EPRI Expert Workshop on Creep Continuum Damage Models for Structural Mechanics in Collaboration with ASME PVP
We look forward to welcoming you to the 2018 Workshop. This meeting will cover State of the Art presentations regarding Creep Continuum Damage Mechanics. It is apparent that a CDM framework is particularly attractive to establishing relevant models which describe the creep behaviour of advanced steels. Particular benefits of this approach are derived for metallurgically complex steels because, for the components and loading scenarios in which they are used, there is an emerging reality that performance cannot simply be explained on the basis of strength, i.e. using deformation dominated expressions. Thus, it is apparent that creep damage susceptibility and ductility must be understood and properly considered in the models to reduce uncertainty and minimize the risks of fracture during service.
This Workshop will build on previous discussions which have considered the principles and requirements that should be followed to establish robust and relevant creep-continuum damage mechanics constitutive models. The three key requirements which should be embodied in a suitable model have been identified as:
Provide "physically reasonable" responses for relevant stresses and temperatures,
Activation energies, stress exponents and other parameters should have reasonable values,
State variables representing key aspects of the material response should be related to underlying physical (metallurgical) mechanisms, and
Multiaxial forms should represent the underlying deformation and damage phenomena
Key features of the creep response (creep rate, rupture time, etc.) should be readily derived
Scalable for use in applications from simple calculations (e.g. constant stress) to complex finite element models, and
Overall representation of the material response which can be simplified for specific cases by switching on or off features of the model
Pragmatic approach to Data fitting:
A relevant, but minimal number of vital coefficients (consistent with physical meaning),
Easy-to-determine coefficients without the need to adopt complex regression, and
Simple scaling to represent upper/lower bounds on material response by considering both strength and damage susceptibility.
In addition to discussion of a framework for model development, review presentations considered alloy specific applications of Continuum Damage Mechanics (CDM). The meeting sessions included:
Metallurgical Factors affecting high temperature performance for both Tempered Martensitic and Austenitic Stainless Steels with emphasis on:
Pedigree of parent metal, including documenting factors which contribute to deformation and damage,
Metallurgical risk factors identified relating to variability in the as-fabricated condition and which influence changes in service performance,
Assessment of metallurgical risk factors in multiaxial tests, and
Characterization of damage in parent metal and cross-weld creep tests
Evaluation of established Continuum Damage Mechanics methods and potential developments with a view to seeking a unified approach for:
Accommodating microstructural influences on deformation and damage,
Describing alloy specific susceptibilities to the initiation and growth of damage
Incorporation of stress state effects,
Assessment of validity of the selected model by considering trends in behaviour established independently to the results used in model development.
Design by Rule compared to Design by Analysis:
Options for design-by-analysis
Application of design-by-analysis to susceptible component geometries
Complexity – balancing need and simplicity
Venue and booking
JONATHAN PARKER, PHD, CENG, FIM, FIMECHE.
ELIZABETH BENTON (EBENTON@EPRI.COM)