Foreign object damage and fatigue crack threshold: Cracking outside shallow indents

Citation
X. Chen et Jw. Hutchinson, Foreign object damage and fatigue crack threshold: Cracking outside shallow indents, INT J FRACT, 107(1), 2001, pp. 31-51
Citations number
10
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Mechanical Engineering
Journal title
INTERNATIONAL JOURNAL OF FRACTURE
ISSN journal
0376-9429 → ACNP
Volume
107
Issue
1
Year of publication
2001
Pages
31 - 51
Database
ISI
SICI code
0376-9429(200101)107:1<31:FODAFC>2.0.ZU;2-E
Abstract
Foreign Object Damage (FOD) usually happens when objects are ingested into jet engines powering military or civil aircraft. Under extreme conditions, FOD can lead to severe structural damage. More commonly it produces local i mpacted sites of the fan and compressor airfoils, lowering fatigue life of these components. FOD is a prime cause for maintenance and repair in aircra ft engines. In this paper, a framework for analyzing FOD and its effect on fatigue cracking is established. A finite element analysis is used to ident ify three relevant regimes of FOD related to the depth of penetration into the substrate, and to determine the residual stresses. Most of the emphasis in this paper focuses on fatigue cracks emerging from shallow indentations , which are generally expected to be of most practical concern. Full three- dimensional finite element solutions are obtained for semi-circular surface cracks emerging from specific locations at the indentation revealing the i nfluence of the residual stress on the stress intensity factor distribution . For shallow indents, a relatively simple dimensionless formula for the re lation between the residual stress intensity factor, the crack size, and th e indentation width are developed. These results, together with results for the intensity factor variations due to cyclic loading, have been used to a ddress the question: To what extent do the residual stresses caused by the FOD reduce the critical crack size associated with threshold fatigue crack growth? Formulas for the critical crack size are obtained. Specific results are presented for the blade alloy, Ti-6Al-4V, revealing that FOD can reduc e the critical crack size by as much as 60%.