Development of Subroutine Library and Data Transfer Interface for High Temperature Structural Integrity-Creep

Creep plays a critical role in the research of high temperature materials because it is the major failure form of high temperature devices. In the safety assessment of high temperature devices, creep failure is one of the key factors used to evaluate residual lifetime of metal components; however, creep analysis in practical applications is still a great challenge due to the lack of a unified theory of all materials. A number of researchers are conducting research into creep constitutive model based on either experimental approaches or computational approaches, but multifarious computational tools were used because the constitutive model is still in the exploration stage. Traditional commercial software could reach the required capability based on the development of user-developed codes; moreover, some in-house codes were proposed, but just used in a narrow scope. Therefore, the development of a novel universal creep finite element software needs to be carried out to meet the requirements of future research.
This research aims to develop required subroutines and interface for the proposed elastic-creep finite element software called High Temperature Structural Integrity-Creep (HITSI). Basic concepts and situations of creep and its computational tools have been reviewed. General knowledge of programming of finite element method has also been studied. A universal subroutine template of creep constitutive equations has been given to enable users to add their own equations directly. A high order and embedded numerical method called Runge-Kutta-Fehlberg (RKF) method has been applied and discussed in order to enhance the accuracy of traditional methods. A mathematical method used to improve the accuracy and efficiency of constitutive equations subroutine call normalization has been applied and discussed. Formatted input and output of purchased pre- and post-processor has been studied to develop the data transfer interface. Some auxiliary modules such as stress transformation and nodal load arrangement have been developed to satisfy the input conditions of constitutive equations subroutines and data transfer interface.