Full-Scale Structural and NDI Validation Tests of Bonded Composite Doublers for211 Commercial Aircraft Applications

摘要

Composite doublers, or repair patches, provide an innovative repair technique211u001ewhich can enhance the way aircraft are maintained. Instead of riveting multiple 211u001esteel or aluminum plates to facilitate an aircraft repair, it is possible to bond 211u001ea single Boron-Epoxy composite doubler to the damaged structure. Most of the 211u001econcerns surrounding composite doubler technology pertain to long-term 211u001esurvivability, especially in the presence of non-optimum installations, and the 211u001evalidation of appropriate inspection procedures. This report focuses on a series 211u001eof full-scale structural and nondestructive inspection (NDI) tests that were 211u001econducted to investigate the performance of Boron-Epoxy composite doublers. Full-211u001escale tests were conducted on fuselage panels cut from retired aircraft. These 211u001efull-scale tests studied stress reductions, crack mitigation, and load transfer 211u001ecapabilities of composite doublers using simulated flight conditions of cabin 211u001epressure and axial stress. Also, structures which modeled key aspects of aircraft 211u001estructure repairs were subjected to extreme tension, shear and bending loads to 211u001eexamine the composite laminate's resistance to disbond and delamination flaws. 211u001eSeveral of the structures were loaded to failure in order to determine doubler 211u001edesign margins. Nondestructive inspections were conducted throughout the test 211u001eseries in order to validate appropriate techniques on actual aircraft structure. 211u001eThe test results showed that a properly designed and installed composite doubler 211u001eis able to enhance fatigue life, transfer load away from damaged structure, and 211u001eavoid the introduction of new stress risers (i.e. eliminate global reduction in 211u001ethe fatigue life of the structure). Comparisons with test data obtained prior to 211u001ethe doubler installation revealed that stresses in the parent material can be 211u001ereduced 30%--60% through the use of the composite doubler. Tests to failure 211u001edemonstrated that the bondline is able to transfer plastic strains into the 211u001edoubler and that the parent aluminum skin must experience significant yield 211u001estrains before any damage to the doubler will occur.