There are several issues to be solved in the fracture mechanics of shape memory alloys, one of them being the resistance to crack growth and therefore to fracture. This paper discusses the crack growth in a single crystal CoNiAl shape memory alloy under cyclic loading and the effect of micro-structural barriers. To observe the crack growth in detail, tests are conducted on edge-notched specimens. The displacement field is obtained using digital image correlation (DIC), and the fracture parameters are calculated by fitting anisotropic crack tip displacement equations to DIC data. Similar crack growth behaviors are observed in both superelastic and shape memory specimens, with a comparatively higher crack growth rate in the superelastic case: first a crack initiates at the notch and grows, then new cracks are observed to form near the tip of the main crack, or on the notch when the growth slows down. Then, further cyclic loading leads to the growth of the main crack and the new crack simultaneously with the two cracks merging at the end. Test specimens are examined post-failure with optical microscopy to better understand this complicated behavior. Results showed the presence of a non-transforming secondary (
The discrete crack mechanics (DCM) method is a dislocation‐based crack modeling technique where cracks are constructed using Volterra dislocation loops. The method allows for the natural introduction of displacement discontinuities, avoiding numerically expensive techniques. Mesh dependence in existing computational modeling of crack growth is eliminated by utilizing a superposition procedure. The elastic field of cracks in finite bodies is separated into two parts: the infinite‐medium solution of discrete dislocations and an finite element method solution of a correction problem that satisfies external boundary conditions. In the DCM, a crack is represented by a dislocation array with a fixed outer loop determining the crack tip position encompassing additional concentric loops free to expand or contract. Solving for the equilibrium positions of the inner loops gives the crack shape and stress field. The equation of motion governing the crack tip is developed for quasi‐static growth problems. Convergence and accuracy of the DCM method are verified with two‐ and three‐dimensional problems with well‐known solutions. Crack growth is simulated under load and displacement (rotation) control. In the latter case, a semicircular surface crack in a bent prismatic beam is shown to change shape as it propagates inward, stopping as the imposed rotation is accommodated.
more » « less- NSF-PAR ID:
- 10075750
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- International Journal for Numerical Methods in Engineering
- Volume:
- 117
- Issue:
- 1
- ISSN:
- 0029-5981
- Page Range / eLocation ID:
- p. 38-62
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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