Stress Variation Research Articles

A scaling relationship for the width of secondary deformation around strike-slip faults

Simple mechanical arguments suggest that slip along interlocked, rough faults, damages surrounding rocks. The same arguments require that the scale of secondary damage is proportional to the size of geometric irregularities along the main fault. This relationship could apply at all scales, but has, so far, been difficult to observe at the 10s to 100 s of km scales of large, natural faults, often because large-scale deformation is distributed across wide, complex plate-boundary fault systems, like the San Andreas Fault. The geometry and geology of another large-scale plate-boundary strike slip fault—the Queen Charlotte Fault (QCF)—is, in contrast, especially simple. Here, we show that observations of secondary deformation are well-aligned with predictions of stress variations caused by geometric irregularities along the QCF, suggesting a geometric relationship between primary fault geometry and secondary deformation. The analytic stress solution reveals that the highest stresses and highest likelihood of failure are confined to a zone of influence (ZOI) with a width quantified by ZOI=λ/2π, where λ is the wavelength of geometric variations along the main fault. This simple model is consistent with ∼100-km-scale observations along the QCF and can theoretically be used to predict the width of secondary deformation at all scales.

Optical Microscopy on Machined Surfaces in Ti-6Al-4V Reveals Pore Statistics that Correlate with Fatigue

Abstract Optical microscopy on the machined surfaces of 4-point bend fatigue samples 3D printed in Ti-6Al-4V is used to characterize pores larger than ≈15 microns. A large enough number of distinct scan speeds and fatigue tests that span the process window provides a statistically useful dataset. The variation in stress at which runouts (to 10 million cycles) are observed is anti-correlated with the pore density and the same inverse relationship exists for the maximum pore size observed within the area exposed to maximum tensile stress in each test. Total fatigue life is also anti-correlated with maximum defect size albeit with considerable scatter.

The Bend on the Haiyuan Strike‐Slip Fault Leads to Segmented Activity of the Minle‐Damaying Thrust Fault in the Qilian Shan, the Northeastern Tibetan Plateau

AbstractThe present tectonic regime of the Qilian Shan is dominated by large northeast and northwest striking strike‐slip faults and northwest striking thrust faults. Deformation distribution between the subparallel Haiyuan Strike‐slip Fault and the Minle‐Damaying Thrust Fault (MDF) is crucial for understanding the orogenic mechanism of the northeastern Tibetan Plateau. However, the uncertain kinematics of the MDF and the stress variation along the strike‐varying Haiyuan Fault inhibit further discussion of their relationship. Five key sites along the MDF were selected for analysis of terrace abandonment ages and vertical offsets to determine the slip rates. Two finite element models were constructed to calculate the stress‐strain relationship between the Haiyuan Fault and MDF. We find that the activity of the MDF can be divided into two segments by a stepover with less activity and lower terrain at the Xida River site. Shortening rates of the MDF vary between 0.2 and 2.4 mm/a since the late Pleistocene with trapezoidal trends on both fault segments. The two finite element models and GPS data reveal that the strain rates are lower at the Xida River site but higher at the Menyuan Bend on the Haiyuan Fault. We infer that long‐term strain accumulation at the Menyuan Bend may have mitigated the tectonic activity northeast to the bend under the northeastward stress field, including the activity of the MDF at the Xida River site, and resulted in the segmentation of the MDF.

Optimizing crash box design to meet injury criteria: a protocol for accurate simulation and material selection

The design of a deformation element or crash box that meets a given injury criterion based on deceleration requires careful consideration of physical properties and space requirements. Variations in material yield stress or geometry can result in statistical variations in the injury criterion output. Optimizing the crash box to fulfil two different injury criteria and two different energy levels may require more space than initially specified. In this study, we propose a protocol where the crash box is collapsed, and force–displacement is fitted to an equation. This fit is carried out with just two simulations and compared to 30 possible scenarios, obtaining a maximum error of 38.9%. With this initial fit, the appropriate thickness and yield stress can be chosen to perform crashes with two energy levels and monitor four injury values. With the ideal yield stress and sheet metal thickness, we introduce real statistical distributions using Monte Carlo design to perform 200 simulations and obtain 400 injury values for each design proposal. This technique ensures that the design will meet injury requirements for any possible combination of thickness and yield stress accepted by quality inspection. If only one simulation is performed, all designs meet the requirements, but only the last proposed design decreased the average injury to 9.2 g with a standard deviation of 2.68 g and a maximum value of 14.4 g, which is less than the required 15 g. This technique minimizes the risk of finding combinations of yield stress and thickness that produce an undesirable injury criterion.

On the contact of an absolutely rigid stamp with a half-plane taking into account static friction

Abstract The plane deformable state of an elastic half-plane into which an absolutely rigid stamp is pressed with friction is considered. It is assumed that the tangential stresses acting in the contact zone are related to normal pressure by the law of dry friction, the coefficient of which is a linear function of the coordinate of the contacting points of the contacting bodies. A determining singular integral equation for the stated problem is obtained, the solution of which is constructed in closed form. Numerical analysis is conducted, and regularities in the variation of contact stresses are determined depending on the ratios of horizontal and normal loads applied to the stamp.

Finite element simulations of thermal stress distribution in thermal barrier coatings with different mullite whisker arrangements

In recent years, thermal barrier coatings (TBCs) have been extensively employed to safeguard turbine engine blades against high temperatures and harsh operating conditions. Mullite whiskers are frequently utilized to improve the mechanical properties of ceramic matrix composites because of their exceptional characteristics. This study investigates thermal stress in coating systems by analyzing the impact of varying content, aspect ratio, and deflection angle of mullite whiskers using finite element simulations under static conditions. Results demonstrated that incorporating mullite whiskers can mitigate the sudden stress variation between the ceramic coating and the substrate. The addition of mullite whiskers reduced the maximum stress value in the coating system, thereby enhancing its thermal stability and service life. The arrangement of mullite whiskers was controlled during the preparation procedure to ensure their proper orientation. The coating system exhibited higher mechanical properties at a certain position. This study provided a theoretical basis for the design of mullite whisker–reinforced TBCs.

Unraveling Changes of Brachial Artery Residual Stress and Its Relationship to Cardiovascular Disease Risk Factors.

Arterial pressure volume index (API) offers a non-invasive measurement of brachial artery residual stress. This study investigated API distribution characteristics and correlations with cardiovascular disease risk (CVD) factors in a large Chinese population sample. This cross-sectional study surveyed a total of 7620 participants. We analyzed the relationships between API and factors influencing CVD, using regression-based stepwise backward selection and restrictive cubic spline models to express relationships as standardized beta values. Multiple linear regression analysis identified many independent factors influencing API including age, sex, body mass index (BMI), pulse pressure (PP), heart rate (HR), hemoglobin, uric acid (UA), estimated glomerular filtration rate (eGFR), triglyceride (TC), and a history of hypertension. Notably, API values increased at 33 and escalated with advancing age. Increases in API were associated with rises in PP and UA increases, particularly when PP reached 60 mmHg and the UA reached 525 units. Conversely, API was found to decrease with elevated HR and eGFR. Furthermore, there was a significant inverted U-shaped relationship between API and BMI. This study was the first to describe API distribution characteristics in a large sample of the Chinese population, providing references for evaluating API changes in the assessment of residual stress variations in diverse diseases. Notably, API displayed a U-shaped relationship with age and was closely related to traditional CVD risk factors, underscoring its potential as a non-invasive tool for risk assessment in vascular health. This research was registered with the China Clinical Trial Registration Center (Registration Number: ChiCTR2000035937).

Contribution of ankle motion pattern during landing to reduce the knee-related injury risk

BackgroundSingle-leg landing (SL) is an essential technique in sports such as basketball, soccer, and volleyball, which is often associated with a high risk of knee-related injury. The ankle motion pattern plays a crucial role in absorbing the load shocks during SL, but the effect on the knee joint is not yet clear. This work aims to explore the effects of different ankle plantarflexion angles during SL on the risk of knee-related injury. MethodsThirty healthy male subjects were recruited to perform SL biomechanics tests, and one standard subject was selected to develop the finite element model of foot-ankle-knee integration. The joint impact force was used to evaluate the impact loads on the knee at various landing angles. The internal load forces (musculoskeletal modeling) and stress (finite element analysis) around the knee joint were simulated and calculated to evaluate the risk of knee-related injury during SL. To more realistically revert and simulate the anterior cruciate ligament (ACL) injury mechanics, we developed a knee musculoskeletal model that reverts the ACL ligament to a nonlinear short-term viscoelastic mechanical mechanism (strain rate-dependent) generated by the dense connective tissue as a function of strain. ResultsAs the ankle plantarflexion angle increased during landing, both the peak knee vertical impact force (p = 0.001) and ACL force (p = 0.001) decreased significantly. The maximum von Mises stress of ACL, meniscus, and femoral cartilage decreased as the ankle plantarflexion angle increased. The overall range of variation in ACL stress was small and was mainly distributed in the femoral and tibial attachment regions, as well as in the mid-lateral region. ConclusionThe current findings revealed that the use of larger ankle plantarflexion angles during landing may be an effective solution to reduce knee impact load and the risk of rupture of the medial femoral attachment area in the ACL. The findings of this study have the potential to offer novel perspectives in the optimized application of landing strategies, thus giving crucial theoretical backing for decreasing the risk of knee-related injury.

In Situ Velocity‐Strain Sensitivity Near the San Jacinto Fault Zone Analyzed Through Train Tremors

AbstractWe utilize train tremors as P‐wave seismic sources to investigate velocity‐strain sensitivity near the San Jacinto Fault Zone. A dense nodal array deployed at the Piñon Flat Observatory is used to detect and identify repeating train energy emitted from a railway in the Coachella valley. We construct P‐wave correlation functions across the fault zone and estimate the spatially averaged dt/t versus strain sensitivity to be 6.25 × 104. Through numerical simulations, we explore how the sensitivity decays exponentially with depth. The optimal solution reveals a subsurface sensitivity of 1.2 × 105 and a depth decay rate of 0.05 km−1. This sensitivity aligns with previous findings but is toward the higher end, likely due to the fractured fault‐zone rocks. The depth decay rate, previously unreported, is notably smaller than assumed in empirical models. This raises the necessity of further investigations of this parameter, which is crucial to study stress and velocity variations at seismogenic depth.

Morphological human bone features and demography controlling damage accumulation and fracture: a finite element study

Prediction of bone fracture risk is clinically challenging. Computational modeling plays a vital role in understanding bone structure and diagnosing bone diseases, leading to novel therapies. The research objectives were to demonstrate the anisotropic structure of the bone at the micro-level taking into consideration the density and subject demography, such as age, gender, body mass index (BMI), height, weight, and their roles in damage accumulation. Out of 438 developed 3D bone models at the micro-level, 46.12% were female. The age distribution ranged from 23 to 95 years. The research unfolds in two phases: micro-morphological features examination and stress distribution investigation. Models were developed using Mimics 22.0 and SolidWorks. The anisotropic material properties were defined before importing into Ansys for simulation. Computational simulations further uncovered variations in maximum von-Misses stress, highlighting that young Black males experienced the highest stress at 127.852 ± 10.035 MPa, while elderly Caucasian females exhibited the least stress at 97.224 ± 14.504 MPa. Furthermore, age-related variations in stress levels for both normal and osteoporotic bone micro models were elucidated, emphasizing the intricate interplay of demographic factors in bone biomechanics. Additionally, a prediction equation for bone density incorporating demographic variables was proposed, offering a personalized modeling approach. In general, this study, which carefully examines the complexities of how bones behave at the micro-level, emphasizes the need for an enhanced approach in orthopedics. We suggest taking individual characteristics into account to make therapeutic interventions more precise and effective.

The increasing water stress projected for China could shift the agriculture and manufacturing industry geographically

The sustainable development of China has been challenged by the misalignment of water demand and supply across regions under varying climate change scenarios. Here we develop a water stress prediction index using a fuzzy decision-making approach, which analyzes spatiotemporal variations of water stress and concomitant effects on the populace within China. Our results indicate that water stress will increase from 2020 to 2099 under both low and high emission scenarios, primarily due to decreased water supplies like surface runoff and snow water content. Seasonal analysis reveals that annual fluctuations in water stress are mainly driven by changes in spring and autumn. Water stress is projected to be considerably lower in southeastern provinces compared to northwestern ones, where, on average, over 20% of the Chinese population could be severely impacted. These changes in water stress could lead to the north-to-south migration of the agriculture sector, manufacturing sector, and human population.

Statistical distribution of static stress resolved onto geometrically-rough faults

The in-situ stress state within fault zones is technically challenging to characterize, requiring the use of indirect methods to estimate. Most work to date has focused on understanding average properties of resolved stress on faults, but fault non-planarity should induce spatial variations in resolved static stress on a single fault. Assuming a particular stochastic model for fault geometry (band-limited fractal) gives an approximate analytic solution for the probability density function (PDF) on fault stress that depends on the mean fault orientation, mean stress ratio, and roughness level. The mean stress is shown to be equal to the planar fault value, while deviations are described by substituting a second-order polynomial expansion of the stress ratio into the inverse distribution on fault slope. The result is an analytical expression for the PDF of shear-to-normal stress ratio on 2-D rough faults in a uniform background stress field. Two end-member distributions exist, one approximately Gaussian when all points on the fault are well away from failure, and one reverse exponential, which occurs when the mean stress ratio approaches the peak. For the range of roughness values expected to apply to crustal faults, stress deviations due to geometry can reach nearly 100% of the background stress level. Consideration of such a distribution of stress on faults suggests that geometric roughness and the resulting stress deviations may play a key role in controlling earthquake behavior.

Asymmetric nanofracture in WS2 for its local toughness anisotropy

Fracture in crystal lattices usually occurs with discrete atomic bond breakages around the crack tip. WS2 involves three-layer atomic structures, where the atomic stress near the crack front exhibits thickness dependence and significantly relies on the local distortion of lattice geometry. We show that the T-stress obtained by over-deterministic methods, and the continuum circumferential stress, are limited in predicting the nanocrack kinking of WS2 strips by molecular dynamics simulations. As the far-field displacement loads, the T-stress initially increases in negative, followed by a slight jump at the initiation of kinking, and the continuum circumferential stress cannot accurately capture the variation of atomic stresses at the crack tip. This can be attributed to the local anisotropy in atomic lattices, and the crack preferentially extends in the zigzag direction of the local maximum energy release rate. Our work might provide insights into the fabrication and assembly of WS2 nanodevices.

Multiscale Simulation of Laser-Based Direct Energy Deposition (DED-LB/M) Using Powder Feedstock for Surface Repair of Aluminum Alloy.

Laser-based direct energy deposition (DED-LB/M) has been a promising option for the surface repair of structural aluminum alloys due to the advantages it offers, including a small heat-affected zone, high forming accuracy, and adjustable deposition materials. However, the unequal powder particle size during powder-based DED-LB/M can cause unstable flow and an uneven material flow rate per unit of time, resulting in defects such as pores, uneven deposition layers, and cracks. This paper presents a multiscale, multiphysics numerical model to investigate the underlying mechanism during the powder-based DED-LB/M surface repair process. First, the worn surfaces of aluminum alloy components with different flaw shapes and sizes were characterized and modeled. The fluid flow of the molten pool during material deposition on the worn surfaces was then investigated using a model that coupled the mesoscale discrete element method (DEM) and the finite volume method (FVM). The effect of flaw size and powder supply quantity on the evolution of the molten pool temperature, morphology, and dynamics was evaluated. The rapid heat transfer and variation in thermal stress during the multilayer DED-LB/M process were further illustrated using a macroscale thermomechanical model. The maximum stress was observed and compared with the yield stress of the adopted material, and no relative sliding was observed between deposited layers and substrate components.

Numerical investigation on flow-induced wall shear stress variation of metastatic cancer cells in lymphatics with elastic valves

Hematogenous metastasis occurs when cancer cells detach from the extracellular matrix in the primary tumor into the bloodstream or lymphatic system. Elucidating the response of metastatic tumor cells in suspension to the flow conditions in lymphatics with valves from a mechanical/fluidic perspective is necessary. A physiologically relevant computational model of a lymphatic vessel with valves was constructed using fully coupled fluid–cell–vessel interactions to investigate the effects of lymphatic vessel contractility, valve properties, and cell size and stiffness on the variations in magnitude and gradient of the flow-induced wall shear stress (WSS) experienced by suspended tumor cells. Results indicated that the maximum WSSmax increased with the increments in cell diameter, vessel contraction amplitude, and valve stiffness. The decrease in vessel contraction period and valve aspect ratio also increased the maximum WSSmax. The influence of the properties of the valve on the WSS was more significant among the factors mentioned above. The maximum WSSmax acting on the cancer cell when the cell reversed the direction of its motion in the valve region increased by 0.5–1.4 times that before the cell entered the valve region. The maximum change in WSS was in the range of 0.004–0.028 Pa/µm depending on the factors studied. They slightly exceeded the values associated with breast cancer cell apoptosis. The results of this study provide biofluid mechanics-based support for mechanobiological research on the metastasis of metastatic cancer cells in suspension within the lymphatics.

Influence of soil‐structure interaction on the behavior of the tower‐foundation system of a horizontal‐axis wind turbine

AbstractThe ongoing advancement of wind turbines, aiming for taller towers to harness more intense winds, poses substantial structural challenges. Soil‐structure interaction (SSI) assumes fundamental importance, necessitating precise analysis, and mathematical modeling. This study focuses on examining how SSI influences horizontal‐axis wind turbine tower‐foundation systems. Six numerical models, varying from simplified to more complex representations, are created using the finite element method (FEM) in ANSYS software. The analysis reveals significant sensitivity to support conditions, particularly elastic supports, causing the greatest displacement at the tower's top (1.899 m), highlighting the substantial influence of SSI and second‐order effects. Incorporating SSI and second‐order effects results in a 30.11% increase in von Mises stress at the base flange (73.4 MPa), compared to models excluding these factors. Stress variation along the tower height notably increases with second‐order effects; however, the structure maintains a 13.32% safety margin relative to steel load‐bearing capacity. Foundation analyses indicate stresses exceeding concrete's allowable stress by 24.3%, underscoring the need for foundation optimization. These results stress the importance of considering SSI and geometric nonlinearity for wind turbine development. The lack of comparable studies in literature underscores the significance of this research in advancing the field's knowledge.

Barrel effect of high-rate capability determined by anode for LiNi0.5Co0.2Mn0.3O2/graphite lithium-ion battery

To date, charging time remains a critical issue that impedes the widespread application of lithium-ion batteries (LIBs). A comprehensive understanding of the attenuation mechanism of LIBs at high (dis)charging rates is essential for clarifying application strategies for extreme operating conditions and environments, thereby enhancing battery control, and guiding the design of advanced batteries with superior rate capability. In line with this focus, particular commercial NCM/graphite batteries were explored under various high-rate (dis)charging procedures, alongside the investigation of the impact of constant voltage steps on battery performance. This exploration revealed that capacity degradation occurs in three stages, and the rate of capacity decay is directly proportional to the (dis)charging rate. Furthermore, the in-situ temperature and stress of the battery during cycling, primarily caused by side reactions, were monitored to confirm the thermal effects and stress variations under high-rate conditions. By characterizing the morphology and composition of the electrode surface after post-mortem analysis, the “barrel effect” of high-rate capability determined by the anode electrode for LIBs is proposed. This research aims to establish optimal guidelines for designing batteries with excellent high-rate properties and to provide solutions for improving the safety and reliability of batteries applied in high-rate conditions.

Research on Mechanism of Non-Uniform In-Situ Stress Induced Casing Damage Based on Finite Element Analysis

Casing damage is a common problem encountered during oil and gas field development due to the complex stress state of the casing. Despite the large number of studies focusing on this problem, the mechanism of non-uniform in-situ stress-induced casing damage in a low-permeability reservoir is still unclear. In this study, casing damage due to non-uniform in-situ stress variations was investigated, and then the tectonic stress coefficients in the study area were determined by an in-situ stress inversion technique, which led to the derivation of formulas for calculating the maximum and minimum horizontal in-situ stresses. Subsequently, finite element numerical simulations were performed to assess the stress distribution during the formation of the casing cement sheath in a G155 block, a typical low-permeability reservoir. The results indicate that casing damage is caused not only by non-uniform in-situ stresses but also by various additional creep-induced loads. Subsequent finite element investigations into casing behavior under mudstone creep conditions indicated that immersion of mudstone in water instigated further shearing and deformation of the casing, culminating in premature well failure prior to water inundation. Notably, Von Mises stress levels exhibited a positive correlation with injection production ratios, with values exceeding critical thresholds leading to distinct modes of mechanical failure including shear-induced deformations, longitudinal tensile stress, and localized yielding near water wells. Maintenance of an optimal injection production ratio is identified as a key strategy for prolonging casing longevity in the region. To this end, recommendations include augmenting the casing wall thickness or enhancing the steel pressure specifications to mitigate casing damage progression, thereby extending the operational lifespan. This research serves as a pivotal theoretical framework for informing future development strategies aimed at mitigating and preempting casing failures in a low-permeability reservoir.

Variations in the Thermomechanical and Structural Properties during the Cooling of Shape-Memory R-PETG.

One of the useful features of 3D-printed specimens of recycled polyethylene terephthalate glycol (R-PETG) is the ability to repetitively develop free recovery as well as the work-generating, shape-memory effect. This behavior is enabled by the R-PETG's capacity to stiffen during cooling, thus allowing for a new temporary shape to be induced. Aiming to devise an explanation for the polymer's stiffening, in this study, the variation in some of the R-PETG's parameters during cooling are emphasized and discussed. The evolution of an R-PETG filament's shape was monitored during room-temperature-bending heating-cooling cycles. Straight-shape recovery and the complete loss of stiffness were observed at the start and the end of heating, respectively, followed by the forced straightening of the filament, performed by the operator, around 40 °C, during cooling. The tests performed by dynamic mechanical analysis disclosed the rise of the storage modulus (E') after 100 °C heating followed by either liquid-nitrogen- or air-cooling to room temperature, in such a way that E' was always larger after cooling than initially. Static tests emphasized a peculiar stress variation during a heating-cooling cycle applied in air, within the heating chamber of the tensile testing machine. Tensile-failure tests were performed at -10 °C at a rate of 100 mm/min, with specimens printed at various deposition directions between 10 and 40° to the transversal direction. The specimens printed at 40°, which had the largest ultimate strains, were broken with tensile rates between 100 and 500 mm/min. Deformation rate increase favored the shift from crazing to delamination failure modes. The correlation between the structural changes, the sharp E' increase on heating, and the stiffening induced by cooling represents a novel approach that enables the use of 3D-printed R-PETG for the fabrication of the active parts of low-priced lightweight resettable actuators.

Associations between effort-reward imbalance and risk of burnout among Swedish physicians.

The high prevalence of burnout among Swedish physicians may have several possible effects on individuals and society. However, further investigations of work-related factors associated with the risk of burnout among Swedish physicians are needed. We aimed to study the associations between psychosocial work factors, based on the effort-reward imbalance (ERI) model, and the risk of burnout among Swedish physicians. A representative sample of 7200 Swedish physicians was invited in 2021. Data were gathered through questionnaires, with a response rate of 41%. Logistic regression models were used to study the associations between exposure to ERI and the risk of burnout. Approximately 62% of Swedish physicians were exposed to a high ERI. Exposure to a high ERI was associated with 11 times increased risk (95% confidence interval 6.5-20.0) of burnout in adjusted models. Large variations in the prevalence of ERI and risk of burnout across sociodemographic and occupational factors were identified, particularly across different clinical specialties. A majority of Swedish physicians were exposed to high levels of work-related stress, strongly associated with an increased risk of burnout. This population-based cross-sectional study underlines the need to further study variations of work-related stress across clinical specialties and to monitor occupational health among physicians longitudinally.