Hindawi Publishing Corporation Journal of Nanomaterials Volume 2013, Article ID 671469, 4 pages http://dx.doi.org/10.1155/2013/671469 Research Article Analytical and Experimental Study of Residual Stresses in CFRP Chia-Chin Chiang, 1 Vu Van Thuyet, 1 Shih-Han Wang, 2 and Liren Tsai 1 1 Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, 415 Chien-Kung Road, Kaohsiung 807, Taiwan 2 Department of Chemical Engineering, I-Shou University, No. 1, Sec. 1, Syuecheng Rd., Kaohsiung 84001, Taiwan Correspondence should be addressed to Liren Tsai; liren@cc.kuas.edu.tw Received 15 September 2013; Accepted 7 November 2013 Academic Editor: Liang-Wen Ji Copyright © 2013 Chia-Chin Chiang et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Fiber Bragg Grating sensors (FBGs) have been utilized in various engineering and photoelectric felds because of their good environment tolerance. In this research, residual stresses of carbon fber reinforced polymer composites (CFRP) were studied using both experimental and analytical approach. Te FBGs were embedded inside middle layers of CFRP to study the formation of residual stress during curing process. Finite element analysis was performed using ABAQUS sofware to simulate the CFRP curing process. Both experimental and simulation results showed that the residual stress appeared during cooling process and the residual stresses could be released when the CFRP was machined to a diferent shape. 1. Introduction Carbon fber composites have been widely considered as the optimal replacement material for various industrial products. For composite materials, the inherent defects could greatly hamper the reliability and durability of the resultant products. Tere have been many studies of embedded stress sensors, particularly for damage detection in composite materials [1, 2]. FBGs possess great compatibility with CFRP [3], and by embedding FBG inside carbon fber composites, the residual strain of the carbon fber composites during production could be easily monitored. Because of thermal expansion, coef- cient of the elements in the composite materials is diferent, and the shape of the optical spectra changed during curing process. Tese changes induced a shif in wavelengths of the optical fber sensors, which could be converted to residual stress [4]. In this research, residual stresses of carbon fber reinforced polymer composites (CFRP) were studied using both experimental and analytical approach. Te simulation of residual stress during cooling process was carried out using ABAQUS. Trough comparison between experimental and simulation results, the formation of residual stress in the CFRP was confrmed. 2. Materials and Methods 2.1. Fiber Bragg Grating Sensors (FBG). Te FBG involved was fabricated from single cladding photosensitive fber using the side writing method. Te photosensitive fber was produced by Fibercore Co. Ltd. (PS1250/1550). Te FBGs are photoimprinted in photosensitive optical fber by 248 nm UV radiation from a KrF Excimer laser. Te impulse frequency of laser is 10 Hz. Along the fber core, the FBG has periodic refractive index modulation with a period of 1.05∼1.08 m. Tis resulted in a peak Bragg refecting wavelength of 1540∼ 1564 nm. Te refectivity of the resulting FBG was about 99% and the FWHM (Full width Half Maximum) of the FBG is about 0.175 nm. Light sources export energy to the carbon fber composite with FBG by coupler, and the energy change was then recorded and analyzed by oscilloscope. Te residual strain of imbedded carbon fber composites could be determined by comparing the wavelength diference in the FBG before and afer curing process using Δ  = (1 −   )  + ( + ) Δ, (1)