Accession Number:

ADA179268

Title:

Study of the Influence of Metallurgical Factors on Fatigue and Fracture of Aerospace Structural Materials.

Descriptive Note:

Annual rept. 1 Jan-31 Dec 86,

Corporate Author:

SOUTHWEST RESEARCH INST SAN ANTONIO TX

Report Date:

1987-01-30

Pagination or Media Count:

37.0

Abstract:

This report summarizes the results of a two-phase study involving 1 experimental characterization and analytical modeling of fatigue crack tip micromechanics in aerospace structural Aluminum alloys, and 2 identification and modeling of key microstructural factors controlling fracture in AL-Iron-X alloys. Dynamic load cycling within the Scanning Electron Microscopy and stereoimaging strain analysis were used to characterize crack opening loads and crack opening modes for 7091-T7E69 AL alloy. Relationships between Delta K, Delta k sub eff, Delta k sub th, and R wered defined. These data were used to determine compressive residual stresses within the near crack tip region. It was found that at the threshold, crack tips are able to open only in Mode II, i.e., the threshold corresponds to an absence at Mode I crack opening. A model was developed which relates the threshold stress intensity factor to the length of a mirostructure-related dominant slip line length. The validity of the model was tested experimentally, with reasonable agreement between predicted and measured results. The fracture behavior AL-FE-X alloys was investigated with the objectives of identifying the micromechanisms of fracture and establishing microstructureproperty relationships in this series of dispersoid-strengthened, power-metallurgy aluminum alloys. Tensile and fracture toughness tests were performed at room temperature to obtain the yield stress, strain hardening exponent, the local fracture strain, and the critical stress intensity at fracture. The size distribution and volume fraction of dispersoids were characterized using quantitative light and electron microscopies.

Subject Categories:

  • Properties of Metals and Alloys
  • Unmanned Spacecraft

Distribution Statement:

APPROVED FOR PUBLIC RELEASE