Abstract
This paper presents an experimental study into the analysis required for the durability assessment of 7075 and 6061 cold spray repairs to military aircraft. To this end, it is first shown that provided the bulk stress in a 7075 cold spray coating can be kept beneath approximately 150 MPa, then the coating should not crack. A range of examples are presented in which the interface between the coating and the substrate only fails subsequent to crack growth in the substrate. We also show that failure of cold spray repaired/coated panels can also be due to the nucleation and growth of cracks in the substructure immediately adjacent to the coated/repaired region. As such, when performing a durability analysis for a cold spray repair, the growth of such small naturally occurring cracks, both at the interface and immediately adjacent to the ends of the coating, need to be accounted for.
Highlights
IntroductionAs outlined in the detailed reviews presented in [1,2,3,4,5] and in [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22], cold spray, known as Supersonic Particle Deposition (SPD), is increasingly being used to repair military aircraft
It should be noted that, as explained in MIL-STD-1530D, analysis is the key to certification and that the role of testing is merely to validate or correct the analysis. This raises the question: do the crack growth analysis cases needed for a durability analysis of a cold spray repair differ from those commonly used to assess the durability? the question is the focal point of the present paper
The United States Air Force (USAF) requirements for the durability and damage tolerance certification for cold spray repairs to aircraft structural parts are detailed in Structures Bulletin
Summary
As outlined in the detailed reviews presented in [1,2,3,4,5] and in [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22], cold spray, known as Supersonic Particle Deposition (SPD), is increasingly being used to repair military aircraft. The current paper presents a series of experimental studies that reveals the importance of this phenomena, i.e., failure due to cracking that nucleates from material discontinuities in the substrate at the interface between the cold spray and the substrate At this stage, it should be noted that the growth of small naturally occurring lead cracks, i.e., the cracks that determine the operational life of a component [31,32,33], which see the environment often grow in a near exponential fashion [26,31,32,33,34,35,36,37] and follow a da/dN versus ∆K curve that is essentially a. In the thickness cracksthickness in thin skins with coating, should be noted that closed-form analytical case of through cracks incold thin spray skins with colditspray coating, it should be noted that closedsolutions for through thickness cracks repaired cold spray were [11]. first given in form analytical solutions for through thicknessusing cracks repaired usingfirst coldgiven sprayinwere [11]
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