PSI - Issue 20

D. Reznikov / Procedia Structural Integrity 20 (2019) 17–23 D. Reznikov / Structural Integrity Procedia 00 (2019) 000–000

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1. 1. Introduction

Structural failure refers to the loss of structural integrity, or the loss of the ability of a technical system ( TS ) to withstand its intended loading without failing due to fracture, excessive deformation, or fatigue and remain functional for a desired service life in real environmental service conditions.

Nomenclature c i

capacity parameter

{ C }

vectors of capacity parameters

d i

demand parameter

{ D } E { x }

vectors of demand parameters

mathematical mean of the random variable x

K IC fracture toughness, K I max maximum stress intensity factor N C ( σ a ) number of cycles to failure at the specific load amplitude n i safety factor against the i -th failure mechanism [ n i ] normative safety factors against the i -th failure mechanism N ( σ a ) number of loading cycles at a specific load amplitude P f estimated probability of the system’s failure [ P f ] tolerable value of the system’s failure probability t time T d design service life δ C critical displacement,  max maximum displacement * ( ) i t   maintenance function Δ i ( t ) degradation function ε max maximum local strain ε y yield strain, σ max maximum local stress σ y yield strength ζ maintenance program χ societal criterion factor

Structural failure occurs when at least one of the so-called demand parameters (maximum local stress σ max , maximum local strain ε max , maximum stress intensity factor K I max , maximum displacement  max , number of loading cycles at a specific load amplitude N ( σ a ), etc.) exceeds the respective capacity parameter of the structure (yield strength σ y , yield strain ε max , fracture toughness K IC , critical displacement δ C , number of cycles to failure at the specific load amplitude N C ( σ a ), etc.), Makhuov (2008), Doronin et al. (2005):

;

max     max max K K  ; Y Y I max    ( ) a C ;

   

  

;

IC

max    N    

N

( ); 



C a