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Micro-CT Inspection of Impact Damage in Carbon/Epoxy Rods

LINDSEY STANFORD, and DAVID JENSEN

Abstract


Various configurations of unidirectional carbon/epoxy composite rods were impacted radially, inspected using micro-CT scanning equipment, and tested in axial compression to measure the residual strength after impact. The micro-CT data was used to calculate the peak crack area at a cross-section, and the total integrated crack volume along the entire length of the rods. This data was used to correlate the relationship between impact energy, internal damage, and residual strength. Solid cylindrical structural rods represent local members in three-dimensional composite lattice structures (e.g., based on Isogrid or IsoTruss® geometries). Unidirectional core specimens, 8 mm (5/16â€) in diameter, were consolidated with various sleeve configurations and materials: i.e., sleeves differed in types (bidirectional braided or unidirectional spiral wraps), nominal sleeve coverage (full or half), and sleeve material (Nomex thread or Dunstone Hi-Shrink Tape). The unsupported length of the specimens used in this research was 50.8 mm (2â€), ensuring a strength-controlled compression failure. The specimens were radially impacted with 2.5, 5.0, 7.5, 10.0, 15.0, and 20.0 J (1.9, 3.7, 5.6, 7.4, 11.1, and 14.8 ft-lbs), and compared to undamaged control specimens. After impact, the specimens were scanned using a Micro-CT Scanner at resolutions of 50 and 35 microns and subsequently tested in axial compression. The micro-CT scan images were analyzed and the peak crack area and total crack volume along the length of the specimen were measured. Similar to related research, as the impact energy increases, the residual compression-strength-afterimpact decreases. Specimens with shrink tape sleeves had the largest increase in peak crack area and overall crack volume while specimens with full spiral sleeves had the lowest increase in peak crack area and overall crack volume. A minor correlation exists between increases in peak crack area and overall crack volume and decreases in residual compression strength after impact.

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