A new approach to predicting multiple damage states in composite laminates with embedded FBG sensors

In this paper, a new Structural Health Monitoring (SHM) technique for composite laminates through the use of embedded FBG sensors is presented. This method monitors the ply stress states of a laminate and compares them with failure criteria continuously during structures’ service time. The ply stress state of each ply composing the composite laminate can be obtained by embedding three FBG sensors in the laminate based on the classical lamination theory. In this study FBG sensor embedded graphite/epoxy composite laminate specimens were fabricated. With ply stress states being monitored, tension and fatigue tests were performed until laminates’ failure. Experimental results show that laminates experience fracture when the ply stress states are beyond the boundaries of failure criteria. Embedded FBG sensors had good fracture strain and reliability. Therefore, critical damage can be detected by the ply stress states which are close to the boundaries of failure criteria.

Download Full-text

Detection of delamination in composite laminates using small-diameter FBG sensors

10.1117/12.472611 ◽

2002 ◽

Cited By ~ 4

Author(s):

Shin-ichi Takeda ◽

Yoji Okabe ◽

Nobuo Takeda

Keyword(s):

Composite Laminates ◽

Small Diameter ◽

Fbg Sensors

Download Full-text

Monitoring of Multidirectional and Cure-Induced Strain in CFRP Laminates Using FBG Sensors

Materials Science Forum ◽

10.4028/www.scientific.net/msf.953.72 ◽

2019 ◽

Vol 953 ◽

pp. 72-79 ◽

Cited By ~ 1

Author(s):

Cheng Biao Jiang ◽

Li Hua Zhan ◽

Xiao Bo Yang ◽

Xiao Ping Chen ◽

Zi Jun Lin ◽

...

Keyword(s):

Residual Stress ◽

Residual Strain ◽

Composite Laminates ◽

Compressive Strain ◽

Fibre Bragg Grating ◽

Cfrp Laminates ◽

Reinforced Plastics ◽

Fiber Reinforced Plastics ◽

Fbg Sensors ◽

Curing Cycle

During the curing cycle, the residual stress has influence on cure-induced deformation for carbon fiber reinforced plastics (CFRP) laminates, which is highly susceptible to the ply design. Therefore, the change laws of strain and the effect of residual stress in CFRP laminates after curing, which is of great significance to ply design, were cleared by using the combining pattern of thermocouple and fibre Bragg grating (FBG) sensors. For the FBG sensors embedded with different directions in lay-up CFRP laminates, the temperature and strain in different directions of composite laminates were obtained in real-time. Monitoring results show that compared with strain in 45° direction, the carbon fibers (CF) act stronger to inhibit strain in 0° direction and weaker to inhibit strain in 90° direction of resin. After curing, the residual strain in 0° direction is tensile strain, and the residual strain in 45° direction and 90° direction are compressive strain. Meanwhile the value of residual strain in 90° direction is greater than that in 45° direction.

Download Full-text

Low Velocity Impact Localization of Variable Thickness Composite Laminates

Sensors ◽

10.3390/s21186103 ◽

2021 ◽

Vol 21 (18) ◽

pp. 6103

Author(s):

Guan Lu ◽

Yuchen Zhou ◽

Yiming Xu

Keyword(s):

Variable Thickness ◽

Composite Laminates ◽

Composite Structures ◽

Low Velocity Impact ◽

Low Velocity ◽

Localization Performance ◽

Fbg Sensors ◽

The Impact ◽

Impact Localization ◽

Thickness Correction

Variable thickness composite laminates (VTCL) are susceptible to impact during use and may result in irreparable internal damage. In order to locate the internal impact damage of complex composite structures and monitor the impact signals of VTCL at the same time, a low velocity impact (LVI) monitoring system based on an optical fiber sensing network was constructed. Fiber Bragg grating (FBG) sensors are suitable for monitoring strain characteristics. By arranging FBG sensors on the laminate, we studied the spectrum analysis and localization of the impact signal collected by a FBG demodulator at constant temperature. The prior knowledge of variable thickness composite structures is difficult to obtain, and the multi-sensor dynamic monitoring is complex and difficult to realize. In order to locate the LVI of composite structures without prior knowledge, based on empirical mode decomposition (EMD), we proposed an impact localization method with zero-mean normalized cross-correlation (ZNCC) and thickness correction. The experimental results of LVI localization verification show that the ZNCC algorithm can effectively remove the temperature cross-sensitivity and impact energy influencing factors, and the thickness correction can reduce the interference of variable thickness characteristics on localization performance . The maximum localization error is 24.41 mm and the average error is 15.67 mm, which meets engineering application requirements. The method of variable-thickness normalization significantly improves impact localization performance for VTCL.

Download Full-text