TITLE:
Continuous Damage Monitoring of a Thin Composite Structural with Mismatched Stiffener in a Combined Joint Using Fiber Bragg Grating under Tension and Three-Point Loading
AUTHORS:
Agus Trilaksono, Naoyuki Watanabe, Hikaru Hoshi, Atsush Kondo, Yutaka Iwahori, Shin-Ichi Takeda
KEYWORDS:
Carbon Fiber; Joints/Joining; Cohesive Elements; Secondary Bending Moment; Structural Health Monitoring
JOURNAL NAME:
Open Journal of Composite Materials,
Vol.3 No.3,
July
16,
2013
ABSTRACT: A joint
combining riveting and bonding is considered in terms of structural performance
if the composite structure has a mismatched stiffener. The transfer loading is
correlated with high performance aerospace joints to increase delamination
resistance in the out-of-plane direction. However, combined joints
(rivet/bonded) will create a bearing area that induces another potential damage
source aside from secondary bending moment on the edge of the stiffener. Another problem is
that the structure is difficult to be inspected by using conventional methods
because of limited accessibility. The use of embedded fiber Bragg grating (FBG)
technology in the structure as a strain sensor can potentially solve the
problem in structures that have a stiffness mismatch. The FBG can be used to
detect and characterize delamination before it reaches a critical stage. The
model used to represent this problem is a thin composite stiffened skin under two
load cases: tension and three-point bending. Finite element modeling using a
traction versus separation theory is performed to determine the critical area
on the specimen for placement of the FBG before manufacturing and testing. Experiments
were presented to determine the distribution of load in a combined joint under
both loading cases using ideal loads to create a secondary bending moment and
bearing loads in the stiffness-mismatched structure. In this research, the FBG successfully
detected and characterized the delamination caused in both loading cases. In
addition, FBG can predict the delamination growth quantitatively. A spectrum
graph of the FBG results can be used to replace the conventional mechanical
graph in composite structural health monitoring in real applications.