Mohammad Mahdi Nasajpour

Grade:  Master

Thesis Title:

Simulation of Production process of Seamless Pipes by Mannesmann method with Continuum damage mechanics Approach

Year: Sept. 2016- Jun. 2019.

Abstract:

One of the most widely methods for the production of seamless tubes is the Mannesmann rolling method. This method is capable of producing high-quality, high-precision, high-thickness tubes from uniform cylindrical shafts. The purpose of this project is to Simulation of Production process of Seamless Pipes by Mannesmann method with Continuum damage mechanics Approach. Equipment of Mannesmann rolling process includes, rolling rollers, guider rollers, conductor rollers, plug, mandrel and cylindrical shaft. In the Mannesmann rolling process, initially due to asymmetric roller pressure and secondary tensile stresses at the center of the billet, axial hole is created in the center of the billet, Then, This axial cavity is opened by the plug and reaches the final diameter. Simulation of axial cavity created in the center of billet with damage model is a new approach to simulation of the Mannesmann rolling process. The damage model used to simulation of this process in this project, The modified lemaitre damage model is capable of modeling the effect of cracking closure on compressive loading. To modeling the dependence of material behavior on temperature and strain rate, The Johnson Cook hardening model is used to modeling this process. According to absence of a model consisting of modified Lemaitre damage model and Johnson Cook hardening model in the Abaqus software, needs to be added This feature in the Abaqus software by the VUMAT subroutine. Therefore, after extracting the constitutive equations, The subroutine of Lemaitre damage model and Johnson Cook hardening model has been formulated. In simulation of the Mannesmann rolling process, First, the simulation was performed without the presence of a plug in order to identify the effect of temperature, strain rate, friction and geometric parameters on the problem results and determine the appropriate values for these parameters. Then, the simulation of the Mannesmann rolling process with the presence of plug for production of pipe is investigated. The analyzes and simulations carried out, show that increasing the temperature and reducing the strain rate have the same effect on the amount of damage to the center of the billet and it reduces damage to the billet. The friction analysis has shown that increasing the temperature, reduces the friction force created between the billet and the rolling roller. According to these analyzes, the minimum coefficient of friction required to start the billet moving forward in the rolling process is 0.4.

Keywords:  Mansmann effect, Damage mechanics, Modified lemaitre damage model, Johnson Cook hardening model.