Effects of prior ductile tearing on cleavage fracture in the ductile-to-brittle transition region
Experimental studies demonstrate a significant effect of specimen size, a/W ratio and prior ductile tearing on cleavage fracture toughness values ($J\sb{c}$) measured in the ductile-to-brittle transition region of ferritic materials. In the lower-transition region, cleavage fracture often occurs under conditions of large-scale yielding but without prior ductile crack extension. The increased toughness develops when plastic zones formed at the crack tip interact with nearby specimen surfaces which relaxes crack-tip constraint (stress triaxiality). In the mid-to-upper transition region, small amounts of ductile crack extension (typically $<$1-2 mm) routinely precede termination of the ${J-\Delta a}$ curve by brittle fracture. Large-scale yielding, coupled with small amounts of ductile tearing, magnifies the impact of small variations in microscale material properties on the macroscopic fracture toughness which contributes to the large amount scatter observed in measured $J\sb{c}$-values.
Applied Mechanics, Engineering, Civil, Engineering, Mechanical
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign