A study of the damaging effect of fatigue stressing on SAE X4130 steel

Abstract

The damaging effect of fatigue stressing above the endurance limit was investigated with notched specimens of SAE X4130 steel. The damage was measured by the decrease in endurance at another stress. A deflection method for detecting the formation of a fatigue crack permitted the damage measurement to be limited chiefly to the pre crack stage. The results showed that the apparent rate of damage depends on the stress history. If the prestress is higher than the test stress, the damage occurs rapidly at first, then more slowly. The reverse is true if the damaging stress is lower than that used to measure the damage.Tests also were made with smooth specimens in an effort to determine the cumulative damage caused by fatigue at more than one stress. Two methods were developed for extrapolating to determine the point at which fatigue cracking starts, so the damaging cycle ratios could be based on the life of the specimens prior to cracking. Complete S-N curves were determined for specimens after each of eight different damaging treatments. With these curves a method of expressing damage was developed that permitted the direct addit ion of damage occurring at different stresses. The reliability of this method was checked by testing specimens after fatigue loading at two or more different stresses and comparing the results with predictions based on the addition of the indicated damage. The agreement was within the p.xperimental error.

Effect of chromium plating on the endurance limit of steels used in aircraft

“…Bennett [11] has shown that notches reduce the endurance limit of normalized X4130 steel approximately 20 p ercent and that fine cracks reduce the endurance limit by more than 50 p er cent. The presence of cracks in the chromium plated at 55° and 70° C might explain the r eduction in the endurance limits of steel specimens plated at these temperatures.…”

Fatigue notch sensitivity of some aluminum alloys

“…In previous investigations at the Bureau small cracks have been detected by (1) measurement of the increased deflection under the test load [9], (2) observation of the specimen under stroboscopic ligh t [6], and (3) the use of fracture wires [10] .…”

Intrinsic Factors that Trigger the Coaxing Effect in Binary Fe–C Ferritic Alloys with a Focus on Strain Aging

“…The latter factor likely plays an important role in the appearance of the coaxing effect in ferritic steels. 10) Assuming that strain-age hardening is important, the coaxing effect must be a kinetic problem. More specifically, the coaxing effect is considered to depend on the aging time (not the number of cycles), the plastic strain at a crack tip, and the carbon concentration.…”

“…Interestingly, a specimen fatigued at the fatigue limit does not show failure even after a slight increase in the stress amplitude. 9,10) This phenomenon is called the "coax-…”