stress space. In order to determine coefficients of the governing equation, a number of uniaxial, biaxial, and triaxial experiments are required. Details of these experiments and a complementary ultrasonic investigation are described in detail. Finally, validity of the criterion and newly determined mechanical properties is established through experiments on structures composed of SR200 sheet material. These experiments include a plate-plug arrangement under a complex state of stress and a series of plates with an out-of-plane central point load. Both criteria have been incorporated into a general purpose finite element analysis code. Numerical simulation incrementally applied loads to a structural component that is being designed and checks each nodal point in the model for exceedance of a failure criterion. If stresses at all locations do not exceed the failure criterion, the load is increased and the process is repeated. Failure results for the plate-plug and clamped plate tests are accurate to within 2 percent.

Roschke, Paul N.↗

NASA NTRSDate not supplied

Metal Additive Manufacturing Process Selection and Development for Propulsion Components

Metal additive manufacturing (AM) is a generic term that captures a variety of fabrication processes. Each of these manufacturing process has unique advantages and challenges for use in aerospace propulsion applications. The most commonly used AM processes include Powder Bed Fusion (PBF), Directed Energy Deposition (DED), and solid-state processes as in Cold Spray, Ultrasonic Additive Manufacturing, and Additive Friction Stir Deposition. While detailed research has been conducted among many of the AM processes to mature processing parameters and material properties, navigating which processes are best to select is difficult as it is based on specific component requirements. The focus of this presentation is to provide an overview of considerations for each of metal AM process selection for aerospace components based on various key attributes. These key attributes include geometric considerations, metallurgical characteristics, cost basis, post-processing and maturity of the processes. The data for these trade selections are based on studies that NASA as performed internally and with academic and industry partners. These studies include multiple AM build experiments to evaluate (1) geometric variations and constraints within the processes, (2) alloy characterization and mechanical testing, (3) pathfinder component development and hot-fire evaluations, and (4) certification approaches. This presentation summarizes these results and is meant to introduce specific examples which show what to consider when designing a metal AM component for aerospace propulsion applications.

Additive Manufacturing↗

NASA NTRSDate not supplied

Metal Additive Manufacturing Process Selection and Development Lifecycle for Propulsion Components

Paul Gradl↗

NASA NTRSDate not supplied

Innovations in Continuous Ultrasonic Welding of Thermoplastic Composites and Evaluation for Space Applications

The goals of NASA’s Thermoplastic Development for Exploration Applications (TDEA) Project include and assessment of thermoplastic composite joints for space structures by developing and maturing design capabilities, analysis tools and techniques, and manufacturing processes for thermoplastic composites. Through this effort the TDEA project will expand NASA’s in-house thermoplastic composite manufacturing capabilities, develop an understanding of advanced thermoplastic joining techniques relevant to space environments, evaluate the feasibility of reconfigurable composite structures, and advance structural analysis capabilities, including failure prediction of thermoplastic composites including joints. This presentation will provide an overview of the materials and manufacturing effort within the TDEA project. Three semi-crystalline and one amorphous thermoplastic composite system were selected for initial screening and provided an opportunity to gain manufacturing experience across a range of processing temperatures, rheological behavior, and composite properties. Equivalency to the National Center for Advanced Materials Performance (NCAMP) test report for Toray’s TC1225 material was established to provide confidence in in-house manufacturing and material properties were generated through baseline mechanical tests for each material. Material characterization data was generated for a subset of materials to (1) provide data for analysis and model development and (2) generate thermal, rheological and conductivity data across relevant temperatures. A key objective of the TDEA project is evaluation of thermoplastic composite joining processes suitable for in-space operations. This presentation will outline the project’s progress in fusion bonding candidate materials by common welding techniques to assess the quality, reproducibility and strength of the bond, as well as identify limitations to in-space manufacturing. The feasibility of joint disassembly and reassembly will be discussed.

thermoplastic composite↗

NASA NTRS2018

Comparison of Staggered Grid Finite Difference Schemes for Ultrasound Simulation in Curving Composites

The optimization of ultrasonic nondestructive evaluation (NDE) simulation tools for composites has the potential to reduce both individual part inspection time and overall certification time for composite parts and structures. Inspection guidance based on simulation provides increased confidence in the veracity of inspection results in addition to time reductions. This paper outlines ongoing work targeted to advance this objective through the use of finite difference (FD) simulation techniques formulated for composite structures with realistic geometries. Two staggered grid explicit FD schemes which show promise for this purpose are assessed: the Lebedev FD scheme and the rotated staggered grid (RSG) FD scheme. Algorithmic points which provide challenges for complex geometries are addressed, in particular handling of traction free surfaces and bi-material interfaces present at lamina boundaries. Code execution time estimates are performed as well to guide feasible domain sizes relative to algorithm choice and available hardware. Three test cases are simulated: a delaminated plate, a cylinder, and a triclinic lamina. These tests demonstrate that the Lebedev FD scheme needs additional work to handle inter-laminar interfaces and traction free boundaries in the presence of stair-stepping approximations. In contrast, the simple structure of the RSG unit cell makes it more straightforward to construct a 3D simulation technique for curved composite laminates.

Frankforter, Erik↗

NASA NTRS1978

The Array Automated Assembly Task for the Low Cost Solar Array Project, Phase 2

During the program a process sequence was proposed and tested for the fabrication of dendritic welb silicon into solar modules. This sequence was analyzed as to yield and cost and these data suggest that the price goals of 1986 are attainable. Specifically, it was shown that a low cost POCL3 is a suitable replacement for the semiconductor grade, and that a suitable CVD oxide can be deposited from a silane/air mixture using a Silox reactor. A dip coating method was developed for depositing an antireflection coating from a metalorganic precursor. Application of photoresist to define contact grids was made cost effective through use of a dip coating technique. Electroplating of both Ag and Cu was shown feasible and cost effective for producing the conductive metal grids on the solar cells. Laser scribing was used to separate the cells from the dendrites without degradation. Ultrasonic welding methods were shown to be feasible for interconnecting the cells. A study of suitable low cost materials for encapsulation suggest that soda lime glass and phenolic filled board are preferred.

Campbell, R. B.↗

NASA NTRS2004

An Overview of My 2004 Summer Internship

This summer I have been working with the Non-destructive evaluation (NDE) group and NASA Glenn Research Center. As this is my second summer with the group, I was able to begin working as soon as I arrived. My first task was to develop a system to acquire an impedance analyzer. The basic setup of the system is as follows: a piezo- electric patch is attached to a sample, and a lead is attached to that patch. Another lead is attached directly to the sample, and the leads are connected to the impedance analyzer. The system then puts a voltage through the material over a range of frequencies, and the corresponding impedances are measured for each frequency. After data is collected, it can be compared to another data set, and through a series of calculations a damage parameter is produced. For the time being, we are using a correlation calculation to find the damage parameter. The hope for this project is that a baseline measurement can be taken, and then sometime later another measurement could be taken, and the damage parameter would determine how much damage had been done to the sample. To test this hypothesis, we took baseline data from a sample, and then sent it out to have a notch cut into it. When it was returned, we again took measurements on the sample, and the damage parameter was significantly lower. Another project that I have been working on pertains to the group's newly acquired acoustography system. This system creates a full field ultrasonic signal on one side of a sample, and an acousto-optic sensor is placed on the other side of the sample.

Hertert, Lucien↗

NASA NTRSDate not supplied

In-Situ Detection of Process-Induced Porosity During Cure of Out-of-Autoclave Composites

Composite materials offer unique benefits in aerospace applications and are becoming increasingly used by industry manufacturers. Current manufacturing and processing methods can lead to defects in the composites, which are identified after fabrication using inspection methods.This study utilized a high-temperature ultrasonic inspection system to detect process-induced porosity in an out-of-autoclave (OOA) composite panel. An ultrasonic scanner was enclosed in a nitrogen-cooled insulating box that prevented thermal damage from the industrial oven to the temperature-sensitive electronics. Inspection of the composite part was performed through the bottom of the enclosure, which served as the tool plate for the part. In this study, a porosity gradient was introduced through a misfit of the part and caul plate. Using the data obtained from B-scans and amplitude C-scans throughout the cure cycle, the high and low porosity regions within the composite laminate were detected and localized. OOA tests aided the transition of this system to an autoclave, which is the primary method of curing aerospace-grade thermoset composites.

In-process, Defect Detection, Cure Monitoring, Por↗

NASA NTRS2000

Ultrasonic Assessment of Impact-Induced Damage and Microcracking in Polymer Matrix Composites

The main objective of this NASA FAR project is to conduct ultrasonic assessment of impact-induced damage and microcracking in polymer matrix composites at various temperatures. It is believed that the proposed study of impact damage assessment on polymer matrix composites will benefit several NASA's missions and current interests, such as ballistic impact testing of composite fan containment and high strain rate deformation modeling of polymer matrix composites. Currently, impact-induced delamination and fracture in 6061-T6 aluminum/cast acrylic sandwich plates adhered by epoxy were generated in an instrumented drop-weight impact machine. Although only a small dent was produced on the aluminum side when a hemispherical penetrator tup was dropped onto it from a couple of inches, a large ring of delamination at the interface was observed. The delamination damage was often accompanied by severe shattering in the acrylic substratum. Damage patterns in the acrylic layer include radial and ring cracks and, together with delamination at the interface, may cause peeling-off of acrylic material from the sandwich plate. Theory of stress-wave propagation can be used to explain these damage patterns. The impact tests were conducted at various temperatures. The results also show clearly that temperature effect is very important in impact damage. For pure cast acrylic nil-ductile transition (NDT) occurs between 185-195 F Excessive impact energy was dissipated into fracture energy when tested at temperature below this range or through plastic deformation when tested at temperature above the NDT temperature. Results from this study will be used as baseline data for studying fiber-metal laminates, such as GLARE and ARALL for advanced aeronautical and astronautical applications.

Liaw, Benjamin↗

NASA NTRSDate not supplied

Thermoplastic Composite Lunar Tower Truss Structure: Design Development and Verification Plans

The National Aeronautics and Space Administration (NASA) Space Technology and Mission Directorate (STMD) is advancing thermoplastic composite (TPC) technologies for exploration missions. The Technology Development for Exploration Applications (TDEA) project goals are to develop and mature TPC materials, designs, analyses tools and techniques, and mature manufacturing processes. This includes development of manufacturing and joining approaches relevant to space environments. To these ends TDEA endeavors toward demonstrating a TPC truss structure for a lunar tower configuration. The design, predicated on robotic assembly, uses open section truss elements fused to a joint splice plate, without a structural adhesive. This presentation details the TDEA lunar truss structure design development approach including design heritage, the requirements established, the mechanical design and analyses, and thermal analyses demonstrating structural requirements conformance, as well as planned building block verification efforts either underway or planned. The mechanical analyses show the most severe environment is a moon-quake the truss dynamic responses. The thermal analyses show the extreme cold for on-orbit welding, the window for less severe on-orbit welding, as well as the large thermal gradients on the truss. The building block approach shown includes ultrasonic welding and lap shear coupon testing on various truss element thicknesses and layups. Knockdown factor determinations due to lunar dust contamination (simulated) and effects of welding in a vacuum are presented. The most highly loaded truss joint configuration sub-element verification test matrix is outlined. Lastly, plans to build, inspect, and test a 2-bay truss representative unit cell that is 1.5 meters by 1.5 meters by 3.0 meters tall are detailed.

Lunar Tower↗

NASA NTRSDate not supplied

Additive Manufacturing and Experimental Characterization of Nickel-Titanium Shape-Memory Alloy Wick Structures and Heat Pipes for Spacecraft Thermal Control

Shape memory alloys (SMA), such as those based on nickel-titanium (NiTi), are increasingly being applied as multifunctional spacecraft components. For thermal management applications, NiTi flow tubing hinges and self-deploying loop heat pipes have been demonstrated. Emerging additive manufacturing (AM) processes are enabling more complex SMA devices than can be formed from conventional plain wire, tubing, and sheet stock materials. This paper presents our progress toward applying powder bed fusion AM to producing porous NiTi wicks and NiTi-H2O heat pipes, which could be embedded in thermally deploying radiators for spacecraft thermal management. AM near-equiatomic NiTi (55.1 wt% Ni) porous wick specimens were produced with a range of deposition parameters. Transient acetone rate-of-rise experiments were performed to estimate wick permeability (K) and average pore radius (r_pore) values and identify parameter sets with high capillary performance. Surface treatments were evaluated to achieve hydrophilic wick structures. Evaluated treatments included chemical oxide growth with H2O2, oxide and sodium titanate growth with NaOH solution, and ultrasonic cleaning with specialty detergents that can remove hydrocarbon contaminants. The most durable hydrophilic surface conditions were obtained with the NaOH treatment. High performing wick deposition parameters were used to produce a full AM NiTi heat pipe, which was treated with NaOH solution to activate the wick. This heat pipe was operated on a test stand in the inverted configuration (upper evaporator and lower condenser), and demonstrated stable nearly isothermal operation for 150 hrs.

Thermal management↗

NASA NTRSDate not supplied

Additive Manufacturing and Experimental Characterization of Nickel-Titanium Shape-Memory Alloy Wick Structures and Heat Pipes for Spacecraft Thermal Control

Thermal management↗