*3.5. Influence of Droplet Size Variations*

The strain-stress analysis contemplates in this part the effect of pondering a distinction on the droplet diameter over the reference case for the testing coupon. Three cases of study are related with variations of the given parameter multiplying its value by 1,2 and 3 for Case 1, 2, and 3, respectively as shown in Table 5.

**Table 5.** Modelling input data for variation cases in droplet diameter and considering semi-infinite substrates, hs > 2d Cs CL .


Figure 31 illustrates the strain evolution for the three different cases. It is noticed a delayed variation in the strain-rate values with longer periods of impact and also the equivalent effect on the strain frequency spectrum, Figures 32 and 33. The main working strain frequency range is evenly increased for bigger droplets (4–6 mm. in diameter) in the periods of time closer to the impact and the reflections with values from 1 MHz, to 3–7 MHz for Cases 2 and 3.

**Figure 31.** Strain-Time evolution for Cases 1–3 at middle coating layer, 50% thickness, considering the substrate-filler as semi-infinite with variation in droplet diameter.

**Figure 32.** Spectrogram for strain evolution at the middle coating layer, 50% thickness, considering substrate-filler as semi-infinite with variation in droplet diameter. Case 2.

**Figure 33.** Spectrogram for strain evolution at the middle coating layer, 50% thickness, considering substrate-filler as semi-infinite with variation in droplet diameter. Case 3.
