Total Fatigue Life Estimation of Notched Structural Components Using Low‐Cycle Fatigue Properties

Abstract

In this investigation, an efficient fatigue life computation method under variable amplitude loading of structural components has been proposed. Attention in this study is focused on total fatigue life estimation of aircraft structural components. Flat specimens with central hole made of quenched and tempered steel 13H11N2V2MF were tested as representatives of different structural components. Total fatigue life of these specimens, defined as sum of fatigue crack initiation and crack growth life, was experimentally determined. Specimens were tested by blocks of positive variable amplitude loading. Crack initiation life was computed using theory of low-cycle fatigue (LCF) properties. Cyclic stress-strain curve, Masing's curve and approximate Sonsino's curve were used for determining stress-strain response at critical point of considered specimens. Computation of crack initiation life was realised using Palmgren-Miner's linear rule of damage accumulation, applied on Morrow's curves of LCF properties. Crack growth life was predicted using strain energy density method. In this method, the same LCF properties were used for crack initiation life and for crack growth life computations also. Computation results are compared with own experimentally obtained results.KEY WORDS: crack growth, crack initiation, FEM, strain energy density method, total fatigue life prediction Ó

Residual life estimation of cracked aircraft structural components

“…Fatigue life prediction concepts can be differentiated by the failure criterion applied, i.e. crack initiation, crack propagation, or -encompassing both -total life [7]. As yet no agreement exists on the crack size at which the initiation phase ends; the selection of the initial flaw size for the crack propagation phase may also create difficulties.…”

“…It was discovered that a phenomenon known as "multiple-site damage" could cause many small cracks in the structure, which grow slowly by themselves, to join one another over time, creating a much larger crack, and significantly reducing the expected time until failure [8,9]. Initially, the only philosophy for designing against fatigue of aerospace structures was the safe-life appro-ach, which means designing for a finite service life during which significant fatigue damage will not occur.…”

“…One way to improve the fatigue life predictions may be to use relations between crack growth rate and the stress intensity factor range. To determine residual life of damaged structural components here are used two crack growth methods: (1) conventional Forman`s crack growth method [10] and (2) crack growth model based on the strain energy density method [9,11]. The last method uses the low cycle fatigue properties in the crack growth model.…”

Determination of fracture mechanics parameters structural components with surface crack under thermomechanical loads

“…A number of works have dealt with crack problems [14][15][16][17][18][19][20][21][22][23][24][25][26]30].…”

“…Emery, at al. [8,16] demonstrated their singularity programming technique to consider the singular temperature field in calculation of the stress field. More recently, Ainsworth at al.…”