Abstract
Results of in situ high resolution X-ray computed tomography are reported for a notched tensile sample of Al-Li 2090 T841. The fatigue crack within the interior of the sample is imaged with 6 μm voxels as a function of applied load, and the crack face morphology is found to be similar to that observed in compact tension samples of this alloy. The loads and approximate stress intensities at which the tomography data were obtained were 82, 50, 25 and 5 kg and 7.1, 4.3, 2.2 and 0.4 MPa√m, respectively. Crack openings measured during unloading as a function of position show that physical closure at portions of the crack tip and at positions behind the crack tip precedes (during unloading) the bend in the sample's load-displacement curve. The three-dimensional pattern of crack opening shows substantial mixed mode I-III contact on the faces of asperities behind the crack tip, even at the maximum load of the fatigue cycle. Mixed mode I-II contact is also observed at loads above the bend in the load-displacement curve. The fraction of voxels open remains nearly constant for the loads immediately above and below the nominal closure load, as determined from the load-displacement curve, of 41 kg; and this suggests that these mixed mode I-III surfaces begin to carry significant load at the point where the load-displacement curve starts to deflect, and is the source of the apparent stiffening of the sample at loads below the nominal closure load.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1977-1987 |
| Number of pages | 11 |
| Journal | Acta Materialia |
| Volume | 45 |
| Issue number | 5 |
| DOIs | |
| State | Published - May 1997 |
Funding
Ackno~~led~emmts~This paper summarizes some of the PhD thesis “Investigation into Asperity-induced Closure in an AI-Li Alloy Using X-ray Tomography,” by A. Guvenilir, Georgia Institute of Technology, December 1995. This research was supported at the Georgia Institute of Technology by the Office of Naval Research (Grants N000144-89-J-1708 and N00014-94-1-0306) and by the Department of Energy (Contracts W-7495ENG-48 and E03802) at Lawrence Livermore National Laboratory. The computed tomography data were recorded at Lawrence Livermore National Laboratory, and the mechanical testing was done at the Mechanical Properties Research Laboratory of the Georgia Institute of Technology. We thank Mr R. C. Brown of Mechanical Properties Research Laboratory for his assistance with mechanical testing; Professor Ashok Saxena of the School of Materials Science and Engineering for his advice concerning approximations for the stress intensity factor in notched tensile samples; Messrs W. N. Massey and R. A. Saroyan for their assistance with the tomographic imaging and Dr G. R. Yoder for numerous valuable discussions. The work of Dr H-Y Jung and Professor S. D. Antolovich, both formerly at Georgia Tech, was a valuable counterpoint to the work described thank them for their interactions.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Polymers and Plastics
- Metals and Alloys