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of 0.023 m and nil saturation behind that point was found with Darcy´s model, demonstrating its inaccuracy. Having validated the Preform 1D code for Saffil fibre preforms (FA24), focus turned to AOPC20. Based on the preform parameters listed in Table 5.1, the modelling results were compared to the experimental results of local saturation after CP infiltration at different pressures, as shown in Figure 5.12. As shown in Figure 5.11 b) the melt did not reach the end of the FA 24 preform and therefore the end drag phenomenon could be omitted which is similar to the experimental infiltration results of AOPC20 at a constant pressure of 0.8 MPa shown in Figure 4.39. In contrast, at 1.2 MPa, the melt fronts contacted each other and therefore influenced each other. In order to allow for this, the centre of the preform was set as an impermeable boundary in the Preform 1D code which led to a time dependent increase in saturation in front of it, as shown by the results at different infiltration times of 2, 4 and 16 s in Figure 5.12. At an early stage, a negative gradient toward higher x-values was found, whereas a homogenous saturation profile was reached at an extended pressurisation (16 s). For applied pressures of 0.8 and 1.2 MPa at 16s, the calculated Sloc were homogenous at 0.23 and 0.61 respectively. At constant pressure, the respective saturation at the ingate (x = 0 m) was similar for different infiltration times. As, by definition, the ingate pressure is constant in the constant pressure mode, similar pressure and hence similar saturations were calculated for all infiltration times at the ingate. This behaviour is expressed by the saturation function in Equation 29 where all preform parameters were assumed to be constant during the entire infiltration process apart from the applied pressure Pappl. 231

Local Saturation saturation S () loc 0.8 0.6 0.4 0.2 p appl = 1.2 MPa experiment p appl = 0.8 MPa experiment α= 3.25x10 -6 / t = 2 s 16 s 0.0 0.00 0.01 0.02 0.03 Position x x / m(m) Figure 5.12 Experimental Sloc of MMC after infiltration of AOPC20 in CP mode at 0.8 and 1.2 MPa and modelling results after different infiltration periods (dashed lines) and variation of α for the applied pressure of 1.2 MPa (red line). With only minor deviations between x = 0.007 and 0.015 m, at 0.8 MPa, the negative slope toward the centre observed in the experiments could be best reproduced at an infiltration time of 2 s. However, in the experiments the pressure was kept constant for more than 60 s. It is therefore assumed that metal flow stopped 2 s after pressurization and therefore prior to pressure release. This has to be attributed to solidification of the metal at the die walls as these were held below the solidus of the alloy. The experimental results for a Pappl of 1.2 MPa showed a steep decrease in saturation which started from 0.73 and reached a minimum of 0.25 at x = 0.028 m. After that point, a steep increase could be observed. A symmetric saturation was assumed in CP infiltration but the centreline was shifted by 0.002 m toward the half of the investigated sample, which may be a 232 16 s result of marginal differences in permeability of the initial half of the preform. 4 s 2 s 4 s 2 s