Microscale Mechanical Behavior of the Subsurface by Finishing Processes

2005 ◽  
Vol 127 (2) ◽  
pp. 333-338 ◽  
Author(s):  
Y. B. Guo ◽  
A. W. Warren
Keyword(s):  
Mechanical Behavior ◽  
Hard Turning ◽  
White Layer ◽  
Subsurface Layer ◽  
Ground Surface ◽  
Small Scale ◽  
Near Surface ◽  
Microstructure Changes ◽  
Shallow Layer ◽  
Finishing Processes

Hard turning, grinding, and honing are common finishing processes in today’s production. The machined subsurface undergoes severe deformation and possible microstructure changes in a small scale subsurface layer <20μm. Mechanical behavior of this shallow layer is critical for component performance such as fatigue and wear. Due to the small size of this region, mechanical behavior of this shallow layer is hard to measure using traditional material testing. With the nanoindentation method, mechanical behavior (nanohardness and modulus) at the microscale in subsurface was measured for AISI 52100 and AISI 1070 steel components machined by hard turning, grinding, and honing. The test results show that white layer increases nanohardness but decreases modulus of a turned surface. Nanohardness and modulus of the ground surface are slightly smaller than the honed one in the subsurface. However, grinding produces higher nanohardness and modulus in near-surface <10μm than honing, while honing produces more uniform hardness and modulus in the near-surface and subsurface, and would improve component performance. Nanohardness and modulus of the machined near-surface are strongly influenced by strain hardening, residual stress, size-effect, and microstructure changes.

Nanoindentation Characterization of Ultrafine-Grained Surface Layer by Turning Versus Grinding

2008 ◽  
Author(s):  
A. W. Warren ◽  
Y. B. Guo
Keyword(s):  
Surface Hardening ◽  
Hard Turning ◽  
Surface Hardness ◽  
Ground Surface ◽  
Machining Processes ◽  
Near Surface ◽  
Machining Conditions ◽  
Ultrafine Grained ◽  
Aisi 52100 Steel ◽  
Research Findings

Hard turning and grinding are competing precision machining processes for the manufacture of mechanical components such as bearings, gears, cams, etc. Surface hardening at gentle machining conditions has often been reported and is attributed to ultrafine-grained and size effect. However, there are controversial results about surface hardness. Due to the great importance of surface property to component performance such as fatigue and wear, it is imperative to clarify surface hardening mechanisms. The purpose of this paper is to investigate surface hardening and mechanism. Hard turning and grinding of AISI 52100 steel was conducted using gentle machining conditions. Surface integrity was then analyzed in terms of surface microstructure, microhardness, and nanohardness. The research findings showed that the apparent softening measured using microindentation in near surface is not due to thermal effects, but rather a misinterpretation of hardness values due to improper testing technique. Hard turning induces a thicker plastically deformed ultrafine-grained (50∼100 nm) layer than grinding. However, the grinding induced grain size may be smaller that by turning, which produces higher hardness on the ground surface.

An Experimental Study on Subsurface Mechanical Behavior, Residual Stress, and Microstructure Induced by Process Dynamics in Machining

2004 ◽  
Author(s):  
A. W. Warren ◽  
Y. B. Guo
Keyword(s):  
Residual Stress ◽  
Strain Hardening ◽  
Surface Integrity ◽  
White Layer ◽  
Cutting Speed ◽  
Small Scale ◽  
Displacement Curve ◽  
Machined Surface ◽  
Microstructure Changes ◽  
Load Displacement

Surface integrity of machined components is critical for product performance in service. Process dynamic parameters, such as cutting speed and the changing contact condition between the tool flank face and machined surface, have a significant influence on surface integrity of a machined surface. Due to the very small scale of surface integrity factors on a machined surface, nanoindentation can be used to determine the surface/subsurface mechanical properties. However, the test data may be significantly influenced by machining induced residual stresses, strain hardening, and microstructure changes. The fundamental relationships between residual stress, microstructure, and nanohardness in the machined surface are yet to be understood. Further, it is not clear how to determine residual stress, at least its nature of tensile or compressive, from the nanoindentation data with the presence of complex residual stress state, strain hardening, and microstructure changes. This study focuses on the effects of cutting speed and machining system damping or rigidity (through varying tool flank wear) on subsurface mechanical state and the basic relationships between residual stress, white layer, and nanohardness. A series of nanoindentation tests were conducted to machined samples with distinct surface integrity by hard turning, grinding, and honing. It was found that white layer increases nanohardness and dark layer decreases nanohardness in subsurface, while strain hardening only slightly increases subsurface hardness. The research results indicate that subsurface residual stress can be qualitatively characterized by the load-displacement curve pattern and its parameters such as slope at initial loading, total depth, residual depth, and the ratio of residual depth to total depth. Residual stress would affect a load-displacement curve shape only at onset of yielding. Microstructure changes would make a significant difference on the characteristics of a load-displacement curve, while strain hardening exerts slight influence on the curve characteristics. In addition, the mechanism of residual stress on indentation depth was explained using a Mohr’s circle.

scholarly journals Permafrost distribution and conditions at the headwalls of two receding glaciers (Schladming and Hallstatt glaciers) in the Dachstein Massif, Northern Calcareous Alps, Austria

2020 ◽  
Vol 14 (4) ◽  
pp. 1173-1186
Author(s):  
Matthias Rode ◽  
Oliver Sass ◽  
Andreas Kellerer-Pirklbauer ◽  
Harald Schnepfleitner ◽  
Christoph Gitschthaler
Keyword(s):  
Active Layer ◽  
Ground Surface ◽  
Ice Age ◽  
Small Scale ◽  
Active Layer Thickness ◽  
High Mountain ◽  
Glacier Surface ◽  
Near Surface ◽  
Rock Stability ◽  
Multi Method Approach

Abstract. Permafrost distribution in rock walls surrounding receding glaciers is an important factor in rock stability and rock wall retreat. We investigated bedrock permafrost distribution in the Dachstein Massif, Austria, reaching up to 2995 m a.s.l. The occurrence, thickness and thermal regime of permafrost at this partly glaciated mountain massif are scarcely known. We applied a multi-method approach with continuous ground surface and near-surface temperature monitoring (GST), measurement of the bottom temperature of the winter snow cover (BTS), electrical resistivity tomography (ERT), airborne photogrammetry, topographic maps, visual observations, and field mapping. Our research focused on several steep rock walls consisting of massive limestone above receding glaciers exposed to different slope aspects at elevations between ca. 2600 and 2700 m a.s.l. We aimed to quantify the distribution and conditions of bedrock permafrost particularly at the transition zone between the present glacier surface and the adjacent rock walls. According to our ground temperature data, permafrost is mainly found at north-facing rock walls. At south-east-facing rock walls, permafrost is probable only in very favourable cold conditions at radiation-sheltered higher elevations (>2700 m a.s.l.). ERT measurements reveal high resistivities (>30 000 Ω m) at ≥1.5 m depth at north-exposed slopes (highest values >100 kΩ m). Deducted from laboratory studies and additional small-scale ERT measurements, these values indicate permafrost existence. Permafrost bodies were found at several rock walls independent of investigated slope orientation; however, particularly large permafrost bodies were found at north-exposed sites. Furthermore, at vertical survey lines, a pronounced imprint of the former Little Ice Age (LIA) ice margin was detected. Resistivities above and below the LIA line are markedly different. At the LIA glacier surface, the highest resistivities and lowest active-layer thicknesses were observed. The active-layer thickness increases downslope from this zone. Permafrost below the LIA line could be due to permafrost aggradation or degradation; however, the spatial patterns of frozen rock point to permafrost aggradation following glacier surface lowering or retreat. This finding is significant for permafrost and cirque erosion studies in terms of frost-influence weathering in similar high-mountain settings.

scholarly journals Permafrost distribution and conditions at the headwalls of two receding glaciers (Schladminger and Hallstadt glaciers) in the Dachstein Massif, Northern Calcareous Alps, Austria

2019 ◽  
Author(s):  
Matthias Rode ◽  
Harald Schnepfleitner ◽  
Oliver Sass ◽  
Andreas Kellerer-Pirklbauer ◽  
Christoph Gitschthaler
Keyword(s):  
Transition Zone ◽  
Slope Failure ◽  
Ground Surface ◽  
Northern Calcareous Alps ◽  
Small Scale ◽  
European Alps ◽  
Glacier Surface ◽  
Near Surface ◽  
Northern Calcareous ◽  
Discontinuous Permafrost

Abstract. Permafrost distribution in rockwalls surrounding receding glaciers is an important factor for rock slope failure and rockwall retreat. The Northern Calcareous Alps of the Eastern European Alps form a geological and climatological transition zone between the Alpine Foreland and the Central Alps. Some of highest summits of this area are located in the Dachstein Massif (47°28'32'' N, 13°36'23'' E) in Austria reaching up to 2995 m a.s.l. Occurrence, thickness and thermal regime of permafrost at this partly glaciated mountain massif are scarcely known and related knowledge is primarily based on regional modeling approaches. We applied a multi method approach with continuous ground surface and near-surface temperature monitoring, measurement of bottom temperature of the winter snow cover, electrical resistivity tomography/ERT, airborne photogrammetry, topographic maps, visual observations and field mapping for permafrost assessment. Our research focused on steep rockwalls consisting of massive limestone above several receding glaciers exposed to different slope aspects at elevations between c.2600–2700 m a.s.l. We aimed to quantify distribution and conditions of bedrock permafrost particularly at the transition zone between the present glacier surface and the adjacent rockwalls. Low ground temperature data suggest that permafrost is mainly found at cold, north exposed rockwalls. At southeast exposed rockwalls permafrost is only expected in very favourable cold conditions at shadowed higher elevations (2700 m a.s.l.). ERT measurements reveal high resistivities (> 30.000 ohm.m) at ≥ 1.5 m depth at north-exposed slopes (highest measured resistivity values > 100 kohm.m). Based on laboratory studies and additional measurements with small scale ERT, these values indicate permafrost existence. Such permafrost bodies were found in the rockwalls at all measurement sites independent of investigated slope orientation. ERT data indicate large permafrost bodies at north exposed sites whereas discontinuous permafrost bodies prevail at northwest and northeast facing rockwalls. In summary, permafrost distribution and conditions around the headwalls of the glaciers of the Dachstein Massif is primarily restricted to the north exposed sector, whereas at the south exposed sector permafrost is restricted to the summit region.

scholarly journals Small-scale variation of snow in a regional permafrost model

2016 ◽  
Vol 10 (3) ◽  
pp. 1201-1215 ◽  
Author(s):  
Kjersti Gisnås ◽  
Sebastian Westermann ◽  
Thomas Vikhamar Schuler ◽  
Kjetil Melvold ◽  
Bernd Etzelmüller
Keyword(s):  
Snow Cover ◽  
Ground Surface ◽  
Grid Cell ◽  
Ground Temperature ◽  
Fine Tuning ◽  
Small Scale ◽  
Near Surface ◽  
Ground Temperatures ◽  
Surface Temperatures ◽  
Scale Variation

Abstract. The strong winds prevalent in high altitude and arctic environments heavily redistribute the snow cover, causing a small-scale pattern of highly variable snow depths. This has profound implications for the ground thermal regime, resulting in highly variable near-surface ground temperatures on the metre scale. Due to asymmetric snow distributions combined with the nonlinear insulating effect of snow, the spatial average ground temperature in a 1 km2 area cannot be determined based on the average snow cover for that area. Land surface or permafrost models employing a coarsely classified average snow depth will therefore not yield a realistic representation of ground temperatures. In this study we employ statistically derived snow distributions within 1 km2 grid cells as input to a regional permafrost model in order to represent sub-grid variability of ground temperatures. This improves the representation of both the average and the total range of ground temperatures. The model reproduces observed sub-grid ground temperature variations of up to 6 °C, and 98 % of borehole observations match the modelled temperature range. The mean modelled temperature of the grid cell reproduces the observations with an accuracy of 1.5 °C or better. The observed sub-grid variations in ground surface temperatures from two field sites are very well reproduced, with estimated fractions of sub-zero mean annual ground surface temperatures within &amp;pm;10 %. We also find that snow distributions within areas of 1 km2 in Norwegian mountain environments are closer to a gamma than to a lognormal theoretical distribution. The modelled permafrost distribution seems to be more sensitive to the choice of distribution function than to the fine-tuning of the coefficient of variation. When incorporating the small-scale variation of snow, the modelled total permafrost area of mainland Norway is nearly twice as large compared to the area obtained with grid-cell average snow depths without a sub-grid approach.

MAGNETIC PROSPECTING FOR IRON ORES IN JAMAICA

Geophysics ◽  
1955 ◽  
Vol 20 (3) ◽  
pp. 593-614 ◽  
Author(s):  
S. A. Vincenz
Keyword(s):  
Remanent Magnetization ◽  
Iron Ore ◽  
Ground Surface ◽  
Natural Remanent Magnetization ◽  
Ore Deposits ◽  
Small Scale ◽  
Rough Terrain ◽  
Near Surface ◽  
Ore Bodies ◽  
Iron Ore Deposits

Two ground magnetometer surveys over iron ore deposits in Jamaica are described and the results of the observations interpreted. An improvised but economical technique is used to measure the main magnetic properties of ore samples obtained from surface exposures, and a suitable statistical analysis is applied to determine the significance of these observations. The interpretation of the magnetic profiles, carried out on the basis of these observations, is complicated by the non‐uniformity of the natural remanent magnetization of the ores and the roughness of Jamaican topography. The ambiguities due to the latter factor are diminished by taking into account in the computations the changes in the elevation of the ground surface. The results of the interpretation are on the whole successful and give the approximate sizes and positions of the main ore bodies. A conclusion is reached that, in the case of small‐scale near‐surface deposits whose approximate position is already known, ground magnetometer surveys can be superior to those made from the air because of their smaller cost and greater power of resolution in rough terrain.

scholarly journals Changes in ground deformation prior to and following a large urban landslide in La Paz, Bolivia revealed by advanced InSAR

2018 ◽  
Author(s):  
Nicholas J. Roberts ◽  
Bernhard T. Rabus ◽  
John J. Clague ◽  
Reginald L. Hermanns ◽  
Marco-Antonio Guzmán ◽  
...  
Keyword(s):  
Ground Deformation ◽  
Ground Surface ◽  
Slope Instability ◽  
Small Scale ◽  
Spatial And Temporal Patterns ◽  
La Paz ◽  
Fine Grained ◽  
Measured Displacement ◽  
Optical Satellite Images ◽  
Displacement Patterns

Abstract. We characterize and compare creep preceding and following the 2011 Pampahasi landslide (∼ 40 Mm3 ± 50 %) in the city of La Paz, Bolivia, using spaceborne RADAR interferometry (InSAR) that combines displacement records from both distributed and point scatterers. The failure remobilised deposits of an ancient landslide in weakly cemented, predominantly fine-grained sediments and affected ∼ 1.5 km2 of suburban development. During the 30 months preceding failure, about half of the toe area was creeping at 3–8 cm/a and localized parts of the scarp area showed displacements of up to 14 cm/a. Changes in deformation in the 10 months following the landslide are contrary to the common assumption that stress released during a discrete failure increases stability. During that period, most of the landslide toe and areas near the headscarp accelerated, respectively, to 4–14 and 14 cm/a. The extent of deformation increased to cover most, or probably all, of the 2011 landslide as well as adjacent parts of the slope and plateau above. The InSAR-measured displacement patterns – supplemented by field observations and by optical satellite images – indicate that kinematically complex, steady-state creep along pre-existing sliding surfaces temporarily accelerated in response to heavy rainfall, after which the slope quickly achieved a slightly faster and expanded steadily creeping state. This case study demonstrates that high-quality ground-surface motion fields derived using spaceborne InSAR can help to characterize creep mechanisms, quantify spatial and temporal patterns of slope activity, and identify isolated small-scale instabilities. Characterizing slope instability before, during, and after the 2011 Pampahasi landslide is particularly important for understanding landslide hazard in La Paz, half of which is underlain by similar, large paleolandslides.

Effects of Sequential Cuts on White Layer Formation and Retained Austenite Content in Hard Turning of AISI52100 Steel

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Xiao-Ming Zhang ◽  
Xin-Da Huang ◽  
Li Chen ◽  
Jürgen Leopold ◽  
Han Ding
Keyword(s):  
Layer Thickness ◽  
Process Parameters ◽  
Retained Austenite ◽  
Hard Turning ◽  
White Layer ◽  
Layer Formation ◽  
White Layer Thickness ◽  
Austenite Content ◽  
Sequential Cuts ◽  
White Layer Formation

This technical brief is the extension of our previous work developed by Zhang et al. (2016, “Effects of Process Parameters on White Layer Formation and Morphology in Hard Turning of AISI52100 Steel,” ASME J. Manuf. Sci. Eng., 138(7), p. 074502). We investigated the effects of sequential cuts on microstructure alteration in hard turning of AISI52100 steel. Samples undergone five sequential cuts are prepared with different radial feed rates and cutting speeds. Optical microscope and X-ray diffraction (XRD) are employed to analyze the microstructures of white layer and bulk materials after sequential cutting processes. Through the studies we first find out the increasing of white layer thickness in the sequential cuts. This trend in sequential cuts does work for different process parameters, belonging to the usually used ones in hard turning of AISI52100 steel. In addition, we find that the white layer thickness increases with the increasing of cutting speed, as recorded in the literature. To reveal the mechanism of white layer formation, XRD measurements of white layers generated in the sequential cuts are made. As a result retained austenite in white layers is identified, which states that the thermally driven phase transformations dominate the white layer formation, rather than the severe plastic deformation in cuts. Furthermore, retained austenite contents in sequential cuts with different process parameters are discussed. While using a smaller radial feed rate, the greater retained austenite content found in experiments is attributed to the generated compressive surface residual stresses, which possibly restricts the martensitic transformation.

Experiments on wind-driven heat exchange processes over melting snow

2021 ◽  
Author(s):  
Michael Haugeneder ◽  
Tobias Jonas ◽  
Dylan Reynolds ◽  
Michael Lehning ◽  
Rebecca Mott
Keyword(s):  
Snow Cover ◽  
Surface Wind ◽  
Infrared Camera ◽  
Snow Accumulation ◽  
Internal Boundary ◽  
Small Scale ◽  
Snow Melt ◽  
Two Dimensional ◽  
Atmospheric Conditions ◽  
Near Surface

&lt;p&gt;Snowmelt runoff predictions in alpine catchments are challenging because of the high spatial variability of t&lt;span&gt;he snow cover driven by &lt;/span&gt;various snow accumulation and ablation processes. In spring, the coexistence of bare and snow-covered ground engages a number of processes such as the enhanced lateral advection of heat over partial snow cover, the development of internal boundary layers, and atmospheric decoupling effects due to increasing stability at the snow cover. The interdependency of atmospheric conditions, topographic settings and snow coverage remains a challenge to accurately account for these processes in snow melt models.&lt;br&gt;In this experimental study, we used an Infrared Camera (VarioCam) pointing at thin synthetic projection screens with negligible heat capacity. Using the surface temperature of the screen as a proxy for the air temperature, we obtained a two-dimensional instantaneous measurement. Screens were installed across the transition between snow-free and snow-covered areas. With IR-measurements taken at 10Hz, we capture&lt;span&gt; the dynamics of turbulent temperature fluctuations&lt;/span&gt;&lt;span&gt; &lt;/span&gt;over the patchy snow cover at high spatial and temporal resolution. From this data we were able to obtain high-frequency, two-dimensional windfield estimations adjacent to the surface.&lt;/p&gt;&lt;p&gt;Preliminary results show the formation of a stable internal boundary layer (SIBL), which was temporally highly variable. Our data suggest that the SIBL height is very shallow and strongly sensitive to the mean near-surface wind speed. Only strong gusts were capable of penetrating through this SIBL leading to an enhanced energy input to the snow surface.&lt;/p&gt;&lt;p&gt;With these type of results from our experiments and further measurements this spring we aim to better understand small scale energy transfer processes over patch snow cover and it&amp;#8217;s dependency on the atmospheric conditions, enabling to improve parameterizations of these processes in coarser-resolution snow melt models.&lt;/p&gt;

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