Flexural Type Research Articles

Design and testing of a large-workspace XY compliant manipulator based on triple-stage parallelogram flexure

This paper proposes a new XY compliant parallel manipulator with large workspace and low coupling motion by resorting to planar arrangement of multistage parallelogram mechanisms. The triple-stage parallelogram flexure is chosen as the basic mechanism for motion transmission and decoupling. Its fixed and moving ends adopt planar and spatial connections, respectively. By this connecting scheme, more types of general multistage parallelogram flexures can be constructed. The driving stiffness and resonant frequency of the manipulator are derived based on statics analysis of theoretical mechanics and dynamics analysis via Lagrangian equation. The accuracy of the analytical model is confirmed by performing finite element analysis simulation, and the performance variances of three manipulators are compared. Moreover, a prototype of the XY compliant manipulator has been fabricated and tested. Results show that the workspace of the parallel manipulator is 1.51 cm × 1.48 cm, and the coupling ratios of the two axes are 1.11% and 1.06%, respectively. The volume ratio is introduced as a compactness indicator for comparison study versus existing designs. The centimeter-level stroke can promote the application of XY parallel manipulators in more industrial scenarios.

A simple and versatile topology optimization formulation for flexure synthesis

High-tech equipment critically relies on flexures for precise manipulation and measurement. Through elastic deformation, flexures offer extreme position repeatability within a limited range of motion in their degrees of freedom, while constraining motion in the degrees of constraint. Topology optimization proves a prospective tool for the design of short-stroke flexures, providing maximum design freedom and allowing for application-specific requirements. State-of-the-art topology optimization formulations for flexure synthesis are subject to challenges like ease of use, versatility, implementation complexity, and computational cost, leaving a generally accepted formulation absent. This study proposes a novel topology optimization formulation for the synthesis of short-stroke flexures uniquely based on strain energy measures under prescribed displacement scenarios. The resulting self-adjoint optimization problem resembles great similarity to ‘classic’ compliance minimization and inherits similar implementation simplicity, computational efficiency, and convergence properties. Numerical examples demonstrate the versatility in flexure types and the extendability of additional design requirements. The provided source code encourages the formulation to be explored and applied in academia and industry.

STATE OF THE ART OF TANK STRUCTURAL EVALUATION REVIEW: A CASE STUDY OF AN ELEVATED CONCRETE WATER TANK CONCERNING CRACK INITIATION

This study aims at the structural evaluation of the elevated concrete water tank condition, including crack initiation, through nondestructive testing. The growing demands for environmental quality have resulted in a rise in the design and construction of tanks and reservoirs in the construction industry. Cracks for water line leakage were found during watertight testing in concrete tanks. Long-term liquid leaking may permanently damage the tank and can contaminate the groundwater. Given the critical existence of leaked cracks in tank serviceability and durability, the contribution examines the triggers and effects of their occurrence. An inspection of the existing water tank system is conducted to ascertain its condition. The investigation included structural design checks, concrete compressive strength tests, visual assessments, hammer inspections, and Ultrasonic Pulse Velocity (UPV) testing with Portable Ultrasonic Non-Destructive Digital Indicating Tester (PUNDIT). This observation is made at many elevations on various sampling points on the tank structure's elements, including columns, beams, tank floor slabs, and tank wall shells. The results indicate the presence of flexural type cracks in the main beam's middle span and diagonal beams. Additionally, cracks attributed to long-term drying shrinkage were discovered on the diagonal of the floor slab and cracks of the same pattern on the main beam's middle span. The deflection estimated by structural remodeling was larger than the deflection estimated by design. The computed crack width in the main and diagonal beam exceeds the acceptable crack width.

Design and Analysis of a Uniform Meander RF MEMS Switch

This paper projected to uniform meander RF MEMS capacitive shunt switch design and analysis. The less pull in voltage is obtained in flexure type membrane by proposed RF MEMS Switch. The materials selection for the dielectric layer and beam is explained in this paper and also shown the performance depends on materials utilized for the design. The good isolation of -31dB is achieved for the pull-in voltage of 11.97V with a spring constant of 2.38N/m is produced by the switch and is obtained by the optimization process at a frequency of 38GHz.

Design and Analysis of a Non-Uniform Meander RF MEMS Switch

This paper aimed to design and analysis of non-uniform meander capacitive shunt RF MEMS switch. The less pull in voltage is obtained in flexure type membrane by proposed RF MEMS Switch. The selection of materials for the beam and dielectric layer is expressed in this paper and also shown the performance depends on materials utilized for the design. The high isolation of -31.15dB actuating at the pull-in voltage of 7.69V with a spring constant of 3.28N/m produced the switch and is obtained by the optimization process. Capacitive contact switches have capability of power handling. The actuated switch state provides an excellent isolation. It shorts the ground by RF signal. MEMS technology is the integration of electrical and mechanical components on single platform i.e. substrate [10]. From the literature, various researchers have proposed different RF MEMS Switch, but still there few challenges on optimization of the Switch for best performance. The electromechanical analysis such as Upstate, Downstate capacitances and stress analysis have been carried out. The performance of the switch is analyzed by taking appropriate materials selected by Ashby’s approach. These optimized dimensions are feasible to fabricate. The substrate height, material for the substrate and coplanar waveguides are used for the impendence matching. For obtaining the less pull in voltage overlapping area is to be increased.

Integrated Anchorage of Thin Façade Panels Made of Textile Reinforced Concrete

This paper discusses the feasibility of an innovative anchoring element which is designed to be integrated into the volume of an ultra-thin coffered façade panel made of textile reinforced concrete and to not increase its external dimensions. The first part of the article describes the composition and shape of the façade panel and focuses on the manufacturing of the composite anchoring element made of carbon technical textile penetrated with polymer matrix which is intentionally identical composition as in the case of the façade panel reinforcement. The second part of the article focuses on the behavior of the composite anchoring element and its effect on its surroundings during the mechanical loading of the façade panel. Specimens of the coffered façade panel with integrated anchoring elements were subjected to four-point bending test to determine the impact of the anchoring elements on the façade panel flexural tensile strength and type of failure. Additional specimens were tested to determine the load-bearing capacity of the anchoring elements.

Tectono-sedimentary characteristics in the area with distributed normal faults: Lower Cretaceous Prosopis Formation in the northern slope of Bongor Basin, Chad

Based on an integrated database (e.g., core observations, well logs, and seismic data), the characteristics of depositional systems, as well as the response to tectonics, are systemically delineated in the Prosopis Formation of the Lower Cretaceous at Bongor Basin, Chad. The tectonic setting of this study area experienced multiple, active sub-basins with narrow-spaced intra-basinal normal faults. The multiple normal faults formed in the initial rifted stage leading to the development of a corridor-shaped basin consisting of small-scale sub-basins. As this basin is attracting increased attention due to further hydrocarbon exploration, deciphering the process of sediment partition, especially in the initial rifted stage, would provide a further understanding of the tectono-sedimentary evolution in lacustrine rift basins. Based on core observations, well logs, and three-dimensional seismic data, fan-delta and sub-lacustrine-fan depositional systems are widely developed in this area. Two depositional systems (e.g., fan-delta and sub-lacustrine-fan) and three categories of slope break belts (single-faulted, step-faulted, and flexure types) have been identified. Overall, during the initial rifted stage, the formation of multiple normal faults mainly dominates the geomorphology and sediment supplies that generate the spatio-temporal features of depositional systems in semi-closed lacustrine basins. Climatic perturbations, furthermore, regulated the composition of sediments (coarse versus fine deposits). For the economic perspective, this study highlights the significance of fault systems in further hydrocarbon exploration during the initial rifted stage of lacustrine basins.

Shear strengthening of RC beams using aluminum plates: An experimental work

Strengthening of the reinforced concrete (RC) beams using Aluminum plates (APs) is the most recent method. In this research, the shear strengthening of the RC beams using APs was studied experimentally. The experimental program consisted of twenty four RC beams (1/2 scale) that were tested under four-point bending flexural experiments. All beams had the same dimensions and the same internal reinforcement. Different shear strengthening techniques using APs were carried out. APs were fixed on the beam sides to enhance the shear strength vertically, inclined by 45°, diagonally and horizontally. Influence of the spacing, height and quantity of the APs was studied. The effect of the APs on the behaviour of RC beams with low compression strength of concrete was investigated. All AP techniques succeeded in enhancing the shear capacity and some of them changed the failure mode to flexural type. The highest ratio of increase of the shear strength was 76.8%. AP techniques had not increased the shear strength of the RC beams made from the weak concrete.

Dimensionless fragility analysis of seismic acceleration demands through low-order building models

This paper deals with the estimation of fragility functions for acceleration-sensitive components of buildings subjected to earthquake action. It considers ideally coherent pulses as well as real non-pulselike ground-motion records applied to continuous building models formed by a flexural beam and a shear beam in tandem. The study advances the idea of acceleration-based dimensionless fragility functions and describes the process of their formulation. It demonstrates that the mean period of the Fourier Spectrum, T_m, is associated with the least dispersion in the predicted dimensionless mean demand. Likewise, peak ground acceleration, PGA-, and peak ground velocity, PGV-based length scales are found to be almost equally appropriate for obtaining efficient ‘universal’ descriptions of maximum floor accelerations. Finally, this work also shows that fragility functions formulated in terms of dimensionless varPi-terms have a superior performance in comparison with those based on conventional non-dimensionless terms (like peak or spectral acceleration values). This improved efficiency is more evident for buildings dominated by global flexural type lateral deformation over the whole intensity range and for large peak floor acceleration levels in structures with shear-governed behaviour. The suggested dimensionless fragility functions can offer a ‘universal’ description of the fragility of acceleration-sensitive components and constitute an efficient tool for a rapid seismic assessment of building contents in structures behaving at, or close to, yielding which form the biggest share in large (regional) building stock evaluations.

Design and simulation of fixed–fixed flexure type RF MEMS switch for reconfigurable antenna

This Paper Presents the design and simulation of RF MEMS switch taken on Microstrip patch antenna loaded with the circular type CSRR. The Tunability of the patch antenna is achieved when the two switches moves from upstate to down state arranged on the feeding line provided with the CPW. The actuation voltage required to move the switch downwards is 7.6 V. The switch operates at transition time of 0.8 µsec with the capacitance ratio 10. The return loss (S11) of antenna − 28.67 dB is observed at the frequency of 19 GHz when one switch is in on state and at 16 GHz frequency the S11 of − 29.31 dB is achieved by actuating the 2 switches at a time, which gives the reconfigurable property of the antenna. The antenna provides 2 GHz and 5 GHz frequency shift when single and both the switches are in on state. The antenna can be tuned for various applications in the range of 15–30 GHz frequency. The characteristics of switch has been observed by simulating the switch design in FEM tool and results have been compared with theoretical calculations. The tunable characteristics of antenna has been observed and presented by using HFSSV.13 tool.

A MITC-based procedure for the numerical integration of a continuum elastic-plastic theory of through-the-thickness-jacketed shell structures

Through-the-Thickness Jacketing (TTJ) is a technique for repairing and retrofitting shell structures by inducing in the shell core a beneficial confining stress state created by a net of broadly distributed retrofitting links crossing the shell thickness and tying externally applied layers. The paper presents the derivation, the algorithmic implementation and the numerical assessment of a predictor-corrector computational strategy for the integration of a shell FE-model obtained by combining a discrete MITC quadrilateral element with a layered continuum-based generalized shell theory of TTJ-reinforced structures, essentially based upon a Winkler-like idealization of TTJ. This theory of Through-the-Thickness-Jacketed Shells (TTJS) captures the onset of complex triaxial stress states originated by the interaction between core and TTJ reinforcements.Results of benchmark numerical applications in OpenSees with flat and curved elastic-plastic shell structures are presented in order to assess and illustrate the consistency and the general modelling features of the proposed TTJS-MITC framework endowed with the Drucker-Prager elastic-perfectly-plastic idealization of the nonlinear behavior of the material composing the shell. Numerical results exhibit quadratic convergence and show that the model captures marked strength increments over the in-plane membrane response, albeit these are lower when the response is predominantly of out-of-plane flexural type.

Debris flow and glacioisostatic-induced soft-sediment deformation structures in a Pleistocene glaciolacustrine fan: The southern Baltic Sea coast, Poland

Middle Pleistocene glaciolacustrine fan sediments are exposed along a cliff at the Baltic Sea coast, where plastic and brittle soft-sediment deformation structures (SSDS) commonly occur: (1) fold structures (various types of folds and flexures); (2) load structures (load casts, pseudonodules) and flame structures; (3) water-escape structures (WES); and (4) brittle deformation structures, such as faults (medium- and small-scale reverse and normal), and fragments of broken-up laminae. The origins of the SSDS can be linked to gravitational processes promoted by shear stresses in subaqueous debris flows on the glaciolacustrine fan and by the weight of overlying sediments; and/or to the glacial rebound of Earth's crust during deglaciation because in the Pleistocene the Baltic Sea and surrounding areas were covered by ice sheets many times. The question investigated here concerns recognition of the trigger mechanisms responsible for the development of SSDS, and the criteria needed to recognize those mechanisms based on the lithological and deformational features of the sediments involved. Some types of SSDS can look similar regardless of trigger mechanisms, but some occur more often as a result of a specific mechanism. Is it possible to distinguish SSDS of seismic origin in a glaciolacustrine fan succession affected by multiple debris flows and of SSDS that evolved as a consequence of slope processes? We suggest criteria to recognize SSDS triggered by the glacioisostatic rebound as well as those which can develop as a result of the rebound and slope processes.

Numerical simulation of the electromagnetic fields variations under the formation of the fault rupture before earthquake

A 2D geoelectric model of a heterogeneous geological medium has been developed taking into account the processes occurred in the geological subj ect of flexure type which transforms into an uplift-thrust structure as a result of deformations. The model is based on a hypothesis of the variation of electrical conductivity of geomaterials in the local area of the fault under subcritical stress-state conditions due to the geodynamical processes. In the shear stress maximum area, in the plane of fracture of the uplift-thrust type, a zone of increased fracturing is developed contributing to the essential decrease of electric resistance due to filling the fractures by fluid - so named «conductive split». A numerical simulation has demonstrated that when transiting from the quasi-stratllied model to a 2D model with the high-resistive shield a redistribution of the total current density in the medium is increased essentially due to the effect of the «conductive split», taking into account the assumed formation of the zone of fracturing. In this case, amplitude of the electromagnetic (EM) field for the longitudinal polarization increases far apart from the area of the «conductive split». The result obtained may be applied as a background for the development of the monitoring technique of the electromagnetic fields measured on a surface of the Earth far apart from the earthquake epicenter and directly over the fault for the controll ing of a level of the fault maturity for the occurrence of the seismic event.

Mechanics of longitudinal and flexural locally resonant elastic metamaterials using a structural power flow approach

Elastic metamaterials are sub-wavelength structures with locally resonant components that contribute to the rise of tunable stop bands, i.e. frequency ranges within which waves do not propagate. A new approach is presented here to model and quantify this stop band behavior by evaluating structural vibrating power flowing in the different constituents of locally resonant metamaterials. It is shown that the patterns of power propagation resemble, to a great extent, steady-state wave profiles derived from displacement fields, and can thus be used to develop an algorithm that numerically predicts stop band frequencies for any given realization with a finite length and a known number of repeating cells. The approach is presented here in the context of one-dimensional metamaterials with single and multiple internal resonators and is applied to two traditional examples constituting both longitudinal and flexural type structures. The presence of dissipative elements is taken into consideration since the active component of vibrational power is shown to depend on the damping matrix of the finite element description. The presented approach can be further extended to complex metamaterials with multi-dimensional locally resonant configurations to locate critical energy transmission paths within the media of such structures.

Mechanical Characterization of Sandwich Composite Structure using a New Experimental Approach

In marine construction, ship hulls are subjected to high fatigue stresses due to the impact of waves and their cyclic solicitations. However, fatigue behaviour evaluation of the constitutive materials of hull is based on standard tests. The objective of this study is to take a critical view on the current standard test method set to investigate the fatigue life of cellular foam core material as used in high performance sandwich materials. The highlight of this study is to develop a new geometry of specimen in order to achieve coherence between the actual fatigue life time of the real structure and the one of specimens tested in a controlled laboratory environment. The tested specimen is made out of a high-density foam core and thin glass fabric faces. Moreover, a new test rig of different flexure types, in quasi-static or fatigue loadings on sandwich specimens, was developed and validated.

Behaviour of RC Beams with non-bonded flexural reinforcement: A numerical experiment

The present work is concerned with a numerical investigation of the behaviour of reinforced-concrete beams with non-bonded flexural tension reinforcement. The numerically-established behaviour of such beams with and without transverse reinforcement is compared with its counterpart of similar beams with bonded reinforcement. From the comparison, it is found that the development of bond anywhere within the shear span inevitably leads to inclined cracking which is the cause of 'shear' failure. On the other hand, the lack of bond within the shear span of the beams is found, not only to prevent cracking within the shear span, but, also, to lead to a flexural type of failure preceded by the formation of horizontal splitting of concrete in the compressive zone. It is also found that delaying the extension of horizontal splitting through the provision of transverse reinforcement in the beam mid span can lead to flexural failure after yielding of the tension reinforcement. Yielding of the tension reinforcement before the horizontal splitting of the compressive zone may also be achieved by reducing the amount of the latter reinforcement.

Integration of advanced stiffness-reduction techniques demonstrated in a 3D-printable joint

This work details the integration of three distinct methods for altering the stiffness of compliant joints: lattice flexures, compound joints, and static balancing. The methodology for applying these strategies is discussed in detail. Lattice flexures are a flexure modification that leads to low motion-direction bending stiffness. Compound joints improve a compliant joint's load-carrying ability and off-axis stiffness. Static balancing in this case is achieved through the addition of an auxiliary energy storage device. To statically balance a compound lattice-flexured cross-axis flexural pivot, the load-dependent stiffness behavior of a cross-axis flexural pivot (CAFP) with two lattice flexure types is determined. A balancer spring design is developed that is fully 3D-printable. The balancer is combined with a compound lattice-flexured CAFP. Physical hardware is 3D printed in titanium and its torque-displacement behavior is measured. The resulting device requires 1% of the actuation energy of a conventional CAFP of the same dimensions and material.

Improving the linear stability of the Beck׳s beam by added dashpots

The effects of lumped dashpots on the linear stability of the Beck׳s beam, internally and externally damped, are studied, with the aim to improve the mechanical performances of the system. A perturbation analysis is carried out, in which the sensitivities of the simple eigenvalues of the undamped and sub-critically loaded beam are evaluated. The analysis provides a simple and very efficient tool for damping design. It is proved that there exists a region along the beam axis assuring that the added dashpots, of extensional and flexural type, increase the critical load of the beam under distributed damping, thus mitigating the detrimental effect of the destabilization paradox. It is also shown that, if the flexural dashpot is located at the tip of the beam, it has a beneficial effect at low level of load, but, counter-intuitively, it is detrimental when the load approaches the critical value of the undamped beam, thus extending analogous findings of the literature concerning the extensional dashpot.

Lattice flexures: Geometries for stiffness reduction of blade flexures

Reducing the motion-direction stiffness of compliant mechanisms reduces their actuation effort and simplifies associated static balancing mechanisms. This work introduces a flexure type called lattice flexures and evaluates some of their fundamental properties. Lattice flexures have a reduced bending stiffness when compared to traditional rectangular-section blade flexures of similar size. The motion-direction bending stiffness of two lattice flexure types, called X-type and V-type, are analytically derived, corroborated with finite element analysis, and validated with measurements of physical prototypes. The lattice flexure has the potential to reduce the bending stiffness of some compliant mechanisms by 60–80%, as demonstrated in devices manufactured using 3D printing technologies. It is shown that some lattice flexures exhibit a torsional/bending stiffness ratio as much as 1.7 times higher than an equal aspect-ratio blade flexure, and a transverse bending/motion-direction bending stiffness ratio up to 6.5 times higher than an equal aspect-ratio blade flexure.

Compound joints: Behavior and benefits of flexure arrays

Because compliant mechanisms achieve their motion through deflection of flexible members, they have a limited range of motion and finite stiffness. Many common flexure geometries also suffer from a non-stationary center of rotation. These properties can be obstacles to their adoption in applications that require large displacements, low stiffness, or stationary centers of rotation. This work presents the concept of compound flexures: by assembling arrays of flexures, we can increase range of motion, decrease stiffness, and reduce center shift. We first develop the theory behind some of the basic behavior of compound joints. Then finite element analysis is used to explore other aspects of compound joint behavior such as off-axis stiffness and quantifying the center shift for two flexure types when used in compound joints of various configurations. It is shown in an example that range of motion can be doubled with no appreciable loss in off-axis stiffness, while the desired stiffness κθz remains unchanged. A method is presented to achieve zero center shift for a specified rotational displacement. Compound joints are shown to exhibit greater ranges of motion, higher off-axis stiffness, and reduced center shift compared to traditional joints.