Synchrotron radiation microcomputed tomography for assessing internal cracks in cold spray repairs

Experimental Studies into the Analysis Required for the Durability Assessment of 7075 and 6061 Cold Spray Repairs to Military Aircraft

“…A range of examples are presented in which the interface between the SPD and the substrate only fails subsequent to crack growth in the substrate. This failure mechanism is similar to those seen in [13][14][15][19][20][21], in that they involve the nucleation and subsequent growth from small material discontinuities in the substructure, at the intersection between the cold spray and the substructure, followed by delamination at the SPD to substrate interface. We also show that failure of cold spray repaired/coated panels can be due to the nucleation and growth of cracks in the substructure immediately outside of the coated/repaired region.…”

“…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, also known as Supersonic Particle Deposition (SPD), is increasingly being used to repair military aircraft. Whilst the initial focus was on geometry restoration [1][2][3][4][5][6], attention has subsequently expanded to include its use to maintain the structural integrity of aircraft structural components [1,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. However, with the exception of [1,[7][8][9]…”

“…Since, as shown in [13][14][15][19][20][21], cracks that determine the fatigue life in cold spray repairs can nucleate, and subsequently grow, from small sub mm internal material discontinuities in the substrate at the intersection of the cold spray coating with the substrate, such cracks may not be exposed to the environment. This is an important distinction since, as explained in [14], such cracks grow in a "vacuum-like" environment and, therefore, as per [27][28][29][30], grow much slower than if they could "see" the environment. As such, the growth of these interior cracks, which nucleate in the substrate at the intersection of the cold spray, will be much slower than interfacial cracks that can "see" the environment.…”

“…(The relationship between the long crack and the small crack da/dN versus ∆K curves, for cracks that are growing in air, is discussed in [38].) However, as discussed in [14,43,44], for small cracks growing in a vacuum, there appears to be a well-defined (non-zero) threshold. Nevertheless, it appears that for such small interior cracks, the crack growth rate (da/dN) can be expressed as a function of (∆K − ∆K thr ) [43], where ∆K thr is the fatigue threshold.…”

On the origin of surface and interface defects associated with the growth of Al‐coated thermoplastic heterostacks

“…To this purpose, we exploited two complementary techniques: scanning electron microscopy (SEM) coupled with energy dispersive X‐ray spectroscopy (EDS), and synchrotron‐radiation X‐ray computed tomography (CT). To our knowledge, the combined use of electron microscopy and synchrotron radiation CT to perform a noninvasive investigation of this kind of multilayer films has not been reported yet, while it has been recently shown that synchrotron radiation CT was effective in the characterization of internal structural failure (cracks) of materials 15,16 …”