Crack Repair in Aerospace Aluminum Alloy Panels by Cold Spray
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Crack Repair in Aerospace Aluminum Alloy Panels by Cold Spray P. Cavaliere1 • A. Silvello1
Submitted: 4 July 2016 / in revised form: 15 January 2017 / Published online: 7 February 2017 Ó ASM International 2017
Abstract The cold-spray process has recently been recognized as a very useful tool for repairing metallic sheets, achieving desired adhesion strengths when employing optimal combinations of material process parameters. We present herein the possibility of repairing cracks in aluminum sheets by cold spray. A 2099 aluminum alloy panel with a surface 30° V notch was repaired by cold spraying of 2198 and 7075 aluminum alloy powders. The crack behavior of V-notched sheets subjected to bending loading was studied by finite-element modeling (FEM) and mechanical experiments. The simulations and mechanical results showed good agreement, revealing a remarkable K factor reduction, and a consequent reduction in crack nucleation and growth velocity. The results enable prediction of the failure initiation locus in the case of repaired panels subjected to bending loading and deformation. The stress concentration was quantified to show how the residual stress field and failure are affected by the mechanical properties of the sprayed materials and by the geometrical and mechanical properties of the interface. It was demonstrated that the crack resistance increases more than sevenfold in the case of repair using AA2198 and that cold-spray repair can contribute to increased global fatigue life of cracked structures. Keywords aluminum alloys cold spray crack behavior repairing
& P. Cavaliere [email protected] 1
Department of Innovation Engineering, University of Salento, Via per Arnesano, 73100 Lecce, Italy
Introduction Cold spray is emerging as a highly innovative technology for repairing metallic components (Ref 1, 2). Cold spray is suitable for depositing a wide range of traditional and advanced materials on many types of substrate material, especially in nontraditional applications that are sensitive to process temperature (Ref 3). Cold spray can provide different surface modifications leading to increased wear, fatigue, repair, and thermal resistance and heat dissipation by eliminating many of the material incompatibilities common to similar coating technologies (Ref 4). As for all coating technologies, the properties of cold-sprayed materials are primarily dependent on the particle–substrate bonding (Ref 5); the bonding strength is mainly determined by the substrate hardness, powder size and morphology, and spray process parameters (gas temperature, type, and pressure, and nozzle–substrate distance) (Ref 6). Physically, bonding is believed to be governed by shear instability, which leads to bonding enhancement because of melting induced by deformation during nonequilibrium strain. It has been demonstrated that this phenomenon is dependent on an optimal choice of processing parameters (Ref 7). Depending on the materials properties and coldspray parameters, various interfacial behaviors
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