The dominant micromechanisms of dynamic failure initiation in high-strength
ductile steels were investigated using 2.3Ni-1.3Cr-0.17C steel. Fracture e
xperiments were conducted in three-point bend and one-point bend configurat
ions. The influence of loading rate on the extent of each micromechanism in
the fracture-initiation process was considered. The fracture surfaces cons
isted of a tunneled region and shear lips. The shear lips are characterized
by microvoids. The tunneled region consists of large voids and microvoids
that coalesced by impingement. At high loading rates, localized molten zone
s are observed at the tunnel-shear lip interface. The material-rate sensiti
vity causes a decrease in the size of the tunneled area at higher loading r
ates.