Accession Number : ADA324137

Title :   Strength and Fatigue Life Enhancements of Cracked Metal.

Descriptive Note : Technical rept.,

Corporate Author : DEFENCE SCIENCE AND TECHNOLOGY ORGANIZATION CANBERRA (AUSTRALIA)

Personal Author(s) : Finney, J. M. ; Neissan, C. ; Absolom, N. ; Lemm, K.

PDF Url : ADA324137

Report Date : OCT 1996

Pagination or Media Count : 31

Abstract : Measures to reclaim both the static strength and the fatigue life of plates with cracks are examined experimentally on 2024 aluminum alloy specimens. The simple measure of stop drilling the crack tips restored most of the tensile strength of the plate. To enhance the fatigue life of a cracked plate the process of stop drilling the crack tips, cold expanding the resulting holes and inserting interference-fit steel plugs has dramatically increased fatigue resistance. For the same spectrum fatigue life the stresses in the life-enhanced plates need to be 2.6 times those in the plain cracked plates. This factor remains practically constant in the presence of secondary bending when the average bending stress/axial stress ratio is 0.5. Surprisingly, the secondary bending reduced the fatigue life by only about 25% for both unenhanced and enhanced specimens. These results have obvious application to the lower wing skin cracking in the F-111 aircraft.

Descriptors :   *TENSILE STRENGTH, *FATIGUE LIFE, *ALUMINUM ALLOYS, LIFE EXPECTANCY(SERVICE LIFE), RESISTANCE, STEEL, CRACK PROPAGATION, PLATES, BIAXIAL STRESSES, AUSTRALIA, STATICS, PLUGS, DRILLING, BENDING STRESS, ALL WING AIRCRAFT.

Subject Categories : Properties of Metals and Alloys
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE