Estimation of residual strain and stress in interply hybrid composite using fiber bragg grating sensor

Residual stress and strain buildup in the hybrid carbon/phenolic (CP) composite was estimated using embedded fiber Bragg grating (FBG) sensors. Two different carbon fabrics made from polyacrylonitrile (PAN)and rayon fibers were used. The partially delaminated hybrid composite was fabricated for the real-time and nondestructive estimation of the residual stress and strain during the cure process. The strain measured by FBG sensors embedded in the delaminated region was assumed to represent the thermal deformation of each reinforcing lamina. After the cure process was finished, PAN-based (PC) and rayon-based (RC) carbon laminae were under compression and tension, respectively, in in-plane direction because the strain of RC was 4.4 times lager than that of PC. The residual stresses of PC and RC laminae under the assumption of elasticity were -16.9 and 7.92 MPa, respectively. The experimental results showed good agreements with those by FEM analysis.