N212-113 TITLE: Modeling of Solid-State Materials Consolidation Repair Process for Static Strength and Fatigue Life Predictions

RT&L FOCUS AREA(S): General Warfighting Requirements (GWR)

TECHNOLOGY AREA(S): Air Platforms;Materials / Processes

OBJECTIVE: Develop a thermal/mechanical/metallurgical-analytical tool to predict static strength and fatigue life of solid-state materials consolidation process for structural repairs via process modeling.

DESCRIPTION: This effort will further the Navy�s push to take advantage of solid-state additive methods for repair/sustainment and reduce reliance on experiments alone by improving our understanding of the physics involved, assisting in selecting appropriate materials, and improving process parameter optimization. Various solid-state materials consolidation processes have proven to be attractive and promising procedures to perform repair of metallic structural aircraft components. An attractive aspect is the ability to add material with a reduced heat input, thermal gradients, and residual stresses compared to melting-based technologies. The plastic flow-induced diffusion process can introduce a stronger bonding at material interfaces, allowing for bonding of dissimilar materials that other methods cannot accomplish [Refs 1, 4]. The various solid-state repair methods involve a large range of interdependent relationships between the microstructure, thermal, and mechanical aspects. Examples of important phenomena include plastic deformation, dynamic recrystallization, and heating-and-cooling rates [Ref 3]. While no melting is involved, the various solid-state processes induce heating, which affects the repair material and substrate and needs to be considered. Minimizing the impact to the substrate material is critical to doing no harm during the repair process.

Given the coupled physical mechanisms, the large number of geometry and process dependent variables to control, and the material evolution associated with solid-state materials consolidation repair, it is imperative to develop a physics-based modeling tool. Such a tool will reduce both testing costs and time to identify important process parameters. The process parameters need to meet the performance requirements in terms of restoring or enhancing the strength and fatigue life of the damaged components. That is, any repair should meet a part's static strength requirements and provide increased fatigue life compared to no repair.

The developed tools should provide conservative estimates of the static strength and fatigue life. In addition, prediction of damage initiation and propagation in repaired components is important, but still in its formative stage due to the complexity associated with material heterogeneity, defects, and residual stress field. To achieve these goals, the tool will need to consider thermal, mechanical, and metallurgical phenomena. The tool should also predict bond strength, damage initiation, and its progression in a repaired component. In order to predict strength and durability, the impact of the thermal history and the plastic strain of the process on the repair and substrate material's microstructure will require consideration [Refs 1, 3]. The focus material should be aerospace-grade aluminum alloy (e.g., 2024 or a 7000 series aluminum alloy). This modeling tool will advance the Navy�s ability to analyze solid-state repairs, setting the stage for improved repair options.

PHASE I: Develop an integrated computational modeling framework for a solid-state materials consolidation repair method. Such a framework should simultaneously consider thermal, mechanical, and metallurgical phenomena. The simulation should consider process simulation and structural analysis. Ensure that the concept methodology in Phase I demonstrates its ability to model the process�s thermal history and residual stresses. At a minimum, provide the methodology for the consideration of bond strength, damage initiation, and its progression of solid-state repaired components under static and fatigue loading in Phase II. The Phase I effort will include prototype plans to be developed under Phase II.

PHASE II: Fully develop, verify, and validate a prototype modeling simulation tool for solid-state materials consolidation repair subject to static and fatigue loading. Demonstrate its ability to optimize repair on aircraft components for improved static strength and fatigue life.

PHASE III DUAL USE APPLICATIONS: Finalize the prototype. Perform final testing to demonstrate the analysis model�s ability to provide conservative, but structurally useful, static strength and fatigue life for a variety of repairs (e.g., hole damage and corrosion) and materials. Transition the tool.

Commercial aviation has similar incentive to repair damaged aircraft and get them airworthy quickly. This analysis capability will be just as useful for the commercial aviation industry.

REFERENCES:

1. Hang, Z. Y., Jones, M. E., Brady, G. W., Griffiths, R. J., Garcia, D., Rauch, H. A., Cox, C. D. and Hardwick, N. "Non-beam-based metal additive manufacturing enabled by additive friction stir deposition." Scripta Materialia, 153, 2018, pp. 122-130. https://doi.org/10.1016/j.scriptamat.2018.03.025.
2. Cai, W., Daehn, G., Vivek, A., Li, J., Khan, H., Mishra, R. S. and Komarasamy, M. "A state-of-the-art review on solid-state metal joining." Journal of Manufacturing Science and Engineering, 141(3), 2019. https://doi.org/10.1115/1.4041182.
3. Griffiths, R. J., Petersen, D. T., Garcia, D. and Yu, H. Z. "Additive friction stir-enabled solid-state additive manufacturing for the repair of 7075 aluminum alloy. Applied Sciences, 9(17), 2019, p. 3486. https://doi.org/10.3390/app9173486.
4. Cavaliere, P. and Silvello, A. "Crack repair in aerospace aluminum alloy panels by cold spray." Journal of Thermal Spray Technology, 26(4), 2017, pp. 661-670. https://doi.org/10.1007/s11666-017-0534-9.

KEYWORDS: Solid-state material consolidation; additive repair; Static strength; Fatigue life prediction; additive friction stir deposition; cold spray