New Design Concepts for Aeronautical Applications by Friction Stir Welding Sergio M. O. Tavares Engineering Design and Advanced Manufacturing focus area (MIT-Portugal) Supervisor: Paulo M. S. T. de Castro (FEUP) Co-supervisors: Pedro Vilaça (IST), Thomas Eagar (MIT), Jorge dos Santos (GKSS) Ciência 2010 Lisbon, July 4-7, 2010

2 Outline Project summary, motivation and arrangement Differential and integral joints Design for manufacturing and assembly in aeronautics Certification Structural requirements – damage tolerant design Friction Stir welding process Process flaws and non destructive inspections Numerical models with residual stress result from FSW Friction Stir Welding in next generation of aircrafts Manufacturing cost evaluation Process assessment Conclusions

3 Project summary (1) New Design Concepts for Aeronautical Applications by Friction Stir Welding  This research is focused in the infusion into production of an emerging joining process, friction stir welding, in aeronautical context  Several inherent benefits may be achieved if traditional joining processes are replaced by this new process that joins the structure continuously, creating leaner joints  Nevertheless, mainly due to the requirements for structural integrity of aeronautical structures, the riveting process keeps a few advantages related to crack path discontinuity

4 Project summary (2) The multidisciplinary approach adopted along this project includes:  Development of new concepts for aeronautical parts and repair of damaged components  Mechanical characterization of FSW joints comprising fatigue and fracture mechanics  Numerical modeling of reinforced panels with stiffeners joined using  FSW taking into account the influence of residual stress fields promoted by FSW in the fatigue crack growth behavior  Non-destructive techniques research for friction stir welds  Cost analysis and assessment  Design for manufacture and assembly focused on the Quality Function Deployment procedure  Application of FSW in fuselage structures

5 Project arrangement

6 Main motivation New joining processes associated with new materials can improve the aeronautical structures, reducing their environmental impact and improving their efficiency. FSW can replace older joining processes in these structures, mainly riveting, creating leaner joints at lower costs.

7 Differential vs. Integral Structure This is the most significant transformation in aircraft fuselage without large design modifications; however, the fuselage should be redesigned for application of these processes.

8 Design for manufacturing and assembly in aeronautics

9 Certification Certification required for process replacement in primary structures for aeronautical components

10 Structural requirements – damage tolerant design (1)  Due to the high reliability and extended life cycle required for aeronautical structures it is unfeasible to produce fuselage structures on the basis of a fail safe design – this would imply either too much weight or too short useful lives.

11 Structural requirements – damage tolerant design (2)  With regular inspections and analysis of the effects of defects sizes it is possible to extend the fatigue life of structures without compromising their integrity (damage tolerant design). The non- destructive techniques are fundamental to ensure the correct detection and control of defects and damages

12 Friction Stir welding process Friction stir welding is a breakthrough joining process with about nearly 20 years maturity, although for aeronautical applications is still an emerging process mainly due to the reluctance in the application of integral welded joints in aeronautics and to the tendency of massification in the application of composite materials.

13 Non destructive techniques - Control of FSW defects  The most predominant and critical defect in FS welds in butt- joint configuration is the lack of penetration (LOP) originating a root flaw, which under fatigue loads will quickly propagates through the structure

14 Non destructive techniques  Three different non-destructive techniques were investigated : Scanning Acoustic Microscope (Ultrasonic Technique) Computed X-Ray Micro Tomography Multi-array eddy currents - Meandering Winding Magnetometer

15 Non destructive techniques Example of results Results fromMulti-array eddy currents - Meandering Winding Magnetometer, JENTEK

16 Numerical models with residual stress result from FSW  Stress field evaluation along crack growth

17 Manufacturing cost evaluation

18 Example of comparison (preliminary estimations of a generic joint)

19 FSW Riveting LBW Fatigue behavior454 Minimum maintenance 535 Aerodynamic (& aesthetics) 533 Minimum fabrication cost 535 Availability of parts434 Minimum weight553 Minimum manufacturing time 535 Process assessment  Quality function deployment analysis for a generic stiffened panel – Cross Method

20 Conclusions  Aeronautical structures can be improved applying new advanced manufacturing technologies as the FSW  The replacement of joining technologies needs to take into account a large complexity of requirements in order to be crashworthiness and at the same time lightweight  This project explores new concepts and examines different aspects related with the performance of the FSW joints  Leaner joints and fuselages with the withdraw of thousands of fastners can be achieved applying this process since the structural integrity is ensured

THANK YOU FOR YOUR ATTENTION!