Finite Element Method (FEM) for Bonded Repair Design

TECHNOLOGY AREA(S): Materials
OBJECTIVE: Develop a repeatable process in which FEM software packages will be effectively and efficiently used to determine the fatigue characteristics of wing structures prior to, and after, the installation Boron and Titanium bolted bonded patches.
DESCRIPTION: The Bonded Repair Center of Excellence (COE) Delegated Engineering Authority (DEA) employs a variety of techniques in the determination of damage extent and optimal repair form. Certain techniques need to be improved upon with the proper utilization of Finite Element Analysis (FEA) tools. The majority of repairs conducted by the bonded repair DEA in recent years, conducted in accordance with T.O. 1-1A-81 and T.O. 1-1-6912, are based on historical, experimental data. The DEA has a need for a repeatable analysis methodology with the ability to estimate crack initiation and propagation under fatigue conditions. This methodology should include high-performance computing programs, such as ANSYS3, incorporating available Finite Element Modeling codes. Utilizing this process will improve the quality and effectiveness of repair designs. Additionally, a quantitative description of damages in the form of material removals would grant the DEA the ability to confidently prepare for unconventional repairs. Proper classroom training specifically for bonded repair of aircraft structures will likely be necessary, and should be developed and administered by the same firm.
FEA offers a convenient means of obtaining several pieces of valuable information significant to understanding structural performance; these pieces of information include, but are not limited to, Von-Mises stress, engineering strain, and stress concentration factors. With this information, the COE can more effectively evaluate the quality of both common fatigue driven wing plank repairs on aircraft and eventually unconventional repairs on weapon systems, as well. As a result, the Bonded Repair COE will be better equipped to develop a vast array of repairs with a higher degree of confidence and accuracy.
PHASE I: Develop a proof of concept, high accuracy, repeatable crack initiation and propagation prediction methodology. In this phase, the methodology will utilize available solid modeling/analysis and FEA software to demonstrate the ability to analyze the available data and predict damage under fatigue conditions. Initial demonstrations may be limited to common fatigue driven wing plank repairs, multiple combinations of a single failure mode, or a combination thereof. Classroom style training should also be prepared and ready to administer.
PHASE II: Develop the repeatable crack initiation and propagation prediction methodology to a deployment ready state. Greater ability to analyze the available data and predict damage under expanded conditions will be implemented, developed processes/models will be validated against current standards. The methodology will utilize the FEA software to provide a quantitative description of damages in the form of material removals, and effectively evaluate the quality and effectiveness of unconventional repairs. The goal of the phase II will be a robust, user friendly methodology useable with available FEA software resulting in measurable improvements in the determination and evaluation of a vast array of bonded repair techniques.
PHASE III: A successful methodology could be marketed to other weapon systems and defense customers who require the ability to analyze and model various bonded repair methods under common and unconventional damage scenarios.
REFERENCES: 1. "AIRCRAFT AND MISSILE REPAIR. STRUCTURAL HARDWARE , Technical Order 1-1A-8, https://sbe85fe43e9b86f2d.jimcontent.com/download/.../1-1A-8%20CHA NGE%203.pdf, 15 February 2006.; 2. CLEANING AND CORROSION PREVENTION AND CONTROL, AEROSPACE AND NON-AEROSPACE EQUIPMENT , Technical Order 1-1-691, https://www.robins .af.mil/Portals/59/documents/technicalorders/1-1-691_CHG%2016.pdf?ver=2019-01-25-105433-723, 02 November 2009.; 3. ANSYS Mechanical Pro Capabilities , ANSYS, Inc., https://www.ansys.com/products/structures/ansys-mechanical-pro, 19 February 2019.KEYWORDS: FEA, Repair, Aircraft