Terminology, concepts and definitions - Probabilistic Safety Assessment for Optimum Nuclear Power Plant Life Management (PLiM) - page 7

Symbols

σ - stress
σ m - membrane stress
σ b - the total bending stress
σ a - stress amplitude
σ QF - local stress amplitude, taking stress concentration into account
(σ F ) max - maximum reduced conventional elastic stress cycle, taking into
account the concentration of conventional elastic stresses
[σ] - nominal permissible stress
R m - tensile strength
R p 0.2 - yield stress
R -1 - endurance limit for symmetric tension-compression cycles
Z - the relative reduction in area of the cross-section of the sample for tensile
tests to failure
E - modulus of elasticity (Young' modulus)
N - number of loading cycles of the structural element in service
N p - number of cycles to fatigue crack initiation
a - cumulate fatigue damage
F - neutron fluence with energy > 0.5 MeV
A p - coefficient of radiation embrittlement
K 1 - stress intensity factor
K 1 C - critical stress intensity factor;
n 0.2 - safety factor for yield strength;
n m - the safety factor for ultimate strength;
n σ - safety factor for stress when calculating fatigue resistance
n N - safety factor for the number of loading cycles when calculating fatigue
resistance
n 1 K - the safety factor for K 1 C in the calculation of brittle fracture resistance.

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1.2 Basic terms and formulas of reliability theory,
probability theory and mathematical statistics

1. 2.1 Reliability measures and information from
probability theory

The most important measures of the reliability of non-repairable items are
reliability parameters which include:
• reliability function;
• probability density function;
• failure rate;
• mean time to failure.
Reliability measures are presented in two forms (definitions):
• statistical (sample estimate);