Experimental analysis of buckling in aircraft skin panels by fibre optic sensors

Abstract

Three blade-stiffened CFRP panels with co-cured stiffener webs, manufactured by means of an elastomeric mould, have been tested under compressive load. Several Bragg grating sensors have been surface bonded on two of the stiffened panels and have been embedded into the stiffener webs of the third panel. The Bragg grating sensors measured the strain distribution in the stiffener web and in the skin panels. The bucking onset was clearly detected in every case, the post-buckling behaviour can be tracked, but the information is heavily dependent on the right choice of the sensor position and the buckling mode. To calibrate the system, and to evaluate the influence of different curing pressures, and the use of unidirectional or fabric prepreg material, tensile test specimens were made on flat panels. The strain measurements provided by the optical fibre sensors in tensile tests were compared with the strain measurements provided by conventional clamp extensometers.

Analysis of Fibre Bragg Gratings Sensors Optimal Placement for Monitoring of Damage Propagation in Laminate Composites

“…Technological solutions allow the optical fibres to be embedded between the plies or to be attached on the surface. The questions of operability of such embedded fibres were also discussed -it has been proved, that fibres can stand different regimes of composite manufacturing, including autoclave forming [10].…”

“…Recent computational and experimental studies showed that embedded fibres effect on initial mechanical properties of laminate composites can be considered negligible [10,11], what is important conclusion for the further development of SHM systems for composite structures based on FBG sensors.…”

Failure and damage identification in woven composites with fiber Bragg grating sensors

“…Before use, the optical fiber's polyimide coating in the vicinity of the Bragg grating gauge was chemically stripped with acetone to increase the sensitivity and transfer of strain to the critical fiber core region 16,19 . After aligning the fibers with the direction of the top lamina's weave, the optical fiber was tensioned slightly to be straight, and it was adhered to the rear face of the composite specimen approximately 1.43 cm from the chosen point of impact on the front face.…”

Instrumentation of integrally stiffened composite panel with fiber Bragg grating sensors for vibration measurements

“…One direction has been to instrument stiffened composite airframe structures with fiber Bragg grating (FBG) sensors for strain measurements. These measurements have provided information for condition monitoring of the airframe, impact damage detection, quality assurance during curing of the composite laminates, and buckling of airframe components [1][2][3][4][5][6][7]. The main benefit to using FBG sensors is the fact that FBGs can be multiplexed in large numbers on a single optical fiber, significantly reducing the weight of instrumenting the structure with a large number of sensors.…”