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Accession Number:
AD0809533
Title:
FATIGUE OF METAL CRYSTALS. PART I. EXTENSION OF FATIGUE LIFE OF CRYSTALS THROUGH CONTROL OF SUBSTRUCTURE.
Descriptive Note:
Annual rept. 1 Feb 65-28 Feb 66,
Corporate Author:
RUTGERS - THE STATE UNIV NEW BRUNSWICK NJ BUREAU OF ENGINEERING RESEARCH
Report Date:
1966-08-01
Pagination or Media Count:
48.0
Abstract:
The structural changes in silver and aluminum crystals fatigued in bending were studied by metallographic, X-ray and electron microscope methods. The fatigue process may be divided into three consecutive broad stages characterized by an increase in dislocation density, formation of substructure and fragmentation into cell structure, respectively. Strain and temperature are the two parameters controlling the development of the dislocation substructure. Both a decrease in strain or an increase in temperature cause growth of subgrains and cells, while variation of the parameters in the opposite direction has an inverse effect on the structure. The growth of subgrains and cells resulting from cycling with lowered strain amplitude is attributed to a mechanism involving dislocation climb. The life of single crystals of silver was nearly two orders of magnitude greater than that of aluminum. The introduction of a grain boundary reduced the life for both to the same level, thus eliminating the beneficial effect of low stacking fault energy on fatigue life. The deleterious effect of boundaries introduced as stress-raisers was, however, eliminated by alternating the cycling between high and low strain amplitudes. The fatigue life of aluminum crystals could thus be extended fourfold. The technique of alternating cycling produced internal decoration of the areas with high internal stresses. Author
Distribution Statement:
APPROVED FOR PUBLIC RELEASE
