Description: Thick, 3D woven carbon/phenolic composites offer potential improvement over legacy thermal protection systems (TPS) for re-entry vehicle heat shield applications. However due to the scale and complexity of typical re-entry vehicle structures, it is likely that multiple 3D woven panels would need to laid up to create the overall heat shield, creating a potential weak spots at the panel joints. T.E.A.M., Inc. proposes to address the joint issue by developing an innovative stitching process capable of forming mechanically reinforced joints between densely woven, 3D carbon fiber pre-forms up to 3" thick. The Phase I scope will include design, model and fabrication of multiple stitched joint specimens, which will be tensile tested to characterize relative strengths of various joint configurations as a function of stitching parameters used. Results will enable calibration of the initial model as well as initial design of a scaled up process capable of producing a full scale, net-shape re-entry vehicle structure within Phase II.

Benefits: The proposed innovation is directly relevant to NASA Ames' 3D-woven carbon/phenolic thermal protection system (3D-TPS) for re-entry vehicle heat shield applications. The proposed innovation will enable the mechanical joining of thick 3D woven carbon fiber preforms (up to 3" thick), which in turn will enable multiple panels of the 3D-TPS material system to be assembled into actual re-entry vehicle geometries. Similarly, the proposed innovation will also enable joining of thinner 3D woven carbon substrates, which will allow the fabrication of the complex geometries required for NASA's deployable aeroshell application.

The proposed innovation will create the capability to stitch/join together carbon fiber preform assemblies with geometries too complex for existing textile processes, including 3D weaving, to achieve. Potential commercial applications thus include those composite applications where through thickness strength AND complex geometry are both required. Examples include composite armor for military vehicles and structural composites for aerospace including stitched skin + core assemblies, stitched joint assemblies and stitched skin + web-stiffener assemblies.