Complex Geometries and Prepreg Format – M.C. Gill Composites Center

Micrographs for the flat laminate baseline. Note how the control is seemingly free of voids, while USCPreg shows visible porosity.

Micrographs for Embedded Ply Drop Parts for both Control and UdSCPreg — Micrographs for the embedded ply-drop parts. Of note is the large bubble and resin accumulation in the edge of the embedded plies for the control.

Micrographs for the thick laminate part for both control and UdSCPreg — Micrographs for the thick laminate parts. While both parts exhibit some porosity, the internal void content for the USCPreg part is much lower than for the control.

Micrographs for the sharp corner parts — Micrographs for some of the corner parts. Comparing the first two shows the lower void content for USCPreg. Comparing the last two shows the difference between convex and concave curvature, with concave resulting in corner thickening, and convex in corner thinning.

Bulk Porosity Results Graph — Graph showing the results for internal porosity for all seven geometries.

Researcher – Patricio Martinez

Carbon fiber composite parts commonly include complex features such as corners and curvature, internal ply drop-offs, and thick sections. These features can cut off or limit internal air evacuation pathways, or provide pressure gradients in the part, resulting in entrapped voids and resin accumulation. We seek to, by using a novel prepreg format, minimize the effects these geometric features have on internal porosity.

A prepreg format being currently studied and developed, USCPreg, has been shown to reduce the impact of non-ideal processing conditions on internal porosity. This study adds upon that, showing that similarly, USCPreg can be used to minimize the increase in internal porosity due to complex part geometry.

The study compared a common industry UD prepreg, the control, to USCPreg. Seven different geometries were studied: A flat laminate to use as baseline, a laminate with an internal ply-drop, a laminate with 8 times as many plies, and two different corners, sharp and smooth, each with a concave and convex geometry.

From the results, it was seen that while USCPreg may not have as low internal porosity for the flat baseline, the increase in porosity due to complex geometries is lower when compared to the control.