High Cycle Fatigue: A Mechanics of Materials Perspective part 38. The nomenclature used in this book may differ somewhat from what is considered standard or common usage. In such instances, this has been noted in a footnote. Additionally, units of measurement are not standard in many cases. While technical publications typically adhere to SI units these days, much of the work published by the engine manufacturers in the United States is presented using English units (pounds, inches, for example), because these are the units used as standard practice in that industry. The graphs and calculations came in those units and no attempt was made to convert. | 356 Effects of Damage on HCF Properties nothing changes during the SR process other than the removal of residual stresses. This finding is consistent with that discussed in the previous section for impact on leading edge geometries. Of greater significance is the observation that ballistic impacts to the same depth as pendulum or quasi-static indentations are more severe in terms of the resulting fatigue limit strength reduction. This is especially true for the deeper indents corresponding to ballistic impacts at 300 m s. In the work of Peters et al. 2 the impacts at 300 m s produced small amounts of cracking at the crater whereas the impacts at 200 m s produced no observable cracks. This shows that low velocity pendulum or quasi-static indentation does not produce the same amount of damage as ballistic impact for this material under the specific impact conditions depth of indent described particularly at higher velocities. Results for the tests in torsion are summarized in Table . Here only ballistic impacts were evaluated at R 0 for both AR and SR samples and R -1 for AR only. The SR samples show a reduction in kf which is equivalent to an increase in ctfls. This is attributed to the implied existence of tensile residual stresses in the failure region. The value of kt in Table for a deep notch in tension indicates that fracture would be expected at the bottom of the notch. This is confirmed by the observed location of initiation near the notch bottom as shown in Figure a . On the other hand torsion tests of a specimen Table . Experimental values of kf for ballistic notches under torsion Notch type R 0 R -1 AR shallow AR deep SR shallow SR deep - - a b Figure . Fractographs showing initiation sites in a tension b torsion. Foreign Object Damage 357 with a shallow notch would be expected to produce a failure near the surface because of the higher value of kt as listed in Table . The fractograph Figure b .
