Compressibility measurement of composite reinforcements for flow simulation of vacuum infusion

In flow simulation of liquid composite molding under a flexible cover, such as vacuum infusion (VI), the accuracy can be improved by accounting for the compressibility of the reinforcement. The compressibility has been predominately measured using a universal testing machine (UTM) but discrepancies have been observed between the compressibility determined by UTM testing and that in situ during VI processing. The differences between the two are thought to be due to (1) differences in hydrodynamic loading and (2) precision difficulties related to the small displacements being measured. In situ VI compressibility characterization is more difficult and requires specialized equipment. This study aims to validate the use of UTM‐measured compressibility in VI flow simulation, by investigating the agreement between the two measurement methods, and to develop an experimental methodology to optimize that agreement. Wet UTM testing was instrumented with pressure sensors, which allowed for a thorough investigation of the validity of model predictions of the fluid pressure. Matching the test conditions, as well as careful thickness calibration, resulted in good agreement between dry UTM and VI compressibility. Dry UTM testing resulted in better agreement with VI than wet UTM testing. This suggests that dry UTM measurement of the compressibility is sufficient and wet testing is ultimately unnecessary for the purposes of flow simulation. POLYM. COMPOS., 40:961–973, 2019. © 2018 Society of Plastics Engineers