SBIR-STTR Award

The present corrosion repair requirement specified by Navy is to restore the components previously un-corroded remaining useful life, while maintaining acceptable static strength capability. To meet these requirements, an extensive testing matrix has to be established to ensure a sufficient level of safety margin for a repaired system, not mentioning that the conventional corrosion repair methods could be costly and labor intensive. The additive friction stir deposition (AFSD) integrates the friction stir principle with a robust material feeding mechanism to enable the site-specific deposition along with the metallurgical bond formation. In Phase I, the research team will develop a thermal/metallurgical/mechanical analytical tool for AFSD enabled repair of aluminum structures under static loading. A multiphysics modeling approach will be constructed to simulate the temperature, material flow, and the resulting microstructure evolution. The temperature- and microstructure-dependent properties will be generated via a digital material library. An accumulative plastic strain driven damage initiation and propagation model will be applied for static failure prediction of AFSD repaired samples. Verification and validation of the multiphysics tool will be performed using the in-situ and ex-situ measurement data.

Benefit:
The prediction of damage initiation and propagation of as-processed components via AFSD is still in its formative stage due to the complexity associated with material heterogeneity, defects, and the residual stress field. The existing technology gap for rapid and reliable repair of corroded aluminum aircraft components has provided a great potential for the transition of this SBIR product into the fleet. Using the performance informed AFSD technique, a strong metallurgical bond between the deposited material and the side wall can be established to resist the potential debonding. In addition, the optimal AFSD process condition can be achieved via the application of the validated analysis tool to best balance the degree of thermal exposure and the degree of material mixing and flow. Considerably reduced residual stress and warpage can be achieved in the repaired system in comparison to the use of a trial-and-error approach for deposition. The developed technique can be used for 1) repairing unweldable metals, especially 7xxx Al alloys, 2) fabricating parts with wear-resistant coatings, 3) adding features after the completion of initial fabrication, and 4) bonding dissimilar metallic components. It also provides emergency field repair to realize immediate operation. The developed technology can have wide applications for the design, modification, and sustainment of metallic structures.

Keywords:
corrosion repair, corrosion repair, Nondestructive inspection, Residual Stress, aluminum alloys, Plasticity, additive friction stir deposition, material flow, fatigue and fracture

Global Engineering and Materials, Inc. (GEM), along with its team members, Professor Hang Yu at Virginia Tech (VT) and Professor Rajiv Mishra at the University of North Texas (UNT), propose to develop a multiphysics based PSPP (process-structure-property-performance) approach and its associated toolkit for tailoring of additive friction stir deposition (AFSD) repair of aluminum components for improved static strength and fatigue life. The salient feature of our multiphysics modeling approach includes thermal, mechanical, and metallurgical interaction to predict bond strength, defects formation, damage initiation, and its propagation in a repaired component. The novelty of the proposed AFSD Repair and Fabrication Analysis Tool (AFSD-RFAT) includes: 1) a high-fidelity, computational fluid dynamics (CFD) based process model that captures thermal response, plastic flow, material mixing, and tool-workpiece interaction; 2) a microstructure evolution model that predicts the grain and precipitate size distribution; 3) a digital constitutive model that creates partitions and local stress-strain relations of distinct zones from the heterogeneous microstructure; 4) a customized Abaqus performance evaluation model with property mapping, bond interface, and initial flaws at stress concentration sites for crack propagation prediction; 5) a multi-stage total life prediction to capture the microstructure-driven crack initiation, plasticity-controlled small crack growth, and the stress ratio dependent long crack growth due to the presence of the residual stress field. In order to validate the physics of each module and the static and fatigue performance of hole repair coupons, advanced in-situ and ex-situ techniques, particle tracing, and high-resolution X-ray computed tomography (X-ray CT) scan will be used to measure the material flow, thermal history, grain structure, precipitates distribution, hardness distribution, residual stress field, initial defects, and fractography. A full validation for each stage of the PSPP modeling tool will be performed using the blend hole restoration data and divot repair data generated by the VT and UNT teams, respectively.

Benefit:
The research will result in a versatile, user-friendly, and computationally efficient toolkit for tailoring of additive friction stir deposition (AFSD) repair of aluminum components for improved static strength and fatigue life. The validated tool will be used for the optimal selection of process parameters in the extended process parameter space to achieve tailored thermal history, improved metallurgical bonding, and desired microstructure, which reduces stress concentration for crack initiation and the harmful tensile residual stress for fast crack growth. The developed technique can be used for 1) repairing unweldable metals, especially 7xxx Al alloys, 2) fabricating parts with wear-resistant coatings, 3) adding features after the completion of initial fabrication, and 4) bonding dissimilar metallic components. It also provides emergency field repair to realize immediate operation. The developed technology can have wide applications for the design, modification, and sustainment of metallic structures.

Keywords:
aluminum alloys, Residual Stress, additive friction stir deposition, process-structure-property-performance, fatigue and fracture, material flow, Plasticity, corrosion repair