PSI - Issue 8

L. Landi et al. / Procedia Structural Integrity 8 (2018) 3–13 L. Landi et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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In figure 3, we have underlined the dependence from the strain rate, reporting in black the static model obtained from (17) and the two constitutive JC models developed for the maximum strain rate possible for the ballistic penetration of guards, equal to approximately 1000 1/s.

4. Impact simulation on safety guards

In order to demonstrate the appliance of impact simulations for the design of safety guards of machine tools, we report the results obtained simulating impacts under the standardized conditions defined by Mewes (2000). These conditions were used to define normative appendices of ISO 23125: tested steel plates are of DC01 with 3 mm thickness. Dimensions, mass and initial velocity of the projectile changes in relation of three different standardized test expressly designed for turning machine. In the paper, for every bullet (see the masses reported in table 5) two different energy are reported by Mewes: the lower where there is bulging (B) found and the higher where full penetration (P) was found (see figure 4).

Table 5. Geometry of the projectiles Mass [Kg]

Diameter [mm]

Square side [mm]

0.625 1.250 2.500

30 40 50

19 25 30

Using simple Eq. (9), we calculated the impact velocities for which bulging or penetration is expected by the data of Mewes (2000, 2011). The energy and velocity data obtained are shown on Table 6. = 1 2 2 → = √ 2 (9) Table 6.Calculated impact velocities Mass of the projectile[kg] Bulging Penetration 0.625 E [J] 1500 2050 v [m/s] 69.28 80.99 1.250 E [J] 2500 2800 v [m/s] 63.25 66.93 2.500 E [J] 3800 4050 v [m/s] 55.14 56.92

Figure 4 shows the different energy levels of bulging and penetration for each type of bullet by Mewes (2000).

5. FE and experimental settings

Because it is not possible to have axial symmetry hypothesis, a 3D model of the impacting projectile and target has been created. The complete drawing of the projectile is reported on annex B of the ISO 23125 standard and it is omitted for brevity. The target used in the experimental test is a square 500 x 500 mm 2 plate, clamped for 25 mm on each side. In order to reduce the number of elements, the dimension of the plate are reduced to 450 x 450 mm 2 and the edges were clamped. In order to decrease the size of elements on the impact area of the target, we defined a volume on the center of the target with more refined mesh dimensions defined as in Table 7.