Techno Press
Tp_Editing System.E (TES.E)
Login Search


sss
 
CONTENTS
Volume 24, Number 2, August 2019
 

Abstract
This study investigated the effects of the geometric parameters of superelastic shape memory alloy (SE SMA) fibers on the pullout displacement recovering and self-healing capacity of reinforced cementitious composites. Three diameters of 0.5, 0.7 and 1.0 mm and two different crimped lengths of 5.0 and 10.0 mm were considered. To provide best anchoring action and high bond between fiber and cement mortar, the fibers were crimped at the end to create spear-head shape. The single fiber cement-based specimens were manufactured with the cement mortar of a compressive strength of 84 MPa with the square shape at the top and a dog-bone shape at the bottom. The embedded length of each fiber was 15 mm. The pullout test was performed with displacement control to obtain monotonic or hysteretic behaviors. The results showed that pullout displacements were recovered after fibers slipped and stuck in the specimen. The specimens with fiber of larger diameter showed better displacement recovering capacity. The flag-shaped behavior was observed for all specimens, and those with fiber of 1.0 mm diameter showed the clearest one. It was observed that the length of fiber anchorage did not have a significant effect on the displacement recovery, pullout resistance and self-healing capacity.

Key Words
cement-based composites; superelastic SMA fibers; self-healing capacity; crack-closing capacity; displacement recovery; flag-shaped behavior

Address
Eunsoo Choi and Behzad Mohammadzadeh: Department of Civil Engineering, Hongik University, Seoul 04066, Korea
Jin-Ha Hwang: Department of Material Science and Engineering, Hongik University, Seoul 04066, Korea
Jong-Han Lee: Department of Civil Engineering, Inha University, Incheon 22212, Korea

Abstract
Due to the degradation of beamforming properties at angles close to 0 to 180, linear array does not have a complete 180 inspection range but a smaller one. This paper develops a improved sensor array with two additional sensors above and below the linear sensor array, and presents time difference and two dimensional multiple signal classification (2D-MUSIC) based impact localization for omni-directional localization on composite structures. Firstly, the arrival times of impact signal observed by two additional sensors are determined using the wavelet transform and compared, and the direction range of impact source can be decided in general, 0 to 180 or 180 to 360. And then, 2D-MUSIC based spatial spectrum formula using uniform linear array is applied for locate accurate position of impact source. When the arrival time of impact signal observed by two additional sensors is equal, the direction of impact source can be located at 0 or 180 by comparing the first and last sensor of linear array. And then the distance is estimated by time difference algorithm. To verify the proposed approach, it is applied to a quasi-isotropic epoxy laminate plate and a stiffened composite panel. The results are in good agreement with the actual impact occurring position.

Key Words
improved linear array; omni-directional; impact localization; 2D-MUSIC; time difference

Address
Yongteng Zhong and Jiawei Xiang: College of Mechanical and Electrical Engineering, Wenzhou University, Wenzhou, 325035, P.R. China

Abstract
A piezoelectric paper feeder actuator using Micro Virtual Roller (MVR) is proposed, designed, fabricated and tested. This actuator can drive a sheet of paper forward or backward without any mechanical parts, such as the costly and heavy rollers used in traditional paper feeders. In this paper feeder actuator, two vibrating stators which produce traveling waves are used to drive the paper. The vibrations of the stators are similar to those of piezoelectric motors and follow a similar procedure to move the paper. A feasibility study simulated the actuator in COMSOL Multiphysics Software. Traveling wave and elliptical trajectories were obtained and the dimensions of the stator were optimized using FEM so that the paper could move at top speed. Next, the eigenfrequencies of the actuator was determined. Experimental testing was done in order to validate the FEM results that revealed the relationships between speed and parameters such as frequency and voltage. Advantages of this new mechanism are the sharp decrease in power consumption and low maintenance.

Key Words
piezoelectric paper feeder actuator; piezoelectric motors; Micro Virtual Roller (MVR); elliptical trajectories; traveling wave

Address
Shahryar Ghorbanirezaei and Yousef Hojjat: Department of Mechanical Engineering, Tarbiat Modares University, Jalal Ale Ahmad, No. 7, Iran
Mojtaba Ghodsi: Department of Mechanical and Industrial Engineering, Sultan Qaboos University, Al Khoudh, No. 123, Oman

Abstract
This study concerns with morphing structures, e.g. as applied in the aerospace industry. A morphing aerofoil structure capable of variable geometry was developed, which was shown to be able to cater for the different aerodynamic requirements at different stages of flight. In this work, the useful and relatively simple method has been applied, which provides a direct method for calculating required morphing shape displacements via finding the most effective bar through calculating bar sensitivity to displacement and calculating set of length actuations for bar assembly to control/adjust shape imperfection of prestressable structural assemblies including complex elements (\"macro-elements\", e.g., the pantographic element), involving Matrix Condensation. The technique has been verified by experiments on the physical model of an aerofoil shaped morphing pantographic structure. Overall, experimental results agree well with theoretical prediction. Furthermore, the technique of multi-iteration adjustment was presented that effective in eliminating errors that occur in the practical adjustment process itself. It has been demonstrated by the experiments on the physical model of pantographic morphing structure. Finally, the study discusses identification of the most effective bars with the objective of minimal number of actuators or minimum actuation.

Key Words
morphing aerofoil; shape control; shape morphing; pantographic structure; matrix condensation.

Address
Najmadeen M. Saeed : Department of Civil Engineering, University of Raparin, Rania, Kurdistan Region, Iraq
Alan S.K. Kwan: Cardiff School of Engineering, Cardiff University, Cardiff CF24 3AA, U.K.

Abstract
The classical Kalman filter (KF) provides a practical and efficient way for state estimation. It is, however, not applicable when the external excitations applied to the structures are unknown. Moreover, it is known the classical KF is only suitable for linear systems and can\'t handle the nonlinear cases. The aim of this paper is to extend the classical KF approach to circumvent the aforementioned limitations for the joint estimation of structural states and the unknown inputs. On the basis of the scheme of the classical KF, analytical recursive solution of an improved KF approach is derived and presented. A revised form of observation equation is obtained basing on a projection matrix. The structural states and the unknown inputs are then simultaneously estimated with limited measurements in linear or nonlinear systems. The efficiency and accuracy of the proposed approach is verified via a five-story shear building, a simply supported beam, and three sorts of nonlinear hysteretic structures. The shaking table tests of a five-story building structure are also employed for the validation of the robustness of the proposed approach. Numerical and experimental results show that the proposed approach can not only satisfactorily estimate structural states, but also identify unknown loadings with acceptable accuracy for both linear and nonlinear systems.

Key Words
Kalman filter; state estimation; load identification; limited measurements; nonlinear hysteretic structures

Address
Jia He, Xiaoxiong Zhang: College of Civil Engineering, Hunan University, Changsha, China;
Hunan Provincial Key Lab on Damage Diagnosis for Engineering Structures, Hunan University, Changsha, China
Naxin Dai: The School of Civil Engineering, The University of South China, Hengyang, China


Abstract
The properties of Electroactive Polymer (EAP) materials are attracting the attention of engineers and scientists from many different disciplines. From the point-of-view of robotics, Ionic Polymer Metal Composites (IPMC) belong to the most developed group of the EAP class. To allow effective design of IPMC-actuated mechanisms with large induced strains, it is necessary to have adequate analytical tools for predicting the behavior of IPMC actuators as well as simulating their response as part of prototyping methodologies. This paper presents a novel IPMC motor construction. To simulate the bending behavior that is the dominant phenomenon of motor movement process, a nonlinear model is used. To accomplish the motor design, the IPMC model was identified via a series of experiments. In the proposed model, the curvature output and current transient fields accurately track the measured responses, which is verified by measurements. In this research, a three-dimensional Finite Element Method (FEM) model of the IPMC motor, composed of IPMC actuators, simultaneously determines the mechanical and electrical characteristics of the device and achieves reliable analysis results. The principle of the proposed drive and the output signals are illustrated in this paper. The proposed modelling approach can be used to design a variety of controllers and motors for effective micro-robotic applications, where soft and complex motion are required.

Key Words
Electroactive polymer;IPMC; FEM; motor

Address
Jakub Kotota: Faculty of Computing, Poznan University of Technology ul. Piotrowo 3A, 60-965 Poznan, Poland

Abstract
In this paper, an inverse approach based on uniform load surface (ULS) is presented for structural damage localization and quantification. The ULS is excellent approximation for deformed configuration of a structure under distributed unit force applied on all degrees of freedom. The ULS make use of natural frequencies and mode shapes of structure and in mathematical point of view is a weighted average of mode shapes. An objective function presented to damage detection is discrepancy between the ULS of monitored structure and numerical model of structure. Solving this objective function to find minimum value yields damage\'s parameters detection. The teaching-learning based optimization algorithm has been employed to solve inverse problem. The efficiency of present damage detection method is demonstrated through three numerical examples. By comparison between proposed objective function and another objective function which make use of natural frequencies and mode shapes, it is revealed present objective function have faster convergence and is more sensitive to damage. The method has good robustness against measurement noise and could detect damage by using the first few mode shapes. The results indicate that the proposed method is reliable technique to damage detection in structures.

Key Words
damage detection; uniform load surface; inverse approach; modal parameters; teaching-learning based optimization

Address
Alborz Mirzabeigy: School of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran, 16846, Iran;
Department of Structural, Building and Geotechnical engineering, Politecnico di Torino,Corso Ducadegli Abruzzi, Turin, 10129, Italy


Abstract
Determination of the most meaningful structural modes and gaining insight into how these modes evolve are important issues for long-term structural health monitoring of the long-span bridges. To address this issue, modal parameters identified throughout the life of the bridge need to be compared and linked with each other, which is the process of mode tracking. The modal frequencies for a long-span bridge are typically closely-spaced, sensitive to the environment (e.g., temperature, wind, traffic, etc.), which makes the automated tracking of modal parameters a difficult process, often requiring human intervention. Machine learning methods are well-suited for uncovering complex underlying relationships between processes and thus have the potential to realize accurate and automated modal tracking. In this study, Gaussian mixture model (GMM), a popular unsupervised machine learning method, is employed to automatically determine and update baseline modal properties from the identified unlabeled modal parameters. On this foundation, a new mode tracking method is proposed for automated mode tracking for long-span bridges. Firstly, a numerical example for a three-degree-of-freedom system is employed to validate the feasibility of using GMM to automatically determine the baseline modal properties. Subsequently, the field monitoring data of a long-span bridge are utilized to illustrate the practical usage of GMM for automated determination of the baseline list. Finally, the continuously monitoring bridge acceleration data during strong typhoon events are employed to validate the reliability of proposed method in tracking the changing modal parameters. Results show that the proposed method can automatically track the modal parameters in disastrous scenarios and provide valuable references for condition assessment of the bridge structure.

Key Words
Gaussian Mixture Model (GMM); baseline modal properties; automated mode tracking; long-span bridge; structural health monitoring (SHM)

Address
Jian-Xiao Mao: Key Laboratory of C&PC Structures of Ministry of Education, Southeast University, Nanjing 211189, China;
Nathan M. and Anne M. Newmark Endowed Chair of Civil Engineering, University of Illinois at Urbana-Champaign,
Urbana, IL 61801, U.S.A.
Hao Wang: Key Laboratory of C&PC Structures of Ministry of Education, Southeast University, Nanjing 211189, China
Billie F. Spencer Jr.: Nathan M. and Anne M. Newmark Endowed Chair of Civil Engineering, University of Illinois at Urbana-Champaign,
Urbana, IL 61801, U.S.A.



Abstract
The benefit of data fusion in improving the performance of Higher Order Sliding Mode (HOSM) observer is brought out in this paper. This improvement in the performance of HOSM observer, resulted in the improvement of active vibration control of a piezo actuated structure, when controlled by a Discrete Sliding Mode Controller (DSMC). The structure is embedded with two piezo sensors for measuring the first two vibrating modes. The fused output of sensors is applied to the HOSM observer for generating state estimates, these states generated are applied to the DSMC, designed for the fourth order linear time invariant model of the structure. In the simulation study, the structure is excited at the first and second mode resonance. It is found that better vibration suppression is obtained, when the states generated by the fused output of sensors is applied as controller input, than the vibration suppression obtained by applying the states generated by using individual sensor output. The closed loop performance of DSMC obtained with HOSM observer is compared with the closed loop performance obtained with the conventional observer. Results obtained shows that better vibration suppression is obtained when the states generated by HOSM observer is applied as controller input.

Key Words
piezo actuated structure; data fusion; higher order sliding mode observer; discrete sliding mode controller

Address
J. Arunshankar: Department of Instrumentation and Control Systems Engineering, PSG College of Technology,
Coimbatore – 641 004, India


Abstract
The present article addresses the coupled free vibration problem of skew magneto-electro-elastic plates (SMEE) considering the temperature-moisture dependent material properties. The plate kinematics follows Reddy\'s s higher order shear deformation theory. With the aid of finite element methods, the governing equations of motion are derived considering the Hamilton\'s principle and solved by adopting condensation technique. The influence of different temperature and moisture dependent empirical constants on the frequency response of SMEE plate has been assessed. In addition, the natural frequencies corresponding to various fields are evaluated and the effect of empirical constants on these coupled frequencies is determined. A detailed parametric study has been carried out to assess the individual effects of temperature and moisture dependent empirical constants along with their combined effect, aspect ratio, length-to-width ratio, stacking sequence and boundary conditions. The results reveal that the external environment as well as the geometrical skewness has a significant influence on the stiffness of the SMEE plates.

Key Words
coupling; magneto-electro-elastic; hygrothermal; geometrical skewness; empirical constants

Address
Vinyas Mahesh: Department of Aerospace Engineering, Indian Institute of Science, Bangalore-560012, India;
Department of Mechanical Engineering, Nitte Meenakshi Institute of Technology Bangalore – 560064, Karnataka, India
Subhaschandra Kattimani:Department of Mechanical Engineering, National Institute of Technology Karnataka, Surathkal-575025, India
Dineshkumar Harursampath: Department of Aerospace Engineering, Indian Institute of Science, Bangalore-560012, India
Nguyen-Thoi Trung: Division of Computational Mathematics and Engineering, Institute for Computational Science,
Ton Duc Thang University, Ho Chi Minh City, Vietnam;
Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam




Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2020 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-2-736-6801, Email: info@techno-press.com