Maximum Stress Research Articles

Changes in hydraulic and physico-water parameters of surface waters under the influence of anthropogenic activities in the Western Carpathians

To evaluate the quality of watercourses in the Western part of Carpathians from a hydro-chemical perspective, a systematic approach is required. This involves gradually excluding factors that contribute to the washing, mixing, and transportation of contaminants in the watercourse pathway. The model that considers spatial dependencies by autoregression was implemented in this study to determine the correlation between hydrodynamic and physico-chemical characteristics of waters at surface in different groups and forms of catchment use. The surface water at forested areas had the maximum average shear stress of 0.178 N∙m−2. The watercourse at sustained grassland had the maximum average Reynolds number (Re) of 23,654 and the minimum number of 0.426 at arable lands. Spatial autoregression analysis revealed space-time relations in various measurement points. When constructing the space-physical model, it is important to consider the influence of hydraulic characteristic parameters on the generation of physicochemical indicators in the flysch basin. Specifically, it may be beneficial to take into account the turbulent diffusion coefficient. The autoregression analysis demonstrated that for the ions P-PO43− and K+ in surface water on cropland and for total iron and the cation K+ ion grassland (p < 0.05), the turbulent diffusion coefficient proved to be of great importance. The study did not identify any physicochemical dependency for woodland surface waters. The findings can be utilised to create an erosion model that considers the contribution of material supply in a catchment area, specifically from weathered Carpathian flysch or surface runoff, to the alimentation of alluvial deposits.

Development and characterization of sustainable epoxy resin composites reinforced with palm kernel shell particulate and sisal fiber

This study explores the development and characterization of epoxy resin composites reinforced with palm kernel shell (PKS) particulate and sisal fibers, aiming to create sustainable and high-performance materials. Elemental composition analysis using energy dispersive X-ray revealed significant increases in carbon and oxygen content with higher PKS particulate content, indicating successful reinforcement integration. The mechanical properties were evaluated through Brinell hardness, impact energy, impact strength, tensile stress, and wear resistance tests. The Brinell hardness increased from 31.8 kg/mm2 in the control sample to a peak of 60.6 kg/mm2 in sample SP4, demonstrating enhanced hardness with PKS particulate addition. Impact tests identified an optimal reinforcement level in sample SP3, which achieved the highest impact energy (83 J) and impact strength (47.43 kJ/m2). Tensile stress analysis showed a maximum tensile stress of 28.7991 MPa for SP3, while excessive PKS content in SP4 reduced this to 20.4612 MPa. Wear tests indicated a trade-off between mechanical reinforcement and wear resistance, with the control sample exhibiting the lowest wear rates and SP4 the highest having a 91.9% increase. Based on the obtained results, SP3 with 0.8 g PKS particulate, 0.2 g sisal fiber in epoxy resin matrix seems the optimized composite with enhance mechanical properties without compromising wear resistance.

Pore and fracture pressures prediction — A new geomechanic approach in deepwater salt overthrusts: Case histories from the Gulf of Mexico

Along this active exploration belt, applying the conventional effective stress methods and algorithms, wherein the maximum stress ([Formula: see text]) is vertical and can be attained from the subsurface overburden (OB), would lead to unintended and unrealistic results. In the frontier active thrust belt of the Gulf of Mexico, the unique geomechanical setting of [Formula: see text] as the lateral salt creep and the minimum stress ([Formula: see text]) as the OB greatly impact the formation geopressure framework. The buoyancy of thick salt produces two different pressure gradients (PGs) above and below the salt. Moreover, the inclusion of rafted sediments in the salt and the plowing rubble zone at the salt base substantially affects the pore and fracture pressures (PP-FP) profiles. These proceeding geologic settings are the foundation for the conceptual framework. Building an alternative predrilling prediction numerical model based on these anomalous geomechanical settings and the lack of adequate seismic velocity is a challenge. All the available direct measured or pertained PP-FP data from the key wells are collected and tabulated. Prediction models are established by correlating the populated database and generating the empirical algorithm for each data gather. A substantial discrepancy occurs between above and below the salt sections where high PG in the sediment above the salt and slow PG development below the salt. There is considerable regressive pressure (average 2 ppg) in PP-FP subsalt sections. The PP within the salt is contingent on the presence of sediment inclusions, and a substantial FP drop in the rubble zone leads to the extensive loss of mud circulation. The trend lines of each data gather led to generating two depth-dependent equations for the PP-FP above and within the salt and two others for the subsalt. The prediction models are validated against a blind data set. Before drilling, this model establishes the PP-FP versus the sediment subsea depth in an abnormal geomechanical setting and the lack of coherent vertical seismic velocity for PP-FP predictions.

Design and Testing of a Crawler Chassis for Brush-Roller Cotton Harvesters

In China’s Yangtze River and Yellow River basin cotton-growing regions, the complex terrain, scattered planting areas, and poor adaptability of the existing machinery have led to a mechanized cotton harvesting rate of less than 10%. To address this issue, we designed a crawler chassis for a brush-roller cotton harvester. It is specifically tailored to meet the 76 cm row spacing agronomic requirement. We also conducted a theoretical analysis of the power transmission system for the crawler chassis. Initially, we considered the terrain characteristics of China’s inland cotton-growing regions and the current cotton agronomy practices. Based on these, we selected and designed the power system and chassis; then, a finite element static analysis was carried out on the chassis frame to ensure safety during operation; finally, field tests on the harvester’s operability, stability, and speed were carried out. The results show that the inverted trapezoidal crawler walking device, combined with a hydraulic continuously variable transmission and rear-drive design, enhances the crawler’s passability. The crawler parameters included a ground contact length of 1650 mm, a maximum ground clearance of 270 mm, a maximum operating speed of 6.1 km/h, and an actual turning radius of 2300 mm. The maximum deformation of the frame was 2.198 mm, the deformation of the walking chassis was 1.0716 mm, the maximum equivalent stress was 216.96 MPa, and the average equivalent stress of the entire frame was 5.6356 MPa, which complies with the physical properties of the selected material, Q235. The designed cotton harvester crawler chassis features stable straight-line and steering performance. The vehicle’s speed can be adjusted based on the complexity of the terrain, with timely steering responses, minimal compaction on cotton, and reduced soil damage, meeting the requirements for mechanized harvesting in China’s inland small plots.

Investigating formability of AZ31B magnesium alloy sheet with different texture and thickness in combination of the Erichsen experiment and CPFEM model

In this study, the formability of the AZ31B magnesium alloy sheets was investigated in combination of experiment and CPFEM modelling. The deformation mechanisms during the Erichsen forming were revealed and the effect of the related parameters were discussed. It was shown that the simulation results based on the normalized Cockcroft-Latham criterion are consistent with the experimental results. The maximum stress and strain concentrate at the center of dome, and exhibit an elliptical distribution shape. The difference of asymmetry situation between the sheets results from the different textures. The basal <a> slip is the dominant mode, and the prismatic <a> slip is also active to accommodate plastic strain in sheet plane. The relative activity of the pyramidal <c+a> slip is low, but very effective to accommodate the plastic strain in thickness direction. The sheet with higher relative activity of the prismatic <a> and pyramidal <c+a> slips exhibit higher formability. The sheet thickness influences the formability through changing the stress-strain response, as well as the orientation-relationship between stress state and grains which can affect the deformation mechanisms. The formability depends on the plastic strain accommodation ability that is comprehensively related to the averaged plasticity, orientation-relationship between stress state and grains, r-value and n-value. CPFEM modeling is convenient pathway to predict the formability.

Experimental and numerical investigations on the tensile response of pin-loaded carbon fibre reinforced polymer straps

Carbon fibre reinforced polymer (CFRP) pin-loaded looped straps are increasingly being used in a range of structural load-bearing applications, notably for bridge hanger cables in network arch rail and highway bridges. The static performance of such CFRP straps is investigated through experimental and numerical analyses. Finite element (FE) models based on both one-eighth and half pin-strap assembly geometries were modelled. The resulting strains, stresses, and applied loads were compared against experimental data obtained using Digital Image Correlation, Distributed Fibre Optic Sensing (DFOS), and Fibre Bragg Grating (FBG) Sensing. The FE models effectively captured local strain distributions around the vertex area, close to the pin ends of the straps, as well as in the mid-shaft region, and aligned reasonably with experimental observations. The half FE model accurately predicted the overall strain distribution when compared to DFOS data; however, higher strain magnitudes (by 0.45–10.2 %) and larger strain reductions were observed in some locations. Regarding failure loads, the FE models agreed well with Schürmann's analytical solution and the maximum stress criterion, exhibiting less than 2.5 % deviations from the experimental data. Furthermore, the predicted onset of strap failure (by delamination) in the half model agreed with experimental values, with a maximum variance of 9.2 %.

Modelling of enhanced gas extraction in low permeability coal seam by controllable shock wave fracturing

The controlled shock wave (CSW) fracturing is an effective method for enhancing permeability of coal seam to promote gas extraction. Based on Fick’s law, Darcy’s law, the ideal gas law and the Langmuir equation, a damage-seepage-deformation coupling mathematical model of CSW fracturing in coal seam combined with the maximum tensile stress and the Mohr-Coulomb criterion is established. This model is implemented into COMSOL Multiphysics to simulate the coal seam CSW fracturing and subsequent gas extraction. When the shock wave and isotropic in-situ stress are applied on the borehole wall, the coal damage zone is an annular shape, and the permeability in the damage zone increases sharply. The CSW can effectively increase the efficiency of gas extraction and reduce the gas pressure and gas content in coal seam. With the increase of CSW action times, the damage in coal mass reaches a threshold and tends to be stable after several shocks. The damage area and the gas extraction efficiency are positively correlated with the shock intensity. Under the anisotropic ground stress, the larger diversity of the stress in different directions is, the more obvious damage extension in the fractured coal along the maximum stress direction is. Ground stress can inhibit the extension of cracks in the CSW fractured coal seam. This inhibition effect becomes more obvious with the increase of in-situ stress. Parameters are substantiated of controlled shock wave impact on the coal seam, which ensures increased methane extraction from low-permeability reservoirs, are substantiated.

Biomechanical significance of intervertebral discs on growthplate stresses in scoliotic trunks following unilateral muscle weakening: A hybrid approach of finite element and musculoskeletal modeling.

This study aimed to ascertain the relevance of intervertebral discs (IVD) in the stress distribution on growthplates (GPs) of a trunk model with adolescent idiopathic scoliosis (AIS) following a unilateral weakening of muscles. A thoracolumbar spine finite element (FE) model of a young female healthy and an AIS spine comprising GPs linked to the T12 through sacrum vertebrae. Two scenarios of including (FEI) and excluding (FEE) IVDs were considered. Then, using optimization-driven musculoskeletal models of the AIS and healthy trunks, the FE models were examined under subject-specific muscle forces and gravity loads. Results of this study demonstrate that when IVDs included in the FE model, an increase, ranging from 0.2 to 1.7 MPa, with the highest value occurring at the apex of the AIS model, in the von Mises stresses in the GPs. The ratio of 1.5 was found for the maximum von-Mises stress value on the most tilted GP in the FEI over the FEE model. Unilateral paralysis of muscles caused a reduction of 50% and 63% in the von Mises stress ratio of the concave-over-convex side of the most tilted GP in the FEI and FEE models of the AIS spine with healthy muscles, respectively. The intradiscal pressures, found for FEE and FEI models, assented to recent in-vivo investigations. Nonetheless, employing IVDs in the simulations provides an indispensable tool to anticipate the effects of neuromuscular disorders on GP stresses in an AIS spine and predict deformity progression during growth.

Density Functional Theory Study of Adhesion Mechanism between Epoxy Resins Cured with 4,4'-Diaminodiphenyl Sulfone and 4,4'-Diaminodiphenylmethane and Carboxyl Functionalized Carbon Fiber.

The molecular mechanism of adhesion of two epoxy resins based on diglycidylether of bisphenol A (DGEBA) cured with 4,4'-diaminodiphenyl sulfone (DDS) and 4,4'-diaminodiphenylmethane (DDM) to the carbon fiber (CF) surface is investigated by employing density functional theory (DFT) calculations. The CF surface was modeled by the armchair-edge structure of graphite functionalized with carboxyl (COOH) groups. Two adhesion interfaces were constructed using the CF surface: one with the DGEBA-DDS molecule (CF/DGEBA-DDS interface) and the other with the DGEBA-DDM molecule (CF/DGEBA-DDM interface). The interfacial properties were analyzed by calculating the maximum adhesion stress (Smax) at the interface. The adhesion stress-displacement curve revealed that Smax is 1160.37 MPa, higher for the CF/DGEBA-DDS interface compared to the CF/DGEBA-DDM interface, which is 1060.48 MPa. The energy decomposition analysis showed a similar DFT contribution to adhesion stress for both interfaces, but the dispersion contribution is more significant at the CF/DGEBA-DDS interface. The crystal orbital Hamilton population (COHP) analysis revealed distinct interfacial interactions despite similar DFT contributions. Hydrogen bonding (H-bonding) between the functional groups at both interfaces including feeble OH-π interactions between the benzene rings of epoxy resins and COOH groups on the CF surface were observed. The orbital interaction energies calculated from integrated COHP, i.e., IpCOHP, revealed that the CF/DGEBA-DDS interface has six H-bonding interactions with large absolute IpCOHP values (>1 eV), whereas the CF/DGEBA-DDM interface has five. The interaction between the amine group of the DGEBA-DDM molecule and the CF surface has a large IpCOHP value among all interactions. The sulfone group being at the center of the DDS molecule and its strong surface interaction positioned the DGEBA-DDS molecule closer to the CF surface than the DGEBA-DDM molecule, enhancing dispersion interaction at the CF/DGEBA-DDS interface. Hence, the CF surface exhibits a stronger affinity toward the DGEBA-DDS molecule than the DGEBA-DDM molecule through dispersion interaction.

Design and Testing of an Integrated Corn Stubble Residual Film-Recycling Machine

The existing residual film-recycling machines struggle to efficiently recover and separate film stubble in a single operation. With roller-type film-rolling device unloading difficulties and other problems, in order to improve the recovery efficiency of film stubble and the separation effect while reducing human labor and to improve work efficiency, we designed an automatic hydraulic unloading film stubble-recycling integrated residual film-recycling machine. The angle of the membrane lifting device was determined by theoretical calculations using the method of coupled simulation of EDEM and ANSYS Workbench. We analyzed the amount of resistance as well as the maximum stress and deformation during the working process of the membrane-lifting device and focused on the design of the membrane–soil separating device and membrane-rolling device. The depth of the film shovel, the forward speed of the machine, and the rotational speed of the driving wheel of the jogging chain were selected as the test factors, and the residual film recovery rate was taken as the evaluation index. A three-factor, three-level test was designed by applying the principles of the Box–Behnken experimental design. The results show that when the forward speed is 1.36 m/s, the soil depth is 147.16 mm, and the rotational speed of the driving wheel of the shaking chain is 77.89 r/min, the recovery rate of the residual film is 87.56%, and the relative error between the experimental value and the optimized value is 2.73%. The experimental results can provide a theoretical basis for the design of the residual film-recycling machine.

Numerical simulation of friction characteristics of bionic flexible contact surface of front axle rocker arm sleeve of car

Based on the finite element software ABAQUS, the friction process of the flexible friction pair of the front axle rocker bushing of a car with a convex structure similar to the mantis head is established.The finite element model of the process is constructed and its friction characteristics are verified. By selecting a suitable hyperelastic constitutive model and changing the size of the convex structure on the surface of the sleeve,The simulation analysis of the mechanical characteristics of the flexible friction pair in radial and torsional directions shows that the bionic convex hull design changes the maximum stress of the bushing when it is subjected to force.The force and strain position are adjusted to reduce the possibility of cracking of the rubber bushing; the contact friction force and friction coefficient of the bionic bushing surface are significantly reduced, and the type 2 modelThe drag reduction and wear resistance of the profiled surface are the best.

The mouthguard for sports is capable of protecting the implant/crown complex when there is a frontal impact? Responding with finite element analisys

For athletes, the use of a mouthguard is fundamental. This device allows for the absorption and dissipation of energy from the impact. These rehabilitated patients will be subjected to oral-facial injuries and trauma again once they return to contact sports. Evaluate the mechanical effect of an impact over a maxilla region where implant-abutment-crown are present, and this mechanical behavior will be analyzed through the evaluation of maximum stress distributions. A three-dimensional geometry of an implant system (implant-abutment-crown and the bone) was obtained from computed tomography and transformed into separate meshes. A mouthguard was created to cover the surface, and a steel ball with a velocity of 1 m/s was used as the impact object. The results were divided into the individual analysis of the stress generated on each variable studied. The mouthguard was capable of reducing the stress on the implant by 71.81%, stress on the abutment by 73.20%, on both pieces by 74.30%, as well as reducing the impact on the prosthetic crown by 98.32%, thus preventing its fracture. A mouthguard is capable of reducing stress on the implant-abutment-crown complex and bone cortex. Clinical implications The present data contribute to the specialties of Sports Dentistry and Implantology, offering scientific evidence of the importance of a mouthguard to provide the best protection for athletes rehabilitated with dental implants.

An Experimental Study and Result Analysis on the Dynamic Effective Bond Length of a Carbon Fiber-Reinforced Polymer Sheet Attached to a Concrete Surface

A carbon fiber-reinforced polymer (CFRP) is a common material utilized for the enhancement in reinforced concrete (RC) constructions. Previous research indicates that the bonding performance between a CFRP sheet and concrete determines whether the bonding of CFRP material is effective. However, the majority of existing research on the bonding performance of the CFRP–concrete interface is concentrated on static loading conditions. In order to clarify the effect of dynamic load on the bonding performance of the CFRP sheet–concrete interface, this study adopts the double-sided shear test method to carry out dynamic experimental research. The test findings reveal that the damage pattern of the CFRP sheet–concrete interface remains consistent across different loading rates. The ultimate bearing capacity increases as the strain rate increases. As the strain rate increases from 10−5 s−1 to 10−2 s−1, the effect of bond length on ultimate bearing capacity increases by about 7%. As the strain rate increases, both the maximum strain of CFRP and the maximum interfacial shear stress demonstrate a corresponding increase, with respective increase rates of 60% and 20%. The effective bond length decreases by about 20% when the strain rate rises from 10−5 s−1 to 10−2 s−1. Finally, a formula for calculating the dynamic effective bond length of a CFRP sheet, grounded in the Chen and Teng formula, has been proposed and verified.

Effect of Hydrodynamic Shear Stress on Algal Cell Fate in 3D Extrusion Bioprinting

The 3D bioprinting of aquatic photosynthetic organisms holds potential for applications in biosensing, wastewater treatment, and biofuel production. While algae cells can be immobilized in bioprinted cell‐friendly matrices, there is a knowledge gap regarding the thresholds of hydrodynamic shear stress that affect the cells’ functionality and viability during bioprinting. This study examines the effect of hydrodynamic shear stress on the fate of Chlamydomonas reinhardtii cells. Computational fluid dynamics models based on the Navier–Stokes equations are developed to numerically predict the shear stresses experienced by the cells during extrusion. Parallelly, cell culture experiments are conducted to evaluate the functionality, growth rates, and viability of algae cells within bioprinted constructs. By correlating cell culture and simulation results, the causal link between shear stress in the nozzle and cell viability and function has been characterized. The findings highlight that cell viability and function are significantly impacted by process factors. Notably, algae cell function is more sensitive to shear stress than cell viability. Functional impairments occur at maximum shear stresses around 5 kPa, while viability remains unaffected. Beyond 14 kPa, both functionality and viability decline significantly and irreversibly. The results emphasize the importance of assessing viability and function after bioprinting, rather than just viability.

Mechanism and application of drill pipe bending induced borehole collapse in soft coal seam drilling

AbstractGas extraction drilling is a necessary measure for managing gas hazards. For soft coal seams where gas extraction drilling holes are prone to collapse, it is believed that drill rod disturbance is the main cause of hole collapse. This study proposes a research approach to reduce wall stress by optimizing the drill rod structure. Through theoretical analysis, numerical simulation, and industrial tests, a stress model for the drill rod inside the hole was established, and a wall stress equation was derived. The effects of various parameters on wall stress were analyzed. The study suggests optimizing the drill rod structure to reduce the disturbance‐induced wall stress. SolidWorks was used for drilling stress simulation, and a four‐winged concave groove drill rod was developed. After strength verification, comparative industrial tests were conducted. The research results show that as the line density increases, the wall stress of the drilling hole increases. As the length of the suspended section increases, the wall stress initially decreases and then increases. With increasing drilling thrust, wall stress increases linearly, and the growth rate is greater with a larger diameter difference between the drill hole and the drill rod. Numerical simulation results indicate that the critical point maximum stress at the hole entrance, the critical point maximum stress at the hole bottom, and the average stress at the bottom section of the four‐winged concave groove drill rod with a concavity of 5 are significantly reduced compared to those of circular and grooved drill rods. Industrial test results show that using the four‐winged concave groove drill rod significantly reduces the extent of hole collapse. This study provides a reference for addressing the issue of hole collapse in gas extraction drilling for soft coal seams.

Stress analysis and dislocation cluster generation in silicon crystal with artificial grain boundaries

We conducted a dislocation and stress analysis on various grain boundaries (GBs) using silicon ingots that contained artificial GBs to permit systematic comparison of experimental and analytical results. Through photoluminescence imaging, we found that the number of dislocation clusters generated around the 〈110〉-oriented GBs was significantly higher than those around the 〈100〉-oriented GBs. The stress analysis revealed that this difference is linked to the maximum shear stress around the GB. However, there were some GBs where dislocation cluster generation was not observed despite the presence of high shear stress. For most of these GBs, the direction of the maximum shear stress in the 12 slip system of silicon crystal was found to be oblique downward to the growth direction, which appears to inhibit dislocation propagation.

A Finite Element Analysis for Investigating the Effects of Moving Loads on Flexible Pavements

To assist researchers in solving challenging structural mechanics engineering problems, finite element modeling (FEM) has grown to be a very popular technique. The several layers of various materials that make up a pavement&amp;apos;s complicated structure and affect how it responds to stress have an impact on how it behaves. In this study, finite element analysis is done on a real existing road which is named Nowhata-Chowmasia road, situated in Rajshahi, Bangladesh. FEM is used to study this flexible pavement, which consists of 7 layers (surface, binder, base type-1, base type-2, sub-base, enhanced subgrade, and subgrade). The effect of the depth of the base layer on vertical stresses and displacements is examined using the ABAQUS/CAE 2017 modeling and simulation program. The base layer of the real existing road is 150 mm provided by the Roads and Highways Department (RHD) Rajshahi, Bangladesh. The analysis is done by measuring stress and displacement under wheel load by decreasing the base layer thickness to 100 mm and further increasing it to 200 mm. The modeling approach assumes that all materials function in a linear elastic manner. The Poisson&amp;apos;s ratio, layer thickness, and material elastic modulus are the major inputs used in the modeling procedure. In this work, flexible pavement is simulated using a conventional axle load of 100 kN, which corresponds to a single four-wheeled axle. Finally, FEM analysis showed that the maximum stresses are 0.35 MPa, 0.27 MPa, and 0.21 MPa and maximum displacements are 0.52 mm, 0.34 mm, and 0.21 mm for 100 mm, 150 mm, and 200 mm base layer thickness respectively. So, for the increase of base layer thickness the stress and displacement are decreased.

A 3D finite element analysis of biomechanical effects on teeth and bone during true intrusion of anteriors using miniscrews

The primary objective of this study was to investigate the biomechanical effects and stresses on bone, periodontal ligament (PDL), cementum and displacement along X-, Y- and Z-axis during true intrusion of incisors using mini-implants with Finite Element Analysis; the secondary objective of the study was to find out the best method for anterior intrusion in clinical practice to treat anterior deep bite malocclusions. A 3D finite element method was used to simulate true anterior intrusion with sliding mechanics using mini-implants. Two groups were modelled with mini-implants placed distal to lateral incisors for Model1, and below the anteriornasalspine (ANS) for Model2, to achieve intrusion. von Mises stress, principal stress on PDL and alveolar bone, displacements in all 3 planes were determined. Amongst the modalities compared in the present study, the stresses on bone and PDL were showing best behavior for mini-implants placed distal to lateral incisors (Model1). The teeth showed controlled tooth movement in Model1. Maximum stress was found in the cortical bone and in the PDL. Nature of the stress changed from compressive to tensile from cervical area to root apex, concentrating mainly at the apical area. Amongst the modalities compared, the best controlled tooth movements for anterior intrusion to treat anterior deep bite malocclusions, was for mini-implants placed distal to lateral incisors (Model1).

Quasi-static and fatigue performance of Ti-6Al-4V triply periodic minimal surface scaffolds manufactured via laser powder bed fusion for hard-tissue engineering

Additive manufacturing of Triply Periodic Minimum Surface scaffolds offers a promising solution for bone defect restoration and an alternative to traditional implants in hard tissue engineering. This study investigates the quasi-static and tension-compression cyclic properties of laser powder bed fusion-produced Ti6Al4V lattice-based architectures, specifically gyroid and diamond scaffold geometries. The scaffolds were designed to emulate the mechanical properties of bones, with pore sizes (650–1000 μm) suitable for tissue engineering, and porosities ranging from to 30–60 %. The quasi-static tensile properties of the stiffness and yield strength were characterized experimentally and validated numerically using the finite-element method. The results showed that the stiffness and tensile strength of the scaffolds were comparable to those of cortical bone, reducing the risk of scaffold failure. The influence of post-processing by heat treatment and hot isostatic pressing resulted in an increased fatigue limit and ductility compared with non-treated materials reported in the literature. Fractography analysis revealed that fatigue fracture initiation occurred at the outer surface of the skeleton structures, where the maximum tensile stress was concentrated. These findings support the assumption that the designed scaffolds accurately replicate the mechanical and fatigue characteristics of cortical bone, offering suitable alternatives for bone replacement and orthopedic implants.

Biomechanical investigation of positive reduction in the femoral neck fracture: a finite element analysis.

Gotfried positive reduction offers an alternative strategy for femoral neck fracture (FNF) when achieving anatomical reduction is challenging. However, the biomechanical consequences of positive reduction remain unclear. The purpose of this study was to investigate the biomechanical behavior of positive reduction across different Pauwels classification, providing a reference for quantifying positive reduction in clinical practice. Three-dimensional (3D) models of FNF were established and categorized according to the Pauwels classifications (Pauwels I, II, and III), each of them contained seven models with different reduction qualities, including an anatomical reduction model, two negative reduction models, and four positive reduction models, all of which were stabilized with dynamic hip screws (DHS) and cannulated screws (CS). We investigated the maximal von-Mises stress of internal fixation and proximal femoral, femoral fragment displacement, and maximal von-Mises strain at the proximal fragment fracture site when a 2100N load was applied to the femoral head. The maximum von-Mises stress on the internal fixators in each Pauwels group was lowest in the anatomical reduction model. In the Pauwels I group, positive reduction exceeding 3mm resulted in the maximum von-Mises stress on the internal fixators surpassing that of the negative reduction model. For the Pauwels II group, positive reduction beyond 2mm led to the maximum von-Mises stress on the internal fixators exceeding that of the negative reduction model. In the Pauwels III group, positive reduction beyond 1mm caused the maximum von-Mises stress on the internal fixators to be higher than that of the negative reduction model. The maximum von-Mises strain at the fracture site of proximal femur fragment increased with positive reduction. Varus displacement increased in positive reduction models as the Pauwels angle rose, potentially exacerbating rotation deformity in Pauwels III group. Excessive positive reduction may increase the risk of FNF failure after internal fixation. From a biomechanical stability perspective, positive reduction should be limited to 3mm or below in the Pauwels I group, restricted to not exceed 2mm in the Pauwels II group, and should not exceed 1mm in the Pauwels III group. Negative reduction should be avoided in all Pauwels groups.