Stress Distribution Research Articles

Kinetic Analysis and Stability Evaluation of Femoral Neck Fracture with Internal Fixation Based on Gait Rehabilitation Training

To explore the biomechanical effects of different internal fixation methods on femoral neck fractures under various postoperative conditions, mechanical analyses were conducted, including static and dynamic assessments. Ultimately, a mechanical stability evaluation system was established to determine the weights of each mechanical index and the evaluation scores for each sample. In static analysis, it was found that the mechanical stability of each model met the fixation requirements post-fracture. During the healing process, the maximum stress on the hollow nail slightly increased, and stress distribution shifted from multi-point to a more uniform single-point distribution, which contributes to fracture healing and reduces the risk of stress concentration. In dynamic analysis, resonance points frequently occurred at low frequencies. With increasing walking speed, the maximum stress increased significantly. At slow speeds, the maximum stress approached the material's yield limit. Under cyclic dynamic loading, the number of cycles barely met the requirements of the healing period, and increasing walking speed may lead to fatigue fractures. The evaluation model established in this study comprehensively considers different mechanical performances in static and dynamic analyses. Based on various mechanical analyses and evaluation systems, the applicability of internal fixation treatment plans can be assessed from multiple dimensions, providing the optimal simulated mechanical solution for each case of femoral neck fracture treatment.

Radial Inertia Effect of Ultra-Soft Materials from Hopkinson Bar and Solution Methodologies

The split-Hopkinson pressure bar technique is widely used to determine the dynamic mechanical behavior of materials. However, spike-like stress features appear in the initial stress behavior of ultra-soft materials tested with a split-Hopkinson bar. These features are not intrinsic characteristics of the materials. Potential causes were investigated through experiments and numerical simulations. It was found that the spike feature represents derived stress resulting from the radial inertia effect during dynamic loading. In this work, we propose and experimentally verify effective methods to reduce this effect. The influences of density, strain acceleration, ratio between inner and outer diameter, and Poisson’s ratio on the radial inertia effect were investigated. The spike stress was found to change linearly with density and strain acceleration but decrease significantly when the inner/outer diameter ratio was below 0.3, after which it remained nearly constant. A parabolic stress distribution was observed along the radial direction due to the Poisson effect, especially when the ratio exceeded 0.3, leading to higher spike stress. Finally, suggestions were proposed as experimental guidance when testing ultra-soft materials.

Experimental and numerical investigation of the solid cold-welding properties of the APB process of Al/Cu bulk composites

AbstractNowadays, the use of bimetallic laminates with special capabilities is increasing and has experienced high growth. These properties include high mechanical properties, corrosion resistance, lightweight, and thermal stability. Among the technologies of multilayer composite materials, Accumulative Press Bonding (APB) as a solid-phased method of welding is one of the most common techniques for the production of multilayer composites. One of the most important aims for this choice is the press pressure, which can create a strong and suitable mechanical connection between produced metal layer components. In this study, the APB method has been used to produce bimetal aluminum/copper bulk composites as its novelty for the first time. After that, the effect of pressing parameters such as strain and number of layers on the stress distribution has been investigated. The shear stress among the layers reached 4 MPa for the samples with eight layers which is a good condition to generate a successful bonding. With increasing the thickness reduction ratio, the stress applied to the layers has also increased. As the thickness decreases, the interlayer shear stresses also increase which leads to a better bonding between layers. With increasing the thickness reduction ratio, the amount of layers sinking in each other was greater than before, which led to the crushing of copper layers along the entire length of the sample. During the process, as the number of passes increased, the volume of virgin material in the direction of the press rose, which led to increased compaction and better adhesion of Al and Cu layers to each other. The bonding strength enhances from 47 to 95 N for samples manufactured with one and four cycles of APB due to the increment of virgin metal normal to the pressing direction showing a 102% enhancement.

Residual Strain and Joint Pressurization Maintain Collagen Tension for On-Joint Lumbar Facet Capsular Ligaments.

Modeling the lumbar facet capsular ligament's mechanical behavior under various physiological motions has often been a challenge due to limited knowledge about the on-joint in situ ligament state arising from attachment to the bone or other internal loads. Building on prior work, this study presents an enhanced computational model of the lumbar facet capsular ligament by incorporating residual strain and joint pressurization strain, factors neglected in prior models. Further, the model can predict strain and stress distribution across the ligament under various spinal motions, highlighting the influence of the ligament's attachment to the bone, internal synovial fluid pressurization, and distribution of collagen fiber alignment on the overall mechanical response of the ligament. Joint space inflation was found to influence the total observed stress and strain fields, both at rest and during motion. A significant portion of the ligament was found to be in tension, even in the absence of external load. Additionally, the model's ability to account for residual strain offers a more realistic portrayal of the collagen fibers and elastin matrix's role in ligament mechanics. We conclude that (1) computational models of the lumbar facet capsular ligament should not assume that the ligament is unloaded when the joint is in its neutral position, and (2) the ligament is nearly always in tension, which may be important in terms of its long-term growth and remodeling.

Study on Deformation Behavior of Glass in High-temperature Molding for Massive Unit Microlens Arrays.

Microlens arrays (MLAs) with a large number of units, known as massive unit microlens arrays (MUMLAs), are increasingly sought after for their ability to achieve high-power conversion in infrared optical systems. Precision glass molding (PGM) is considered the ideal manufacturing method for MUMLAs. However, the stress distribution and deformation behavior during molding lack detailed understanding, resulting in poor filling consistency and forming accuracy. Consequently, this leads to inconsistent diffuse spot size and irradiance in MUMLAs. This study aims to comprehensively analyze the glass filling behavior during the molding process of MUMLAs using both simulation and experimental approaches. It explains the impact of glass filling behavior and consistency on the optical performance of MUMLAs. Additionally, the effects of molding parameters on the filling consistency of the lenses are investigated. By optimizing these parameters, a high-consistency 128 × 128 MUMLA is fabricated.

Dual‐gradient Concentration Distribution in Sb‐Cu Alloy Nanoarrays for Robust Sodium‐ionStorage

Alloy‐type materials are attractive for anodes in sodium‐ion batteries (SIBs) owing to their high theoretical capacities and overall performance. However, the accumulation of stress/strain during repeated cycling results in electrode pulverization, leading to rapid capacity decay and eventual disintegration, thus hindering their practical applications. Herein, we report a 3D coral‐like Sb‐Cu alloy nanoarray with gradient distribution of both elements. The array features a Sb‐rich bottom and a Cu‐rich top with increasing Sb and decreasing Cu concentrations from top to bottom. The former is the active component that provides the high capacity, whereas the latter serves as an inert additive that acts against volume variation. The gradual transition in composition within the electrode introduces a ladder‐type volume expansion effect, facilitating a smooth distribution and effective release of stress, thereby ensuring the wanted mechanical stability and structural integrity. The as‐developed nanoarray affords a high reversible capacity (460 mAh g−1 at 0.5 C), stable cycling (89% retention over 120 cycles at 1.0 C), and superior rate capability (354 mAh g−1 at 10 C). The concentration dual‐gradient strategy paves a new pathway of designing alloy‐type materials for SIBs.

Dual-gradient Concentration Distribution in Sb-Cu Alloy Nanoarrays for Robust Sodium-ionStorage.

Alloy-type materials are attractive for anodes in sodium-ion batteries (SIBs) owing to their high theoretical capacities and overall performance. However, the accumulation of stress/strain during repeated cycling results in electrode pulverization, leading to rapid capacity decay and eventual disintegration, thus hindering their practical applications. Herein, we report a 3D coral-like Sb-Cu alloy nanoarray with gradient distribution of both elements. The array features a Sb-rich bottom and a Cu-rich top with increasing Sb and decreasing Cu concentrations from top to bottom. The former is the active component that provides the high capacity, whereas the latter serves as an inert additive that acts against volume variation. The gradual transition in composition within the electrode introduces a ladder-type volume expansion effect, facilitating a smooth distribution and effective release of stress, thereby ensuring the wanted mechanical stability and structural integrity. The as-developed nanoarray affords a high reversible capacity (460 mAh g-1 at 0.5 C), stable cycling (89% retention over 120 cycles at 1.0 C), and superior rate capability (354 mAh g-1 at 10 C). The concentration dual-gradient strategy paves a new pathway of designing alloy-type materials for SIBs.

Modified constitutive models and cutting finite element simulation of Ti-6Al-4V alloy at cryogenic

Mastering the high strain characteristics at cryogenics and constructing an accurate constitutive model are critical for establishing a cryogenic cutting simulation of Ti-6Al-4V alloy. The traditional constitutive model is inadequate for accounting for high and cryogenic conditions. In this paper, cryogenic split Hopkinson pressure bar (SHPB) experiments are conducted, specifically for Ti-6Al-4V alloy, to develop a modified Johnson–Cook (J–C) constitutive model that incorporates the cryogenic effect. A coupled two-dimensional orthogonal finite element simulation involving temperature displacement was conducted for the cryogenic cutting of Ti-6Al-4V alloy. This simulation was performed using ABAQUS, based on a modified J–C constitutive model subroutine. It was observed that the smallest discrepancy between the simulation results and the data from ice-fixed milling experiments was just 2.12%. The modified J–C constitutive model is more adept at simulating the chip morphology under cryogenic conditions. It was also found that cryogenic machining enhances the distribution of temperature and stress within the chip. For every 5°C reduction in processing temperature, the tool temperature diminishes by more than 2%.

Stress analysis of mandibular Kennedy class I partial overdenture submitted to different implant length and clasp designs - An in vitro study.

To analyze the distribution of stresses for mandibular Kennedy class I removable partial overdentures submitted to different implant lengths and clasp designs. Twenty-seven heat-cured acrylic resin casts with a uniform soft acrylic layer were constructed from models representing the mandibular Kennedy class I removable partial denture with the first premolars terminal abutment on both sides. The casts were grouped into a control group, group I, and group II with three casts of each for designing a different clasp on the last abutment with Rest, Proximal plate, Aker circumferential (RPA), Rest, Proximal plate, I-bar (RPI), and wrought wire (WW). All casts were submitted to vertical load for stress analysis after preparing channels at the buccal/distal surface of abutments, the crest of the ridge, and the buccal/lingual of the implant for placement of uniaxial strain gauges that can convert the electro-signals to micro-strain by using the software. Kolmogorov-Smirnov normality test, independent t-test, and one-way anlysis of Variance (ANOVA) test followed by Tukey`s Post Hoc for multiple comparisons test were used for statistical analysis. The control group results revealed more significant stresses on the ridge with RPA and RPI clasps but on the abutment with WW clasp as P < 0.05. In group I, the ridge was significantly stressed more than the implant followed by the abutment when the RPA clasp was used while there was insignificance on the implant with RPA and RPI as p > 0.05. In group II, the stresses were more on the abutment with RPA, RPI, and WW clasps followed by lower on the implant and lowest on the ridge. Proper implant and clasp type selection are critical for stress distribution on the ridge, abutment, and implant when using removable partial overdenture. The stresses on longer implants are tolerated and more widely distributed than shorter ones.

Flexural performance of innovative thin-walled steel–timber composite floor slabs

A floor slab carries and distributes the floor load in a structure and is an important component that affects overall structural performance. Therefore, it is important to investigate the mechanical properties of such materials. In this study, flexural performance tests under static load are conducted for an innovative thin-walled steel–timber composite floor slab, and the failure mode, bearing capacity, stiffness, deflection, and strain development are investigated. The results show that the floor slab can be quickly assembled using self-tapping and wood screws and exhibits good flexural performance. Using ABAQUS finite-element software, the effects of the oriented-strand board (OSB) thickness, thin-walled–steel-plate height, steel strength, and boundary conditions on the flexural performance of composite floor slabs are investigated. Furthermore, based on the EN1995–1-1 code and equal-section conversion principle, the simplified beam-unit model is established for the theoretical calculation of the composite floor slab. The effective bending stiffness is calculated by considering the influence of the slip modulus of the connector, and the stress distribution law of the section is analysed. The results provide a reliable design basis and reference for the application of thin-walled steel–timber composite floor slabs in engineering practice.

Influence of a Meandering Channel on the Threshold of Sediment

River meanders and channel curvatures play a significant role in sediment motion, making it crucial to predict incipient sediment motion for effective river restoration projects. This study utilized an artificial intelligence method, multiple linear regression (MLR), to investigate the impact of channel curvature on sediment incipient motion at a 180-degree bend. We analyzed 42 velocity profiles for flow depths of 13, 15, and 17 cm in a laboratory flume. The results indicate that the velocity distribution was influenced by the sediment movement threshold conditions due to channel curvature, creating a distinct convex shape based on the bend’s position and flow characteristics. Reynolds stress distribution was concave in the upstream bend and convex in the downstream bend, underscoring the bend’s impact on incipient motion. Bed Reynolds stress was highest in the first half of the bend (0 to 90 degrees) and lowest in the second half (90 to 180 degrees). The critical Shields parameter at the bend was approximately 8–61% lower than the values suggested by the Shields diagram, decreasing from 0.042 at the beginning to 0.016 at the end of the bend. Furthermore, our findings suggest that the MLR method does not significantly enhance the understanding of sediment movement, highlighting the need for a more comprehensive physical rationale and an expanded dataset for studying sediment dynamics in curved channels.

Impact of screw tip design on screw anchorage: mechanical testing and numerical simulation

BackgroundScrew loosening is a commonly reported issue following spinal screw fixation and can lead to various complications. The initial cause of screw loosening is biomechanical deterioration. Previous studies have demonstrated that modifications in screw design can impact the local biomechanical environment, specifically the stress distribution on bone-screw interfaces. There are several different designs of screw tips available for clinically used pedicle screws; however, it remains unclear whether these variations affect the local stress distribution and subsequent screw anchorage ability.MethodsThis study conducted comprehensive biomechanical research using polyurethane foam mechanical tests and corresponding numerical simulations to investigate this topic. Models of pedicle screw-fixed osteoporotic polyurethane foam were created with two different clinically used screw tip designs (flat and steep) featuring varying tip lengths, taper angles, and diameters, as well as identical flank overlap areas and thread designs. The anchorage ability of the different models was assessed through toggle and pull-out test. Additionally, numerical mechanical models were utilized to compute the stress distributions at the screw and bone-screw interfaces in the different models.ResultsMechanical tests revealed superior anchorage ability in models utilizing flat-tipped screws. Furthermore, numerical modeling indicated improved anchorage ability and reduced stress concentration tendency in these models.ConclusionChanges in screw tip design can significantly impact the biomechanical anchoring capability of screws. Specifically, flatter tip pedicle screws may mitigate the risk of screw loosening by alleviating stress concentration on bone-screw interfaces.

High-resolution measurement of contact stresses and friction in indentation and machining by full-field photoelasticity

An experimental study has been made of the sliding plastic contact in wedge indentation and machining of ductile metals. The use of full-field photoelasticity has allowed direct determination of interface pressure and shear stress distribution along the tool (indenter) and workpiece sliding contact at micron-scale resolution. Sapphire, a transparent photoelastic material that possesses sufficiently high hardness to indent and machine metals, is used as the tool material. It is shown that the Coulomb friction model applies only at the edges of the contact where the interface pressure falls below a certain value associated with the material's flow stress. Within the plastic contact zone, the mode of friction as well as the relationship between interface pressure and shear stress are very complex. In both cases, it is shown that shear stress neither remains constant nor varies in proportion to the pressure. It is proposed that the complex nature of friction and stress field at the sliding contact can be understood through simultaneous observations of the metal plastic flow at and near the interface. Using in situ measurements of the velocity field near the interface and local stress distribution at the contact from photoelasticity, friction contribution to the overall work is calculated and shown to be substantial (greater than one-third) in the case of machining.

Application of Surface-Based Smoothing Methods for Topology Optimization Results

Topology optimization (TO) is becoming an essential part of designing new or modifying current parts to improve their properties. A typical problem of TO in structural applications is minimizing compliance with volume (mass) constraints. TO is often complemented by additive manufacturing which allows the printing of complex geometries. Resulting geometries are dependent on the used method, most of the time it is the finite element method. The exported geometry from the optimization procedure, however, tends to have a lot of sharp edges, which causes problems with stress distribution, aesthetics and manufacturing (even if it is additive manufactured). The aim of this paper is to review, apply smoothing techniques on the surface of bodies, Laplacian and Taubin smoothing, and compare the results of smoothing. To fulfill this aim, we developed a smoothing procedure and evaluated the criteria of smoothed-out polymer geometries.

Classical and Bayesian estimation of multicomponent stress–strength reliability with power Lindley distribution under progressive first-failure censored samples

This research article presents a methodology for estimating the multicomponent reliability based on progressively first-failure censored samples, where the underlying distribution of stress and strength is modelled using the power Lindley distribution. The classical and Bayesian estimation methods are utilized for estimating the multicomponent reliability. In the Bayesian estimation, the Markov Chain Monte Carlo approximation method is employed to obtain the posterior mean under a generalized entropy loss function. Various intervals including asymptotic confidence, bootstrap-p confidence, bootstrap-t confidence, Bayesian credible, and highest posterior density credible intervals are computed. A simulation study is conducted to evaluate the performance of the proposed methodology. Also, two different real data applications are presented to illustrate the practicality of the approach.

Stress Distribution Pattern of a Calculated Standardized Force on Maxillary and Mandibular Jaws with Proclined Maxillary Anterior Teeth with and without the Use of Mouthguard: A 3D Finite Element Analysis

Stress Distribution Pattern of a Calculated Standardized Force on Maxillary and Mandibular Jaws with Proclined Maxillary Anterior Teeth with and without the Use of Mouthguard: A 3D Finite Element Analysis

Особенности обрабатываемости резанием новых высокопрочных титановых сплавов с ультрамелкозернистой структурой для деталей авиационной техники

The results of experimental studies of the cutting parameters effect (cutting speed, feed, depth-of-cut) on the roughness of Ra, the microstructure of the surface layer of Ti-6Al-4V alloy samples with a conventional coarse-grained (CG) and ultrafine-grained (UFG) structure obtained by equal-channel angular pressing are presented. In framework of solving the problem connected with studying the machinability of a new VT6 alloy having an UFG structure, the development of a methodology for experimental research under turning was carried out. Physical parameters such as vibrations and noise under cutting, power consumption, numerical parameters of roughness, the magnitude and the pattern of residual stresses distribution and others are determined according to cutting modes and the tool used for the operation. It is shown that when turning at a low cutting speed, the roughness of CG sample is better than UFG of the alloy. With an increase in the cutting speed by 1,5 times, on the contrary, a sample with an UFG structure has a lower roughness Ra compared to a CG sample. Differences in the morphology and microstructure of the chips formed within comparative machining are discussed, taking into account types of microstructure of the alloy being treated, namely, presence of plastic flow lines in the chip microstructure after turning an UFG sample, the formation of large shifts, chips and tiny fractures in the chips after turning a CG alloy. It is found that new titanium alloys under turning obtain better cutting machinability in terms of such parameters as surface roughness, noise and vibration under cutting, and a more favorable character of residual stresses and riveting in the surface layer. Studying these factors, it is possible to predict a significant reduction of tool wear and stabilization of its durability compared to conventional coarse-grained titanium treatment.

Finite element analysis of precise puncture vertebral augmentation in the treatment of different types of osteoporotic vertebral compression fractures

BackgroundOsteoporosis vertebral compression fracture (OVCF) secondary to osteoporosis is a common health problem in the elderly population. Vertebral augmentation (VA) has been widely used as a minimally invasive surgical method. The transpedicle approach is commonly used for VA puncture, but sometimes, it is limited by the anatomy of the vertebral body and can not achieve good surgical results. Therefore, we propose the treatment of OVCF with precise puncture vertebral augmentation (PPVA). This study used finite element analysis to explore the biomechanical properties of PPVA in the treatment of osteoporotic vertebral compression fractures (OVCFs) with wedge, biconcave, and collapse deformities.MethodThree-dimensional finite element models of the fractured vertebral body and adjacent superior and inferior vertebral bodies were established using Computed Tomography (CT) data from patients with OVCF, both before and after surgery. Evaluate the stress changes of the wedged deformed vertebral body, biconcave deformed vertebral body, collapsed deformed vertebral body, and adjacent vertebral bodies before and after PPVA.ResultIn vertebral bodies with wedge deformity and collapsed deformity, PPVA can effectively reduce the stress on the vertebral body but increases the stress on the vertebral body with biconcave deformity. PPVA significantly decreases the stress on the adjacent vertebral bodies of the wedge deformed vertebral body, and decreases the stress on the adjacent superior vertebral body of biconcave deformity and collapsed deformed vertebral bodies, but increases the stress on the adjacent inferior vertebral bodies. PPVA improves the stress distribution of the vertebral body and prevents high-stress areas from being concentrated on one side of the vertebral body.ConclusionPPVA has shown positive surgical outcomes in treating wedge deformed and collapsed deformed vertebral bodies. However, its effectiveness in treating biconcave vertebral body is limited. Furthermore, PPVA has demonstrated favorable results in addressing adjacent superior vertebral body in three types of fractures.

Effects of In-Situ Stress on Damage and Fractal during Cutting Blasting Excavation

Blasting excavation of rock masses under high in-situ stress often encounters difficulties in rock fragmentation and a high boulder rate. To gain a deeper understanding of this issue, the stress distribution of rock masses under dynamic and static loads was first studied through theoretical analysis. Then, the ANSYS/LS-DYNA software was employed to simulate the blasting crack propagation in rock masses under various in-situ stress conditions. The fractal dimension was introduced to quantitatively analyze the influence of in-situ stress on the distribution of blasting cracks. The results indicate that in-situ stress primarily affects crack propagation in the later stages of the explosion, while crack initiation and propagation in the early stages are mainly driven by the explosion load. In-situ stress significantly influences the damage area and fractal dimension of cut blasting. Under hydrostatic in-situ stress, as the in-situ stress increases, the damage area and fractal dimension of blasting cracks gradually decrease. Under non-hydrostatic in-situ stress, when the principal stress difference is small, in-situ stress promotes the damage area and fractal dimension of the surrounding rock, enhancing rock fragmentation. However, when the principal stress difference is large, in-situ stress inhibits the damage area and fractal dimension of the surrounding rock, hindering effective rock breaking.

Heterogeneous Solid Electrolyte Interphase Interactions Dictate Interface Instability in Sodium Metal Electrodes.

Sodium (Na) metal batteries have attracted recent attention due to their low cost and high abundance of Na. However, the advancement of Na metal batteries is impeded due to key challenges such as dendrite growth, solid electrolyte interphase (SEI) fracture, and low Coulombic efficiency. This study examines the coupled electro-chemo-mechanical interactions governing the electrodeposition stability and morphological evolution at the Na/electrolyte interface. The SEI heterogeneities influence transport and reaction kinetics leading to the formation of current and stress hotspots during Na plating. Further, it is demonstrated that the heterogeneity-induced Na metal evolution and its influence on the stress distribution critically affect the mechanical overpotential, contributing to a faster SEI failure. The analysis reveals three distinct failure mechanisms-mechanical, transport, and kinetic-that govern the onset of instabilities at the interface. Finally, a comprehensive comparative study of SEI failure in Na and lithium (Li) metal anodes illustrates that the electrochemical and mechanical characteristics of the SEI are crucial in tailoring the anode morphology and interface stability. This work delineates mechanistic stability regimes cognizant of the SEI attributes and underlying failure modes and offers important guidelines for the design of artificial SEI layers for stable Na metal electrodes.