Development of Validated Crack Measurement System for Vibrating Structures

In-service failures are known to occur in aircraft structures due to vibratory loads. Structural design and test engineers are constantly striving to develop techniques to predict life of components, prevent the initiation and propagation of damage, andenhance the service life of structural components. Recent advances in crack growth measurement techniques such as Visual Crack Measurement System (VCMS), and repairing metallic structures with composites has provided opportunities to: 1) Develop a unifiedsystem for measuring crack growth in complex structures under random vibratory loads, 2) Prevent acoustic fatigue failures from initiating in the remainder life of an aircraft, and 3) Retard the growth of the cracks that have already initiated. Theproposed program will: 1) Develop an integrated VCMS for structures subjected to vibratory loads, 2) Evaluate the capabilities of present analyses and AFGROW software to predict crack initiation and growth in structures subjected to vibratory loads, 3)Evalute the application of current AFGROW bonded repair analytical techniques to predict crack growth in structures with bonded repairs and subjected to vibratory loads, 4) Verify the application of the VCMS with test data, and 5) Modify, if needed,present life prediction techniques for application to vibratory structures.The proposed program will develop and demonstrate the application of validated Visual Crack Measurement System which can be used by aerospace, pipeline, automotive, and otherindustries to carry out reliable acoustic fatigue tests. This will significantly cut down on test time and cost. The anlaytical techniques evaluated in the proposed program along with the methodology developed will provide efficient tools that can be usedby aerospace and other industries to predict life of structures without heavy emphasis on testing. In addition, the developed methodology will provide means to design composite patches to enhance the service life of in-service structures subjected tovibraoary loads. This will significantly reduce maintenance cost of aircraft structures.