Localized Frictional Heating Research Articles

Frictional Strength, Stability, and Potential Shear Heating on Icy Satellite Faults

AbstractWe determined the frictional strength and stability of polycrystalline ice and ice‐ammonia to constrain fault behavior on icy satellites such as Enceladus and Europa. Friction experiments including velocity steps and slide‐hold‐slide tests were conducted to measure the steady‐state coefficient of friction, velocity dependence and healing between temperatures of 98 and 248 K at a normal stress of 100 kPa. Rate‐state friction parameters determined from velocity steps provide stability values. The friction results are used to infer fault strength and frictional heating of an icy crust with depth for both a pure ice crust and one containing ammonia. We find a reduced coefficient of friction for an ammonia‐bearing crust and stronger velocity dependence in the presence of partial melt. The temperature dependence of fault stability maps a seismogenic zone with depth analogous to the synoptic model for terrestrial fault stability, where we find instability between 0.7 and 3.9 km with a return to stability from 4.6 km if we assume a 6 km ice shell. We consider the role of sliding velocity and fault thickness on localized frictional heating in both systems and estimate the depth of melt generation in an ammonia‐bearing crust. Our results imply that faults at conditions similar to icy satellites can be seismogenic.

Ultrasonic welding of AZ31B magnesium alloy

Abstract

Thermal Explosions of Polymer-Bonded Explosives with High Time and Space Resolution

It has always been difficult to observe thermally induced explosions, because the onset is unpredictable. By use of ultrasound to induce intense, localized frictional heating at the surface of crystals embedded in a flexible polymer, we have created a new method for the initiation of microexplosions under conditions where temporal and spatially resolved observations can be made. Specifically, we report the use of ultrasound to flash-heat polymer-embedded 10 000 K/s. By using this extremely rapid heating on small samples, we were able to confine the explosion to narrow regions in time and space. The explosion was measured using dual thermal imagers providing temporal and spatial resolutions of 1 μs and 15 μm. Surprisingly, the explosions always occurred in two stages, an initial 0.1 ms stage and a subsequent 100 ms stage. The first stage of RDX explosion (2500 K lasting 140 μs) was less violent than that for HMX (4400 K lasting 70 μs), which is c...

Finite element modelling of the dynamics of groovy ball bearings

Geometry modified thrust bearings exposed to rolling and sliding contact are subjected to wear and localized frictional heating caused by relative slip between the two sliding surfaces. This leads to a rise in temperature, thermal stresses and changes in the elastic and plastic strength and physical properties of the material. The changes in the properties in turn alter the stress state, the displacement field, life and reliability of the bearing. Hence, a finite-element model is created to study the dynamics of groovy thrust bearing. In this paper, Hertz contact theory and numerical method are used to simulate the dynamics and kinematics of groovy ball bearings. The optimal loading parameters are identified in this study based on the analysis of the system responses and properties. The results of the numerical analysis and validation are presented. The numerical analysis proves the concept of transforming rotational motion into axial oscillation and demonstrates the capabilities of the numerical simulation to accurately model the dynamics of the groovy ball bearing.

Friction stir incremental forming of AA7075-O sheets: investigation on process feasibility

Abstract Friction Stir Incremental Forming (FSIF), as a simple and effective hot incremental forming technology, has attracted increasing attentions from researchers in recent years. In FSIF, frictional heat generated by tool rotation on the interface between tool and workpiece is utilized to soften localized deformation zone, thus enhancing material formability. In order to facilitate the development of FSIF, a comprehensive analysis of process feasibility is needed for the performance evaluation of formed parts. In this work, FSIF has been employed to process 7075-O aluminum alloy sheets (a kind of hard-to-form light alloy materials) for assessing the formability, surface quality, tensile strength and micro-hardness of two typical parts (truncated funnel and pyramid frustum). Experimental results show that the formability generally enhances with the help of local frictional heating as tool rotation speeds increase. On the tool-sheet contact surface, surface roughness shows a different trend of variation in horizontal (parallel to tool path) and vertical directions (perpendicular to tool path). Furthermore, mechanical properties including tensile strength and surface micro-hardness in formed parts are obviously enhanced compared to the initial sheet, of which the micro-hardness values begin to fall down gradually when the tool rotation speed is greater than 3000 rpm.

The influence of surface properties on sliding contact temperature and friction for polyetheretherketone (PEEK)

Abstract Polyetheretherketone (PEEK) polymers are increasingly used in tribological applications. An important aspect of PEEK tribology is the surface temperature reached during sliding. At present, most knowledge of frictional heating in PEEK is based on post-hoc analysis of debris and wear surfaces. In this study, infrared thermography was used to observe the full field temperature map of PEEK against sapphire counterface during ball-on-disc sliding. The measured temperatures matched closely those predicted by flash temperature models. Additionally, friction studies were performed with steel and sapphire counterfaces. It was observed that PEEK debris readily deposited on steel but not on sapphire. The friction studies also indicated a greater adhesive friction response for PEEK against steel compared to PEEK against sapphire. The transfer of PEEK material to the steel surface may elevate the temperature at the sliding interface. Analysis of transfer films on steel suggests that the transferred PEEK was oriented in the direction of sliding. The deposition of debris and formation of oriented films resembled a high temperature drawing process, which was likely to be due to localized frictional heating. The results of this study illustrate the important role transfer films play in determining both the friction and temperature of the PEEK wear interface.

Strain localization and the onset of dynamic weakening in calcite fault gouge

To determine the role of strain localization during dynamic weakening of calcite gouge at seismic slip rates, single-slide and slide–hold–slide experiments were conducted on 2–3-mm thick layers of calcite gouge at normal stresses up to 26 MPa and slip rates up to 1 m s−1. Microstructures were analyzed from short displacement (<35 cm) experiments stopped prior to and during the transition to dynamic weakening. In fresh calcite gouge layers, dynamic weakening occurs after a prolonged strengthening phase that becomes shorter with increasing normal stress and decreasing layer thickness. Strain is initially distributed across the full thickness of the gouge layer, but within a few millimeters displacement the strain becomes localized to a boundary-parallel, high-strain shear band c. 20 μm wide. During the strengthening phase, which lasts between 3 and 30 cm under the investigated conditions, the shear band broadens to become c. 100 μm wide at peak stress. The transition to dynamic weakening in calcite gouges is associated with the nucleation of micro-slip surfaces dispersed throughout the c. 100 μm wide shear band. Each slip surface is surrounded by aggregates of extremely fine grained and tightly packed calcite, interpreted to result from grain welding driven by local frictional heating in the shear band. By the end of dynamic weakening strain is localized to a single 2–3-μm wide principal slip surface, flanked by layers of recrystallized gouge. Calcite gouge layers re-sheared following a hold period weaken nearly instantaneously, much like solid cylinders of calcite marble deformed under the same experimental conditions. This is due to reactivation of the recrystallized and cohesive principal slip surface that formed during the first slide, reducing the effective gouge layer thickness to a few microns. Our results suggest that formation of a high-strain shear band is a critical precursor to dynamic weakening in calcite gouges. Microstructures are most compatible with dynamic weakening resulting from a thermally triggered mechanism such as flash heating that requires both a high degree of strain localization and a minimum slip velocity to activate. The delayed onset of dynamic weakening in fresh calcite gouge layers, particularly at low normal stresses, may inhibit large coseismic slip at shallow crustal levels in calcite-bearing fault zones.

Coefficient of friction between a rigid conical indenter and a model elastomer: Influence of local frictional heating

We investigate the coefficient of friction between a rigid cone and an elastomer with account of local heating due to frictional dissipation. The elastomer is modeled as a simple Kelvin body and an exponential dependency of viscosity on temperature is assumed. We show that the coefficient of friction is a function of only two dimensionless variables depending on the normal force, sliding velocity, the parameter characterizing the temperature dependence as well as shear modulus, viscosity at the ambient temperature and the indenter slope. One of the mentioned dimensionless variables does not depend on velocity and determines uniquely the form of the dependence of the coefficient of friction on velocity. Depending on the value of this controlling variable, the cases of weak and strong influence of temperature effects can be distinguished. In the case of strong dependence, a generalization of the classical “master curve” procedure introduced by Grosch is suggested by using both horizontal and vertical shift factors.

Model of the effect of local frictional heating on the tribodesorbed gases from metals in ultra-high vacuum

In this paper, a model of thermal desorption of gases from the friction zone of metals in ultra-high vacuum is presented. Comparison of the model with the experimental data of tribodesorbed gases from AISI 304 steel shows that for mild friction the amount of desorbed gases owing to the local temperature increase is much lower than the experimentally obtained values. This finding supports the hypothesis that structural modification of material is the main driving process for tribodesorption. The study also shows that a significant volume of material around the friction zone contributes to the tribodesorption process.

Radiofrequency thermal ablation in the treatment of malignant tumors

Radiofrequency ablation (RFA) provides an effective technique for minimally invasive tissue destruction. An alternating current delivered via a needle electrode causes localized ionic agitation and frictional heating of the tissue around the needle. Image-guided, percutaneous ablation techniques have been developed in most parts of the body, but the most widely accepted applications are for the treatment of hepatocellular carcinoma (HCC) in early cirrhosis, inoperable colorectal liver metastases, inoperable renal cell carcinoma and inoperable primary or secondary lung tumors. The procedures are well tolerated and the complication rates low. Most treatments in the lung, kidney and for HCC are performed under conscious sedation with an overnight hospital stay or as a day-case. Limitations of RFA include the volume of tissue that can be ablated and most centers will treat 3–5 tumors up to 4–5 cm in diameter. Early series reporting technical success and complications are available for lung and renal ablation. Liver ablation is better established and 5-year survival figures are available from several centers. In patients with limited but inoperable colorectal metastases, the 5-year survival ranges from 26 to 30% and for HCC it is just under 50%. In summary, RFA provides the opportunity for localized tissue destruction of limited volumes of tumor; it can be offered to nonsurgical candidates and used in conjunction with systemic therapy.

On the Use of Actively Controlled Auxiliary Bearings in Magnetic Bearing Systems

Auxiliary bearings are used to prevent rotor/stator contact in active magnetic bearing systems. They are sacrificial components providing a physical limit on the rotor displacement. During rotor/auxiliary bearing contact significant forces normal to the contact zone may occur. Furthermore, rotor slip and rub can lead to localized frictional heating. Linear control strategies may also become ineffective or induce instability due to changes in rotordynamic characteristics during contact periods. This work considers the concept of using actively controlled auxiliary bearings in magnetic bearing systems. Auxiliary bearing controller design is focused on attenuating bearing vibration resulting from contact and reducing the contact forces. Controller optimization is based on the H∞ norm with appropriate weighting functions applied to the error and control signals. The controller is assessed using a simulated rotor/magnetic bearing system. Comparison of the performance of an actively controlled auxiliary bearing is made with that of a resiliently mounted auxiliary bearing. Rotor drop tests, repeated contact tests, and sudden rotor unbalance resulting in trapped contact modes are considered.

Optimum thickness of a cooled wall subjected to local frictional heating in the regime of spinning friction

Using the methods of mathematical simulation, the characteristic features of a stationary temperature field in a cooled plane isotropic wall subjected to local frictional heating from a circular source in the regime of spinning friction are investigated. The possibility of the existence of an optimal wall thickness which ensures a minimum temperature of its most heated point has been established.

Beyond Heat Checking: Frictional Heating Causes Drillpipe Failure in an Extended-Reach Well

Summary Failure of a 5-in. proprietary hole-cleaning drillpipe joint occurred during platform drilling of a North Sea extended-reach well. The joint was run in heavyweight drillpipe above the bottomhole assembly (BHA). Its failure resulted in the loss of the BHA, including high-value rotary-steerable tools, at 23,250 ft measured depth (MD). The failure occurred when the string was being rotated out through a tight spot. Topdrive stallouts and intermittent circulation were experienced. The maximum overpull applied was 50,000 lbf. The appearance of the recovered pipe indicated ductile failure, despite a zone of abnormally high hardness adjacent to the fracture. Investigation established that local frictional heating had heated the drillpipe above 1,441°F and that ductile failure had occurred when hot, although the string had not been overloaded in tension or torsion. After the rupture, the mud-flow quench hardened the hot pipe to above 572 Vickers of 10kg load Hardness (HV10) [approximately 54 Rockwell Hardness on a C scale (HRC)—Note: hardness values are given "as measured"; conversions are approximate and for information only]. "Heat checking" (i.e., downhole surface hardening of frictionally heated drillpipe) is an established phenomenon that is described in the literature. The case reported herein represents an extreme consequence of frictional heating that has important implications for the management of topdrive drilling operations.

Symmetric Stress Tensor Formulation of Horizontal Momentum Diffusion in Global Models of Atmospheric Circulation

Abstract In climate and weather forecast models, small-scale turbulence in the free atmosphere is usually parameterized by horizontal diffusion of horizontal momentum. This study proposes a formulation that is based on a symmetric stress tensor. The advantage over conventional methods is twofold. First, the Eulerian law of angular momentum conservation is fulfilled. Second, a self-consistent formulation of the momentum and thermodynamic equations of motion becomes possible due to incorporation of the local frictional heating rate, that is, the proper dissipation. The importance of these issues is demonstrated by numerical experiments performed with a simple general circulation model. For example, the new scheme precisely accounts for the irreversible increase of total potential energy during the decay of a baroclinic life cycle. Also the stress generated by horizontal momentum diffusion is found to be significant in the angular momentum budget of multiple life cycle experiments.

A thermal problem of friction for a half-space with a crack

We investigate the effect of local frictional heating of the surface of a half-space on the stress intensity factors at the vertices of a surface cut.

The spatial distribution of ESR signals in fault gouge revealed by Abrading technique

The spatial distribution of ESR signal intensity and equivalent dose ( D E) has been predicted within the quartz grains from fault gouge by the localized lattice deformation and frictional heating theory (Lee and Schwarcz, 1994). The abrading technique was applied to a fault gouge sample in order to see the distribution as the technique removes the surface semi-quantitatively. Both intensities of E′ 1 and Al centers become larger after abrasion, being consistent with the theory, but not all the D ES.

Global and local Joule heating effects seen by DE 2

In the altitude region between 350 and 550 km, variations in the ion temperature principally reflect similar variations in the local frictional heating produced by a velocity difference between the ions and the neutrals. Here we show the distribution of the ion temperature in this altitude region and discuss its attributes in relation to previous work on local Joule heating rates. In addition to the ion temperature, instrumentation on the DE 2 satellite also provides a measure of the ion velocity vector representative of the total electric field. From this information we derive the local Joule heating rate. From an estimate of the height‐integrated Pedersen conductivity it is also possible to estimate the global (height‐integrated) Joule heating rate. Here we describe the differences and relationships between these various parameters.

Ion‐neutral coupling in the high‐latitude F region: Evaluation of ion heating terms from Dynamics Explorer 2

We study a set of south (summer) polar passes from the Dynamics Explorer 2 data base that provide measurements of ion and neutral velocities along the track of the spacecraft for various geomagnetic conditions. The ion velocities are obtained from the ion drift meter and the retarding potential analyzer instruments; the neutral velocities are obtained from the Fabry‐Perot interferometer and the wind and temperature spectrometer instruments. These data enable a direct determination of the in situ ion‐neutral difference velocity. Simultaneous measurements of atmospheric composition using the neutral atmosphere composition spectrometer and of electron temperatures and densities using the Langmuir probe enable the ion heating and cooling rates to be determined. The rates are discussed in relationship to values for the electron, ion, and neutral kinetic temperatures. The comprehensive nature of the data set allows for a quantitative study of ion‐neutral coupling and, in particular, affords a more rigorous test of the common assumptions used in the ion energy equation than has been previously possible. From our study we find the following: (1) The ion‐neutral difference velocities, which drive the Joule heating, have a complex morphology that depends on the stability of the high‐latitude ion convection and the inertia of the neutral gas. (2) Ionospheric “hot spots” are observed to be related to large perpendicular electric fields that give rise to frictional (Joule) heating. (3) These events are often seen to occur in conjunction with troughs in the electron density and with decreases in the ratio of atomic oxygen to molecular nitrogen. In such cases, momentum transfer to the neutral gas is reduced, and the ion‐neutral velocity difference and associated Joule heating can be maintained over longer time periods. (4) An approximate balance between local frictional heating of the ions and local cooling of the ions to the neutrals is seen in regions of strong ion convection. The commonly used approximate form of the ion energy equation involving only local processes appears at times, however, to be inadequate for large regions of the summer polar cap. The ion temperatures observed in these regions are higher than expected from simple local heating/local cooling arguments. Additional source(s) of ion heating would be required to provide energy balance.

The friction of solids at very high speeds I. Metal on metal; II. Metal on diamond

The friction of metal surfaces and of metals sliding on diamond at very high speeds has been studied. A ball spinning in vacuo at surface speeds up to 800 m/s ( ca . 1800 miles/h) is trapped between symmetrically arranged flat plates so that the friction causes it to slow down. The deceleration is measured electronically and recorded. The results show that the sliding resistance of metals decreases as the speed increases and reaches very low values. There is evidence that frictional heating produces high surface temperatures and a softening and melting of the metal at the regions of contact. An analysis of the heat flow in a specimen shows that the area of intimate contact is very small compared with the apparent interface. Since the temperature falls very rapidly with increasing distance from the shearing zone the metal behaves like a combination of a thin film of low shear strength supported by a hard substrate. This can explain the low friction at high sliding speeds. It is also suggested that the real area of contact depends on the velocity with which plastic strains are propagated in the metal. The shearing occurs so rapidly that full plastic yielding under the normal load is not possible. Some metals disintegrate in a brittle fashion when a critical speed is exceeded. When metals slide on diamond even the hard octahedral face is abraded and polished if appropriately high sliding speeds are used. Metals with a high melting point are most effective in this polishing process and it is concluded that the wear of diamond is due to an allotropic transformation into graphite or amorphous carbon under the influence of localized frictional heating.