Temperature effects on dynamic fracture of pipeline steel

• Author / Creator

  Chanda, Sourayon

• The effective layout of pipelines for mass transportation of oil/gas is a major area of research in the present world. Due to fracture of pipelines, long-lasting and catastrophic hazards may be initiated. Hence, study of dynamic fracture of pipeline steel (PS) is a major research topic in pipeline industry. In many colder parts of the world, like northern Canada, the temperature varies from about -50°C in winter to +35°C in summer. Hence a thorough knowledge of the temperature dependent performance of PS is crucial for efficient design of pipelines. The present thesis aims to address this issue by studying the effects of temperature variation on dynamic fracture characteristics of PS. The present work aims to develop a temperature dependent cohesive zone model (CZM)-based finite element (FE) analysis to simulate drop weight tear test (DWTT). The primary work of this project is to identify the key CZM parameters that are affected by temperature variations and co-relate these parameters with known mechanical properties of PS. Based on these correlations, a temperature dependent cohesive zone model has been presented. To achieve this goal, the true stress strain behavior of pipeline steel have been represented by a modified form of Johnson & Cook model and a non-linear temperature dependency of fracture toughness for PS has been employed. The FE modeling of the CZM has been done using Abaqus/CAE 6.13. The model has been validated by comparing with the load-displacement curves from actual DWTT. The FE simulations of DWTT enable us to study the dynamic fracture behavior of PS at different temperatures. In this analysis, the time history of crack propagation for six different temperatures has been plotted. The obtained relationships show a region of steady-state crack growth during which toughness parameters like crack tip opening angle (CTOA) and crack tip opening displacement (CTOD) remain almost constant. This observation corresponds to experimental findings in this area. Further, the steady state energy from load-displacement curve seems to decrease steeply with decrease in temperature. The steady state toughness parameters like CTOA and CTOD have been obtained for each simulation. These toughness parameters were found to exhibit an increase with increase in temperature which can be formulated using an exponential relation. These results are consistent with temperature variation of experimentally determined CTOD values for steel reported in the literature. In short, the present thesis reports a simple but holistic approach to analyze the fracture behavior of PS at varying temperature using a temperature dependent CZM-based FE model.

• Subjects / Keywords

  • Temperature effect
  • Cohesive zone model
  • Traction separation law
  • Dynamic fracture
  • Pipeline steels

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3695Q

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.