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. 2015 Mar 9;15(3):5710-21.
doi: 10.3390/s150305710.

Optical Sensing of the Fatigue Damage State of CFRP Under Realistic Aeronautical Load Sequences

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Free PMC article

Optical Sensing of the Fatigue Damage State of CFRP Under Realistic Aeronautical Load Sequences

Pablo Zuluaga-Ramírez et al. Sensors (Basel). .
Free PMC article

Abstract

We present an optical sensing methodology to estimate the fatigue damage state of structures made of carbon fiber reinforced polymer (CFRP), by measuring variations on the surface roughness. Variable amplitude loads (VAL), which represent realistic loads during aeronautical missions of fighter aircraft (FALSTAFF) have been applied to coupons until failure. Stiffness degradation and surface roughness variations have been measured during the life of the coupons obtaining a Pearson correlation of 0.75 between both variables. The data were compared with a previous study for Constant Amplitude Load (CAL) obtaining similar results. Conclusions suggest that the surface roughness measured in strategic zones is a useful technique for structural health monitoring of CFRP structures, and that it is independent of the type of load applied. Surface roughness can be measured in the field by optical techniques such as speckle, confocal perfilometers and interferometry, among others.

Figures

Figure 1
Figure 1
Evolution of the surface topography due to fatigue damage of a CFRP specimen.
Figure 2
Figure 2
“Dog bone” geometry of the CFRP coupons used for tensile variable amplitude tests. Inspection area of one of the faces of the coupon.
Figure 3
Figure 3
Experimental setup to measure the surface roughness by the confocal microscope.
Figure 4
Figure 4
Fragment of the FALSTAFF load sequence with two different magnitudes of maximum peak load.
Figure 5
Figure 5
Gassner curve in semi-log graphic, for the coupons cycled with the FALSTAFF load sequence at different levels of maximum peak load.
Figure 6
Figure 6
Stiffness degradation in semi-log graphic, for the coupons cycled with the FALSTAFF load sequence at different levels of maximum peak load.
Figure 7
Figure 7
Evolution of the surface roughness magnitude quantified by the parameter Rq during the VALs.
Figure 8
Figure 8
Correlation between stiffness degradation and surface roughness magnitude (Rq) at VALs. The trend line is obtained combining the roughness and stiffness data of all the coupons.
Figure 9
Figure 9
Comparison between the data obtained for VAL in the present work, and the data obtained for CAL in a previous study [18]. The trend line is obtained for the combination of both studies.

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