Smaaart task order SOW - slit-tape buckling AFP process characterization. 1.0 introduction and background: as part of the advanced composites project (ACP), NASA is partnering with the aerospace…

Smaaart task order SOW - slit-tape buckling AFP process characterization. 1.0 introduction and background: as part of the advanced composites project (ACP), NASA is partnering with the aerospace industry to significantly reduce the timeline to certify composite structure for commercial and military aeronautic vehicles. Three main focus areas, or technical challenges, have been identified by NASA and industry as having major impact on the current certification timeline. The ACP third technical challenge (TC3), manufacturing process and simulation, is concerned with reducing the occurrence of defects which commonly occur in aerospace composite structures as a result of the processing methods utilized to fabricate these large, highly complex vehicles. One of the objectives in TC3 is to develop physics-based process models which are capable of accurately predicting the formation of defects during robotic, automated fiber placement (AFP) of composite structure. While the efficiency demonstrated in AFP has led to its adoption by the aerospace industry for fabrication of aircraft fuselage, wing, and engine nacelle primary composite structures, the potential advantages have not been fully realized due to the occurrence of performance reducing defects which result in costly and time-consuming rework. The development of accurate AFP process models will give aircraft manufacturers the ability to predict defects which occur due to the physical relationship between the material, the part tooling, and the AFP processing parameters. This science-based approach to maximizing part quality has proven successful in other composite processing methodologies such as infusion flow prediction and cure process defects such as residual stress. However, currently no validated physics-based process model exists to predict defects such as fiber / tape buckling, also referred to as fiber waviness, wrinkling, puckering, or window-shading. An AFP process model which accurately predicts process defects will significantly reduce the trial and error fabrication effort required to meet production certification of aerospace composite structure. The work described in this SOW is intended to address fabrication issues that have a negative impact on the timeline required to certify composite structures. The intention of this task order is to characterize the AFP process parameters during the fabrication of parts which in the past have been demonstrated to contain defects such as wrinkling or puckering. The government will utilize a well characterized aerospace toughened epoxy material, hexcel IM7 / 8552-1 prepreg, so that the characterization study is focused on the AFP placement parameters which affect the formation of the wrinkling / puckering defects. These processing parameters, for example, include but are not limited to: placement speed, compaction load, material temperature, and/or head turning radius. The geometry used to evaluate the various AFP processing parameters will be limited to the type and form which has been demonstrated in previous builds by the fabricator to result in formation of the wrinkling / puckering defects. The results of this AFP processing characterization effort will be utilized in the future development of an AFP physics-based process model to predict these types of defects. 2.0 scope & objective(s): 2.1 the scope of this task order is to fabricate composite panels using the AFP process and characterize the AFP process by measuring the processing parameters which result in fiber / tape buckling defects (wrinkling / puckering). 2.2 the objectives of this task order are to: a. Determine AFP placement parameters and placement parameter interactions which influence the formation and magnitude of wrinkling / puckering defects for the fixed part geometry fabricated using 0.25 wide hexcel IM7 / 8552-1 slit-tape prepreg. B. Empirically characterize the AFP processing parameters and quantify