Interpretation of small ring creep test data

Abstract

The small ring creep test method can be used to generate uniaxial secondary creep strain rate data from small samples of material. The technique used is based on the reference stress method; it enables the load-line displacement rates, obtained from testing the rings, to be converted to equivalent uniaxial creep strain rates. Accurate conversion relationships are required, in order to ensure that accurate creep properties are obtained. In this article, an analysis of the creep behaviour of small, ring-type specimens and the associated test procedures are described. This includes the determination of the conversion factors, which are used to convert the minimum creep displacement rate to the equivalent uniaxial minimum creep strain rate and to convert the nominal stress to the equivalent uniaxial stress, using the finite element method. In addition, an assessment of the effects of ring dimensions, for example, the radial thickness and mean radius, on the conversion factors, is made. Finally, the effects of the small geometry changes that occur during a test, on the conversion factors, are investigated.

A study on the evolution of the contact angle of small punch creep test of ductile materials

“…The contact radii for the two tests, required to obtain the contact angles by equation (17), were identified by the values of y that satisfy equation (19), i.e. equating to 0 the second derivative of f(y) with respect to y.…”

“…A representative analytical model of SPCT would be significantly complicated, as it should account for the effects of moving contact edges, nonlinear friction conditions between the test rig components and the tested specimen, and highly localised initial plastic deformation [7,10,15,19]. However, Chakrabarty's theory of membrane stretch forming over a rigid hemispherical punch head, reported in ref.…”

Use of small specimen creep data in component life management: A review

“…The correlation factor is set to 1 during initial testing and by performing a recommended minimum of 5 tests at a single temperature; the correlation factor can be corrected to the actual value that allows for the alignment with uniaxial data tested on the same sample of material. What this correlation fails to incorporate is the large initial plastic deformation [21] involved upon first contact, which has an effect on the creep properties of the material. Consequently this section is disregarded from the considered deflection (Δ c = Δt-Δi), otherwise a curve is produced which resembles the three stages of a conventional creep curve (Fig.4a) although it is debatable as to whether the curve represents pure creep behaviour [17].…”

Small Two-Bar Specimen Creep Testing of Grade P91 Steel at 650°C

“…[2][3][4]. The small ring creep test method [4,5]and the impression creep test technique [6][7][8], have been used to determine secondary creep rate data for materials but they are unable to provide tertiary creep data. Small, sub-sized uniaxial specimen tests have been used to obtain the full creep strain curves.…”