Subsurface Mechanical Properties Research Articles

A Seismic Monitoring Tool for Tidal-Forced Aquifer Level Changes in the Río de la Plata Coastal Plain, Argentina

Ambient seismic noise has gained extensive applications in seismology and plays a pivotal role in environmental seismic studies. This study focuses on the Río de la Plata Coastal Plain, employing the horizontal-to-vertical spectral ratio (HVSR) method on ambient seismic noise records to analyze subsurface dynamics. The region’s hydrogeology is complex, featuring partially interconnected coastal aquifers. The HVSR analysis reveals two peaks, with P0 associated with the sediment-basement interface and P1 linked to a shallower stratigraphic discontinuity. Temporal analysis of P1 highlights cyclical patterns correlated with estuarine levels, suggesting a relationship between variations in seismic velocities and tidal dynamics. Comparisons with aquifer data support the hypothesis that tidal variations influence subsurface mechanical properties, impacting the HVSR function. The study hints at the potential of ambient seismic noise analysis as a non-invasive and cost-effective method for studying coastal aquifers and understanding groundwater dynamics. Ongoing research aims to further explore these relationships for enhanced groundwater resource management.

Wear mechanism, subsurface structure and nanomechanical properties of additive manufactured Inconel nickel (IN718) alloy

Inconel nickel (IN718) superalloy is a cutting-edge material for high temperature applications owing to its superior mechanical properties in both cryogenic and high temperatures. Although the selective laser melting (SLM) processed IN718 superalloy has extraordinary properties, the tribological behavior of this new class of material is unclear. This study aims to explore the tribological behavior and subsurface mechanical properties of SLMed IN718 superalloy with the aid of nanomechanical and structural characterization techniques. The worn subsurface structure was revealed against the mechanical properties of the material using the ball-on-disk contact sliding test. Structural analysis confirmed that the SLMed IN718 superalloy consisted of Fe, Ni, Cr, Nb and Mo elements. EBSD analysis showed that a mixture of equiaxed and columnar grains emerged in <001>, <101> and <111> of SLMed IN718 superalloy. In-situ wear track investigations using 3D profilometer integrated tribometer revealed that its width and depth significantly increased with applied sliding load. Severe abrasive wear occurred at a low load. Under a high load, however, frictional heating brought about plastic deformation and led to increase wear in absence of any significant subsurface damages. The plastic deformation also generated shear-bands in the immediate subsurface and refined the grain structure, which significantly increased the nanohardness and elastic modulus of the deformed material layer.

The impact of free-radical stabilization techniques on in vivo subsurface mechanical properties in highly cross-linked polyethylene acetabular liners.

Highly cross-linked polyethylene (HXLPE) for total hip arthroplasty was developed to improve wear resistance in vivo and associated complications in comparison to ultrahigh molecular weight polyethylene. This material typically goes through various free-radical stabilization techniques by remelting, single-annealing, or sequentially annealing the polyethylene to improve in vivo oxidation and wear properties. The purpose of this study is to determine if there is evidence of subsurface microhardness changes in retrieved HXLPE liner at the rim and articular subsurface after extended in vivo time that could be associated with oxidation and its effects on mechanical properties and implant integrity. Retrieved HXLPE liners were chosen based on peak subsurface Fourier transform infrared spectroscopy oxidation values. Each was mechanically tested for subsurface microhardness at both the rim and articular surface using a validated microindentation technique. Rim testing demonstrated a decrease in mechanical integrity that corresponded to higher subsurface oxidation values regardless of the free-radical stabilization technique. At the articular surface, a decrease in mechanical integrity was observed near the surface corresponding to peak oxidation and Vicker's hardness, which decreased with increasing depths. This was found in all groups, with the exception of the single-annealed liners, which demonstrated decreased mechanical integrity trends at greater depths between 1.0 and 2.0 mm. Our results suggest that subsurface mechanical properties do change in vivo for certain implants. Though it is likely that the mechanical failures are multifactorial, we have shown that mechanical property degradation of HXLPE liners does occur with long-term in vivo exposure and should be considered a possible risk factor.

A review of the use of optimal transport distances for high resolution seismic imaging based on the full waveform

This study is a review of recent applications to seismic imaging of optimal transport based numerical tools. Modern seismic imaging methods used in the industry rely on the interpretation of the full signal. The characterization of the subsurface mechanical properties is formulated as a PDE-constrained optimization problem, solved through local optimization strategies. The choice of the misfit function used to measure the distance between actual seismic recordings and those synthetized by the solution of wave propagation PDE is crucial. Indeed, the conventional least-squares distance function leads to a non-convex optimization problem whose solution through local optimization then strongly depends on the initial guess. Using an optimal transport distance is an interesting alternative from its convexity properties with respect to translation and dilation. Specific strategies need however to be implemented as seismic data are oscillatory, while the optimal transport theory has been developed for the comparison of positive measures. In this study we review two optimal transport based misfit functions, from their mathematical formulation to their application to field data through their numerical implementation. Advantages and drawbacks of both strategies are discussed. Numerical experiments show that they represent two interesting and complementary alternative to the classical least-squares misfit function, mitigating the dependency to the choice of the initial guess.

On the use of nonlinear anisotropic diffusion filters for seismic imaging using the full waveform

Nonlinear anisotropic diffusion filters have been introduced in the field of image processing for image denoising and image restoration. They are based on the solution of partial differential equations involving a nonlinear anisotropic diffusion operator. From a mathematical point of view, these filters enjoy attractive properties, such as minimum–maximum principle, and an inherent decomposition of the images in different scales. We investigate in this study how these filters can be applied to help solving data-fitting inverse problems. We focus on seismic imaging using the full waveform, a well known nonlinear instance of such inverse problems. In this context, we show how the filters can be applied directly to the solution space, to enhance the structural coherence of the parameters representing the subsurface mechanical properties and accelerate the convergence. We also show how they can be applied to the seismic data itself. In the latter case, the method results in an original low-frequency data enhancement technique making it possible to stabilize the inversion process when started from an initial model away from the basin of attraction of the global minimizer. Numerical results on a 2D realistic synthetic full waveform inversion case study illustrate the interesting properties of both approaches.

Search for Infrasound Signals in InSight Data Using Coupled Pressure/Ground Deformation Methods

ABSTRACT The unprecedented quality and sampling rate of seismometer and pressure sensors of the InSight Mars mission allow us to investigate infrasound through its pressure and ground deformation signals. This study focuses on compliance effects induced by acoustic waves propagating almost horizontally close to the surface. The compliance of acoustic waves is first estimated using the compliance estimates from pressure perturbations moving at wind speed. Then, a marker of compliance events is used to detect events of ground deformation induced by pressure variations, in three frequency bands from 0.4 to 3.2 Hz, from InSight sol 180 to 690. Additional selection criteria are imposed on the detected events to focus on acoustic waves and to remove various noise sources (e.g., wind effects or seismometer artifacts). After an automated selection, the visual inspection of the records allows us to validate two infrasound candidates that cannot be related to pressure perturbations moving at wind speed nor to known noise sources. For our highest quality infrasound candidate, the relation between this event and a convective vortex occuring 10 s later is tested. The azimuth of the vortex position at the time of infrasound detection is not consistent with the arrival azimuth of the suspected infrasound inferred from the polarization of seismometer records, thus the link between these two phenomena cannot be demonstrated. Further investigations would require a better understanding of wind-related noise impacting InSight sensors and of the effects of lateral variations of subsurface mechanical properties on the ground deformations induced by atmospheric pressure variations.

On cycle-skipping and misfit function modification for full-wave inversion: Comparison of five recent approaches

Full-waveform inversion, a high-resolution seismic imaging method, is known to require sufficiently accurate initial models to converge toward meaningful estimations of the subsurface mechanical properties. This limitation is due to the nonconvexity of the least-squares distance with respect to the kinematic mismatch. We propose a comparison of five misfit functions promoted recently to mitigate this issue: adaptive waveform inversion, instantaneous envelope, normalized integration, and two methods based on optimal transport. We explain which principles these methods are based on and illustrate how they are designed to better handle kinematic mismatch than a least-squares misfit function. By doing so, we can exhibit specific limitations of these methods in canonical cases. We further assess the interest of these five approaches for application to field data based on a synthetic Marmousi case study. We illustrate how adaptive waveform inversion and the two methods based on optimal transport possess interesting properties, making them appealing strategies applicable to field data. Another outcome is the definition of generic tools to compare misfit functions for full-waveform inversion.

New geomechanical application utilizing MWD gamma ray logs: An Eagle Ford case study

Understanding mechanical rock properties is essential for optimal well placement and hydraulic stimulation design which directly impacts hydrocarbon productivity from shale reservoirs with ultra-low permeability. Current industrial practice is to assess spatial variability of subsurface mechanical properties through analyzing core and dipole sonic logs. Seismic inversion is another commonly applicable approach. However, although numerous existing approaches have contributed to upstream operators mitigating operational risk, these individual or combined evaluations ultimately require significant cost and time for exploration. These approaches also have limitations identifying fine-scale variability within inter-well spacing or along the length of a horizontal well due to sparse pilot-well control and the intrinsic limitation of seismic resolution. In this study, we propose a new approach to capture spatial variability of Young's modulus utilizing MWD (Measurement While Drilling) gamma ray logs of horizontal wells. The MWD gamma ray log is essentially acquired for the purpose of having geometric and stratigraphic information on well position while drilling in real time. And, due to cost and time related issues, shale operators commonly acquire only MWD log rather than core or wireline log set for horizontal production drilling while the massive pad drilling has the advantage of large areal coverage. Under the circumstance, MWD gamma ray log is often only data having geological implication. In purpose of utilizing MWD gamma ray log for geomechanical approaches, we examined a relationship between gamma ray and Young's modulus acquired from pilot wells. The MWD gamma ray logs were converted into Young's modulus logs and ultimately populated for three-dimensional property modeling. To validate the property model, an integrated assessment using wireline logs, microseismic, and three-dimensional seismic data was conducted. The study results demonstrate that this new geomechanical approach utilizing MWD gamma ray logs can be supportive or even serve as an alternative to the existing approaches. The method enables identification of finer-scale spatial variability than sparse pilot-well control and conventional seismic analysis, which is attributed to the advantage of long-lateral, multi-benched, staggered, and dense production well placement. Based on the reliability and cost-effectiveness of the new approach, we expect it could help upstream operators mitigate risk and uncertainty related to geomechanical properties without excessive spending for exploration and ultimately improve hydrocarbon productivity with optimal well completion strategies.

Subsurface mechanical properties and subsurface creep behaviour of modified nanoclay-based wood–plastic composites studied by nanoindentation

Wood–plastic composites (WPCs) were prepared by polypropylene, wood flour, maleic anhydride-grafted polypropylene and pristine (Na+ montmorillonite)/TMI-modified nanoclay using extruder followed by injection moulding technique. The surface mechanical properties of the nanoclay-based WPC were investigated by means of nanoindentation technique. The results show that the hardness, elastic modulus and creep resistant of the WPC dramatically enhanced with the incorporation of nanoclay. This enhancement was dependent on the nanoclay content as well as the dispersion of nanoclay in the polymer matrix. At 1 wt% nanoclay content, the hardness, elastic modulus and creep resistant of pristine nanoclay-reinforced WPC (WPC/MMT) improved by approximately 35%, 30% and 15%, respectively, compared to WPC without nanoclay. For the TMI-modified nanoclay-based WPC (WPC/MMT Cu), the improvements in these properties were about 1.2, 1.5 and 1.5 times higher than the WPC/MMT. Viscoelastic model was applied to examine the effect of nanoclay loadings on the creep performance of the WPC. Results exhibited that the model was in good agreement with the experimental data. Incorporation of nanoclay leads to an increase in elastic deformation, especially in WPC/MMT Cu, and induces a higher initial displacement at the early stage of creep.

Sub-surface mechanical properties and sub-surface creep behavior of wood-plastic composites reinforced by organoclay

Abstract Wood-plastic composites (WPC) were manufactured from polypropylene, wood flour, maleic anhydride grafted polypropylene and organoclay. The sub-surface mechanical properties and the sub-surface creep behavior of the organoclay-based WPC were examined by the nanoindentation technique. The results showed that the hardness, elastic modulus and creep resistance of the WPC enhanced with the loading of C20 organoclay. This enhancement was subject to the organoclay content and the dispersion of organoclay in the polymer matrix. The hardness, elastic modulus and creep resistance of WPC with 1 wt% organoclay content enhanced by approximately 36%, 41% and 17%, respectively, in contrast with WPC without organoclay. To study the impact of organoclay content on the creep performance of WPC, a viscoelastic model was actualized. The results demonstrated that the model was in good agreement with the experimental information. Reinforcement of organoclay prompts expansion in elastic deformation and instigates a higher initial displacement at the early stage of creep.

SWIP: An integrated workflow for surface-wave dispersion inversion and profiling

The simultaneous estimation of 2D pressure (P-) and S-wave velocities ([Formula: see text] and [Formula: see text], respectively) is a promising approach for imaging subsurface mechanical properties. It can be performed with a single acquisition setup by combining P-wave refraction and surface-wave (SW) analysis. Although SW methods are commonly applied for the 1D estimation of [Formula: see text], 2D profiling requires the implementation of specific processing and inversion tools not yet widely available in the community. We have developed an open-source MATLAB-based package that performs SW inversion and profiling (SWIP) so as to retrieve 1D to 2D variations of [Formula: see text] from any kind of linear active-source near-surface seismic data. Each step of the workflow involves up-to-date processing and inversion techniques and provides ready-to-use outputs with quality control tools. First, windowing and stacking techniques are implemented to enhance the signal-to-noise ratio and extract local dispersion images along the line. Then, dispersion curves are picked for each window with an uncertainty range in the phase velocity including higher uncertainties at low frequency. These curves are next inverted using a Monte Carlo approach with various parameterizations (e.g., user defined, refraction based). The best models are finally selected according to their fit to the data to build an average final model with a suggested investigation depth. As an example, we used SWIP to process data collected at a Yellowstone hydrothermal system. Our results show the benefits of estimating [Formula: see text] and [Formula: see text] from a single seismic setup to highlight subsurface gas pathways.

Surface modification of aluminium by graphene impregnation

In this study, graphene nanoplatelets (GNPs) were mechanically impregnated into aluminium substrates to form surface nanocomposites, which enhance the surface properties of aluminium. The impregnation was achieved by application of pressure on graphene coated aluminium plates which are locally softened by electrical resistance heating. The extent of softening of aluminium can be controlled by the process parameters current and time used for electrical resistance heating. Micro-structural characterization of the graphene impregnated aluminium surface was done through Raman spectroscopy, XRD, SEM and TEM. It was observed that GNPs were impregnated up to a depth of 200–220μm on the aluminium surface. GNPs were mostly occupied along the grain boundaries which lead to strengthening of the composite by various mechanisms. Raman spectroscopic analysis indicates a noticeable shift and change in intensity ratios of the corresponding G, D and 2D bands of the impregnated graphene. A detailed study of surface and subsurface mechanical properties was done through nano-indentation and microhardness tests. >400% improvement in surface hardness and 200% improvement in reduced Young's modulus were observed.

Nanoscale tomographic reconstruction of the subsurface mechanical properties of low-k high-aspect ratio patterns

In this work, intermittent contact resonance atomic force microscopy (ICR-AFM) was performed on high-aspect ratio a-SiOC:H patterned fins (100 nm in height and width from 20 to 90 nm) to map the depth and width dependencies of the material stiffness. The spatial resolution and depth sensitivity of the measurements were assessed from tomographic cross-sections over various regions of interest within the 3D space of the measurements. Furthermore, the depth-dependence of the measured contact stiffness over the scanned area was used to determine the sub-surface variation of the elastic modulus at each point in the scan. This was achieved by iteratively adjusting the local elastic profile until the depth dependence of the resulted contact stiffness matched the depth dependence of the contact stiffness measured by ICR-AFM at that location. The results of this analysis were assembled into nanoscale sub-surface tomographic images of the elastic modulus of the investigated SiOC:H patterns. A new 3D structure-property representation emerged from these tomographic images with direct evidence for the alterations sustained by the structures during processing.

Compound technology of manufacturing and multiple laser peening on microstructure and fatigue life of dual-phase spring steel

The present work proposes an advanced double quenching and tempering heat treatment based laser surface modification process of dual-phase spring steel. Multiple laser peening without coating process utilized the decarburized surface as the protective layer for the further cold working process. The electron backscattering diffraction analysis on crystallographic orientation of individual grains and phase map exhibits a perfect dual-phase steel. Also, the high resolution transmission electron microscopic study explains the high strain induced microstructural grain refinement features and plastic deformation behaviors. The laser peening technique taking an advantage that it induces a large and high magnitude compressive residual stress with good thermal stability. The micro and nano-hardness profile provides better surface and sub-surface mechanical properties. The controlled average surface roughness is achieved in this course of work. The stress-strain characteristics on tensile properties are analyzed through the pre-fatigued specimens. The fully reversed high cycle fatigue test indicates that the current laser peening has substantially improves the fatigue life of the specimens.

Warm laser shock peening without coating induced phase transformations and pinning effect on fatigue life of low-alloy steel

The current study proposes warm laser peening without coating process utilizing decarburized surface as the protective ablation layer and is directly intended towards the experimental evolution of existing laser shock peening technology. The interlath-retained austenites are transformed into martensites during warm laser peening. Also, the depth-wise compressive residual stress and its thermal relaxation behavior are comparatively prevailing. The scanning and transmission electron microscopic analysis identify the severe plastic deformation features of microstructures. So, the grain refinement and pinning force mechanisms on the mechanical properties are recognized. Further, the micro and nano-hardness studies provide a significant improvement in the surface and sub-surface mechanical properties. Moreover, the optimized fatigue life of low-alloy steel is achieved through the thermal engineering process. The present work increased the fatigue life of the specimen by 26 times and it is effectively repairing the partially pre-fatigued specimen.

Surface modification of Ti6Al4V alloy by pulsed Yb-laser irradiation for enhanced adhesive bonding

This work presents a comprehensive experimental study on the effect of pulsed laser ablation (Yb-fiber) on Ti6Al4V titanium alloy substrates for adhesive bonding. The modification of surface morphology and chemistry is assessed by means of SEM, XRD and wettability measurements. In addition, surface and subsurface mechanical properties are probed through an extensive series of instrumented indentation tests. Based on the results of the aforementioned analyses, a suitable processing window is identified and adhesive bonded T-peel joints are fabricated and tested. The obtained results indicate that pulsed laser irradiation can substantially improve the performance of Ti6Al4V/epoxy joints.

Evaluation of Burnished Subsurface Mechanical Behavior Using Nanoindentation

The performance and life of machined components in service are mainly effect by their surface integrity. Burnishing process is a kind of chipless processing which improve the surface integrity obviously. A subsurface “hardness film” is formed during the processing. Subsurface mechanical behavior is the main part of surface integrity. Since the very small scale of the subsurface in burnished surface nanoindentation is used to identify how the local changes of microstructure influence the hardness distributions of subsurface mechanical properties. This study focuses on the relationships between burnishing parameters (burnishing feed and burnishing depth) and nanohardness. A series of burnishing processing experiments and nanoindentation tests were conducted on the surface of the burnished samples. The microstructure and nanoindentation research results indicate that there is no visible phase transformed region in the subsurface of burnished specimens, the hardening film is larger than 4 micro meters, the nanohardness is about 2.2~3.5Gpa which depends on the burnishing parameters and distribution and position of the second phase particles, while the nanohardness in turned material is about 1.8Gpa.

Superficial severe plastic deformation of 316 LVM stainless steel through grit blasting: Effects on its microstructure and subsurface mechanical properties

The microstructure and mechanical properties of austenitic stainless steel 316 LVM (Low Vacuum Melting) blasted with either small and rounded ZrO2 particles or larger and angular shaped Al2O3 particles are analysed through magnetic force microscopy, synchrotron radiation diffraction and ultramicroindentation techniques. It is shown that blasting causes a severe plastic deformation that roughens the surface and produces a significant subsurface grain refinement and work hardening. The gradient in the plastic deformation and the volume increase associated with the deformation induced α′-martensite account for the development of compressive residual stresses with a maximum value close to the surface. All these features yield a gradient in hardness with a maximum value beneath the surface. Compared with the Al2O3 particles, the ZrO2 particles cause a higher value of compressive residual stress and a lower increase in hardness. Also, the Al2O3 particles lead to more α′-martensite formation at deeper regions from the surface than the ZrO2 particles. The different results are related with the specific morphology of the particles and their specific role in the blasting process.

Subsurface mechanical properties of polyurethane/organoclay nanocomposite thin films studied by nanoindentation

A series of the exfoliated or intercalated PU/organoclay nanocomposite thin films were prepared by in situ polymerization of polyol/organoclay mixture, chain extender and diisocyanate. The surface mechanical properties of the PU/organoclay nanocomposite films were investigated by means of nanoindentation. The results show that the hardness, elastic modulus and scratch resistant of the nanocomposites dramatically improved with the incorporation of organoclay. This improvement was dependent on the clay content as well as the formation structure of clay in the PU matrix. At 3% clay content, the hardness and elastic modulus of intercalated nanocomposites increased by approximately 16% and 44%, respectively, compare to pure PU. For exfoliated nanocomposite, the improvements in these properties were about 3.5 and 1.6 times higher than the intercalated ones. The exfoliated PU nanocomposites also had greater hardness and showed better scratch resistance compared to the intercalated ones.

Interrogations on the sub-surface strain hardening of grit blasted Ti–6Al–4V alloy

In this work we characterize the microstructural changes induced by grit blasting of the Ti6Al4V alloy and their effect on the sub-surface mechanical properties by means of micro- and ultramicro indentations techniques. It has been observed that the severe plastic deformation at the surface produces an increase in roughness. Such deformation, however, does not cause any evident hardening at the sub-surface zone, which contrast with the work hardening observed on blasted cp Ti and austenitic stainless steel 316 L. It is proposed that the different behaviour of the Ti-base alloy is related to its lower strain hardening exponent. The implications of the absence of subsurface hardening on the loss of fatigue strength observed by other authors are analysed.