Stiffness Mode Research Articles

Comparison of the Dynamic Characteristics of Tuned Liquid Column Dampers with Different Elbow Forms

This study aims to examine experimentally the damping performance of Tuned Liquid Column Dampers (TLCD) by considering different elbow forms. Experiments carried out within the scope of the study point out the dynamic characteristics of TLCD, which has 45 (open) and 90 (closed) degree-elbow forms with theoretical angular frequencies that are the same. Experiments consist of ±5 and ±10 mm harmonic excitation amplitude to observe the relationship between the damping ratio and head loss coefficient with the mass ratio of the TLCD. These experiments with an incremental mass ratio of 0.05% from 0.80% to 1.00% and with an incremental mass ratio of 0.10% from 1.00% to 1.20% had been carried out in detail. Mass and stiffness Modification Factors (MF) are suggested to minimize the difference between numerical and experimental results. Determined MFs are used to examine the earthquake performance of TLCD on a Single-Degree-of-Freedom (SDOF) system. It is shown that the open elbow has an advantage of approximately 25% over the close elbow under earthquake performance on the SDOF system.

A lightweight passive ankle exoskeleton adjusted stiffness by shape memory alloy

PurposeThe purpose of this paper is to actively calibrate power density to match the application requirements with as small an actuator as possible. So, this paper introduces shape memory alloy to design variable stiffness elements. Meanwhile, the purpose of this paper is also to solve the problem of not being able to install sensors on shape memory alloy due to volume limitations.Design/methodology/approachThis paper introduces the design, modeling and control process for a variable stiffness passive ankle exoskeleton, adjusting joint stiffness using shape memory alloy (SMA). This innovative exoskeleton aids the human ankle by adapting the precompression of elastic components by SMA, thereby adjusting the ankle exoskeleton’s integral stiffness. At the same time, this paper constructs a mathematical model of SMA to achieve a dynamic stiffness adjustment function.FindingsUsing SMA as the driving force for stiffness modification in passive exoskeletons introduces several distinct advantages, inclusive of high energy density, programmability, rapid response time and simplified structural design. In the course of experimental validation, this ankle exoskeleton, endowed with variable stiffness, proficiently executed actions like squatting and walking and it can effectively increase the joint stiffness by 0.2 Nm/Deg.Originality/valueThe contribution of this paper is to introduce SMA to adjust the stiffness to actively calibrate power density to match the application requirements. At the same time, this paper constructs a mathematical model of SMA to achieve a dynamic stiffness adjustment function.

Flexural behavior of a UHPC slab - FRP truss hybrid beam implementing a novel FRP joint and tailored shear connector

A full-scale hybrid beam consisting of a UHPC slab and FRP truss girder was fabricated. The novel side plate FRP joint characterized with improved load-carrying capacity, stiffness, and preferred failure mode along with the tailored shear connector validated in the previous studies of the authors were adopted. Its flexural performance was characterized and compared with that of hybrid beams employing NC or UHPC slab but I-profile girder. The failure of the proposed hybrid beam subjected to bending was pseudo ductile whereas those of the other two hybrid beams were brittle. The load-carrying capacity and stiffness of the proposed hybrid beam outperformed the other two hybrid beams with comparable dimensions and material properties.

Structural performance of hybrid reinforced concrete beams containing polyvinyl alcohol fibers under thermal loads

This study focused on the efficiency of concrete beams containing polyvinyl alcohol fibers (PVA) under thermal loads. The eighteen concrete beams were reinforced with hybrid bars or a combination of GFRP bars and steel reinforcement bars (hybrid scheme). The main experimental variables were the level of temperature (25o, 300o, and 600o C), PVA fiber volume (0 %, 0.50 %, and 1.0 %), and the flexural reinforcement bars. The experimental test results are discussed in terms of the first crack load, flexural capacity, and load-deflection curves. Moreover, the initial and post-crack stiffness, ductility factor, and failure modes are discussed. The test results demonstrated a significant increase in the capacity of PVA concrete beams reinforced with hybrid reinforcement bars. At a temperature of 300o C, the inclusion of 0.50 % and 1.0 % PVA ratios improved the flexural capacities by 11 % and 24 %, respectively. Furthermore, the addition of PVA fibers enhanced the toughness by 34 % and 67 %, respectively, when compared to normal concrete beams. The results also demonstrate that using PVA fibers prevents the spalling of concrete beams after exposure to elevated temperatures. At 600 °C, beams containing 0.50 % and 1.0 % PVA fibers exhibited flexural capacities that were 9 % and 6 % higher, respectively, compared to normal concrete beams. Additionally, the inclusion of PVA fibers increased the toughness by 27 % and 21 % for the respective fiber ratios. Finally, a nonlinear finite element analysis (NLFEA) simulation was performed to verify the experimental test results and supplement experiments by predicting the results that are difficult to accomplish through experiments. With an average ratio of 1.02 between experimental and NLFEA ultimate capacity, the numerical results were an exact match of the patterns observed in the experimental results.

Timber-timber composite (TTC) joints made of short-supply chain beech: Push-out tests of inclined screw connectors

This paper presents the results of experimental investigations on six-layered, homogeneous glulam beams made of Italian short supply chain beech (Fagus sylvatica L.). At first, the beams were produced and mechanically characterized for bending, then, they were employed to realize timber-timber composite joints and tested under quasi-static monotonic loading. The test configurations were adopted to reproduce connections used in timber-to-timber composite structures for applications in new constructions. Outcomes in terms of connection stiffness, strength, static ductility and failure modes are presented and discussed. Moreover, the experimental stiffness were used to carry out analytical verification at the serviceability and ultimate limit states to extend the validity of the proposed screw and specimen’s configurations.

The ultimate capacity of geopolymer recycled aggregate concrete filled steel tubular columns: Numerical and theoretical study

Concrete-filled steel tubular (CFST) columns have been extensively used due to their numerous advantages including high load-bearing capacity, stiffness, energy absorption, and ductile failure mode. Human awareness toward environmental problems is increasing and research on geopolymer recycled aggregate concrete (GRAC) has gained much attention as a green and sustainable material. However, there is little experimental and numerical research on the behavior of CFST columns with the GRAC as an infill material with the available design codes not yet modified for addressing the utilization of unconventional concrete mixes, such as the GRAC. This research introduces a critical modification of the ACI code provisions using the nonlinear finite element analysis method (FEA) on the behavior of square GRACFST columns under axial compression where the proposed modification was verified using experimental data from the literature. The influence of the length-to-width ratio, width-to-thickness ratio, geopolymer concrete strength, and the recycled aggregate replacement ratio was investigated. Results show that the outward local buckling was the primary failure mode for both short and slender columns. Considerable improvements were observed in the column's load-bearing capacity, initial stiffness, ductility, and energy absorption by (81.0, 101.9, 46.5, and 87.8)%, respectively, achieved upon increasing the steel tube thickness from 3 mm to 9 mm. However, the increase in length-to-width ratio negatively affects the energy absorption by 39 % while the ductility was reduced up to 20.4 %. The predictability of the AISC360-16, ACI318-19, and BS5400-5 codes on the capacity of GRACFST columns was evaluated where conservative predictions were guaranteed with the closest one recorded for the ACI318-19 code with a 24.5 % overestimation percentage. Finally, a modification was proposed to the ACI code prediction, taking into account the inclusion of recycled aggregate and geopolymer concrete with only a 2 % average error.

Mechanical Properties of Eco-Friendly, Lightweight Flax and Hybrid Basalt/Flax Foam Core Sandwich Panels.

Greener materials, particularly in sandwich panels, are in increasing demand in the transportation and building sectors to reduce environmental impacts. This shift is driven by strict environmental legislation and the need to reduce material costs and fuel consumption, necessitating the utilisation of more sustainable components in the transportation and construction sectors, with improved load-bearing capabilities and diminished ecological footprints. Therefore, this study aims to analyse and evaluate the structural performance of polyethylene terephthalate (PET) core and flax or basalt/flax FRP sandwich panels as an alternative to conventional synthetic materials. The novel eco-friendly sandwich panels were manufactured using the co-curing technique. Four-point bending, edgewise compression and core shear tests were performed and insights into how the skin properties affect the strength, stiffness and failure mode of specimens were provided. The stress-strain behaviour, facing modulus and strength, flexural rigidity, core shear strength and failure modes were evaluated. The flexural facing modulus of the flax and flax/basalt sandwich skins were found to be 5.1 GPa and 9.8 GPa, respectively. The flexural rigidity of the eco-friendly sandwich panel was compared with published results and demonstrated a promising structural performance. The environmental benefits and challenges were outlined and critically evaluated focusing on transportation and construction applications.

Strengthening of flexural behavior of reinforced concrete beams by using hybrid fibers: experimental and analytical study

The research investigates the flexural behavior of reinforced concrete (RC) beams by incorporating hybrid fibers (a combination of glass and steel fibers). Ten specimens measuring 150 mm x 200 mm x 1500 mm were cast and tested under two-point loading. The specimens were divided into three groups, each containing three specimens. Additionally, a control specimen was examined. Comparing the strength performance of each group to the control specimen revealed that the hybrid fiber-reinforced beams exhibited increased strength. The optimal hybrid fiber composition was 0.4% steel and 0.2% glass fiber. Similarly, the optimal steel and glass fiber percentages were both 0.4%. Experimental results showed that the load-carrying capacity improved significantly: 28.80% with glass fiber, 63.74% with steel fiber, and 79.23% with hybrid fiber compared to conventional RC beams. The study evaluated load-carrying capacity, load deflection, ductility, stiffness, and failure modes of RC beams. An analytical study using finite element modelling was conducted, and the analytical results were compared to experimental findings. Fundamental statistical values included mean, standard deviation, and coefficient of variation for load and deflection. Finite element analysis (FEA) was employed to predict experimental outcomes, and the analytical results closely correlated with experimental data. The load mean, standard deviation and coefficient of variation were 0.98, 0.01, and 0.56, respectively. The deflection exhibited corresponding values of 0.97, 0.01, and 1.41. The graphical abstract of the present study is displayed in Figure 1.

The effect of the number of strands and knot throws of core suture techniques on the mechanical properties of the repaired flexor tendon.

Flexor tendon injury is a common hand trauma that requires surgical repair. The objective was to compare the repaired strength and gliding resistance with a varied number of repair strands and of square knots using a two-strand-overhand locking (TSOL) knot. First, isolated suture loops with different number of suture strands and number of closing knots were compared in mechanical strength and failure mode. Then, 90 flexor digitorum profundus (FDP) tendons from turkey digits were used for the tendon repair experiment. Both phases followed a similar 3 × 3 matrix comparing the knot type including TSOL+1SK (square knot), TSOL+2SK, and TSOL+3 SK and repair techniques including two-, four-, and six-strand repairs techniques respectively. The repaired tendons were tested for tendon resistance against pulley (friction), maximum force, force at 2 mm displacement, stiffness, and failure mode. Increasing the number of strands and closing square knots increases the tensile strength and stiffness of flexor tendon repairs and isolated suture loops without a significant effect on tendon friction. An increase in the number of square knots have shown increased strength only in Pennington repair, which correlated with the increased number of knot unraveling, a weak knot failure model. Our data demonstrated that increasing the number of strands is effective for improving the overall strength of tendon repair. When a two-strand repair is chosen, increasing knot number can improve repair strength. However, the number of knots appears not affecting repair strength in six-strand repair technique.

Monotonic and cyclic flexural performance of timber beams strengthened with glass fiber-reinforced polymer rods using near-surface mounted technique

Wood has gained widespread use as a construction material for structures. The strengthening of timber structures using fiber-reinforced polymer (FRP) reinforcement remains challenging. This paper presents an experimental investigation of timber beams strengthened with glass FRP (GFRP) rods subjected to flexure. Sixteen specimens, including four un-strengthened beams (control beams) and twelve strengthened beams, were tested. The beam dimensions were 45 mm in width, 95 mm in depth, and 1800 mm in length. The GFRP rods were retrofitted the beam soffit applying near-surface mounted (NSM) method. The test variables included the GFRP ratios by volume (i.e., 0 %, 0.59 %, 0.88 %, and 1.32 %) and the loading types of monotonic and cyclic loading conditions. The flexural performance of the beams, including the capacity, mid-span deflection versus load, displacement at the peak load, initial stiffness, energy absorption, and failure mode are assessed. Additionally, the cross-section equilibrium analysis of the GFRP-reinforced timber beams is implemented to compare against the experimental results. The experimental results indicated that the GFRP rods can enhance the flexural effectiveness of the strengthened beams subject to both monotonic and cyclic tests. Compared with the reference beams, the GFRP-retrofitted beams showed an increase by 20 %− 61 % in load-carrying capacity, by 58 %− 71 % in initial stiffness, and by 35 %− 96 % in energy absorption under monotonic loading. Meanwhile, under cyclic loading, the GFRP-reinforced timber beams exhibited an increase by 22 %− 75 % in maximum load, by 58 %− 90 % in initial stiffness, and by 19 %− 37 % in energy absorption. On other hand, the flexural moment resistance of GFRP-reinforced timber beams predicted by the section analysis depicts a good agreement compared to experimental results.

Novel steel connection for modular houses in indigenous communities: An experimental study

Remote Indigenous communities across Canada are facing housing shortages and the need for major repairs, which resulted from engineering challenges that obstructed the construction phases. Prefabricated steel moment-resisting frame modular houses are currently utilized as alternatives to typical conventical houses because of their technical advantages, such as better-quality control, lightweight structures, and ease of transportation to remote and rural regions. To explore the potential use of hollow structural sections (HSS) in panelized steel modular structures, this study presents a novel steel-bolted connection for connecting HSS beams to HSS columns using high-strength long bolts, indicating that the connections can be easily installed without requiring skilled workers and heavy machinery. Six specimens were fabricated and tested under monotonic load with a Digital Image correlation (DIC) camera to capture full-field 3D displacement and deformation until failure accurately. The impact of different geometric parameters such as bolt arrangement, extended plate thickness, number of bolts, and the existence of stiffener on the mechanical performance of the joint, stiffness, inelastic rotation, ductility, and failure modes were analyzed. Bolt arrangement with an aspect ratio of 1:1 was found to increase the connection capacity, initial stiffness, and ductility by 7%, 216%, and 26%, respectively. The yielding and rotation of the extended plate were eliminated using a stiffener. Increasing the number of bolts triggered the connection's ability to gain more capacity at earlier stages and reduced joint rotation by 60%.

Optimization of column-in-column system based on non-conventional TMD concept

Previous studies showed that the non-conventional tuned mass damper (TMD) with large mass ratio outperforms the traditional one in respect to the structural vibration control efficiency and robustness. The authors recently proposed a novel control system based on the non-conventional TMD concept, namely the column-in-column (CIC) system, which was composed of a primary column, a secondary column and a series of interconnected springs/dashpots. In this novel system, the secondary column connected to the primary one with springs/dashpots could act as a large TMD to attenuate adverse vibration of the primary structure, and its control effectiveness was preliminarily verified through numerical investigations. However, the control robustness was found not sufficient based on the existing optimal formulae in the literature for CIC optimization. This paper presents a new design method for optimizing the CIC system for better harnessing its control effectiveness and robustness in reducing structural response. The CIC system consists of two columns with distributed mass and uniform flexural rigidity, connected by springs along the column height. The effective modal mass and modal stiffness of a specific vibration mode of the system can be straightforwardly calculated by using the Euler-Bernoulli beam theory. Considering the fundamental vibration mode of the system as the target response mode for vibration control, the multiple degree-of-freedom (DOF) CIC is simplified into a two DOF with three springs (2DOF3S) structural model, the design parameters, i.e., the optimal tuning frequency ratio and damping ratio of this system are derived to minimize the displacement response of the primary structure. To demonstrate the proposed design method, the effectiveness and robustness of the CIC system in controlling seismic induced structural vibrations are assessed in both the frequency and time domains. Results show that the derived optimum formulae are applicable for optimizing the TMD system with consideration of the distributed mass and deformation of the mass damper, i.e., a column in this study. The optimized CIC system has good control robustness even if the CIC is mistuned with its design parameters deviate from the optimal values by ±50 %. The conventional TMD system with lumped mass as the mass damper is a special case of the proposed CIC system. The optimized CIC system has favorable control efficiency in mitigating the seismic responses of structures with reduction ratios averagely varying within the range of 15 % ∼ 55 % with a probability of 92.67 %. It is concluded that the proposed method is reliable and can be used for the optimum design and control of the CIC system.

The effect of number of knots per throw, knot technique, and suture type on strength properties of suspensory fixation button surgical procedures

Previous studies of the cortical suspensory button (CSB) implant have analyzed fixation strength as a function of suture type and surgical technique, but knot configuration remains an area of interest. This study investigates 4-strand knot configurations in CSB suspensory fixation, specifically comparing the use of 2 separate knots with a single knot. We hypothesize that using 2 knots on the distal side of the CSB with #2 suture will yield the strongest and stiffest suspensory fixation. Two types of knot configurations were compared: a single knot with all 4 suture strands versus 2 independent knots with 2 suture strands each (1 knot from inner strands and 1 knot from outer strands). They were tested using #2 or 2-0 suture, and at distal (on top of the button) or proximal (underneath the button) knot positions. Mechanical testing on the Instron measured ultimate failure load, elongation at failure, and stiffness. Statistical analyses (Shapiro-Wilk, unpaired Student's t-tests, and Chi-square tests) assessed differences in strength, stiffness, elongation, and failure mode between knot configurations within each CSB construct combination. With #2 suture, 2 knots across the CSB resulted in higher load to failure compared to 1 knot in both proximal (467.00 N vs. 554.66 N, P= .026) and distal (395.18 N vs. 526.51 N, P < .001) locations. Furthermore, 2 knots provided higher stiffness than 1 knot in both proximal (53.24 N/mm vs. 67.89 N/mm, P < .001) and distal (47.08 N/mm vs. 56.73 N/mm, P= .041) knot locations. However, using 2-0 suture showed no significant differences in failure load and stiffness regardless of knot location. Using #2 suture and tying 2 independent knots across the CSB increased load to failure and stiffness compared to using only 1 knot regardless of knot position. Thus, if using #2 suture, it is recommended to tie 2 knots to enhance construct strength. However, with 2-0 suture, the number of knots did not impact construct strength. Therefore, if using 2-0 suture, 1 knot can be used to save time. Knot position did not significantly affect the strength or stiffness of the CSB construct, emphasizing the importance of considering knot prominence and surgical approach for determining knot location.

Development of a Digital Model for Predicting the Variation in Bearing Preload and Dynamic Characteristics of a Milling Spindle under Thermal Effects

The spindle tool is an important module of the machine tool. Its dynamic characteristics directly affect the machining performance, but it could also be affected by thermal deformation and bearing preload. However, it is difficult to detect the change in the bearing preload through sensory instruments. Therefore, this study aimed to establish a digital thermal–mechanical model to investigate the thermal-induced effects on the spindle tool system. The technologies involved include the following: Run-in experiments of the milling spindle at different speeds, the establishment of the thermal–mechanical model, identification of the thermal parameters, and prediction of the thermal-induced preload of bearings in the spindle. The speed-dependent thermal parameters were identified from thermal analysis through comparisons with transient temperature history, which were further used to model the thermal effects on the bearing preload and dynamic compliance of the milling spindle under different operating speeds. Current results of thermal–mechanical analysis also indicate that the internal temperature of the bearing can reach 40 °C, and the thermal elongation of the spindle tool is about 27 µm. At the steady state temperature of 15,000 rpm, the bearing preload is reduced by 40%, which yields a decrease in the bearing rigidity by approximately 16%. This, in turn, increases the dynamic compliance of the spindle tool by 22%. Comparisons of the experimental measurements and modeling data show that the variation in bearing preload substantially affects the modal frequency and stiffness of the spindle. These findings demonstrated that the proposed digital spindle model accurately mirrors real spindle characteristics, offering a foundation for monitoring performance changes and refining design, especially in bearing configuration and cooling systems.

Comparative analysis of mechanical characteristics in masonry walls: impact of aspect ratios and opening percentages

In this research, we undertake an extensive investigation focusing on masonry walls with aspect ratios of one and two, both confined and unconfined, while also accounting for a range of opening percentages. Employing a combination of finite element analysis and a simplified micro-modeling approach, we meticulously scrutinized and validated several masonry wall with an objective to investigate effects of aspect ratios and varying percentages of openings on key seismic characteristics such as lateral capacity, stiffness, and failure modes. Results reveal that with openings, wall lateral stiffness reduced by up to 54%. For a 4% opening, aspect ratio 1.0 walls saw reductions of 53.9% (unconfined) and 26.0% (confined). Aspect ratio 2.0 walls experienced 50.8% (unconfined) and 52.3% (confined) reductions. Notably, confined aspect ratio 2.0 walls showed significant stiffness reduction compared to aspect ratio 1.0 walls. Results highlight aspect ratio one walls’ superior performance over aspect ratio two walls in both confined and unconfined conditions. A four-parameter logistic regression quantifies opening percentages’ impact on lateral stiffness. This equation aids design professionals, enabling cost-effective and sustainable decision-making before construction.

Active vibration control for flexible towers based on displacement observation and reduced-order controller in modal space: Theory and experiment

Active vibration control is not only suitable but also urgently needed in order to mitigate excessive vibration for dynamic systems such as wind turbine towers. However, there is a challenge of directly observing displacement and developing an efficient reduced-order control strategy. With this in view, a reduced-order controller based on displacement observation is developed for the vibration mitigation of flexible high towers, where the problems of low signal-to-noise ratio (SNR) and intricate acceleration-based control algorithms are eliminated completely. The displacement can be measured by laser or modern videometrics technology. A reduced-order model with an active mass damper (AMD) at the top of the tower is created using modal truncation approach based on modal participation factor (MPF), which successfully preserves the dominant modes of the original structure, and reduces the influence of high-frequency uncertainties. Considering structure uncertainties caused by environmental factors and aging process, an unscented Kalman filter (UKF) is introduced to identify the modal stiffness of the reduced-order model. The present study, using a 5 MW onshore wind turbine as an example, investigates active vibration control under wind and seismic loads and compares it with traditional tuned mass damper (TMD). From a dynamic perspective, the simplified model of wind turbine tower takes the form of a multi-degree-of-freedom series model. Consequently, a six-story steel frame platform has been constructed to experimentally validate the efficacy of the reduced-order controller. According to numerical simulation and laboratory testing, the control effect of the reduced-order controller with a few displacement states as feedback can be utilized as an active control strategy for high-rise flexible towers.

Torsion and Combined Torsion-Axial Load Behaviour of Concrete Filled Steel Tube Columns with and without ECC/CFRP Wrap

ABSTRACT Concrete-filled tube columns may experience coupled torsion and axial compression under seismic and wind loading. Fifteen square, rectangular, and circular concrete filled steel/aluminium tube (CFST/CFAT) are tested under pure torsion to understand the behaviour and develop/validate finite element (FE) models. Parametric studies under pure torsion are conducted using FE models to study the effect of geometric (tube cross-section, length, and thickness) and tube/concrete material parameters on torsional strength, stiffness, and tube-concrete composite interaction. FE models are used to study strength, stiffness, and failure modes of CFST columns under combined torsion and axial compression load at various preload levels of axial and torsion. Coupled torsional preloading and subsequent axial load reduce the axial load capacity significantly, while coupled axial preloading and subsequent torsional loading have shown no significant influence on the torsional strength of CFST columns. Implementation of FE models developed for CFST columns with engineered cementitious composite (ECC) and carbon fibre reinforced polymer (CFRP) wraps showed significant enhancement of axial strength and stiffness compared to control (without wrap) even under high torsional preload level. The energy absorption capacity and ductility of the CFRP wrapped CFST column are about 1.38 and 1.1 times higher than its counterpart with ECC wrap of same axial load capacity. Overall, the results suggest that use of both CFRP and ECC wrap is an effective approach to enhance the torsional behaviour and ductility of CFST columns under combined torsion and axial loading conditions. However, high crack resistance and better post-peak ductility of ECC wrapped CFST compared to sudden CFRP rupture failure in CFRP-wrapped counterpart should be taken into consideration for seismic applications.

Displacement response waveform restoration of simply supported bridge during train passage using measured acceleration integration based on linear vibration theory

This study proposes a method for restoring the displacement waveform during train passage using the acceleration integration based on linear vibration theory and noise cancellation techniques. This method replaces the low-frequency region affected by noise with a linear theoretical solution; however, this method uses the actual measurement data around the natural frequency, where nonlinearities (such as concrete member cracks and the train–bridge interaction) can be observed. The method identifies only the ratio of single axle weight to modal stiffness. Numerical experiments clarify that the method can estimate the maximum displacement of a bridge from acceleration with an error of approximately 5% or less. Improved prediction accuracy can be achieved using the proposed noise cancellation technique not only in the high-speed range but also into the lower-speed ranges as well. Furthermore, the proposed method is applied to acceleration monitoring data, and results show that the displacement waveform can be restored from the acceleration waveform.

Biomechanical Characteristics of All-Suture Meniscal Repair Devices Compared With PEEK-Anchored Devices and Inside-Out Suture for Meniscal Repair: A Porcine Study.

Recently, all-suture, all-inside meniscal repair devices-including devices containing flat sutures or tapes-have been introduced. Similar to those in suture anchors, these modifications may have different performance characteristics than conventional sutures and polyether ether ketone (PEEK)-anchored devices. To compare the biomechanical characteristics of all-suture meniscal repair devices with those of a conventional PEEK-anchored device and an inside-out meniscal suture construct. Controlled laboratory study. A total of 48 adult porcine menisci with simulated bucket-handle tears were included. Single-device repairs were performed with the SuperBall Meniscal Repair System, FiberStitch, and FAST-FIX 360 with 2 PEEK anchors, and a vertical mattress inside-out suture repair was performed using a Ti-Cron No. 2-0 braided polyethylene terephthalate suture. All specimens were preloaded (10 N) and cycled 200 times (between 10 and 50 N). Specimens surviving cyclic loading were then destructively tested. Endpoints included maximum failure load, stiffness, cyclic displacement, and failure mode. The goal was 12 successful tests in each group. Metrics between groups were compared using analysis of variance with post hoc tests to control for multiple comparisons. The SuperBall (108.9 N) was significantly stronger than the FAST-FIX 360 (67.3 N) and Ti-Cron (75.2 N), and the FiberStitch (102.8 N) was significantly stronger than the FAST-FIX 360 (P≤ .01 for all). Cyclic stiffness increased during cyclic loading for all constructs (P < .001). The Ti-Cron was significantly stiffer than the SuperBall during 5 to 200 cycles (P < .001). Cyclic displacement significantly increased in all constructs during cycling (P < .001) but did not differ between devices. Failure mode varied by device: the Ti-Cron repairs failed because of suture breakage, the SuperBall and FAST-FIX 360 failed at the anchor, and the FiberStitch showed both failure modes. The all-suture, all-inside meniscal repair devices demonstrated superior strength to the PEEK-anchored device and the classic inside-out suture meniscal repair but no statistically significant difference in cyclic displacement.

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.