Interim report: directional stability of a propagating crack
Various theories on the angle of initial crack extension are reviewed and compared. The maximum circumferential stress theory including second order effects describes adequately the behavior of crack growth. In addition, other theories currently in the literature reduce the maximum circumferential stress theory if one investigates only the stress singularity. Note that this stress is generally not a principal stress, as is often assumed, because of an inherent difference in the second order terms. If crack initiation occurs at some critical distance in front of the crack tip, it is shown that the maximum circumferential stress theory yields the following simple directional stability criterion: The crack geometry critical distance must be greater than the distance to crack initiation. For photoelastic specimens, this criterion requires that the fringe angle at the crack tip be less than 123 deg. Preliminary tests verify these results. A new fracture test to further investigate the directional stability criteria was designated. Applying lengthwise compression parallel to the crack direction enabled us to control crack direction; thus, unstable specimens can yield valid fracture data.
- Research Organization:
- California Univ., Livermore (USA). Lawrence Livermore Lab.
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 7277520
- Report Number(s):
- UCID-17717
- Country of Publication:
- United States
- Language:
- English
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