Maximum Shear Stress Research Articles

Discrete Element Modeling of Fracture Behavior and Stress Analyses in Thermal Barrier Coatings During Wear Tests

Abstract Thermal barrier coatings (TBCs) are extensively used in various industrial applications due to their high-temperature thermal insulation and environmental protection when applied to the surfaces of engine components. Wear and frictional behaviors are important when the TBCs are subject to foreign object contact. To characterize the wear performance of TBCs, this study presents an improved discrete element method (DEM)-based model to investigate the wear mechanisms induced by friction at the microscopic level. The studied TBCs consist of a ceramic top layer, a metallic bond coat, and a high-temperature nickel superalloy as the substrate, with the assumed thicknesses of 0.25 mm, 0.15 mm, and 0.8 mm, respectively. The simulation results indicate that the wear of the coating occurs in four stages: initial microcrack formation stage, particle detachment and small pit formation stage, extensive detachment and increased pit formation stage, and intensified extrusion and surface damage stage. The growth trend of crack and bonding failure energy resembles an “S” shape. The calculated coefficients of friction show a good agreement with experimental data in terms of normal force dependence. Using the Hertzian contact theory, the DEM shows that the maximum stress-induced crack formation was greatest at the contact edge. The maximum tensile stress, maximum compressive stress, and maximum shear stress increase with contact load. The shear stress distribution is entirely confined within the coating and did not significantly affect the coating substrate.

Effect of Cross-sectional Designs on Torsional Resistance of Endodontic Nickel-Titanium Files: A Finite Element Study.

This study aimed to assess the influence of two key design parameters on the torsional resistance of endodontic rotary files: the ratio of the equivalent radius (re ) to the polar moment of inertia (J), or re /J ratio, and the percentage of the inner core area. Understanding these factors can guide the development of files with improved performance during root canal procedures. Finite element analysis was employed to simulate the behavior of rotary files under torsional loading conditions. This method allowed for the investigation of maximum shear stress across various cross-sections (D4-D16) of the files. The relationship between the re /J ratio and the maximum shear stress was also evaluated. To assess the impact of cross-sectional design modifications on stress distribution, the study analyzed files with progressively changing configurations. Regions situated outside the inner core circle experienced lower shear stress compared with a circular shaft. Furthermore, a strong linear correlation was observed between the maximum shear stress experienced by the file, the applied torque during operation, and the re /J ratio. Significantly, the study established a connection between the percentage of the inner core area and the torsional resistance of the file. Files with a larger inner core area exhibited a lower coefficient (C) within a newly derived torsional formula. This lower C value directly translated to a reduction in the maximum shear stress experienced by the file. In essence, files with a higher percentage of inner core area demonstrated enhanced torsional resistance, allowing them to withstand higher torsional loads encountered during root canal procedures. This study identified the re /J ratio and the percentage of inner core area as the most critical design factors influencing the torsional resistance of rotary files. Files with a lower re /J ratio and a larger inner core area experienced lower shear stress, resulting in enhanced torsional resistance and potentially reducing the risk of torsional fracture during use. These findings offer valuable insights for both clinicians selecting rotary files and manufacturers designing future iterations, ultimately contributing to improved safety and efficacy during root canal treatments.

Quantitative polarization microscopy as a potential tool for quantification of mechanical stresses within 3D matrices.

Quantitative polarization microscopy as a potential tool for quantification of mechanical stresses within 3D matrices.

Orientation-Dependent Nanomechanical Behavior of Pentaerythritol Tetranitrate as Probed by Multiple Nanoindentation Tip Geometries

Nanoindentation can be leveraged to aid in the high fidelity modeling of dislocation mediated plasticity in pentaerythritol tetranitrate (PETN), an anisotropic energetic molecular crystal. Moreover, nanoindentation tip parameters such as tip geometry, size, and degree of acuity can be utilized to target anisotropic behavior. In this work, nanoindentation was conducted across a range of orientations on the (110) face of PETN to characterize resultant yield behavior, mechanical property measurements, and resultant slip behavior and fracture initiation. Three different indentation tips were utilized: a 3-sided pyramidal Berkovich tip, a 4-sided high aspect ratio Knoop tip, and a 90° conical tip. Ultimately, indenter tip radius was documented to impact yield behavior, whereas tip geometry affected larger scale processes such as slip, and tip acuity was the dominating factor that led to fracture. The axisymmetric conical tip, serving as a baseline, showed the least amount of variation in mechanical property measurements but also the largest distribution of maximum shear stress at which initial yielding occurred. Its high degree of acuity, however, was more prone to induce fracture at higher loads. The Knoop tip was shown to be suitable for average measurements, but also for elucidation of certain anisotropic features. A distinctly higher perceived hardness at 45° was measured with the Knoop tip, indicating less dislocation motion in that direction also observed in this work via scanning probe microscopy. Lastly, the commonly used Berkovich tip was a good compromise whereby it provided a representative volume element describing the average behavior of the material. These results can be utilized to target desired anisotropic behavior in a wider range of molecular crystals, as well as to inform theoretical considerations for dislocation mediated plasticity in PETN.

Analytical Solution for the Frictional Anisotropy of a Corrugated Fault

AbstractFault surfaces exhibit anisotropic roughness, with elongate ridges and grooves aligned in the slip direction. When inactive faults are reactivated under a new stress regime, induced by natural processes or human activities, the maximum resolved shear stress is likely to act obliquely to inherited surface corrugations increasing the fault shear strength. Analytical solutions for the shear strength of a corrugated fault, idealized as a frictional serrated surface of infinite extent separating rigid blocks under any shear stress direction, have been derived. The solutions show that the shear strength increases with increasing angle between the corrugation axes and the shear stress direction, and with fault roughness. Further, the fault slip direction may deviate significantly from the maximum resolved shear stress direction toward the corrugation axes. Finally, the reactivation potential does not only depend on stress state, fault orientation and friction, but also on surface roughness and the orientation of the corrugations.

Comparative Study of Residual Stress and Defects in Single‐Crystalline (0001) AlN Wafers by Scanning Infrared Depolarization and White‐Beam X‐ray Topography

The residual shear stress and the defect distribution in single‐crystalline c‐plane AlN wafers prepared from crystals which were grown by physical vapor transport are visualized by scanning infrared depolarization (SIRD) and compared to synchrotron white‐beam X‐ray topography (WB‐XRT) measurements. Although at lower resolution, the SIRD images resemble the defect distribution seen in WB‐XRT, which provides an order of magnitude higher spatial resolution and, in this case, enables discerning individual dislocations. For a wafer prepared from a crystal grown at high lateral temperature gradients dT (5 K cm−1), the global maximum shear stress is determined to be about 6 MPa, and both SIRD and WB‐XRT reveal a global hexagram‐shaped pattern that is formed by prismatic glide of a‐type dislocations on m‐planes while a wafer prepared from a crystal grown at low lateral dT (3 K cm−1) with a global maximum shear stress of 3 MPa does not show a similar pattern. The results are in good agreement with previous investigations that observed dislocation glide and additional cross glide in crystals with a two‐inch diameter grown at a dT of ≈5 K cm−1.

Numerical and analytical stress analysis for a FGM beam

Abstract This study investigates the importance of material selection and the material index in FGM beam stress analysis. The stress distribution in functionally graded beams (FGMBs) using, FEA, numerical methods are investigated. Three different material distribution functions are examined, power law, modified symmetric power law, and sigmoid. The maximum equivalent and shear stresses occurs for each function and at different values of the material index (k) are considered. Overall, the study emphasizes the importance of material distribution function selection and material index values in determining the stress distribution and behavior of FGM beams. The study uses ANSYS 2020 for numerical analysis. The material properties of aluminum and alumina are used for the FGM beam. The results indicate that power law functions has a higher stress compared to modified symmetric power law. The best formula can be used in making FGM is modified symmetric power law as it produce minimum equivalent and shear stresses in comparison with the other formulas. The value of the material index (k) significantly affects the magnitude of both shear and equivalent stress for power law, modified symmetric power law only. The value of the material index (k) significantly influences the magnitude of both shear and equivalent stress.

Optimization of Hybrid Composite-Metal Joints: Single Pin.

Deepening the understanding of composite and metal joint methodologies applied in the aerospace industry is crucial for minimizing operational expenditures. Current investigations are focusing on innovative joining techniques that incorporate additive manufactured rivet pins. This research aims to analyze the mechanical strength of these joints for the effective optimization of pin profiles. Through extensive study of the impact of pin geometry on joint performance, we derived the optimal pin design, considering various initial parameters with the objective of minimizing stress concentration in the pin structure. The joint configurations of metal to composite interfaces were systematically examined using finite element analysis and lap shear testing, which included a singular pin and an adhesive-bonding layer. Numerical simulations reveal that the maximum shear stress in the pin is located at the junction between the base of the pin and the metal plate. By optimizing the shape and dimensions of the pin, both the shear and axial stresses can be significantly mitigated. Following the numerical optimization process, a series of enhanced pins have been produced via additive manufacturing techniques to facilitate mechanical testing. The experimental data obtained align closely with the simulation results, thereby reinforcing the validity of the optimization. The optimal configuration for a single pin, involving a 60° angle and a total height of 3.43 mm, achieves the minimum shear stress. Based on these findings, further investigations are underway to explore optimized designs utilizing multiple pins. This paper presents the results of the single pin study, whereas the findings pertaining to the ongoing investigation on the multi-pin configuration will be disseminated in subsequent publications.

The formation of cave scallops

We present a mathematical model for the formation of scallops in ice or limestone caves. The mechanism in each case is similar, and is opaquely related to the mechanism for the formation of dunes and drumlins. Turbulent fluid flow over a wavy bed induces a shift of the maximum bed shear stress upstream of the maximum elevation of the bed. The resulting enhanced shear rate causes enhanced melting or dissolution as appropriate upstream, and this causes an instabilty, which takes the form of a travelling wave. Nonlinear evolution of the waves requires a description of flow separation, and this is empirically accommodated in the model by allowing the melt or dissolution rate to depend on the slope angle of the interface. The resulting model predicts the formation of the cusps which are observed.

Transiently propagating crack tip fields in anisotropic functionally gradient materials

Transiently propagating crack tip fields in anisotropic functionally gradient materials

Numerical analysis of the three-dimensional model of pulsatile and non-Newtonian blood flow in a carotid artery with local occlusion

The analysis of blood flow in blood vessels, particularly in arteries, is a topic with important clinical applications. The blood can undergo a reduction in its viscosity under shear stress, which is called shear thinning. In this study, the effect of the shear thinning of blood is simulated using the Carreau-Yasuda model, neglecting the viscoelastic effects. The purpose of this investigation is to analyze the pulsatile blood flow in a three-dimensional model of the carotid artery and the effects of occlusion using Ansys Fluent. The results obtained in this study show that, compared to Newtonian fluids, non-Newtonian fluids exhibit significant differences in secondary flow patterns and shear flow behavior. Additionally, the axial velocity in the non-planar branch decreases with obstruction. The maximum shear stress of the walls with Newtonian fluid viscosity exhibits a significant error, and the values are lower than those of walls with non-Newtonian viscosity in most cases. In continuation of this research, vessel occlusion models with different occlusion sizes are analyzed. In the case where the outlet of the vessel is narrowed, an increase in velocity is observed in the furcation area. Although the software cannot simulate rupture, occlusion of the vessel at 80\% and 50\% of the internal diameter is analyzed.

Investigation on the influence of crystal orientation on the fatigue characteristics of thin-walled specimens with varying bending angles of nickel-based single-crystal alloys with film cooling hole

Abstract In this paper, nickel-based single crystal thin-walled specimens with different bending angles were designed. The effect of crystal orientation on the fatigue properties of thin-walled specimens with film cooling hole at 900 °C was investigated by using crystal plastic slip theory. The results show that the Mises stress around the film cooling hole under three crystal orientations [001], [011] and [111] is concentrated in the vertical loading direction, forming four banded stripes, and the order of maximum Mises stress is [111] > [011] > [001]. The change of crystal orientation leads to the difference of stress distribution and stress gradient, and the stress gradient increases with the increase of curvature. The distribution of maximum shear stress under different crystal orientations is different, and the change of bending degree does not affect its direction distribution. In addition, the activation of the octahedral slip system around the film cooling hole under different crystal orientations was analyzed. It was found that the number of octahedral slip systems activated by [001] and [011] orientations was the same, while the number of octahedral slip systems activated by [111] orientation was less.

Mixed-Mode Crack Growth Behavior of Compact Tension Shear (CTS) Specimens: A Study on the Impact of the Fatigue Stress Ratio, Loading Angle, and Geometry Thickness.

The majority of engineering structures are subjected to intricate loading scenarios or possess intricate geometries, resulting in a mixed-mode stress within the component. This study aims to investigate the fracture behavior of these components under mixed-mode loading conditions by examining the relationship among the fatigue stress ratio (R), loading angle, and geometry thicknesses in compact tension shear (CTS) specimens. Using advanced ANSYS simulation techniques, this research explores how these factors affect the fatigue life cycles of engineering materials. To simulate real-world loading scenarios and study various mixed-mode configurations, compact tension shear (CTS) specimens were subjected to three specific loading angles: 30°, 45°, and 60°. These angles were applied in combination with various stress ratios (0.1-0.5) to capture a wide range of loading conditions. This study employed ANSYS Workbench 19.2, featuring cutting-edge technologies such as separating, morphing, and adaptive remeshing (SMART), to precisely model crack growth, calculate fatigue life, and analyze stress distribution. A comparative analysis with experimental data revealed that the loading angle has a profound effect on both the trajectory of fatigue crack growth (FCG) and the number of fatigue life cycles. The results demonstrate that the loading angle significantly influences the trajectory of FCG and the number of fatigue life cycles. Specifically, a loading angle of 45 degrees resulted in the maximum principal and shear stresses, indicating a state of pure shear loading. The findings reveal critical insights into the interaction between stress ratios, geometry thicknesses, fatigue life cycles, and loading angles, enhancing the understanding of engineering components' behavior under mixed-mode stress situations.

Experimental, Analytical, and Numerical Analyses of Slurry Erosion Resistance of Austenitic 1.4301 Stainless Steel

Abstract The degradation of 1.4301 (AISI 304, X5CrNi18-10) stainless steel with two different impact angles (30 deg and 90 deg) has been investigated using a slurry pot tester. Spherical solid particles were used in the experiment. The impact angle significantly influenced the erosion resistance of 1.4301 steel. Tests conducted at an impact angle of 30 deg showed a higher erosion rate of approximately 91%. The test results showed that with a normal impact angle, the final and subsurface hardness were higher. Numerical analyses of contact stresses were carried out based on Hertz's theory. The calculation results were compared with the simulation results, showing a low error level (0.70–4.63%), depending on the analyzed parameter, i.e., Hertzian stress or maximum shear stress. The numerical results confirm the significant dependence of the erosion resistance on the impact angle. It has been found that the tallest peak height decreased with increasing hardness and impact angle. Scanning electron microscopic analysis showed that after the erosion tests, indentations, craters, microcutting, and microploughing were observed.

Numerical modelling investigation of finite‐amplitude subaqueous dune saturation

ABSTRACTObservations of bedform development under various flow conditions show that an initially flatbed evolves through different phases leading to a fully developed dune field. However, the mechanisms limiting dune growth in flows with limited depth and suspended sediment transport are not fully understood. This paper presents a novel methodology to characterise the evolution of phase shifts in bed shear stress and sediment flux maxima in relation to finite‐amplitude bedform crests, using a 2D Reynolds‐averaged Navier–Stokes model (RANS) to simulate dune profile evolution. Our results indicate that increasing both profile wavelength and height enhances turbulent mixing, thereby reducing flow inertia and decreasing the phase advance of bed shear stress. We then demonstrate that increased turbulent kinetic energy levels entrain significant amounts of suspended sediment in the water column, eventually leading to profile saturation at specific parameter thresholds. This research sheds light on important mechanisms controlling the equilibrium dimensions of finite‐amplitude dunes. The various saturation modes presented in this paper provide deeper insights into the diverse dune profiles found in nature.

Structural and Rheological Properties of Modified Water Yam Starch Through Partial Hydrolysis and Retrogradation for Enhanced Functional Applications

Water yam starch, distinguished by its high amylose content and small granule size, presents significant potential for diverse industrial applications through targeted structural modifications. This study systematically examined the combined effects of partial acid hydrolysis and retrogradation on the structural and rheological properties of water yam starch to enhance its functional utility. Acid hydrolysis resulted in a reduction of starch chain length, as indicated by increased reducing power, while subsequent retrogradation facilitated molecular re-association, leading to an increase in relative crystallinity. X-ray diffraction analysis confirmed these structural transformations, revealing diminished peak intensities in hydrolyzed starch and enhanced crystallinity in retrograded samples. Rheological assessments demonstrated substantial alterations in pasting behavior due to these modifications. Hydrolysis lowered pasting and peak temperatures while increasing peak and final viscosities, whereas retrogradation further influenced these parameters, similarly reducing pasting and peak temperatures while enhancing viscosity profiles. All modified starches exhibited Herschel-Bulkley (pseudoplastic) fluid, with retrograded samples displaying lower maximum shear stress compared to hydrolyzed counterparts. Oscillatory rheometry revealed predominantly viscous behavior across all samples (loss modulus exceeding storage modulus), though select modifications contributed to increased elasticity. These findings underscore the efficacy of controlled hydrolysis and retrogradation in precisely tuning the physicochemical properties of water yam starch, yielding materials with thixotropic behavior and adjustable viscosity. The results highlight the potential of modified water yam starch for applications in food, pharmaceuticals, and biodegradable packaging, emphasizing its versatility as a sustainable and functional biopolymer.

Safety Analysis of Agricultural Implement for Mulching and Soil Covering

In recent years, the increasing use of mulching in agricultural practices has been driven by its benefits in weed suppression, soil moisture retention, and improved soil structure. However, Korean farms typically perform mulching and soil covering separately, leading to excessive labor requirements. To address this issue, this study analyzes the safety of a newly developed mulching and soil covering machine. To evaluate its structural safety, strain gauges were attached to critical points of the machine, and strain data were collected under various Power Take-Off (PTO) and engine speed conditions. The measured strain was converted into von Mises stress and maximum shear stress, and the safety factor was calculated using the maximum shear stress theory and the strain energy theory. Additionally, fatigue life was predicted using the rainflow counting method, the Goodman equation, and Palmgren–Miner’s rule. The results indicate that the safety factor ranged from 1.65 to 16.54 based on the maximum shear stress theory and 2.42 to 19.83 based on the strain energy theory, confirming that the machine can withstand operational loads without failure. Furthermore, fatigue life prediction revealed that the lowest estimated fatigue life is 14,575 h, equivalent to approximately 607 years of continuous use. These findings demonstrate that the developed machine possesses high safety, making it a viable solution for improving efficiency in mulching and soil covering operations.

A combined 4D flow MR imaging and fluid-structure interaction analysis of ascending thoracic aortic aneurysms.

This study aimed to characterize the altered hemodynamics and wall mechanics in ascending thoracic aortic aneurysms (ATAA) by employing fully coupled two-way fluid-structure interaction (FSI) analyses. Our FSI models incorporated hyperelastic wall mechanical properties, prestress, and patient-specific inlet velocity profiles (IVP) extracted from 4D flow magnetic resonance imaging (MRI). By performing FSI analyses on 7 patient-specific ATAA models and 6 healthy aortas, the primary objective of the study was to compare hemodynamic and biomechanical features in ATAA versus healthy controls. A secondary objective was to examine the need for 4D flow MRI-derived IVP in FSI simulations by comparing results with those using two commonly adopted idealized IVPs: Flat-IVP and Para-IVP for selected cases. Our results show that, compared to the healthy aortas, the ATAA models exhibited highly disturbed blood flow in the ascending aorta. Consequently, maximum turbulent kinetic energy (TKE) at peak systole (155.0 ± 188.4Pa) and maximum time-averaged wall shear stress (TAWSS) (8.6 ± 6.5Pa) were significantly higher in the ATAA cohort, compared to 0.6 ± 0.5Pa and 2.8 ± 0.7Pa in the healthy aortas. Peak wall stress was also nearly doubled in the ATAA group (414 ± 108kPa vs. 215 ± 31kPa). Additionally, comparisons of simulation results across models with different IVPs underscore the importance of prescribing 3D-IVP at the inlet, especially for ATAA cases. Using idealized IVPs in two selected ATAA models (P1 and P7) substantially reduced the maximum TKE from 571Pa to 0.01Pa (Flat-IVP) and 0.02Pa (Para-IVP) in P1 and from 73Pa to 0.01Pa (Flat-IVP) and 0.08Pa (Para-IVP) in P7, while the maximum TAWSS in the ascending aorta decreased from 9.6Pa to 0.7Pa (Flat-IVP) and 0.9Pa (Para-IVP) in P1, and from 3.6 Pato 1.2Pa and 0.9Pa, respectively, in P7. Moreover, idealized IVPs also caused the peak wall stress to reduce by up to 11.5% in P1 with severe aortic valve stenosis, and by up to 2% in P7 with mild aortic regurgitation. These results highlight the importance of FSI simulations combined with 4D flow MRI in capturing realistic hemodynamic and biomechanical changes in aneurysmal aortas.

Consistency assessment of tissue-level brain injury criteria in FEHM

Tissue-level brain injury criteria are essential for analyzing brain injuries using finite element head models (FEHMs), but their consistency remains unclear. This study applied the data-driven method previously proposed for maximum principal strain (MPS) injury criterion to determine thresholds for von Mises stress (VMS), pressure, maximum shear stress (MSS), and the rate of MPS. It then assessed the consistency of these criteria in terms of injury status, injury location, and injury overlap rate in 18 impact simulations. The results showed that the MPS, VMS, and MSS criteria had strong consistency, enhancing the utility of FEHMs in clinical brain injury analysis.

The deformation and stress mechanism of water conveyance tunnel crossing strike-slip fault

Based on the Xianglushan water conveyance tunnel of the central Yunnan water diversion project, a large-scale finite element numerical model was established to study the lining deformation and failure mechanism of the Xianglushan water conveyance tunnel under the action of strike-slip faults. The lining damage law of the tunnel was revealed and the corresponding fortification position was proposed. The results show that the displacement distribution of cross-fault tunnel under the action of strike-slip fault generally presents an elongated S-shaped distribution. In the fault fracture zone, the tensile failure is prevented at the arch waist convex from the fault dislocation surface, and the compressive failure is prevented at the concave. The range of compressive and tensile strains is mainly concentrated in the fault fracture zone ± 0.6 times of the width of the fault zone. The shear damage of the top and bottom of the tunnel is relatively close. Therefore, combined with the strain distribution law of the left and right side walls of the tunnel and the maximum shear stress distribution law of the top and bottom of the tunnel, it is considered that the left and right side walls located in the fault fracture zone should prevent tensile and compressive failure, and the top and bottom of the tunnel should prevent shear failure. The results of this study can provide a theoretical reference for the key vulnerable parts of the tunnel.