Optimizing material parameters for better formability of DQ steel pipe

Abstract

As Pipelines are subjected to bursting failure, the prediction of the burst capacities of corroded pipelines is of significant relevance to the pipeline industry. The Single mode deformation processes, most commonly used in laboratory evaluations like tensile test, may not realistically predict formability performance. Therefore, limit strains tests that use multiple deformation stages would better simulate actual material performance hence bulge test is widely used in pipeline industry for analyzing formability. The tube bulge test is an advanced testing material in which the tube is placed in a die cavity and is sealed from both the ends, the water is injected from the hole inside the sealing punch and hydraulic pressure is increased and the tube gets deformed at the center. The objective of this work is to utilize Taguchi coupled finite element computational methodology to determine the optimum material parameters to attain better formability without necking-splitting failure. To evaluate the dependence of the slope of the forming limit diagram on the material parameters, the simulation under various combinations of strain-hardening exponent (n), plastic strain ratio (r) and thickness of tube (t) is carried out and using thickness gradient criterion, the occurrence of necking i. e. forming limit strains during tube bulging is examined. By observing the optimum condition obtained for maximum plain strain it is concluded that higher the n, r and t more the limit strains will be. It is also observed that among n, r and t, n is the most prominent factor contributing on limit strains followed by r and t. The verification of optimum process parameters obtained through Taguchi technique is carried out using additive model and it is found that the observed value is well in agreement with the predicted value, the extra validation simulation is carried out to validate the Taguchi results.