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Kim S.-W.,Korea Aerospace Research Institute | Jeong M.-S.,Automotive Research and Development Division | Lee I.,KAIST | Kwon I.-B.,Korea Research Institute of Standards and Science
Sensors and Actuators, A: Physical | Year: 2014

Tin-coated FBG sensors, which can be used to evaluate the maximum strain experienced by host structures through the quantity of residual strain induced by the tin coating, were fabricated by a dipping method. The residual strain development of the tin-coated FBG sensors was quantitatively investigated by performing increased cyclic loading tests, and compared to that of bare FBG sensors. It was found that the quantity of residual strain showed a quadratic relationship with respect to the maximum strain experienced by the tin-coated FBG sensors, while the quantity of residual strain of bare FBG sensors was negligible. Moreover, after increased cyclic loading tests, the tensile failure strength of the tin-coated FBG sensors was additionally examined using Weibull failure statistics and compared to that of bare FBG sensors. The median failure strength of the tin-coated FBG sensors was 111.8% greater than that of the bare FBG sensors, and the Weibull moduli of the bare FBG sensors and the tin-coated FBG sensors were 13.5 and 8.1, respectively. The static mechanical characteristics of the tin-coated FBG sensors, i.e., residual strain development and the failure strength, can be used as a basis and guidelines for the installation of tin-coated FBG sensors into structures in actual applications. © 2014 Elsevier B.V.

Lee D.,Korea University | Kim Y.-D.,Automotive Research and Development Division | Lee N.-Y.,Automotive Research and Development Division | Lee S.-W.,Automotive Research and Development Division
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering | Year: 2015

This article aims to develop a measure that can estimate the isolator performance in joint design problems. The relationships between the receptances of the connection points and the isolator bushes in multi-structural car-body systems are explored from the perspective of a frequency-response-function-based substructuring method. From the formulation for the frequency-response-function-based substructuring method, the desirable magnitude difference between the receptances is proposed through an order analysis of a one-dimensional system. The receptance magnitude concept is extended to a multi-structural system using a singular-value diagram. In order to represent the magnitude of the receptance matrices, matrix measures are introduced. Using the defined measures, a joint design index is proposed in order to assess the structural joint system which consists of two structures and isolator bushes. Finally, two numerical examples are used to demonstrate the relationships between the suggested joint design concept and the relevant responses (i.e. the vibrations, the force and the power) of the structures. The proposed joint design index can estimate the isolator performance and indicate the possibilities for improvement in multi-structural systems, which is very useful for noise and vibration reduction in the automotive industry. © 2015 Institution of Mechanical Engineers.

Kim S.-W.,Korea Aerospace Research Institute | Kim E.-H.,University of Washington | Jeong M.-S.,Automotive Research and Development Division | Lee I.,KAIST
Composites Part B: Engineering | Year: 2015

Background/purpose The impact-induced damage of composite structures induced by low-velocity impacts were evaluated to verify the damage evaluation concept using the "memory effects" of tin-coated FBG sensors. Methods Low-velocity impact tests for the composite cylinder with tin-coated FBG sensors were performed at three impact energies. Hoop ring tests for the composite cylinder including impact-induced damage were additionally undertaken in order to measure the burst pressure and to study the parameter correlations. The test results were compared with the numerical results obtained by a finite element analysis (FEA) based on a continuum damage mechanics (CDM) considering damage model. The parameter correlations among the impact parameters and the residual strains induced by tin-coated FBG sensors were investigated based on the tests results. Results Impact behaviors obtained by the tests and the numerical simulation were agreed well. It was found that tin-coated FBG sensors can monitor the strain of the composite cylinder under low-velocity impacts and their strain monitoring capability is comparable to that of normally used FBG sensors. The residual strains of tin-coated FBG sensors were correlated with the impact parameters such as the impact energy, the sensing position of the sensors, and the burst pressure of the composite cylinder. Conclusion The correlations among the residual strains and the parameters proved the damage evaluation concept for composite cylinders using the "memory effects" of tin-coated FBG sensors under low-velocity impact conditions; that is, the impact-induced damage, impact location, and burst pressure can be inversely evaluated by referring to the correlations. © 2015 Published by Elsevier Ltd.

Chu K.,Automotive Research and Development Division | Kim J.,Automotive Research and Development Division | Jo K.,Hanyang University | Sunwoo M.,Hanyang University
International Journal of Automotive Technology | Year: 2015

This paper presents a path planning algorithm for autonomous vehicles to generate feasible and smooth maneuvers in unstructured environments. Our approach uses a graph-based search algorithm and a discrete kinematic vehicle model to find a primitive path that is non-holonomic, collision-free, and safe. The algorithm then improves the quality and smoothness of the identified path by making local shortcuts. This shortcut for smoothing the path is determined by connecting the internal state of the primitive path to the initial state based on the Pythagorean Hodograph (PH) cubic curve. The formulation of the PH cubic curves in the smoothing path provides arc-length parameterization of the curve in a closed form. We present examples and experimental results for the real time path planning in unstructured road from an implementation on an autonomous vehicle. © 2015, The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg.

Yim K.H.,Hanyang University | Jang J.W.,Hanyang University | Jang G.H.,Hanyang University | Kim M.G.,Automotive Research and Development Division | Kim K.N.,Automotive Research and Development Division
IEEE Transactions on Magnetics | Year: 2012

This paper discusses a method to analyze the forced vibration of an interior permanent magnet (IPM) motor due to magnetic force. A structural finite element (FE) model of the IPM motor that includes stiffness of ball bearings and laminated effect of core is developed and verified by comparing the simulated natural frequencies and mode shapes with experimental data. A magnetic FE model is also developed and both the radial and tangential magnetic forces are calculated in the air-gap. These forces are subsequently transformed into equivalent nodal forces and applied to the structural FE model to investigate the forced vibration characteristics of the IPM motor. It was found that the magnetically induced vibration of a stator mainly results from the contribution of the dominant harmonics of the magnetic force and structural resonance. In addition, the magnetically induced vibration of the rotor mainly appeared as rigid body modes due to the flexibility of ball bearings. © 1965-2012 IEEE.

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