Thixoforming : Semi-solid Metal Processing

Figure 6.33 Experimentally determined flow stress tc of shell
specimen and inverse modelled flow stress t 0 of X210CrW12 for
three strain rates.
6.1 Empirical Analysis of the Flow Behaviourj195
The resulting flow curves of this modified method still include the influence of the
bulging and the shell material, therefore they are indicated as tc (c ¼ composite)
(Figure 6.33). To obtain a precise flow curve without these influences, a further data
processing step is necessary. For this purpose, the inverse modelling method using a
FEM simulation with LARSTRAN/SHAPE (see Section 6.2.3) is applied. In the
simulation, the unknown flow stress of the semi-solid material is given as mathematical
equations with a set of parameters (m1–m8) and the flow stress of the shell
material is given as a table form from the separately executed measurements. Two
equations are used for different strain ranges (j) (low strain range 0–0.18 and high
strain range 0.19–0.7) to describe the characteristic form of the flow curves:
t 1ðj:0 0:18Þ ¼ m1 _j m2 j m3 e jm4 ; for 0