Influence of consolidation and interweaving on compression behavior of IsoTruss™ structures

摘要

The patented IsoTruss™ grid structure is a revolutionary configuration that utilizes a unique geometry with lightweight composite materials to efficiently support loads. IsoTruss™ structures consist of interwoven longitudinal and helical members composed of intersecting fiber tows at joints. Spreading the fibers to achieve mechanical interlocking for increased joint integrity introduces gaps and curvilinear fiber paths. Such nonlinearities could initiate local de-lamination, reducing the overall structural strength and potentially limiting fatigue life. These effects can be minimized by optimizing tow interweaving pattern and proper fiber consolidation. This research quantified the effects of these parameters on the local compressive strength of composite lattice structures. Test specimens were fabricated on a special braiding machine using 12K tow TCR T300C-200NT carbon fiber pre-impregnated with Thiokol UF3325-95 resin. Two configurations of longitudinal and helical fiber interlocking at the joints were investigated: 1) complete encapsulation; and, 2) uniform interweaving. Six local member consolidation methods were investigated: 1) braided sleeves; 2) coiled sleeves; 3) sparse spiral wraps; 4) shrink tape sleeves; 5) twisted tows; and, 6) cinched tows. The unsupported length of the specimens during compression testing was approximately 1.50 inches (3.81 cm). Interwoven joints reduced the compressive strength by 30%, compared to a 5% reduction for encapsulated joints. Braided sleeves yielded the highest strength, with twisted members yielding the lowest strength.