A hybrid crack-tip element approach to therom-elastic cracks
- McDonnell Douglas Aerospace, Long Beach, CA (United States)
Airframe structures in High Speed Civil Transport (HSCT) are exposed to elevated temperatures during their service life due to aerodynamic heating. The thermally induced stresses may reduce the fatigue life and influence the crack growth rate in the structures. It has been shown that the characteristic of the stress field near a thermal crack is similar to that for a mechanically loaded crack. However, the value of J-integral is no longer path-independent in the presence of thermal loading. To evaluate the parameter, sometime called modified-J, additional integration over the area covered by the contour is required. An efficient solution method for stress intensity solutions is, therefore, needed to account for the thermal effect in the prediction model. The purpose of this paper is to extend the hybrid crack-tip element approach by Luk and Pian to thermoelastic cracks. First, the problem is reformulated in terms of an isothermal problem with a prescribed equilibrium body force and tractions by using Duhamel-Newman Analogy . The crack tip region is modeled by hybrid assumed stress approach in which the formulation is based on the assumed stresses in the interior and assumed displacements along the boundaries. In this way, the compatibility with the neighboring displacement-based elements can be assured. The crack-tip element consists of four subelement, within each the assumed stresses consist of three parts: a common singular K-field (the first two terms of William`s 2-D asymptotic series), a polynomial which is independent from one subelement to another, and a known thermal stress term. The stress intensity factors for a thermal crack are determined directly from the crack-tip singular stress field as it was embedded in the crack-tip element. As can be seen from the illustrated example problems, the current approach provides accurate solutions in terms of stress intensity factors with relatively small computational effort.
- OSTI ID:
- 175312
- Report Number(s):
- CONF-950686--
- Country of Publication:
- United States
- Language:
- English
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