Computing the Fatigue Life of Cold Spray Repairs to Simulated Corrosion Damage

Abstract

This paper summarises the findings of an investigation into the durability of cold spray repairs, also known as supersonic particle deposition or SPD repairs, to simulated corrosion damage in AA7075-T7351 aluminium alloy specimens. A feature of this paper is that it is the first to show how to perform the mandatory durability analysis of repaired corroded structures, where the corroded material is first removed by machining and then repaired using cold spray, in a fashion consistent with the requirements delineated in USAF Structures Bulletin EZ-19-01, MIL-STD-1530D, and the US Joint Services Structural Guidelines JSSG2006.

Computing the durability of WAAM 18Ni 250 maraging steel specimens

“…A view of the failure surface is also shown in Figure 6. The fatigue surface was essentially Mode I and, as such, resembled those seen in previous papers 24,32,[39][40][41][42] for Mode I fatigue crack growth in materials that ranged from bridge steels to the highstrength aerospace quality aluminum alloys AA7075-T7351 and AA7050-T7451. As a result, as we will see in the next section, the growth of this naturally occurring crack is consistent with the exponential crack growth histories associated with the growth of naturally occurring sub millimeters cracks seen in both RAAF and USAF aircraft.…”

“…Fortunately, as noted by Sanaei and Fatemi, 15 and also in a range of references, 1,14,16,18–34 the Hartman–Schijve crack growth equation, namely, can frequently be used to model the growth of both small and long cracks. Here, N is the number of cycles, a is the crack length/depth, and D and p are material constants.…”

“…Consequently, the durability analysis of an AM part requires the use of the associated small crack da/ dN versus ΔK curve. A more detailed review of the certification requirements and analysis methods associated with AM parts is given by Kundu et al 19 Fortunately, as noted by Sanaei and Fatemi, 15 and also in a range of references, 1,14,16,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] the Hartman-Schijve crack growth equation, namely,…”

“…The value of ΔK thr associated with the fastest growing naturally occurring small cracks is small 20,37,38 and often lies in the range 0.1-0.3. 1,19,21,22,[24][25][26][27][28][29]33 As such, the focus of the present paper is to investigate if Equations ( 1) and ( 2) can be used to compute the durability of WAAM 18Ni 250 maraging steel specimens with as built surfaces. To this end, the surface topography is measured and used to create a three-dimensional (3D) finite element model.…”

Mechanical Properties of Cold Sprayed Aluminium 2024 and 7075 Coatings for Repairs

“…A new axial fatigue test specimen design was also proposed to substantiate the fatigue performance of cold spray repair on a localised cavity [17,18]. With the release of USAF Structures Bulletin EZ-19-01 and the consideration of existing military standards (MIL-STD-1530D and JSSG-2006), a few applicability studies of Hartman-Schijve crack growth for cold spray repairs showed promising correlation with experimental data for durability and damage tolerance analysis (DADTA) [19][20][21]. However, these papers were for specific components and conducted with less than eight sample sizes in controlled environments.…”