Good Stiffness Research Articles

Analysis of Force Distribution and Motion Characteristic of Hybrid-Driven Tensegrity Parallel Mechanism

Abstract Tensegrity parallel mechanisms is a novel spatial structure composed of cable-based and rigid-based chains, which is characterized by lightweight, multi-stability, high precision, good stiffness, and high load-bearing capacity. This paper focuses on the six-degree-of-freedom tensegrity parallel mechanism, analyzing its static equilibrium and presenting the force equilibrium equations. A model for cable tension distribution optimization is established, utilizing different P-norm objective functions to optimize the distribution of tension in cables and rigid links, discussing the reasons for unreasonable tensions in the system. Under given constraints on the motion pairs of the mechanism, the workspace of the mechanism is plotted, and factors influencing the size of the workspace are analyzed. Finally, the singularity of the mechanism is addressed based on the Jacobian matrix, demonstrating the feasibility of reaching the space volume by the mechanism. It has certain reference significance for the configuration theory and analysis methods of tensegrity parallel mechanisms and rigid-flexible coupling mechanisms, and provides a reference for the further promotion and application of mechanisms.

Optimal design of vibration resistance of fiber-reinforced composite sandwich plates embedded in a viscoelastic square honeycomb core

This work focuses on investigating the optimal design of composite sandwich plates (FCSPs) with a viscoelastic square honeycomb core (VSHC). Firstly, using the cross-fill theory, the complex modulus technique, the first-order shear deformation theory, the minimum strain energy principle, and the Newmark-β method, a theoretical model of the VSHC-FCSPs under half-sine pulse excitation is formulated to calculate the inherent frequencies, the peak and vibration decay time of the transient response in time domain. The peak and vibration decay time are taken as the indexes of the anti-vibration performance. Considering an index of structural stiffness performance, the average value of the inherent frequencies is adopted to calculate the overall stiffness. After a set of literature validations and optimization validations, the multi-objective genetic algorithm is employed to study the optimization issue of VSHC-FCSPs. The optimization objectives are to minimize the three design variables of the transient response peak, vibration decay time, and reciprocal of overall stiffness. Then, the fiber laying angle of each layer, the core thickness ratio and the modulus ratio are assumed as optimization variables. Finally, the results with good vibration resistance and structural stiffness in the Pareto front are chosen as references, and these corresponding variations of the design variables and optimization objectives are obtained. The optimization results have revealed that the optimization variables corresponding to the intermediate points should be selected as references to improve the anti-vibration capacity and ensure the structural stiffness performance.

Seismic behavior of innovative reinforced concrete composite shear wall with PEC boundary columns

Considering the inadequate integrity between boundary elements and wall connections in shear walls with PEC columns. A new type of PEC shear wall is proposed to enhance the connection between the PEC columns and the wall by introducing T-section connectors to improve the bearing capacity as well as the deformation capacity. In this study, the seismic behavior of composite shear walls was investigated in terms of the failure process, hysteresis, energy consumption, etc. The test results showed that the specimens had good stiffness and energy dissipation capacity. The combination of PEC columns with RC shear walls under the action of the T-section connector was effective. An increase in the width-to-thickness ratio can lead to shear bonding failure. In the PEC-RCSW structure with a shear-to-span ratio of 1.35, the bearing capacity and deformation capacity of the T-section connectors and PEC columns are slightly higher in the major axis direction than in the minor axis direction. Based on the test results, the finite element model was established and further research was conducted on the shear span ratio and T-section connector size. And provided engineering application suggestions for the innovative composite shear wall shear wall. Finally, flexural and shear capacity calculation formulae of the innovative composite shear wall were proposed.

Prediction and optimization framework of shear strength of reinforced concrete flanged shear wall based on machine learning and non-dominated sorting genetic algorithm-II

Reinforced concrete (RC) flanged shear wall has good lateral strength and stiffness, which has been widely used in building structures. Due to the coupling effect of many factors such as wall section shape, shear span ratio, so the shear performance evaluation of flanged wall is still very limited. This paper proposed a prediction framework for the shear capacity of RC flanged shear walls. A database containing 14 input variables, 1 output variable and 153 samples was constructed to evaluate the prediction accuracy of 11 existing design methods. The Pearson coefficient was used to preliminarily analyze the correlation between variables. The grid search was used to optimize the hyperparameters of 4 machine learning models, and six statistical indicators ( R2, R, RMSE, SD, MAE, and MAPE) were used to comprehensively compare the prediction results of the ML models to determine the best model. On this basis, SHapley Additive exPlanations (SHAP) was used to enhance the interpretability of the prediction models, and the mechanism of the input variables on the shear capacity was quantified. A graphical user interface (GUI) was proposed to guide the engineering design. A multi-objective model (MOO) was established to analyze the trade-off between shear performance and cost, thereby determining the best optimal scheme. The results show that the prediction accuracy of the ML models is better than the existing design methods. The XGB model has the best prediction performance, with R2, R, RMSE are 0.99, 0.99, 118.96, respectively. The SHAP method can effectively enhance the interpretability of the ML models, and tw, lw and f ′c are the key parameters affecting the shear capacity of the flanged shear wall.

Bacterial-responsive biodegradable silver nanoclusters composite hydrogel for infected wound therapy

Skin wounds are susceptible to bacterial infections, which hinder healing and extend recovery. Herein, we designed a silver nanoclusters (Ag NCs) composite hydrogel for infected wound treatment via bacterial enzymatic degradation and Ag release. Using biocompatible gelatine and polyethylene glycol as the main components, DNA-templated Ag NCs were covalently linked to a polymer network to obtain the final nanocomposite hydrogel. This hydrogel exhibited good compressive and tensile stiffness, bioadhesion and water absorption. The overexpressed bacterial enzymes protease and DNase in the infected wound were hydrolysed by the gel matrix, subsequently releasing antibacterial Ag ions. In vitro experimental results proved that the hydrogel demonstrated excellent bactericidal effect on Staphylococcus aureus and Escherichia coli, which are commonly implicated in clinical wound infections. Animal experiments revealed that the hydrogel considerably promoted cell proliferation and wound healing with less inflammatory responses. Thus, these results demonstrate strategies for bacterial enzyme–responsive Ag release for infected wound healing, facilitating further development of intelligent bandages.

Cyclic behavior of cold-formed stainless steel sandwich tubular brace: An experimental investigation

Stainless steel shows promise for application in seismic-active regions. Previous research showed that stainless steel dampers could exhibit good energy dissipation capacity and high post-yield stiffness under cyclic loading. In light of that, a novel type of cold-formed stainless steel sandwich tubular brace (STB) is presented in this study, featuring one stainless steel square hollow section (SHS) tube as the load-carrying component and two additional stainless steel SHS tubes providing a buckling-restraining effect. Six specimens were tested under cyclic loading, varying parameters including the cross-section slenderness of the core tube, restraining ratio and loading histories. Loading protocols encompassed standardized ones following the Chinese specification (CN) and American provision (US), as well as a protocol representing the near-fault earthquakes (NF). Failure modes, hysteretic response and seismic performance indexes were obtained. Results showed that the hysteretic curves could maintain stable. Under the CN loading protocol, the specimen with a slender core cross-section exhibited uniform local buckling. The strain hardening coefficient ω stayed within the range of 1.46–1.58. The specimens exhibited a slow decay rate of tangent stiffness, highlighting their relatively high post-yield stiffness. The cumulative energy dissipation factor could reach 658, signifying good energy dissipation capacity. Additionally, under NF loading, specimens exhibited enhanced cumulative ductility compared to CN or US loading. Furthermore, an evaluation was conducted to assess the suitability of existing design methods for preventing overall buckling and local bulging in stainless steel STBs. It indicated that the current design approaches tended to be overly conservative for both overall and local stability design of stainless steel STBs, primarily due to the lack of consideration for SHS core stiffness and the interactions between flanges and webs, respectively.

Morphological analysis of a novel scissor-type deployable cable dome structure

A novel deployable scissor-type strut cable dome structure was proposed, which can improve the lateral stiffness of the traditional cable structure and achieve the characteristics of fast unfolding and closing during construction. However, the geometric stability and optimal initial prestressing theory of traditional cable dome structures cannot be applied to the new structure. Based on the equilibrium matrix theory, the geometric stability analysis was conducted and the number of self-stress modes, mechanism displacement modes, and feasible prestress modes was calculated. Then, the formula for the initial prestress distribution of the structure was derived based on the node equilibrium equation. Furthermore, the geometric stability and initial prestress distribution of the structure with different rise-to-span ratios, number of circumferential struts, and hoop cables were studied. Finally, the dynamic properties of the structure are explored by finite element simulation. The analysis results show that the structure has excellent structural stability. The rise-to-span ratios, the number of circumferential struts, and hoop cables are the important factors affecting the geometric stability and the initial prestress distribution. The rise-to-span ratios have no effect on the number of structural modes, while the number of circumferential struts and cables will cause significant changes in the number of self-stress modes. The internal force of the structural members decreases with the rise-to-span ratio and the number of circumferential struts increases, and the number of circumferential struts has the greatest influence on its internal force. The structural natural frequency exhibits a dense distribution, which indicates that the structure has good stiffness. In summary, the research has provided an idea for the application of the deployable scissor-type strut cable dome structure as a new structural system in the field of structural engineering.

Effect of Chemical Doping on Ion Transport in Sulfide Solid Electrolytes

Rechargeable solid-state batteries (SSBs) offer tremendous promise as a safe and energy-dense storage technology for use in electric transportation, robotics, and portable electronics. Lithium argyrodites (e.g., Li7PS6, and its halogen-doped derivatives) have emerged as a lucrative class of solid-state electrolytes (SSEs) for SSBs owing to their high Li-ion conductivity (~10-3 S/cm), good elastic stiffness (~30 GPa), and low flammability. Meanwhile, sulfide-based solid electrolytes such as Na3SbS4 (NSS) also showcase substantial potential for SSBs with their high theoretical specific capacity, enhanced safety, and abundance of resources. Despite their promise, both lithium and sodium-based SSBs remain far from commercialization due to lack of atomic-scale understanding of ion-conduction, charge transport, structural evolution, and interfacial reactions (e.g., dendrite growth, electrolyte decomposition etc.). Here we employ a combination of density functional theory calculations, ab initio molecular dynamics simulations, and nudged elastic band calculations to understand ion transport mechanism in chemically doped lithium argyrodites and NSS.In lithium-based systems, using accurate materials modeling, we design fluorine-containing argyrodite electrolytes that offers enhanced Li-ion conduction facilitated by unique Li-disorder induced by fluorine and other halogen co-dopants. Our results show the opening up of new pathways for Li inter-cage hops in these fluorine -containing argyrodite electrolytes which increases the Li-ion conductivity. In the case of sodium-based systems, we focus on atomic-scale mechanisms underlying Na-ion conduction in the presence of cation dopants. Ab initio molecular dynamics simulations reveal the significant impact of cation dopants on NSS, where the introduction of charge-compensating Na-vacancies enhances Na-ion conduction. The size of the cation dopant is found to be a critical factor, with examples such as Ca-doped NSS (rCa2+ / rNa+ = 0.98) showing a conductivity approximately 10 times that of pristine NSS, while larger Ba2+ as a dopant (rBa2+ / rNa+ = 1.35) hinders Na-ion hops due to local strain, resulting in a Na-ion conductivity ~5 times that of NSS. We will discuss these results in the context of accelerating design of novel solid-state electrolytes for long-lived, stable, and high-energy density SSBs.

Heavy-load Nonapod: A novel flexible redundant parallel kinematic machine for multi-DoF forming process

The high-performance multi-DoF forming process (MDFP) necessitates a 6-DoF forming machine tool with high normal and lateral stiffness to bear large normal and lateral forming force of millions of Newton (MN). However, the payload of parallel kinematic machine (PKM) is generally limited to thousands of Newton (kN), which restricts its application in MDFP. Therefore, this paper aims to develop a novel heavy load PKM with high stiffness for MDFP. To maximise the normal stiffness, a 6-PSS PKM with zero base angle and horizontal driver is proposed. Further, the inner force transfer model of 6-PSS PKM is established, indicating that the normal stiffness will be maximised when the link force approaches to be vertical. Consequently, a design criterion for maximising normal stiffness, i.e., the root mean square error (RMSE) for horizontal projection of all links should be minimised, is established. To maximise the lateral stiffness, general force balance equations of 6-PSS PKM are derived, indicating that lateral force can cause unintended negative force of links, significantly reducing the lateral stiffness. Thus, a novel auxiliary 3-SPS configuration is employed to provide additional force system to mitigate this negative force via hydraulic links. Correspondingly, a design criterion for maximising lateral stiffness, i.e., all link force should remain positive, is proposed. By combining aforementioned design criterion and kinetostatic models, a near-singular 6-PSS PKM with maximising normal stiffness is achieved, and dimension parameters of 3-SPS PKM with maximising lateral stiffness are optimised. On this basis, a novel flexible redundant 6-PSS/3-SPS PKM with both high normal and lateral stiffness is proposed, and a novel heavy load Nonapod with payload of 8 MN and payload-mass ratio of 40 is developed, showing good stiffness performance. The plastic deformation mechanisms of multi-DoF formed aviation bevel gear are revealed, and experimentally formed aviation bevel gear in the new Nonapod achieves good accuracy, microstructure and mechanical performance. This work provides a new methodology for synthesis of heavy load PKM with high normal and lateral stiffness, and has significant application prospect in PKM under heavy load working condition.

Thermomechanical Collaborative Design and Experimental Verification of a Sandwich Structure with a Polyimide Foam Core

This paper introduces the technology and performance of a new sandwich structure consisting of carbon fiber composite face sheets, a polyimide foam core, and an aluminum honeycomb panel with both heat insulation and load-bearing functions. The heat-resistant performance of the sandwich structure was evaluated. The vacuum thermal conductivity of the sandwich structure in the vertical direction ranges from 0.54 to 0.92 (W/[m⋅K]) with increasing temperature from −170 to 135°C. A multilayer finite element model of carbon fiber cloth, polyimide foam, and aluminum honeycomb was established. Finally, a comprehensive evaluation of the mechanical and thermal insulation performance of the sandwich structure was conducted through random vibration testing and thermal vacuum testing. The results showed that the sandwich structure had good stiffness and thermal insulation performance, successfully verifying the effectiveness of the collaborative design.

Crack Behavior of Eccentrically Braced Frame Type-V with Ground Granulated Blast Furnace Slag

To make the structure stronger and stiffer, which is more susceptible to earthquake forces, a special mechanism is required to improve the structure's lateral stability. EBF-V with a horizontal link beam is a brace that can enhance structural performance by providing good stiffness and ductility. On the other hand, GGBFS, as a partial OPC replacement material, was applied to contribute to using more environmentally friendly materials. Besides offering a smaller carbon footprint, GGBFS also positively improves the mechanical properties of concrete. Thus, this study focuses on investigating the crack propagation pattern of reinforced concrete braced frames combined with 20% GGBFS in EBF-V with three variations of link beam element lengths of 0 cm (CBF), 15 cm (EBF-V-) and 25 cm (EBF-V-25). As a result, the CBF specimen showed the best seismic performance. In EBF specimens, there is an increase in the collapse mechanism to be more ductile. The link beam plays a role in making the crack pattern more focused. EBF-V-15 performs well under seismic loading with large lateral capacity and ductility. The cracks in the frame are evenly distributed, dominated by fine cracks, and symmetrical on both sides. This validates that GGBFS plays a good role in improving the frame performance with its pore-filling effect and pozzolanic reaction.

Axial compressive properties of intermediately slender circular ancient timber columns reinforced with high-performance bamboo-based composites

The use of circular, medium-length timber columns reinforced with high-performance bamboo-based composite (HPBBC) is a sustainable reinforcement method without damage. This study conducted axial compression tests on seven circular medium-length wooden columns strengthened using the sustainable reinforcement method with different HPBBC materials and reinforcement thicknesses. The test results revealed that bamboo scrimber with Sinocalamus affinis fibers (BSS) of 10, 20, and 30 mm thicknesses, respectively, increased the supplementary load-bearing capacity by 29.30 %, 85.74 %, and 153.68 % compared to unreinforced wooden columns. The transverse deformation of the wooden columns destabilized the reinforcement system when the high-stiffness BSS was used as reinforced materials. In contrast, the wooden columns were destabilized broken by the transverse deformation of the hollow structures made of laminated bamboo lumber (LBL) and bamboo scrimber with Moso bamboo fibers (BSM). Using reinforcing materials with good stiffness can prevent the destabilization of timber columns. Based on the damage model, an equation of the load-bearing capacity of sustainable reinforcement wood columns based on the buckling stress of the columns was proposed. The calculated results revealed that the equations proposed in this study agree with the test result when the Euler buckling stress is used.

A multicrosslinked network composite hydrogel scaffold based on DLP photocuring printing for nasal cartilage repair.

Natural hydrogels are widely employed in tissue engineering and have excellent biodegradability and biocompatibility. Unfortunately, the utilization of such hydrogels in the field of three-dimensional (3D) printing nasal cartilage is constrained by their subpar mechanical characteristics. In this study, we provide a multicrosslinked network hybrid ink made of photocurable gelatin, hyaluronic acid, and acrylamide (AM). The ink may be processed into intricate 3D hydrogel structures with good biocompatibility and high stiffness properties using 3D printing technology based on digital light processing (DLP), including intricate shapes resembling noses. By varying the AM content, the mechanical behavior and biocompatibility of the hydrogels can be adjusted. In comparison to the gelatin methacryloyl (GelMA)/hyaluronic acid methacryloyl (HAMA) hydrogel, adding AM considerably enhances the hydrogel's mechanical properties while also enhancing printing quality. Meanwhile, the biocompatibility of the multicrosslinked network hydrogels and the development of cartilage were assessed using neonatal Sprague-Dawley (SD) rat chondrocytes (CChons). Cells sown on the hydrogels considerably multiplied after 7 days of culture and kept up the expression of particular proteins. Together, our findings point to GelMA/HAMA/polyacrylamide (PAM) hydrogel as a potential material for nasal cartilage restoration. The photocuring multicrosslinked network ink composed of appropriate proportions of GelMA/HAMA/PAM is very suitable for DLP 3D printing and will play an important role in the construction of nasal cartilage, ear cartilage, articular cartilage, and other tissues and organs in the future. Notably, previous studies have not explored the application of 3D-printed GelMA/HAMA/PAM hydrogels for nasal cartilage regeneration.

Livmats Pavilion: Design and Development of a Novel Building System Based on Natural Fibres Coreless-Wound Structural Components for Applications in Architecture

Robotic coreless filament winding with natural fibres and bio-based resin systems offers potential solutions to address productivity and sustainability challenges in the construction sector. Their use in modular, prefabricated structures enables efficient, controlled, and eco-friendly production, yielding high-quality building components with minimal production waste. Plant fibres like flax provide good strength and stiffness while requiring less non-renewable energy compared to traditional fibres like glass or carbon. This research focuses on the use and implementation of flax fibre for coreless filament wound structural components by describing the conceptualization, design, fabrication, and assembly of a full-scale architectural demonstrator, the livMats Pavilion.

Truss topology optimization for additively manufactured components with respect to structural stiffness and active cooling

This paper focuses on the use of truss topology optimization in the setting, where we aim to design structures with good structural stiffness and heat dissipation properties. Our technique takes advantage of the truss formulation to incorporate a cooling circuit inside the truss, using identified bars as tubes. This approach is closely connected to additive manufacturing, as the inherent complexity of the resulting structures and the inner cooling circuit make conventional techniques impractical or outright impossible. The traveling salesman problem is used as the basis for the optimized cooling path computation by a modified ant colony optimization algorithm, complemented by Dijkstra’s algorithm for finding the shortest path in a graph. The found cooling channels are then taken as inputs to the problem of minimizing static structural compliance, formulated as a semidefinite program. The method is used to solve two example problems, one two-dimensional and a more complex three-dimensional problem.

Mechanical Design of Variable Stiffness Joint Based on Planetary Gear Train and Modular Elastic Element

Methods:: By referring and combining existing mechanical design ideas of some series configuration VSJs with good stiffness adjustment mechanism schemes, a novel series configuration VSJ based on an equivalent lever mechanism and relying on adjusting the position of the lever pivot to change joint stiffness has been implemented through CAD drawing, 3D printing, and assembly. Results:: Due to the wide movable range of the lever pivot, the designed VSJ has a wide adjustable range of stiffness. Moreover, assembly design and modular design have been achieved in terms of elastic output and power transmission, for easy installation and maintenance. The movability and stiffness adjustability of the designed VSJ were preliminarily verified through manual adjustment. Conclusion:: The assembly model of the VSJ demonstrates the feasibility of structural design. The stiffness adjustment experiment showed the variable stiffness ability of the designed VSJ.

Bending behavior of segmental precast diaphragm walls using bolted sleeve joints

AbstractTo study the bending behavior of segmental precast diaphragm walls using bolted sleeve joints, 2 full size specimens were tested. Both BC and EC specimens were connected using bolts with steel sleeves as positioner. BC specimen was consisted of two fully RC plates while EC specimen had precast holes in the concrete walls for lightweight treatment. Ultimate strengths, deformations, strains and failure modes were obtained from the test results. Finite element models were developed using ABAQUS and verified against the test results. The verified finite element models were used to further analyze the stress state of specimens under different loading. It indicated that the bolted sleeve joint exhibited good bearing capacity and bending stiffness. The lightweight treatment in the concrete part had minor effect and the design requirement could be satisfied.

Research on mechanical properties of metal rubber based on planar lattice design

Metal rubber is a common vibration is olation material. Because the arrangement of the internal spiral coil will affect the mechanical properties of the metal rubber, this paper draws on the crystal lattice theory in metallurgy, changes the mesoscopic arrangement of the spiral coil through the design of the two-dimensional blank plane lattice structure, and prepares three kinds of lattice structures, and optimizes the mass ratio of the three metal rubber lattice structures, so as to improve the average stiffness and energy dissipation coefficient of the metal rubber. The quasi-static compression experiments passed. The results show that the triangular lattice structure design can reflect the good average stiffness, and the square lattice structure design can obtain the maximum energy dissipation coefficient. The study confirms that the fabrication of metal rubber materials based on planar lattice design is an effective way to improve stiffness and energy dissipation.

Low diffusion barrier in black phosphorene/graphdiyne heterostructure for ultrafast Li-ion battery anode

Black phosphorene (BlackP) with low diffusion barriers has been extensively researched as one of the new Li-ion batteries (LIBs) anode materials. Nevertheless, the poor mechanical properties and elastic stiffness of BlackP obviously limit its practical application. Thus, owing to the excellent mechanical properties and good elastic stiffness exhibited by Graphdiyne (GDY), the BlackP/GDY Van der Waals (vdW) heterostructure was investigated in our study to overcome those disadvantages on the basis of the density functional theory (DFT). Our results suggest that the BlackP/GDY vdW heterostructure has favorable mechanical properties and high thermodynamic stability with a small lattice mismatch, which is owing to the synergistic effect existed in BlackP and GDY. Besides, the adsorption energy of Li adsorption on the BlackP/GDY vdW heterostructure evidently enhanced along with the changing of the heterostructure from semiconductor to metallic. Moreover, the maximum theoretical storage capacity (384.703 mA h/g) of the BlackP/GDY vdW heterostructure is larger than that of Graphite (372 mA h/g). Above all, the minimum diffusion barrier (0.083 eV) is extremely low, which is vital for achieving ultrafast charge and discharge rates. These favorable advantages suggest that the BlackP/GDY vdW heterostructure is a viable ultrafast LIBs anode material.

Research on Dynamic Characteristic Coefficients of Integral Squeeze Film Damper

Integral squeeze film damper (ISFD) is a new type of structure that appeared on the basis of traditional squeeze film damper (SFD). Since the oil film in ISFD is a segmented structure without annular flow, the nonlinearity of the oil film force has been improved to a great extent. The dynamic characteristic coefficients of ISFD have a close relationship with its damping performance. This work investigates and studies the dynamic characteristic parameters of ISFD by means of numerical analysis and experimental validation techniques in order to examine the dynamic features and unveil the damping mechanism. The ISFD solid and fluid analysis models are created, and the computational fluid dynamics (CFD) and mechanical performance analyses are completed. The force acting on the ISFD’s S-type elastomer under excitation conditions is revealed in the mechanical property analysis, and the flow characteristics of the internal oil film are investigated in the CFD analysis. It is discovered that the ISFD has good linear damping and stiffness characteristics, and numerical analytical values for the ISFD’s damping and stiffness coefficients are obtained. By constructing a bi-directional excitation test rig, the experimental values of the ISFD stiffness coefficient and damping coefficient are determined. These values are in close agreement with the results of the numerical analysis, confirming the accuracy of the ISFD’s numerical analysis conclusions.