Use of Residual Compression in Design to Improve Damage Tolerance in Ti-6AI-4V Aero Engine Blade Dovetails

Abstract

The deep stable layer of compressive residual stress produced by low plasticity burnishing (LPB) has been demonstrated to improve the damage tolerance in engine alloys IN718, Ti-6Al-4V, and 17-4PH. This paper describes the application of LPB to the dovetail bedding surface of a Ti-6Al- 4V fan blade to mitigate the adverse effects of fretting-induced microcracks. Blades removed from fielded engines were LPB processed to protect the dovetail region of the blade and specially designed feature specimens were used to simulate the dovetail region of the blades. Both feature specimens and actual dovetail sections were fatigue tested in cantilever bending mode at a stress ratio, R of 0.5 using specially designed test fixtures. Coalescing microcracks were simulated with electrical discharge machined (EDM) notches. Residual stress and cold work distributions were measured using x-ray diffraction mapping techniques. LPB produced compression in the dovetail region up to a depth of 0.065 in. The HCF performance with EDM notches up to 0.040 in. deep was tested. LPB processed specimens with 0.020 in. deep EDM notch showed an endurance limit of 100 ksi, greater than that of the baseline undamaged surface. LPB treated blades and feature specimens with 0.030 in. and 0.040 in. deep notches showed endurance limits of 60 and 45 ksi, respectively. LPB was shown to fully mitigate the fretting debit, whether applied before or after the fretting damage occurred. Linear elastic fracture mechanics analysis including the residual stress fields confirms the HCF performance in the presence of high residual compression. A novel approach for determining the residual stress field design to provide a desired fatigue life and microcrack tolerance is introduced.

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Document Details

Document Type
Technical Report
Publication Date
Mar 01, 2005
Accession Number
ADA444126

Entities

People

  • N. Jayaraman
  • Paul S. Prevey
  • Ravi A. Ravindranath

Tags

Communities of Interest

  • Air Platforms

DTIC Thesaurus Topics

  • Compression
  • Compressor Blades
  • Compressors
  • Cracks
  • Damage
  • Damage Tolerance
  • Fatigue Life
  • Foreign Object Damage
  • Fracture (Mechanics)
  • Materials
  • Mechanical Properties
  • Mechanics
  • Residual Stress
  • Stress Corrosion Cracking
  • Stresses
  • Turbines
  • X Rays

Fields of Study

  • Materials science

Readers

  • Structural Health Monitoring of Composite Structures.