The lay-up performance during automated material placement (AMP) is significantly affected by the quality of adhesion (tack) at the interface. To optimize AMP process parameters, tack of different surfaces was characterized for multiple aerospace grade unidirectional tapes. A peel test fixture, developed jointly with the University of Nottingham and currently residing at multiple Boeing locations, was initially used to measure tack between a prepreg and a steel substrate. Modifications of the test methodology enabled the measurement of prepreg-to-prepreg tack and prepreg-to-fluorinated ethylene propylene (FEP) tack. In general, the test parameters, feed rate, and temperature affect the balance between cohesion within the resin and adhesion between resin and substrate. Changes in molecular mobility in the resin related to specimen conditioning (i.e., aging or moisture uptake) result in maximum tack to occur at lower or higher feed rates, respectively. The developed test method was released as ASTM D8336 in 2021 as a way to quantify prepreg tack as a function of speed and temperature. Additionally, the prepreg peel data can be can be used to fit the material constants for physics-based tack models as demonstrated by Convergent Manufacturing Technologies. These tack models can be used in a finite element simulation for prediction of layup defects during AMP.

Augmenting automated material placement via material characterization

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