Compressibility measurement of composite reinforcements for flow simulation of vacuum infusion

Abstract

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., 00:000-000, FIG. 4. Compaction (a,c) and expansion (b,d) P R (r) measurement (symbols) and calculation (lines) for carbon UD weave (top) and biax NCF (bottom). Dashed black line indicates the start of dwell (a,c) or end of expansion (b,d). [Color figure can be viewed at wileyonlinelibrary.com]

Monitoring and modeling of part thickness evolution in vacuum infusion process

“…The characterization is mainly performed in two-sided rigid molds to maintain a constant thickness, and the spatial and temporal variation of thickness in VI contradicts with this requirement. However, as recently demonstrated by George et al, 69,70 experimental data of thickness variation and its dependence on compaction pressure can be used to adequately characterize permeability and compaction behaviors. A single mold filling experiment was conducted in a setup similar to the VI setup introduced in this work, and the approach is based on minimization of the deviation between experimental results and results of an analytical flow propagation model.…”

Advances in composite forming through 25 years of ESAFORM

“…Local permeability is affected by compaction of the preform, which directly changes the fibre volume fraction. The in-plane permeability phenomenon was studied experimentally in coupled compression-permeability experiments [59,238] and directly during infusion involving progressive preform compression [239]. Theoretical treatment of the flow/ deformation coupling can be found in [240,241].…”

Optical measurement of voids in situ during infusion of carbon reinforcements

“…The primary differences between parts produced via LCM and prepreg-autoclave manufacturing methods are part homogeneity and void content. Part homogeneity is particularly a problem in VI processes due to the thickness gradient inherent to using a flexible mold, 3 but can also be a problem in RTM processing due to the pressure gradient’s effects on the distribution of voids. 4 Void content is a measure of the amount of gas that is trapped within a finished composite part.…”