Mechanical Properties of Optical Fiber Strain Sensing Cables under γ-Ray Irradiation and Large Strain Influence

Abstract

Optical fiber strain sensing cables are widely used in structural health monitoring; however, the impact of a harsh environment on them is not assessed despite the huge importance of the stable performances of the monitoring systems. This paper analyzes (i) the impact of the different constituent layers on the behavior of a strain sensing cable whose constitutive materials are metal and polyamide, (ii) the radiation influence on the optical fiber strain sensing cable response (500 kGy of γ -rays), and (iii) the behavior of the cable under high axial strain (up to 1%, 10,000 μ ε ). Radiation impact on strain sensitivity is negligible for practical application, i.e., the coefficient changes by 4% at the max. The influence of the composition of the cable is also assessed: the sensitivity differences remain under 15%, a standard variation range when different cable compositions and structures are considered. The elasto-plastic behavior is at the end evaluated, highlighting the residual strain (about 1600 μ ε after imposing 10,000 μ ε ) of the cable (especially for metallic parts).

In-situ monitoring of micro-tunnel geometry change based on distributed optical fiber strain sensing

“…Measurements are acquired with the Neubrescope NBX-7020 from Neubrex, with the TW-COTDR technique [25] and a spatial resolution of 100 mm, a sampling interval of 50 mm, an averaging count of 2 13 , a pump output power of +25 dBm, a frequency range of [194-194.4] THz and a frequency span of 200 MHz. The measurements frequency goes from every 40 min in the early stages to every 6 h when the behavior of the loading is more regular.…”

“…Distributed optical fiber sensors are well suited to perform this kind of measurement. They are nowadays widely used in structural health monitoring [9][10][11] thanks to their desirable features like the tiny dimension, the measurement range, versatility or resistance to harsh environment [12,13]. These sensors are sensitive to strain and temperature thanks to the backscattering mechanism occurring inside the fiber, namely Brillouin and Rayleigh scatterings [14].…”

“…It is therefore necessary to develop a reliable method to convert orthoradial measurements into this radial quantity. In a previous work [13], a method using finite element (FE) simulation was proposed to perform this task and it was validated on a surface laboratory mock-up, with a fiber bonded on the perimeter of a straight section of the cylinder and under well-defined loads. In the present case, the problem is much more complex.…”

Performance Assessment of Distributed Strain Sensing Techniques for Convergence Monitoring of Radioactive Waste Repository

“…This outer coating protects the fiber against mechanical damage and acts as a barrier to lateral forces and moisture [ 20 , 21 ]. The cable considered here is a BRUsens V9 cable made by Solifos AG [ 22 ]. It is a 3.2 mm diameter shielded cable comprising an optical fiber with its primary coating surrounded by a multilayers buffer, a metal tube and then a structured polyamide outer sheath.…”