Damage Identification After Impact in Sandwich Composites Through Embedded Fiber Bragg Sensors

Abstract

Based on the full-spectral response of fiber Bragg grating sensors, embedded at the facesheet-core interface, we identify the progression of failure modes in foam core sandwich composites during multiple, low-velocity impacts. By considering the characteristic shape of the reflected spectrum from the FBG sensor in the post-impact, residual strain state, it is shown that we can classify the extent of damage into one of three states. Unlike the previous FBG peak wavelength measurements; this identification does not require the full strain history to identify the current state of damage in the composite. The disparate material properties between the facesheet and core materials, which create significant challenges for conventional non-destructive evaluation methods, enhance the damage detection through large deformations in the core at the impact location with sharp strain gradients.

A Simple, Reusable and Low-Cost LVDT-Based in Situ Bolt Preload Monitoring System during Fastening for a Truck Wheel Assembly

“…Strain gages need to be mounted on a bolt using a special adhesive, so they are not reusable. Optical FBG sensors might be reusable, but a hole penetrating through a bolt is necessary for an optical fiber and the sensor should be glued to the bolt using an adhesive [15][16][17]. For measuring the preload of a bolt using an ultrasonic wave based on the acoustoelastic effect, there are some conditions required to ensure accuracy: the grip length has to be sufficiently large to minimize errors [18]; the bolt material should be isotropic, and both end surfaces of the bolt need to be flat and parallel [19]; in addition, the measurement accuracy is not ensured under the external vibration, which can change the position of ultrasonic transducer [20,21].…”

The performance of embedded fiber Bragg grating sensors for monitoring failure modes of foam cored sandwich structures under flexural loads

“…Hackney et al. exposed a sandwich structure with embedded FBG sensor to repetitive low-velocity impact loads and monitored the residual strains and spectrum changes during the test in order for characterizing the damage in the specimens [8].…”

“…The propagation of these defects upon loading can cause failures between the core and the face sheet. Moreover, impact loads can cause local indentation failures endangering the structural integrity [8]. Thus, to assess the structural reliability of the components during their service life, it is essential to detect the damage formation.…”

“…Moreover, they conducted cyclic threepoint bending tests on the sandwich composite to assess the structural integrity of the sandwich structure through using FBG sensors [22]. Hackney et al exposed a sandwich structure with embedded FBG sensor to repetitive low-velocity impact loads and monitored the residual strains and spectrum changes during the test in order for characterizing the damage in the specimens [8].…”

Real-time impact identification algorithm for composite structures using fiber Bragg grating sensors

“…Wang et al . tried to develop a remote identification of impact damage, and other researchers used fiber Bragg grating sensors for monitoring of impact damage. Although most efforts produced good estimated results, there are some limitations in applying these techniques to real structures because of the complexity of sensing and signal processing systems, electromagnetic interference problems associated with electrical sensors, relatively low sampling frequencies and multiplexing problems of optical fiber sensors .…”