fuh-gwo yuan - Academia.edu (original) (raw)

Papers by fuh-gwo yuan

SPIE Proceedings, 2009

Image segmentation for quantifying damage based on Bayesian updating scheme is proposed for diagn... more Image segmentation for quantifying damage based on Bayesian updating scheme is proposed for diagnosis and prognosis in structural health monitoring. This scheme enables taking into account the prior information of the state of the structures, such as spatial constraints and image smoothness. Bayes' law is employed to update the segmentation with the spatial constraint described as Markov Random Field and the current observed image acting as a likelihood function. Segmentation results demonstrate that the proposed algorithm holds promise of searching a crack area in the SHM image and focusing on the real damage area by eliminating the pseudo-shadow area. Thus more precise crack estimation can be obtained than the conventional K-means segmentation by shrinking the fuzzy tails which often exist on both sides of the crack tips.

In this work, a magnetostrictive sensor (MsS) is d e igned and tested for monitoring damage in a ... more In this work, a magnetostrictive sensor (MsS) is d e igned and tested for monitoring damage in a non-ferromagnetic plate. Firstly, the m echanism of the MsS to generate and detect guided shear horizontal (SH) waves in a non-ferroma gnetic plate is described. Both theoretical and experimental studies are conducted in order to p ove that the sensor can generate the first non-dispersive shear horizontal wave mode (SH 0) suitable for monitoring of the structural health. The sensor encompasses a nickel strip, a pa ir of permanent magnets, C-shaped cores wound by a figure-of-eight coil. The incident wave emitted from the MsS propagates in the plate and is reflected from the plate boundaries. S ince the time of the arrival can be determined from the reflected wave signal through signal proce ssing, the velocity of the wave can be extracted. Comparing the calculated velocity with t he velocity predicted by the theory, the mode of the wave can be identified with a priori kn owledge of plate ...

Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2020, 2020

A physics-based approach to structural health monitoring (SHM) has practical shortcomings which r... more A physics-based approach to structural health monitoring (SHM) has practical shortcomings which restrict its suitability to simple structures under well controlled environments. With the advances in information and sensing technology (sensors and sensor networks), it has become feasible to monitor large/diverse number of parameters in complex real-world structures either continuously or intermittently by employing large in-situ (wireless) sensor networks. The availability of this historical data has engendered a lot of interest in a data-driven approach as a natural and more viable option for realizing the goal of SHM in such structures. However, the lack of sensor data corresponding to different damage scenarios continues to remain a challenge. Most of the supervised machine-learning/deep-learning techniques, when trained using this inherently limited data, lack robustness and generalizability. Physics-informed learning, which involves the integration of domain knowledge into the learning process, is presented here as a potential remedy to this challenge. As a step towards the goal of automated damage detection (mathematically an inverse problem), preliminary results are presented from dynamic modelling of beam structures using physics-informed artificial neural networks. Forward and inverse problems involving partial differential equations are solved and comparisons reveal a clear superiority of physics-informed approach over one that is purely datadriven vis-à-vis overfitting/generalization. Other ways of incorporating domain knowledge into the machine learning pipeline are then presented through case-studies on various aspects of NDI/SHM (visual inspection, impact diagnosis). Lastly, as the final attribute of an optimal SHM approach, a sensing paradigm for non-contact full-field measurements for damage diagnosis is presented.

Journal of Intelligent Material Systems and Structures, 2016

This article identifies and studies key parameters that characterize a horizontal diamagnetic lev... more This article identifies and studies key parameters that characterize a horizontal diamagnetic levitation mechanism–based low frequency vibration energy harvester with the aim of enhancing performance metrics such as efficiency and volume figure of merit. The horizontal diamagnetic levitation mechanism comprises three permanent magnets and two diamagnetic plates. Two of the magnets, lifting magnets, are placed co-axially at a distance such that each attracts a centrally located magnet, floating magnet, to balance its weight. This floating magnet is flanked closely by two diamagnetic plates which stabilize the levitation in the axial direction. The influence of the geometry of the floating magnet, the lifting magnet, and the diamagnetic plate is parametrically studied to quantify their effects on the size, stability of the levitation mechanism, and the resonant frequency of the floating magnet. For vibration energy harvesting using the horizontal diamagnetic levitation mechanism, a co...

Smart Structures and Systems, 2007

International Journal of Solids and Structures, 2005

Transient wave propagation of isotropic thin plates using a higher-order plate theory is presente... more Transient wave propagation of isotropic thin plates using a higher-order plate theory is presented in this paper. The aim of this investigation is to assess the applicability of the higher-order plate theory in describing wave behavior of isotropic plates at higher frequencies. Both extensional and flexural waves are considered. A complete discussion of dispersion of isotropic plates is first investigated. All the wave modes and wave behavior for each mode in the low and high-frequency ranges are provided in detail. Using the dispersion relation and integral transforms, exact integral solutions for an isotropic plate subjected to pure impulse load and a number of wave excitations based on the higher-order theory are obtained and asymptotic solutions which highlight the physics of waves are also presented. The axisymmetric three-dimensional analytical solutions of linear wave equations are also presented for comparison. Results show that the higher-order theory can predict the wave behavior closely with exact linear wave solutions at higher frequencies.

Smart Structures and Materials 2005: Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems, 2005

Conventional wireless sensors for structural health monitoring do not accommodate the need of hig... more Conventional wireless sensors for structural health monitoring do not accommodate the need of high frequency data acquisition. Lack of development of this type of wireless smart sensors will without doubt hinder the applications of active diagnostic methods, normally used in local damage interrogation. In this paper, a novel wireless smart sensor design, using FPGA as co-controller with ultra sensing capability, is presented. The development and some outstanding issues of the sensor are discussed in detail, and a preliminary experimental result is given to verify the effectiveness of this wireless smart sensor design.

Journal of Vibration and Acoustics, 2015

This paper investigates a horizontal diamagnetic levitation (HDL) system for vibration energy har... more This paper investigates a horizontal diamagnetic levitation (HDL) system for vibration energy harvesting in contrast to the vertical diamagnetic levitation (VDL) system recently proposed by Wang et al. (2013, “A Magnetically Levitated Vibration Energy Harvester,” Smart Mater. Struct., 22(5), p. 055016). In this configuration, two large magnets, alias lifting magnets (LMs), are arranged co-axially at a distance such that in between them a magnet, alias floating magnet (FM), is passively levitated at a laterally offset equilibrium position. The levitation is stabilized in the horizontal direction by two diamagnetic plates (DPs) made of pyrolytic graphite placed on each side of the FM. This HDL configuration mitigates the limitation on the amplitude of the FM imposed in the VDL configuration and exploits the ability to tailor the geometry to meet specific applications due to its frequency tuning capability. A simple circular coil geometry is designed to replace a portion of the pyrolyt...

Journal of Sound and Vibration, 2015

ABSTRACT A detailed analysis of a mono-stable vertical diamagnetic levitation (VDL) system for op... more ABSTRACT A detailed analysis of a mono-stable vertical diamagnetic levitation (VDL) system for optimal vibration energy harvesting is presented. Initial studies showed that simple analytical techniques such as the dipole model and the image method provide useful guideline for understanding the potential of a diamagnetic levitation system, however, it is discussed here that the more accurate semi-analytical techniques such as the thin coil model and the discrete volume method are needed for quantitative optimization and design of the VDL system. With the semi-analytical techniques, the influence of the cylindrical geometry of the floating magnet, the lifting magnet and the diamagnetic plate are parametrically studied to assess their effects on the levitation gap, size of the system and the natural frequency.

Experimental Mechanics, 2014

This paper presents a new method for direct measurement of Mode-I stress intensify factor of crac... more This paper presents a new method for direct measurement of Mode-I stress intensify factor of cracks using Ba 0.64 Sr 0.36 TiO 3 flexoelectric strain gradient sensors. Firstly, strain gradient field around the opening mode crack tip was analyzed, followed by the derivation of induced flexoelectric polarization in the strain gradient sensors attached in the vicinity of a crack tip. It was found that the constant stress term makes no contribution to the strain gradient, thus the flexoelectric output directly reflects the singular effect. This unique property eliminates the special requirement for sensor placement coordinates and improves the accuracy of the stress intensify factor predication. A specimen with Mode-I crack was then prepared with two strain gradient sensors (4.7 mm×0.9 mm×0.3 mm) attached close to the crack tip to verify the analytical model for measurements of stress intensity factor. The experimental results matched well with the empirical estimation confirming that flexoelectric strain gradient sensing can be a convenient and accurate avenue for measuring the stress intensify factor.

physica status solidi (RRL) - Rapid Research Letters, 2011

AIP Advances, 2014

A fabrication method by combining precision mechanical dicing and wet etching was developed to pr... more A fabrication method by combining precision mechanical dicing and wet etching was developed to prepare micro-pyramid structures based on (Ba 0.67 Sr 0.33)TiO 3 ceramics. The effective piezoelectric properties of flexoelectric pyramid structures in ten micrometers scale were investigated and measured through converse flexoelectric effect. The scaling effect of the flexoelectric response was demonstrated as the structure size shrinks down. The results do suggest the great potential of flexoelectric micro pyramids as an alternative to lead-free piezoelectric material.

Applied Physics Letters, 2014

ABSTRACT The objective of this research is to develop a macroscopic theory, which can provide the... more ABSTRACT The objective of this research is to develop a macroscopic theory, which can provide the connection between macromechanics and micromechanics in characterizing the micro-stress of composite laminates near edges and holes. The micropolar theory, a class of higher-order elasticity theory, of composite laminate mechanics is implemented in a well-known Pipes-Pagano free edge boundary problem. The micropolar homogenization method to determine the micropolar anisotropic effective elastic moduli is presented. A displacement-based finite element method based on micropolar theory in anisotropic solids is developed in analyzing composite laminates. The stress response based on micropolar theory

This paper introduces the benefits of exploiting elasticity in the engineering design of surgical... more This paper introduces the benefits of exploiting elasticity in the engineering design of surgical tools, in general, and of minimally invasive procedures, in particular. Compliant mechanisms are jointless mechanisms that rely on elastic deformation to transmit forces and motion. The lack of traditional joints in these singlepiece flexible structures offers many benefits, including the absence of wear debris, pinch points, crevices, and lubrication. Such systems are particularly amenable to embedded sensing for haptic feedback and embedded actuation with active-material actuators. The paper provides an overview of design synthesis methods developed at the Compliant Systems Design Laboratory and focuses specifically on surgical applications. Compliant systems have potential to integrate well within the constraints of laparoscopic procedures and telerobotic surgery. A load-path representation is used within a genetic algorithm to solve two gripper example Contributed by the Bioengineering Division for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received by the Bioengineering Division April 19, 2005; revision received July 26, 2005. Associate Editor: William K. Durfee. problems. In addition, the paper illustrates the design and construction of an organ (kidney) manipulator for use in minimally invasive procedures. �DOI: 10.1115/1.2056561�

International Journal of Solids and Structures, 2006

Reconstructing damage geometry with computationally efficient algorithms is of primary importance... more Reconstructing damage geometry with computationally efficient algorithms is of primary importance in establishing a robust structural health monitoring system (SHMS). In this paper electromagnetic migration, a linearized imaging algorithm, is adopted to image the damages in reinforced concrete structures. This algorithm is formulated in time-domain for 3-D inhomogeneous isotropic and lossy structures. In order to reduce the computational cost and to examine the damage resolution of this imaging algorithm, different imaging conditions are introduced. Numerical simulations in 2-D transverse magnetic (TM) wave for a reinforced concrete slab with multiple damages are performed to test the effectiveness of the algorithm. All synthetic sensor data, incident field, and migration field are computed via a finite difference time-domain (FDTD) method. It is concluded that the proposed imaging algorithm is capable of efficiently identifying the damages geometries, is robust against measurement noise, and may be employed in a SHMS.

$Research paper thumbnail of Mode-I fracture toughness of IM7/LaRC-RP46 composites under thermal aging$

39th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference and Exhibit, 1998

High temperature Mode-I interlaminar fracture tests were conducted to evaluate the effect of ther... more High temperature Mode-I interlaminar fracture tests were conducted to evaluate the effect of thermal aging at various temperatures on the fracture behavior of DVI7/LaRC-RP46 composites. The Double Cantilever Beam (DCB) specimens made of unidirectional laminates were used in the test program. The specimens have been aged at high temperatures for times up to and including 6000 hours. Changes in fracture behavior that occurred over periods of aging time and aging temperature have been measured and determined for variations of test temperature and loading rate. As expected, the crack growth at high temperature showed nonlinear load-displacement response due to rate dependent nature of the matrix. High temperature increased G,c values of aged and unaged specimens at temperature near Tg and decreased at temperature above Tg. Longer time thermal aging had also significantly reduced G!C initiation values of aged specimens. In contrast, thermal aging increased GK propagation values due to the occurrence of increased fiber bridging, fiber breakage and microcracks. Results also indicated that high temperature slowed crack growth rate. However, thermal aging and higher loading rates accelerated crack growth rate. The effect of thermal aging and temperature on the crack growth rate da/dt can be correlated with C* parameter in a power law relation.

International Journal of Solids and Structures, 2003

The objective of this research is to develop a macroscopic theory, which can provide the connecti... more The objective of this research is to develop a macroscopic theory, which can provide the connection between macromechanics and micro-mechanics in characterizing the micro-stress of composite laminates in regions of high macroscopic stress gradients. The micro-polar theory, a class of higher-order elasticity theory, of composite laminate mechanics is implemented in a well-known Pipes-Pagano free edge boundary problem. The micro-polar homogenization method to determine the micro-polar anisotropic effective elastic moduli is presented. A displacement-based finite element method based on micro-polar theory in anisotropic solids is developed in analyzing composite laminates. The effects of fiber volume fraction and cell size on the normal stress along the artificial interface resulting from ply homogenization of the composite laminate are also investigated. The stress response based on micro-polar theory is compared with those deduced from the micro-mechanics and classical elasticity theory. Special attention of the investigation focuses on the stress fields near the free edge where the high macro-stress gradient occurs. The normal stresses along the artificial interface and especially, the micro-stress along the fiber/matrix interface on the critical cell near the free edge where the high macro-stress gradient detected are the focus of this investigation. These micro-stresses are expected to dominate the failure initiation process in composite laminate. A micro-stress recovery scheme based on micro-polar analysis for the prediction of interface micro-stresses in the critical cell near the free edge is found to be in very good agreement with ''exact'' micro-stress solutions. It is demonstrated that the micro-polar theory is able to capture the micro-stress accurately from the homogenized solutions.

Structural Health Monitoring, 2011

In structural health monitoring, crack identification using scattered ultrasonic waves from a cra... more In structural health monitoring, crack identification using scattered ultrasonic waves from a crack is one of the most active research areas. Crack size estimation is important for judging the severity of the damage. If measurements are frequently performed as the crack grows, then a better estimation of crack size may be possible by analyzing sensor signals for the same crack location with different sizes. The objective of this article is to explore the relationship between the sensor signal amplitude and crack size through experiments and simulation for estimating the size. Cracks are machined into an aluminum plate and measurements are carried out with ultrasound excitation using piezoelectric transducer arrays that alternate their role as actuators or sensors. Initially, a hole of 2.5 mm diameter is drilled in the plate, and it is gradually machined to a crack with a size up to 50 mm. Signal amplitude is measured from the sensor arrays. The migration technique is used to image t...

Smart Materials and Structures, 2013

ABSTRACT In this paper a novel electromagnetic vibration type energy harvester that uses a diamag... more ABSTRACT In this paper a novel electromagnetic vibration type energy harvester that uses a diamagnetic levitation system is conceptualized, designed, fabricated, and tested. The harvester uses two diamagnetic plates made of pyrolytic graphite between which a cylindrical magnet levitates passively. Two thick cylindrical coils, placed in grooves which are engraved in the pyrolytic graphite plates, are used to convert the mechanical energy into electrical energy efficiently. The geometric configurations of the coils are selected based on the field distribution of the magnet to enhance the efficiency of the harvester. A thorough theoretical analysis is carried out to compare with experimental results. At an input power of 103.45 μW and at a frequency of 2.7 Hz, the harvester generated a power of 0.74 μW with a system efficiency of 0.72%. Both theoretical and experimental results show that this new energy harvesting system can capture low frequency broadband spectra.