2012 IEEE Control and System Graduate Research Colloquium (ICSGRC 2012) Research in Characterization of Cyclic Load Parameters using Fiber Bragg Gratings System Mohamad Adli Bin Adam Faculty of Mechanical Engineering Universiti Teknologi MARA Shah Alam, Malaysia adliadam@gmail.com Abstract- Fatigue is the primary cause of structural failure. Fatigue failures are caused by fatigue loadings in the form of cyclic loads. To avoid fatigue failures, structures need monitoring. This paper reports a study of optical iber Bragg grating responses under variable amplitude fatigue load. Use of optical iber in monitoring structural condition becomes extensive research nowadays due to its advantageous characteristics than conventional method such as using strain gauges. A standard specimen (ASTM E606) is used for initial study. The specimens were attached with iber Bragg grating sensor and test coniguration were set up. All the data and information were analyzed and comparisons with strain gauge sensor were performed. It was observed that response from FBG sensor is consistent with applied cyclic loads. Keywors-fatigue; structural monitoring; iber Bragg gratings; strain gauge I. INTRODUCTION Fatigue is a beginning for a catastro phic structural failure. When repeated stresses are a pplied to he structure, fatigue failure will start to ha ppen. Fatigue failures ha ppen in a sudden and total nature, hus it is very dangerous.Continuous monitoring on structure can avoid he structure rom fatigue failure. Structural healh monitoring (SHM) is a process of gaining information of the curent condition of a structure. Early detection of damage can be s potted in his mehod; hence the life of structure can be extended. The prediction of structural deterioration over time can be made so remaining life cn be calculated by analyzing he gahered history data hrough SHM methodology [1]. In analyzing fatigue failures by using SHM, fatigue parameters must be known so he prediction of remaining life time of he structure can be done. To obtain these parameters, a good sensor shall be attached to he structure. A sensor must be Fundamental Research Grant Scheme (FRGS), MOHE Research Grant, RMIUiTM 978-1-4673-2036-8/12/$31.00 ©2012 IEEE 237 Wahyu Kuntjoro\ Mohd Kamil Bin Abdul Ra Faculty of Mechanical Engineering \ Faculty of Applied Science 2 Universiti Teknologi MARA Shah Alam, Malaysia wkuntjoro@yahoo.com 1 , drkamil@salam.uitm.edu.m l sensitiveto the measured parameters, do not inluence the behavior of structure and also not responding to oher constraints. Sensor also must be durable, sensitive to small changes, non-electric, and immune to intensiy luctuation. Fiber Bragg grating (FBG) provides advantages com pared to conventional sensor. FBG sensor is sensitive to he change of physicalparameters in the fom of wavelength shit of he relected light. Since the relected light hasa very narow bandwidth (ty pically 0.1-0.5 m ), it is ideally suited for sensing applications [2]. A research on he a pplication of optical iber Bragg grating sensor for structure monitoring was re ported by M. Kamil Abd Rahman et.al. They were able to show that the Fiber Bragg Grating (FBG) sensorsshow matching srains wih applied forces to the vibrating wire srain gauge (VWSG) sensor had a small eror. The experiment done usng three FBG sensors and vibrating wire stran gauge (VWSG) were mounted on 650mm (R12.5) mild steel rod. The tensile stress test was conducted. It can be concluded that the sensitivity of FBG sensor is substantially high, the measurement of tensile stress and oher related parameters on structures and environment can be accurately nd precisely determined [3]. Development of fatigue monitoring to ighter aircrats were reported by W Kuntjoro et.al [4]. Local strain a pproach has been used for strain estimation techniques on life prediction. Neuber's rule was used to predict the notch geometry effect. Rain low cycle counting method was em ployed to extract cycle rom random loading s pectrum. Mean stress corection factor was based on Smih-Watson-Topper (SWT) equation and Pamgren-Miner rule was used to conduct summation of he cycle damage. The monitoring was based on the accelerometer nd strain-gauges installed on he aiplanes. A study of FBG sensor and electrical strain gauge for strain measurement by B. A. Thir et.al was conducted to make a comparison of boh sensor performance and advntages. It