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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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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Evaluation of Surface Residual Stresses in Friction Stir Welds Due to Laser and Shot Peening

The effects of laser, and shot peening on the residual stresses in Friction Stir Welds (FSW) has been investigated. The surface residual stresses were measured at five different locations across the weld in order to produce an adequate residual stress profile. The residual stresses before and after sectioning the coupon from the welded plate were also measured, and the effect of coupon size on the residual stress relaxation was determined and characterized. Measurements indicate that residual stresses were not uniform along the welded plate, and large variation in stress magnitude could be exhibited at various locations along the FSW plate. Sectioning resulted in significant residual stress relaxation in the longitudinal direction attributed to the large change in dimensions in this direction. Overall, Laser and shot peening resulted in a significant reduction in tensile residual stresses at the surface of the specimens.

Hatamleh, Omar↗
NASA NTRS2013

Defect Detectability Improvement for Conventional Friction Stir Welds

This research was conducted to evaluate the effects of defect detectability via phased array ultrasound technology in conventional friction stir welds by comparing conventionally prepped post weld surfaces to a machined surface finish. A machined surface is hypothesized to improve defect detectability and increase material strength.

Hill, Chris↗
NASA NTRS2004

Friction Stir Welding of GR-Cop 84 for Combustion Chamber Liners

GRCop-84 is a copper-chromium-niobium alloy developed by the Glenn Research Center for liquid rocket engine combustion chamber liners. GRCop-84 exhibits superior properties over conventional copper-base alloys in a liquid hydrogen-oxygen operating environment. The Next Generation Launch Technology program has funded a program to demonstrate scale-up production capabilities of GR-Cop 84 to levels suitable for main combustion chamber production for the prototype rocket engine. This paper describes a novel method of manufacturing the main combustion chamber liner. The process consists of several steps: extrude the GR-Cop 84 powder into billets, roll the billets into plates, bump form the plates into cylinder halves and friction stir weld the halves into a cylinder. The cylinder is then metal spun formed to near net liner dimensions followed by finish machining to the final configuration. This paper describes the friction stir weld process development including tooling and non-destructive inspection techniques, culminating in the successful production of a liner preform completed through spin forming.

Russell, Carolyn K.↗
NASA NTRS2010

Large Spun Formed Friction-Stir Welded Tank Domes for Liquid Propellant Tanks Made from AA2195: A Technology Demonstration for the Next Generation of Heavy Lift Launchers

Improving structural efficiency while reducing manufacturing costs are key objectives when making future heavy-lift launchers more performing and cost efficient. The main enabling technologies are the application of advanced high performance materials as well as cost effective manufacture processes. This paper presents the status and main results of a joint industrial research & development effort to demonstrate TRL 6 of a novel manufacturing process for large liquid propellant tanks for launcher applications. Using high strength aluminium-lithium alloy combined with the spin forming manufacturing technique, this development aims at thinner wall thickness and weight savings up to 25% as well as a significant reduction in manufacturing effort. In this program, the concave spin forming process is used to manufacture tank domes from a single flat plate. Applied to aluminium alloy, this process allows reaching the highest possible material strength status T8, eliminating numerous welding steps which are typically necessary to assemble tank domes from 3D-curved panels. To minimize raw material costs for large diameter tank domes for launchers, the dome blank has been composed from standard plates welded together prior to spin forming by friction stir welding. After welding, the dome blank is contoured in order to meet the required wall thickness distribution. For achieving a material state of T8, also in the welding seams, the applied spin forming process allows the required cold stretching of the 3D-curved dome, with a subsequent ageing in a furnace. This combined manufacturing process has been demonstrated up to TRL 6 for tank domes with a 5.4 m diameter. In this paper, the manufacturing process as well as test results are presented. Plans are shown how this process could be applied to future heavy-lift launch vehicles developments, also for larger dome diameters.

Stachulla, M.↗
DOE OSTI2025

Exploration of High Depth-to-Width Ratio Micro Friction Stir Welding on Thin 6061-T6 Aluminum Butt Joints

In the autogenous joining process of thin 6061-T6 aluminum plates, micro friction stir welding (μFSW) is employed to explore the limitations of high depth to width ratio (HDWR) welding. In this explorative study, 1.25mm plate is joined in a butt joint fashion, multiple HDWR μFSW tools are developed, and the welding parameters are optimized to create a DWR greater than 0.4. A proposed method of implementing induction preheating to the joint is presented and the subsequent characterization of the welds are discussed. Upon completion of the project, the limitations on HDWR μFSW will be more accurately defined, and the best weld will be characterized to determine some of metallurgical properties. This study further expands the operating window for autogenous welding with solid state processes on thin aluminum plate as well as highlight methods for process improvement for tooling design and pre-heating methods.

Shambaugh, Colton↗
NASA NTRS2001

Friction Stir Welding Development at National Aeronautics and Space Administration-Marshall Space Flight Center

This paper presents an over-view of friction stir welding (FSW) process development and applications at Marshall Space Flight Center (MSFC). FSW process development started as a laboratory curiosity but soon found support from many users. The FSW process advanced very quickly and has found many applications both within and outside the aerospace industry. It is currently being adapted for joining key elements of the Space Shuttle External Tank for improved producibility and reliability. FSW process modeling is done to better understand and improve the process. Special tools have been developed to weld variable thickness materials including very thin and very thick materials. FSW is now being applied to higher temperature materials such as copper and to advanced materials such as metal matrix composites. FSW technology is being successfully transferred from MSFC laboratory to shop floors of many commercial companies.

Bhat, Biliyar N.↗
NASA NTRS2006

Laser Peening and Shot Peening Effects on Fatigue Life and Surface Roughness of Friction Stir Welded 7075-T7351 Aluminum

The effects of laser peening, shot peening, and a combination of both on the fatigue life of Friction Stir Welds (FSW) was investigated. The fatigue samples consisted of dog bone specimens and the loading was applied in a direction perpendicular to the weld direction. Several laser peening conditions with different intensities, durations, and peening order were tested to obtain the optimum peening parameters. The surface roughness resulting from various peening techniques was assessed and characterized. The results indicate a significant increase in fatigue life using laser peening compared to shot peened versus their native welded specimens.

Hatamleh, Omar↗
NASA NTRS2012

Damage Tolerance Assessment of Friction Pull Plug Welds

Friction stir welding is a solid state welding process developed and patented by The Welding Institute in Cambridge, England. Friction stir welding has been implemented in the aerospace industry in the fabrication of longitudinal welds in pressurized cryogenic propellant tanks. As the industry looks to implement friction stir welding in circumferential welds in pressurized cryogenic propellant tanks, techniques to close out the termination hole associated with retracting the pin tool are being evaluated. Friction pull plug welding is under development as a one means of closing out the termination hole. A friction pull plug weld placed in a friction stir weld results in a non-homogenous weld joint where the initial weld, plug weld, their respective heat affected zones and the base metal all interact. The welded joint is a composite, plastically deformed material system with a complex residual stress field. In order to address damage tolerance concerns associated with friction plug welds in safety critical structures, such as propellant tanks, nondestructive inspection and proof testing may be required to screen hardware for mission critical defects. The efficacy of the nondestructive evaluation or the proof test is based on an assessment of the critical flaw size in the test or service environments. Test data relating residual strength capability to flaw size in two aluminum alloy friction plug weld configurations is presented.

McGill, Preston↗
NASA NTRS2011

Effects of Annealing Process on the Formability of Friction Stir Welded Al-Li Alloy 2195 Plates

Large rocket cryogenic tank domes have typically been fabricated using Al-Cu based alloys like Al-Cu alloy 2219. The use of aluminum-lithium based alloys for rocket fuel tank domes can reduce weight because aluminum-lithium alloys have lower density and higher strength than Al-Cu alloy 2219. However, Al-Li alloys have rarely been used to fabricate rocket fuel tank domes because of the inherent low formability characteristic that make them susceptible to cracking during the forming operations. The ability to form metal by stretch forming or spin forming without excessive thinning or necking depends on the strain hardening exponent "n". The stain hardening exponent is a measure of how rapidly a metal becomes stronger and harder. A high strain hardening exponent is beneficial to a material's ability to uniformly distribute the imposed strain. Marshall Space Flight Center has developed a novel annealing process that can achieve a work hardening exponent on the order of 0.27 to 0.29, which is approximately 50% higher than what is typically obtained for Al-Li alloys using the conventional method. The strain hardening exponent of the Al-Li alloy plates or blanks heat treated using the conventional method is typically on the order of 0.17 to 0.19. The effects of this novel annealing process on the formability of friction stir welded Al-Li alloy blanks are being studied at Marshall Space Flight Center. The formability ratings will be generated using the strain hardening exponent, strain rate sensitivity and forming range. The effects of forming temperature on the formability will also be studied. The objective of this work is to study the deformation behavior of the friction stir welded Al-Li alloy 2195 blank and determine the formability enhancement by the new annealing process.

Chen, Po-Shou↗
NASA NTRS2008

Phased Array Ultrasound: Initial Development of PAUT Inspection of Self-Reacting Friction Stir Welds

This slide presentation reviews the development of Phased Array Ultrasound (PAUT) as a non-destructive examination method for Self Reacting Friction Stir Welds (SR-FSW). PAUT is the only NDE method which has been shown to detect detrimental levels of Residual Oxide Defect (ROD), which can result in significant decrease in weld strength. The presentation reviews the PAUT process, and shows the results in comparison with x-ray radiography.

Rairigh, Ryan↗
NASA NTRS2000

Autogeneous Friction Stir Weld Lack-of-Penetration Defect Detection and Sizing Using Directional Conductivity Measurements with MWM Eddy Current Sensor

Al 2195-T8 plate specimens containing Friction Stir Welds (FSW), provided by Lockheed Martin, were inspected using directional conductivity measurements with the MWM sensor. Sensitivity to lack-of-penetration (LOP) defect size has been demonstrated. The feature used to determine defect size was the normalized longitudinal component of the MWM conductivity measurements. This directional conductivity component was insensitive to the presence of a discrete crack. This permitted correlation of MWM conductivity measurements with the LOP defect size as changes in conductivity were apparently associated with metallurgical features within the first 0.020 in. of the LOP defect zone. Transverse directional conductivity measurements also provided an indication of the presence of discrete cracks. Continued efforts are focussed on inspection of a larger set of welded panels and further refinement of LOP characterization tools.

Goldfine, Neil↗
DOE OSTI2020

Texture and precipitation behavior of friction stir welded Inconel 825 alloy

The microstructure, texture pattern, and precipitation behavior of friction stir butt welded Inconel 825 alloy are highlighted here. The microstructure of bright regions and black-banded regions in the stir zone (SZ) is characterized by SEM, EBSD, and TEM with EDS. EBSD analysis justifies that the SZ exhibits a dynamic recrystallized structure. Grain boundary mapping corroborates the insignificant difference in the low- and high-angle grain boundaries fraction between the SZ, the thermo-mechanically affected zone, and the base metal. TEM analysis confirms the formation of nano twins and dispersion of nano-size precipitations in the grains, and at the grain boundaries as well. Grain refinement and nano-size precipitation formation in the SZ significantly enhanced both microhardness and tensile strength.

Das, Hrishikesh↗
DOE OSTI2022

Friction stir welding and self-ion irradiation effects on microstructure and mechanical properties changes within oxide dispersion strengthened steel $\mathrm{MA956}$

We report the joining process for oxide dispersion strengthened (ODS) alloys remains a key challenge facing the nuclear community. The microstructure and mechanical properties were characterized in the base material and friction stir welded ODS MA956 irradiated with 5 MeV Fe 2+ ions from 400 to 500°C up to 25 dpa. Nanoindentation was performed to assess changes in hardness and yield stress, and the dispersed barrier hardening (DBH) model was applied to described results. A combination of scanning transmission electron microscopy (STEM) and atom probe tomography (APT) were used to assess evolution of the microstructure including dispersoids, network dislocations and dislocation loops, nanoclusters, and solid solution concentrations. Overall, softening was observed as a result of increased dose, which was exacerbated at 500°C. The formation and coarsening of new dispersoids was noted while nanoclusters tended to dissolve in the base material, and were not observed in the stir zone. Solute nanocluster evolution was identified as a primary driver of the changes in mechanical properties.

36 MATERIALS SCIENCE↗
NASA NTRS1999

Friction Stir Welding for Aluminum Metal Matrix Composites (MMC's) (Center Director's Discretionary Fund, Project No. 98-09)

This technical memorandum describes an investigation of using friction stir welding (FSW) process for joining a variety of aluminum metal matrix composites (MMC's) reinforced with discontinuous silicon-carbide (SiC) particulate and functional gradient materials. Preliminary results show that FSW is feasible to weld aluminum MMC to MMC or to aluminum-lithium 2195 if the SiC reinforcement is <25 percent by volume fraction. However, a softening in the heat-affected zone was observed and is known to be one of the major limiting factors for joint strength. The pin tool's material is made from a low-cost steel tool H-13 material, and the pin tool's wear was excessive such that the pin tool length has to be manually adjusted for every 5 ft of weldment. Initially, boron-carbide coating was developed for pin tools, but it did not show a significant improvement in wear resistance. Basically, FSW is applicable mainly for butt joining of flat plates. Therefore, FSW of cylindrical articles such as a flange to a duct with practical diameters ranging from 2-5 in. must be fully demonstrated and compared with other proven MMC joining techniques for cylindrical articles.

Lee, J. A.↗
NASA NTRS2006

Comparison of the Effects of Tool Geometry for Friction Stir Welding Thin Sheet Aluminum Alloys for Aerospace Applications

In this presentation, the results of a recent study on the effect of pin tool design for friction stir welding thin sheets (0.040") of aluminum alloys 2024 and 7075 are provided. The objective of this study was to investigate and document the effect of tool shoulder and pin diameter, as well as the presence of pin flutes, on the resultant microstructure and mechanical properties at both room temperature and cryogenic temperature. Specifically, the comparison between three tools will include: FSW process load analysis (tool forces required to fabricate the welds), Static Mechanical Properties (ultimate tensile strength, yield strength, and elongation), and Process window documenting the range of parameters that can be used with the three pin tools investigated. All samples were naturally aged for a period greater than 10 days. Prior research has shown 7075 may require post weld heat treatment. Therefore, an additional pair of room temperature and cryogenic temperature samples was post-weld aged to the 7075-T7 condition prior to mechanical testing.

Merry, Josh↗
NASA NTRS2022

Friction Stir Welded Aluminum-Lithium (Al-Li) 2050 Blanks for Spin Forming

Spin forming is a metalworking process used to produce axially-symmetric parts by the application of lateral pressure from a forming tool to a circular blank mounted on a revolving, heated mandrel. This process enables production of cones, domes, or caps that can incorporate features such as flat bulkheads. Friction stir welded (FSW) Al-Li 2195 blanks have been spin formed for single-piece, launch vehicle domes up to 5 m in diameter. Al-Li 2050 plate has the advantage of availability up to 165 mm thick,whereas 2195 plate is traditionally only available up to 57 mm thick. Increased plate thickness enables greater design flexibility for machining of taller structural elements, such as stiffeners. However, 2050 is only available in plate widths up to ~3.9 m. This study demonstrated the capability of making custom 2050 blanks for spin forming large (>7.8 m in diameter), single-piece, light-weight flight articles (e.g., lunar habitats and landers) by FSW two (or more) plates together. Spin forming of welded 2050 blanks has not been attempted before this investigation. The objective was to evaluate the mechanical properties of 2050 parent material and FSW regions after spin forming and subsequent T6 heat treatment. A 3 m diameter x 38 mm thick 2050 blank was fabricated from two 1.5 m wide pieces by FSW and subsequently spin formed into a cone article. Additionally, three 1.2 m diameter x 8.1 mm thick 2050 blanks were produced by FSW and spin formed into subscale cone articles with varying strain input. Mechanical properties are reported for spin formed 2050-T6 parent material and FSW regions on the articles. Abnormal grain growth (AGG) in the FSW during heat treatment was expected based on prior experience with 2195. Implementation of an AGG suppression strategy during heat treatment reduced AGG in the FSW regions and improved ductility.

Spin forming↗
NASA NTRS2004

Inspecting Friction Stir Welding using Electromagnetic Probes

A report describes the use of advanced electromagnetic probes to measure the dimensions, the spatial distribution of electrical conductivity, and related other properties of friction stir welds (FSWs) between parts made of the same or different aluminum alloy(s). The probes are of the type described in in another Tech Brief. To recapitulate: A probe of this type is essentially an eddy-current probe that includes a primary (driver) winding that meanders and multiple secondary (sensing) windings that meander along the primary winding. Electrical conductivity is commonly used as a measure of heat treatment and tempering of aluminum alloys, but prior to the development of these probes, the inadequate sensitivity and limited accuracy of electrical-conductivity probes precluded such use on FSWs between different aluminum alloys, and the resolution of those probes was inadequate for measurement of FSW dimensions with positions and metallurgical properties. In contrast, the present probes afford adequate accuracy and spatial resolution for the purposes of measuring the dimensions of FSW welds and correlating spatially varying electrical conductivities with metallurgical properties, including surface defects.

Kinchen, David G.↗
DOE OSTI2024

Impact of Backing Plate and Thermal Boundary Conditions for High-Speed Friction Stir Welding of 25-mm Thick Aluminum Alloy 7175-T79

Here this study demonstrates high-speed (150 mm/min) single pass friction stir butt joining of 25 mm thick aluminum alloy 7175-T79. To understand the impact of quenching and cooling rate on process responses, joint strength, and grain size distributions across the weld thickness, we performed a series of friction stir welding (FSW) trials in air and with a trailing water spray using steel and composite backing plates (BP). Welds made in air and trailing water spray exhibit significantly different hardness distributions across the nugget, heat affected zone (HAZ), and HAZ minimum hardness as evidenced by detailed microhardness mapping. The effect of trailing water spray (TWS) on joint efficiency overshadows the influence of BP composition due to the vastly different contribution to quenching. TWS also resulted in a multifaceted effect on FSW such as lowering processing temperature, increasing X and Z forces while lowering Y force, and narrow heat affecting zone. Finally, digital image correlation (DIC)-based fracture mode analysis and grain size measurements correlate with the hardness distribution.

42 ENGINEERING↗