Predicting post-impact damage growth and fatigue failures in stitched composites
- Clemson Univ., SC (United States). Dept. of Mechanical Engineering
This investigation modeled the post-impact fatigue failure and damage growth response of stitched This investigation modeled the post-impact fatigue failure and damage growth response carbon/epoxy panels. Uni-woven AS4 graphite [45/0/45/90]{sub 6S} laminates with four stitch densities were evaluated. Each preform was reinforced by a modified lock stitch using a stitch row spacing of either 1/4, 3/16, or 1/8 inches. The preforms were then consolidated with either a brittle or toughened resin. All test samples were initially damaged utilizing a drop-weight impactor set to deliver a uniform 1,500-in.-lb/in. energy level. Dye-enhanced radiography was used to monitor the state throughout the test phase of each sample. The fatigue tests were all conducted at 4-Hz and a stress ratio of {minus}5. All of the post-impact samples developed stable damage growth emanating from the damage site during fatigue loading. While circular delaminations are known to elongate into ellipses in unstitched samples, the stitched samples propagated narrow damage zones transverse to the loading direction, Experimental data from static compression-after-impact (CAI) evaluations are used to predict sample failure in the post-impact fatigue samples. Damage zone dimensions taken from the dye-enhanced radiographs of the CAI tests provided information on the critical damage zone length expected to develop prior to fatigue sample failure. These critical damage lengths are modeled using a point-stress failure criterion and an open-hole stress profile. The propagation of these narrow damage zones is also modeled empirically. A parameter is introduced which allows damage propagation states between stitched samples from the same material configuration to be correlated with a single exponential damage growth model.
- OSTI ID:
- 89881
- Report Number(s):
- CONF-9409291-; ISBN 1-56676-220-0; TRN: IM9536%%311
- Resource Relation:
- Conference: 9. technical conference of the American Society for Composites, Newark, DE (United States), 20-22 Sep 1994; Other Information: PBD: 1994; Related Information: Is Part Of Proceedings of the American Society for Composites: Ninth technical conference; PB: 1319 p.
- Country of Publication:
- United States
- Language:
- English
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