Subsurface Stress Distribution Research Articles

Contact fatigue life forecasting model considering micro-scale subsurface stress for aerospace spiral bevel gears

Focusing on stress distribution at subsurface layer under aerospace service condition in roughness tooth flank meshing interface, a new loaded contact fatigue life forecasting model is developed by considering micro-scale surface effect for aerospace spiral bevel gears. Firstly, tooth flank modeling considering the actual manufacturing process is used for accurate tooth flank point determination having high and uniform grid density. Then, with application geometric approximation and operation, discrete convolution and fast Fourier transformation (DC-FFT) based conjugate gradient (CG) method is applied to determine time-varying load distribution. While at normal direction of each point from the high-density tooth flank discretization after accurate interpolation is added the roughness height from the actual micro-scale geometric topography measurement, a tooth flank reconstruction is performed to determine the micro- scale geometric topography. Then, elastic half-space loaded contact model and DC-FFT method are employed to compute subsurface stress distribution for roughness tooth flank. Von Mises stress is selected as design variable and introduced into Zaretsky model to establish the contact fatigue life forecasting model. Finally, a spiral bevel gear set in aerospace industrial application is exercised to verify the impact of subsurface stress on contact fatigue life.

Novel application of unsupervised machine learning for characterization of subsurface seismicity, tectonic dynamics and stress distribution

Our study pioneers an innovative use of unsupervised machine learning, a powerful tool for navigating unclassified data, to unravel the complexities of subsurface seismic activities and extract meaningful patterns. Our central objective is to comprehensively characterize seismicity within an active region by identifying distinct seismic clusters in spatial distribution, thereby gaining a deeper understanding of subsurface stress distribution and tectonic dynamics. Employing a diverse range of clustering algorithms, with particular emphasis on Fuzzy C-Means (FCM), our research meticulously dissects the intricate physical processes that govern a complex tectonic zone. This technique effectively delineates distinct tectonic zones, aligning seamlessly with established seismological knowledge and underscoring the transformative potential of Artificial Intelligence (AI) in analyzing regional subsurface phenomena, even under conditions of data scarcity. Moreover, associating earthquakes with specific seismogenic structures significantly enhances seismic hazard analyses, potentially paving the way for autonomous insights that inform engineering hazard assessments.

A Systematic Review of Modeling and Simulation for Precision Diamond Wire Sawing of Monocrystalline Silicon.

Precision processing of monocrystalline silicon presents significant challenges due to its unique crystal structure and chemical properties. Effective modeling and simulation are essential for advancing the understanding of the manufacturing process, optimizing design, and refining production parameters to enhance product quality and performance. This review provides a comprehensive analysis of the modeling and simulation techniques applied in the precision machining of monocrystalline silicon using diamond wire sawing. Firstly, the principles of mathematical analytical model, molecular dynamics, and finite element methods as they relate to monocrystalline silicon processing are outlined. Subsequently, the review explores how mathematical analytical models address force-related issues in this context. Molecular dynamics simulations provide valuable insights into atomic-scale processes, including subsurface damage and stress distribution. The finite element method is utilized to investigate temperature variations and abrasive wear during wire cutting. Furthermore, similarities, differences, and complementarities among these three modeling approaches are examined. Finally, future directions for applying these models to precision machining of monocrystalline silicon are discussed.

Analysis investigation of the influence of sub-surface shear stress distribution of spur gear

Spur gears endure contact fatigue loads that can lead to surface damage on the gear teeth. Contact fatigue typically arises from dedendum during engineering and experiments, primarily caused by maximum sub-surface shear stress. This study presents a contact model incorporating profile-shift to examine sub-surface shear stress in relation to the occurrence of tooth root pits. Accurate calculations are performed to determine the distribution of sub-surface stress and meshing duration, considering various modification coefficients. The geometric cause affecting the shear stress near the tooth root is found. A deviation coefficient from base circle is proposed to analyze the influence of modification coefficient and pressure angle, which can be used in design reference. The investigation comprehensively explores the effects of profile-shift and pressure angle of spur gears on stress distribution.

An efficient 3D finite element procedure for simulating wheel–rail cyclic contact and ratcheting

Various models for simulating rail ratcheting behaviour were developed to study rolling contact fatigue (RCF) damage in rails. However, limitations remain in terms of the accuracy of wheel–rail contact modelling and computational efficiency of the cyclic loading simulation. This study developed an efficient 3D finite element (FE) procedure to simulate ratcheting in rails subjected to numerous load cycles. The procedure simulates a wheel rolling repeatedly over a rail section with updated stress–strain states, enabling automatically executed cyclic loading simulation given a predefined number of cycles. To ensure the accuracy of the contact modelling, the effect of meshing schemes on subsurface stress distribution was examined. In addition, the FE contact model with the selected meshing scheme, which balances accuracy and computational efficiency, was verified against the widely accepted CONTACT program. Subsequently, a non-linear kinematic hardening (NLKH) steel material was used in the FE model for ratcheting simulations with up to 100 wheel-loading cycles. The rail surface and subsurface stress states were replicated under partial-slip wheel–rail rolling contact conditions with traction coefficients of 0.10, 0.20 and 0.35, respectively. The ratcheting behaviour was extensively analysed in terms of plastic deformation, contact patch evolution, and ratcheting rates. The simulated plastic deformation was found to alter the contact geometry and thus contact stresses, which in turn affect further accumulation of plastic deformation and subsequent ratcheting strains. These findings highlighted the importance of considering the interplay between the rail ratcheting behaviour of the rail and evolving contact conditions for predicting ratcheting and RCF damage in rails.

A simplified spherical roller bearing model and its application in the wind turbine main bearing system finite element modeling

Different from most bearing design guidelines, deformation of bearing rings and supporting structures usually influences the bearing performance significantly. Finite element analysis (FEA) can be used in bearing system design considering the structure deformation, but the contact region between rolling elements and raceways modeling is very complex and usually causes non-convergent problems. As to a spherical roller bearing (SRB), the model must also consider both its misalignment ability and roller contact stiffness. This paper presents a simplified SRB model considering the angular misalignment ability. In order to define the SRB roller raceway load deformation relationship, a lamina model is developed. And this simplified model is validated by solid roller model of a bearing sector. A wind turbine main bearing system is analyzed using the developed SRB model. Load distribution considering the system deformation and angular misalignment are discussed. With the help of fine meshed solid elements roller raceway contact model, the raceway contact pressure and subsurface stress distribution can also be obtained.

Enhancing high-temperature fretting wear resistance of TC21 titanium alloys by laser cladding self-lubricating composite coatings

Fretting wear is one of the main factors restricting the fastener service reliability for the high-temperature titanium alloys. Enhancing the high-temperature fretting wear resistance of titanium alloys with laser cladding coatings is an effective method. Thus, in this work, a self-lubricating composite coating was designed and fabricated on the surface of TC21 titanium alloy with laser cladding. Special attentions were made to the effect of the fractions of the hard and self-lubricating phases on high-temperature fretting resistance. In addition, the contribution of laser cladding power was also concerned. The primary phases of the self-lubricating composite coatings are α-Co, CaF2, WC, TiC and Cr23C6, and the reasons for the formation of TiC and Cr23C6 are investigated from a thermodynamic point. The prepared composite coatings are dense and uniform. The crystallographic characteristics and the volume fractions of the hard phases (WC, TiC and Cr23C6) and self-lubricating phase (CaF2) were revealed, and the effect of grain size on the coating properties was analyzed. The hardness of the coatings were all maintained around 700 HV0.2, which was significantly higher than that of the substrate. The composite coating significantly improves the friction and wear resistance at 500 ℃. The hard phase was also found to be the most resistant to friction and wear. The frictional performance of the coating gets better when the hard phase and the self-lubricating phase increase. However, the hard phase contributes more to the high-temperature friction and wear resistance than the self-lubricating phase and the wear volume is 1/40 that of substrate. For the laser cladding power, the higher power can lead to a higher fraction of CaF2 but a lower fraction of hard phase, causing a decline in COF but an increase in wear volume. The wear mechanisms of the coating and the substrate were analyzed, the subsurface stress distribution state of the wear scars were further analyzed. The current results present new insights on the anti-wear design strategy to the composite coatings consist of hard and self-lubricating phase.

Stress Constraints From Shear‐Wave Analysis in Shallow Sediments at an Actively Seeping Pockmark on the W‐Svalbard Margin

AbstractMechanisms related to sub‐seabed fluid flow processes are complex and inadequately understood. Petrophysical properties, availability of gases, topography, stress directions, and various geological parameters determine the location and intensity of leakage which change over time. From tens of seafloor pockmarks mapped along Vestnesa Ridge on the west‐Svalbard margin, only six show persistent present‐day seepage activity in sonar data. To investigate the causes of such restricted gas seepage, we conducted a study of anisotropy within the conduit feeding one of these active pockmarks (i.e., Lunde Pockmark). Lunde is ∼400–500 m in diameter, and atop a ∼300–400 m wide seismic chimney structure. We study seismic anisotropy using converted S‐wave data from 22 ocean‐bottom seismometers (OBSs) located in and around the pockmark. We investigate differences in symmetry plane directions in anisotropic media using null energy symmetries in transverse components. Subsurface stress distribution affects fault/fracture orientations and seismic anisotropy, and we use S‐wave and high‐resolution 3D seismic data to infer stress regimes in and around the active seep site and study the effect of stresses on seepage. We observe the occurrence of changes in dominant fault/fracture and horizontal stress orientations in and around Lunde Pockmark and conclude minimum (NE‐SW) and maximum (SE‐NW) horizontal stress directions. Our analysis indicates a potential correlation between hydrofractures and horizontal stresses, with up to a ∼32% higher probability of alignment of hydrofractures and faults perpendicular to the inferred minimum horizontal stress direction beneath the Lunde Pockmark area.

Wear and Subsurface Stress Evolution in a Half-Space under Cyclic Flat-Punch Indentation

Wear is a tremendously important phenomenon, which takes place on the surfaces of two solids in contact under cyclic loads and constitutes one of the most-significant ways of failure for mechanical elements. However, it is not the only source of failure in contacting solids. The subsurface stresses should also be considered, due to the fatigue and crack initiation problems. Nevertheless, these stresses (i.e., their maximum values and distributions) evolve with the solids’ surface wear (i.e., with the load cycles) and also depend on the friction intensity. Therefore, their evolution should be properly computed to predict failures in mechanical elements under wear conditions. This work focused on the study of the evolution of the surface wear and the subsurface stress distributions generated—in an elastic half-space—by a cylindrical flat-ended punch, under cyclic indentation loading (i.e., radial fretting wear conditions). Based on a numerical scheme recently presented by the authors, this is the first time that, for this contact problem, the surface wear and subsurface stress distribution (i.e., maximum value and its location)—and its evolution—were simultaneously analyzed when orthotropic friction and fretting wear conditions were considered. The studies presented in this work were developed for purely elastic contact assumptions.

Analysis on the effect of starved elastohydrodynamic lubrication on the adhesion behavior and fatigue index of wheel-rail contact

Friction modifiers (FMs) are widely used in wheel-rail applications. This paper presents a method to analyze the starved elastohydrodynamic lubrication (EHL) of the wheel-rail surface coated with FMs. Combined with rough surface simulation techniques, starved EHL analysis and film thickness analysis, the pressure distribution and adhesion coefficient under different film thickness states are obtained. The effect of film thickness of the FM supply layers and surface roughness on the adhesion coefficient is studied. The adhesion coefficient increases with the decrease in the effective FM film thickness and increase in the surface roughness. Based on the subsurface stress model, the subsurface stress distribution is studied. Then the influence of FMs on the fatigue of wheel and rail is analyzed on the basis of the shakedown map. Finally, the fatigue index of rail is explored in starved EHL state.

Subsurface stress evolution under orthotropic wear and frictional contact conditions

This work presents a computational framework to study the evolution of the subsurface stresses in 3D solids under orthotropic frictional contact and wear conditions. The formulation is based on the influence coefficients methodology to relate the discrete elastic response (i.e., displacements and stresses) to the sampled excitation (i.e., surface contact tractions). The proposed methodology is validated by solving several benchmark problems and is applied to analyze how the subsurface stress distribution (i.e. maximum value and its location) – and its evolution – caused by orthotropic wear conditions are clearly affected not only by the considered wear problems (i.e., sliding wear or fretting wear) but also by the friction coefficient values and the sliding direction angle — relative to the tribological axes. Several numerical examples are presented to show the importance of these last two aspects when orthotropic wear conditions are considered. In other case, we could over- or underestimate the maximum values of the subsurface stresses during the wear process.

Soft Contact Mechanics with Gradient-Stiffness Surfaces.

The stiffness in the top surface of many biological entities like cornea or articular cartilage, as well as chemically cross-linked synthetic hydrogels, can be significantly lower or more compliant than the bulk. When such a heterogeneous surface comes into contact, the contacting load is distributed differently from typical contact models. The mechanical response under indentation loading of a surface with a gradient of stiffness is a complex, integrated response that necessarily includes the heterogeneity. In this work, we identify empirical contact models between a rigid indenter and gradient elastic surfaces by numerically simulating quasi-static indentation. Three key case studies revealed the specific ways in which (I) continuous gradients, (II) laminate-layer gradients, and (III) alternating gradients generate new contact mechanics at the shallow-depth limit. Validation of the simulation-generated models was done by micro- and nanoindentation experiments on polyacrylamide samples synthesized to have a softer gradient surface layer. The field of stress and stretch in the subsurface as visualized from the simulations also reveals that the gradient layers become confined, which pushes the stretch fields closer to the surface and radially outward. Thus, contact areas are larger than expected, and average contact pressures are lower than predicted by the Hertz model. The overall findings of this work are new contact models and the mechanisms by which they change. These models allow a more accurate interpretation of the plethora of indentation data on surface gradient soft matter (biological and synthetic) as well as a better prediction of the force response to gradient soft surfaces. This work provides examples of how gradient hydrogel surfaces control the subsurface stress distribution and loading response.

Molecular Dynamic Investigation of the Anisotropic Response of Aluminum Surface by Ions Beam Sputtering

Aluminum optics are widely used in modern optical systems because of their high specific stiffness and high reflectance. With the applied optical frequency band moving to visible, traditional processing technology cannot meet the processing precision. Ion beam sputtering (IBS) provides a highly deterministic technology for high-precision aluminum optics fabrication. However, the surface quality is deteriorated after IBS. The interaction between the bombard atoms and the surface morphology evolution mechanism are not clear, and systematic research is needed. Thus, in this paper, the IBS process for single crystal aluminum with different crystallographic orientations are studied by the molecular dynamics method. The ion beam sputter process is firstly demonstrated. Then, the variation of sputter yield of the three crystal faces is analyzed. The sputter yield difference of different crystal surfaces causes the appearance of the relief structure. Then, the gravel structure generates on the single crystal surfaces and dominates the morphology evolution. The state of the atom diffusion of the specific crystal surfaces will determine the form of the gravel structure. Furthermore, the form and distribution of subsurface damage and stress distribution of three different crystal surfaces are analyzed. Although there are great differences in defect distribution, no stress concentration was found in three workpieces, which verifies that the ion beam sputter is a stress-free machining method. The process of IBS and the mechanism of morphology evolution of aluminum are revealed. The regularity and mechanism will provide a guidance for the application of IBS in aluminum optics manufacture fields.

Molecular Dynamic Simulation of Micro-Structured Diamond Tool in Silicon Carbide Cutting

Abstract Silicon carbide (SiC) is an important material in many industrial applications. However, due to the hardness and brittleness nature, achieving ultra-precision machining of SiC is still challenging. In recent years, function surface with micro-structures has been introduced in cutting tool to suppress wear process. But the wear mechanism of the structured tool has not been revealed completely. Therefore, in present research, molecular dynamic simulations were conducted to investigate the cutting performance of the micro-structure on the nano scale cutting process of 3C-SiC. The simulation results showed that the dislocation propagation in workpiece can be suppressed with a structured tool. The micro-structures have a significant influence on the stress distribution in the workpiece subsurface. Furthermore, the abrasive wear of the structured tool is obvious smaller since the edges of the tool became blunt and the contact face between tool and workpiece changed to the close-packed plane of diamond. Moreover, the amorphization of the structured tool is effectively suppressed. This study contributes to the understanding of the material behavior involved in the ultra-precision cutting of SiC.

Experimental investigation on the subsurface stress distributions in specimens with different strengths after ultrasonic impact treatment

Experimental investigation on the subsurface stress distributions in specimens with different strengths after ultrasonic impact treatment

Modeling the effects of individual layer thickness and orientation on the tribocorrosion behavior of Al/Cu nanostructured metallic multilayers

Nanostructured metallic multilayers (NMMs) are emerging materials with excellent mechanical, tribological, and corrosion properties, making them ideal candidates to be used under extremely conditions. The high wear and corrosion resistance lead to enhanced tribocorrosion resistance of NMMs compared to many traditional metals and alloys. In this work, a multiphysics finite element model was developed to study the material deformation and degradation during tribocorrosion from wear, corrosion, as well as their synergy. Specifically, this model accounts for elastic-plastic mechanical deformation during wear and galvanic corrosion between exposed inner layers after wear. The effects of individual layer thickness (from 10 to 100 nm) and layer orientation (horizontally and vertically aligned) on the tribocorrosion behavior of Al/Cu NMMs was studied. Both factors were found to affect the subsurface stress and plastic strain distribution and localized surface corrosion kinetics, hence affecting the overall tribocorrosion rate. This model and the obtained understanding could shed light on future design and optimization strategies of NMMs against tribocorrosion.

Modeling In-situ tectonic stress state and maximum horizontal stress azimuth in the Central Algerian Sahara – A geomechanical study from El Agreb, El Gassi and Hassi Messaoud fields

Central Algerian Sahara hosts many prolific hydrocarbon accumulations in the Paleozoic successions. In this work a contemporary stress field of the Saharan platform has been evaluated using the dataset from recently drilled wells in El Agreb, El Gassi and Hassi Messaoud fields. A pore fluid pressure gradient of 0.56 PSI/feet is interpreted from the in-situ measurements in the Paleozoic reservoir units. Vertical stress (Sv) modeled from the bulk-density data indicates an average of 1.02 PSI/feet gradient. Rock elastic property-based approach is employed to model the magnitudes of minimum (Shmin) and maximum horizontal stress (SHmax) components, which were calibrated with leak off test/minifrac and breakout widths, respectively. Paleozoic stress profiles reveal Shmin/Sv range of 0.74–0.84, while SHmax/Sv varies between 1.1 and 1.33. Subsurface stress distribution indicates that the present-day stress field in the Saharan platform is principally strike-slip faulting (SHmax > Sv > Shmin). A cumulative 1490 m of B-D quality wellbore breakouts, inferred from the acoustic image logs, suggest a NW-SE/WNW-ESE SHmax orientation, which is parallel to the absolute African plate motion and Africa-Eurasia plate convergence direction, implying ridge push force to be the dominant contributor to the tectonic stress field. Mean SHmax orientation shows slightly anticlockwise rotation (126°N to 144°N) from south (El Agreb) to north (Hassi Messaoud field). Inferences are discussed regarding the fault slip potential and hydrocarbon reservoir development.

The use of FEM to evaluate the influence of logarithmic correction parameters of roller generators on the axle box bearing life

Abstract In the roller-raceway contacts of the radial cylindrical roller bearing used in the axle boxes of a railway bogie, pressure accumulation may occur, reducing the fatigue life. This accumulation can be eliminated by applying logarithmic correction of generators and in particular varieties of the modified logarithmic correction. The correction parameters should be adapted to the operating conditions of the bearing. This article presents a comparison of the predicted fatigue life of an axle box bearing on correctly selected correction parameters with bearing life, in which correction of roller generators was used, typical for cylindrical roller bearings of general application. The finite element method was used to determine the subsurface stress distributions necessary to calculate the fatigue life.

Effects of initial stress state on the subsurface stress distribution after ultrasonic impact treatment on thick specimens

Thick welded specimens with different initial stress states were prepared and treated with the ultrasonic impact treatment (UIT). The subsurface stresses before and after UIT were measured by the X-ray diffraction (XRD) method combined with layer removal. The measured results were corrected based on the finite element correction method. The effects of initial high tensile stress and low compressive stress on the in-depth after-UIT stress distributions were investigated. The results show that initial stress has no effects on the stresses induced by the UIT within 1 mm depth and within that depth, UIT can induce almost the same longitudinal and transverse stress curves beneath the surface with a peak compressive stress close to the material yield strength at the depth of near 0.6 mm and 0.8 mm. UIT induces almost the same longitudinal and transverse stresses along with the measured depth under initial low compressive stress state. While under the initial high tensile stress state, the initial stress dominates the final stress distribution over 1 mm depth. Initial high tensile stress (welding residual stress) can reduce the depth of the after-UIT compressive stresses to 62.5% to 75% of that under the initial low-compressive stress state.

Prediction of critical undeformed chip thickness for ductile mode to brittle transition in the cutting of single-crystal silicon

In order to achieve the ductile mode cutting of silicon and avoid the generation of subsurface crack damage, the undeformed chip thickness in the diamond cutting process must be controlled below the critical value. Therefore, the critical undeformed chip thickness (CUCT) for the ductile mode cutting of silicon is studied in this paper for guiding the selection of cutting parameters in the diamond cutting of silicon. Considering the anisotropy of single-crystal silicon, the prediction method of the CUCT in the ductile cutting of silicon is proposed on the basis of calculating the anisotropic fracture strength of silicon and subsurface stress distribution induced by the cutting force. Moreover, the influence of the anisotropy of single-crystal silicon, cutting tool parameters and friction coefficient in the cutting process on the CUCT are discussed, respectively. The results show that the anisotropic CUCT depends on the cutting surfaces and cutting directions. In addition, the diamond cutting tool with a negative rake angle of −40° is generally suitable for ductile cutting on the silicon (001), (110) and (111) surface when the friction coefficient in the cutting process is in the range of 0.05–0.30. Under this cutting condition, the minimum CUCT on the silicon (001), (110) and (111) surface is in the range of 150 ∼ 250 nm, 160 ∼ 290 nm and 150 ∼ 250 nm, respectively. The lower limit of the minimum CUCT on the three surfaces corresponds to the friction coefficient of 0.30 in the cutting process, and the upper limit corresponds to the friction coefficient of 0.05. Furthermore, a sharp-nosed cutting tool is also beneficial to improve the CUCT in the cutting process.