*2.3. Fatigue Test Setup*

Compression–compression fatigue tests were carried out according to protocols in the scientific literature [34–37].

A variable maximum load of 80%, 60%, 40% and 20% of the static yield (*σ*<sup>02</sup> calculated according to ASTM E9) was imposed in order to obtain the Wohler curves. The ratio parameter of *R = 0.1* implies that the compressive load on the specimens oscillates with a sinusoidal from 10% to 100% of the imposed load with a frequency speed of 50 cyclic loads per second (50 Hz).

The maximum value of the compression is defined as *σ<sup>M</sup>* and can be obtained from Equation (1); the parameter *x* corresponds to a linear multiplying value of 80%, 60%, 40% and 20%; *σ*<sup>02</sup> is the average yield load of the static uniaxial compression tests on the corresponding trabecular specimens. This value has been separately calculated by previous experimental static compressive test on analogous specimens [38].

The minimum value of the compression is reported as *σm*, obtained from Equation (2), where the *R* parameter is maintained equal to 0.1. The median value between *σ<sup>M</sup>* and *σ<sup>m</sup>* is *σa*, calculated using Equation (3). In order to evaluate the Wohler curve, it is then necessary to record the Number of cycles (N) corresponding to the specimen failure. The imposed upper limit for the cycles is N equal to 1.5 × <sup>10</sup>7, suitable for airframe structures and the systems safe-life approach [39].

$$
\sigma\_M = \ge \sigma\_{02} \tag{1}
$$

$$
\sigma\_m = R \sigma\_M \tag{2}
$$

$$
\sigma\_{\mathfrak{a}} = (\sigma\_M - \sigma\_{\mathfrak{m}})/2 \tag{3}
$$

The values of *σM*, *σm*, *σ<sup>a</sup>* and N are tabulated in Appendix A. All the specimens, three for each type, were processed with an Instron machine. The test machine setup has been prepared with a flat attachment, a load cell of 50 kN and a constant displacement of 1 mm/min, as shown in Figure 3.

**Figure 3.** Testing Machine Setup.

The same AlSi10Mg material as [7] was used. The specimen's size was maintained as much as possible to be coherent to the 20 mm × 20 mm × 40 mm proposed in [7] in order to preserve the comparability of the data.
