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Design for elevated temperature applications
If the temperature is high enough, all materials may experience failure in service by a mechanisms known as creep. In metals and alloys, creep and oxidation determine the lifetime in service. Moreover, long term exposure to high temperature expose materials to structural changes in the microstructure that makes unreliable models based on extrapolation of short duration data. Roboust design tools are necessary to provide reliable and accurate prediction of service life and durability.
At TECHDYN, in collaboration with the University of Cassino and Sourthern Lazio, we have developed advanced mechanism-based models that allows to predict material response over the entire temperature and stress range.
Creep rate in pure Al: red line, our model prediction
Our advanced modelling covers primary, secondary and tertiary creep stages. The model provides the creep rate equation that can be easily implemented in commercial finite element codes. Presently, the model is avaliable for MSC MARC in form of user subroutine. The model has been validated on pure metals (copper, aluminum, iron, etc..) and high temperature alloys (P91, P92, SANICRO, 316L, Renè, etc.). Since the model is formulated on the mechanisms responsible for high temperature deformation and damage, it proved successful in predicting creep rupure under a number of complex scenarios including:
- Multiaxial state of stress (resulting from geometry variations or loadig conditions)
- Creep crack growth
- TYPE IV fracture
- Single crystal
Creep design rules are provided in different codes and standard. At TECHDYN, we have strong expertise in the use of deign code such as R5 Assessment Procedure for High Temperature Response of Structure.
Finite Element Analysis
Modelling techniques are sometimes needed to increment these standardized methods such as Finite Element Analysis (FEA) to determine the crack loading and collapse loads of cracked structures undergoing complex modes of loading. TECHDYN uses FEA to determine time for crack initiation, location of developing cracks and crack tip constraint in parent materials as well as welds.
At TECHDYN we have the experimental capabilities to investigate long-term high temperature material properties up to 750°C. Usually, we use our testing machine for planning and performing dedicated validation tests to support model and numerical imulation validation.
Simulation of TYPE IV fracture in welded high chromium steel test sample
Examples of our recent high temperature applications: