Shaking table tests of a three-dimensional isolation system with variable vertical stiffness based on multi-hydraulic-cylinder series connection

An experimental study of interaction process between sea ice and variable stiffness elastic plates at various speeds

Effect of variable stiffness characteristics on the propulsion performance of biomimetic caudal fin flexible plates

Design and control of a parallel electromagnetic variable stiffness manipulator for robotic compliant grinding

Variation in muscle stiffness, reflected by changes in shear modulus (G) measured via shear wave elastography (SWE), is linked to muscle fatigue and athletic performance. Although fatigue recovery varies across populations due to sex and training background, quantitative evidence remains limited. This study aimed to assess changes in passive muscle G during fatigue and recovery and to evaluate the applicability of SWE for monitoring muscle fatigue. Thirty-five athletes and 16 non-athletes participated. Muscle fatigue was induced using unilateral eccentric dumbbell elbow flexion at 90% one-repetition maximum (three sets of 10 repetitions plus a final set to exhaustion). G was measured using SWE at baseline, immediately post-exercise, and at 24 and 48h. Linear mixed-effects models examined the effects of group and time on G, with arm dominance included as a controlled factor. A significant main effect of time on G was observed (P < 0.001), with no main effects of group or arm dominance and no significant interactions (all P > 0.05). At baseline, non-athlete females showed lower G than athletes in the dominant arm and lower G than male athletes in the non-dominant arm (P < 0.05, effect size [ES] = 1.05-1.39). Immediately, G increased in male athletes, non-athlete males, and non-athlete females (P < 0.05, ES = 0.43-1.34), with non-athlete males showing higher G in the dominant arm than non-athlete females (P < 0.05, ES = 0.95). At 24-hour follow-up, non-athlete females exhibited higher dominant-arm G and lower non-dominant-arm G than non-athlete males and male athletes (P < 0.05, ES = 1.16-1.57). By 48h, G returned to baseline in male athletes and non-athlete males, while non-athlete females showed a significant decrease in dominant-arm G compared to 24h measurement (P < 0.05, ES = 1.06). An inter-limb difference occurred only in non-athlete females at 24h (P < 0.05, ES = 1.14). Passive muscle modulus G reflects muscle stiffness and can be non-invasively monitored using a portable SWE device. Our findings suggest that passive G is a valid indicator for tracking muscle fatigue and recovery across populations.

This paper presents a robotic solution to assist older adults with mild cognitive impairments in navigation. The system is based on a passive robotic walker, called FriWalk, which features actuated front steering wheels. Its key contribution is a guidance mechanism designed to follow a path while maintaining the user’s freedom of movement. When the user strays from the path, the system becomes rigid to ensure safe realignment. When the user’s movements are closely aligned with the path, the walker switches to ‘vehicle compliance mode’, allowing shared control through adjustable stiffness. In this mode, the system provides minimal interference, giving the user full control when s/he is very close to the planned path. However, as the user’s deviation increases, the walker gradually stiffens to keep the user on track. The paper includes theoretical validation of this mechanism, as well as simulations and experiments that demonstrate a strong balance between safety and user comfort.

This prospective study evaluates the exploratory value of tumor and liver stiffness, measured pre-operatively by 2D shear wave elastography (2D-SWE), in patients with liver cancer undergoing locoregional therapies, including ablation, transarterial chemoembolization (TACE), and transarterial radioembolization (TARE). The aim is to assess whether stiffness changes occur after treatment and to explore their possible association with clinical outcomes. 100 patients with liver cancer eligible for locoregional treatment were enrolled. Tumoral tissue, peritumoral area, and proximal liver tissue stiffness were evaluated by 2D-SWE before treatment and one month afterward. Clinical and radiological data were collected, including tumor response up to 6 months. The final series consisted of 76 patients due to exclusion based on technical limitations in elastography acquisition, inability to undergo treatment, or loss to follow-up. Correlations between stiffness, pathological characteristics, and clinical outcomes were statistically assessed. Subgroup analyses were performed by treatment type but given the sample size, these results should be interpreted with caution and as exploratory. Baseline tumor stiffness showed no correlation tumor type (p = 0.48) or lesion size (p = 0.35). Tumor stiffness increased after ablation (p = 0.02) and TACE (p = 0.04) but remained stable following TARE (p = 0.69). No significant changes were detected in peritumoral or liver stiffness after treatment. Despite these findings, no significant correlation was found between baseline tumor stiffness (p = 0.72), peritumoral stiffness (p = 0.61), liver stiffness (p = 0.29) and short-term clinical outcomes. 2D-SWE showed measurable changes in tumor stiffness after locoregional treatments, suggesting a potential role in monitoring tissue alterations. However, no evidence was found to support its ability to predict treatment response or clinical outcomes. These findings should be interpreted as preliminary, and further validation in larger and homogeneous cohorts is needed.

Design, modeling, and experimental study of variable stiffness pneumatic bio-inspired soft actuators

ABSTRACT This study presents a comprehensive experimental–numerical investigation of the load‐bearing behaviour of octahedral and pillar‐reinforced octahedral lattice structures fabricated via stereolithography (SLA) using a bio‐based UV‐curable KS408B (PAR‐based) resin. Lattice specimens were produced with three nominal strut thicknesses (300, 400 and 500 μm), enabling systematic variation of infill density and architectural stiffness. Mechanical performance was evaluated under compression, shear and torsional loading to capture geometry‐dependent responses across multiple deformation modes. Experimental results reveal a pronounced nonlinear sensitivity of mechanical properties to slight variations in infill density at low porosity. At a strut thickness of 300 μm, a modest increase of 1.7 percentage points in infill density resulted in a 255% increase in elastic modulus and a 63% increase in compressive yield stress. Under shear loading, pillar‐reinforced lattices exhibited enhancements of up to 86% in shear modulus and 33% in yield stress compared to the pure octahedral topology. Torsional tests further demonstrated geometry‐dependent trade‐offs: pillar reinforcement generally improved torque capacity, whereas the octahedral architecture exhibited greater deformation tolerance and stress homogenization. Finite element analysis (FEA), incorporating experimentally measured bulk material properties, showed good agreement with experimental data, particularly for yield‐related parameters, with deviations of 3%–14%, while stiffness‐related deviations remained within 16%–26%. Stress distribution analyses highlighted increased rigidity and localized stress concentrations in pillar‐reinforced structures, in contrast to the more uniform stress fields observed in pure octahedral lattices. Overall, this work establishes a unified multi‐loading experimental–numerical framework for evaluating SLA‐fabricated porous lattices and provides new quantitative insights into the interplay between lattice geometry, infill density and mechanical efficiency. The findings offer practical design guidelines for tailoring architectured polymeric structures for load‐bearing biomedical scaffolds and lightweight structural applications, where balancing stiffness, strength and deformation capability is critical.

Accurate estimation of vehicle sideslip angle is vital for the stability and safety of four-wheel independent drive electric vehicles (4WIDEVs), but it faces challenges, including model uncertainties caused by tire yaw stiffness variations and system delays. This paper proposes a novel adaptive fusion strategy that combines the dynamic robust observer (DRO) and the improved adaptive square-root unscented Kalman filter (ASUKF). The DRO is designed based on a two-degrees-of-freedom vehicle model and ensures stability through linear matrix inequalities (LMIs), effectively handling parameter uncertainties and time delays; the ASUKF utilizes a three-degrees-of-freedom model and the magic formula tire model, combined with Sage–Husa adaptive filtering, to address the nonlinear tire dynamics. The key innovation of this paper is the introduction of a fuzzy-rule-based adaptive weighting mechanism that dynamically adjusts the fusion weights of the DRO and ASUKF in real time, thereby exploiting their complementary advantages under uncertainty and nonlinear conditions. The simulation and experimental validations demonstrate that this method significantly improves estimation accuracy, reducing the estimation error of vehicle sideslip angle by an average of 9.36%, and maintains robust performance and dynamic adaptability in various conditions, providing a reliable solution for the real-time state estimation of intelligent electric vehicles.

Lower-limb damping characteristics during various repetitive jumping forms: Reliability and sensitivity analysis.

Matrix stiffness modulates YAP-mediated glycolysis and proliferation in human corneal endothelial cells.

Cable-driven redundant manipulators feature a slender structure, large workspace, and flexible motion, making them suitable for operation in confined spaces. However, their positioning accuracy and load capacity are limited, thus restricting their overall performance. This article focuses on a novel linkage quaternion joint and proposes a variable stiffness optimization method to improve positional accuracy, enhance load capacity, and ensure safer interaction through null-space motion. First, a simplified analytical stiffness model is developed to reduce computational complexity and improve efficiency. Next, a null-space variable stiffness optimization method is introduced, with multidirectional composite flexibility as the evaluation metric. Iterative vectors are designed to enable bidirectional continuous control of the end-effector stiffness. Finally, experiments are conducted to validate the performance. The results demonstrate that the proposed variable stiffness optimization method significantly improves positioning accuracy, load capacity, and compliance, thereby broadening the applicability of cable-driven redundant manipulators.

Non-linear forced vibration and sound radiation characteristics of viscoelastic variable stiffness laminated composite plates

Towards accurate simulation of variable stiffness composites: a refined model bridging macro-micro defects and structural performance

Non-Linear thermal instability behavior of moderately thick variable stiffness laminated composite cylindrical shell panels

Multi-scale variable stiffness design optimization of continuous fiber-reinforced composite with multi-point shape preserving constraints and integrated design-manufacturing

Abstract This paper proposes a lateral combined variable stiffness wheel system, aiming to resolve three key challenges in current wheel technologies: traditional pneumatic tires are susceptible to skidding and blowouts in complex terrains; it is difficult for conventional tires to balance lightweight design and structural durability; and existing non-pneumatic tires suffer from high maintenance costs. The design of this system is based on the concepts of modularity and adjustability. The main structure includes a main tire, three auxiliary units, and corresponding wheel hubs. Multi-level adjustment of wheel width is achieved by adding or removing auxiliary units, thereby modifying the wheel stiffness and improving the overall tire performance. In this study, finite element models of a combined non-pneumatic tire with different numbers of auxiliary units are established using Abaqus, and the load-bearing and grounding performances are analyzed. In addition, the fatigue performance of the wheel hub is investigated using FE-SAFE.The results show that when the number of auxiliary units increases to three, the tire stiffness increases significantly from 310 N/mm to 659 N/mm, representing an improvement of approximately 112.9%. Consequently, the contact area increases by 57.3%, the tire vertical deflection decreases by 52.9%, and the contact pressure distribution becomes more uniform. As a result, the overall load-bearing capacity, impact resistance, and traction performance of the tire are markedly enhanced. For wheel hubs of different sizes, the maximum stress under the specified radial load is 76.79 MPa, which is lower than the yield strength of 235 MPa, and the fatigue life reaches 1 million cycles at a stress amplitude of 0.2 MPa. While the overall wheel performance is improved, the proposed structure still satisfies the fatigue strength requirements of the wheel hub. Therefore, the lateral combined variable stiffness wheel system combines non-pneumatic tire safety and modular structural adaptability, which can effectively improve the passability and stability of the wheel in extreme terrain, reduce maintenance costs, and provide new ideas for wheel technology innovation.

Closed-loop subsonic flutter control of smart symmetric variable stiffness composite laminates in tapered-swept configurations

Fatigue failure mechanism of metro bogie frames under P2 resonance and track stiffness variation