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Eighty-eight automobile rear axles taken from production stock were subjected to fatigue loading in rotating bending. These axles were made from NE 8650 steel, quenched and tempered to 388 to 444 Brinell. These axles were unmachined in the tapered body portion between the splined end and bearing seat adjacent to the wheel; fatigue failure in service and in these tests developed in this body section. Seven different conditions were investigated as to their influence on axle fatigue strength, which included the effect of straightening, three degrees of shot peening, and recarburization. Unstraightened axles had about 25 per cent higher endurance limit than straightened ones. This decrease in fatigue resistance was accompanied by surface tensile stresses of about 120,000 psi. induced by cold-straightening. Shot peening of straightened axles gives about three times the endurance limit of those not peened. Axles were also recarburized and then accidentally became slightly decarburized in heat treatment. Their fatigue resistance was not improved by this process even though the decarburization was shallow compared with axles not given a carbon-restoration treatment.
Horger, O. J.
Chief, Timken Roller Bearing Co., Canton, Ohio
Lipson, C. H.
Head, Chrysler Corp., Detroit, Mich.