Motivation for this research comes from the development of the heavy lift helicopter CH-53K Super Stallion by Sikorsky Aircraft for the United States Marine Corp (USMC). The design of the helicopter incorporates the use of polymer matrix carbon fiber composite structures to reduce overall weight and utilizes their superior structural performance (high strength, high stiffness, and long fatigue life). With the increased use of composite structures in aircraft, comes the need for an effective repeatable repair method that can return full structural integrity to a damaged structure.
A carbon fiber composite field-level vacuum assisted resin transfer molding (VARTM) repair method has been developed by Purdue University. The VARTM approach has been adapted into a 'repair kit' containing all the required materials and equipment to perform the repair. Using the VARTM method allowed for simultaneous impregnation through infusion, adhesion between the carbon fiber patch/ damaged parent composite structure, and matrix curing to occur, thus eliminating the need for a conventional prepreg or wet lay-up repair procedure. This allowed for a replicable process resulting in a uniform volume fraction and consolidation enhancing the overall structural performance of the repair.
The purpose of this thesis was to determine the structural efficiency of the repair under shear loading conditions. Structural efficiency was characterized by the large-scale testing of pristine, damaged, and repaired sandwich composite panels representative of the CH-53K airframe. A Finite Element (FE) model of the composite panel and repair were constructed by Butler America using FEMAP and used to estimate the elastic strain response and failure modes for each testing condition. Load and strain data were extracted and compared to the experimental data for model verification.
Two different Phases of shear testing were conducted using two different VARTM repair types. Phase I (2009-2010) featured a VARTM repair impregnated using Crosslink XRD1014/ CLH6372 as the epoxy matrix material while Phase II (2011-2012) used a higher glass transition matrix material, Endurance 4505A/ 4507B. From large scale testing it was determined that full strength and structural performance were recovered in addition to an increase in strength of +3.29% and +24.1% for Phase I and II repair types. For each repaired test performed, the failure was observed to initiate in the facesheet of the testing panel while the repair remained intact and fully adhered to the facesheet, verifying the VARTM repair as an effective repair method for composite structures subject to shear loading.
|Advisor:||Pipes, R. Byron|
|Commitee:||Adams, Douglas, Sun, Chin-Teh|
|Department:||Aeronautics and Astronautics|
|School Location:||United States -- Indiana|
|Source:||MAI 55/06M(E), Masters Abstracts International|
|Subjects:||Engineering, Aerospace engineering, Materials science|
|Keywords:||Applied science, Composite materials, Repair, Testing, VARTM, Vacuum assisted resin transfer molding|
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