<p>When a composite laminate is
transversely impacted by a projectile at the ballistic limit, its failure mode
transits from global conical deformation to localized perforation. This Ph.D.
dissertation aims to reveal the fundamental material failure mechanism at the
ballistic limit to control perforation. First, transverse impact experiments
were designed on composite strips to isolate the interaction between plies and
tows. Three failure modes were identified, divided by no, partial, and complete
failure before the transverse wave deformed the entire composite strip. The
failure phenomenon and critical velocity region can differ with the fiber type
and projectile nose geometry and dimension. In most impact events, the
composite strips all failed in tension in the front of the projectiles,
although they failed at different positions as the projectile nose geometry and
fiber type changed. A special failure phenomenon was uncovered when the composite
strips were impacted onto razor blades above the upper limit of the critical
velocity region: the composite strips seemed to be cut through completely by
the razor blades. To further investigate the failure by razor blade, a
microscopic method was developed to cut a single fiber extracted from the
composite strip and simultaneously image the failure process inside a Scanning
Electron Microscope (SEM). The experiments revealed that the razor blade cannot
cut through the inorganic S-2 glass fibers while can partially incision the
aramid Kevlar<sup>® </sup>KM2 Plus fibers and completely shear through the ultra-high-molecular-weight
polyethylene (UHMWPE) Dyneema<sup>®</sup> SK76 fibers. Further investigations
on the fiber’s failure under dynamic cut revealed that there was no variation
in the failure mode when the cut speed was increased from 1.67 μm/s to ~5.34
m/s. To record the local dynamic failure inside the composite strips and single
fibers at high-velocity impact, an advanced imaging technique, high-speed
synchrotron X-ray phase-contrast imaging, was introduced, which allows to
capture the composite’s internal failure with a resolution of up to 1.6
μm/pixel and at a time interval 0.1 μs. Integrated with a reverse impact
technique, such an advanced imaging technique is believed to be capable of
revealing the mechanism involved in the impact-induced cut in single fibers,
yarns, and composite strips. The relevant studies will be the extended work of
this Ph.D. dissertation and published in the future.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/15049095 |
| Date | 30 July 2021 |
| Creators | Jinling Gao (8330913) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/CHARACTERIZATION_OF_FAILURE_OF_COMPOSITE_STRIPS_AND_SINGLE_FIBERS_UNDER_EXTREME_TRANSVERSE_LOADING/15049095 |
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