Structural Stiffness Research Articles

Inflammation and Arterial Stiffness as Drivers of Cardiovascular Risk in Kidney Disease.

Patients with chronic kidney disease (CKD) have an increased cardiovascular (CV) risk. The lower the glomerular filtration rate, the higher the CV risk. Current data suggest that several uremic toxins lead to vascular inflammation and oxidative stress that, in turn, lead to endothelial dysfunction, changes in smooth muscle cells' phenotype, and increased degradation of elastin and collagen fibres. These processes lead to both functional and structural arterial stiffening and explain part of the increased risk of acute myocardial infarction and stroke reported in patients with CKD. Considering that, at least in patients with end-stage kidney disease, the reduction of arterial stiffness is associated with a parallel decrease of the CV risk, vascular function is a potential target for therapy to reduce the CV risk. in this review, we explore mechanisms of vascular dysfunction in CKD, paying particular attention to inflammation, reporting current data in other models of mild and severe inflammation, and discussing the vascular effect of several drugs currently used in nephrology.

A mortise-tenon inspired variable stiffness finger for multi-mode grasping

Variable stiffness soft robots feature low stiffness during deformation and high stiffness during operation, making them versatile for various tasks. In this study, we propose a mortise-tenon inspired variable stiffness mechanism (VSM) capable of continuously regulating the structural stiffness within a wide range. The relationship between the structural stiffness of the VSM and the pneumatic pressure applied to a driving airbag was theoretically modeled and experimentally verified. A soft-rigid hybrid finger, integrating soft actuators and the VSM, was developed to explore its deformation capabilities through numerical simulations and experimental tests. Furthermore, a four-fingered hand prototype was assembled, and its grasping performance was systematically evaluated. The results demonstrated that the four-fingered hand could actively switch grasping modes by leveraging the variable stiffness of the VSM, exhibiting exceptional adaptability to various shapes and loads. The variable stiffness mechanism proposed in this study provides new technological support for the design of reprogrammable stiffness soft robots, significantly enhancing their adaptability.

Parametric analysis of self-excited aeroelastic instability of an isolated single-axis two-dimensional flat solar tracker

The escalating global energy demand is driving a transition towards sustainable energy sources, particularly solar power, which is experiencing significant growth. Single-axis, horizontally mounted photovoltaic (PV) solar trackers are emerging as one of the most cost-effective methods for solar energy generation. However, the reduction in structural stiffness has led to an increase in aeroelastic issues, some of which have resulted in catastrophic failures around the world, posing significant challenges. Recent aerodynamic studies have attributed these instabilities to stall flutter. The absence of a validated theory hampers early estimation of these aeroelastic phenomena. The primary aim in this work is to develop a semi-empirical framework to predict aeroelastic instabilities in isolated two-dimensional solar trackers, focusing on dynamic self-excited responses. This effort aims to improve the reliability and efficiency of solar tracker designs, optimizing energy utilization in the context of the evolving renewable energy landscape. The semi-empirical formulation developed here reveals the influence of geometric and mechanical characteristics on the critical wind speed at which aeroelastic instabilities set in. The effects of reduced inertia (m⁎) and mechanical damping coefficient (ξmech) of the structure on the critical wind speed at which aeroelastic instabilities arise are analyzed here. It is shown that increasing either inertia or damping has a minor impact on the critical speed when the initial values of these parameters are large, while the changes are significant when these initial values are small.

Parametric assessment of new O-ring bracing performance under progressive collapse using nonlinear analysis

Progressive collapse poses a significant threat to the structural integrity of buildings under extreme loading conditions, necessitating robust design strategies to mitigate its effects. This paper extends prior research by the same authors on the performance of O-ring bracing during progressive collapse in comparison with other bracing systems. The primary objective is to investigate various design parameters and configurations that optimize the performance of O-ring bracing systems under progressive collapse scenarios through a comprehensive parametric assessment. Nonlinear finite element analysis is employed to evaluate different design parameters, including the size, shape, orientation, and strength of O-ring braced sections, and connection detailing. These factors are assessed for their influence on structural strength, stiffness, and ductility. The parametric study identifies configurations that significantly enhance structural resilience, providing recommendations for future designs aimed at preventing progressive collapse in O-ring braced frames. Data AvailabilityAll data is available from the Authors upon reasonable request.

Implicit conformal design for gradient architected materials

This paper develops a conformal architected materials design method based on implicit modeling, which enables functional gradient modulation. This method utilizes the mapping relationship between conformal hexahedral element and the cubic bounding box of architected material to construct the signed distance field. To enhance strength and stiffness of the structure, this study integrates the relative density distribution obtained from topology optimization to regulate the density of conformal architected materials through density mapping. Compared to traditional methods, the proposed method not only reduces the damage of the boundary structure caused by cutting, achieving a mutual match between the architected materials and curved geometry, but also retains the ability to control the distribution of relative density. The numerical analysis and experimental results demonstrate that conformal gradient architected materials exhibit better structural strength and stiffness compared to array-generated gradient architected materials, which indicates that the proposed method has potential applications in lightweight design.

Design and optimization of TPMS-based heterogeneous metastructure for controllable displacement field

Lightweight structures with tailored mechanical properties are highly sought after in various engineering fields, including aerospace, automotive, and civil engineering. Mechanical metastructures, with their intricate microstructural designs, offer a promising route to achieve these desired properties. However, designing metastructures for specific applications, particularly those requiring precise control over local deformations (displacement fields) while maintaining overall stiffness, remains a significant challenge. This paper introduces a novel structural stiffness optimization strategy for TPMS-based heterogeneous metastructures. By carefully controlling the relative density, structural parameter, and rotation angle of the microstructure, the ability to achieve significant reductions in displacement in targeted regions while preserving overall structural stiffness is demonstrated. The effectiveness of the proposed method is verified through both numerical simulations and experimental validation. Results show a maximum displacement reduction of 42.51 % under uniaxial compression and 31.32 % under biaxial compression. Notably, in a case study focused on protecting sensitive components within satellite structural frames, the optimized design achieved a remarkable 70 % reduction in displacement, highlighting the potential of the method for real-world engineering applications.

Analysis and experimentation of lamb wave transmission characteristics in the stiffened plates

ABSTRACT Ultrasonic Lamb wave technology holds extreme significance in the structural health monitoring of integral metal wall plates. However, its application is limited due to complex Lamb wave transmission characteristics caused by stiffeners. In the study, the transmission characteristics of Lamb waves in common types of stiffener cross sections (I-type and Γ-type) of large wall plates were investigated. A 2D-FFT (Two-Dimensional Fast Fourier Transform) calculation method was developed to accurately analyse the transmission characteristics of Lamb waves in stiffened plates with different stiffener cross-sections. The stiffener structure could be considered as a comb filter through the experimental and simulation results. Theoretical and experimental evidence shows that the characteristics of the filter are mainly affected by the dimensions of the height direction of the stiffeners. The variations of comb filtering characteristics of Lamb waves with stiffener geometry were deeply analysed. In addition, the formation mechanism of the comb-filtering effect of the stiffeners on the transmitted wave has been validated through experimental measurement. This study provides the basis for the reasonable frequency selection of Lamb waves for detecting the stiffened plate structure, and it significantly advances the application of Lamb waves in the structural health monitoring of integral metal wall plates.

Optimisation design and experimental analysis of rotary blade reinforcing ribs using DEM-FEM techniques

This study addresses the prevalent issue of rotary blade fractures in tillage operations by designing a new type of reinforcing rib that mitigates neck force and alleviates stress concentration. Initially, utilising traditional design concepts, the side-plate reinforcing rib was segmented into units and analysed using ANSYS to develop an initial model. Evaluation indices such as specific strength structural efficiency and specific stiffness structural efficiency were employed to perform orthogonal optimisation of the rib dimensions, achieving optimal measurements of 72.9 mm in length, 15.7 mm in width, and 3.5 mm in thickness. These dimensions enhance the specific strength structural efficiency by 14.14% and the specific stiffness structural efficiency by 0.95% compared to the initial model. Further, the rib's mathematical model was refined and generalised by a curve-fitting method across different rotary blade models (IT series), followed by topological optimisation to fine-tune morphological features. This optimisation reduced the model's mass by 9.78% and improved efficiency metrics by 2.6% (strength) and 0.5% (stiffness). Comparative experiments using DEM-FEM coupled analysis were conducted on three optimised models to assess the redesigned blade's performance. The experiments evaluated key performance metrics such as neck force, maximum stress, fatigue life, and ultimate fracture stress. The results indicate that after two rounds of optimisation, the blade's neck force was reduced by 16.85%, the maximum stress decreased by 15.22%, the fatigue life increased by 76.03%, and the ultimate fracture stress improved by 20.16%. These changes align with the optimisation objectives. Subsequent control and calibration tests produced a load-strain curve that validated the simulation data with a marginal error range of 3%–10%, validating the simulation's accuracy. This research provides a robust theoretical framework for optimising the reinforcing rib and fracture resistance of rotary blades.

Analytical Modeling of Bistable Beam With Double-Ring-Shaped Deformation Element

Abstract The field of negative stiffness structures has recently seen an increase in attention as a result of advancements in additive manufacturing (AM) technology. These advancements have made it possible to produce materials in a more expedient manner. The purpose of this research is to demonstrate a highly tunable and reusable bistable beam design that is based on a double-ring-shaped deformation element that undergoes pure bending, unlike traditional bistable mechanisms with buckling-based deformation elements. Further, an analytical model is developed and then validated by means of experimental and numerical results to precisely predict the snap-through behavior of a beam. It has been shown that the analytical model that was proposed has accuracy in terms of foreseeing the snap-through transition. A detailed study is conducted to explore the influence of geometric parameters on the snap-through characteristics. By carefully modifying these geometric properties, the required mechanical behavior of negative stiffness metamaterial (NSM) may be achieved for specific applications.

Associations of circulating T-cell subsets with carotid artery stiffness: the Multi-Ethnic Study of Atherosclerosis.

Background: Arterial stiffness measured by total pulse wave velocity (T-PWV) is associated with increased risk of multiple age-related diseases. T-PWV can be described by structural (S-PWV) and load-dependent (LD-PWV) arterial stiffening. T-cells have been implicated in arterial remodeling, arterial stiffness, and hypertension in humans and animals; however, it is unknown whether T-cells are risk factors for T-PWV or its components. Therefore, we evaluated the cross-sectional associations of peripheral T-cell subpopulations with T-PWV, S-PWV, and LD-PWV. Methods: Peripheral blood T-cells were characterized using flow cytometry, and carotid artery stiffness was measured using B-mode ultrasound to calculate T-PWV at the baseline examination in a participant subset of the Multi-Ethnic Study of Atherosclerosis (MESA, n=1,984). A participant-specific exponential model was used to calculate S-PWV and LD-PWV based on elastic modulus and blood pressure gradients. The associations between five primary (p-significance<0.01) and twenty-five exploratory (p-significance<0.05) immune cell subpopulations, per 1-SD increment, and arterial stiffness measures were assessed using adjusted linear regression models. Results: For the primary analysis, higher CD4+CD28-CD57+, but not CD8+CD28-CD57+, T-cells were associated with higher LD-PWV (β=0.04 m/s, p<0.01) after adjusting for co-variates. None of the remaining T-cell subpopulations in the primary analysis were associated with T-PWV or S-PWV. For the exploratory analysis, several memory and differentiated/senescence-associated CD4+ and CD8+ T-cell subpopulations were associated with greater T-PWV, S-PWV, and LD-PWV after adjusting for co-variates. Conclusions: We highlight novel associations in humans between CD4+ and CD8+ memory and differentiated/senescence-associated T-cell subpopulations and measures of arterial stiffness in MESA. These results warrant longitudinal, prospective studies that examine changes in T-cell subpopulations and arterial stiffness in humans.

Impact resistance of biomimetic gradient sinusoidal composites by 3D printing: Tunable structural stiffness and damage tolerance

Taking inspiration from the remarkable impact resistance of the dactyl club of Odontodactylus scyllarus and utilizing the material extrusion-based 3D printing process for continuous fiber reinforced composites (CFRCs), the biomimetic gradient sinusoidal CFRCs (BGS-CFRCs) was designed and manufactured. This material combines the bidirectional sinusoidal structure with a gradient layering configuration, mimicking the natural design found in the dactyl club. Experimental tests revealed that BGS-CFRCs achieved a Charpy impact strength of up to 63.24 kJ/m2, surpassing flat-layered polylactic acid (PLA) and continuous carbon fiber reinforced PLA (CCF/PLA) specimens by 143 % and 80 %, respectively. Moreover, BGS-CFRCs exhibited tunable structural stiffness and damage tolerance. This can be attributed to the innovative in-plane fiber architecture and out-of-plane material gradient, revealing the synergistic effects of composite materials, bidirectional sinusoidal structure, and gradient layering configuration. Overall, this study combines multi-degree-of-freedom 3D printing of CFRCs with biomimetic structural design, providing new dimensions of design space. This breakthrough surpasses the limitations of traditional additive manufacturing techniques and structural design of composites, opening new possibilities for developing next-generation high-performance structural materials.

A non-classical computational method for modelling functionally graded porous planar media using micropolar theory

The current study proposes a computational-based method to employ the non-classical micropolar continuum for modelling plates with in-plane functionally graded porosities. Initially, a homogenisation method is developed to derive the micropolar parameters of porous heterogenous plates based on strain energy equivalence in various designed deformations simulated via finite element analysis. The modelling procedure is further augmented to accommodate structures with functionally graded porosities. The established method offers an effective framework for studying the mechanical behaviour of porous plates with various porosity distributions and a wide range of aspect ratios. Results indicate that the micropolar theory-based modelling surpasses traditional Cauchy theory in accurately predicting the stiffness and displacement distribution of the FG porous structures. The novelty of this study lies in the integration of micropolar theory with the homogenisation of graded porosity patterns, offering enhanced predictions for materials with microstructural features. Additionally, a custom finite element formulation is developed in COMSOL to implement micropolar elasticity, significantly improving the computational efficiency to account for complex geometry, loading, and boundary conditions. To show the applicability of the method, the modelling is used to design a dental implant with its functional property mimicking that of the natural bone to avoid stress-shielding while ensuring proper occlusivity.

Enhancing 3D printing accuracy of cassava starch gel through temperature-controlled freezing

Starch is an important renewable resource, however, the performance of 3D printing inks prepared from it requires improvement. This study revealed the effects of different freezing temperatures (25 °C, 4 °C, 0 °C, −20 °C, −40 °C, −80 °C) on the 3D printing accuracy of cassava starch (CS) gels in terms of starch gel properties (rheological properties, moisture distribution, submicroscopic structure) and multiscale structure (molecular size, chain length distribution, short-range ordered structure). As the freezing temperature decreased, the molecular size and the amylose (Am) content in CS gel were increased, particularly for short Am chains (X∼100–1000). These resulted in a greater orderly structure of the starch, enhancing the elastic modulus of the gel. Moreover, the lower the freezing temperature, the higher mobility of water molecules within the gel matrix after thawed, which in turn caused the reduction of gel viscosity and facilitated the smooth squeezing of the gel. After freeze-thawing at cryogenic temperatures, the above changes in CS gel properties improved the stiffness and support performance of the gel structure, thereby enhancing the 3D printing precision. This study provides insights into the development of 3D printing technology for starchy food materials, emphasizing its potential to transform the customization of starch-based food processing by enabling customized food products, enhancing texture, and offering consumers personalized food choices and improved sensory experiences.

Modal analysis of concrete gravity dam incorporating pre-stress condition along with soil–structure interaction

Purpose The fundamental period of the structure plays an important role in the seismic analysis. This study aims to analyze the modal response of dam, the two-dimensional (2D) FEM model is developed by using ANSYS 2022 R1 software. Design/methodology/approach To examine the optimized mesh size to achieve grid independence, the variable element size has been considered, and its optimal value is calculated using the technique of response surface optimization. Further, the effect of damping ratios of 5%, 8% and 10% is also considered for the free vibration analysis of the dam structure. Findings The results show that the natural frequencies of the dam decrease with a reduction in stiffness of the whole structure. Further, the effect of pre-stress conditions is analyzed and the study has proved that the natural frequency increases after considering the pre-stress as initial condition during modal analysis. Further, it is found that the damping has a substantial effect on frequency for higher modes of vibrations. Research limitations/implications The study only focused on modal analysis of the gravity dam, and this study’s results can be used further to evaluate the dynamic behavior of the dam including hydrodynamic conditions. Originality/value The finite element tool is used to evaluate the modal response of gravity dam incorporating pre-stress and damping ratio along with soil–structure interaction. Moreover, to the best of the authors’ knowledge, no earlier study has been conducted to evaluate the effect of damping and pre-stress conditions on the stability and natural frequency of the system.

Free vibration characteristics of honeycomb sandwich cylindrical shells reinforced with graphene nanoplatelets/polymer coatings

This study conducts a comprehensive analysis of the free vibration characteristics of honeycomb sandwich cylindrical shells reinforced with graphene nanoplatelets (GNPs). The shells are modeled with a hexagonal honeycomb core, which not only provides a lightweight structure but also enhances the stiffness and dynamic stability. This core design is ideal for high-performance applications such as aerospace and light transport equipment. In addition, the incorporation of graphene nanoplatelet/polymer coatings further improves the structural stiffness, making these shells suitable for demanding environments where both strength and lightweight properties are critical. In the theoretical model, the refined trigonometric shear deformation theory (RTSDT) is applied to accurately represent both bending and shear deformations, capturing the complex behavior of honeycomb sandwich cylindrical shells without requiring shear correction factors. Various parameters, including axial and circumferential wave numbers, as well as geometry and material properties, are examined to assess their impact on natural frequencies. Comparisons with existing literature validate the theoretical models, demonstrating strong agreement with previous results. The analysis reveals that the fundamental natural frequency and other natural frequencies are significantly affected by the inclusion of GNPs and variations in sandwich cylindrical shell geometry. The findings underscore the effectiveness of the RTSDT in modeling these complex sandwich structures.

Bioinspired Microhinged Actuators for Active Mechanism‐Based Metamaterials

AbstractMechanism‐based metamaterials, comprising rigid elements interconnected by flexible hinges, possess the potential to develop intelligent micromachines with programmable motility and morphology. However, the absence of efficient microactuators has constrained the ability to achieve multimodal locomotion and active shape‐morphing behaviors at the micro and nanoscale. In this study, inspiration from the flight mechanisms of tiny insects is drawn to develop a biomimetic microhinged actuator by integrating compliant mechanisms with soft hydrogel muscle. A Pseudo‐Rigid‐Body mechanical model is introduced to analyze structural deformation, demonstrating that this hydrogel‐based microactuator can undergo significant folding while maintaining high structural stiffness. Furthermore, multiple microhinged actuators are combined to facilitate folding in multiple degrees of freedom and arbitrary directions. Fabricated by a multi‐step four‐dimensional (4D) direct laser writing technique, the microhinged actuators are integrated into 2D and 3D metamaterials enabling programable shape morphing. Additionally, micro‐kirigami with photonic structures is demonstrated to show the pattern transforming actuated by the microhinges. This bioinspired design approach opens new avenues for the development of active mechanism‐based metamaterials capable of intricate shape‐morphing behaviors.

Functional characterization reveals the importance of Arabidopsis ECA4 and EPSIN3 in clathrin mediated endocytosis and wall structure in apical growing cells

Summary Localized clathrin mediated endocytosis is vital for secretion and wall deposition in apical growing plant cells. Adaptor and signalling proteins, along with phosphoinositides, are known to play a regulatory, yet poorly defined role in this process. Here we investigated the function of Arabidopsis ECA4 and EPSIN3, putative mediators of the process, in pollen tubes and root hairs. Homozygous eca4 and epsin3 plants exhibited altered pollen tube morphology (in vitro) and self‐pollination led to fewer seeds and shorter siliques. These effects were augmented in eca4/epsin3 double mutant and quantitative polymerase chain reaction data revealed changes in phosphoinositide metabolism and flowering genes suggestive of a synergistic action. No visible changes were observed in root morphology, but atomic force microscopy in mutant root hairs showed altered structural stiffness. Imaging and FRET‐FLIM analysis of ECA4 and EPSIN3 X‐FP constructs revealed that both proteins interact at the plasma membrane but exhibit slightly different intracellular localization. FT‐ICR‐MS metabolomic analysis of mutant cells showed changes in lipids, amino acids and carbohydrate composition consistent with a role in secretion and growth. Characterization of double mutants of eca4 and epsin3 with phospholipase C genes (plc5, plc7) indicates that phosphoinositides (e.g. PtdIns(4,5)P2) are fundamental for a combined and complementary role of ECA4‐EPSIN3 in cell secretion.

Experimental study on internal damage mechanisms and performance state perception of tunnel linings under different loading paths

The state of tunnel lining structures plays a crucial role in determining safety and service quality throughout their serving life. Therefore, establishing a quantitative method for evaluating the bearing capacity of linings is crucial. Understanding the process and status of crack propagation is key to ensuring structural safety. The three-dimensional development of lining damage cracks is closely related to structural safety. Unveiling the spatial growth of these cracks and the evolution of structural performance is vital for an accurate assessment of lining safety. Key factors in crack propagation, along with non-destructive detection methods, serve as primary approaches for evaluating the safety condition. This paper explores the evolution law and evaluation model of the bearing capacity of plain concrete linings under different loading paths. The distribution of structural stiffness changes significantly under different boundary settings. Therefore, full-scale loading tests of lining components were conducted, designing two types of linings: one intact and the other with initial defects, to simulate the failure of plain concrete linings under diverse loading conditions. The results show that: (1) The damage development of linings exhibits clear staged evolution characteristics; (2) The spatial development of lining cracks can be divided into three stages; (3) There are significant differences in ultrasonic parameters at different stages. Consequently, a method for evaluating the local bearing capacity state of linings based on the coupling of crack characteristics and ultrasonic parameters is proposed; (4) This method is also applicable to linings with initial damage, where damage evolution follows similar stages. The findings provide theoretical guidance for predicting and preventing crack propagation in operational tunnel linings.

Experimental study on seismic performance of ancient wooden buildings considering the influence of geshan

The geshan is an essential component of ancient wooden buildings. They provide ventilation and lighting while playing a significant role in the structure's seismic performance. This article presents the results of quasi-static tests conducted on three sets of four-column lifting beam 1:2 scale test specimens. The study investigated the influence of geshan on structural torsion, joint tenoning, column root sliding, and lifting deformation characteristics. Additionally, the study examined the impact of these characteristics on seismic performance, including strength, stiffness, and energy dissipation capacity. The results indicate that the geshan had positive and negative effects on the structure. While they reduced the torsion of the structure during loading and prevented the pullout of the dovetail joints, they also exacerbated the lifting and slipping of the column root. The geshan increased the structure's stiffness, bearing capacity, and energy dissipation capacity, but reduced its ductility. The article analyzes the relationship between the initial damage, deformation characteristics, and stress performance of geshan and structures, highlighting their mutual influence. The research results can be used as a reference for accurately evaluating the seismic performance of ancient wooden buildings with geshan.

A straight-arch-straight beam tandem quasi-zero stiffness structure

Extremely low dynamic stiffness is essential for the successful utilization of quasi-zero stiffness (QZS) structures for vibration isolation, energy harvesting, and micromechanical sensing. However, most conventional QZS structures are based on a parallel connection of positive and negative stiffness mechanisms, which poses challenges for stiffness matching, structure design, and fabrication. We propose a QZS structure based on a straight-arch-straight (SAS) tandem connection, in which the integrated design of the structure overcomes the problem of stiffness matching, and more importantly, the simple design of the structure greatly reduces the difficulty of fabrication and enables the design of a wide range of load-carrying capacity by only adjust the ratio of the length of the straight beam to the arch and the ratio of the height of the arch to the thickness. The symmetric deformation of the SAS structure extends the working range of the QZS structure, which can be further extended several times or divided into several different QZS intervals by connecting several identical or different SAS units in parallel. The experimental results show that the SAS structure has excellent vibration isolation performance in the low-frequency region, and more importantly, the low preload requirement also provides an important reference for structural design in the field of micromechanical sensing.