Friday, December 9, 2005
1:00pm – 2:00pm
Professor Michael Worswick
Department of Mechanical Engineering
University of Waterloo
Ontario, Canada
“Effect of Pre-Bending on the Hydroformability
of Light Weight Tube Alloys” *
Abstract:
Industrial tube hydroforming operations generally require a number of pre-forming steps, including tube bending prior to insertion of the tube into the hydroforming die. One result of these pre-forming operations is a dramatic change in strain path history between manufacturing steps that often invalidates the use of conventional strain-based forming limit diagram approaches to predicting formability. This problem is exacerbated by the adoption of light weight materials, such as aluminum alloy and advanced high strength steel (AHSS) tubes, which offer an inherently lower formability limit than, say, drawing quality steel.
This presentation will cover recent research addressing the impact of pre-bending on
hydroformability and approaches to account for large strain path variations. Experimental data
from instrumented mandrel-rotary draw bending and subsequent hydroforming trials on pre-bent
tubes will be presented. Both aluminum alloy (AA5754 and EN-AW5018) and AHSS (DP600)
tubes have been tested. Supporting numerical simulations of these multi-stage processes have
been performed and have considered both damage-based and so-called stress-based forming limit
approaches to predict formability. The damage models consider the Gurson-Tvergaard-
Needleman family of yield functions and have been applied to simulate the aluminum alloy
tubes. In addition, an extended stress-based FLC has been developed that accounts for the
through-thickness component of stresses induced during hydroforming; this model has been
applied to experiments on both aluminum alloy and DP600 tube stock. Comparison between
predicted and measured conditionswill be presented and strengths and weaknesses of these
approaches will be highlighted.
*Published with H. Simha, A. Bardelcik, J. Gholipour