#### Vol. 3, No. 2, 2008

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Investigation of mode II crack growth following a very high speed impact

### Wei Ma and Zhuping Duan

Vol. 3 (2008), No. 2, 271–290
##### Abstract

A recoverable plate impact testing technology has been developed for studying fracture mechanisms of mode II crack. With this technology, a single duration stress pulse with submicrosecond duration and high loading rates, up to $1{0}^{8}$ MPa m${}^{1∕2}$s${}^{-1}$, can be produced. Dynamic failure tests of Hard-C $6{0}^{#}$ steel were carried out under asymmetrical impacting conditions with short stress-pulse loading. Experimental results show that the nucleation and growth of several microcracks ahead of the crack tip, and the interactions between them, induce unsteady crack growth. Failure mode transitions during crack growth, both from mode I crack to mode II and from brittle to ductile fracture, were observed. Based on experimental observations, a discontinuous crack growth model was established. Analysis of the crack growth mechanisms using our model shows that the shear crack extension is unsteady when the extending speed is between the Rayleigh wave speed and the shear wave speed . However, when the crack advancing speed is beyond , the crack grows at a steady intersonic speed approaching . It also shows that the transient mechanisms, such as nucleation, growth, interaction and coalescence among microcracks, make the main crack speed jump from subsonic to intersonic and the steady growth of all the subcracks causes the main crack to grow at a stable intersonic speed.

##### Keywords
plate impact tests, dynamic fracture, failure mode transition, intersonic crack extension, discontinuous crack growth model
##### Milestones
Received: 19 June 2006
Revised: 30 May 2007
Accepted: 31 May 2007
Published: 1 February 2008
##### Authors
 Wei Ma Institute of Mechanics Chinese Academy of Sciences 15 Beisihuanxi Road Beijing 100080 China Zhuping Duan Institute of Mechanics Chinese Academy of Sciences 15 Beisihuanxi Road Beijing 100080 China