Results for “FRICTION” — Page 6

NASA NTRS2003

Tool For Friction Stir Tack Welding of Aluminum Alloys

A small friction-stir-welding tool has been developed for use in tack welding of aluminum-alloy workpieces. It is necessary to tack-weld the workpieces in order to hold them together during friction stir welding because (1) in operation, a full-size friction-stir-welding tool exerts a large force that tends to separate the workpieces and (2) clamping the workpieces is not sufficient to resist this force. It is possible to tack the pieces together by gas tungsten arc welding, but the process can be awkward and time-consuming and can cause sufficient damage to necessitate rework. Friction stir tack welding does not entail these disadvantages. In addition, friction stir tack welding can be accomplished by use of the same automated equipment (except for the welding tool) used in subsequent full friction stir welding. The tool for friction stir tack welding resembles the tool for full friction stir welding, but has a narrower shoulder and a shorter pin. The shorter pin generates a smaller workpiece-separating force so that clamping suffices to keep the workpieces together. This tool produces a continuous or intermittent partial-penetration tack weld. The tack weld is subsequently consumed by action of the larger tool used in full friction stir welding tool.

Bjorkman, Gerald W.↗

NASA NTRS2012

Damage Tolerance Assessment of Friction Pull Plug Welds in an Aluminum Alloy

Friction stir welding is a solid state welding process used in the fabrication of cryogenic propellant tanks. Self-reacting friction stir welding is one variation of the friction stir weld process being developed for manufacturing tanks. Friction pull plug welding is used to seal the exit hole that remains in a circumferential self-reacting friction stir weld. A friction plug weld placed in a self-reacting 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. Test data relating residual strength capability to flaw size in an aluminum alloy friction plug weld will be presented.

McGill, Preston↗

NASA NTRS2017

Development and Testing of a Friction-Based Post-Installable Sensor for Subsea Fiber-Optic Monitoring Systems

This paper presents the design and development of a friction-based coupling device for a fiber-optic monitoring system that can be deployed on existing subsea structures. This paper provides a summary of the design concept, prototype development, prototype performance testing, and design refinements of the device. The results of the laboratory testing of the first prototype performed at the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) are included in this paper. Limitations of the initial design were identified and future design improvements were proposed. These new features will enhance the coupling of the device and improve the monitoring system measurement capabilities. A major challenge of a post-installed instrumentation monitoring system is to ensure adequate coupling between the instruments and the structure of interest for reliable measurements. Friction-based coupling devices have the potential to overcome coupling limitations caused by marine growth and soil contamination on subsea structures, flowlines or risers. The work described in this paper investigates the design of a friction-based coupling device (friction clamp), which is applicable for pipelines and structures that are suspended in the water column and those that are resting on the seabed. The monitoring elements consist of fiber-optic sensors that are bonded to a metal clamshell with a high-friction coating. The friction clamp has a single hinge design to facilitate the operation of the clamp and dual rows of opposing fasteners to distribute the clamping force on the structure. The friction clamp can be installed by divers in shallow depths or by remotely operated vehicles in deep-water applications. NASA-JSC was involved in the selection and testing of the friction coating, and in the design and testing of the prototype clamp device. Four-inch diameter and eight-inch diameter sub-scale friction clamp prototypes were built and tested to evaluate the strain measuring capabilities of the design under different loading scenarios. The testing revealed some limitations of the initial design concept, and subsequent refinements were explored to improve the measurement performance of the system. This study was part of a collaboration between NASA-JSC and Astro Technology, Inc. within a study called Clear Gulf. The primary objective of the Clear Gulf study is to develop advanced instrumentation technologies that will improve operational safety and reduce the risk of hydrocarbon spillage. NASA provided unique insights, expansive test facilities, and technical expertise to advance these technologies that would benefit the environment, the public, and commercial industries.

Bentley, Nicole↗

NASA NTRS2017

Development and Testing of a Friction-Based Post-Installable Sensor for Subsea Fiber-Optic Monitoring System

This paper presents the design and development of a friction-based coupling device for a fiber-optic monitoring system that can be deployed on existing subsea structures. This paper provides a summary of the design concept, prototype development, prototype performance testing, and design refinements of the device. The results of the laboratory testing of the first prototype performed at the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) are included in this paper. Limitations of the initial design were identified and future design improvements were proposed. These new features will enhance the coupling of the device and improve the monitoring system measurement capabilities. A major challenge of a post-installed instrumentation monitoring system is to ensure adequate coupling between the instruments and the structure of interest for reliable measurements. Friction-based coupling devices have the potential to overcome coupling limitations caused by marine growth and soil contamination on subsea structures, flowlines or risers. The work described in this paper investigates the design of a friction-based coupling device (friction clamp), which is applicable for pipelines and structures that are suspended in the water column and those that are resting on the seabed. The monitoring elements consist of fiber-optic sensors that are bonded to a metal clamshell with a high-friction coating. The friction clamp has a single hinge design to facilitate the operation of the clamp and dual rows of opposing fasteners to distribute the clamping force on the structure. The friction clamp can be installed by divers in shallow depths or by remotely operated vehicles in deep-water applications. NASA-JSC was involved in the selection and testing of the friction coating, and in the design and testing of the prototype clamp device. Four-inch diameter and eight-inch diameter sub-scale friction clamp prototypes were built and tested to evaluate the strain measuring capabilities of the design under different loading scenarios. The testing revealed some limitations of the initial design concept, and subsequent refinements were explored to improve the measurement performance of the system. This study was part of a collaboration between NASA-JSC and Astro Technology, Inc. within a study called Clear Gulf. The primary objective of the Clear Gulf study is to develop advanced instrumentation technologies that will improve operational safety and reduce the risk of hydrocarbon spillage. NASA provided unique insights, expansive test facilities, and technical expertise to advance these technologies that would benefit the environment, the public, and commercial industries.

Bentley, Nicole L.↗

NASA NTRS2017

Development and Testing of a Friction-Based Post-Installable Fiber-Optic Monitoring System for Subsea Applications

This paper presents the design and development of a friction-based coupling device for a fiber-optic monitoring system capable of measuring pressure, strain, and temperature that can be deployed on existing subsea structures. A summary is provided of the design concept, prototype development, prototype performance testing, and subsequent design refinements of the device. The results of laboratory testing of the first prototype performed at the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) are also included. Limitations of the initial concept were identified during testing and future design improvements were proposed and later implemented. These new features enhance the coupling of the sensor device and improve the monitoring system measurement capabilities. A major challenge of a post-installed instrumentation monitoring system is to ensure adequate coupling between the instruments and the structure of interest for reliable measurements. Friction-based devices have the potential to overcome coupling limitations caused by marine growth and soil contamination on flowlines, risers, and other subsea structures. The work described in this paper investigates the design and test of a friction-based coupling device (herein referred to as a friction clamp) which is suitable for pipelines and structures that are suspended in the water column as well as for those that are resting on the seabed. The monitoring elements consist of fiberoptic sensors that are bonded to a stainless steel clamshell assembly with a high-friction surface coating. The friction clamp incorporates a single hinge design to facilitate installation of the clamp and dual rows of opposing fasteners to distribute the clamping force along the structure. The friction clamp can be modified to be installed by commercial divers in shallow depths or by remotely operated vehicles in deep-water applications. NASA-JSC was involved in the selection and testing of the friction coating, and in the design and testing of the prototype clamp device. Four-inch diameter and eight-inch diameter sub-scale friction clamp prototypes were built and tested to evaluate the strain measuring capabilities of the design under different loading scenarios. The testing revealed some limitations of the initial design concept, and subsequent refinements were explored to improve the measurement performance of the system. This study was part of a collaboration between NASA-JSC and Astro Technology Inc. within a study called Clear Gulf. The primary objective of the Clear Gulf study is to develop advanced instrumentation technologies that will improve operational safety and reduce the risk of hydrocarbon spillage. NASA provided unique insights, expansive test facilities, and technical expertise to advance technologies that will benefit the environment, the public, and commercial industries.

Bentley, Nicole L.↗

DOE OSTI2017

The Impact of Frictional Healing on Stick-Slip Recurrence Interval and Stress Drop: Implications for Earthquake Scaling: The impact of healing on stick-slip

We report that interseismic frictional healing is an essential process in the seismic cycle. Observations of both natural and laboratory earthquakes demonstrate that the magnitude of stress drop scales with the logarithm of recurrence time, which is a cornerstone of the rate and state friction (RSF) laws. However, the origin of this log linear behavior and short time “cutoff” for small recurrence intervals remains poorly understood. Here we use RSF laws to demonstrate that the back-projected time of null-healing intrinsically scales with the initial frictional state θ i . We explore this behavior and its implications for (1) the short-term cutoff time of frictional healing and (2) the connection between healing rates derived from stick-slip sliding versus slide-hold-slide tests. We use a novel, continuous solution of RSF for a one-dimensional spring-slider system with inertia. The numerical solution continuously traces frictional state evolution (and healing) and shows that stick-slip cutoff time also scales with frictional state at the conclusion of the dynamic slip process θ i (=D c /V peak ). This numerical investigation on the origins of stick-slip response is verified by comparing laboratory data for a range of peak slip velocities. Slower slip motions yield lesser magnitude of friction drop at a given time due to higher frictional state at the end of each slip event. In conclusion, our results provide insight on the origin of log linear stick-slip evolution and suggest an approach to estimating the critical slip distance on faults that exhibit gradual accelerations, such as for slow earthquakes.

58 GEOSCIENCES↗

DOE OSTI2021

Nanoscale friction of CVD single-layer MoS 2 with controlled defect formation

Two-dimensional (2D) layered nanomaterials such as graphene, molybdenum disulfide (MoS 2 ), or tungsten disulfide offer a promising solution in areas of solid-state lubrication, due to their excellent mechanical properties as well as low friction. However, defects can influence their friction and reduce their superior tribological properties. Thus, it is crucial to understand the effects of defects on sliding behavior in 2D nanomaterials, to foster a functional strategy for utilizing 2D nanomaterials as solid-state tribological films. In this study, frictional effects of defects, grain boundaries, and atomic-scale structural defects were explored on chemical vapor deposition (CVD) grown single layer MoS 2 . Selective patterning of defects into MoS 2 was accomplished via controlled irradiation of helium ions with varying ion doses. The friction of MoS 2 was characterized by friction force microscopy (FFM) and was found that friction depends on the defect formation controlled by helium ion irradiation. This approach offers a correlation between surface topography, defects and friction. Understanding the relative friction of MoS 2 in the presence of different levels of defects is foundational to studying tribological properties of a single layer MoS 2 at both nanoscales and macroscales.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Frictional stability-permeability relationships for fractures in shales

There is wide concern that fluid injection in the subsurface, such as for the stimulation of shale reservoirs or for geological CO 2 sequestration (GCS), has the potential to induce seismicity that may change reservoir permeability due to fault slip. However, the impact of induced seismicity on fracture permeability evolution remains unclear due to the spectrum of modes of fault reactivation (e.g., stable versus unstable). As seismicity is controlled by the frictional response of fractures, we explore friction-stability-permeability relationships through the concurrent measurement of frictional and hydraulic properties of artificial fractures in Green River shale (GRS) and Opalinus shale (OPS). We observe that carbonate-rich GRS shows higher frictional strength but weak neutral frictional stability. The GRS fracture permeability declines during shearing while an increased sliding velocity reduces the rate of permeability decline. By comparison, the phyllosilicate-rich OPS has lower friction and strong stability while the fracture permeability is reduced due to the swelling behavior that dominates over the shearing induced permeability reduction. Furthermore, we conclude that the friction-stability-permeability relationship of a fracture is largely controlled by mineral composition and that shale mineral compositions with strong frictional stability may be particularly subject to permanent permeability reduction during fluid infiltration.

58 GEOSCIENCES↗

DOE OSTI2017

Development of a New Method to Investigate the Dynamic Friction Behavior of Interfaces Using a Kolsky Tension Bar

In order to understand interfacial interaction of a bi-material during an impact loading event, the dynamic friction coefficient is one of the key parameters that must be characterized and quantified. In this study, a new experimental method to determine the dynamic friction coefficient between two metals was developed by using a Kolsky tension bar and a custom-designed friction fixture. Polyvinylidene fluoride (PVDF) force sensors were used to measure the normal force applied to the friction tribo pairs and the friction force was measured with conventional Kolsky tension bar method. To evaluate the technique, the dynamic friction coefficient between 4340 steel and 7075-T6 aluminum was investigated at an impact speed of approximately 8 m/s. Additionally, the dynamic friction coefficient of the tribo pairs with varied surface roughness was also investigated. The data suggest that higher surface roughness leads to higher friction coefficients at the same speed of 8 m/s.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Effect of laser surface texturing (LST) on tribochemical films dynamics and friction and wear performance

Surface texturing or topographical design is one of the primary techniques to control friction and wear performance of surfaces in tribological contact. Laser surface texturing (LST), whereby a laser beam is used to produce regular arrays of dimples on a surface, has been demonstrated to reduce friction in conformal lubricated contacts. Friction and wear behavior under boundary lubrication is also known to be dependent on the formation and durability of the tribochemical film formed from lubricant additives. In this paper, the effects of LST on the formation and durability of tribochemical films and its consequent impacts on friction and wear behavior in various lubrication regimes were evaluated. Friction and wear tests that cycled through different lubrication regimes were conducted with both polished and LST treated surfaces using a synthetic lubricant with and without model additives of ZDDP and MoDTC mixture. In the base oil without additives, LST produced noticeable reduction in friction in all lubrication regimes. However, with low-friction model additives, friction was higher in tests with LST due to significant differences in the tribochemical film formation in the polished and LST surfaces, as well as the sliding counterface. Continuous tribo-films were formed on ball conterface rubbed against polished surfaces while the films were streaky and discontinuous in ball rubbed against LST surfaces. LST produced more wear on the ball counterface in both base and additized oils. Lastly, no measurable wear was observed in both the polished and LST flat specimens.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Influence of the chemical surface structure on the nanoscale friction in plasma nitrided and post-oxidized ferrous alloy

Friction is a ubiquitous phenomenon in everyday activities spanning from vehicles where efficient brakes are mandatory up to mechanical devices where its minimum effects are pursued for energy efficiency issues. Recently, theoretical models succeed correlating the friction behavior with energy transference via phonons between sliding surfaces. Therefore, considering that the energy losses by friction are prompted through phonons, the chemical surface structure between sliding surfaces is very important to determine the friction phenomenon. In this work, we address the issue of friction between a conical diamond tip sliding on different functionalized flat steel surfaces by focusing the influence of the chemical bonds in the outermost layers on the sliding resistance. This geometry allows probing the coupling of the sharp tip with terminator species on the top and underneath material surface at in-depth friction measurements from 20 to 200 nm. Experimentally, the friction coefficient decreases when nitrogen atoms are substituted for oxygen in the iron network. This effect is interpreted as due to energy losses through phonons whilst lower vibrational frequency excitation modes imply lower friction coefficients and a more accurate adjustment is obtained when a theoretical model with longitudinal adsorbate vibration is used.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

Atomic-scale friction modulated by potential corrugation in multi-layered graphene materials

Friction is an important issue that has to be carefully treated for the fabrication of graphene-based nano-scale devices. So far, the friction mechanism of graphene materials on the atomic scale has not yet been clearly presented. Here, first-principles calculations were employed to unveil the friction behaviors and their atomic-scale mechanism. We found that potential corrugations on sliding surfaces dominate the friction force and the friction anisotropy of graphene materials. Higher friction forces correspond to larger corrugations of potential energy, which are tuned by the number of graphene layers. The friction anisotropy is determined by the regular distributions of potential energy. The sliding along a fold-line path (hollow-atop-hollow) has a relatively small potential energy barrier. Thus, the linear sliding observed in macroscopic friction experiments may probably be attributed to the fold-line sliding mode on the atomic scale. These findings can also be extended to other layer-structure materials, such as molybdenum disulfide (MoS{sub 2}) and graphene-like BN sheets.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Methods to Measure, Predict and Relate Friction, Wear and Fuel Economy

High-fidelity measurements of the coefficient of friction and the parasitic friction power of the power cylinder components have been made for the Isuzu 5.2L 4H on-highway engine. In particular, measurements of the asperity friction coefficient were made with test coupons using Argonne National Lab’s (ANL) reciprocating test rig for the ring-on-liner and skirt-on-liner component pairs. These measurements correlated well with independent measurements made by Electro-Mechanical Associates (EMA). In addition, surface roughness measurements of the Isuzu components were made using white light interferometer (WLI). The asperity friction and surface characterization are key inputs to advanced CAE simulation tools such as RINGPAK and PISDYN which are used to predict the friction power and wear rates of power cylinder components. Finally, motored friction tests were successfully performed to quantify the friction mean effective pressure (FMEP) of the power cylinder components for various oils (High viscosity 15W40, low viscosity 5W20 with friction modifier (FM) and specially blended oil containing consisting of PAO/ZDDP/MoDTC) at 25, 50, and 110°C.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

NASA NTRSDate not supplied

Gimbal Bearing Friction in the SLS Core Stage Thrust Vector Control System

The Space Launch System (SLS) Core Stage Thrust Vector Control (TVC) system is comprised of eight mechanical feedback Shuttle heritage Type III TVC actuators that vector the four Shuttle heritage RS-25 engines about a Shuttle heritage gimbal block/bearing. The MSFC Controls community has long regarded gimbal friction to be a negligible effect on the overall control of gimbaled RS-25 engines. This is corroborated by Space Shuttle test and flight data that does not appear to show degraded effects, nor limit cycling at the end of the shuttle flight. For this reason, friction was not expected to be a driving factor of performance and control of the reused RS-25 engines aboard the SLS. However, after test data showed a large shift in frequency behavior and a highly damped step-response in the time series, there was further investigation into what could have caused this behavior. Heritage friction models used in previous gimbal and ball bearings were evaluated such as Coulomb, Dahl and LuGre, but the single degree of freedom friction models alone were not enough to explain the behavior and shifts seen in the test data. This paper presents the additional findings and modeling efforts regarding friction on the RS-25 engines. Using the Two Actuator Operational Simulation (TAOS), the difference from modeling separate friction degrees of freedom to coupled degrees of freedom was investigated to deduce the effects of one axis’s movement on the other. Next, due to the vibration environment, a modified LuGre model has been proposed that adds an additional term to decrease the friction coefficient at low engine velocity amplitudes. Lastly, the addition of the stiffness in each half of the gimbal bearing has increased modeling fidelity by also adding the effect on the gimbal bearing bending in compliance to both the friction torque on the surface of the gimbal bearing and the actuator force that is forcing the engine in a specified direction. Through these effects, the time and frequency domain behavior seen in test can be characterized accurately.

Friction↗

NASA NTRSDate not supplied

Gimbal Bearing Friction in the SLS Core Stage Thrust Vector Control System

The Space Launch System (SLS) Core Stage Thrust Vector Control (TVC) system is comprised of eight mechanical feedback Shuttle heritage Type III TVC actuators that vector the four Shuttle heritage RS-25 engines about a Shuttle heritage gimbal block/bearing. The MSFC Controls community has long regarded gimbal friction to be a negligible effect on the overall control of gimbaled RS-25 engines. This is corroborated by Space Shuttle test and flight data that does not appear to show degraded effects, nor limit cycling at the end of the shuttle flight. For this reason, friction was not expected to be a driving factor of performance and control of the reused RS-25 engines aboard the SLS. However, after test data showed a large shift in frequency behavior and a highly damped step-response in the time series, there was further investigation into what could have caused this behavior. Heritage friction models used in previous gimbal and ball bearings were evaluated such as Coulomb, Dahl and LuGre, but the single degree of freedom friction models alone were not enough to explain the behavior and shifts seen in the test data. This paper presents the additional findings and modeling efforts regarding friction on the RS-25 engines. Using the Two Actuator Operational Simulation (TAOS), the difference from modeling separate friction degrees of freedom to coupled degrees of freedom was investigated to deduce the effects of one axis’s movement on the other. Next, due to the vibration environment, a modified LuGre model has been proposed that adds an additional term to decrease the friction coefficient at low engine velocity amplitudes. Lastly, the addition of the stiffness in each half of the gimbal bearing has increased modeling fidelity by also adding the effect on the gimbal bearing bending in compliance to both the friction torque on the surface of the gimbal bearing and the actuator force that is forcing the engine in a specified direction. Through these effects, the time and frequency domain behavior seen in test can be characterized accurately.

Friction↗

DOE OSTI2018

Mineralogical Controls on Frictional Strength, Stability, and Shear Permeability Evolution of Fractures

Massive fluid injection into the subsurface can induce microearthquakes by reactivating preexisting faults or fractures as seismic or aseismic slip. Such seismic or aseismic shear deformationsmay result in different modes of permeability evolution. Previous experimental studies have explored frictional stability-permeability relationships of carbonate-rich and phyllosilicate-rich samples under shear, suggesting that friction-permeability relationship may be primarily controlled by fracture minerals. We examine this relationship and identify the role of mineralogy (i.e., tectosilicate, carbonate, and phyllosilicate content) using direct-shear experiments on smooth saw-cut fractures of natural rocks and sintered fractures with distinct mineralogical compositions. These results indicate that the friction-permeability relationship is controlled by mineralogy. Frictional strength and permeability change upon reactivation decrease with phyllosilicate content but increase with tectosilicate content. In contrast, the reverse trend is observed for frictional stability (a-b). However, the permeability change decreases with carbonate content while both frictional strength and stability increase. The permeability change always decreases with an increase in frictional stability. This relationship implies a new mechanical-hydrochemical coupling loop via a linkage of frictional properties, mineralogy, and permeability.

58 GEOSCIENCES↗

DOE OSTI2020

Literature Review on the Theory and Measurement of Dry Sliding Friction of Metals

Understanding the friction behavior between two sliding bodies can inform the design of machines, processing of materials, and simulation of dynamic processes. Kinetic friction is a complex phenomenon that depends on a multitude of factors such as sliding velocity, normal force, contact area, surface roughness, material properties, lubrication conditions, and thermal effects. This literature review covers the major known effects of sliding velocity, normal load, and surface roughness on the measured kinetic friction coefficient in the context of microscopic friction phenomena. Classic macroscale friction models are reviewed to illustrate approaches for simulating friction behavior. Prominent experimental friction setups within the literature are discussed with respect to achievable velocity and pressure regimes. The background information gathered here will be used to inform experimental procedures and modeling strategies of the exploratory research (ER) project titled “Measurement of Dynamic Friction via Kolsky Bar” (20200418ER).

36 MATERIALS SCIENCE↗

NASA NTRS1989

Current status of Joint FAA/NASA Runway Friction Program

Tests with specially instrumented NASA B-737 and FAA B-727 aircraft together with several different ground friction measuring devices have been conducted for a variety of runway surface types and wetness conditions. This effort is part of the Joint FAA/NASA Aircraft Ground Vehicle Runway Friction Program aimed at obaining a better understanding of aircraft ground handling performance under adverse weather conditions and defining relationships between aircraft and ground vehicle tire friction measurements. Aircraft braking performance on dry, wet, snow-, and ice-covered runway conditions is discussed together with ground vehicle friction data obtained under similar runway conditions. For the wet, compacted snow- and ice-covered runway conditions, the relationship between ground vehicles and aircraft friction data is identified. The influence of major test parameters on friction measurements such as speed, test tire characteristics, and surface contaminant type are discussed. The test results indicate that use of properly maintained and calibrated ground vehicles for monitoring runway friction conditions should be encouraged particularly under adverse weather conditions. The current status of the runway friction program is summarized and future test plans are identified.

Yager, Thomas J.↗