Variable Stiffness Research Articles

Sensitivity Analysis of Modal Parameters of an RC Joint Subject to Progressive Damage under Cyclic Loads

This paper presents the results of an experimental study that focused on the gradual modification of the modal parameters of reinforced concrete beam–column frames subjected to progressive damage under cyclic loading. As is commonly found in structures of the 1970s, the specimen was characterized by the absence of specific shear reinforcement in the nodal panel. The frame modal parameters were investigated using the ambient vibrations test (AVT) as a modal identification technique. In particular, quasi-static cyclic tests with increasing amplitudes were performed on the reinforced concrete frame specimen and the modal parameters were assessed at various stages of frame degradation. By establishing a correlation between the changes in the modal parameters and the mechanical indicators of the structural damage in the frame, this study aimed to determine whether the ambient vibration tests could offer meaningful insights for evaluating the structural health of this type of structural component. As a result of the damage that occurred in the tested RC frame, the residual experimental value of the first natural frequency of the specimen was found to reduce at 52.7% of the original reference value (undamaged stage). Similarly, the residual value of the frame stiffness was found to be as low as 43.82% of the initial one. Both these results confirmed that changes when monitoring the modal frequencies may provide quantitative indexes to describe the structural health of RC frames. In combination with static tests for a direct measure of the structural stiffness variations, the AVT technique was shown to have interesting potential in detecting the type, level, and distribution of the progressive damage in civil structures. In particular, exponential and polynomial regression curves were defined to describe the decay of the first natural frequency as the structural damage increased in various parts of the frame, and it was shown that the variation in the first natural frequency was determined more by the damage on the beam than by the damage on the joint.

Impact of Silk-Ionomer Encapsulation on Immune Cell Mechanical Properties and Viability.

Encapsulation of single cells is a powerful technique used in various fields, such as regenerative medicine, drug delivery, tissue regeneration, cell-based therapies, and biotechnology. It offers a method to protect cells by providing cytocompatible coatings to strengthen cells against mechanical and environmental perturbations. Silk fibroin, derived from the silkworm Bombyx mori, is a promising protein biomaterial for cell encapsulation due to the cytocompatibility and capacity to maintain cell functionality. Here, THP-1 cells, a human leukemia monocytic cell line, were encapsulated with chemically modified silk polyelectrolytes through electrostatic layer-by-layer deposition. The effectiveness of the silk nanocoating was assessed using scanning electron microscopy (SEM) and confocal microscopy and on cell viability and proliferation by Alamar Blue assay and live/dead staining. An analysis of the mechanical properties of the encapsulated cells was conducted using atomic force microscopy nanoindentation to measure elasticity maps and cellular stiffness. After the cells were encapsulated in silk, an increase in their stiffness was observed. Based on this observation, we developed a mechanical predictive model to estimate the variations in stiffness in relation to the thickness of the coating. By tuning the cellular assembly and biomechanics, these encapsulations promote systems that protect cells during biomaterial deposition or processing in general.

In Situ Quantitative Imaging of Plasma Membrane Stiffness in Live Cells Using a Genetically Encoded FRET Sensor.

Cell membrane stiffness is critical for cellular function, with cholesterol and sphingomyelin as pivot contributors. Current methods for measuring membrane stiffness are often invasive, ex situ, and slow in process, prompting the need for innovative techniques. Here, we present a fluorescence resonance energy transfer (FRET)-based protein sensor designed to address these challenges. The sensor consists of two fluorescent units targeting sphingomyelin and cholesterol, connected by a linker that responds to the proximity of these lipids. In rigid membranes, cholesterol and sphingomyelin are in close proximity, leading to an increased FRET signal. We utilized this sensor in combination with confocal microscopy to explore changes in plasma membrane stiffness under various conditions, including differences in osmotic pressure, the presence of reactive oxygen species (ROS) and variations in substrate stiffness. Furthermore, we explored the impact of SARS-CoV-2 on membrane stiffness and the distribution of ACE2 after attachment to the cell membrane. This tool offers substantial potential for future investigations in the field of mechanobiology.

Stability analysis of multi-insert rotating boring bar with stiffness variation

Manufacturing faces challenges in boring processes, critical for hole enlargement and finishing, due to low stiffness leading to static deflection and regenerative chatter. Stiffness variation has emerged as a promising solution for effectively suppressing chatter, while multi-insert rotating boring bars offer a viable approach to addressing static deflection in long and slender boring bars, enabling better tolerance with a large operational length-to-diameter ratio. However, integrating technological innovations to suppress chatter and prevent static deflection complicates the problem from a modeling and stability analysis perspective, making it challenging to find a comprehensive solution in the existing literature. This study explores the stability of multi-insert rotating boring bars with stiffness variation, providing insights into selecting optimal stiffness variation parameters. It introduces a novel extension of the multi-dimensional cutting force model to rotating boring tools with multiple inserts, employing the zero-order harmonic solution to analyze the stability of boring processes with time-varying dynamics. Experimental validation demonstrates the effectiveness of the proposed methodology, achieving 5 out of 6 matches in stability lobe diagrams for multi-insert rotating boring bars without stiffness variation. The model’s comprehensiveness is further demonstrated by comparing the results with those of existing studies in the literature for single-insert stationary boring bars. In the case without stiffness variation, the model successfully reproduces 4 out of 5 operating points, and with stiffness variation, it accurately predicts all 5 operating points. Sensitivity analyses guide the selection of optimal stiffness variation parameters for effective chatter suppression, favoring moderate frequencies and up to a 30% amplitude ratio.

Cyclic and uniaxial tensile properties of superelastic niti shape memory alloy cables

This study investigates the impact of various factors, including annealing duration, strain amplitude, cyclic loading, loading rate, and pre-training, on the mechanical properties of Nickel–Titanium shape memory alloy (SMA) cable. The primary focus is on evaluating their recovery ability and energy dissipation capabilities. The tested SMA cable has an outer diameter of 9 mm and a 7 × 7 configuration. The variation of strength, stiffness, residual strain, hysteretic energy, and equivalent viscous damping ratio of SMA cable with the loading cycle is analyzed. Furthermore, the impact of various annealing durations on the tensile strength and elongation of both SMA cables and wires was examined through monotonic tensile tests. The results indicate that the annealing duration considerably affects the superelastic behavior of SMA cables by shifting the stress-strain loops down and widening them. The recovery ability of SMA cable degrades more progressively with increasing loading amplitude and the number of loading cycles. The mechanical properties gradually stabilized after 20 times of constant strain amplitude loading and unloading training. The strain selection for cyclic training should not make the SMA cable in the martensite hardening stage. The recovery ability and peak stress of SMA cable can be significantly improved by pre-training. With the increase of annealing duration, the tensile strength of the SMA cable decreases gradually. Compared with SMA wire, SMA cable has better ductility and robustness and provides sufficient restoring force under large deformation.

The local mechanosensitive response of primary cardiac fibroblasts is influenced by the microenvironment mechanics

Cardiac fibroblasts (CFs) are essential for preserving myocardial integrity and function. They can detect variations in cardiac tissue stiffness using various cellular mechanosensors, including the Ca2+ permeable mechanosensitive channel Piezo1. Nevertheless, how CFs adapt the mechanosensitive response to stiffness changes remains unclear. In this work we adopted a multimodal approach, combining the local mechanical stimulation (from 10 pN to 350 nN) with variations of culture substrate stiffness. We found that primary rat CFs cultured on stiff (GPa) substrates showed a broad Piezo1 distribution in the cell with particular accumulation at the mitochondria membrane. CFs displayed a force-dependent behavior in both calcium uptake and channel activation probability, showing a threshold at 300 nN, which involves both cytosolic and mitochondrial Ca2+ mobilization. This trend decreases as the myofibroblast phenotype within the cell population increases, following a possible Piezo1 accumulation at focal adhesion sites. In contrast, the inhibition of fibroblasts to myofibroblasts transition with soft substrates (kPa) considerably reduces both mechanically- and chemically-induced Piezo1 activation and expression. Our findings shed light on how Piezo1 function and expression are regulated by the substrate stiffness and highlight its involvement in the environment-mediated modulation of CFs mechanosensitivity.

Development of a Prandtl-Ishlinskii hysteresis model for a large capacity magnetorheological fluid damper

Magnetorheological (MR) fluid (MRF) dampers, serving as fail-safe semi-active devices, exhibit nonlinear hysteresis characteristics, emphasizing the necessity for accurate modeling to formulate effective control strategies in smart systems. This paper introduces a novel stop operator-based Prandtl-Ishlinskii (PI) model, featuring a reduced parameter set (seven), designed to estimate the nonlinear hysteresis properties of a large-scale bypass MRF damper with variable stiffness capabilities under varying applied current. With only seven parameters, the model realizes current, displacement, and rate dependencies. The force-displacement and force-velocity responses of the designed MRF damper were experimentally characterized under broad ranges of applied current (0–2 A), excitation frequency (0.5–4 Hz), and displacement amplitude (1–2.5 mm). A training dataset was subsequently used to develop a novel field-dependent modified PI model, incorporating multiple hysteresis operators with and without a friction element. The proposed model accurately predicted the MRF damper behavior within the training dataset, and its validity was assessed against data from diverse experimental conditions. The PI model with friction element generally outperformed the model without friction when frequency exceeds 0.5 Hz, demonstrating its ability to characterize nonlinear hysteresis force-displacement and force-velocity properties of the MRF damper under the ranges of applied current and excitations considered with reasonable accuracy. Experimental data were also estimated by the Bouc–Wen model, and compared with those obtained via the formulated PI model, affirming the overall superiority of the proposed PI models considering the computational cost, and total number of parameters. Leveraging the simplicity, minimal parameter requirements, and analytic invertibility of PI models, the proposed PI model is considered a superior choice for modeling and subsequently controlling smart structures employing MRF dampers.

Research on performance degradation patterns of metal rubber components under the coupling of static compression and full immersion corrosive environment

Metal rubber component (MRC) is commonly used in special work conditions such as high temperature/corrosive environments primarily due to its excellent vibration damping/insulation properties. But in special work conditions for a long time, the performance of MRC will deteriorate to a failure to meet the work requirements. Therefore, it is imperative to enhance the performance of MRC and study its performance degradation in special work conditions. In this paper, pickling, silanization and pickle-silanization surface treatments for metal rubber components (MRCs) were carried out. The properties of MRCs after surface treatment under static compression and full immersion corrosive test were studied, and a remaining service life prediction model of MRCs under corrosion condition was established. Compared with MRC without surface treatment (U-MRC), the performance degradation degree of several MRCs was evaluated based on four physical and mechanical parameters - the amplitude of variation in height, average stiffness, energy dissipation, and loss factor. The results indicated that MRCs exhibited different degrees of performance degradation. Among them, pickling-silanized MRC (PS-MRC) has the best corrosion resistance. The stiffness variation amplitude must be nearly 8% smaller than that of U-MRC, and the energy consumption variation amplitude is about 12% smaller than that of U-MRC.

Postoperative Long-Term Monitoring of Mechanical Characteristics in Reconstructed Soft Tissues Using Biocompatible, Immune-Tolerant, and Wireless Electronic Sutures.

Accurate postoperative assessment of varying mechanical properties is crucial for customizing patient-specific treatments and optimizing rehabilitation strategies following Achilles tendon (AT) rupture and reconstruction surgery. This study introduces a wireless, chip-less, and immune-tolerant in vivo strain-sensing suture designed to continuously monitor mechanical stiffness variations in the reconstructed AT throughout the healing process. This innovative sensing suture integrates a standard medical suturing thread with a wireless fiber strain-sensing system, which incorporates a fiber strain sensor and a double-layered inductive coil for wireless readout. The winding design of Au nanoparticle-based fiber electrodes and a hollow core contribute to the fiber strain sensor's high sensitivity (factor of 6.2 and 15.1 pF for revised sensitivity), negligible hysteresis, and durability over 10,000 stretching cycles. To ensure biocompatibility and immune tolerance during extended in vivo periods, an antibiofouling lubricant layer was applied to the sensing suture. Using this sensing system, we successfully monitored the strain responses of the reconstructed AT in an in vivo porcine model. This facilitated the postoperative assessment of mechanical stiffness variations through a well-established analytical model during the healing period.

Optimization of pulmonary artery mechanical testing

Pulmonary arterial hypertension (PAH) is an incurable disease with mortality within 3 years in 28-55% of high-risk patients. The progression of PAH has been known to be associated with increased vascular stiffness and vascular remodeling. Recent studies have suggested that increased stiffness may in fact be a driver for some of the metabolic abnormalities observed during PAH. To gain more insights into this relationship, we need to quantify the differences in mechanical properties of healthy and hypertensive pulmonary arteries. The stress-strain relationship is the gold standard for the ex-vivo stiffness measurement of arteries. This is obtained by obtaining force vs. distension data by tensile testing and using sample dimensions, i.e. length, lumen diameter, and wall thickness, to calculate engineering stress and strain. While this approach is well-optimized for large muscular arteries, it has not been used to test pulmonary arteries as their thin walls and low basal tone make it challenging to make precise measurements of sample wall thickness and lumen diameter. Thus, the goals of this study were to: 1) establish a reliable protocol for rat pulmonary artery tensile testing and 2) quantify the differences in stiffness between hypertensive and healthy pulmonary arteries. First, a methodology to improve the fidelity of determining the lumen diameter and wall thickness was developed. Using this approach, we observed that the modulus was negatively correlated with the length of the vessel segment tested. This suggests that vessel length should be standardized to perform reliable comparisons between groups. Next, we performed tensile tensing on both control and hypertensive pulmonary arteries, after standardizing vessel segment lengths. We initially modeled this tensile testing data using a one-term exponential equation and we observed that intact hypertensive arteries were ~2.7 times stiffer than control arteries at low strain (strain = 0.8). Whereas at high strain (strain = 2.8) intact and decellularized hypertensive arteries were 20 and 29 times stiffer than control arteries respectively. To better capture the viscoelastic properties of both, the cellular and ECM components of the vessels we also fit the tensile testing data using a two-term exponential equation. Using this two-term exponential model, we observed that hypertensive vessels were 2.2 times stiffer than the controls at normal hoop stress (20 kPa), and at the hypertensive hoop stress (66 kPa) the diseased vessels showed less variability in stiffness as compared to the controls. These findings and the methods developed in this study will be helpful in conducting and analyzing experiments to investigate the relationship between changes in biomechanical signals and the progression of PAH. R01HL151530 (KS), R01HL126514 (LS). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

An improved hypoplastic model incorporating intergranular strain for overconsolidated clay

Hypoplastic constitutive models are able to describe overconsolidated behaviors of clay with a single nonlinear tensor function using a set of parameters. For instance, an advanced hypoplastic model by Wang and Wu (2020) has successfully reproduced overconsolidated history by incorporating a structure tensor. To simulate the recent stress history effects and the stiffness variations at small strains of clay, the intergranular strain tensor is introduced by Niemunis and Herle (1997) to reproduce stress-path dependent stiffness of clay. The improved hypoplastic model is examined against experiments on overconsolidated Chicago clay. It is evidently concluded that the improved model is capable of replicating stress-path dependency on the small-strain behavior of overconsolidated clay.

In Vivo Optical Coherence Elastography Unveils Spatial Variation of Human Corneal Stiffness.

The mechanical properties of corneal tissues play a crucial role in determining corneal shape and have significant implications in vision care. This study aimed to address the challenge of obtaining accurate in vivo data for the human cornea. We have developed a high-frequency optical coherence elastography (OCE) technique using shear-like antisymmetric (A0)-mode Lamb waves at frequencies above 10 kHz. By incorporating an anisotropic, nonlinear constitutive model and utilizing the acoustoelastic theory, we gained quantitative insights into the influence of corneal tension on wave speeds and elastic moduli. Our study revealed significant spatial variations in the shear modulus of the corneal stroma on healthy subjects for the first time. Over an age span from 21 to 34 (N = 6), the central corneas exhibited a mean shear modulus of 87 kPa, while the corneal periphery showed a significant decrease to 44 kPa. The central cornea's shear modulus decreases with age with a slope of -19 +/- 8 kPa per decade, whereas the periphery showed non-significant age dependence. The limbus demonstrated an increased shear modulus exceeding 100 kPa. We obtained wave displacement profiles that are consistent with highly anisotropic corneal tissues. Our approach enabled precise measurement of corneal tissue elastic moduli in situ with high precision (<7%) and high spatial resolution (<1 mm). Our results revealed significant stiffness variation from the central to peripheral corneas. The high-frequency OCE technique holds promise for biomechanical evaluation in clinical settings, providing valuable information for refractive surgeries, degenerative disorder diagnoses, and intraocular pressure assessments.

Constitutive modeling of anisotropic small-strain stiffness behavior of Shanghai soft clay

Small strain stiffness plays an important role in determining the deformation of geotechnical engineering in soft soils. To model the anisotropic small strain stiffness behavior of soft clay, an enhancement to the bounding surface plasticity model is proposed. This enhancement involves incorporating the anisotropy in soil stiffness at very small strains and its non-linear degradation. Small strains are considered via cross-anisotropy elasticity, while the concept of intergranular strain is used to reflect the non-linear degradation of stiffness with strains and the effect of recent stress history. Using the proposed model, the triaxial test results on K0 consolidated Shanghai clay specimens are simulated to investigate the model’s performance. In the simulation, three typical shear stress paths are adopted. The comparison of the model simulations against experimental evidence is discussed, where the effects of anisotropy in initial soil stiffness and stress-induced anisotropy on the variation of small-strain stiffness, pore pressure, and shear-volume coupling response are highlighted.

Simplified nonlinear model and 3D printing model experiment verification of longitudinal joints of shield tunnel segments

The segment joints represent vulnerable and core-bearing areas within shield tunnel structures. Their flexural stiffness, starting from the contact surface of longitudinal joints to the bolt hole, exhibits continuous changes under bending loads, typically demonstrating nonlinear mechanical characteristics. This study investigates the influence of joint contact surfaces on flexural stiffness, extending from the joint contact surface to damaged concrete in the compressed zone. A new simplified model for the variable nonlinear stiffness of longitudinal segment joints in shield tunnels is proposed, considering the flexural stiffness of the joint contact surface and the width of the damaged concrete zone in the segment ring while simulating the flexural stiffness decay induced by the opening of segment joints. Based on the minimum potential energy principle, a design calculation method for joint flexural stiffness is derived, establishing the nonlinear bending stiffness coupling relationship between the segment and the joint. Through similarity theory, 3D printing technology, and indoor loading tests, the theoretical model's accuracy regarding tunnel segment joints is verified. This theoretical model provides a basis for designing and assessing the performance of tunnel-segment joints.

A Soft Variable Stiffness Gripper with Magnetorheological Fluids for Robust and Reliable Grasping

A Soft Variable Stiffness Gripper with Magnetorheological Fluids for Robust and Reliable Grasping

Optimization design and 3D printing of curvilinear fiber reinforced variable stiffness composites based on polar coordinate sweeping

The 3D printing of curvilinear fiber reinforced variable stiffness structures (CFRVSSs) provides new opportunities for innovative design and fabrication of complex components in response to rising demand for high-performance and lightweight components in aerospace, railway, and other fields. In this paper, we get rid of the limitations of existing research on the structure of open-hole plates and aim to investigate complex structures with large curvature. Considering the characteristics of 3D printing and service load, an optimization design method based on polar coordinate sweeping was proposed for CFRVSSs. The consistency factors between the fiber distribution (direction, content) and stress distribution (direction, magnitude) were established. Through quantitative analysis, the directional consistency factor between the optimized local fibers and stresses was enhanced by a factor of 3.69, and the correspondence factor between the fiber content and the stress magnitude was enhanced by a factor of 3.8. Furthermore, the calculation method for curve spacing and curve arc length based on polar coordinate sweeping were proposed to minimize the forming errors caused by CFRVSSs 3D printing. The design and fabrication of a high-speed rail tie rod structure were carried out using the optimization design method and 3D printing process in current research. As a result, the ultimate tensile strength of the optimized curvilinear fiber reinforced tie rod structure increased by 156 % compared to the unoptimized straight-line fiber reinforced tie rod structure. The method proposed in this study has a wide range of applications for the design and fabrication of complex components with large curvature in the engineering field.

Objectively Measured Hot Flashes and Moderate-Vigorous Activity Predict Arterial Stiffness in Healthy Perimenopausal Women

Perimenopause is the period of transition when midlife women experience increases in cardiovascular disease (CVD) risk. Arterial stiffness (AS) is a preclinical CVD risk factor that precedes the manifestation of clinical CVD. Hot flashes (HF) are bothersome symptoms of menopause which are correlated with some subclinical CVD risk factors, but the exact relationship between HF and CVD risk factors remain equivocal. Habitual physical activity (PA) is effective in the prevention and treatment of CVD in many populations. However, the relationship between PA and CVD risk remains unclear for perimenopausal women. Therefore, the objective of our study was to determine the effects of HF and PA on AS in healthy perimenopausal women. We hypothesized that HFs would be associated with AS and PA would influence the association between HFs and AS. There were 61 participants (age 43-54) free from CVD risk factors included in this analysis. Arterial stiffness was measured via augmentation index (AIx), backwards wave (PB, mmHg), and reflection magnitude (RM, %). Hot flashes were measured objectively for 24 hours using ambulatory sternal skin conductance monitoring. Objective HF rate was calculated by normalizing HF count to wear time. Habitual PA activity was quantified objectively as average daily minutes of waking moderate-vigorous PA (MVPA) over 7-day using actigraphy and the R package GGIR. All statistical analyses were performed using R (version 4.2.3) and RStudio (2023.06.2+561). Pearson’s correlation and multiple regression were used to evaluate the associations between dependent and outcome variables. Age and body mass index (BMI) were controlled, and assumption testing was completed for all models. Objective HF rate was significantly positively correlated with PB, r(53) = 0.38, p &lt; 0.01, and RM, r(53) = 0.35, p &lt;0.01. Objective MVPA was significantly negatively associated with AIx, r(61) = -0.45, p &lt;0.001, PB, r(61) = -0.29, p &lt;0.05, and RM, r(61) = -0.34, p &lt; 0.01. Objective HF rate significantly predicted arterial stiffness variables, AIx (β = 14.58, p =0.05; adjR2 = 0.38), PB (β = 6.48, p&lt;0.01; adjR2 = 0.24), and RM (β = 17.79, p &lt;0.01; adjR2 = 0.39). Objective MVPA significantly predicted AIX (β = -0.12, p &lt;0.01; adjR2 = 0.41), and RM (β = -0.06, p = 0.05; adjR2 = 0.29). When HF and MVPA were added in the same model, HF and MVPA were both significant predictors of RM (βHF = 16.25, p &lt;0.01, βMVPA = -0.06, p &lt;0.05; adjR2 = 0.42), MVPA only was significant with AIx (βHF = 11.38, p = 0.10, βMVPA = -0.13, p &lt;0.01; adjR2 = 0.49), and HF only was significant with PB (βHF = 6.11, p &lt;0.01, βMVPA = -0.02, p = 0.212; adjR2 = 0.25). Adding the interaction between HF and MVPA did not help explain variation in any AS variable. In conclusion, our data showed that more objectively-measured HF were associated with negative AS outcomes and that greater MVPA may be worth considering in decreasing arterial stiffness in perimenopausal women. Contrary to our hypothesis, MVPA did not help to explain the effects of HF on AS. Future studies should focus on understanding the mechanisms behind the negative relationship between hot flashes and arterial stiffness in midlife women. NIH NHLBI R15 Grant 1R15HL145650-01A1 (Witkowski); Smith College McKinley Honors Fellowship (Tha Ra Wun). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Development of novel fish-inspired robot with variable stiffness

In nature, real fish can adjust stiffness to improve their swimming speed and efficiency, which prompted us to apply the variable stiffness mode to a fish-inspired robot. In this paper, we adopt a mechanically adjustable compliance and controllable equilibrium position actuator (MACCEPA) to achieve a wide range of rotational stiffness change of the robotic fish body. Fish-inspired robots with offline/online variable stiffness mechanisms are developed. Then, swimming experiments are carried out to study the effect of the rotational stiffness of robot body on the swimming performance. Experimental data are processed using the undulatory reconfiguration technique. The offline variable stiffness fish-inspired robot achieved a maximum stride length of 0.7 BL/cycle (body length per cycle), which is basically equal to that of real fish. Experimental results revealed that in addition to the rotational stiffness of caudal fin, the rotational stiffness of fish body is also important and should increase with the driving frequency to achieve a better swimming performance. The rotational stiffness of fish body is the key factor for keeping the stride length stable, which offers a new insight for performance improvement of the high-frequency fish-inspired robot. The findings of this study are beneficial to the design of variable-stiffness fish-inspired robots.

СТАТИЧЕСКИЙ РАСЧЕТ НЕРАЗРЕЗНОЙ БАЛКИ ПЕРЕМЕННОЙ ЖЕСТКОСТИ МЕТОДОМ ЗАДАННЫХ ДЕФОРМАЦИЙ

This article presents a methodology for a static calculation of an uncertain two-span beam of a variable stiffness, based on the method of specified deformations, in which one of the parameters of a curved axis is used as external exposure, for example, curvature in a section on an intermediate support, and the solution of the equated axis is carried out relative to the load size . When solving problems associated with physical non-linearity, the organization of the iteration process is required, and the use of the method under consideration allows you to organize a stable iteration process with which it is possible to solve the problems of calculating uncertain beams at all stages of their work, including crickets. On the basis of the presented methodology, an algorithm and a computer for computers on a static calculation of an uncertain two-span beam variable stiffness have been developed. As the acting parameter, curvature in the section on an intermediate support is set on the beam. The results of calculating the beam are the value of the load perceived by the beam, bending moments, deflection, curvatures, rigidity in the sections in each of the spans of the beam. To test the developed methodology, a computer calculation of unreasonable two-span beams with variable stiffness and various loading schemes was carried out. The analytical and graphic results of the completed calculation are presented.

Stiffness Change for Reconfiguration of Inflated Beam Robots.

Abstract Active control of the shape of soft robots is challenging. Despite having an infinite number of passive degrees of freedom (DOFs), soft robots typically only have a few actively controllable DOFs, limited by the number of degrees of actuation (DOAs). The complexity of actuators restricts the number of DOAs that can be incorporated into soft robots. Active shape control is further complicated by the buckling of soft robots under compressive forces; this is particularly challenging for compliant continuum robots due to their long aspect ratios. In this study, we show how variable stiffness enables shape control of soft robots by addressing these challenges. Dynamically changing the stiffness of sections along a compliant continuum robot selectively "activates" discrete joints. By changing which joints are activated, the output of a single actuator can be reconfigured to actively control many different joints, thus decoupling the number of controllable DOFs from the number of DOAs. We demonstrate embedded positive pressure layer jamming as a simple method for stiffness change in inflated beam robots, its compatibility with growing robots, and its use as an "activating" technology. We experimentally characterize the stiffness change in a growing inflated beam robot and present finite element models that serve as guides for robot design and fabrication. We fabricate a multisegment everting inflated beam robot and demonstrate how stiffness change is compatible with growth through tip eversion, enables an increase in workspace, and achieves new actuation patterns not possible without stiffening.