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A simple probabilistic approach to the derivation of minimum yield strength values of steels at elevated temperatures
Author(s) -
Rohde Walter
Publication year - 1997
Publication title -
steel research
Language(s) - English
Resource type - Journals
eISSN - 1869-344X
pISSN - 0177-4832
DOI - 10.1002/srin.199700559
Subject(s) - mathematics , r value (soils) , residual , yield (engineering) , polynomial , standard deviation , simple (philosophy) , austenite , function (biology) , value (mathematics) , analytical chemistry (journal) , thermodynamics , mathematical analysis , combinatorics , statistics , chemistry , materials science , physics , metallurgy , microstructure , philosophy , structural engineering , epistemology , algorithm , subgrade , chromatography , evolutionary biology , biology , engineering
For the derivation of minimum yield strength values of steels at elevated temperatures, the formula R p 0.2/ T /min = R p 0.2/20/min (1.1· f av/ T − 0.1) is proposed, where f av/ T is the interpolated average trend value at a specified temperature, obtained by polynomial interpolation of the individual ratio values f T = R p 0.2/ T / R p 0.2/20 at all the test temperatures. The values of f av/ T characterize the trend of the R p 0.2 ‐mean value line in function of the temperature. They are dependent on the material and on the temperature. The factor 1.1 and the reduction value 0.1 are interpreted in terms of a simple probability model. The model is based on the assumption that the total scatter of the test results is composed of two parts. One of these two parts is the correlation induced scatter due to the correlation between R p 0.2/ T − and R p 0.2/20 ‐values. The other one is the residual scatter. By evaluation of a number of data groups it is demonstrated that, for engineering purposes, the standard deviation of the residual scatter may be taken as about 5% of R p 0.2/20/min independent of the temperature. The validity of the formula is confirmed for ferritic and austenitic steels with minimum yield strength values at room temperature between 200 and 800 MPa and for f av/ T ‐values between 1 and 0.3. The connections with the ISO‐method set down in ENV 22605‐1 and ENV 22605‐2, with the trend curve method set down in ENV 22605‐3 and with the recently proposed modified trend curve method are explained.