Description / Abstract:
INTRODUCTION
This project resulted from ASME Pressure Technology Codes and
Standards (PTCS) Standards Committee requests to identify,
prioritize and address technology gaps in PTCS Codes, Standards and
Guidelines, and is intended to establish and maintain the technical
relevance of ASME codes and standards products. In this context the
inclusion of sound stress-strain curves for design purpose is
required. As a first step a study shall provide:
a. Literature review to evaluate material strength models and
the required material parameters for high priority materials in
Section VIII, Divisions 1, 2 and 3.
b. Modification of existing, or development of new, models for
the monotonic and cyclic stress-strain curves.
c. Collection of the required material parameters for these
models and introduction into Divisions 2 and 3. d. Preparation of a
proposal for providing information on lower priority materials.
e. Documentation of materials where data does not exist
including a proposal for a test program.
After evaluation of the data and examination of potential
constitutive models to be used, a recommendation will be made to
ASME for an efficient and simplified format of conveying behavior
for the purposes of design.
Special emphasis will be placed on the most common materials or
high priority materials, as determined by ASME, used for
construction such as
- Carbon steel (all strength levels)
- Chromium molybdenum (vanadium) steels like 1.25Cr-1Mo and 2.25
Cr-1Mo, including enhanced alloys (all strength levels)
- Ferritic –martensitic steels (e.g. 9-12% Cr) including enhanced
alloys
- Stainless steels (austenitic, ferritic-martensitic, duplex,
precipitation hardening)
- Nickel-base alloys (e.g. N06600, N06625 and N08800)
- Aluminum based alloys
- Titanium based alloys
- Copper based alloys
- Zirconium based alloys
True stress-strain diagrams should be made available for
inclusion into the code. Currently, different approaches for
determination of stress-strain curves are in use: For the true
stress strain curves Sect. VIII Div. 2 employs a two-slope approach
discriminating between low plastic strains and high plastic
strains. Cyclic stress-strain diagrams (which show basically the
same behavior) are covered with a traditional Ramberg-Osgood
parameterization and within Sect. III NH, another (different)
method is used. In the case of Sect. III Div. 2, formulae to
determine the true strain for a given true stress and the tangent
modulus are given for certain classes of materials using Y-1 and
U-table values. The current project should develop a procedure
along the following guidelines.
- The procedure shall be able to predict true (and engineering)
stress-strain curves for the classes of materials specified in the
whole stress range from elastic to ultimate tensile stress.
- The curves shall be based on yield strengths and ultimate
tensile strengths given in the Y- 1 and U-tables.
- The procedure shall allow a quick determination of the whole
true and engineering stressstrain curves in the range
specified.
- The procedure should cover several Code needs (true
stress-strain, engineering stress strain, cyclic stress strain) for
a wide temperature range