Techniques for Multiaxial Creep Testing

ISBN-13: 9789401080279 / Angielski / Miękka / 2011 / 364 str.

D. J. Gooch

Opis

The design and assessment of modern high temperature plant demands an understanding of the creep and rupture behaviour of materials under multi axial stress states. Examples include thread roots in steam turbine casing bolts, branch connections in nuclear pressure vessels and blade root fixings in gas or steam turbine rotors. At one extreme the simple notch weakening/notch strengthening characterization of the material by circumferentially vee-notched uniaxial rupture tests, as specified in many national standards, may be sufficient. These were originally intended to model thread roots and their conservatism is such that they frequently are considered adequate for design purposes. At the other extreme full size or model component tests may be employed to determine the safety margins built into design codes. This latter approach is most commonly used for internally pressurized components, particularly where welds are involved. However, such tests are extremely expensive and the use of modern stress analysis techniques combined with a detailed knowledge of multiaxial properties offers a more economic alternative. Design codes, by their nature, must ensure conservatism and are based on a material's minimum specified properties. In the case of high temperature components the extension of life beyond the nominal design figure, say from 100000 to 200000 h, offers very significant economic benefits. However, this may require a more detailed understanding of the multiaxial behaviour of a specific material than was available at the design stage.

Spis treści

I: Data Requirements.- 1. Multiaxial Data Requirements for Structural Integrity Assessments in Creep.- II: Biaxial Testing.- 2. The Application of Torsional and Double Shear Tests.- 3. Requirements for Thin-walled Torsion Testing.- 4. A Tension-Torsion Testing Technique.- 5. A Biaxial Tension-Torsion, Constant Stress, Creep Testing Machine.- 6. Torsion Testing in an Inert Atmosphere.- 7. Biaxial Testing Using Cruciform Specimens.- 8. Effects of Overloads and Creep on the Yield Surface of a Nickel-based Superalloy.- III: Triaxial Testing.- 9. An Overview on Studies of Stress State Effects During Creep of Circumferentially Notched Bars.- 10. Practical Aspects of Testing Circumferential Notch Specimens at High Temperature.- 11. Creep Tests on Axisymmetric Notched Bars: Global Displacement Measurements and Metallographic Determination of Local Strain and Damage.- 12. Computer Modelling of Creep Damage in Components with Variable Metallurgical Structure.- 13. Multiaxial Creep Testing Using Uniaxially Loaded Specimens with a Superimposed Hydrostatic Pressure.- Editors’ Note: Creep Rupture Testing under Triaxial Tension.- IV: Pressurised Tubes and Components.- 14. Stress State Distributions in Thick-walled Pressurised Tubes under Creep Loading.- 15. Potential for Standardisation of Techniques for Creep Testing of Internally Pressurised Tubular Components.- 16. Experiments on Multiaxial Creep Above 800°C.- 17. Some Experiences in the Creep Testing of Piping Elbows.- 18. Creep Rupture Testing of Tubular Model Components.- 19. Full Size Component Testing under Creep Conditions.