engleski

Modified Hydraulic Bulging in Determination of Flow stress Curve

The objective of this study is an original method of the stress strain diagram acquisition named modified hydraulic bulging on the sphere. The method has been derived from the hydraulic bulging test. The flow stress-true strain curves were established for aluminium sheet on the experimental apparatus designed for both methods. For the purpose of comparing the two researched methods, appropriate expressions, i.e. expressions for kinematics and particular equivalent stresses were derived. In both cases, the assumption of the membrane stress state was used and the flow rule was determined, which was necessary for establishing the flow stress-true strain curves. The comparison between the used methods has shown the advantages of the new modified method. New method allows more accurate determination of membrane state of stress in the deforming material. Assumption on the bulge geometry is no longer needed since modification, using sphere as an obstacle, determines the radius of curvature needed in acquisition of membrane stress. Performing modified hydraulic bulging upon just one test specimen yields three points of stress-strain curve. Experimentally obtained points have different strains, covering different areas of strain ; small, medium and large deformations, within a single experiment.

modified hydraulic bulging; flow curve; hydroforming

nije evidentirano