A. Brickler, University of Maryland, Hampton, VA; E. W. Nelson, Virginia Tech, Hampton, VA; R. Kapania, Virginia Polytechnic Institute and State University, Blacksburg, VA; E. K. Hoffman, NASA Langley Research Center, Hampton, VA
The goal of this study is to validate advanced fabrication techniques for aircraft components. The test specimens are aluminum alloy blade-stiffened panels which represent a component of skin-stiffener compression panels used in aircraft fuselage and wings. The four different fabrication methods tested and compared are a stiffener riveted onto the skin, an integral stiffener machined from plate, a stiffener friction stir welded onto the skin, and a stiffener built by electron beam freeform fabrication (EBF3). To validate the fabrication techniques, first the buckling characteristics are determined with compression tests and analysis. Then the results for the panels made with the new technique of EBF3 are compared with the results for the panels made with the more proven manufacturing methods. All panels failed in global buckling. The results show that the integrally stiffened panels on average carried a 19% higher compression load than the EBF3. The friction stir welded panels on average carried a 14% higher compression load and the riveted panels on average carried a 10% higher compression load than the EBF3 panels. Three test panels for EBF3 were manufactured using the EBF3 process to apply stiffeners. The biggest problem that affected the EBF3 panels was the induced residual stress during the manufacturing process due to a thermal gradient in the base plate. This also resulted in some distortion of the plates. Different procedures were used for each panel to help remove some of the residual stresses. Test results show that the EBF3 process has potential as a manufacturing technique for aerospace structures, but that more work needs to be done to understand and reduce the residual stresses in the skin.
Summary: The purpose of this study was to analyze and compare different fabrication techniques for aircraft components. In this experiment aluminum alloy blade-stiffened panels were manufactured out of 4 different techniques: a stiffener riveted onto the skin, an integral stiffener machined from plate, a stiffener friction stir welded onto the skin, and a stiffener built by electron beam freeform fabrication (EBF3). The goal of the experiment was to compare the EBF3 technique to other industry proven manufacturing techniques.
