Accession Number : ADA119199

Title :   Study of Fatigue Mechanisms in Aerospace Structural Materials.

Descriptive Note : Annual scientific rept. 1 Jan-31 Dec 81,

Corporate Author : SOUTHWEST RESEARCH INST SAN ANTONIO TX

Personal Author(s) : Lankford,James ; Davidson,David L ; Leverant,Gerald R ; Hack,John E ; Arrowood,Roy M

PDF Url : ADA119199

Report Date : Feb 1982

Pagination or Media Count : 64

Abstract : This report summarizes the results of a three-phase study of (1) fatigue crack growth and load interaction modeling in aluminum alloys, (2) the effect of microstructure on susceptibility to hydrogen embrittlement in titanium alloys, and (3) micromechanisms of fatigue crack growth in titanium matrix composites. In the aluminum alloy phase of the work, crack tip strains and micromechanics have been determined using a new high resolution technique. These strains were used to evaluate which of several possible failure criteria (strain range, stress range, critical strain to fracture, cumulative damage, and critical work to failure) should be incorporated into a crack growth model. It was found that only the critical strain to fracture model was compatible with all of the observed crack tip parameters. In addition, progress was made in developing computational codes for transforming crack tip strains into the corresponding local stress fields; these results can be used in determining the residual stress fields caused by overloads. In the titanium alloy phase, previous results had shown that the dwell-debit associated with beta heat-treated IMI-685 tested at room temperature was due to a hydrogen embrittlement phenomenon rather than a creep-fatigue interaction. Hydrogen enrichment due to diffusion to the hydrostatic stress field generated at the tip of a long, blocked shear band was found to be responsible for the embrittlement. In the titanium matrix composite phase, the effect of heating the as-received B4C coated boron fiber, Ti-6Al-4V matrix composite was to weaken the interface between matrix and fiber.

Descriptors :   *Composite materials, *Aluminum alloys, *Matrix materials, *Titanium alloys, *Fatigue(Mechanics), Crack propagation, Hydrogen embrittlement, Failure(Mechanics), Stress strain relations, Microstructure, Structural properties, Creep, Plastic properties, Front ends and surfaces, Construction materials, Aerospace craft, Augers, Electron microscopy, Heat treatment, Cracks, Equations, Fractography

Subject Categories : Laminates and Composite Materials
      Properties of Metals and Alloys
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE