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Title: RESEARCH ON STRAIN-AGEING, HARDENING AND SOFTENING OF METALS BY FATIGUE. Technical Summary Report for September 1957-February 1959

Abstract

Previous work relating to the fatigue of aluminummagnesium alloys was extensively reviewed. Room temperature fatigue experiments were conducted to find ihe condition under which true fatigue limits occur in aluminum-magnesium alloys. In the solution-treated condition, these materials do not have fatigue limits, but in the as-extruded they do. Metallographic observations show that increasing magnesium content reduces the widih of slip marks (striations) and surface cracking which occur during fatigue. Cracks were observed in aluminum - 1% magnesium, and aluminum - 3% magnesium in as-extruded specimens remaining unfailed below the fatigue limit. Tensile experiments at - 196 deg C subsequent to fatiguing at - 196 deg C, with intermediate testing at temperatures in ihe range -80 to +120 deg C in aluminum and aluminum-magnesium alloys, showed hardening and softening effects which are probably due to interactions of vacancies and solute atoms with dislocations. Preliminary experiments are reported showing the effect of temperature on fatigue life for a given stress in aluminum -3% magnesium. These indicate that there is an increase in fatigue life corresponding to the hardening effects in the fatigue-tensile experiments. A technique is outlined for growing large seeded zinc crystals of any desired orientation, and a method of acidmore » machining gage lengths in these crystals is described. Zinc crystals of five different orientations (X, Chi, between 30 deg and 60 deg ) were fatigued to fracture at room temperature in push-pull tests at a frequency of 100 c/s. S-N curves were found for each orientation, and when the curves are re-plotted in terms of resolved shear stress they superimpose, indicating that the fatigue life of a crystal is determined by the shear component of the applied stress. A few crystals were also fatigued at 50 c/s, and it is shown that failure is dependent on time of testing rather than on ihe number of cycles. Fracture of zinc crystals by fatigue usually takes place by cleavage across the basal plane, and this initiates in a direction parallel to the active slip direction. During fatigue, specimens harden during approximately ihe first 3 x 10/sup 4/ cycles, and the flow stresses produced are one hundred times that of a virgin crystal A logarithmic law of recovery has been deduced for fatigue-hardened crystals rested at room temperature. A method has been developed for measuring hysteresis loops during fatigue, and it has been found that the amount of plastic strain per cycle decreases with ineleasing number of reversals for the first 10% of life and then remains constant for the remainder. (auth)« less

Publication Date:
Research Org.:
Birmingham. Univ., England
OSTI Identifier:
4217509
Report Number(s):
AFOSR-TN-59-774; AD-219717
NSA Number:
NSA-14-000613
DOE Contract Number:  
AF61(514)-1182
Resource Type:
Technical Report
Resource Relation:
Other Information: Orig. Receipt Date: 31-DEC-60
Country of Publication:
United States
Language:
English
Subject:
METALS, CERAMICS, AND MATERIALS; ALUMINUM ALLOYS- ATOMIC MODELS- CRACKS- CRYSTALS- DEFECTS- DEFORMATION- EXTRUSION- FATIGUE- HEAT TREATMENTS- LOW TEMPERATURE- MACHINING- MAGNESIUM ALLOYS- MATERIALS TESTING- METALLOGRAPHY- SLIP- SOLID SOLUTIONS- STRESSES- SURFACES- TEMPERATURE- TEMPERING- TENSILE PROPERTIES- VACANCIES- ZINC; DIAGRAMS- HYSTERESIS- RECOVERY- SHEAR- TENSILE PROPERTIES

Citation Formats

. RESEARCH ON STRAIN-AGEING, HARDENING AND SOFTENING OF METALS BY FATIGUE. Technical Summary Report for September 1957-February 1959. United States: N. p., 1960. Web.
. RESEARCH ON STRAIN-AGEING, HARDENING AND SOFTENING OF METALS BY FATIGUE. Technical Summary Report for September 1957-February 1959. United States.
. Mon . "RESEARCH ON STRAIN-AGEING, HARDENING AND SOFTENING OF METALS BY FATIGUE. Technical Summary Report for September 1957-February 1959". United States.
@article{osti_4217509,
title = {RESEARCH ON STRAIN-AGEING, HARDENING AND SOFTENING OF METALS BY FATIGUE. Technical Summary Report for September 1957-February 1959},
author = {},
abstractNote = {Previous work relating to the fatigue of aluminummagnesium alloys was extensively reviewed. Room temperature fatigue experiments were conducted to find ihe condition under which true fatigue limits occur in aluminum-magnesium alloys. In the solution-treated condition, these materials do not have fatigue limits, but in the as-extruded they do. Metallographic observations show that increasing magnesium content reduces the widih of slip marks (striations) and surface cracking which occur during fatigue. Cracks were observed in aluminum - 1% magnesium, and aluminum - 3% magnesium in as-extruded specimens remaining unfailed below the fatigue limit. Tensile experiments at - 196 deg C subsequent to fatiguing at - 196 deg C, with intermediate testing at temperatures in ihe range -80 to +120 deg C in aluminum and aluminum-magnesium alloys, showed hardening and softening effects which are probably due to interactions of vacancies and solute atoms with dislocations. Preliminary experiments are reported showing the effect of temperature on fatigue life for a given stress in aluminum -3% magnesium. These indicate that there is an increase in fatigue life corresponding to the hardening effects in the fatigue-tensile experiments. A technique is outlined for growing large seeded zinc crystals of any desired orientation, and a method of acid machining gage lengths in these crystals is described. Zinc crystals of five different orientations (X, Chi, between 30 deg and 60 deg ) were fatigued to fracture at room temperature in push-pull tests at a frequency of 100 c/s. S-N curves were found for each orientation, and when the curves are re-plotted in terms of resolved shear stress they superimpose, indicating that the fatigue life of a crystal is determined by the shear component of the applied stress. A few crystals were also fatigued at 50 c/s, and it is shown that failure is dependent on time of testing rather than on ihe number of cycles. Fracture of zinc crystals by fatigue usually takes place by cleavage across the basal plane, and this initiates in a direction parallel to the active slip direction. During fatigue, specimens harden during approximately ihe first 3 x 10/sup 4/ cycles, and the flow stresses produced are one hundred times that of a virgin crystal A logarithmic law of recovery has been deduced for fatigue-hardened crystals rested at room temperature. A method has been developed for measuring hysteresis loops during fatigue, and it has been found that the amount of plastic strain per cycle decreases with ineleasing number of reversals for the first 10% of life and then remains constant for the remainder. (auth)},
doi = {},
url = {https://www.osti.gov/biblio/4217509}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1960},
month = {10}
}

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