THE STATISTICAL AND PROBABILISTIC ANALYSIS OF THE MECHANICAL PROPERTIES FOR DIFFERENT TECHNOLOGICAL SAMPLES

A computational and experimental modeling of the scatter in technologies is presented for steel 15Kh2NMFA at room temperature  to reveal possible variations in the ultimate strength at a limited number of melts. The developed method of step-by-step  “mixing” of technological samples (up to seven samples) is used to  determine and assess the values of the parameters of the  distribution functions and probability density functions. An increase  in the total number of samples and melts makes it possible to  improve the accuracy of the determination of the material  characteristics in the region of large and small probabilities (1 – 5%) and estimate the features of intra-melt scattering. The results showed that with the extension of the range of distribution functions  to probabilities of 1 – 99% with increasing number of samples and  the number of melts, the normal distribution functions of the mechanical properties usually remain similar and close to the two- threshold distribution both for single melt and for the sum of several  melts (a trend to 3 – 3.5 -fold increase of intra-melt scattering is  observed). “Heavy tails” can appear on the distribution curves at low  probabilities (below the defective level). Presence of “heavy  tails” interferes with direct use of the minimum guaranteed roperties without relevant tests and leads to violation in strength and resource calculations. The considered problems also touch on the analysis of safety and risks.

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