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Identification of Material Damage Precursors using novel Nondestructive Evaluation and/or Structural Health Monitoring Hardware


OBJECTIVE: The objective of this program is to develop a nondestructive evaluation or a structural health monitoring product (hardware) to be able to detect fatigue damage precursors in a metallic or a composite air vehicle (aircraft or rotorcraft) component and develop an accurate remaining useful life methodology. The overall objective is to develop quantitative methods and tools to improve life prediction of materials by identifying the damage precursors at an earlier stage than current state of the art. DESCRIPTION: Current service life prediction methodology, especially for critical air vehicle structures, often fails to provide adequate warning of impending failure. Fatigue life prediction based on crack length measurements and existing analytical methods can be grossly inaccurate, when based on early service life data, and often too late for effective action, when based on easily measurable crack lengths during the final service life regime. Thus to improve remaining useful life prediction of structural components, the study of damage precursors is important. For the purposes of this program damage is defined as a process that compromises the structural integrity of the structure. Examples of structural damage are delamination, cracks, accumulated dislocations, porosity, surface galling et al. The structural integrity is the ability of the structure to perform the designed task e.g. structural load carrying capacity, thermal barrier and lift. A damage precursor is defined as the progression of structural material property degradation or morphology that can evolve into damage. Some of the known damage precursors are dislocation density, adiabatic shear bands, crazing, slip bands, residual stress, and structural inclusions. Precursor indicator is the measurand of the precursor, direct or indirect, e.g. measurement of change in electrical resistivity as a measurand of dislocation buildup due of fatigue of a metallic component. This program is initiated to develop novel non-destructive evaluation techniques resulting in development of the appropriate nondestructive evaluation / structural monitoring hardware for damage assessment and life prediction, enabling an earlier start of the inspection cycle focused not only on the detection of damage but on the detection of precursors to damage, appearing earlier in the service life. This requires understanding the relationship with how the damage precursors evolve into damage. The objective of the nondestructive method is to identify the fundamental property changes that occur during processing as well as during service that lead to precursors to damage. The nondestructive evaluation hardware will be developed based upon the measurands that quantify changes in electronic and magnetic structure, crystal and crystal defect structure, grain, grain boundary and phase structure, chemical and electrochemical structure, thermal properties, density, and internal residual stresses. This project is intended to study the use of acousto-ultrasonics, eddy current-, thermography-, x-ray diffraction, multiscale modeling and other techniques, to detect pre-damage indicators, such as plastic regions, crazes, shear bands, dislocation tangles etc resulting in development of the nondestructive evaluation product. A multi-spectral or multi-domain approach can be proposed to expand the horizon for material state awareness using new nondestructive evaluation or structural health monitoring hardware or tools. This allows the user to make decisions based upon information across multiple domains and spectrum. This will lead to improved existing experimental and analytical tools as well as creating new tools and methods for successful characterization of potential precursors. PHASE I: This phase is primarily intended for identifying and developing a novel nondestructive evaluation product to detect damage precursors. The proposed nondestructive evaluation product will need to be able to measure the precursor indicators to satisfy the goals of this program. A nondestructive evaluation method needs to be applied on a structural (metallic or composite) coupon subjected to fatigue loads will be a requirement for Phase II funding. Prognosis methods based on data from the chosen NDE technique should be able to predict remaining useful life (RUL) of the coupon within 10% error on or before 50% of the total useful life of the coupon had been expended. PHASE II: This phase is primarily focused on further development of the nondestructive evaluation product (hardware) and deployment strategies. The probability of detection by the developed product for nondestructive evaluation of the damage precursors leading to damage needs to be at 90% with a 95% confidence rate. The validation and the verification of the method ought to be demonstrated on a military rotorcraft or aircraft primary structural component or subcomponent at laboratory environment. Prognosis methods based on data from the chosen nondestructive evaluation product should be able to predict remaining useful life (RUL) of the component within 5% error on or before 25% of the total useful life of the component had been expended. PHASE III: This phase is to miniaturize, package and transition the developed nondestructive evaluation technology to the original equipment manufacturers of both military and commercial aircraft. The developed nondestructive evaluation product should be demonstrated on a military air vehicle (rotorcraft or aircraft) component inspection for damage precursors at relevant environment. The developed nondestructive evaluation product needs to be a handheld or a miniature device that can be used during line maintenance or at the overhaul and repair maintenance depots for periodic inspection or structural health monitoring both military and commercial air vehicles. REFERENCES: 1. Christodoulou, L, and Larsen, J. M.,"Using materials prognosis to maximize the utilization potential of complex mechanical systems,"JOM Journal of the Minerals, Metals, and Materials Society, Volume 56, Number 3, pp 15-19, March 2004. 2. Larsen, J., John R., and Lindgren, E.,"Opportunities and Challenges in Damage Prognosis for Materials and Structures in Complex Systems,"AFOSR Discovery Challenge Thrust (DCT) Workshop on Prognosis of Aircraft and Space Devices, Components and Systems, Cincinnati, Ohio, February 19-20, 2008 3. Ghoshal, A. and Ayers, J., T.,"Embedded Sensing in Rotorcraft Composite Components - A Rethink?", AFRL ISHM Conference July 20-22, 2011 Boston MA 4. Butler, S., Gurvich, M., Ghoshal, A., Welsh, G., Winston, H. A., Attridge, P., Urban, M., and Bordick, N.,"Effect of Embedded Sensor on Interlaminar Damage in Composite Structures,"Journal of Intelligent Material Systems and Structures, November 2011, vol. 22 no. 16, 1857-1868. 5. LeMaitre, J., and Desmorat, R.,"Engineering Damage Mechanics: Ductile, Creep, Fatigue, and Brittle Failures,"Springer-Verlag, Berlin Heidelberg, 2005.
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