In the second part of the research. the required
force for bending of the sheets was also measured
and plotted. as shown in Fig. 9. The bending forces
showed some fluctuation with increasing the temperatures.
Three different regions were observed in the
force vs displacement plots. In the first region. the
force was raised rapidly from zero at the beginning of
region 2 (plastic region). This mainly corresponds
to the elastic behavior of the material. The bending
forces showed some variations with temperatures
and rose from S16 to S19 N for other directions up to
200 ·C. Then. it fell down to 400 N at 300 'C for all
directions. In region 2. there is an increase and then
gradual decrease until it reaches region 3. It was
thought that the increase in the load was owing to
the developing and spreading of the plastic zone
whereas the decrease resulted from the relatively large
rigid body displacement and the lower deformation
resistance of the specimen in this stage[20]. Similar
behaviors were observed for this region like elastic
region and it rose from RT to 200 'C and then fell
down. In region 3. the bending force was sharply raised
with the movement of the punch and it was contributed
to the full contact between blank and rigid die