Stress Contours Research Articles

Investigation on the biaxial stretching deformation mechanism of PA6 film based on finite element method

Abstract This study employed the finite element method to investigate the biaxial stretching deformation mechanism of polyamide 6 (PA6) Film. First, the PA6 film was subjected to biaxial stretching experiments under various conditions. Then, a three-dimensional finite element model of PA6 film was established. The biaxial stretching experiments of PA6 films under various conditions were simulated by the established finite element model. The results show that the biaxial stretching of the films under various conditions exhibited a transition from elastic deformation to plastic deformation. Meanwhile, as the stretching ratio increases, the more uniform stress and strain distribution on the film surface can be found in the stress and strain contour diagrams. The stress and strain distributions were found to be largely consistent under various annealing temperatures. However, lower stretching rates resulted in higher internal stress intensity, making the films more resistant to biaxial stretching. The findings of this study provide a theoretical reference for a deeper understanding of the deformation mechanisms of PA6 films during the biaxial stretching process.

Influence of physiological conditions on hemodynamics of internal carotid artery aneurysms

This study investigates the influence of body physiology on the rupture risk of cerebral saccular aneurysms. Comprehensive hemodynamic analyses were conducted using computational fluid dynamics to assess the potential for aneurysm rupture under three physiological conditions: rest, normal activity, and exercise. Contours of wall shear stress, oscillatory shear index, and pressure were analyzed and compared to identify regions at high risk of rupture. Additionally, statistical analysis was performed to evaluate the rupture risk of aneurysms. Blood flow dynamics during the peak systolic phase were also examined under these conditions. Our findings indicate that the dome area, where blood pressure is highest and the incoming blood flow first contacts the aneurysm sac, is the critical region with a heightened risk of rupture.

Influence of connection design and material properties on stress distribution and fatigue lifetime of zygomatic implants: A finite element analysis

Zygomatic implants (ZIs) were developed as a graftless alternative to rehabilitate severely reabsorbed maxillae. This study aims to employ three-dimensional finite element analysis (FEA) to simulate the impact of external hexagonal implant connection (EHC) and internal hexagonal implant connection (IHC) on the stress distribution and fatigue lifetime within the ZI systems using parameters defined in ISO 14801:2016. Two ZI assemblies (Nobel Biocare and Noris Medical) were scanned in a micro-CT scanner and reconstructed using Nrecon software. Three-dimensional models were generated by Simpleware ScanIP Medical software. All models were exported to FEA software (ABAQUS) and subsequently to a fatigue analysis software (Fe-safe). A compressive 150 N load was applied at a 40° angle on the cap surface. A 15 Hz frequency was applied in the in silico cyclic test. The implant components had material properties of commercially pure grade 4 titanium (CPTi) and Titanium-6Aluminum-4Vanadium alloy (Ti64). Von Mises stress data, contour plots, and fatigue limits were collected and analyzed. EHC models exhibited higher peak stresses in implant components for both materials compared to IHC models. However, simulated bone support results showed the opposite trend, with higher stresses on IHCthan EHC models. The fatigue analysis revealed that assemblies with both designs exceeded ISO 14801:2016 number of cycles limits using Ti64, while CPTi groups exhibited comparatively lower worst life-repeats. In conclusion, ZIs with IHC were found to have a more homogeneous and advantageous stress distribution within both materials tested. Ti64 demonstrates a prolonged service life for both design connections.

Determination of mining-induced stress based on mining face hydraulic support stress and micro-seismicity

Understanding dynamic visualization of mining-induced stress is of great significance to disaster prevention and control in coal mining activities. In this study, three theoretical models, including linear, polynomial, and exponential models, are proposed to inverse the mining-induced stress through the acquisition and analysis of hydraulic support stress and micro-seismicity in the coal mining face. The distribution of mining-induced stress in the coal seam are graphed by fitting two key stress parameters including hydraulic support stress and peak stress, and two key zones including goaf zone and in situ stress zone. These key stress parameters and zones are defined based on the critical nodes of the model curve. According to the geological background of Mataihao coal mine in Erdos, Inner Mongolia Autonomous Region, China, the contours of mining-induced stress are graphed through the stress calculation of these three inversion theoretical models. The multi-monitoring data of micro-seismicity, drilling chips, advanced borehole stress and bolts axial force are used to verify the key stress parameters and zones of the theoretical models. It shows that the monitoring data are in good agreement with the distribution of inversed results. It should be emphasized that, if the fault structure exists around the mining face, the mining-induced stress decreases obviously when the mining face is passing through the faults, and the location of the peak stress will be closer to the mining face. The results in this study could provide methods for early prevention of extreme mining-induced stress and disaster control in the mining activities.

Computational design of auxetic microstructures via stress-based topology optimization

Material design plays a pivotal role in industries dedicated to lightweight manufacturing. In response to the needs of such industries, topology optimization (TO) has evolved beyond structural optimization to include designing material microstructures for improved structural performance. While conventional approaches often prioritize stiffness-oriented designs as a foundational aspect of structural integrity, it is equally imperative to emphasize strength-based design principles to ensure robustness against localized stress concentrations and potential failure modes. This paper explores the application of stress-constrained topology optimization (SCTO) for designing auxetic microstructures. The study commences with a comprehensive parametric analysis to examine the influence of the P-norm parameter, variations in volume fraction, and initial design adjustments on the resulting microstructures. Several optimized structures, accompanied by stress contours, are generated to showcase how the optimization process responds to these parameters. The approach employs the density-based solid isotropic material with penalization material interpolation scheme, and it utilizes the stress penalization technique to mitigate the singularity phenomenon. The multi-constraint optimization employs the method of moving asymptotes algorithm to update design variables. The effectiveness of the proposed approach to utilize actual strain fields, derived from macroscopic finite element analysis under service loads, for TO of an auxetic microstructure according to strength requirements is demonstrated. The application of the designed microstructure is explored through its integration into an auxetic cushion pad. This analysis confirms the microstructure’s effectiveness in practical applications, demonstrating its potential for broader usage in similar applications.

Hysteretic behavior optimization of hollow laminated viscoelastomer-filled steel tube damper

This study proposes a shape optimization approach for designing hollow laminated viscoelastomer-filled steel tube dampers (HLVSTDs), aiming to reduce stress concentration, enhance energy dissipation capacity, and improve low-cycle fatigue performance. The shape optimization curve is obtained based on the definition of stress contours for HLVSTD bending moments and shear forces, with the assumption that points on the same contour yield simultaneously. Cyclic loading experiments were conducted on four HLVSTDs. Numerical models were established and validated to further investigate the mechanical properties, energy dissipation capacity, and seismic performance of the shape-optimized HLVSTDs. The results demonstrate that the shape-optimized HLVSTDs specimen exhibits excellent energy dissipation capacity and improved low-cycle fatigue performance. The calculated initial stiffness and yield force closely align with experimental values. Compared to non-optimized HLVSTDs, the shape-optimized HLVSTDs exhibit more uniform stress and equivalent plastic strain distributions, effectively reducing the concentration of plastic strains. Additionally, structures equipped with shape-optimized HLVSTDs demonstrate superior seismic performance.

Influence of solvent viscosity ratio on the creeping flow of viscoelastic fluid over a channel confined circular cylinder

In this study, the role of solvent viscosity ratio (β) on the creeping flow characteristics of Oldroyd-B fluid over a channel-confined circular cylinder has been explored numerically. The flow governing equations have been solved by RheoTool, an open-source toolbox based on OpenFOAM, employing the finite volume method for extensive ranges of Deborah number (De=0.025–1.5) and solvent viscosity ratio (β=0.1–0.9) at a fixed wall blockage (B = 0.5). The present investigation has undergone extensive validation, with available literature under specific limited conditions, before obtaining detailed results for the relevant flow phenomena, such as stream function, pressure and stress contour profiles, pressure coefficient (Cp), wall shear stress (τw), normal stress (τxx), first normal stress difference (N1), and drag coefficient (CD). The flow profiles have exhibited a distinctive behavior characterized by a loss of symmetry in the presence of pronounced viscoelastic effects. The results for low De notably align closely with those for Newtonian fluids, and the drag coefficient (CD) remains relatively constant regardless of β, as the viscoelastic influence is somewhat subdued. These observations indicate that at high De and low β, viscoelasticity causes asymmetry in creeping flow around a circular cylinder. With an increase in De, the maximum velocity in gap between cylinder and channel walls increases; however, the cylinder experiences significantly less drag force. Within this parameter range, the prevailing force governing the flow is the pressure drag force.

Effects of periodic sequential arrangement of subscale miura-foldcore under quasi-static compression

This study presents experimental and numerical investigations on the quasi-static compressive responses of various subscale Miura-foldcore composites. A series of quasi-static compression tests were conducted on standard Miura foldcore specimens fabricated using carbon/epoxy woven fabric prepregs. Representative volume element (RVE) models, incorporating periodic boundary conditions (PBCs), were developed to predict the size-dependent compressive response of subscale Miura foldcores. The effective properties of the carbon/epoxy woven fabric composite used in this study were calculated using the NASA multiscale analysis tool (NASMAT) via two-step homogenization process. The FE model exhibited comparable agreement with experimental results, showcasing variations of less than 7% and 12% in maximum compressive load and compressive stiffness, respectively. The implementation of PBC in the foldcore RVE models improved modeling accuracy by <4%, but drastically increased total computational time (>50%). The periodic pattern of foldcore unit-cells, where two single foldcore unit-cells were placed in parallel or perpendicular, imposed geometric constraints, resulting in small variations in predicted stress and strain distribution contours. The key findings highlighted in this study suggest that a 1 × 1 foldcore unit-cell model without PBC is sufficient to predict accurate quasi-static compressive responses of foldcore composites. This study advances the understanding of subscale Miura-foldcore composites and provides valuable insights into the limitations associated with the use of PBC in foldcore RVE models. The findings also offer a practical guide for fabricating and analyzing traditional Miura folding patterns, promoting a more efficient and accurate approach for optimizing foldcore composite designs considering both structural performance and manufacturability.

A semi-analytical simulation method for bi-directional functionally graded cantilever beams under arbitrary static loads

This paper presents a novel semi-analytical simulation approach for analysing the behaviour of bi-directional functionally graded cantilever beams subjected to arbitrary static loads, such as concentrated moments, concentrated forces, distributed force and their combinations applied at any location along the beam. The fundamental equations governing the cantilever beam’s response are derived, on the basis of which the proposed semi-analytical method is implemented using MATLAB programming language. The simulation results include field variables as well as stress contours, providing a compressive understanding of the beam’s behaviour. To validate the accuracy and reliability of the proposed method, a convergence study is conducted in comparison with the graded finite element method (GFEM) and analytical solutions. In the end, the developed method is applied to simulate the bending behaviour of bi-directional functionally graded cantilever beams under various loads individually and their combinations. The stress contours and deflection curves obtained from the simulation are compared with the solutions obtained using GFEM, revealing that the developed method possesses excellent capability in accurately simulating the bending behaviour of cantilever beams.

Structural Design Analysis Torque Links of Nose Landing Gear on Light Aircraft

Torque links are components of Nose Landing Gear on the designed lightweight aircraft, that connect between the inner and outer cylinders of an oleo-pneumatic shock strut. They prevent torsion or twisting between those components and vibrations at retractable nose landing gear, the safety of these components is very important, especially when landing aircraft. This paper studies the stress and deformation contours of the torque link design with variations of hole geometry to get the optimal design, with the lightest possible weight but still reliable and safe. The upper torque link is modeled as a simply supported beam with a moment on one end derived from impact force when landing. Maximum bending stresses occur in areas near holes and the connection part of the torque link. This analysis with a tetra mesh by changing the hole position and geometry. The final torque link design results in a weight reduction of up to 23.75% with a maximum stress is 157.4 MPa and displacement is 0.0166 mm. Torque link design optimization results are then modally analyzed, and four natural frequencies and the mode shape are done. The natural frequency of vibration of different mode shapes obtained ranges from 4.2259 kHz to 6.1319 kHz, and this is still below the limit of 0.1 kHz (around 6,000 rpm engine). Finally, the optimal design torque links were obtained, safe from static and dynamic loads with a Factor of Safety 1.78 (>1.5) according to the FAR-23 standard.

Numerical investigation of LDL nanoparticle collision in coronary artery grafts with porous wall and different implantation angles and two state of inlet velocity.

This study aimed to reduce the risk of graft occlusion by evaluating the two-phase flow of blood and LDL nanoparticles in coronary artery grafts. The study considered blood as an incompressible Newtonian fluid, with the addition of LDL nanoparticles, and the artery wall as a porous medium. Two scenarios were compared, with constant inlet velocity (CIV) and other with pulsatile inlet velocity (PIV), with LDL nanoparticles experiencing drag, wall-induced lift, and induced Saffman lift forces, or drag force only. The study also evaluated the concentration polarization of LDLs (CP of LDLs) near the walls, by considering the artery wall with and without permeation. To model LDL nanoparticles, the study randomly injected 100, 500, and 1000 nanoparticles in three release states at each time step, using different geometries. Numerical simulations were performed using COMSOL software, and the results were presented as relative collision of nanoparticles to the walls in tables, diagrams, and shear stress contours. The study found that a graft implantation angle of 15° had the most desirable conditions compared to larger angles, in terms of nanoparticle collision with surfaces and occlusion. The nanoparticle release modes behaved similarly in terms of collision with the surfaces. A difference was observed between CIV and PIV. Saffman lift and wall-induced lift forces having no effect, possibly due to the assumption of a porous artery wall and perpendicular outlet flow. In case of permeable artery walls, relative collision of particles with the graft wall was larger, suggesting the effect of CP of LDLs.

Coronary hemodynamic simulation study.

In this paper, a two-way fluid-structure coupling model is developed to simulate and analyze the hemodynamic process based on dynamic coronary angiography, and examine the influence of different hemodynamic parameters on coronary arteries in typical coronary stenosis lesions. Using the measured FFR pressure data of a patient, the pressure-time function curve is fitted to ensure the accuracy of the boundary conditions. The average error of the simulation pressure results compared to the test data is 6.74%. In addition, the results related to blood flow, pressure contour and wall shear stress contour in a typical cardiac cycle are obtained by simulation analysis. These results are found to be in good agreement with the laws of the real cardiac cycle, which verifies the rationality of the simulation. In conclusion, based on the modeling and hemodynamic simulation analysis process of dynamic coronary angiography, this paper proposes a method to assist the analysis and evaluation of coronary hemodynamic and functional parameters, which has certain practical significance.

Continuous carbon fiber 3D printing partitioning method based on stress distribution

3D printing of continuous carbon fiber composites presents a need for the directivity of fiber distribution. For parts with actual working conditions, the stress distribution of the same part under the same stress condition is different, but the existing partitioning algorithm mainly fills the path of the subregion according to the shape of the part, and does not combine the working condition of the part. To solve this problem, a partitioning algorithm based on stress contour density is proposed. Based on the results of finite element analysis, the stress contour of the parts is obtained, and the stress concentration area is partitioned by calculating the stress contour density. The stress concentration area is filled with a more suitable path to improve the performance of the parts.

Unsteady solute transport in Casson fluid flow and its retention in an atherosclerotic wall

In the current study, a mathematical model of convective solute transport and its retention in an atherosclerotic wall is examined. The artery wall is supposed to be permeable and has cosine-shaped stenosis caused by various sorts of abnormal growth or plaque formation. The flowing blood is modeled as the suspension of all red blood cells in plasma, thought to be Casson fluid. The Immersed Boundary Method (IBM) and the Marker and Cell (MAC) method are used to numerically solve the unsteady governing equations of motion along with the appropriate initial and boundary conditions. The final results of the quantitative studies contain the corresponding flow-field and solute distribution profiles for the full arterial length. The essential components are evaluated, including the wall shear stress, wall concentration, and concentration contours. According to simulation data, the permeability of the wall directly affects the solute transport within the therapeutic region. The yield stress does, however, increase flow resistance and decrease solute uptake within the tissue. The projected outcomes are remarkably in line with previously published findings, which supports the applicability of the model under investigation.

A Study on the Effects of Punch-to-Span Ratio and Longitudinal Reinforcement Eigenvalues on the Bearing Capacity of RC Slab–Column Connections

The region of the RC slab–column connection is subject to complex forces and is susceptible to localized damage, leading to progressive collapse incidents, which has raised considerable concern among the engineering community. At present, the research on slab–column connections exhibits several shortcomings, including a limited number of specimens, incomplete consideration of various factors, and unclear boundaries in defining failure modes. A comprehensive consideration of the punch–span ratio (a/h0) and longitudinal reinforcement eigenvalues (ρƒy/ƒc) is lacking, and the calculation formula for load bearing is not subdivided based on distinct failure modes. In this study, finite element software is utilized to construct 42 models of slab–column connections. The variables considered encompass three factors: the punch–span ratio, the longitudinal reinforcement ratio, and concrete strength. The examination and evaluation encompass the analysis of the load–displacement curve, reinforcement stress change curve, section crack distribution pattern, and stress contour map obtained through model loading. The primary parameters defining the boundaries of the three failure modes in the slab–column connection are the punch–span ratio and longitudinal reinforcement eigenvalues. Utilizing the punch–span ratio and longitudinal reinforcement eigenvalues as key parameters, a punching and flexural failure model for slab–column connections without abdominal bars is formulated. The calculation formula for bearing capacity, encompassing flexural, flexural and punching, and punching shear failure, is derived. A comparison between the revised formula and the standard formulas from major countries indicates that the revised formula is more comprehensive, providing a more accurate and secure prediction within the scope of this study.

Mechanical properties and failure mechanism of rock-like specimens with arc-shaped flaws under freeze–thaw cycles

To investigate the failure characteristics of jointed rock masses in cold regions after freeze–thaw (F-T) cycles, uniaxial compressive tests are conducted on rock-like specimens (a type of cement mortar) with prefabricated arc-shape flaws subjected to 0, 25, 50 and 100F-T cycles to determine their mechanical properties. Test results reveal that F-T cycles greatly affect the uniaxial compressive strengths (UCS) of the specimens, and the relationship between the peak strength and the number of freeze–thaw cycles is exponentially fitted. Notably, the initial 50 cycles have a more pronounced effect on UCS reduction compared to the subsequent 50 cycles, indicating that early F-T cycles are more detrimental to UCS. To further investigate the failure mechanism of the specimens, two-dimensional particle flow code (PFC2D) is utilized to simulate the F-T cycle process of the specimens. The mechanical properties and failure mechanism of specimens can be obtained after F-T cycles under uniaxial compression through numerical simulations. The findings indicate that F-T cycles can obviously deteriorate the ductility of the specimens, and to some extent, they also affect crack propagation during specimen failures. Through crack classification statistics and stress contour analysis of the simulated specimens, it reveals that different prefabricated flaw morphologies lead to distinct stress distributions, subsequently affecting crack propagation and specimen failure. It is also worth mentioning that the large curvature and inclination angle of the flaws may generate additional tensile and shear stress zones at the top of the flaw vault, which in turn may contribute to the development of crack propagation. The relevant experimental and numerical results are useful for investigating mechanical properties and failure mechanisms of rock masses in cold regions subjected to F-T cycles.

Unified theoretical solutions for describing the crack-tip stress fields of mode-II cracked specimens under the fully plastic condition

Potential novel singular solutions to the crack-tip stress fields beyond the asymptotic solution frame are discussed in this study. It is believed that one of them is not only suitable for the crack-tip stress fields of mode-I cracked specimens but also for those of mode-II cracked specimens. The crack-tip stress fields of mode-II cracked specimens are investigated based on the singular solution and the stress factor of mode-II cracked specimen derived from energy density equivalence principle. Further, special functions for describing the coefficients of normalized stress distributions of mode-II cracked specimens are proposed. The method to determine the parameters in the theoretical solutions are introduced. To give an example, one set of parameters for compact shear specimen under plane-strain conditions are determined by the finite element analysis of a few typical materials and geometries conditions. Finally, comparisons of radial and circumferential stress distributions and contour lines of equivalent stress are completed for the compact shear specimens and Arcan-shaped shear specimens of power-law plastic materials under plane-strain and plane-stress conditions. And the results show that the applicability and reliability of the proposed unified theoretical solutions are verified.

Experimental and numerical investigation on axial behavior of circular and square slender reinforced columns

To investigate the axial performance of slender concrete-filled steel tube (CFST) columns reinforced by outer steel tube and sandwiched concrete jackets, an axial compression test was conducted on 20 circular and square slender reinforced columns. The study aimed to examine the influence of the cross-sectional shape, steel content of the outer tube, the strength of sandwiched concrete, and slenderness ratio on the failure mode, load-displacement curves, and ultimate load. A comparative test on six slender CFST columns was also conducted. The test results showed that the local buckling degree of the outer steel tube in square reinforced columns was greater than that in circular reinforced columns, while the overall bending deformation was smaller. The influence of the sandwiched concrete strength on the load-displacement curve was weaker compared to the influence of the outer tube thickness and slenderness ratio. As the slenderness ratio increased, both the longitudinal and lateral strains of the specimens tended to decrease. The difference in strain between the tension and compression sides was more pronounced in circular reinforced columns than in square reinforced columns. The average SI values of circular and square reinforced specimens were 1.05 and 1.00, respectively, but the gap in SI values between the two types of reinforced columns is reduced as the slenderness ratio increases. Then, a numerical model on the slender reinforced columns was established by the finite element software ABAQUS. A good agreement was obtained between test results and simulation results. The mechanical mechanism of typical slender reinforced columns was further analyzed, including longitudinal stress contour map of concrete, the development of longitudinal stress of steel tube, as well as distribution of transverse confinement stress. A formula was subsequently proposed based on a design code to predict the load-bearing capacity of the retrofitted columns, the prediction results agreed well with the experimental data.

Suggested method of utilizing soil arching for optimizing the design of strutted excavations

An expression was derived for the soil arching effect behind foundation pits by considering the natural static equilibrium. An optimization strategy for super-large deep foundation pits was proposed based on the arching-related stress transformation and the limit span of soil arching. Steel–concrete composite piles that act as arching feet to formulate the soil arching are introduced. The proposed arching-effect methodology is supported using numerical modelling that reveals the stress arching in the principal stress contours. Once the interval between piles is less than the analyzed limit span of the soil arch, introducing steel–concrete composite piles can cause a sharp decline (by one third) in the wall deflection. It is essential that the steel struts are moved to the diaphragm wall where the steel–concrete composite piles form the arching feet and that the total number of steel supports remains unchanged. The formation of an arching foot can also significantly reduce the lateral wall deflection, enhancing the stability of the deep foundation pit during construction. Grouping the piles efficiently is a reliable tool for stabilizing deep foundation pits from the point of view of multi-arching action. Furthermore, the maximum principal stress contours reveal the arched trajectory between adjacent piles.

Seismic performance of prefabricated replaceable graded-yielding energy-dissipating connectors

In conventional reinforced concrete and assembled monolithic concrete frame structures, considerable damage typically occurs in the beam–column joint zone under strong seismic activity. To improve seismic performance and earthquake resilience, a novel replaceable graded-yielding energy-dissipating connector (RGEC) for prefabricated concrete beam–column joints is proposed. In these joints, RGECs are assembled on the upper and lower sides of the beam end. These connectors enable the concentration of plastic deformation on their bending–shear components (BSCs) and buckling segment (BS). Consequently, structural seismic performance can be rapidly restored by replacing the RGECs after an earthquake. An RGEC can realize graded-yielding energy dissipation under earthquakes of different intensities with the successive yielding of BSCs and BS. Mechanical models of the BSC and BS are developed, and a series of tests is performed on 11 specimens. The tests examine the effects of key design factors (such as core plate thickness, width–thickness ratio of the BS, limit gap width, yield stress contour height ratio, and height–width ratio of the BSC) on the seismic behavior of the proposed damper. Results indicate that the RGEC exhibits excellent seismic performance in terms of strength capacity, deformation capacity, energy dissipation capacity, and stiffness degradation. The RGEC can effectively achieve energy dissipation through graded yielding under loads of multilevel intensities. Additionally, based on finite element models validated using available test data, the deformation behavior of the RGEC is analyzed by considering the influences of the yield stress contour height ratio and height–width ratio of the BSC, width–thickness ratio of the BS, and out-of-plane restraint gap width.