Aj. Mcevily et al., COMPARISON OF THE FRACTOGRAPHIC FEATURES OF A CARBURIZED STEEL FRACTURED UNDER MONOTONIC OR CYCLIC LOADING, Materials characterization, 36(4-5), 1996, pp. 153-157
In failure analysis, in order to determine whether a component has fai
led under monotonic or cyclic loading, it is sometimes necessary to de
velop standards for each type of failure, especially when the fracture
surface of a part that has failed in service contains features which
may be ambiguous in their interpretation. Such is the case in the pres
ent instance, where in order to categorize the fractographic features
of an AISI 9310 carburized steel, failures under monotonic and cyclic
loading had to be obtained, The specimens were round bars which contai
ned a circumferential semicircular notch, and were loaded in four-poin
t bending. The effective case depth of the carburized layer was 1 mm,
with a hardness of 60 HRC. The core hardness was 40 HRC (''R(c)''). Un
der monotonic loading, a circumferential crack developed in the case n
ear the case-core interface, and striationlike markings were observed
at low magnification on the fracture surface of the core which might b
e interpreted as fatigue markings. On the other hand, under cyclic loa
ding, no circumferential cracks were observed in the case near the fra
cture origin, but they did develop in the region of final separation.
In addition, the fracture surface in the core was markedly different i
n appearance from that obtained under monotonic conditions. These diff
erences were further established by scanning electron microscopy analy
sis. The factors giving rise to the various fractographic features are
discussed. (C) Elsevier Science Inc., 1996.