Single-mode polymer optical fiber sensors for large strain applications

This paper characterizes an intrinsic, single-mode, polymer optical fiber (POF) sensor for use in large-strain applications such as civil infrastructures subjected to earthquake loading or systems with large shape changes such as morphing aircraft. The opto-mechanical response was formulated for the POF including a second-order (in strain) photoclastic effect as well as a second-order (in strain) solution for the deformation of the POF during loading. It is shown that four independent mechanical and opto-mechanical constants are required for the small deformation regime and six additional independent mechanical and opto-mechanical constants are required for the large deformation regime. The mechanical nonlinearity of a typical polymer optical fiber was experimentally measured in tension at various loading rates. The secant modulus of elasticity measured at small strains, roughly up to 2% strain, was measured to be similar to 4GPa whereas at larger strains, roughly up to 4.5% strain, the secant modulus was measured to be similar to 4.8GPa. As the loading rate was increased the yield strain increased, ranging from similar to 3.2% at 1mm/min to similar to 5% at 305 mm/min.