Strain Transfer Characteristic of a Fiber Bragg Grating Sensor Bonded to the Surface of Carbon Fiber Reinforced Polymer Laminates

Abstract

Structural health monitoring is of great importance for the application of composites in aircrafts. Fiber Bragg grating (FBG) sensors are very suitable for structure strain measurement. However, the strain measured by FBG sensors is different from the original strain in host materials. The relationship between them is defined as strain transfer. As composites are anisotropic, the traditional strain transfer model, which regards the elasticity modulus of host materials as a constant, is inadaptable. In this paper, a new strain transfer model is proposed for FBG sensors bonded to the surface of carbon fiber reinforced polymer (CFRP) laminates. Based on the measurement structure, the model is established and the transfer function is derived. The characteristics influencing the strain transfer are analyzed. The stacking directions, stacking numbers, and stacking sequences of CFRP laminates have a distinct effect on the transfer efficiency, which is different from the isotropy host materials. The accuracy of the proposed model was verified by experiments on a nondestructive tensile system, and the maximum model error is less than 0.5%. Moreover, the model was applied to the strain measurement of CFRP wing skin, which indicates that measurement errors decrease by 11.6% to 19.8% after the compensation according to the model.

Numerical and experimental analysis of the reliability of strain measured by surface‐mounted fiber‐optic sensors based on Bragg gratings

“…Recommendations for the gluing technology are given based on the obtained results. It is also noted in Wang et al 28 that the strain recorded by the FBG differs from the strain in the host material. A feature of this work is the study of strain transfer from composite anisotropic materials.…”

A Strain-Transfer Model of Surface-Bonded Sapphire-Derived Fiber Bragg Grating Sensors

“…When the core's radius increased to that of the cladding, the cladding layer disappeared, and the four-layer model regressed to a three-layer model that only had a core, an adhesive, and a host material, as shown in Figure 2. Like traditional models [8,11,20,22], the three-layer model treated the core and cladding as essentially the same homogeneous material. The stress state in the four-layer model is presented in Figure 3.…”

“…Unfortunately, strain loss inevitably occurs in the transfer process because of shear deformation of the intermedium between fiber and host material. Thus, strain-transfer theory was developed to describe the actual strain-transfer process [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. In the case of embedded strain sensors, an analytical model based on force equilibrium and compatibility was developed to present the real strain on the host material on the basis of a number of realistic assumptions, such as materials behaving in a linear elastic manner, and the existence of a perfect bond [8].…”

“…To investigate the interfacial-failure mechanism, the strain-transfer model was also extended to diagnose local interfacial debonding [18]. In the case of surface-bonded sensors, various stacking parameters of carbon-fiber-reinforced polymer laminates were analyzed by establishing a finite-element (FE) model [20]. The sensor was tested under fatigue load to derive the transfer formula in response to dynamic strain [23].…”

Numerical Investigation of Stress-Strain State Effects on Strain Measurements with Fiber Bragg Grating Sensors

“…When utilizing FBG sensors, especially those embedded within the structure of the material, several challenges arise. These include the redistribution of the stress-strain state in the vicinity of the embedded optical fiber [9,10] and the issue of strain transfer from the material to the optical fiber [11,12].…”