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202 Ovidiu Niţă et al.
a b
Fig. 5 – Roughness evolution depending on elongation:
a – steel specimens 30 0 ; b – comparative graph.
It is noted that the graphs and the regression functions were determined
using Microsoft Office Excel software facilities.
4. Conclusions
1. After analysing the results obtained here, we can say that the
lamination direction has a strong influence regarding deformation capacity of
the specimens consider in this study. Thus, it was noted that, for sheet
specimens cut after a direction perpendicular to the rolling direction of material,
the elongation value was approximately 20…25% lower than the situation when
the blanks retain the same orientation to the lamination direction.
2. If we were to make a classification of the three analysed materials we
can certainly say that steel specimens have the highest elongation until the
breaking point. Instead, when we used aluminium specimens the failure point
occurred much sooner than expected. This indicates that the aluminium used in
the experimental research does not lead itself to getting through the stamping
process of stamping.
3. Establishing a mathematical relationship of interdependence between
surface roughness (Ra) and deformation of specimens strengthens the
hypothesis that this phenomenon, a sudden increase in roughness, can be used
as a criterion for developing localized necking. Thus, for defining the moment
when a work-piece deformation reaches the critical region is sufficient to
measure roughness at different stages of deformation and to represent it
depending on the maximum deflection.
4. In conclusion we can say that tensile testing is one of easiest ways of
experimental testing because it allows the use of a conventional test machine,
present in most research laboratories. Also, the specimens, used for this type of
testing, are easy to achieve, especially ones with the rectangular calibrated
zones.
Acknowledgements. This paper was realized with the support of EURODOC
“Doctoral Scholarships for research performance at European level” project, financed
by the European Social Fund and Romanian Government.