In this paper, a new small-sized (two-bar) specimen type, which is suitable for use in obtaining both uniaxial creep strain and creep rupture life data, is described. The specimen has a simple geometry and can be conveniently machined and loaded (through pin-connections) for testing. Conversion relationships between the applied load and the corresponding uniaxial stress, and between the measured load-line deformations and the corresponding uniaxial minimum creep strain rate, have been obtained, based on the reference stress method (RSM), in conjunction with finite element analyses. Using finite element analyses the effects of the specimen dimensions on reference stress parameters have been investigated. On this basis, specimen dimension ratio ranges are recommended. The effects of friction, between the loading pins and the specimen surfaces, on the specimen failure time, are also investigated. Test results obtained from two-bar specimen tests and from corresponding uniaxial specimen tests, for a P9I steel at 600°C, are used to validate the test method. These results demonstrated that the specimen type is capable of producing full uniaxial creep strain curves. The advantages of this new, small, creep test specimen, for determining uniaxial creep data, are discussed and recommendations for future research are given.

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.

Full size creep test specimens, i.e., conventional uniaxial creep test specimen andBridgman notch specimens are usually used to determine the full set of material constants for any creep model. However, in many situations, sufficient material is not available for theses specimens to be manufactured from it. Therefore, small creep test specimens have been introduced and used to determine (i) creep constants and (ii) the remaining life time for engineering components. Two commonly used small creep specimen types, i.e., the impression and the small ring creep tests, are used in this paper to determine the steady state creep constants. However, these specimen types are limited for use in determining the secondary creep properties, i.e., they are unable to determine the full set of material creep constants for creep damage models. In this paper the recently developed small twobar creep test specimen and the newly developed small notched specimen test are described and used to determine a full set of material constants for Kachanov and LiuMurakami creep damage models. The small notched specimen manufacturing, loading and testing procedures are described in this paper. P91 steel at P91 steel at 650° C have been used to compare the material constants obtained from the small two-bar and the small notched creep test specimens with those obtained from the conventional uniaxial creep test specimens and Bridgman notch specimens. The results show remarkably good agreement between the two sets of results.

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The degradation of metallic materials under the effect of the environment is defined as a corrosion process. Under the aggressive environment, corrosion leads to the formation of corrosion products. The use of inhibitor substance is considered as one way to protect the metal surface against corrosion. The inhibitor is chemically adsorbed py the surface of the metal and forms a protective thin film with inhibitor effect. The protection can also be achieved by a combination of inhibitor ions and metallic surface. The current work was evaluated using corrosion inhabitation of carbon steel in NaCl solution by carbimazole\Zn system. The ability of carbomazole as a good corrosion inhibitor is enhanced by the presence of Zn 2+ when the concentration of carbomazole increased and this may be attributed to the protective film formed on the metal surface was withstand the continuous attack of corrosive ions. Also, the formation of complex Fe-carbomizole/Zn +2 linkages on the anodic sites of the metal surface during the immersion time may play a role in the improvement in adsorption of inhibiter system via coverage more area of the metal surface which reduced the exposure of anode sites to the corrosive media. By using Langmuir isotherm model to identify the inhibitor mechanism performance, the values of linear correlation coefficient were close to (1) suggested that the adsorption of the studied inhibitors follows Langmuir isotherm model. Generally, values of ∆G ads up to-9.7 kJ/mol are attributed to the electrostatic interaction between the inhibitor molecules and the metal surface (physical adsorption), whilst those at-10.6 kJ/mol or a little more negative are consistent with chemical bonding of the inhibitor to the sample (Chemisorption).

A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. AbstractCommonly used small creep specimen types, such as ring and impression creep specimens, are capable of providing minimum creep strain rate data from small volumes of material. However, these test types are unable to provide the creep rupture data. In this paper the recently developed Two-bar specimen type, which can be used to obtain minimum creep strain rate and creep rupture creep data, from small volumes of material is described. Conversion relationships are used to convert (i) the applied load to the equivalent uniaxial stress, and (ii) the load line deformation rate to the equivalent uniaxial creep strain rate. The effects of the specimen dimension ratios on the conversion factors are also discussed in this paper. This paper also shows comparisons between Two-bar specimen creep test data and the corresponding uniaxial creep test data, for grad P91 steel at 650 o C.

The work presented in this paper forms part of the research related to the development of small specimen creep testing techniques, which can be used when only small volumes of materials are available. Commonly used small creep test specimen types such as the impression and small ring creep tests can be only used to determine the minimum creep strain rate data. In this paper, two novel small-sized creep test specimens are described: (i) the recently developed small two-bar specimen, which is suitable for use in obtaining both uniaxial creep strain rate and creep rupture life data, and (ii) the newly developed small notched specimen, which can be used to determine the multiaxial stress state parameter. The two specimen types have been used to determine a full set of material constants for Norton model, Kachanov and Liu-Murakami creep damage models. Conversion relationships have been obtained based on the reference stress method in conjunction with the finite elements analyses and have been used to convert the two-bar specimen data to the corresponding uniaxial data. Two P91 power plant steels have been used to assess the accuracy of the two testing methods, (i) a weak P91 (Bar-257) steel at 650°C and (ii) a normal P91 (as received) steel at 600°C. The correlation between the data obtained from the two small specimens testing techniques and the corresponding uniaxial and Bridgeman specimens tests is excellent. The major advantages of the two novel small specimens testing techniques, over some existing small specimen creep testing techniques, are also highlighted in this paper.