Structural Stiffness Research Articles

Structural and load-dependent arterial stiffness across the adult life span.

The arterial stiffening is attributed to the intrinsic structural stiffening and/or load-dependent stiffening by increased blood pressure (BP). The respective lifetime alterations and major determinants of the two components with normal aging are not clear. A total of 3053 healthy adults (1922 women) aged 18-79 years were enrolled. The carotid intima-media thickness, diameter, and local BPs were automatically determined by the radio frequency ultrasound system. The Peterson and Young elastic moduli were then calculated to represent total arterial stiffness. Structural stiffness was recalculated at a reference BP of 120/80 mmHg with established models. Load-dependent stiffness was the difference between total and structural stiffness. Both structural and load-dependent stiffness increased with aging, with much larger changes in the structural components. The age-related increasing rates were higher in women for the structural stiffness than men (P < 0.05), but similar for the load-dependent stiffness. The clinical characteristics and arterial stiffness were widely correlated, but most correlations were quite weak (r < 0.3) other than BPs. Multiple regression analyses adjusted for sex, age and other clinical correlates showed that structural stiffness increased with pulse pressure (PP) and load-dependent stiffness increased with mean arterial pressure (MAP), respectively. The age-related arterial stiffening is mainly caused by the intrinsic structural stiffening, which demonstrated significant age-sex interaction. BPs were the major clinical determinants of arterial stiffness, with PP and MAP associated with different arterial stiffness components. The differentiation of the structural and load-dependent arterial stiffness should be highlighted for the optimal vascular health management.

Research of tangential cyclic loading on mechanical properties between cosine contact surfaces

Abstract The investigation of the mechanical properties of contact surfaces under tangential cyclic loading is very important for understanding the stiffness and damping of combined structures. In this paper, using Hertzian contact theory and Coulomb's friction law, the contact mechanical mechanism of a common cosine cylindrical contact model subjected to tangential loading, unloading, and reloading is investigated, and the load-displacement curves (hysteresis curves) and the energy equations of a complete displacement cycle are deduced. The results show that under the action of tangential cyclic load, the shear stress increases immediately, and the micro slip zone outside the contact area gradually expands inward until it becomes a slip zone. At this point, the hysteresis curve changes from a "shuttle shaped" to a "quadrilateral" shape. In addition, nonlinear finite elements are used for static simulation to verify the accuracy of the hysteresis curve, tangential stiffness, and energy dissipation analysis of the cosine contact model under different axial crossing angles. The energy equation's fluctuation with tangential displacement under different conditions, as well as the impact of friction coefficient, axial intersection angle of the contact surface, external load, and cosine surface characteristics on the mechanical properties of the contact surface. With the increase of surface roughness or normal load, energy increases nonlinearly with the increase of displacement. Finally, when the Von Mises stress reaches the yield limit, reciprocating displacement loading will lead to plastic accumulation, resulting in wear and tear.

Hysteretic Performance of Composite Damper with Yielding Reserve Stiffness

Previous research on composite dampers has rarely addressed the issue of large deformations of structures under limit state. However, the proposed damper in this paper takes this issue into account and could provide yielding reserve stiffness for structures, ensuring structural resilience. A composite damper with yielding reserve stiffness (YRSD), consisting of a friction unit and a metal yield unit, was proposed. Low cyclic loading tests with different energy-dissipating steel plate thicknesses and bolt preloads were carried out and experimental results were compared with that of numerical simulation. This paper focuses on the synergistic energy dissipation mechanism of the proposed damper and the effects of various factors on its hysteretic performance, including the bolt preload and thickness of X-shaped steel plates. The results show that the synergistic energy dissipation mechanism of the proposed damper is well, exhibiting the behavior of hardening post-yielding stiffness and multi-stage energy dissipation characteristics, which could provide yielding reserve stiffness for the structure. The experimental hysteresis curve of YRSD is full, indicating its strong energy dissipation capacity, and the skeleton curve of experiment is consistent with that of the theoretical model. The envelope area of the rectangular hysteresis curve of YRSD increases by 107.3% with the preload increased by 100%. When the thickness of the X-shaped steel plates is increased by 2 mm, the resistance of YRSD increases by 26.2% and the post-yield stiffness increases by 37.9%. The stiffness degradation trend of all specimens initially decreases and then increases. The energy dissipation capacity of the friction unit increases by 53.8% as the preload is doubled. The capacity of the metal yield unit increases by 31.7% as the thickness of the X-shaped steel plates is increased by 2 mm. When the energy dissipation capacities of the friction unit and the metal yield unit are close to equal, the optimal energy dissipation capacity of the proposed damper is achieved. The error of results between the numerical analysis and experimentation is less than 10%, providing a basis for the parametric analysis of similar composite damper with yielding reserve stiffness.

Research on the Simplified Calculation Model and Parameter Analysis of Large-Size PBL-Stiffened Steel–Concrete Joints

To investigate the design principles and simplified calculation model of large-size PBL-stiffened steel–concrete joints, this study uses a Y-shaped rigid frame-tied arch composite bridge as an engineering background. Based on deformation coordination theory, a combination of theoretical analysis and numerical simulation was employed to derive a simplified calculation model that accounts for boundary conditions such as the stiffness of steel beam end restraints and the local bearing effect of the bearing plate. Parametric analysis of the steel–concrete joint was conducted. The results indicate that the derived simplified calculation model exhibits good accuracy and is suitable for calculating force transfer in various components of the steel–concrete joint under different boundary conditions. Using the simplified model, the effects of parameters such as steel–concrete joint length, connector stiffness, and structural axial stiffness on the axial force transfer in primary force-bearing components (connectors and bearing plates) were studied. The findings reveal that an excessively long steel–concrete joint does not effectively reduce maximum shear force; variations in connector stiffness primarily affect connectors farther from the bearing plate without changing the shear force distribution. Increasing the axial stiffness of the steel structure within a certain range can improve the maximum shear force in connectors, whereas increasing the axial stiffness of the concrete structure has the opposite effect.

Magnetic kirigami dome metasheet with high deformability and stiffness for adaptive dynamic shape-shifting and multimodal manipulation.

Soft shape-shifting materials offer enhanced adaptability in shape-governed properties and functionalities. However, once morphed, they struggle to reprogram their shapes and simultaneously bear loads for fulfilling multifunctionalities. Here, we report a dynamic spatiotemporal shape-shifting kirigami dome metasheet with high deformability and stiffness that responds rapidly to dynamically changing magnetic fields. The magnetic kirigami dome exhibits over twice higher doming height and 1.5 times larger bending curvature, as well as sevenfold enhanced structural stiffness compared to its continuous counterpart without cuts. The metasheet achieves omnidirectional doming and multimodal translational and rotational wave-like shape-shifting, quickly responding to changing magnetic fields within 2 milliseconds. Using the dynamic shape-shifting and adaptive interactions with objects, we demonstrate its applications in voxelated dynamic displays and remote magnetic multimodal directional and rotary manipulation of nonmagnetic objects without grasping. It shows high-load transportation ability of over 40 times its own weight, as well as versatility in handling objects of different materials (liquid and solid), sizes, shapes, and weights.

Studying the performance of quasi zero stiffness structure added to seat’s suspension based on various vehicle types

To elucidate the performance of quasi zero stiffness structure (QZSS) added to seat’s suspension on various vehicle models, three typical models of the vehicle including the car, soil compactor, and vehicle truck are used and established to study the QZSS under various simulations of vehicles. The experiment of soil compactor with seat suspension using QZSS has been also done to strengthen the research results. The result research at the time domain and frequency domain shows that QZSS added into seat’s suspension system is very effective in isolating operator’s seat vibrations in all three models. Especially, the QZSS is very effective when the vehicles are moving on poor road surfaces and high speeds. Besides, the performance of QZSS on the soil compactor’s seat is better than that of the vehicle truck and car. Therefore, this discovery can be a very useful reference for researching and applying QZSS to seat suspension in all off-road vehicles including earth-moving machinery and soil compactors.

The Computational Design of Corrugated Tube Lattice Structure with Negative Stiffness Property Under Axial Compression Load

Negative stiffness (NS) structures have singular mechanical properties and potential applications in various scenarios. A corrugated tube (CT) and an NS lattice structure (NLS) composed of CTs and connection plates are proposed. The mechanical properties of CT and NLS under axial compression are investigated by experiments and simulations. The deformation modes of CT and NLS are layer-by-layer folding of structural layers. The influences of geometric parameters on the compression performance of CT and NLS have been studied. Through a reasonable design of the thickness of upper and lower conical structures, CT and NLS can exhibit periodic changes in peak and valley forces during the compression process, resulting in significant NS behavior. In addition, the increase of CT’s number does not significantly affect the NS effect, and the load-carrying capacity of NLS increases significantly as the number of CT increases. The energy absorption (EA) and peak force values of NLS-[Formula: see text], NLS and NLS-[Formula: see text] are approximately 16, 9, and 4 times those of CT-3.0-0.6-f0.5, and the EA value of an NLS model is the sum of the EA values of its all CTs. In addition, the effects of geometric parameters on the mechanical properties of NLS are systematically investigated. With reasonable parameter values, NLS exhibits strong NS effect and excellent EA capacity.

Mechanism of Multi-Physical Fields Coupling in Macro-Area Processing via Laser–Electrochemical Hybrid Machining (LECM)

Laser–electrochemical hybrid machining (LECM) is promising in the processing of thin-wall parts, which avoids problems such as the weak stiffness of structures and thermal defects. However, while most studies focus on precision machining via LECM, few investigate the potential of this technique in macro-area processing. In this paper, the synergistic effects on the coupling of thermal field and electrochemical field on bulk material removal mechanisms in the LECM of additively manufactured Ti6Al4V are comprehensively analyzed experimentally and theoretically. According to the experimental results, LECM improved the material removal rate (MRR) by up to 28.6% compared to ECM. The induction of the laser increases local heating, accelerating the temperature rise of the electrolyte, eventually promoting the electrochemical reaction. The hydrogen bubble flow promotes overall heat convection between the electrode and workpiece, which facilitates the removal of the facial precipitates and increases the efficiency of electrochemical dissolution. Higher voltages and laser powers promote the formation of hydrogen bubble flow; meanwhile, they also aggravate laser energy scattering, limiting the overall machining efficiency. Additionally, laser irradiation causes the ablation and rupture of hydrogen bubbles, which weakens the bubble flow effect and ultimately decreases the material removal efficiency. This study reveals the underlying mechanisms of the joint effects of the laser field and electrical field in LECM, and the findings can provide valuable insights for the optimization of LECM parameters in industrial applications.

An Innovative Adaptive-Dimension Accordion Honeycomb for Circumferential Deformation

This work presents a novel variable-dimension accordion honeycomb structure capable of achieving circumferential deformation, characterized by its uneven structural stiffness properties. Unlike current accordion honeycombs, our design employs a variable-dimension honeycomb configuration defined in the polar coordinate system, using independent shape and size parameters. We derive the circumferential stiffness of both the unit cell and the honeycomb through analytical and theoretical approaches based on the series–parallel mechanism (SPM), validated using finite element modeling (FEM). We evaluate the influence of unit cell angles and the number of units along orthogonal directions on circumferential stiffness, finding excellent agreement between theoretical and numerical models. Additionally, the results demonstrate that the novel honeycomb maintains a zero Poisson ratio during circumferential deformation, with the SPM remaining unaffected by geometric nonlinearity.

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.

Corrosion impact analysis: a numerical model for reinforced concrete structures using the Finite Element Method based on Position

Reinforced concrete (RC) structures face environmental challenges like carbonation and chloride ingress, leading to decreased stiffness, serviceability, and security. A key issue is accurately simulating structural responses to environmental effects and their impacts. This article addresses this by proposing a numerical model based on the Finite Element Method with Positions (FEMP), employing frame elements to forecast post-corrosion structural behavior. Subsequently, a probabilistic study is conducted using Monte Carlo simulations to predict failure probabilities amidst changing environmental conditions. The study reveals corrosion's significant impact on structural stiffness and a high probability of failure within 50 years. These findings underscore the necessity of constructing structures with future climate change challenges in mind.

Influence of the unilateral elastic base on the backbone curves of an imperfect cylindrical panel

This work evaluates the influence of a discontinuous unilateral elastic base and an initial geometrical imperfection on the nonlinear free vibration of cylindrical panels. The Donnell’s nonlinear shallow shell theory is considered to describe the cylindrical panel, then the equations are discretized by the Galerkin method. The unilateral elastic base is represented by the Signum function, and the Heaviside function describes the discontinuity of the elastic base. The results show the analysis of the nonlinear free vibrations of the cylindrical panel through the backbone curves, investigating the influence of the hypothesis of contact of the unilateral elastic base and the initial geometrical imperfection of the cylindrical panel. The modal solution employed has with five degree-of-freedom, being sufficient to describe the nonlinear softening behavior of the imperfection cylindrical panel in contact with the discontinuous unilateral elastic base. The numerical results reveal that the imperfect cylindrical panel in contact with unilateral elastic base presents less structural stiffness than in contact with bilateral elastic base, with decreasing the natural frequencies. In conclusion, the backbone curves are strongly influenced by discontinuous unilateral elastic base and the imperfections of the cylindrical panel.

Research on the design of the magazine lifting mechanism based on double scissor structure

Abstract In view of the urgent needs of lightweight and modularization of a certain type of vehicle-mounted anti-aircraft gun, a design scheme of the magazine lifting mechanism based on the double scissor structure is proposed, the mathematical model of the lift and fulcrum of the hydraulic cylinder based on the principle of virtual displacement is established, the sensitivity of different fulcrum position parameters to the distance between the lift and the fulcrum of the hydraulic cylinder is studied, the local optimal solution is determined and the optimal lift design is realized by considering the actual installation space constraints, and the structural stiffness is verified to meet the design requirements through finite element simulation calculation. It provides a certain technical basis for the design of lightweight magazine lifting mechanism.

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.

Thermal aggregation and gelation behaviors of glucono-δ-lactone-induced soy protein hydrolysate gels: Effects of protein and coagulant concentrations.

In this study, a novel acid-induced heat-set soy protein hydrolysate (SPH) gel was successfully developed. The effects of protein (7 and 8wt%) and glucono-δ-lactone (GDL, 4, 6, 8, and 10wt%) concentrations on its aggregation and gelation behaviors were investigated by evaluating the structural, rheological, textural, and physical properties of the SPH gel. The structural properties revealed that GDL promoted the formation of SPH aggregates and gels, primarily via disulfide bonds and hydrophobic interactions, which were closely related to the unfolding of the protein structure, exposed hydrophobic groups, decreased protein solubility, and increased particle size and turbidity during the heating process. Subsequently, the gelling properties demonstrated that acidification with GDL (4-8wt%) significantly improved the viscosity, viscoelasticity, water-holding capacity, and stiffness of the network structures, decreased their hardness and springiness, and facilitated the formation of well-supported, soft-stiff gels, particularly for those made with 8wt% protein. In addition, the changes in relaxation time measured via low-field nuclear magnetic resonance and magnetic resonance imaging confirmed that the SPH gels effectively retained water that was trapped in the gel network by strengthening the binding between water and protein molecules. The research could provide useful gelling technique for the protein hydrolysate products.

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.

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.

Total and Structural Carotid Artery Stiffness are related to Cognitive Decline and ADRD Pathology: The Multi‐Ethnic Study of Atherosclerosis (MESA)

Total and Structural Carotid Artery Stiffness are related to Cognitive Decline and ADRD Pathology: The Multi‐Ethnic Study of Atherosclerosis (MESA)

Prestress state, parametric analysis study and genetic algorithm-based tentative design of a novel pentagonal cable dome structure with tri-strut layout

To improve the structural performance and economy of the large-span roof structure from the structural system level, a novel structural form of pentagonal cable dome with tri-strut layout and large central opening is proposed, which can be applied to the large-span stadium ring canopy structure. Different from Fuller's traditional conception of the tensioning whole, this type of system has three struts intersecting at the same chord node, which reduces the amount of ring and diagonal cables, facilitates tensioning construction, and improves overall stability. For this large-opening cable dome, a general formula for calculating the internal force of prestressed state rods was derived based on the nodal equilibrium equations, and the effects of several parameters on the distribution of pre-tension in the cable dome were analyzed and studied to understand the distribution pattern and characteristics of the cable dome pre-stress. A large-opening stadium canopy with a span of 100m is taken as an example. The parameter sensitivity and correlation analysis of the structural performance reveals that the main influence of the economy of this cable dome is the pre-tension level. In contrast, the geometric parameter produces a much lower effect on the structural economy. The optimal design and trade-off analysis of this cable dome structure based on two genetic algorithms show that appropriately increasing the structural vector height and decreasing the thickness while satisfying the stability improves the structural stiffness and economy. The analysis results show that this new type of cable dome has superior technical and economic indicators, and the research in this paper provides a new form and new ideas for the analysis and design, optimization research, and modeling of the cable dome.

Design and characteristic analysis of quasi-zero stiffness inertial actuator

Abstract In order to solve the problem of low frequency vibration control more effectively, a new type of inertial actuator is proposed in this paper, which is different from the conventional type in that the linear stiffness is replaced by the quasi-zero stiffness. In this design, the structure mainly consisting of a horizontal spring and connecting rod provides negative stiffness to offset the positive stiffness of the vertical spring, which not only ensures sufficient static load capacity, but also reduces the dynamic stiffness of the mass near the equilibrium position. In this study, a restoring force characteristic of the actuator (i.e., the influence of the quasi-zero stiffness structure on the mapping relationship between the restoring force and displacement) is investigated. Then the nonlinear differential equations of the quasi-zero stiffness actuator are derived. The dynamic characteristic of the actuator is discussed based on the harmonic balance method, and the accuracy is proved by numerical verification. The dynamic simulation results show that the quasi-zero stiffness structure can effectively reduce the natural frequency of the actuator, and its performance in low frequency band is better than that of the corresponding linear actuator.