Strain  is a parameter which reflect the material and mechanical properties of  structures [1, 2]. On the basis of structure strain distribution, we are able  to obtain the strength reserve information of main components, thus determine the  position of local stress concentration and the actual stress state [3, 4].        
        The  aim of a lot of scientists research is to understand the factors which improve  the performance characteristics of different devices. We need to know the  deformations of the device components. The strain gauge measurements are effective,  but obsolete . It is a method where the number of faults outweighs the  advantages. Is there another way to measure deformation? Simpler, cheaper and  above all faster? Bragg's research on fiber-optic cables for over a dozen years  have given hope.        
        In  1989, Morey discovered that the optical fiber grating sensor has the advantages  of high corrosion resistance,  accuracy, and  antielectromagnetic interference [5,6]. Its features of being able to transfer  and sense at the same time and the strong multiplexing functions plus its  convenience in forming sensor networks make it overwhelm the limitations of  traditional electric detection technologies. The FBG sensors have gradually become  the alternatives of traditional electric sensors [7,8].       
        In  2004, Zhao et al. [9] designed two schemes of FBG strain rosettes: the  rectangular and triangular strain rosettes. They pasted these two forms of  strain rosettes on the surface of equal strength beam with an angle and studied  the performance of plane strain measurement of FBG rosettes. The experimental results  show good agreement with simulation.  In  2006, Tan et al. [10] revealed the influence of transverse effects on FBG  strain measurement through equal strength beam tests. In 2011, Ramos et al. [11]  adopted the embedded FBG strain sensors to design a composite strain rosette.  With the comparative analysis between numerical method and experiments under  the tensile, bending and other alternating loadings, they got the stress  response of the composite strain rosette. In 2012, based on the important role  of FBG sensor playing in the concrete bridge strain measurement, as well as the  fatigue load of concrete and the steel strain characteristics. Tang et al. [12]  carried on the related experimental study to discuss the effects of fatigue  loading on concrete and steel strain characteristics.
        In  this paper I will focus on measuring distortion using FBG sensors. The  numerical results and the corresponding experimental data reveals that the FBG strain  sensors are stable to be used in the rope health monitoring.                                                  
References:
[1] X.Y. Chen, X.Q. Wang, Application of fiber Bragg  grating sensors on smart ship structure, Ship Eng. 28 (2) (2006) 29–31.   
[2] J.N. Wang, J.L. Tang, Feasibility of fiber Bragg grating  and long-period fiber grating sensors under different environmental conditions,  Sensors 10 (2010)10105–10127.   
[3] P. Moyoa, J.M.W. Brownjohnb, R. Sureshc, et al.,  Development of fiber Bragg grating sensors for monitoring civil infrastructure,  Eng. Struct. 27 (2005)1828–1834.   
[4] J.R. Casas, P.J.S. Cruz, Fiber optic sensors for  bridge monitoring, Bridge Eng. 8(6) (2003) 362–373.
[5] X.F. Zhao, S.Z. Tian, et al., Experimental  analysis of state-of-strain with fiber Bragg grating rosettes, J. Optoelectron.  Laser 15 (1) (2004) 65–68.   
[6] W.M. Sun, L. Zhao, et al., Multi-directional  strain and temperature measurement with the help of fluorescent fiber gratings,  in: Proceeding of the11th Chinese Conference on Photoelectric Technology and  System, 2005, pp.779–784.     
[7] C.D. Liu,  P. Chen, et al., Application of the fiber Bragg grating transverse effect in  measurement of plain strain, Opt. Optoelectron. Technol. 6 (6) (2008) 29–32.
[8] Y. Botsev, E. Arad, M. Tur, et al., Using fiber  Bragg gratings to measure Lamb waves in an anisotropic composite plate, in:  19th International Conference on Optical Fiber Sensors, 2008, v7004.   
[9] X.F. Zhao, S.Z. Tian, et al., Experimental  analysis of state-of-strain with fiber Bragg grating rosettes, J. Optoelectron.  Laser 15 (1) (2004) 65–68   
[10] M.F. Tan, S.P. Zhu, The Sensor Characteristics  and Test Technology of Fiber Bragg Grating, Wuhan University of Technology  Press, Wuhan, China, 2006   
[11] C.A. Ramos, R.D. Oliveira, et al., Design and experimental  evaluation of a composite strain rosette using fiber Bragg grating source,  Microw. Opt. Technol. Lett. 53 (8) (2011) 1853–1857
[12] X.X. Tang, X.Z. Tang, et al., Application of  fiber Bragg grating in strain measurement of concrete bridge, Adv. Mater. Res.  368 (2012) 2286–2290.