Warping of flat composite isogrid panels

This paper describes the analyses performed to determine why nominally flat composite isogrid panels designed for the Clementine satellite were warping during the autoclave cure cycle. Analytical models indicated that the largest factor was the mismatch in the coefficient of thermal expansion of different parts of the tooling. The next most important factor was the coefficient of thermal expansion mismatch between the skin and rib materials of the composite isogrid itself. A new tooling design eliminated the first factor, producing a rib only panel with no warping. An analytical model was developed, which predicted that warping caused by the rib/skin mismatch would be 3.31 mm over a length of 147.32 cm. A panel with the skin was manufactured and found to have a warp of 3.80 mm. Further improvements in producing flat panels will depend on finding appropriate materials for the rib and skin.