Flexible Beam Research Articles

Simulation and Experiment of Active Vibration Control Based on Flexible Piezoelectric MFC Composed of PZT and PI Layer.

In order to improve the vibration suppression effect of the flexible beam system, active control based on soft piezoelectric macro-fiber composites (MFCs) consisting of polyimide (PI) sheet and lead zirconate titanate (PZT) is used to reduce the vibration. The vibration control system is composed of a flexible beam, a sensing piezoelectric MFC plate, and an actuated piezoelectric MFC plate. The dynamic coupling model of the flexible beam system is established according to the theory of structural mechanics and the piezoelectric stress equation. A linear quadratic optimal controller (LQR) is designed based on the optimal control theory. An optimization method, designed based on a differential evolution algorithm, is utilized for the selection of weighted matrix Q. Additionally, according to theoretical research, an experimental platform is built, and vibration active control experiments are carried out on piezoelectric flexible beams under conditions of instantaneous disturbance and continuous disturbance. The results show that the vibration of flexible beams is effectively suppressed under different disturbances. The amplitudes of the piezoelectric flexible beams are reduced by 94.4% and 65.4% under the conditions of instantaneous and continuous disturbances with LQR control.

Extreme parametric resonance oscillations of a cantilever: An exact theory and experimental validation

Flexible cantilevered beams are capable of undergoing motions of extremely large amplitudes which are relevant to both conventional and emerging applications. However, modelling and capturing such behaviour is not a straightforward task and requires the application of a geometrically exact model. In this study, the extreme parametric resonance responses of a cantilever with a tip mass are captured through carefully conducted experimental measurements and compared to the predictions of a centreline-rotation-based geometrically exact cantilever beam model. For the experimental part, a state-of-the-art in-vacuo base excitation set-up consisting of a vacuum chamber and a long-stroke shaker is utilised to excite the cantilever in the axial direction near parametric resonance and drive the cantilever to very large oscillation amplitudes. This set-up is accompanied by a high-speed camera to capture footage of the deformed configurations of the cantilever in a period of steady-state oscillations at each excitation frequency. The cantilever motion amplitudes are then extracted from the videos through use of a robust image processing code. For the theoretical modelling and numerical analysis parts of the study, the cantilever is modelled via the Euler–Bernoulli beam theory assuming an inextensible centreline, while considering the centreline rotation as the main motion variable. All nonlinear terms in the model are kept intact throughout the derivation, discretisation, and simulation procedures to ensure accurate model predictions. Comparisons between experimental and theoretical results are conducted for three axial base-acceleration levels. It is shown that the geometrically exact model’s predictions are in excellent agreement with experimental results at various oscillation amplitudes.

Dynamic response and breakage of trees subject to a landslide-induced air blast

Abstract. Landslides have been known to generate powerful air blasts capable of causing destruction and casualties far beyond the runout of sliding mass. The extent of tree damage provides valuable information on air blast intensity and impact region. However, little attention has been paid to the air blast–tree interaction. In this study, we proposed a framework to assess the tree destruction caused by powerful air blasts, including the eigenfrequency prediction method, tree motion equations and the breakage conditions. The tree is modeled as a flexible beam with variable cross-sections, and the anchorage stiffness is introduced to describe the tilt of the tree base. Large tree deflection is regarded when calculating the air blast loading, and two failure modes (bending and overturning) and the associated failure criteria are defined. Modeling results indicate that although the anchorage properties are of importance to the tree eigenfrequency, tree eigenfrequency is always close to the air blast frequency, causing a dynamic magnification effect for the tree deformation. This magnification effect is significant in cases with a low air blast velocity, while the large tree deflection caused by strong air blast loading would weaken this effect. Furthermore, failure modes of a specific forest subject to a powerful air blast depend heavily on the trunk bending strength and anchorage characteristics. The large variation in biometric and mechanical properties of trees necessitates the establishment of a regional database of tree parameters. Our work and the proposed method are expected to provide a better understanding of air blast power and to be of great use for air blast risk assessment in mountainous regions worldwide.

Deflection Analysis of Flexible Cantilever Beam with a Drop Impact

Deflection Analysis of Flexible Cantilever Beam with a Drop Impact

Numerical modelling, parametric analysis and design of UHPFRC beams exposed to fire

A non-linear sequentially-coupled thermal–mechanical finite element (FE) paradigm that reasonably tracks the coupled fire-structure response of ultra-high performance fibre reinforced concrete (UHPFRC) beams subjected to the ISO 834 fire is established and presented. A fire resistance parameter study is conducted on UHPFRC beams via the developed FE paradigm, and then flexural based fire-structural assessment is demonstrated, as an avenue to substantiate the viability of numerical performance-based structural fire design. The parameter study considered two variables, notably heating mechanism and load levels. Comparison of results revealed that the fire-structure response was more severe under the hydrocarbon than the ISO 834 heating mechanism and hydrocarbon fire resistance ratings estimation were found to be 30 minutes lower than those determined using the ISO 834 fire. Predicted failure of the beams under the ISO 834 and hydrocarbon fires was observed at load ratios exceeding 0.6 and 0.4, respectively. By reposing on ACI544’s analytical model for UHPFRC beams in flexure, and numerically acquired heat-transfer response, the time-variant reduced nominal moment capacities of UHPFRC beams were computed. Failure predicted via computed residual moment capacities was somewhat consistent with that reckoned by load ratio parameter study.

Active vibration control of flexible beam system based on cuckoo search algorithm

<p>A flexible beam is recognized as a lightweight structure that is prone to excessive vibration, resulting in poor performance. Thus, controlling unwanted vibration is necessary to maintain the system’s performance. Therefore, this study presents a technique to suppress undesired vibration in a flexible beam structure by introducing active vibration control (AVC). However, to develop an effective controller, an appropriate flexible beam model must first be obtained. In recent times, one of the best methods employed to model a flexible beam structure is system identification via a swarm intelligence algorithm. In this study, an intelligent algorithm acknowledged as cuckoo search (CS) was acquainted. The capability of the proposed algorithm was verified using three robustness techniques which were correlation test, pole-zero diagrams and mean square error (MSE). The simulation result showed that the CS algorithm achieved superior performance by achieving the lowest MSE of 6.1547x10<sup>-9</sup>, a correlation test between a 95% confidence level and high stability. Next, a proportional-integral-derivative (PID) controller tuned by the Ziegler-Nichols method was developed using the transfer function accomplished from the CS model. Two types of interference, namely single and multiple sine waves were introduced to validate the effectiveness of the controller. The controller successfully achieved a 30.2 dB of attenuation level for both disturbances.</p>

Structural behavior of reinforced geopolymer concrete beams – A review

A potential novelconstructionmaterial that is relativelyeco-friendly in manufacturing and has a comparatively low carbon footprint is geopolymer concrete (GPC). GPC is a largely unexplored topic in the literature due to its novelty as a material, particularly in terms of itsstructural behaviour. Reinforced concrete (RC) beams are the most common concrete application in the construction industry. Therefore, this review study intends to provide a greater understanding of GPC by summarizing and discussing the most updated data on the structural performance of reinforced geopolymer concrete (RGPC) beams. The evaluation highlights the flexural and shear behaviour of RC beams made with GPC and compared with those of ordinary Portland cement concrete (OPCC). The reported literature demonstrated that the structural behaviour of RGPC beams is comparable to that of conventional OPCC beams. Further, the failure mode of RGPC beams in flexure and shear was nearly identical to that of OPCC beams. Review of the literature showed that GPC beams might be employed safely with the existing standards. However, to assure its viability in the industry, full-scale investigations on the structural behaviour are required for mass use in a variety of application areas and to promote cleaner and sustainable choices in the construction industry. Overall, this review offers guidance for researchers and civil engineers in conducting future studies on GPC.

Shear and flexure of FRP-reinforced concrete beams and slabs – A review

The article reviews structural response of flexural members reinforced with fiber-reinforced polymer (FRP) as a sustainable alternative to conventional carbon steel. It overviews experimental studies and code-based models that characterize shear and flexural response of concrete beams and slabs reinforced with FRP bars. Discussion on lower resistance to fire being key limitation of FRP bars is also included. The most commonly used fibers to manufacture FRP bars include carbon, glass, basalt, aramid, or combinations of these materials. Consequently, each material plays its role in contributing to shear and flexure differently. Basalt FRP are characterized by higher tensile capacity and resistance to corrosion, carbon FRP bars can withstand exposure to harsh environments; glass FRP bars possess lower modulus of elasticity that may cause large deflection and wider cracks. FRP bars are generally preferred over carbon steel for use in concrete elements where exposure to chlorides or chemicals is expected, or places where non-magnetic properties are essential. Beams and slabs reinforced with FRP bars are likely to undergo larger deflections due to lower stiffness of FRP bars. The dominant failure mode of FRP-reinforced concrete flexural members is discussed in comparison to conventional steel-reinforced members. The article identifies increasing interest and research in using green concrete reinforced with FRP bars that helps to make construction serviceable and sustainable. However, premature de-bonding of bars remains a concern with more research needed to avoid deterioration of mechanical properties by underutilization of materials. Although concrete is practically fire-resistant, FRP is likely to undergo damage of resin due to the presence of combustible organic polymers. The bulk of research implies that the thermal instability of the resin in FRP reinforcing bars is not a disadvantage that outweighs the possible benefits of its usage in the construction industry.

Adaptive Vibration Iterative Learning Control of an Euler–Bernoulli Beam System With Input Saturation

This article focuses on solving the problem of vibration attenuation of an Euler–Bernoulli beam system considering imprecise system parameters, asymmetric input saturation, and external period disturbance. By employing the backstepping technique, a kind of boundary control scheme composed of parameter adaptive laws and iterative learning terms is recommended to attenuate vibration for the flexible beam system. And a functional auxiliary system is devised to make up for the influence of input nonlinearity on the system. With the presented control scheme, the well-posedness of the beam system is proved via semigroup theory and the output signal is guaranteed bounded with the aid of rigorous Lyapunov analysis. Eventually, a simulation experiment is available in the MATLAB to expatiate on the suggested controllers’ availability and simulation diagrams also highlight that the boundary controller based on parameter adaptive law with iteration term shows better control performance than that without iteration terms.

A versatile strategy to compute nonlinear normal modes of flexible beams

A versatile strategy to compute nonlinear normal modes of flexible beams

On the static failure behaviour of co-cured composite joints with enhanced interlaminar fracture energies via multiscale toughening

This paper is focused on the multiscale toughened co-cured composite interfaces of carbon/epoxy laminates using vacuum infusion and out-of-autoclave curing—with an emphasis on the role of enhanced interlaminar fracture energies on the static failure of laminate joints. To toughen co-cured interlaminar regions, three toughening routes are used: (i) epoxy matrix toughening with 10 wt% core–shell rubber (CSR) nanoparticles, (ii) 10 g/m2 polyphenylene sulfide (PPS) non-woven micro-fibre veil toughening, and (iii) multiscale toughening by combining epoxy matrix toughening with 10 wt% CSR nanoparticles and 10 g/m2 PPS veils. Double cantilever beam and end-notch flexure tests are conducted with the toughened interfaces for mode-I and mode-II fracture energies. Moreover, three co-cured joint configurations (viz. double-notch single lap, stepped scarf and skin-stiffener joints with the three toughening routes) are tested to characterise the role of enhanced interlaminar fracture energies on the static failure of laminate assemblies. The results show that the three toughening routes have significantly altered the R-curve behaviour and interlaminar fracture energies and that the degree of enhancement in mode-I and mode-II fracture energies is sensitive to the type of toughening route. Based on the material systems tested, the mode-I fracture initiation energy is enhanced by ∼150% with multiscale toughening, ∼65% with particle toughening, and ∼60% with veil toughening; whereas, the mode-II fracture initiation energy is enhanced by ∼85% with veil toughening and ∼35% with multiscale toughening—but reduced by ∼20% with particle toughening. The joint tests show that the toughening routes affect the static failure of the three joint configurations and that the strength and damage evolution of the co-cured joints depend on the interlaminar fracture energies. The strength of the co-cured single lap joints is increased by ∼50% with multiscale toughening and ∼40% with veil toughening; whereas, the strength of the co-cured skin-stiffener joints is enhanced by ∼35% with multiscale toughening and ∼45% with veil toughening. The failure mechanisms observed on the fracture surfaces indicate that the strength/failure behaviour of the co-cured joints depends on the dominant interlaminar fracture mode and the corresponding fracture energies. Overall, it is shown that the multiscale interlaminar toughening routes that are used to address the issue of delamination can also be effectively explored to enhance the static failure of co-cured laminate assemblies by toughening the co-cured interfaces/bondlines.

Study on static and dynamic mechanical properties of glass fiber reinforced polypropylene laminated self-reinforced polypropylene composite structure

In this work, the static and dynamic mechanical properties of glass fiber reinforced polypropylene (GRPP) laminated self-reinforced polypropylene (SRPP) composite structure were studied, which includes the influences of the SG (SRPP/GRPP) internal and external positions (with two SG positions which are S/G/S, G/S/G) and the SG thickness ratios (with three SG ratios which are 1: 1, 1: 2, 1: 3). Results show that the tensile modulus improvement of laminates was obvious compared with SRPP. A hypothesis is constructed based on the elementary flexural beam theory. The flexural responses of S/G/S and G/S/G are highly similar to SRPP and GRPP respectively, the flexural strength and modulus of S/G/S are less than 50% of G/S/G. The flexural modulus of G/S/G- SG1: 3 is 111 % of GRPP. The impact responses of S/G/S and G/S/G are similar to GRPP and SRPP respectively, but more energy was absorbed in S/G/S. With the increase of SG ratio, less damage and deformation were shown in two structures, which their modes converge.

Multiplexed photoinjector optimization for high-repetition-rate free-electron lasers

The multiplexing capabilities of superconducting X-ray free-electron lasers (FELs) have gained much attention in recent years. The demanding requirements for photon properties from multiple undulator lines necessitate more flexible beam manipulation techniques to achieve the goal of “beam on demand”. In this paper, we investigate a multiplexed configuration for the photoinjector of high-repetition-rate FELs that aims to simultaneously provide low-emittance electron beams of different charges. A parallel, multi-objective genetic algorithm is implemented for the photoinjector parameter optimization. The proposed configuration could drastically enhance the flexibility of beam manipulation to improve multiplexing capabilities and realize the full potential of the facility.

A Numerical Study for a Flexible Euler-Bernoulli Beam with a Force Control in Velocity and a Moment Control in Rotating Velocity

In this paper, we numerically study a flexible Euler-Bernoulli beam with a force control in velocity and a moment control in rotating velocity. First, we show the existence and uniqueness of the weak solution using Faedo-Galerkin’s method with the intermediate spaces. Then, we use the finite elements method with the cubic Hermite polynomials for the approximation of (1.1)–(1.5) in space such that the semi-discrete scheme obtained is stable and convergent. In addition, an a-priori error estimate is obtained. Finally, we perform numerical simulations in order to validate this method.

Effect of aging on the in-plane and out-of-plane mechanical properties of composites for design of marine structures

This paper describes an approach allowing aging to be included in the design of marine structures. Two types of aging are considered, physical aging and seawater saturation. The latter is shown to be more severe for this material, with losses in properties of up to 30% being measured after aging. A complete set of in-plane and out-of-plane properties was generated for a carbon/epoxy composite, and these were then used as input data to model the response of a flexural beam under a mixed shear/bending load. Reasonable agreement is found between model and test results; both show the strong influence of seawater conditioning on the composite performance, with a reduction in strength after aging of around 35%. This approach can be applied to account for seawater aging during the design of composite structures.

Multimodal MEMS vibration energy harvester with cascaded flexible and silicon beams for ultralow frequency response

Scavenged energy from ambient vibrations has become a promising energy supply for autonomous microsystems. However, restricted by device size, most MEMS vibration energy harvesters have much higher resonant frequencies than environmental vibrations, which reduces scavenged power and limits practical applicability. Herein, we propose a MEMS multimodal vibration energy harvester with specifically cascaded flexible PDMS and “zigzag” silicon beams to simultaneously lower the resonant frequency to the ultralow-frequency level and broaden the bandwidth. A two-stage architecture is designed, in which the primary subsystem consists of suspended PDMS beams characterized by a low Young’s modulus, and the secondary system consists of zigzag silicon beams. We also propose a PDMS lift-off process to fabricate the suspended flexible beams and the compatible microfabrication method shows high yield and good repeatability. The fabricated MEMS energy harvester can operate at ultralow resonant frequencies of 3 and 23 Hz, with an NPD index of 1.73 μW/cm3/g2 @ 3 Hz. The factors underlying output power degradation in the low-frequency range and potential enhancement strategies are discussed. This work offers new insights into achieving MEMS-scale energy harvesting with ultralow frequency response.

On the mode I and mode II fatigue delamination growth of CFRPs modified by electrospun Bis-maleimide resin

In the current work, fatigue life estimation for delamination growth of modified unidirectional (UD) carbon fiber reinforced plastics (CFRPs) with Bis-maleimide (BMI) resin under Mode I and Mode II loading conditions is assessed. More precisely, BMI resin containing or not four layered (4L) graphene nanoplatelets (GNPs) at the amount of 1 wt% was integrated locally into the mid-thickness area of high performance CFRPs by solution electrospinning process (SEP) technique. After manufacturing process, reference and modified CFRPs with (a) BMI and (b) BMI containing GNPs were used for fatigue onset and propagation tests. All double cantilever beam (DCB) and end-notched flexure (ENF) samples were both tested under displacement control conditions. During the tests, a travelling microscope was utilized to measure the crack length at the end of precise loading cycles while load and delamination length were recorded at the same time. Based on experimental results, BMI modified CFRPs presented the best resistance to delamination under Mode I fatigue loading conditions, while the BMI and GNP modified CFRPs exhibited the best performance under Mode II fatigue loading conditions. Taking into consideration of the obtained results, this approach can be considered a viable solution for increasing the delamination resistance of CFRPs.

Influences of space perturbations on robotic assembly process of ultra-large structures

The space assembly of two flexible beams by a dual-arm space robot is a typical assembly scenario to construct ultra-large space structure. Yet, previous studies mainly focused on the assembly of small structures, neglecting the influences of space perturbations. Two models are developed in this research to investigate the effects of space perturbations on the space assembly process of ultra-large space structures. Firstly, a theoretical modelling method is proposed based on quasi-static hypothesis and linear structural mechanics. The theoretical model can be utilized for analytically estimating the transverse and axial distributed forces of the flexible beams, structural vibrations, and the control moments of the space robot. An orbit–attitude–structure coupled simulation model is then established to validate the theoretical model and study the dynamic behaviours more accurately, using absolute nodal coordinate formulation and natural coordinate formulation. Finally, the effects of the attitude angle, orbital radius, and lengths of beams on the dynamic responses during assembly are investigated. Theoretical and simulation results show that the control moments and structural vibration amplitude increase dramatically with the length of the beams. The effects of Coriolis force and gravity gradient must be considered for ultra-large space structures during assembly, otherwise the control moments and structural vibrations would be substantially underestimated. The results are instructive to the assembly strategy design as well as modular component design of ultra-large space structures.

A novel artificial neural network-based interface coupling approach for partitioned fluid–structure interaction problems

This paper presents a novel interface technique employing Artificial Neural Networks (ANN) for efficient data transfer between incompressible fluid and deformable solid domains in a partitioned fluid–structure interaction (FSI) framework. Governing differential equations (GDE) with potential flow assumptions are solved to obtain pressure values at computational nodes in the fluid domain. Pressure values are then used to train an ANN-based model to interpolate pressure loads for application at non-collocated nodes on the solid boundary. Both finite element method (FEM) and meshfree element free Galerkin (EFG) formulations are used to calculate the solid deformation. Proposed methodology is applied to solve a two-dimensional (2D) unidirectional flow problem, consisting of a flexible cantilever beam immersed in a laminar, steady, and inviscid fluid. Overwhelming mathematical intricacies of computational solvers are avoided for the sake of simplistic interface treatment, flux transfer and associated phenomena. Dedicated partitioned solvers are developed for both solid and fluid domains, which are individually benchmarked for established problems from the literature. The presented ANN-based interpolation scheme provides an alternative to higher-order polynomial algorithms at the interface boundary. The proposed scheme is simple to employ, computationally efficient, and offers competitive accuracy as well as stability.

Developing methods and strategies to reduce the impact of rumble strips (RS) on pavement performance

ABSTRACT Despite numerous research studies inspecting the safety benefits of centreline and shoulder rumble strips (RS) on pavements, there has been limited exploration into the impact on pavement durability due to the installation of RS. The RS milling process creates micro-cracks in the pavement structure that could propagate to macro cracks over time with freeze and thaw, moisture damage, and traffic loading, thereby decreasing the lifespan of the pavements. The primary objective of this study was to develop testing procedures for RS samples as well as analysis methods to determine the impact of potential controlling factors such as permeability and resulting moisture damage; freeze–thaw; the presence of microcracks; surface layer sealants (chip seal); RS size, depth, type, and RS location in relation to the longitudinal construction joint. The flexural beam fatigue test suggests that sinusoidal rumble strips had 38% increased fatigue cracking resistance. Moreover, the sinusoidal rumble strip resulted in 41% improved cracking and structural performance in the Hamburg Wheel Tracking Test (HWTT) tests. Also, the rutting performance of sinusoidal rumble strips was similar to the control section without rumble strips. In addition, 0% moisture infiltration was observed in sinusoidal rumble strip specimens.