“…The paper by Yoshinaka et al, 1 which used synchrotron radiation microcomputed tomography to study the problem of crack growth from internal defects, adds further support to the seminal paper by Schijve, 2 which established that the reduction in the growth of interior cracks was due to the environment, ie, with interior cracks growing in a "vacuum-like" environment (a review of the effect of internal defects in steels and their role in very high cycle fatigue [VHCF] is given by Jeddi and Palin-Luc 3 ). Given that as can be seen in the papers by Yoshinaka et al, 1 Wu et al, 4 and Shiozawa et al, 5 synchrotron radiation microcomputed tomography can be used to study the growth of internal cracks in titanium and aluminium alloys and steels, the paper by Yoshinaka et al 1 has particular relevance to additively manufactured (AM) replacement parts 6 and to cold spray repairs to aircraft structures 7 where interior near-surface defects due to a localized lack of fusion can occur (see Figure 1). In this context, the memo 8 by the Under Secretary, Acquisition and Sustainment stated that, as of March 21, 2019, the DoD will use AM to "enable the transformation of maintenance operations and supply chains, increase logistics resiliency, and improve selfsustainment and readiness for DoD forces."…”