Compression strength after impact tests were conducted on unidirectional composite rods with sleeves. These elements represent local members of open three-dimensional composite lattice structures (e.g., based on isogrid or IsoTruss® technologies). The unidirectional cores composed of carbon, glass, or basalt fiber/epoxy composites were co-cured in aramid sleeves. Sleeve patterns included both bi-directional (unsymmetric) braids and unidirectional spiral wraps with sleeve coverage ranging from nominally half to full. The diameters were nominally 8 and 11 mm (5/16 and 7/16 in). The larger diameter had nominally twice the cross-sectional area, to quantify the effects of scaling. The specimens were long enough to encourage local buckling failure as expected in members of typical composite lattice structures. The unsupported lengths varied from 127 mm (5.0 in) to 160 mm (6.3 in). Specimens were radially impacted at mid-length with energy levels ranging from 0 to 20 J (0 to 14.8 ft-lbs) and tested in longitudinal compression to quantify the effects of local impact damage on the buckling strength. In undamaged specimens, sleeve type and sleeve coverage have no effect on the ultimate compression strength of carbon, glass, or basalt composites (7% or less standard deviation for each material). When impacted, the influence of sleeve type and sleeve coverage varies with the type of fiber in the unidirectional core. Sleeve type and coverage did not affect the compression strength after impact for fiberglass composites. On the other hand, both carbon and basalt composites exhibited improved performance with braided (vs. spiral) sleeves (up to 34% stronger) and full (vs. half) coverage (up to 38% stronger). The compression strength of carbon configurations decreases with increasing impact energy regardless of sleeve type or coverage. The higher flexibility of glass and basalt composites, however, allowed some configurations to maintain the same compression strength after impact as their undamaged counterparts, at lower impact energy levels. Doubling cross-sectional area of basalt composites significantly improves the stiffness and compression strength after impact, more than doubling the impact energy required to achieve the same compression strength.



College and Department

Ira A. Fulton College of Engineering and Technology; Civil and Environmental Engineering



Date Submitted


Document Type





carbon, glass, basalt, fiber/epoxy composite, damage tolerance, IsoTruss®, compression strength after impact (CSAI), unidirectional, aramid/kevlar sleeves