Title: Fiber Optic Measurement of Residual Stress in Ti-6Al-4V/SiC Fiber Composites Using Cr³⁺ Doped Sapphire Fibers

Abstract:
Sapphire fibers containing dilute concentrations of Cr³⁺ ions have been used to determine stress in a titanium matrix composite. The R1 and R2 luminescence peaks of the Cr³⁺ doped sapphire have been measured before and after the processing of a Ti-6Al-4V/SIGMA (SiC) fiber reinforced composite. The peak shifts have been related to the sapphire fiber's principal stresses using the well established piezospectroscopic relationships. A fiber located near the center of the sample had an axial stress value, sigma_zz = 876 +- 147 (MPa), while the sum of the inplane stress components, (sigma_rr + sigma_ee) = -61 +- 93 (MPa). The thermal stresses that developed after processing have been modeled using the Generalized Method of Cells and used to develop a relationship between the stress of the sapphire witness fiber and that of the surrounding SIGMA fibers and the Ti-6AI-4V matrix.

Source: Proceedings of the 'NDE applied to Process Control of Composite Fabrication' - Conference, 1-2 Oct 1996 St. Louis, Missouri. Publisher and Organizer: Nondestructive Testing Information Analysis Center (NTIAC) Texas Research Institute Austin, Inc. Austin, Texas [http://www.ntiac.com] [Buying the Proceedings]