Flexure Mechanism Research Articles

Enhancement of ductility characteristics of fiber-reinforced ternary geopolymer mortar

There is a need for ambient-cured geopolymer as a potential replacement for conventional ordinary Portland cement (OPC) based concrete. But geopolymers, that belong to the ceramic family, behave in a brittle manner and hence this research focusses on the enhancement of ductility using fibers. Thus, this experimental work was conducted to investigate the performance of polypropylene (PP) and micro steel fiber (MS) of fiber-reinforced geopolymer mortar (FRGM) on the hardened properties. The volume fractions of fiber used were 0%, 0.5%, 1%, and 1.5%. The ternary blended geopolymer mortar consisted of fly ash (FA), ground granular blast furnace slag (GGBS), and palm oil fuel ash (POFA). The hardened properties investigated are compressive strength, splitting tensile strength, modulus of elasticity (MoE), and ultrasonic pulse velocity (UPV). Furthermore, the load-deflection response was investigated in terms of deflection, load, flexural, and toughening mechanisms. The morphology of matrix mortar with the bonding of the fibers was examined through field emission scanning electron microscope (FESEM). The results revealed that the splitting tensile strength was enhanced with the inclusion of 0.5% of PP fibers and up to 1.5% of MS fibers by 27% and 177%, respectively. The enhancements in the ultimate flexural strength with 1.5% fiber were found 173% and 33% higher for MS and PP fibers, respectively compared to the control mixes. The inclusion of both MS and PP fibers showed a significant enhancement in the post-cracking flexural and toughness energy measured at L/150 mm. Furthermore, the addition of fiber volume of 0.5–1.5% enhanced the toughness by 33% (T600), 62% (T150), and 28% (T600), 46% (T150) for MS and PP mixes, respectively.

Improving the behavior of concentrically braced frame braces using a flexural damper: Experimental and numerical study

SummaryAlthough the concentrically braced frames (CBFs) systems have high lateral elastic stiffness and strength, they reflect a low seismic energy absorption capacity mainly due to their diagonal buckling under compressive loading. To overcome this problem, researchers have proposed metallic shear damper as the most popular due to its satisfactory performance and affordable cost. In this paper, an innovative metallic damper with a flexural mechanism is proposed to improve the behavior of CBF systems. It provides ease of fabrication and replacement after damage, competitive cost, and improved resistance to buckling of the CBF member. The performance of the damper was evaluated experimentally and numerically. Subsequently, two types of dampers, (a) made of rectangular flexural plates (RFP) and (b) made of I‐shaped flexural plates (IFP), were designed and evaluated. Experimental as well as numerical results indicated that both dampers provide stable and symmetrical hysteresis curves with a high energy absorption capacity. Results indicated that the IFP damper has greater stiffness (1.94–2.3 times) and ultimate strength (1.76 times) but a lower overstrength (66% less) and ductility (47% less) than the RFP damper. Moreover, design expressions were presented for the proposed damper and showed a good agreement with finite element results.

Experimental and analytical studies on the behavior of connections between high-rise braced steel storage racks and the spine bracing

The primary lateral load resisting system of the high-rise braced steel storage racks is the spine bracing located at a short distance away from the rear rack frames. The connections between the rack frames and spine bracing, which transmit the horizontal stabilizing forces, dictate the effectiveness of the spine bracing and the global performance of the entire high-rise racking system. The first part of this paper experimentally establishes the behavior of the connections between the racks and the spine bracing under lateral loads, utilizing four groups of three nominally identical test specimens. A digital image correlation (DIC) measurement system is employed to generate comprehensive data associated with the behavior of individual components of such connections. The behavior of the connection components is quantified and discussed based on the three-dimensional deformation field recorded by the DIC system. The second part of this paper develops a component-based elastic analytical model for the connections between the racks and the spine bracing under consideration. The endplate spatial flexural bending mechanism, as well as the upright cross-section distortional behavior, are explicitly considered by the analytical model. The contributions of each individual component towards the total deformation of the connections are quantified. The paper concludes with design and construction recommendations for the enhancement of the connections between the racks and the spine bracing, while recognizing the limitations of this research.

Incorporating Geometric Nonlinearity in Theoretical Modeling of Muscle-Powered Soft Robotic Bio-Actuators

Abstract Biohybrid actuators aim to leverage the various advantages of biological cells over artificial components to build novel compliant machines with high performance and autonomy. Significant advances have been made in bio-fabrication technologies, enabling the realization of muscle-powered bio-actuators. However, the mechanics of muscle-scaffold coupling has been relatively understudied, limiting the development of bio-actuators to intuitive or biomimetic designs. Here, we consider the case of implementing muscle-based actuation for soft robotic swimmers operating at low Reynolds numbers. We develop an analytical model to describe the elasto-hydrodynamic problem and identify key design parameters. Muscle contraction dynamics is characterized experimentally and the implications of nonlinear amplitude-frequency relationship of muscle-based actuation are discussed. We show that a novel bio-actuator with high performance can be developed by introducing compliant flexural mechanisms undergoing large deflection. Geometric nonlinearities are accounted for in the analysis of the force-deflection relationship for the flexural mechanism. Our results show that for expected muscle contraction forces, this novel bio-actuator can outperform previous muscle-powered swimmers by up to two orders of magnitude in swimming speed.

Three-dimensional ultra-wide elastic metamaterial with inertial amplification mechanisms having optimized flexure hinges

The aim of this paper is to obtain an ultra-wide low-frequency stop band in three dimensions by using inertial amplification mechanisms. A two-stage remote center flexure mechanism design is introduced that allows 3D assembly of inertial amplification mechanisms while enabling ends of the inertial amplification mechanisms to bend in two orthogonal axes so that broadband excitations coming from all directions can be impeded. Cross flexure and split flat flexure hinges that restrain undesired torsional, in-plane and out-of-plane bending modes of the inertial amplification mechanisms are utilized for the first time in order to maximize the stop band frequency range. An octahedron and 3D arrays of octahedrons are generated with the use of these mechanisms. By making design improvements and topological changes on the mechanisms forming the octahedron, the stop band of the octahedron is widened. Finally, the bandwidth is maximized by optimizing the thicknesses of the flexures in the inertial amplification mechanisms. Eventually, a 3D elastic metamaterial with an ultra-wide band gap between 33.7 Hz and 457.5 Hz is obtained, yielding arithmetic mean normalized bandwidth of 172.6%.

Tectonic controls on effective elastic thickness of lithospheres around the Southeast Asian subduction zones

Southeast Asia has the most complicated convergent system on the Earth. The effective elastic thickness (Te) can be a constraint on the long-term flexural strength and deformation mechanism of the lithosphere. In this paper, we estimate Te over the Southeast Asia via the free-air admittance function calculated by the continuous wavelet transform. Sedimentary correction is performed to avoid the biases induced by the low density of sediments. The spatial variations of Te coincide well with the tectonic settings. The Northeast Indian Seamount Province and young oceanic basins correspond to the lowest Te (≤10km). The Sunda Shelf displays relatively low Te (10–20 km), where Cenozoic rifting and extension weakened the lithosphere. The Molucca Sea and most continental regions show high Te (≥40 km). Overall, Te shows dependence on the oceanic crustal age in our study area, and is influenced by intensive tectonic activities. Low Te (≤10km) in northern Sumatra and central Java subduction zone is consistent with the presence of a slab tear/window and mantle upwelling. Moreover, Te in Southeast Asia is either non-correlated with surface heat flow, or weakly correlated to Curie-point depth and seismic velocities at the 100 km depth. In some regions, e.g., the South China Sea and Sumatra-Java Trench, Te shows poor correlation with all geothermal proxies we employed. We argue that the geothermal state of lithosphere exerts very limited effects on integrated lithospheric strength in the tectonically active Southeast Asia, and apart from the temperature and composition, tectonic factors dynamically control the rigidity of the lithosphere.

Parameters Affect Flexural Mechanism to Prevent Progressive Collapse of RC Buildings

This study investigates the effect of spans length, reinforcement ratio and continuity of flexural reinforcement on the progressive collapse performance of double span beams over failed columns. The investigations focus on initial flexural resisting mechanism to prevent the progressive collapse. Detailed nonlinear finite element simulation of double span beam-column sub-assemblages subjected to residual gravity loads that initially carried by the failed column is adopted for the investigations. Nonlinear static pushover analysis is conducted in which capacity curves are derived and compared with demanded capacities. The effect of spans length, reinforcement ratio and number of continuous bottom flexural reinforcement on progressive collapse are considered in the investigations. Analysis results show that the strength to resist progressive collapse has decreased by 25.4 % and the ductility increased by 103 % following the increasing in span length from 5 m to 7 m. On the other hand, increasing reinforcement ratio of top flexural reinforcement from 0.447 to 1.089 leads to 26.27 % increasing in strength accompanied with a decrease in ductility equal to 16.42 %. In addition, extending all bottom bars rather than the minimum specified two bars resulted in 12 % increasing in strength and 40.28 % decreasing in ductility.

A Bionic Type Piezoelectric Actuator Based on Walking Motion and Asymmetrical L-Shaped Flexure Mechanisms

A bionic type piezoelectric actuator based on the walking motion of L-shaped flexure mechanisms has been proposed. By mimicking the walking motion of “human legs,” the proposed actuator is able to not only eliminate the backward motion to improve the motion efficiency, but also achieve the large working stroke with high output load easily. The special L-shaped flexure mechanism is employed as the “leg,” and the bionic walking motion is realized by applying two L-shaped flexure mechanisms alternately. The driving principle of the proposed piezoelectric actuator is discussed in detail, and the simulation is carried out to study the feasibility. An experimental system has been set up to investigate the actual working performance. According to the experimental results, the suitable phase difference between the two L-shaped flexure mechanisms to eliminate the backward motion is around <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</i> = 5°, the maximum speed is <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> = 1887.3 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m/s, the minimum stepping distance is 0.084 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m, and the maximum load is more than <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F_v</i> = 1100 g. The motion speed and the maximum load under the proposed bionic walking motion (two flexure mechanisms work together as “legs”) could be improved greatly for almost 3.7 and 1.7 times, respectively, compared with that of the traditional friction–inertial motion (only one flexure mechanism works). By eliminating the backward motion, the motion efficiency is improved about 52.9% under the condition of 120 V and 1 Hz. This article shows the feasibility of applying the bionic motion to improve the performance of piezoelectric actuators, which may be instructive for the design of piezoelectric actuators with large working stroke. In the future, it may be helpful for the real application of piezoelectric actuators in the fields of ultraprecision machining, optical engineering, and aerospace technology.

Derivation of a superelement with deformable interfaces – applied to model flexure joint

Design and optimization, as well as real time control, of flexure mechanisms require efficient but accurate models. The flexures can be modelled using beam elements and the frame parts can be modelled using superelements. Such a superelement efficiently models arbitrarily shaped bodies by few coordinates, using models obtained by model order reduction. The interfaces between the frame parts and the flexures often experience considerable deformation which affects the stiffness. To define the interface deformation in a reduced order model, this paper derives a multipoint constraint formulation, which relates the nodes on the deformable interface surface of a finite element model to a few coordinates. The multipoint constraints are imposed using a combination of the Lagrange multiplier method and master–slave elimination for efficient model order reduction. The resulting reduced order models are used in the generalized-strain multi-node superelement (GMS) that was defined in (Dwarshuis et al. in Multibody Syst. Dyn. 56(4):367–399, 2022). The interface deformations can be coupled to the cross-sectional deformation of higher order beam elements (i.e. beam elements of which the deformation of the cross-sections is explicitly taken into account).This paper applies this technique to model flexure joints, where the flexures are modelled with beam elements, and the frame components and critical connections using the GMS. This approach gives generally over 94% accurate stiffness, compared to nonlinear finite element models. The errors were often more than 50% lower than errors of models which only contain beam elements.

Development of a novel XZ workpiece vibration generator for cooperative vibration cutting of hierarchical grating structures

This paper presents a novel piezoelectrically-driven XZ workpiece vibration generator (WVG) enabling the cooperative vibration cutting, which serves as a promising alternative for machining hierarchical micro/nano-structured surfaces. The WVG features a double symmetric configuration and the integration of two flexural lever mechanisms and an eight legs Z-shaped mechanism for dual-stage displacement amplification as well as decoupled 2D motion modulation. By utilizing the matrix-based stiffness modeling and Lagrange principle with motion properties of the piezoelectric actuators treated as boundary conditions, the kinetostatics and dynamics of proposed WVG are analytically described and verified using finite element analysis. The experimental performance assessments of proposed WVG show a working space of 44.7 μm × 38.9 μm with a positioning resolution less than 20 nm in both motion directions. The capability of delivering harmonic elliptical as well as non-harmonic triangular and trapezoidal motion trajectories has been demonstrated. In addition, the developed WVG was integrated into a newly cooperative vibration cutting system for one-step machining of hierarchical grating structures. The cutting performances of three kinds of hierarchical grating structures demonstrate not only the feasibility and flexibility of proposed cooperative vibration cutting process but also the accuracy and robustness of the developed WVG mechanism.

Experimental study of tensile and flexural performances and failure mechanism of none-felt needled composites

None-felt needled composite material is a novel type of composite with excellent interlayer connection performance. Nonetheless, the tensile and flexural properties and failure mechanism have not been clarified. In this work, none-felt needled fabrics and reinforced composites were manufactured, which were then characterized structurally using Micro-CT. Moreover, the tensile and flexural performances were researched with digital image correlation (DIC) technology, and the fracture morphology was observed employing SEM. The results showed that more needled fiber bundles were implanted along the thickness direction, and the fiber diameter and length were increased by 127.2% and 148.2% respectively. The tensile strengths and modulus also enhanced by 31.5% and 32.8%, and the flexural strengths and modulus improved by 13.1% and 26.7%. The tensile and flexural failure modes of none-felt needled composites and conventional felt needled composites consisted of matrix fracture, in-plane fiber pull-out and brittle fracture. Besides, the flexural specimens of none-felt needled composites had a shorter delamination length. The none-felt needled composites with high tensile and flexural performances are expected to be used in key core components such as radome, cabin and skin of hypersonic aircraft.

A Compact Electromagnetic Dual Actuation Positioning System with a 10 mm Range and Nanometer Resolution

In this manuscript, a compact electromagnetic dual actuation positioning system (CEDAPS) based on the Lorentz force principle that features a 10 mm range and nanometer-scale resolution with flexure guides is presented. Firstly, the stiffness of the flexure mechanism is modelled. Secondly, based on it, the primary coil is designed, and from its performance, a suitable secondary coil is made to compensate for the deficiency of the primary actuation subsystem. The characteristics of the forces generated by these coils are also evaluated by an electromagnetic FEA simulation. Thirdly, a control scheme is presented that combines the performances of these two actuators, and finally, a prototype is fabricated to evaluate the performance. The results show a 10 nm resolution for a 10 mm (±5 mm) stroke with low sub-micron sinusoidal tracking errors and nanometer accuracy for step tracking under the proposed control scheme. The thermal properties of the system are also presented.

Experiments on the flexural behavior of full-scale PC box girders with service damage strengthened by prestressed CFRP plates

Two full-scale PC box girders with typical damage were derived from an in-situ bridge that was in service about 20 years, to understand the strengthening effects of prestressed CFRP plates for the entire bottom slab, casting of a RC layer in composite action with the entire top slab and steel plates anchored on the webs of the shear span. The flexural tests were conducted on the two full-scale PC box girders with and without strengthening measures, and comparative analysis was conducted regarding flexural capacity, failure mechanism, rigidity, ductility and overall structural behavior. The test results showed that the strengthening measures improved the girder rigidity by 40 % before reaching cracking state and increased the yielding and ultimate capacity by 39 % and 28% respectively. The theoretical analysis was conducted to discuss failure modes for PC box girder strengthened by prestressed CFRP plates. Theoretical equations are derived to calculate the flexural capacity of strengthened PC box girder according to typical failure modes. Good agreement with tested results was obtained. The strengthening design of the prestressing CFRP plate was verified by application in a PC box girder bridge.

Push-pull large stroke flexure-based micropositioning stage driven by electromagnetic actuators with complementary double configuration.

This paper aims at presenting a solution to overcome the problems of small driving force and the evident nonlinear characteristics of the large stroke flexure-based micropositioning stage driven by a voice coil motor (VCM). The push-pull mode of complementary configurations of VCMs on both sides is adopted to improve the magnitude and uniformity of the driving force, and model-free adaptive control (MFAC) is combined to achieve accurate control of the positioning stage. First, the micropositioning stage based on the compound double parallelogram flexure mechanism driven by double VCMs in the push-pull mode is proposed, and its most prominent features are introduced. Then, a comparison of the driving force characteristics of a single VCM and dual VCMs is conducted, and the results are empirically discussed. Subsequently, the static and dynamic modeling of the flexure mechanism was carried out and verified by finite element analysis and experimental tests. After that, the controller for the positioning stage based on MFAC is designed. Finally, three different combinations of different controllers and VCM configuration modes are used to track the triangle wave signals. The experimental results show that compared with the other two combinations, the maximum tracking error and root mean square error of the combination of MFAC and push-pull mode are significantly reduced, which fully proves the effectiveness and feasibility of the method proposed in this paper. At the same time, the reduction of current in the coil confirms the advantages of the push-pull mode.

Effect of out-of-plane displacements on the in-plane capacity of lightly precompressed rocking unreinforced masonry piers

Unreinforced masonry (URM) buildings subject to bidirectional seismic excitation are under the effects of simultaneous in-plane and out-of-plane actions. Seismic assessment carried out without considering the combined effects due to these actions could result in non-conservative capacity estimates and inadequate strengthening requirements. Bidirectional effects are not explicitly considered in the seismic assessment of existing URM buildings, owing to the limitations in existing protocols and analytical models and the simplicity achieved in performing the assessment. The current work attempts to quantify the effect of out-of-plane displacements on the in-plane capacity of masonry walls undergoing a flexural rocking mechanism of failure, thereby improving the existing understanding of bidirectional interaction in masonry structures. Response of lightly precompressed masonry piers with different aspect ratios in the presence of out-of-plane displacements, were studied experimentally and replicated using numerical and analytical studies. Results indicate that the interaction problem in URM structures should not be considered only from a force capacity reduction perspective. The force capacity reduction predicted using the interaction equations employing an exceedance of net tensile stress-based approach shall be applicable only for the flexural cracking strength and not the ultimate flexural capacity. The in-plane flexural cracking capacity reduces in proportion to the applied out-of-plane displacements when the applied out-of-plane displacements are in the elastic range. In the inelastic range of out-of-plane displacements, the ultimate flexural capacity corresponding to toe-crushing and also the initial stiffness of the pier was observed to decrease due to the reduction in net area available for compression. Also, even small range of out-of-displacements could result in inelasticity in a URM pier leading to a reduced toe-crushing capacity. Hence, it may not be conservative to define the in-plane restoring shear as the failure capacity for rocking URM piers under bidirectional loading. Accordingly, modifications are proposed for the response of masonry walls undergoing rocking mechanism.

Development of a Flexure Mechanism for High-Precision Applications in Scanning Applications

The utilization of the Planar XY Flexural Mechanism is extensive in precision motion systems, where it induces relative motion between a fixed support and a motion stage through the utilization of material flexibility. In contrast to rigid link mechanisms, this mechanism presents noteworthy advantages, including zero backlash, frictionless motion, and high-order repeatability, all within a considerably more compact form. Notably, flexure mechanisms are characterized by their construction from a single monolith. This research primarily concentrates on modeling the flexural process to achieve precise scanning across a broader range at increased speeds. In the assessment of the motion stage's static deflection, Finite Element Analysis (FEA) is employed in the static analysis. Subsequently, the mechanism undergoes activation using a weight pan and weights, with displacement being monitored through a Dial Gauge Indicator. The experimental setup encompasses the flexural mechanism, Dial Gauge, Weight Pan and Weights, Pulley, String, Small metal strip, and Optical Bread Board. A comparison of experimental and analytical findings reveals minimal variation, affirming the effectiveness of the flexural mechanism in delivering precise motion for high-precision applications.

Review on the design and application of concrete canvas reinforced with spacer fabric

Concrete canvas reinforced with spacer fabric has increasingly gained popularity due to its lightweight, great flexibility, high strength and low contamination compared to ordinary concrete. In order to fully explore the structure and performance of this novel composite, this review illustrates how to design high-performance concrete canvas and presents a summary of recent application status of it. Firstly, the structure and properties of knitted and woven spacer fabric and concrete material that comprise concrete canvas is introduced. Secondly, internal and external mechanisms affecting the properties of concrete canvas have been described. To illustrate how to evaluate and test the mechanical behavior of concrete canvas, typical mechanical experiments such as tensile and flexural experiment and failure mechanisms are explained. In terms of the characteristics of concrete canvas, the present article reviews current applications of it in disaster relief tent, slope protection, ditch lining and furniture design areas. Nevertheless, its practical applications are still in the preliminary stage, it is of great necessity to expand its application from the point of view of replacing traditional materials, changing structural design, external reinforcement and perfecting performance evaluation system.

Validation of nonlinear finite element model of reinforced concrete beams subjected to monotonic loading

The nonlinear behavior of reinforced concrete beams is complex due to their heterogenic properties and crack formations. Thus, a more accurate estimation through experimental testing and nonlinear finite element modeling is necessary to understand better such behavior. Experimental testing of a reinforced concrete beam subjected to monotonic loading was conducted in laboratory. The test specimen along with seven specimens from various literature were then modeled and analyzed using VecTor2 software to investigate the capability of the software in predicting the load-displacement curves and crack patterns of the specimens. The analysis results show that the finite element model used in VecTor2 software is able to predict well the load-displacement curves and crack patterns of the specimens failing in flexure and shear mechanisms.

Dual-stage fast tool servo cascading a primary normal-stressed electromagnetic stage with a secondary piezo-actuated stage

The dual-stage actuation effectively extends the dynamic response and tracking accuracy of conventional fast tool servos (FTS). In this study, a normal-stressed electromagnetic stage is deliberately designed as the primary stage to cascade with a secondary piezo-actuated stage, constructing a new medium-range dual-stage FTS. Analytical models for both the normal-stressed actuator and the flexure mechanisms are established. The mechanical and electromagnetic parameters are selected and verified by finite element simulation, targeting the desired motion stroke and the maximized natural frequency. The prototype using the designed parameters is tested to have an actual stroke of 80μm and a first resonant frequency around 814 Hz. The dual-stage FTS employs a decoupled control strategy to track the desired trajectory precisely. As for the main controller, an additional disturbance observer is designed to work with the typical PID controller to compensate for both the internal nonlinear dynamics and external disturbances for each stage. The practical result demonstrates that the closed-loop bandwidth can be improved from 220 Hz to 500 Hz by cascading the secondary stage. As for the tracking of a complex trajectory with multiple frequencies, a motion error of around ±0.8μm was achieved, which is less than 30% of that obtained by the primary stage alone.

An Improved Dynamic Model and Matrix Displacement Model for Distributed-Compliance Bridge-Type Amplification Mechanism

This paper establishes a matrix displacement model and an improved dynamic model for the static and dynamic performances analysis for a kind of bridge-type displacement amplification mechanism with distributed-compliance, which has better performances than traditional lumped-compliance bridge-type mechanisms. In the matrix displacement model, the stiffness matrix for two rigid bodies connected by flexures is first obtained by regarding the displacements and the forces on two mass centers of the rigid bodies as the node displacements and node forces. By extending and superimposing each elemental stiffness matrix, the global stiffness matrix for the flexure mechanism can be obtained to calculate the displacement amplification ratio and input stiffness of the bridge-type mechanism. In the improved dynamic model, in order to establish the Lagrangian dynamic model more accurately, the deflectional, axial, and rotational velocities of any point on the beam flexure are calculated by solving the derivatives of the deformation curves of beam flexures versus time to obtain the expression of the kinetic energy in the vibrating beams. On this basis, the three-degree-of-freedom vibration differential equation for the bridge-type mechanism is established by using the Lagrange method, and the natural frequency in the working direction is obtained accurately. The presented models are compared with the finite element analysis, and experiments for two case studies of the bridge-type distributed-compliance mechanism are presented. The comparisons results demonstrate the high prediction accuracy of the improved dynamic model.