Jeong Kim/Woo-Jin Song/Beom-Soo Kang
The Journal of Mechanical Science and Technology, vol. 23, no. 11, pp.2891-2902, 2009

Abstract : Recently a stress-based FLD due to its path-independency has become a new mainstream technology for prediction of forming limit in tube hydroforming processes, which usually have non-linear strain path. However, the random characteristics owing to experimental errors, inherent measuring equipment errors, dimensional tolerance of asreceived blank, inconsistent lubrication condition and so on lead to uncertainty with regard to the position of the forming limit curve on the stress-based FLD. In this work, to take into account the uncertainty on the stress-based FLD, a probabilistic modeling on the stress-based FLD with confidence level is firstly attempted. With the assumption of all experimentally measured data as normally distributed random variables, stochastic evaluation of the reliability of the stress-based FLD is carried out. Moreover the statistical correlation between measured data during a bulge test and the material parameters is investigated by using the first-order approximated mean value and variance. The reliability is analytically calculated based on first-order reliability method (FORM) and verified with Monte-Carlo simulation (MCS). Finally, at a given deviation of measured data, the band width of forming limit curve on the stress-based FLD to be able to satisfy the required confidence level is determined.

Keyword : Hydroforming; Stress-based FLD; Probabilistic modeling; Reliability; First-order reliability method