Search NASA⌕ Search

SEARCH · Search NASA

Results for “WELDED JOINT”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Creep Deformation and Rupture Behavior of P92 Steel Weld Joint Fabricated by NG-TIG Welding Process

The creep deformation and rupture behavior of P92 steel weld joint fabricated by narrow-gap TIG (NG-TIG) welding process have been investigated at 923 K over a stress range of 80-140 MPa. The prior-austenite grain size, M{sub 23}C{sub 6} precipitate size and hardness have been found to vary significantly in the weld joint. The reduction in hardness from weld metal to base metal with a trough at the outer edge of heat-affected zone (HAZ) has been observed. Coarsening of M{sub 23}C{sub 6} precipitate, recovery of martensite lath dislocation structure and formation of subgrain structure led to lower hardness in the intercritical HAZ. The creep rupture life of NG-TIG weld joint was lower than the base metal, the difference in creep rupture life between base metal and weld joint has been increased significantly with decrease in applied stress. The fracture location in the joint changed from base metal at high-stress regime to the fine grain (FG) HAZ (Type IV cracking) under lower stress level. Fracture in the FGHAZ evidenced the significant reduction in ductility, localized deformation and extensive localized cavitation. Extensive Laves phase formation with significant loss of solution strengthening contribution from tungsten and coarsening of M{sub 23}C{sub 6} precipitate with prolonged creep exposure led to reduction in hardness and more extensive cavitation in the FGHAZ resulting in premature Type IV failure of the weld joint. Weld strength reduction factor about 0.59 has been evaluated for 10{sup 5} h at 923 K.

36 MATERIALS SCIENCE↗
NASA NTRS1991

Welding technology transfer task/laser based weld joint tracking system for compressor girth welds

Sensors to control and monitor welding operations are currently being developed at Marshall Space Flight Center. The laser based weld bead profiler/torch rotation sensor was modified to provide a weld joint tracking system for compressor girth welds. The tracking system features a precision laser based vision sensor, automated two-axis machine motion, and an industrial PC controller. The system benefits are elimination of weld repairs caused by joint tracking errors which reduces manufacturing costs and increases production output, simplification of tooling, and free costly manufacturing floor space.

Looney, Alan↗
DOE OSTI2019

Statistical Strength Analysis of Dissimilar AA2024-T6 and AA6061-T6 Friction Stir Welded Joints

Friction stir welding has been emerged as one of the most reliable processes for joining aerospace-grade aluminum alloys. However, limited studies have been focused so far on the reliability of these joint types. In this study, the effect of welding parameters (traverse and rotation speeds) on the fracture strength of dissimilar AA2024-T6 and AA6061-T6 friction stir welded joints was statistically analyzed by the Weibull approach. Based on the results, the Weibull approach was found to be much more accurate than widely used standard deviation for evaluating the scatter of the fracture strength data. The improper selection of the process parameters not only decreased the average fracture strengths of the joints, but also scattered them around the mean value, and increased the failure probability under the same applied tension. According to the microscopic and macroscopic examinations and microhardness measurements, although the microstructural inhomogeneities caused by the improper setting of the welding parameters negatively affected the joints hardness and fracture strength, the welding defects were likely to be the most responsible factor affecting the fracture strength and its reliability.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Evaluation of the Microstructure and Performance of Fe-21Cr-15Ni-6Mn-Nb Nonmagnetic Stainless Steel Welded Joints

In the present study, double-sided gas shield welding (GSW), in a single pass, was applied to Fe-21Cr-15Ni-6Mn-Nb nonmagnetic stainless steel plate. The microstructure and performance of the welded joint were investigated via microstructural and phase analysis, mechanical testing and magnetic analysis. The results showed a satisfactory micrographic appearance with full penetration, and no solidification defects observed in the welded joint, which showed typical epitaxial growth characteristics in the welding solidification. Slight grain growth, with an average size of ~ 18.9 μm, occurred in the heat-affected zone (HAZ). The primary dendrite arms, on both sides of welding joint, grew along the direction of the temperature gradient and met at the centerline of the weld with no parting microstructure in evidence. The secondary dendrite arm spacing was stable in all parts of the weld zone (WZ). The hardness of the weld zone was higher than that of the HAZ and the base metal (BM), with the lowest hardness occurring in the HAZ. The results of tensile testing showed a higher strength of the welded metal (WM) compared to the BM, and a good strength-ductility balance of the welded joint. The impact energy of the HAZ was higher than that of the WZ, corresponding to 60.5 J at room temperature and 52.7 J at − 196 °C. Microvoid coalescence, concurrent with crack propagation along the direction of the long axis of the dendritic sub-grains, was observed during plastic deformation in the WZ. Additionally, the excellent paramagnetic characteristics of the welded specimens were revealed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructural Characteristics and Mechanical Properties in the Laser Beam Welded Joints of High-Strength Microalloyed Steel

The laser beam welded joints of the high-strength microalloyed steel consist of the base metal (BM), the partially transformed heat-affected zone I (PTHAZ-I), the partially transformed heat-affected zone II (PTHAZ-II), the fully transformed heat-affected zone (FTHAZ) and the fusion zone (FZ). The martensite/austenite (M/A) islands of the bainites in the PTHAZ-II are dense versus those in the PTHAZ-I, and the martensites exist in the FTHAZ and the FZ together with the bainites under the slow welding speed. The M/A islands of the bainites and/or the martensites in the PTHAZ become denser under the high welding speed, and the martensites in the FTHAZ and the FZ predominate. The low-angle boundary density and the high local misorientation proportion are used to identify the constituents roughly, consistent with the microstructural characteristics in the welded joints. The misorientation angle distributions are employed to evaluate the degree of the phase transformation, reflecting the change law of the degree of the phase transformation in the welded joints. The hardness and the tensile tests indicate that the HAZ and the FZ are stronger than the BM, dependent on the microstructures in the welded joints. The strengthening in the HAZ and the FZ is mainly attributed to the products of non-equilibrium phase transformation with the high dislocation density.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Design of a welded joint for robotic, on-orbit assembly of space trusses

In the future, some spacecraft will be so large that they must be assembled on-orbit. These spacecraft will be used for such tasks as manned missions to Mars or used as orbiting platforms for monitoring the Earth or observing the universe. Some large spacecraft will probably consist of planar truss structures to which will be attached special purpose, self-contained modules. The modules will most likely be taken to orbit fully outfitted and ready for use in heavy-lift launch vehicles. The truss members will also similarly be taken to orbit, but most unassembled. The truss structures will need to be assembled robotically because of the high costs and risks of extra-vehicular activities. Some missions will involve very large loads. To date, very few structures of any kind have been constructed in space. Two relatively simple trusses were assembled in the Space Shuttle bay in late 1985. Here the development of a design of a welded joint for on-orbit, robotic truss assembly is described. Mechanical joints for this application have been considered previously. Welded joints have the advantage of allowing the truss members to carry fluids for active cooling or other purposes. In addition, welded joints can be made more efficient structurally than mechanical joints. Also, welded joints require little maintenance (will not shake loose), and have no slop which would cause the structure to shudder under load reversal. The disadvantages of welded joints are that a more sophisticated assembly robot is required, weld flaws may be difficult to detect on-orbit, the welding process is hazardous, and welding introduces contamination to the environment. In addition, welded joints provide less structural damping than do mechanical joints. Welding on-orbit was first investigated aboard a Soyuz-6 mission in 1969 and then during a Skylab electron beam welding experiment in 1973. A hand held electron beam welding apparatus is currently being prepared for use on the MIR space station. Presently, Marshall Space Flight Center is evaluating processes appropriate for on-orbit welding. A low gravity environment has been found to have very minor effects on the welding processes appropriate for this application. This is based on tests run on-orbit as well as low gravity environments achieved by flying aircraft in parabolic trajectories. It appears that a modified form of gas tungsten arc welding (GTAW) will be most appropriate for welding together structures on-oribt. The process has been modified to work in a vacuum by providing gas to the arc zone by means of a hollow tungsten electrode with special shielding. A commercial tube welding head has been successfully modified for use on-orbit with a gas leakage rate of approximately 2.5 liters/min. To develop as realistic a joint as possible, a specific truss structure was selected on which to base the design. The structure considered was based on the 120 foot diameter aerobrake tetrahedral truss structure. The truss members were assumed to consist of graphite/epoxy tubes. Also, it was assumed that the nodes were constructed of 2219-T87 aluminum alloy. The magnitude of the member load assumed for design purposes was 100 kips.

Rule, William K.↗
NASA NTRS1985

Investigation of weld joint detection capabilities of a coaxial weld vision system

This report describes the second phase of a series of evaluations of a vision-based welding control sensor for the Space shuttle Main Engine Robotic Welding System. The robotic welding system is presently under development at the Marshall Space Flight Center. This evaluation determines the factors influencing the minimum joint gap required for consistent detection of the weld joint.

Gangl, K. J.↗
NASA NTRS1982

Plating To Reinforce Welded Joints

Electrodeposition used to strengthen welded joints gouged, nicked, or suffered other mechanical damage. Plating cell, typically of acrylic plastic such as poly (Methylmetacrylate), is assembled around part to be plated. Areas not to be plated are masked with plater's tape. Weld area is plated in standard nickel-plating process.

Otousa, J. E.↗
DOE OSTI2019

Cooling Environment Effect on the Microstructure and Mechanical Properties of Friction Stir-Welded Joints

The heat input in friction stir welding (FSW) influences the localized properties in welded joint. The external cooling during FSW reduces the localized heating and post-weld cooling time by extracting heat comparatively at a faster rate. In the present study, we have investigated the effect of different cooling environments on the performance of friction stir-welded (FSWed) AA5052 strain-hardenable aluminum alloy. Welding was performed under three different cooling environments such as natural air, water and liquid nitrogen in order to understand their effects on grain structure, metallurgical changes and mechanical properties of the joints. It has been noted that the width of weld nugget zone, thermo-mechanically affected zone and heat-affected zone has been decreased with the respective change in cooling environments. Welding speed could also influence the width of different zones in weldment alike the cooling environments. Finer grain size has been noticed with water cooling against the liquid nitrogen cooling. Comparatively, water was observed to be more favorable cooling environment against liquid nitrogen because of its better weld quality (97%) compared with base metal. The favorable mechanical properties resulting from the different weldment regions for different cooling environments have been elaborated in the present study.

36 MATERIALS SCIENCE↗
DOE OSTI2025

ASSESSING THE EFFECTIVENESS OF ULTRASONIC IMPACT TREATMENT ON RESIDUAL STRESS PROFILES IN DISSIMILAR WELDED JOINTS

Residual stresses (RS) induced during welding processes are a critical concern in materials engineering, as they can significantly impair the mechanical performance of components by reducing fatigue strength and tensile load capacity. This challenge is especially pronounced in dissimilar metal welds (DMWs), where variations in thermal expansion properties between the joined alloys exacerbate the formation of tensile RS. Conventional post-weld heat treatments, though effective for homogeneous materials, often require substantial energy, specialized equipment, and extensive processing time, making them less practical for DMW applications. Thus, there is a clear need for innovative, energy-efficient techniques to mitigate these detrimental stresses. This study investigates ultrasonic impact treatment (UIT) as a possible alternative for mitigating tensile RS in both similar and dissimilar metal welds. To evaluate UIT’s effectiveness, neutron diffraction (ND) was employed as a nondestructive technique to quantify RS in three orthogonal directions—longitudinal, transverse, and normal. The results showed that UIT significantly reduced peak tensile RS, particularly in the longitudinal direction, by up to 180 MPa in similar welds and up to 150 MPa in dissimilar welds. Given the limited literature on UIT application in DMWs, this work contributes valuable data on stress redistribution mechanisms and highlights UIT’s potential as a practical stress-relief method. The findings lay the groundwork for further investigations aimed at optimizing process parameters and understanding long-term performance in welded joints.

EisaZadeh, Hamid [Western Carolina University, Cul↗
DOE OSTI2019

Effect of Welding Parameters on Junction Structure and Fracture Behavior of Friction-Stir-Welded Joints of 2024 Aluminum Alloys

In this paper, the effect of welding speed and tool rotation speed on the junction structure and fracture behavior of friction-stir-welded joints was investigated with use of 2024 aluminum alloys of 3.2 mm thick. Results show that the formation of junction structure is more affected by tool rotation speed than by welding speed due to the differences of heat input levels. When welding speed is at 100 mm/min and tool rotation speed is in the range of 400-600 r/min, the joint junction structure causes complete bonding with no welding defects. While under improper welding parameters, the junction structure causes the precipitate aggregation on the bonding line and the partial bonding with the appearance of both tunnel defects and kissing bond defects. Meanwhile, the results of tensile tests show that the tensile fracture of all FSW joints occur at the weld center. The failure mode of joints with defects-free junction structure characterized by shear fracture is ductile. While the failure mode of joints with defects-existent junction structure characterized by layered fracture surface is brittle. Furthermore, that heterogeneous microstructure, precipitate aggregation and welding defects converge inside the junction structure is the main factor affecting the tensile properties and fracture behavior of the friction-stir-welded joint.

36 MATERIALS SCIENCE↗
NASA NTRS1988

Flexible Protective Shield For Newly Welded Joints

Simple device promotes defect-free welds in oxidation-prone metals. Welding torch pulls trailing shield behind to provide protective shield of argon gas over hot weld bead. Guide at front of torch holder feeds welding wire to joint. Shield bent or straightened to fit closely against weld joint.

Dyer, Gerald E.↗
NASA NTRS1994

Yield detection in aluminum welded joints using photostress

Previous work using photostress to analyze behavior of aluminum welded joints was useful to determine mechanical properties of the weld and parent materials along the centerline of the joint. It was shown that significant differences exist in the stress-strain characteristics at points beginning at the centerline of the weld and extending for a distance of one inch to either side of the weld. Because of the highly variable behavior detected in the previous work, it was decided to extend the work to investigate behavior of joints 1/8, 1/2, and 1.40 inches thick.

Gambrell, S. C., Jr.↗