Structural Stiffness Research Articles

Comparison of Bending Properties in Paired Human Ribs with and without Costal Cartilage

<div class="section abstract"><div class="htmlview paragraph">Thoracic injuries, most frequently rib fractures, commonly occur in motor vehicle crashes. With an increased reliance on human body models (HBMs) for injury prediction in various crash scenarios, all thoracic tissues and structures require more comprehensive evaluation for improvement of HBMs. The objective of this study was to quantify the contribution of costal cartilage to whole rib bending properties in physical experiments. Fifteen bilateral pairs of 5th human ribs were included in this study. One rib within each pair was tested without costal cartilage while the other rib was tested with costal cartilage. All ribs were subjected to simplified A-P loading at 2 m/s until failure to simulate a frontal thoracic impact. Results indicated a statistically significant difference in force, structural stiffness, and yield strain between ribs with and without costal cartilage. On average, ribs with costal cartilage experienced a lower force but greater displacement with a longer time to fracture compared to isolated ribs. Comparisons were complicated by varying levels of calcification between costal cartilages and varying geometry with the inclusion of the costal cartilage. This study highlights the important effects of costal cartilage on rib properties and suggests an increased focus on costal cartilage in HBMs in future work.</div><div class="htmlview paragraph"/></div>

Research on structural vertical stiffness evaluation of track-specific suspension bridge under the action of the no-load first train

The track-specific bridge has the characteristics of a large volume of passenger traffic, narrow transverse width, and large excitation. The long-term and high-frequency operating conditions put forward strict requirements for the safety and comfort of the bridge. Aiming at the problem of achieving fast, accurate, and intelligent evaluation of bridges under the coupling action of trains and temperatures, this paper proposes a method for evaluating the structural vertical stiffness of track-specific suspension bridges under the action of the no-load first train. Firstly, the [Formula: see text] (deformation-velocity-time) data of trains on the bridge are analyzed through linkage numerical simulation, track train transponder, and structural safety monitoring system. Secondly, the CART algorithm establishes a regression model for data correction. The mapping relationship between the modified deformation monitoring value and the theoretical calculation value is analyzed to realize the current structural vertical stiffness evaluation. Finally, it is verified by the world’s largest span self-anchored track-specific suspension bridge. The results show that the theoretical deformation value of the most unfavorable deformation section is 268.55 mm, the actual monitoring value is 232.80 mm, the difference is 35.75 mm, and the relative error is 13.3%. The R2 score of the CART regression model is 0.94, and the accuracy of the CART regression model is higher than that of other algorithm regression models. The modified dynamic check coefficient is less than 1, and the ratio of the modified residual deformation value to the maximum deformation value is 7.6%, which meets the specification requirement not exceeding 20%, indicating that the current structural vertical stiffness is in normal operating conditions.

Adaptive stiffness structures via additively manufactured fluid accumulators

Abstract Lightweight mechanical structures often have low stiffness that prevents their use in structural applications. The demand for lightweight mechanical structures that operate under wide-ranging loading conditions motivates the development of adaptive stiffness structures. The ability to control the stiffness of a mechanical structure allows for tailored static and dynamic properties, including resonant frequencies. However, adaptive stiffness structures that are low cost, offer design flexibility, and can be additively manufactured still remain a challenge. To this end, we introduce adaptive stiffness devices called Pressure-actuated Adaptive Structural Cells (PASCells) with controllable axial stiffness. The proposed PASCells consist of four, flat arches that seal at the edges to contain a working fluid. The axial stiffness of the PASCell increases when the enclosed working fluid is compressed due to volume reduction under an axial load. Axial compression of a PASCell creates large internal volume change and internal pressure that resists this compression, increasing stiffness when the fluid volume is constrained by, for example, closing an outlet valve. Designed for additive manufacturing, PASCells can be integrated with mechanical structures to enable adaptive stiffness. In this paper, we derive the governing equations that describe the static deformation of PASCells under an axial load and internal pressurization and experimentally evaluate the stiffness of the PASCells in empty (or open valve) and filled (or closed valve) configurations. Single, series-connected, and parallel-connected PASCells are additively manufactured and experimentally tested, verifying the model predictions, and experimentally demonstrating a 70% stiffness increase.

Vibration response analysis of hydraulic pipeline based on finite element method

The oil pipeline is a critical component that influences the vibration and noise levels of the hydraulic system. Inadequate design may result in resonance or leakage issues, rendering it susceptible to external vibration excitation. To enhance the reliability of the hydraulic pipeline, simulations and analyses were conducted on its modal, harmonic response, and fatigue characteristics. Based on the results of harmonic response analysis and strength analysis, an effective reinforcement scheme was proposed and validated. By inputting the acceleration load to the pipeline system for frequency response analysis, the influence of different excitation forces on the pipeline stress can be determined. The findings indicate that pipeline vibration primarily occurs in the outlet pipe of the transmission, with significant stress and vibration displacement observed at the thermostat valve support. Following structural improvements, there was a notable reduction in stress levels at the transmission outlet pipe, along with a shift in maximum stress position due to additional support. This enhancement has improved both structural stiffness of the outlet pipe and overall stability of the pipeline system.

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

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

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.

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.

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.

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.

Hierarchical negative stiffness structures with improved resilience and energy absorption capability

Hierarchical negative stiffness structures with improved resilience and energy absorption capability

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.