EXTEND STRESS-STRAIN CURVE PARAMETERS AND CYCLIC STRESS-STRAIN CURVES TO ALL MATERIALS LISTED FOR SECTION VIII, DIVISIONS 1 AND 2 CONSTRUCTION
|Publication Date:||5 April 2013|
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