PSI - Issue 17

Grigorii Serovaev et al. / Procedia Structural Integrity 17 (2019) 371–378 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

376

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Fig. 3. а ) calculation scheme for a parallelepiped with embedded optical fiber and a capillary in the Bragg grating area; b) finite element model.

In the numerical simulations the following mechanical properties of materials were used: for an optical fiber made of silica glass 71.4 o E = GPa, 0.17 o  = and polyimide coating 2.5 p E = GPa, 0.35 p  = ; for controlled material 30 h E = GPa, 0.18 h  = (these properties correspond to concrete). The connecting elements (binders) between the capillary coating and the optical fiber are made of epoxy resin with properties 3 b E = GPa, 0.35 b  = . The material properties of the capillary coating may vary. The external pressure P substantially exceeds (10 times) the compressive strength for the material under consideration and is equal to 410 P = MPa. The study of the cavity size t c between the optical fiber and the external coating is carried out on the basis of estimation of the parameter d , corresponding to the relative change in the initial distance between the external coating and the optical fiber 0 c t and the minimum distance 1 c t after application of the critical load P (figure 4). 1 0

0 c t t d t − = c

(5)

100%



c

Fig. 4. The scheme of deformation of the cavity between the external coating and the optical fiber.

In the performed calculations, the value of the initial cavity size 0 c t varied in the range from the size of the optical fiber protective coating, which is equal to 0.012 mm, up to 0.024 mm. The material properties of the external coating coincide with the properties of controlled material. Figure 5 shows the dependence of the parameter d on the cavity size t c under compressive load.

Fig. 5. а ) change in parameter d depending on cavity size; b) change in parameter d depending on the modulus of elasticity of the external coating.