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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Turbomachinery Design Quality Checks to Avoid Friction Induced Structural Failure

A unique configuration of the P&W SSME Alternate Fuel Turbopump turbine disk/blade assembly, combined with a severe thermal environment, resulted in several structural anomalies that were driven by frictional contact forces. Understanding the mechanics of these problems provides new quality checks for future turbo machinery designs. During development testing in 1997 of the SSME alternate fuel turbopump at Stennis Space Center, several potentially serious problems surfaced with the turbine disk/blade assembly that had not been experienced in extensive earlier testing. Changes to the operational thermal environment were noted based on analytical prediction of modifications that affected performance and on stationary thermal measurements adjacent to the rotor assembly. A detailed structural investigation was required to reveal the mechanism of distress induced by the change. The turbine disk experienced cracking in several locations due to increased thermal gradient induced stress during start and shutdown transients. This was easily predictable using standard analysis procedures and expected once the thermal environment was characterized. What was not expected was the curling of a piston ring used for blade axial retention in the disk, indentation of the axial face of the blade attachment by a spacer separating the first and second stage blades, and most significantly, galling and cracking of the blade root attachment that could have resulted in blade release. Past experience, in gas turbine environments, set a precedent of never relying on friction for help and to evaluate it only in specific instances where it was obvious that it would degrade capability. In each of the three cases above, friction proved to be a determining factor that pushed the components into an unsatisfactory mode of operation. The higher than expected temperatures and rapid thermal transients combined with friction to move beyond past experience. The turbine disk/blade assembly configuration contributed to the potential for these problems to occur by limiting the radial deflection from thermals and centrifugal loading. The cooled solid bore configuration was chosen to improve rotordynamic stability by limiting the length of rotor overhang while still protecting the roller bearing by maintaining zero slope under the inner race. During a start transient, the rim area of the disk heats rapidly and expands axially and circumferentially and requires corresponding radial and axial growth of the disk to maintain relative positioning of the disk, blades, spacers and retainer rings. The stiffness, large thermal mass, and bore cooling flow combine to severely limit the disk rim radial growth which results in the potential for relative movement between these parts. Friction then becomes a player in the determination of component stress.

Moore, Jerry H.↗
NASA NTRS2004

Auto-Adjustable Tool for Self-Reacting and Conventional Friction Stir Welding

A friction stir welding dcvice that is configured to perform convention friction stir welding as well as self-reacting friction stir welding is described. A pin passes hrough an upper shoulder and can selectively attach 10 and detach from a lower shoulder in a preferred embodiment. A controller maintains thc discrete position of, and/or force applied by, the upper and lower shoulders during self-reacting friction stir welding, or maintains the pin at a desired depth and/or applied force during conventional friction stir welding.

Robert W Carter↗
NASA NTRS1998

Microblowing Technique Demonstrated to Reduce Skin Friction

One of the most challenging areas of research in aerodynamics is the reduction of skin friction, especially for turbulent flow. Reduced skin friction means less drag. For aircraft, less drag can lead to less fuel burned or to a greater flight range for a fixed amount of fuel. Many techniques and methods have been tried; however, none of them has significantly reduced skin friction in the flight environment. An innovative skin-friction reduction technique, the Microblowing Technique (MBT), was invented in 1993. This is a unique concept in which an extremely small amount of air is blown vertically at a surface through very small holes. It can be used for aircraft or marine vehicles, such as submarines (where water is blown through the holes instead of air). As shown in the figure, the outer layer, which controls vertical flow, is a plate with high-vertical holes. The inner layer, which produces evenly distributed flow, is a low-permeability porous plate. Microblowing reduces the surface roughness and changes the flow velocity profile on the surface, thereby reducing skin friction.

Hwang, Danny P.↗
NASA NTRS2001

Friction plug welding

Friction plug welding (FPW) usage is advantageous for friction stir welding (FSW) hole close-outs and weld repairs in 2195 Al--Cu--Li fusion or friction stir welds. Current fusion welding methods of Al--Cu--Li have produced welds containing varied defects. These areas are found by non-destructive examination both after welding and after proof testing. Current techniques for repairing typically small (<0.25) defects weaken the weldment, rely heavily on welders' skill, and are costly. Friction plug welding repairs increase strength, ductility and resistance to cracking over initial weld quality, without requiring much time or operator skill. Friction plug welding while pulling the plug is advantageous because all hardware for performing the weld can be placed on one side of the workpiece.

Takeshita, Riki↗
NASA NTRS2004

Mechanism for Self-Reacted Friction Stir Welding

A mechanism has been designed to apply the loads (the stirring and the resection forces and torques) in self-reacted friction stir welding. This mechanism differs somewhat from mechanisms used in conventional friction stir welding, as described below. The tooling needed to apply the large reaction loads in conventional friction stir welding can be complex. Self-reacted friction stir welding has become popular in the solid-state welding community as a means of reducing the complexity of tooling and to reduce costs. The main problems inherent in self-reacted friction stir welding originate in the high stresses encountered by the pin-and-shoulder assembly that produces the weld. The design of the present mechanism solves the problems. The mechanism includes a redesigned pin-and-shoulder assembly. The welding torque is transmitted into the welding pin by a square pin that fits into a square bushing with set-screws. The opposite or back shoulder is held in place by a Woodruff key and high-strength nut on a threaded shaft. The Woodruff key reacts the torque, while the nut reacts the tensile load on the shaft.

Venable, Richard↗
NASA NTRS2012

Mitigating Abnormal Grain Growth for Friction Stir Welded Al-Li 2195 Spun Formed Domes

Formability and abnormal grain growth (AGG) are the two major issues that have been encountered for Al alloy spun formed dome development using friction stir welded blanks. Material properties that have significant influence on the formability include forming range and strain hardening exponent. In this study, tensile tests were performed for two 2195 friction stir weld parameter sets at 400 F to study the effects of post weld anneal on the forming range and strain hardening exponent. It was found that the formability can be enhanced by applying a newly developed post weld anneal to heat treat the friction stir welded panels. This new post weld anneal leads to a higher forming range and much improved strain hardening exponent. AGG in the weld nugget is known to cause a significant reduction of ductility and fracture toughness. This study also investigated how AGG may be influenced by the heating rate to the solution heat treatment temperature. After post-weld annealing, friction stir welds were strained to 15% and 39% by compression at 400 F before they were subjected to SHT at 950 F for 1 hour. Salt bath SHT is very effective in reducing the grain size as it helps arrest the onset of AGG and promote normal recrystallization and grain growth. However, heat treating a 18 ft dome using a salt bath is not practical. Efforts are continuing at Marshall Space Flight Center to identify the welding parameters and heat treating parameters that can help mitigate the AGG in the friction stir welds.

Chen, Po-Shou↗
NASA NTRS2013

Ultrasonic Low-Friction Containment Plate for Thermal and Ultrasonic Stir Weld Processes

The thermal stir welding (TSW) process is finding applications in fabrication of space vehicles. In this process, workpieces to be joined by TSW are drawn, by heavy forces, between "containment plates," past the TSW tool that then causes joining of the separate plates. It is believed that the TSW process would be significantly improved by reducing the draw force, and that this could be achieved by reducing the friction forces between the workpieces and containment plates. Based on use of high-power ultrasonics in metal forming processes, where friction reduction in drawing dies has been achieved, it is believed that ultrasonic vibrations of the containment plates could achieve similar friction reduction in the TSW process. By applying ultrasonic vibrations to the containment plates in a longitudinal vibration mode, as well as by mounting and holding the containment plates in a specific manner such as to permit the plates to acoustically float, friction between the metal parts and the containment plates is greatly reduced, and so is the drawing force. The concept was to bring in the ultrasonics from the sides of the plates, permitting the ultrasonic hardware to be placed to the side, away from the equipment that contains the thermal stir tooling and that applies clamping forces to the plates. Tests demonstrated that one of the major objectives of applying ultrasonics to the thermal stir system, that of reducing draw force friction, should be achievable on a scaled-up system.

Graff, Karl↗
NASA NTRS2016

Evaluation of Skin Friction Drag for Liner Applications in Aircraft

A parameter that is gaining significance in the evaluation of acoustic liner performance is the skin friction drag induced by air flow over the liner surface. Estimates vary widely regarding the amount of drag the liner induces relative to a smooth wall, from less than a 20% increase to nearly 100%, and parameters such as face sheet perforate hole diameter, percent open area, and sheet thickness are expected to figure prominently in the skin friction drag. Even a small increase in liner drag can impose an economic penalty, and current research is focused on developing 'low drag' liner concepts, with the goal being to approach the skin friction drag of a smooth wall. The issue of skin friction drag takes on greater significance as airframe designers investigate the feasibility of putting sound absorbing liners on the non-lifting surfaces of the wings and fuselage, for the purpose of reducing engine noise reflected and scattered toward observers on the ground. Researchers at the NASA Langley Research Center have embarked on investigations of liner skin friction drag with the aims of: developing a systematic drag measurement capability, establishing the drag of current liners, and developing liners that produce reduced drag without compromising acoustic performance. This paper discusses the experimental procedures that have been developed to calculate the drag coefficient based on the change in momentum thickness and the companion research program being carried out to measure the drag directly using a force balance. Liner samples that are evaluated include a solid wall with known roughness and conventional liners with perforated facesheets of varying hole diameter and percent open area.

Gerhold, Carl H.↗
DOE OSTI2015

General predictive model of friction behavior regimes for metal contacts based on the formation stability and evolution of nanocrystalline surface films.

The prediction of macro-scale friction and wear behavior based on first principles and material properties has remained an elusive but highly desirable target for tribologists and material scientists alike. Stochastic processes (e.g. wear), statistically described parameters (e.g. surface topography) and their evolution tend to defeat attempts to establish practical general correlations between fundamental nanoscale processes and macro-scale behaviors. We present a model based on microstructural stability and evolution for the prediction of metal friction regimes, founded on recently established microstructural deformation mechanisms of nanocrystalline metals, that relies exclusively on material properties and contact stress models. We show through complementary experimental and simulation results that this model overcomes longstanding practical challenges and successfully makes accurate and consistent predictions of friction transitions for a wide range of contact conditions. This framework not only challenges the assumptions of conventional causal relationships between hardness and friction, and between friction and wear, but also suggests a pathway for the design of higher performance metal alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Co{sub 3}O{sub 4} Addition on Friction and Dry Sliding Wear Characteristics of 8 mol% Yttria-Stabilized Cubic Zirconia

The aim of the present study was to investigate the influence of Co{sub 3}O{sub 4} additive on the microstructure, wear, and tribological properties of 8 mol% yttria-stabilized cubic zirconia (8YSZ) using a pin-on-disk tribometer, surface profilometer, hardness tester, and a scanning electron microscopy system. Specimens were produced by doping 1-15 wt.% Co{sub 3}O{sub 4} in 8YSZ using a colloidal process, sintering at 1500 °C for 1 h, and subsequent annealing at 1500 °C for 10 and 50 h. Microstructural analysis showed that Co{sub 3}O{sub 4} dissolved partially in 8YSZ, with the undissolved Co{sub 3}O{sub 4} precipitating as a secondary phase at the grain boundaries. Further, the addition of Co{sub 3}O{sub 4} enhanced the grain size. Wear tests were carried out using an Al{sub 2}O{sub 3} ball as the counterface against ceramic disk under dry sliding friction conditions at room temperature (24 °C). The wear volume of 8YSZ decreased from 0.30 to 0.11 mm{sup 3} as a result of the addition of 15 wt.% Co{sub 3}O{sub 4}. Additionally, friction coefficient of the 8YSZ significantly reduced from 0.55 to 0.17 at the beginning stage of the sliding after the addition of 15 wt.% Co{sub 3}O{sub 4}. This was because Co{sub 3}O{sub 4} creates a thin lubricating layer on the friction surface. In addition, the undoped and Co{sub 3}O{sub 4}-doped 8YSZ specimens exhibited abrasive wear under the dry sliding friction conditions, owing to the formation and propagation of microcracks, which resulted in the removal of material from the surface. The specific wear rate of 8YSZ decreased with increasing the Co{sub 3}O{sub 4} content. Thus, the addition of Co{sub 3}O{sub 4} to 8YSZ improves its wear resistance and surface topography.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Changes in the surface structure of the heterogeneous body (diorite) under friction

Raman, infrared, and photoluminescent spectroscopy has been used to study changes in the surface structure of quartz diorite caused by friction. Before friction, the diorite surface layer has contained mainly quartz and feldspar crystals. After friction, some quartz and feldspar crystals have been destructed and replaced by a newly formed hydromica mineral with a low friction coefficient such as illite.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Protecting the radiation-damaged skin from friction: a mini review

Radiation-induced skin reactions are an unavoidable side effect of external beam radiation therapy, particularly in areas prone to friction and excess moisture such as the axilla, head and neck region, perineum and skin folds. Clinical studies investigating interventions for preventing or managing these reactions have largely focussed on formulations with moisturising, anti-inflammatory, anti-microbial and wound healing properties. However, none of these interventions has emerged as a consistent candidate for best practice. Much less emphasis has been placed on evaluating ways to protect the radiation-damaged skin from friction and excess moisture. This mini review analyses the clinical evidence for barrier products that form a protective layer by adhering very closely to the skin folds and do not cause further trauma to the radiation-damaged skin upon removal. A database search identified only two types of barrier products that fitted these criteria and these were tested in two case series and six controlled clinical trials. Friction protection was most effective when the interventions were used from the start of treatment and continued for several weeks after completion of treatment. Soft silicone dressings (Mepilex Lite and Mepitel Film) and Cavilon No Sting Barrier Film, but not Cavilon Moisturizing Barrier Cream, decreased skin reaction severity, most likely due to differences in formulation and skin build-up properties. It seems that prophylactic use of friction protection of areas at risk could be a worthwhile addition to routine care of radiation-damaged skin.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2021

Friction of Metals: A Review of Microstructural Evolution and Nanoscale Phenomena in Shearing Contacts

The friction behavior of metals is directly linked to the mechanisms that accommodate deformation. We examine the links between mechanisms of strengthening, deformation, and the wide range of friction behaviors that are exhibited by shearing metal interfaces. Specifically, the focus is on understanding the shear strength of nanocrystalline and nanostructured metals, and conditions that lead to low friction coefficients. Grain boundary sliding and the breakdown of Hall–Petch strengthening at the shearing interface are found to generally and predictably explain the low friction of these materials. While the following is meant to serve as a general discussion of the strength of metals in the context of tribological applications, one important conclusion is that tribological research methods also provide opportunities for probing the fundamental properties and deformation mechanisms of metals.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Stress and Friction Distribution around Slab Corner in Continuous Casting Mold with Different Corner Structures

The non-uniform friction and thermal stress in the mold are important as causes of the transverse cracks around strand corner. To analyze the stress distribution features around strand corner, a three-dimensional thermo-elastoplastic finite-element mold model with different corner structures (right-angle, big-chamfer, multi-chamfer, and fillet) was established. The temperature field in the mold was indirectly coupled through a three-dimensional fluid flow and heat transfer model. In addition, the non-uniform mold friction stress loaded on the strand surface was calculated through a friction model. The results show that the stress distribution on the shell is similar to the temperature distribution. The stress concentration appears in the strand corner and the lower part of wide face. The friction stress enhances the corner stress around the edge of the air-gap. For chamfered molds, the stress around the corner between the wide face and chamfer face is larger than that between the narrow face and chamfer face. Around the corner region, both the stress peak and the area of the large stress zone of the right-angle strand are the largest, while those of big-chamfered, multi-chamfered, and fillet strands decrease in that order. The stress peak position of the chamfered strands is closer to the mold exit than that of the right-angle strand. Compared with the use of the right-angle mold, the application of chamfered molds is able to reduce the stress concentration around the strand corner.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Inverse Thermal Analysis of Ti-6Al-4V Friction Stir Welds Using Numerical-Analytical Basis Functions with Pseudo-Advection

Inverse thermal analysis of Ti-6Al-4V friction stir welds is presented that demonstrates application of a methodology using numerical-analytical basis functions and temperature-field constraint conditions. This analysis provides parametric representation of friction-stir-weld temperature histories that can be adopted as input data to computational procedures for prediction of solid-state phase transformations and mechanical response. These parameterized temperature histories can be used for inverse thermal analysis of friction stir welds having process conditions similar those considered here. Case studies are presented for inverse thermal analysis of friction stir welds that use three-dimensional constraint conditions on calculated temperature fields, which are associated with experimentally measured transformation boundaries and weld-stir-zone cross sections.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of Temperature on Friction and Wear Characteristics of Polyaryletherketones and Their Composites Under Reciprocating Sliding Condition

The tribological behavior of different polyaryletherketones (PAEKs) and their composites was studied under reciprocating sliding conditions at room temperature as well as at elevated temperature (120 °C). The effect of glass, carbon fiber and solid lubricants (PTFE and graphite) filled in PAEK matrix was investigated at different normal loads. It was found that friction and wear characteristics are strongly influenced by the type of PAEK matrix and the material composition. The temperature has a more pronounced influence on the coefficient of friction and specific wear rates of PAEKs and their composites than the normal load. Friction and wear mechanisms are discussed, using scanning electron micrographs of the worn surfaces. A relationship between the average coefficient of friction and specific wear rates of PAEKs and their composites is also reported.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Laser Additive Manufacturing of (Ti-6Al-4V)/10 wt.% Ag Composite Using Spherical Powders to Reduce Wear and Friction

In order to extend the service lifetime of Ti-6Al-4V-based components, friction and wear behaviors of Ti-6Al-4V alloys needed to be further improved. Laser additive manufacturing with a moving laser beam was used to prepare (Ti-6Al-4V)/10 wt.% Ag samples, on a three-dimensional RC-SLM400 printer with laser powers of 2-10 kW. (Ti-6Al-4V)/10 wt.% Ag samples were successfully printed using spherical powders prepared by gas atomization process (SPGAP) and combustion reaction (SP-CR). The tribological properties of the as-prepared samples sliding against Si{sub 3}N{sub 4} balls were examined using a ball-on-disk tribometer. The results showed that the tribological behavior of (Ti-6Al-4V)/10 wt.% Ag printed by SP-CR was better than that of the sample printed by SPGAP. The low friction and reduced wear were mainly attributed to the formation of the lubrication layer containing large amounts of silver, which can exhibit an excellent deformation and plastic ductility. It effectively reduced the friction resistance and material loss and provided the good lubrication for 0-80 min, resulting in low friction and reduced wear of the samples prepared by SP-CR.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Mechanical and Frictional Performance of Ta and Ta-Ag Alloy Films Deposited at Different Sputtering Powers

The mechanical and tribological properties of tantalum and its alloy films are greatly influenced by their phase transformation. In this study, Ta and Ta-Ag films were prepared on carbon steel substrate by DC magnetron sputtering with various sputtering powers. The amorphous and nanocrystalline Ta and Ta-Ag film were produced at different sputtering powers from 40 to 110 W. The frictional properties of Ta and Ta-Ag films were investigated by rubbing against Si{sub 3}N{sub 4} ball from RT to 700 °C. The nanocrystalline Ta-Ag films shows higher hardness values (12 GPa) compared with amorphous phase. The nanocrystalline Ta90-Ag8 film shows a low friction coefficient of about 0.20-0.30 when rubbing against Si{sub 3}N{sub 4} ball at 700 °C. The segregation of Ag can effectively reduce friction coefficients of Ta-Ag film at 700 °C. The Ta-Ag films show high structure stability even after friction at 700 °C.

36 MATERIALS SCIENCE↗