Effects of Material Anisotropy on the Buckling Resistance of High Strength Steel Pipelines
This research investigates the buckling response of high strength steel (HSS) pipes with anisotropic material properties. The stress-strain responses of eight material types of grades X80 and X100 pipes were studied focusing on the elastic, yielding, and early plastic regions that affect the pipe's buckling. Based on the observed hardening patterns in longitudinal and transverse directions, a combined hardening material model was introduced with linear isotropic and Armstrong-Frederick
... -Frederick kinematic hardening rules. A simple method for model calibration was also introduced using longitudinal and transverse tensile stress-strain responses. After validation with experimental stress-strain data, the anisotropic material model was used in the buckling analyses of HSS pipes to improve the accuracy of finite element simulations. Fifteen finite element models were developed for buckling analyses of HSS pipes previously tested under different load combinations. The results showed that using the anisotropic material model results in more precise simulations of the actual behaviour of HSS pipes compared to isotropic models. The anisotropic model was employed in a parametric study to investigate the effects of material anisotropy and five other parameters on the critical buckling strain of HSS pipes. Finite element models were developed and analyzed with different values of diameter to thickness ratio, internal pressure, initial imperfection, material grade, strain hardening rate, and level of anisotropy. The results provide a better understanding of the effects of material properties on the buckling resistance of HSS pipes when there is a significant level of anisotropy. Throughout this work I was surrounded by a spectacular group of people and privileged to have their generous help and support. First I sincerely express my gratitude to my supervisor, Dr. J.J. Roger Cheng, who has supported me throughout my thesis with his patience and knowledge whilst providing me with the freedom to work in my own way. Special thanks to Dr. Samer Adeeb, who shared the material test results of high strength steel pipes with me. Many thanks to all my graduate friends, for sharing their resources and thoughts. Thanks to the University of Alberta, Faculty of Engineering for providing the financial means to complete this project. I would also like to extend my gratitude to my mother and my brothers in Iran, who have done their best to help me in my endeavors. Last, but not least, I would like to thank my dear wife, Salma whose love and support were unconditional during the past few years despite her tight schedule. This thesis is sincerely dedicated to her.