Output-only based damage assessment of delaminated smart composite structures is increasingly appealing due to its easy availability in real engineering applications. In this work, structural vibration responses of the pristine and delaminated composite structures are processed via Fast Fourier Transform (FFT) and Convolutional Neural Network (CNN) for the classification of healthy and various damaged cases. The dynamic model for the healthy and delaminated smart composite laminates is developed by incorporating of improved layerwise theory, higher-order electric potential field, and finite element method. Structural vibration responses are obtained through a surface bonded piezoelectric sensor by solving the electromechanically coupled dynamic model in the time domain. FFT is used to construct vibration-based images from the transient responses of the sensor and CCN is used to classify those images into healthy and damaged classes. The confusion matrix of CNN showed physically consistent results and an overall classification accuracy of 90% was obtained. The pre-trained CNN was also tested to predict labels for new cases of delaminations in the smart composite laminates. The essence of the proposed method is that it requires only low-frequency structural vibration responses for the detection and localization of delamination in smart composite laminates.
Separation along the interfaces of layers (delamination) is a principal mode of failure in laminated composites and its detection is of prime importance for structural integrity of composite materials. In this work, structural vibration response is employed to detect and classify delaminations in piezo-bonded laminated composites. Improved layerwise theory and finite element method are adopted to develop the electromechanically coupled governing equation of a smart composite laminate with and without delaminations. Transient responses of the healthy and damaged structures are obtained through a surface bonded piezoelectric sensor by solving the governing equation in the time domain. Wavelet packet transform (WPT) and linear discriminant analysis (LDA) are employed to extract discriminative features from the structural vibration response of the healthy and delaminated structures. Dendrogram-based support vector machine (DSVM) is used to classify the discriminative features. The confusion matrix of the classification algorithm provided physically consistent results.
In this paper, a new type of haptic system for surgical robot application is proposed and its performances are
evaluated experimentally. The proposed haptic system consists of an effective master device and a precision
slave robot. The master device has 3-DOF rotational motion as same as human wrist motion. It has
lightweight structure with a gyro sensor and three small-sized MR brakes for position measurement and
repulsive torque generation, respectively. The slave robot has 3-DOF rotational motion using servomotors,
five bar linkage and a torque sensor is used to measure resistive torque. It has been experimentally
demonstrated that the proposed haptic system has good performances on tracking control of desired position
and repulsive torque. It can be concluded that the proposed haptic system can be effectively applied to the
surgical robot system in real field.
In this work, a new type of haptic master featuring small-sized MR brake is proposed and its performances are evaluated. The proposed haptic master consists of base frame, stick grip and small-sized four MR brakes for 3-DOF rotational motion and 1-DOF gripper motion. To obtain large braking torque under limited small size of MR brake, dual tapered shape inner magnetic core is proposed and its performance is evaluated via both numerical estimation and experimental test. After design and implementation of control algorithm, it has been demonstrated through experiment that the proposed actuator has good performances on tracking control of desired torques. Then, a new haptic master device is designed and constructed by adopting the proposed MR brakes and light weight frame structures. It is verified that the proposed haptic master device is effective for the real application in the field.
In this work, a new type of MR brake featuring tapered inner magnetic core is proposed and its braking performance is numerically evaluated. In order to achieve high braking torque with restricted size and weight of MR brake system, tapered inner magnetic core is designed and expands the area that the magnetic flux is passing by MR fluid-filled gap. The mathematical braking torque model of the proposed MR brake is derived based on the field-dependent Bingham rheological model of MR fluid. Finite element analysis is carried out to identify electromagnetic characteristics of the conventional and the proposed MR brake configuration. To demonstrate the superiority of the proposed MR brake, the braking torque of the proposed MR brake is numerically evaluated and compared with that of conventional MR brake model.
Recently, light weight structure becomes an object of attention because increase of energy efficiency becomes the most important global hot issue. Then, composite structures, which have inherent high strength and stiffness to weight ratio, are in the limelight for light weight structures. However, complex failure modes of composite structure are still remains unsolved problem and become main obstacle of wide application of composite structures. Delamination is one of frequent damage phenomenon of laminated composite structure. Delamination can cause reduction of structural stiffness and decrement of natural frequencies. This might induce increase of structural vibration and resonant phenomenon of operating structures. Then, delamination should be detected and complemented. In this work, active control scheme and piezoelectric actuators are used to reduce the delamination effect of damaged composite structure. At first, finite element model for delaminated composite structure is constructed based on improved layerwise theory and then state space control model is established. After design and implementation of active controller, dynamic characteristics and structural performances of damaged composite structure are investigated and effectiveness of active healing is evaluated.