Abstract
Creep is one of the main engineering problems facing engineers dealing with high temperature components. These components have to be closely monitored, especially after serving 50% of their residual life. For many reason creep engineers has to use small material samples for creep assessments of these components. Many small creep test specimen types can be manufactured using these small material samples; this include the sup-size uniaxial creep test specimen and the pin loaded small creep test specimen. Considering the limitations and the difficulties associated with each testing method is another factor often taken in to account before choosing which specimen type can be used. Traditionally many of creep engineers tend to go for the sup-size uniaxial creep test specimen, because of it is similarity to the standard creep test specimen. However, this specimen type has some limitations; this is include the high possibility of misalignment during the loading application, and this is due to the small size of the specimen. The misalignment effect on the test results normally ignored which can lead to inaccurate results. This paper will be focusing on the misalignment effect on the sup-size uniaxial creep test specimen, and the one-bar and two-bar creep test specimens. Using different values of misalignment the creep results obtained from one-bar and two-bar specimens and the sup-size uniaxial creep test specimen will be compared. The P91 steel at 650°C, which is one of the high temperature materials, will be used for validation.
Highlights
Creep is one of the main engineering problems facing engineers dealing with high temperature components
The failure times of the two-bar specimen (TBS) and one-bar specimen (OBS) is insensitive to this range of misalignment values as they always fail at 1004h. This is because the OBS and the TBS have a flexible loading fixture during loading, i.e, it can rotate during loading to achieve self-alignment
There isn’t any study previously has been conducted to study the effects of the misalignment on creep test results using the pin loaded creep test specimens
Summary
Creep failure is one of the main problems facing most of the aged conventional power generation plants, Oil refineries and other industries, where the elevated temperature and the high stress levels are the norm in their daily operation [1, 2]. The most common way of determining creep strength of any material, is by manufacturing a conventional cylindrical uniaxial creep test specimens from this particular material, with approximately a gage-length of about 100 mm and diameter of about 10mm. This specimen than should be tested by applying a tensile loading to both ends under elevated temperature, typically about % 30 of the materials milting point, until the rupture of the specimen. This paper has a numerical investigation using the finite element analyses, to assess the effects of the misalignment during loading on creep deformation and failure using the pin-loaded small specimens (OBS and TBS) and the sup-size uniaxial creep tests specimens. Welding the two loading ends in the right position with good alignment achieved, is not an easy task and requires a complicated welding machine
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