Hot Drape Forming Analysis of Thermoset Materials
Composite materials are becoming prevalent in aerospace industries but a full understanding of how processing these materials leads to potential defects still needs to be fully characterized. This paper investigates the effect of forming temperature, ply count, fiber type, and fabric type on out-of-plane wrinkle development for a hot drape formed, double-joggle c-channel. Tensile tests were performed on wrinkled samples to understand the effect that the wrinkle size has on mechanical properties. Influential parameters were identified as the forming temperature affecting the resin viscosity, the weave type, and the fiber type. A decrease of the resin viscosity reduced the generated wrinkles. This is attributed to the improved interlaminar slippage with lower viscosity. The same effect was also observed with increased fiber twist. The 8 harness weaves eliminated out-of-plane wrinkles as compared to tape or plain weave spars. Increasing the ply count increases the complexity and thus the likelihood of wrinkle formation but was not identified as a driving factor for wrinkles. The results show that the primary influencing factor of hot drape forming is the interlaminar slip. Mechanical tests were also performed and showed that wrinkles with an L/D less than 10 create a large reduction of tensile strength as compared to non-wrinkled samples. Wrinkles with L/D ≥15 show comparable tensile strength to non-wrinkled samples.
Author: Zeaid Hasan
Conference: SAMPE Seattle 2017