Subsurface Deformation Research Articles

Three-dimensional thermo-hydro-mechanical coupled modeling of thermal anomalies before the 2008 Wenchuan earthquake

Pre-seismic thermal anomalies have been widely reported, however, there is still no unified understanding of their causes or physical mechanisms. To clarify whether subsurface fluid convection and rock deformation directly related to seismic fault stress release can form thermal anomalies before an earthquake, we carried out thermo-hydro-mechanical (THM) coupled modeling of the Wenchuan earthquake, and considered the influence of maximum horizontal principal stress direction (MPSD) and fault dip. The results show that convective thermal flux (CT) anomalies of subsurface fluid and the deformation induced thermal flux (DT) of the rock mass caused by stress release of the seismic fault can explain the observed thermal anomalies along the fault. The calculated and observed thermal anomalies are comparable in spatial distribution, evolution, and magnitude. Specifically, for the Wenchuan earthquake, seismic fault stress release-induced CT and DT anomalies occur in the fault zone and in the adjacent hanging wall area. In the fault zone, CT and DT induced thermal anomalies were comparable, and superposition of the two was characterized by strong initial warming, followed by weaker warming and then short-term cooling. However, outside of the fault zone, CT induced thermal anomalies had much higher intensities than those induced by DT, and were characterized by band-like warming along the hanging wall of the fault. In addition, variations in the MPSD and fault dip cause the segmentation of thermal anomalies along the Wenchuan earthquake fault. From the southern to the northern segments of the fault, the intensity of thermal anomalies is significantly weakened with rotation of MPSD and an increase in fault dip. Our study provides evidence that seismic fault stress release is the cause of pre-seismic thermal anomalies; furthermore, the results indicate the CT and DT could be important physical mechanisms of pre-seismic thermal anomalies.

Digital volume correlation technique for characterizing subsurface deformation behavior of a laminated composite

In the present study, the digital volume correlation (DVC) technique is used to study the deformation behavior occurring inside a carbon fibre-reinforced epoxy composite. While a tensile test on a symmetric angle-ply laminated composite specimen is being performed, X-ray images are recorded using synchrotron radiation. The radiographs are processed to reconstruct 3D μCT images. The reconstruction process utilizes a filtered back-projection (FBP) algorithm combined with a phase retrieval method to enhance the contrast of the CT images. Phase contrast is crucial since the natural microstructural pattern is analogous to a speckle pattern for digital image correlation (DIC) analysis. A slight misalignment of the specimen, typically negligible at the macroscopic scale, is corrected in the CT images prior to the DVC analysis. The accuracy of the DVC results is improved by implementing a sub-voxel registration approach to achieve a resolution less than one pixel. The DVC results are compared with finite element analysis (FEA) results. Although the overall results agree well with the FEA results, few subvolumes are prone to fail to find their correct pairs within DVC volumes. Raw 2D tomograms are individually examined and compared to show that a high correlation coefficient value does not always guarantee a correct match. Detailed discussions about the misleading correlations are provided and thereby the validations and limitations of the DVC (and DIC) technique are addressed.

The effect of thermostatic test environment on the flexural fatigue performance of hydraulic hose assemblies

The present study investigates the effect of thermostatic subzero (−65°F) and high ambient temperature (+275°F) on the hose performance when tested at a flexing frequency of 70 CPM with an amplitude of ±3.5 inches. The investigation was carried out through hose tear down analysis which includes surface and subsurface deformations at crimp zone, wire braid analysis, over the crimp silicon crack propagation, and microhardness measurements. It was observed that the flexing mechanism of hose when combined with thermostatic subzero and high ambient temperature, it contributes to different deformation mechanisms for the hose and the fitting juncture.

Introduction to special section: Characterization of the subsurface stress, deformation, and pore pressure

Introduction to special section: Characterization of the subsurface stress, deformation, and pore pressure

Surface and sub-surface analysis of rotary ultrasonic elliptical end milling of Ti-6Al-4V

Ultrasonic vibration has received widespread attention for its dramatic effect on grain refinement and microstructure modification during casting, additive manufacturing, cold rolling, and cutting, changes which can significantly improve the mechanical and physical properties of components. As a novel ultrasonic vibration cutting method, rotary ultrasonic elliptical milling (RUEM) has been introduced to mill the alloy Ti-6Al-4V. However, the effects of ultrasonic elliptical vibration on the microstructures of machined surfaces in end milling of Ti-6Al-4V are still unclear. A comprehensive study on the surface characteristics and sub-surface microstructure in RUEM of Ti-6Al-4V was conducted. The results show that the uniform textures, in the form of ridges mapped on the machined surface in RUEM, varied with the cutting speed. Compared with conventional milling, microchip debris adhesion on the machined surface was significantly reduced by using RUEM. Moreover, intense plastic deformation in the sub-surface was obtained, and nanocrystalline layers, with grain dimensions of 10 nm to 100 nm, were fabricated on the processed surfaces of RUEM. Additionally, the improvement in sub-surface microstructure increased the surface micro-hardness from 21.22% to 33.84%. This study allows an in-depth understanding of sub-surface deformation and surface nanocrystallization in RUEM of Ti–6Al–4V.

Effect of machining parameters on surface finish and subsurface damage for diamond-turned germanium

Germanium lenses are widely used in various scientific and technological applications mainly infrared optical components. The performance of these lenses depends upon the surface finish, which is challenging to achieve during ductile-regime machining. It is crucial to provide the optimum parameters to ensure the high-quality surface, without surface and subsurface damage. In the present work, an attempt has been made to analyse the effect of input machining parameters on surface finish and subsurface damage distribution, induced during the diamond turning. Taguchi’s optimization has been performed to optimize the parameters affecting the performance and surface quality of fabricated components. Abbott–Firestone (A–F) curve is utilized to study the distribution of peaks and valleys on the machined surface. Additionally, chip morphology and machining forces are analysed to study the material removal behaviour at varying parameters. Further, indentations are performed on the best and worst combinations to examine the effect of parameters selection on surface cracks propagation. It is found that surface with a greater number of valleys leads to chipping during indentation. In this study, a surface roughness of 2.3 nm is achieved with minimum subsurface deformation.

Industrial Gear Oils: Influence of Bulk Oil Temperature and Contact Pressure on Tribological Performance and Subsurface Changes

This study was designed to investigate the influence of oil temperature and contact pressure on the tribological performance of three industrial gear oils but also on the corresponding changes taking place beneath the metal surfaces in contact. The result shows that increase in the oil temperature and contact pressure increases surface–additive interaction, promoting the formation of low-friction tribofilms. Subsurface characterisation of the worn surfaces shows that higher oil temperature and contact pressure promotes surface hardening of spheroidised AISI 52100 steel, degradation of the near-surface (< 0.8 µm) microstructural integrity and corresponds to an increase in wear. This study clearly shows that the gear oil formulations and the tribofilms they form uniquely influence the extent of subsurface deformation and wear.

Toward Distributed Fiber‐Optic Sensing of Subsurface Deformation: A Theoretical Quantification of Ground‐Borehole‐Cable Interaction

AbstractFiber‐optic sensing is emerging as a superior means for distributed strain sensing of the subsurface. The ability of an embedded fiber‐optic cable to capture accurate strain profiles depends on the degree of rigid mechanical coupling between the ground and the cable. However, a current challenge in this field is to determine the actual level of ground deformation from strain signatures sensed by the cable deployed in the subsurface; addressing this issue has been hampered by the lack of suitable theoretical methods. Here we propose a two‐step ground‐cable coupling evaluation procedure, whereby we develop analytical formulations to quantify the interaction and interface shear transfer of a ground‐borehole‐cable system. We constrain key model parameters using a data set acquired with a fiber optics‐instrumented borehole for monitoring groundwater‐related sediment compaction. Extensive parametric analyses reveal that increasing the backfill modulus and cable gauge length or decreasing the borehole radius and cable stiffness can improve the quality of strain transferred to the cable from the ground; the effect of ground properties is comparably insignificant. Further, we develop design charts and tables at designated transfer thresholds to facilitate the development and field deployment of fiber sensing elements. Taken together, the theoretical quantification of ground‐cable coupling should improve the state‐of‐the‐art performance of distributed fiber‐optic strain sensing for subsurface ground movements detection and monitoring.

The Effect of Surface Ruptures on the Propagation of Tsunamis: An Analysis of 1993 Hokkaido Earthquake

An earthquake occurs when the energy condensed at certain points in the Earth's crust exceeds a certain threshold. Changes in depth of the seabed (induced by subsurface deformation) can cause irregular undulations and tsunamis. Surface ruptures usually start at one point and propagate in diverse directions (typically one or two). In this study, we used numerical analysis to examine the effects of surface ruptures on the generation and propagation of tsunamis. The 1993 Hokkaido earthquake was chosen for the test, and three subfaults were adopted to account for the history and process of the rupture. The results revealed the clear effects of surface rupture near the epicenter, showing either an increase or decrease in run-up heights (depending on spatial locations). Although the effects on run-up heights along the coast of the East Sea were unclear, the maximum effect (observed at specific points) generated twice the normal run-up heights.

The emergence of small-scale self-affine surface roughness from deformation.

Most natural and man-made surfaces appear to be rough on many length scales. There is presently no unifying theory of the origin of roughness or the self-affine nature of surface topography. One likely contributor to the formation of roughness is deformation, which underlies many processes that shape surfaces such as machining, fracture, and wear. Using molecular dynamics, we simulate the biaxial compression of single-crystal Au, the high-entropy alloy Ni36.67Co30Fe16.67Ti16.67, and amorphous Cu50Zr50 and show that even surfaces of homogeneous materials develop a self-affine structure. By characterizing subsurface deformation, we connect the self-affinity of the surface to the spatial correlation of deformation events occurring within the bulk and present scaling relations for the evolution of roughness with strain. These results open routes toward interpreting and engineering roughness profiles.

Flow plane orientation in the upper mantle under the Western/Central United States from SKS shear-wave splitting observations

SUMMARY The causes of seismic anisotropy are still under debate. In particular, it is important to understand the extent to which seismic anisotropy is due to more recent geodynamic activities in the asthenosphere, or to frozen-in deformation in the lithosphere. We show that these two endmember cases can in principle be distinguished using shear-wave splitting observations from SKS waves. This is illustrated by the simple example of pure olivine with horizontal a-axis, and differing orientations of the other two axes, namely, vertical b and vertical c. The azimuthal dependence of shear-wave splitting measurements is described by two parameters, which can provide additional information about subsurface deformation. In particular, the oscillation parameter d1 constrains the orientation of foliation. We demonstrate that shear-wave splitting in the Western and Central United States indeed shows the predicted azimuthal dependence, related to a mainly subhorizontally oriented flow plane of deformation in the upper mantle. This has important implications for asthenospheric flow.

Subsurface integrity studies on the drilling of Al/B4C/mica hybrid metal matrix composites

ABSTRACTWhen components are drilled for use in critical applications, some components might undergo surface defects and subsurface deformations. These defects arise due to microstructural and microhardness variations. This leads to sudden failure of these components. The present investigation focuses on Al/B4C/Mica hybrid composites and Al/B4C composites specimen with drilled surface and sub-surfaces. The goal is to identify measures to reduce surface integrity issues like microhardness, drilled surface morphology, and chip morphology on these specific components. Moreover, as a novel research, elemental and microstructural characterization of mica particles is carried out. The evaluation techniques used are Optical, EDX, SEM, and Vickers microhardness test. The stir cast specimens are drilled with process parameters of weight % B4C and mica at specified cutting speed and feed rate. Tungsten carbide twist drill of 8 mm diameter is used. The investigation reveals that addition of mica particles causes reduction in the microhardness of drilled surfaces. The % of reduction observed is up to 13.7, 5.2 and 3 (in Hv) on 4%, 8%, and 12% B4C reinforced Al/B4C/3%mica hybrid composites, respectively, in comparison with that of Al/B4C composites.

Experimental and numerical study of the subsurface deformation and residual stress during the roller burnishing process

Abstract Roller burnishing process is being extensively used to enhance the fatigue life of the aircraft engine components by introducing compressive residual stress and work hardening. The temperature rise during the burnishing process could be neglected due to the low friction rolling contact between the roller and workpiece, thus simplifying it an elastoplastic deformation process. In this paper, the digital image correlation technique was adopted to obtain the subsurface deformation field during the roller burnishing process. A 3D finite element model was built up to simulate the burnishing process. The predicted surface integrity parameters including subsurface deformation and residual stress are compared with the experimental measurements.

Influence of longwall mining on the stability of gas wells in chain pillars

Longwall mining has a significant influence on gas wells located within longwall chain pillars. Subsurface subsidence and abutment pressure induced by longwall mining can cause excessive stresses and deformations in gas well casings. If the gas well casings are compromised or ruptured, natural gas could migrate into the mine workings, potentially causing a fire or explosion. By the current safety regulations, the gas wells in the chain pillars have to be either plugged or protected by adequate coal pillars. The current regulations for gas well pillar design are based on the 1957 Pennsylvania gas well pillar study. The study provided guidelines for gas well pillars by considering their support area and overburden depth as well as the location of the gas wells within the pillars. As the guidelines were developed for room-and-pillar mining under shallow cover, they are no longer applicable to modern longwall coal mining, particularly, under deep cover. Gas well casing of failures have occurred even though the chain pillars for the gas wells met the requirements by the 1957 study. This study, conducted by the National Institute for Occupational Safety and Health (NIOSH), presents seven cases of conventional gas wells penetrating through longwall chain pillars in the Pittsburgh Coal Seam. The study results indicate that overburden depth and pillar size are not the only determining factors for gas well stability. The other important factors include subsurface ground movement, overburden geology, weak floor, as well as the type of the construction of gas wells. Numerical modeling was used to model abutment pressure, subsurface deformations, and the response of gas well casings. The study demonstrated that numerical models are able to predict with reasonable accuracy the subsurface deformations in the overburden above, within, and below the chain pillars, and the potential location and modes of gas well failures, thereby providing a more quantifiable approach to assess the stability of the gas wells in longwall chain pillars.

Flexural deformation controls on Late Quaternary sediment dispersal in the Garo‐Rajmahal Gap, NW Bengal Basin

AbstractSubsurface deformation is a driver for river path selection when deformation rates become comparable to the autogenic mobility rate of rivers. Here we combine geomorphology, soil and sediment facies analyses, and geophysical data of the Late Quaternary sediments of the central Garo‐Rajmahal Gap in Northwest Bengal to link subsurface deformation with surface processes. We show variable sedimentation characteristics, from slow rates (&lt;0.8 mm/year) in the Tista megafan at the foot of the Himalaya to nondeposition at the exposed surface of the Barind Tract to the south, enabling the development of mature soils. Combined subsidence in the Tista fan and uplift of the Barind Tract are consistent with a N‐S flexural response of the Indian plate to loading of the Himalaya Mountains given a low value of elastic thickness (15–25 km). Provenance analysis based on bulk strontium concentration suggests a dispersal of sediment consistent with this flexural deformation—in particular the abandonment of the Barind Tract by a Pleistocene Brahmaputra River and the current extents of the Tista megafan lobes. Overall, these results highlight the control by deeply rooted deformation patterns on the routing of sediment by large rivers in foreland settings.

In Situ Analysis of Deformation Mechanics of Constrained Cutting Toward Enhanced Material Removal

Abstract Chip formation in conventional cutting occurs by deformation that is only partially bounded by the cutting tool. The unconstrained free surface makes it difficult to determine and to control the deformation of chip formation. The constrained cutting employs a constraining tool in the cutting process to confine the otherwise free surface and enable direct control of the chip formation deformation. The presented work is a study of the deformation mechanics of plane strain constrained cutting using high-speed imaging and digital image correlation (DIC) methods. For different constrained levels (including unconstrained free cutting), the material flow of chip formation is directly observed; the strain rate and strain in the chip as well as the subsurface region are quantified; cutting forces are measured; and surface finish is examined. The study shows that chip formation in constrained cutting can occur in two different deformation modes, i.e., simple shear and complex extrusion, depending on the constrained level. Constrained cutting in the simple shear regime can reduce strain, reduce cutting force and energy, and improve surface finish compared to free cutting; therefore, it is more efficient for material removal than free cutting. Constrained cutting in the extrusion regime imposes a high resistance to the chip flow and causes a significant amount of subsurface deformation, and therefore is not suitable for material removal. Furthermore, the mechanics of chip formation in both free cutting and constrained cutting, especially the roles played by the free surface and the constraining tool, are discussed.

Shear wave velocity changes induced by earthquakes and rainfall at the Rotokawa and Ngatamariki geothermal fields, Taupō Volcanic Zone, New Zealand

SUMMARY Fluid injection for geothermal production has the potential to produce subsidence and microseismicity that can incur heavy financial cost or hazard. Due to this, novel ways to monitor subsurface deformation to supplement existing methods are highly sought after. We use seismic ambient noise to obtain time-dependent measurements of shear velocity within the geothermal reservoirs of Rotokawa and Ngatamariki, two producing geothermal fields in the Taupō Volcanic Zone located in the central North Island of New Zealand and operated by Mercury Energy. We investigate the relationship between shear wave velocity changes and geothermal injection by selecting time periods at the fields when injection and production volumes were significantly altered: 2009–2010 at Rotokawa, when geothermal injection was quadrupled due to the start-up of a new power station, and 2012–2013 at Ngatamariki, the beginning of geothermal injection for electricity production at that field. Shear wave velocity changes are computed from the ambient noise cross-correlation coda using the Moving Window Cross-Spectral (MWCS) technique, with a reference stack encompassing all data prior to the change in injection rate and moving stacks of 10–50 d. Gradual positive and negative shear velocity changes with a periodicity of approximately 12 months were observed at both sites, with maximum amplitude of 0.06 ± 0.04 and –0.08 ± 0.03 per cent at Rotokawa and 0.07 ± 0.03 and –0.06 ± 0.02 per cent at Ngatamariki. We hypothesize that these changes are due to seasonal rainfall, as seismic velocities computed by ambient noise are sensitive to the filling and emptying of near-surface pore space. In addition to these gradual responses, we found several sharp negative changes in velocity that reach minimum values over a few days and then gradually equilibrate to prior values over a few weeks. The amplitude of these responses is between –0.03 and –0.07 per cent and coincides with regional and local earthquakes. We hypothesize that these responses are primarily produced by the creation of new fractures, the same mechanism that produces gradual groundwater level decreases at regional distances from earthquake epicentres. We analyse a periodic signal within the time-delay measurements and determine that it is at least in part caused by the MWCS window size smoothing the cross-coherence of the ambient seismic signal. We do not observe shear wave velocity changes coinciding with geothermal injection, which may suggest that the signal has lower amplitude compared to the seasonal and seismic responses. We use bandstop filters and polynomial curve fitting to remove the contribution of the seasonal signal, but see no evidence of a shear wave velocity response due to geothermal fluid injection.

Grinding force and surface quality in creep feed profile grinding of turbine blade root of nickel-based superalloy with microcrystalline alumina abrasive wheels

Creep feed profile grinding of the fir-tree blade root forms of single crystal nickel-based superalloy was conducted using microcrystalline alumina abrasive wheels in the present study. The grinding force and the surface quality in terms of surface topography, subsurface microstructure, microhardness and residual stress obtained under different grinding conditions were evaluated comparatively. Experimental results indicated that the grinding force was influenced significantly by the competing predominance between the grinding parameters and the cross-sectional root workpiece profile. In addition, the root workpiece surface, including the root peak and valley regions, was produced with the large difference in surface quality due to the nonuniform grinding loads along the root workpiece profile in normal section. Detailed results showed that the surface roughness, subsurface plastic deformation and work hardening level of the root valley region were higher by up to 25%, 20% and 7% in average than those obtained in the root peak region, respectively, in the current investigation. Finally, the superior parameters were recommended in the creep feed profile grinding of the fir-tree blade root forms. This study is helpful to provide industry guidance to optimize the machining process for the high-valued parts with complicated profiles.

DVC analysis of a polymer material subjected to tensile loading with synchrotron radiation tomography

Subsurface deformation behavior of a polymeric material is studied through the digital volume correlation (DVC) technique. Fundamental principles of the DVC technique are presented and the supplemental state-of-the-art algorithmic schemes to improve the efficiency and accuracy of the DVC analysis are also introduced. Tensile tests on an epoxy material are performed in conjunction with synchrotron radiation tomography. In order to create randomly distributed grayscale values in the tomograms for the following image analysis, microscale high-density particles are embedded when the epoxy specimens are fabricated. 3D tomographic images taken at multiple loading steps are utilized for the DVC analysis. The performance of the present DVC analysis is evaluated with the experimental data.

Effect of machining processes on the residual stress distribution heterogeneities and their consequences on the stress corrosion cracking resistance of AISI 316L SS in chloride medium

The effects of machining such as grinding and turning on the microstructural and mechanical changes of the machined surfaces of AISI 316L stainless steel (SS) have been studied. Surface aspects and surface defects have been examined by scanning electron microscopy (SEM). Machining-induced nanocrystallization has been investigated by transmission electron microscopy (TEM). Surface and subsurface residual stress distribution and plastic deformation induced by the machining processes have been assessed by X-ray diffraction (XRD) and micro-hardness measurements, respectively. The susceptibility to stress corrosion cracking (SCC) has been assessed by SEM examination of micro-crack networks which are characteristics of a machined surface immersed in boiling (140 ± 2 °C) solution of MgCl2 (40%) during a 48 h-period. The machined surface properties have been correlated to severe plastic deformation (SPD) resulting from specific cutting state of each process. High cutting temperature and plastic rate are considered to be at the origin of near-surface austenitic grain refinement that leads to equiaxed nanograins with a size ranging from 50 to 200 nm. Ground surface residual stress distribution heterogeneities at the micrometric scale are attributed to the random distribution of the density and the geometry of abrasive grains that represent micro-cutting tools in the grinding process. The relationship between residual stress distribution and susceptibility of the AISI 316L SS to SCC has been demonstrated, and an experimental criterion for crack initiation has been established.