Crack Tip Plasticity By Classic Dislocation Dynamics

Abstract

Under very short pulse loads in range from 25 to 100 μs, crack tip plasticity a head of the crack tip in the mode I condition was investigated by discrete dislocation dynamics. The obtained dislocation array parameters such as the number of dislocations, dislocation distribution density, crack tip opening displacement and plastic zone size increase with the magnitude of stress intensity factor, KI and pulse durations. The numerical results were well compared with the experimental ones.

Experimental and Discrete Dislocation Dynamics Approach to Initiation of Cleavage Fracture under Short Pulse Loads

“…A dynamic stress intensity factor vs. time history is measured by the strain gage mounted near the crack tip. The method and the definition of the pulse duration in this work are the same as those used in the previous works (11)- (13) . The measured stress intensity could be approximated as a sinusoidal function of the time.…”

“…Therefore, the effect of the dislocations on two slip lines at the other crack tip could be neglected to calculate stresses at dislocation positions on the slip lines at a considered crack tip. Instead of four arrays of discrete edge dislocations in the previous work (11) , the present dislocation model is represented by only two arrays at a crack tip in the plane strain condition. The slip lines are symmetric and inclined against the crack plane at angles ±α in an infinite elastic plane.…”

“…Because it is extremely complicated to deal analytically with real dislocation movement in a polycrystalline material such as SM490A used in the experiment, the previous work (11) used a fairly simple model using discrete dislocation movement along a straight slip line in a homogeneous and isotropic material. Although the highly simplified model was used, the calculated result could agree well with the loading time effect on the crack tip opening displacement obtained by the experiment.…”

“…In the previous work (11) , a dislocation model is represented by four symmetrical arrays of discrete edge dislocations ahead of both crack tips. Two slip lines at each crack tip are inclined against the crack line at angles±α and ±(π-α), respectively.…”

“…In the previous work (11) , the authors can successfully represent the crack tip plasticity, especially crack tip opening displacement under short pulse loading by numerical analysis using a discrete dislocation dynamic model. This work aims to extend this model for crack tip plasticity to cleavage fracture initiation and obtain the insight into loading time effect on the cleavage fracture initiation from a crack subjected to very short pulse loading.…”