Yosuke Nagao

Monitoring of a CFRP-Stiffened Panel Manufactured by VaRTM Using Fiber-Optic Sensors

FBG (Fiber Bragg Grating) sensors and optical fibers were embedded into CFRP dry preforms before resin impregnation in VaRTM (Vacuum-assisted Resin Transfer Molding). The embedding location was the interface between the skin and the stringer in a CFRP-stiffened panel. The reflection spectra of the FBG sensors monitored the strain and temperature changes during all the molding processes. The internal residual strains of the CFRP panel could be evaluated during both the curing time and the post-curing time. The temperature changes indicated the differences between the dry preform and the outside of the vacuum bagging. After the molding, four-point bending was applied to the panel for the verification of its structural integrity and the sensor capabilities. The optical fibers were then used for the newly-developed PPP-BOTDA (Pulse-PrePump Brillouin Optical Time Domain Analysis) system. The long-range distributed strain and temperature can be measured by this system, whose spatial resolution is 100 mm. The strain changes from the FBGs and the PPP-BOTDA agreed well with those from the conventional strain gages and FE analysis in the CFRP panel. Therefore, the fiber-optic sensors and its system were very effective for the evaluation of the VaRTM composite structures.

DURABILITY AND DAMAGE TOLERANCE EVALUATION OF VARTM COMPOSITE WING STRUCTURE

Durability and damage tolerance of subcomponent and full-scale wing box structure fabricated by VaRTM are evaluated. Fatigue spectrum with load enhancement factor was applied to the test articles for 1 DSO of 40,000 flights. The Mini-TWIST fatigue spectrum is used for both tests. Then, impact damages are given to the skin stiffened by co-cured stringer and typical skin part by drop-weight to create the delamination. After that, impact damage growth is evaluated during 1 DSO fatigue spectrum and optimal inspection interval is examined. Finally, residual strength of structures is verified by ultimate load test with 150% design limit load. Applied strain level for Subcomponents are intentionally higher than original one in order to evaluate the structural performance in more critical condition. Non-destructive inspection is carried out by 3D ultrasonic scan system with multiple-array sensors to evaluate delamination growth. In Subcomponent test, stringer run-out shows local out-of-plane deformation and that causes disbonding of stringer termination. The disbonding area gradually increases during 1 DSO fatigue test. However, the structure did not show any degradation of structural performance. The damage tolerance tests verify that impact-induced delaminations have not grown throughout the 1 DSO. In the final ultimate load test, the load bearing-capabilities of present VaRTM wing structure have been verified and the structure could survive for 4 seconds without any detrimental deformation and damage growth.

A Study of Quality Assurance of VaRTM Composite Wing Structure

[Abstract] Vacuum assisted resin transfer molding (VaRTM) method is one of the candidates to achieve low cost aircraft structure. A development of 6 m span VaRTM wing box project is conducted to demonstrate VaRTM technology and to make clear the certification procedure of VaRTM by Japan Aerospace Exploration Agency (JAXA). The project result will eventually support the policy and guidance procedures of Japan Civil Aviation Bureau (JCAB), and also a certification procedure of aircraft companies in Japan. This 6 m VaRTM made wing box demonstrator is assumed a 30 passenger aircraft and a static test of this wing box is planed in fiscal year of 2007. A 2 m wingspan specimen was made as an experimental production which contains every technical component to be solved before manufacture of 6 m wing box specimen. Technical expertise and the remaining issues were obtained from this 2 m specimen.