Creep Rupture Analysis Research Articles

Creep-rupture and fractographic analysis of candidate stirling engine superalloys tested in air

The creep-rupture behavior of six candidate Stirling engine iron-base superalloys was determined in air. The alloys tested included four wrought alloys (A-286, INCOLOY® Alloy 800H* N-155, and 19-9DL) and two cast alloys (CRM-6D and XF-818). The wrought alloys were evaluated in the form of sheet, 0.79 to 0.99 mm thick. The cast alloy specimens were investment cast to shape and finish machined to 6.38-mm-gauge diameter. The creep-rupture specimens were tested in air for times up to 3000 hours, over the temperature range 650‡ to 925 ‡C. The rupture life, minimum creep rate, and time to 1 pct creep strain data were statistically analyzed and published.1,2 In this paper, microstructural and fractographic aspects of the ruptured specimens are discussed, with only a few correlational graphical analyses included for XF-818 and 19-9DL. Tests are continuing in 15 MPa hydrogen, and later these data will be correlated with air data and microstructural analysis of the specimens conducted.

On the finite element creep rupture analysis of structures

The analysis of problems involving creep rupture is considered. Two creep material failure criteria are employed, i.e. the Kachanov-Rabotnov damage relations and a new, in conjunction with the finite element method, energy criterion. Calculations are reported for titanium notched tensile specimens, where the plastic strains are evaluated by the Ramberg-Osgood formulas.

On the analysis of creep stability and rupture

The analysis of problems involving creep material failure and creep buckling is considered. Creep buckling analyses are presented for some columns. A finite element creep rupture analysis of a rotating disc is performed and the results are compared with other solutions. Calculations are also reported for titanium notched tensile specimens and the numerical results are compared with experimental creep investigations, in which micrographs have been taken to study the rupture mechanisms. All numerical solutions have been carried out using ADINA in which a creep-damage material law and the updated-Lagrangian-Jaumann formulation for the thermo-elastic-plastic and creep material model were implemented.

Analysis of strain hardening creep under random uniaxial loading

Significant advances have taken place in developing methods of analysis of creep and creep rupture under varying stress conditions. However, the attention so far has been focussed on studying creep under deterministic stress histories. Time dependent stress and environmental history of a typical structure element is often definitely not known and it can, at best be described in statistical terms. Idealizing creep as a Markoff process and considering strain hardening theory, a simplified theory is proposed to characterize creep strain under random loading. The random loading refers to statically determinate uniaxial stressing, changing in a stepwise manner with time only and forms an ergodic process. In the light of the feasibility of characterizing the strain distribution under the random loading, an indication is given how a reliability based design approach to creep problems can be developed. The theory and its application are illustrated by a numerical example.

An Analysis of Creep Crack Initiation, Propagation and Rupture from Circumferential Notches under Torsion

An Analysis of Creep Crack Initiation, Propagation and Rupture from Circumferential Notches under Torsion

Creep rupture of ductile materials subjected to strain-hardening or time-hardening creep

An analysis of creep rupture of ductile materials subjected to strain-hardening creep is presented. The analysis is similar to an earlier one by Hoff, but is based on a different generalization of the primary creep-rate relation. Both approaches are then extended to time-hardening creep. The results of both approaches for the two types of creep are compared. Correlation with experimental data for some aluminum-copper, aluminum-magnesium and aluminum-zinc alloys shows fairly good agreement of rupture times for these very ductile materials. However, attempted correlation with data for other materials which do not exhibit such prominent ductility indicates that the basic assumption of the analysis, that creep rupture is caused primarily by a process of reduction of area, holds only for very ductile materials.