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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 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Precise Truss Assembly Using Commodity Parts and Low Precision Welding

Hardware and software design and system integration for an intelligent precision jigging robot (IPJR), which allows high precision assembly using commodity parts and low-precision bonding, is described. Preliminary 2D experiments that are motivated by the problem of assembling space telescope optical benches and very large manipulators on orbit using inexpensive, stock hardware and low-precision welding are also described. An IPJR is a robot that acts as the precise "jigging", holding parts of a local structure assembly site in place, while an external low precision assembly agent cuts and welds members. The prototype presented in this paper allows an assembly agent (for this prototype, a human using only low precision tools), to assemble a 2D truss made of wooden dowels to a precision on the order of millimeters over a span on the order of meters. The analysis of the assembly error and the results of building a square structure and a ring structure are discussed. Options for future work, to extend the IPJR paradigm to building in 3D structures at micron precision are also summarized.

Komendera, Erik↗
NASA NTRS1963

Selected Welding Techniques

Marshall Space Flight Center specifications for welding large, single tank boosters are rather stringent, calling for no undercutting, no cracking, complete fusion, and a relatively small amount of porosity. In order to maintain design tolerances it is necessary to rely on electronic positioning controls to keep the torch on the joint to be welded. When tests of certain available systems proved conclusively that they were not adequate, Marshall personnel set out on their own development programs. The problems were many but the results were gratifying. It is believed that proximity and seam tracking controls adequate for most anticipated applications are now on hand.

Source record↗
NASA NTRS2018

Understanding Friction Stir Welding

This Technical Memorandum explains the friction stir welding process in terms of two basic concepts: the concentration of deformation in a shear surface enveloping the tool and the composition of the overall plastic flow field around the tool from simple flow field components. It is demonstrated how weld structure may be understood and torque, drag, and lateral tool forces may be estimated using these concepts. Some discrepancies between computations and accompanying empirical data are discussed in the text. This work is intended to be helpful to engineers in diagnosing problems and advancing technology.

Nunes, A. C., Jr.↗
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↗
DOE OSTI2017

System for evaluating weld quality using eddy currents

Electromagnetic and eddy current techniques for fast automated real-time and near real-time inspection and monitoring systems for high production rate joining processes. An eddy current system, array and method for the fast examination of welds to detect anomalies such as missed seam (MS) and lack of penetration (LOP) the system, array and methods capable of detecting and sizing surface and slightly subsurface flaws at various orientations in connection with at least the first and second weld pass.

42 ENGINEERING↗
DOE OSTI2022

Methods for thermal welding of wind turbine blades

Disclosed herein are methods, devices, and systems for manufacturing wind turbine blades which in some instances require using new blade joint designs. The blade joint designs described herein may allow for contact in places where welds will be made, which allows for existing manufacturing tolerances to be used while still enabling the use of thermal welding for wind turbine blades.

17 WIND ENERGY↗
DOE OSTI2021

Some Physics Fundamentals of High Energy Density Welding

The purpose of this section of this document is to provide a brief summary of the physics aspects of high energy density welding (HEDW). One reason for this is to help elucidate some of the differences between EBW and LBW. A fundamental understanding of these differences can help guide an appropriate choice of process for a particular application.

42 ENGINEERING↗
NASA NTRS1929

Welding Rustproof Steels

The following experimental results will perhaps increase the knowledge of the process of welding rustproof steels. The experiments were made with two chrome-steel sheets and with two chrome-steel-nickel sheets having the composition shown in Table I.

STEELS, STAINLESS - ETCHING↗
DOE OSTI2018

Welding Defect Classification from Simulated Ultrasonic Signals

Nondestructive testing is widely used to detect and to size up discontinuities embedded in a material. Among the several ultrasonic techniques, time of flight diffraction (TOFD) combines high speed inspection, high sizing reliability and low rate of incorrect results. However, the classification of defects through ultrasound signals acquired by the TOFD technique depends heavily on the knowledge and experience of the operator and thus, this classification is still frequently questioned. Besides, this task requires long processing time due to the large amount of data to be analyzed. Nevertheless, computational tools for pattern recognition can be employed to analyze a high amount of data with large efficiency. In the present work, simulation of ultrasound propagation in two-dimensional media containing, each one, different kinds of modeled discontinuities which mimic defects in welded joints were performed. Clustering (k-means) and classification (principal component analysis and k-nearest neighbors) algorithms were employed to associate each simulated ultrasound signal with its corresponding modeled defects. The results for each method were analyzed, discussed and compared. The results are very promising.

42 ENGINEERING↗
DOE OSTI2018

Laser Welding-Brazing of Immiscible AZ31B Mg and Ti-6Al-4V Alloys Using an Electrodeposited Cu Interlayer

Metallurgical bonding between immiscible system AZ31B magnesium (Mg) and Ti-6Al-4V titanium (Ti) was achieved by adding Cu interlayer using laser welding-brazing process. Effect of the laser power on microstructure evolution and mechanical properties of Mg/Cu-coated Ti joints was studied. Visually acceptable joints were obtained at the range of 1300 to 1500 W. The brazed interface was divided into three parts due to temperature gradient: direct irradiation zone, intermediate zone and seam head zone. Ti{sub 3}Al phase was produced along the interface at the direct irradiation zone. Ti-Al reaction layer grew slightly with the increase in laser power. A small amount of Ti{sub 2}(Cu,Al) interfacial compounds formed at the intermediate zone and the (α-Mg + Mg{sub 2}Cu) eutectic structure dispersed in the fusion zone instead of gathering when increasing the laser power at this zone. At the seam head zone, Mg-Cu eutectic structure was produced in large quantities under all cases. Joint strength first increased and then decreased with the variation of the laser power. The maximum fracture load of Mg/Cu-coated Ti joint reached 2314 N at the laser power of 1300 W, representing 85.7% joint efficiency when compared with Mg base metal. All specimens fractured at the interface. The feature of fracture surface at the laser power of 1100 W was characterized by overall smooth surface. Obvious tear ridge and Ti{sub 3}Al particles were observed at the fracture surface with increase in laser power. It suggested atomic diffusion was accelerated with more heat input giving rise to the enhanced interfacial reaction and metallurgical bonding in direct irradiation zone, which determined the mechanical properties of the joint.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure Evolution and Mechanical Properties of High-Speed Friction Stir Welded Aluminum Alloy Thin Plate Joints

Sound friction stir welded (FSW) joints of 6061-T6 aluminum alloy sheets with an 0.8 mm thickness were obtained at conventional speed (2000 rpm, 300 mm/min) and high speed (11,000 rpm, 1500 mm/min). The recrystallization mechanism, precipitate evolution, mechanical properties and fracture behavior were investigated in detail. Microstructure analyses revealed that the grain structure evolution in the nugget zone (NZ) was dominated by continuous dynamic recrystallization. In the process of FSW, high speed facilitates the formation of finer equiaxed recrystallized grains, higher density of dislocations and substructures, and a larger number of precipitates in the NZ compared to the conventional speed, which further significantly improves the hardness and tensile strength of the joints. The maximum tensile strength was obtained with 292.6 MPa, 83.2% for the 6061-T6 aluminum alloy and 122.6% for the conventional-speed FSW joints. This work provides an effective method for preparing FSW aluminum alloy thin plate joints with excellent mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced Strength of 304 SS-Ti6Al4V Laser-Welded Joints Containing Composite Interlayers

This paper investigates the microstructural characterization of the fracture propagation edge during laser beam welding of Ti6Al4V and 304 stainless steel using Cu, V, and Ni interlayers as a single Cu interlayer and composite interlayer structures with different Cu interlayer thicknesses. This study attempts to increase the Ti-SS joint strength through the use of the composite interlayers. X-ray diffraction characterization based on a 0.5-mm-thick Cu interlayer showed that the SS/Cu/Ti joint contained considerable brittle IMCs; however, the fracture surface of the SS/Cu-V/Ti composite interlayer sample did not contain any Fe-Ti IMCs or Cr{sub 2}Ti. EBSD observation indicated that the crack propagated transgranularly from solidified CuTi in the interdendritic regions of the FeTi compounds in the composite interlayer sample; however, the crack propagated intergranularly along Fe{sub 2}Ti grain boundaries in the single interlayer sample. The investigation based on a 1-mm-thick Cu interlayer showed that the SS/Ni-Cu1/Ti sample was stronger than the SS/Cu1/Ti sample due to a lack of CuTi at 3.5 kW. The tensile strength of the SS/Cu1-V/Ti joint was greater than that of the SS/Ni-Cu1/Ti joint due to the formation of ductile NiTi instead of brittle NiTi{sub 2}. The microstructures of the fracture edges after tensile testing illustrated that the eutectic CuTi + CuTi{sub 2} fractured at the SS/Cu1/Ti joint after tensile testing, while CuTi{sub 2} and eutectoid αTi + CuTi{sub 2} compounds fractured during the tensile experiment at the SS/Ni-Cu1/Ti and SS/Cu1-V/Ti joints, respectively. Investigations based on both the 0.5- and 1-mm-thick Cu interlayers showed that the tensile strength and elongation of the composite interlayer joints at a laser power of 3.5 kW were greater than those of the single interlayer joints.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influencing mechanism of pre-existing nanoscale Al 5 Fe 2 phase on Mg–Fe interface in friction stir spot welded Al-free ZK60–Q235 joint

Al-free ZK60 magnesium (Mg) alloy sheet was selected as substrate material of Mg–steel pinless friction stir spot welding (FSSW), avoiding the effect of the Al element in the substrate on the alloying reaction of Mg-iron (Fe) interface. The sound FSSW joint of ZK60 Mg alloy and Q235 steel with a hot-dipped aluminum (Al)-containing zinc (Zn) coating was successfully realized. The detailed microstructural examinations proved that Al 5 Fe 2 phase at the Mg-Fe interface came from the pre-existing Al 5 Fe 2 phase in the coating and acted as the transition layer for promoting the metallurgical bonding of Mg and Fe. The interfaces with well-matched lattice sites among Fe, Al 5 Fe 2 and Mg were formed during FSSW. A low energy interface with good match of lattice sites ((002) Al5Fe2 //(110) Fe , [110] Al5Fe2 //[13] Fe ) between Al 5 Fe 2 and Fe was identified. For the interface between Al5Fe2 and Mg, an orientation relationship of ( 6 2 ¯ 2 ) A l 5 F e 2 / / ( 3 1 ¯ 1 ¯ 2 ¯ ) M g and [ 1 5 ¯ 8 ¯ ] A l 5 F e 2 / / [ 2 4 ¯ 23 ] M g was observed. The tensile–shear load of the ZK60–steel joint could reach 4.6 kN. Moreover, the joint fracture occurred at the interface between the Al5Fe2 layer and the Mg alloy substrate, suggesting the brittle fracture characteristic.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The relationship between low-temperature toughness and secondary crack in low-carbon bainitic weld metals

Highlights: • The crack propagation plane was identified with the decreasing possibility of {110}/{100}, {112} and {123}. • Crack path deviates at some middle-angle misorientation boundaries with high strain concentration. • The most effective barrier to arrest crack in Ni0 and Ni2 is the boundaries of inter-Bain in a CPP packet, while in Ni4 the boundaries of inter-CPP and intra-Bain packets impede crack propagation. - Abstract: This paper aims to reveal the relationship among low-temperature toughness, microstructure and secondary crack from both microstructural and crystallographic perspectives. Instrumented Charpy tests were carried out in the upper platform, transition temperature range, as well as at lower temperatures. Quantitative fractographic analysis, microstructural characterization and secondary crack observation were conducted on half of the impact specimen. Crystallographic features were identified in the secondary crack proximity, e.g. variant selection, orientation relationship, cleavage plane of the corresponding crack matrix. Some results in literature are confirmed. Nickel addition is beneficial to hindering crack propagation as a result of microstructure improvement. The most effective barrier for crack propagation is high-angle misorientation boundaries between Bain packets and the boundaries of ferrite matrix with the microstructure of granular bainite. Additionally, high-angle misorientation boundaries between closed-packed plane packets arrest cracks in the mixed microstructure of fine lath bainite and intricate acicular ferrite. Most preferred crack propagation planes are {110} and {100} in our low carbon bainitic weld metals, with the decreasing possibility of {112} and {123}.

36 MATERIALS SCIENCE↗