<p>In this doctoral thesis work, the impacts of alternative
constituent material’s impact on low-cost prepreg manufacturing for high volume
applications will be considered. Unidirectional prepregs offer the potential
for significant increase of specific-properties and thereby weight savings.
Hence the automotive industry is seeking to utilize composite components in
their design, in order to meet new fuel economy ratings and global emissions
targets imposed by governments. New resin formulations to achieve 3-minute
cycle times or low-cost carbon fiber manufacturing have been created to address
the needs of the automotive and other cost-sensitive industries, however these
innovations have led to challenges in the composites manufacturing process.
Quality control issues may include variations in resin saturation of the fiber
bed, consolidation, porosity, and fiber volume fraction. These quality issues
arise in the part forming step or from the initial resin infiltration during
prepregging.</p>
<p> </p>
<p>Some low-cost carbon fiber has a kidney-bean shaped cross-section
which has implications on the compaction and permeability of the fiber bed. The
kidney-bean shaped fibers were shown in this work to follow a different
compaction trend compared to circular fibers. Furthermore, these fibers
required an order of magnitude larger force to compact than circular fibers to
achieve similar fiber volume fraction, which had implications on the
infiltration and consolidation step. A shape correction factor based on the
fiber cross-sectional aspect ratio was proposed to extend the existing
compaction model to fibers with irregular cross-sectional shapes. Additionally,
permeability simulations were performed on the kidney-bean shaped carbon fiber
in various fiber packing unit cells. Since the kidney-bean shaped fiber had
some degree of asymmetry, there are two valid hexagonal packing arrangements.
At a minimum, the hexagonal packed unit cell orientation caused a 17% reduction
in permeability for the same unit cell and fiber volume fraction between
the <u>+</u>90° and 0° orientations. In the most extreme case, a 47% reduction
in the permeability was observed between the <u>+</u>90° and 0°
orientations. Depending on the fiber orientation, comparable permeabilities to
circular fibers were attained or up to a 74% reduction in permeability. This
means a selection of low-cost carbon fiber could cause the infiltration time to
be up to 3.86 longer than for a traditional carbon fiber.</p>
<p> </p>
<p>The low-cost carbon fiber was paired with a rapid cure epoxy resin
which contained internal mold-release to further improve part cycle times to
3-minutes and reduce part costs. The effect of polar and non-polar internal
mold-release was studied for its potential influence on cure kinetics. The
polar internal mold-release caused a 20 second delay in the 3-minute part
cycle, which increased the cycle time by 10% and would therefore influence part
production schedules. This prepreg system was reported to have prepreg quality
issues related to solids filtering during infiltration. A hot-melt prepregging
process was modeled for S-wrap and nip-roller configurations. The S-wrap
process was found to better suited for prepregging multi-phase resins since
lower pressures were used. Additionally, a general rule was established when
working with multi-phase resins was established, particle diameters should not
exceed fiber radii.</p>
<p> </p>
<p>The general design principles from the thermoset hot-melt
prepregging were used to develop a thermoplastic prepreg tape line.
Thermoplastic composites lend themselves to efficient manufacturing processes
such as hybrid overmolding which is suitable for the automotive industry.
polyamide-66/Kevlar<sup>®</sup> prepreg tapes were manufactured at various
line tensions. Neat, rubber toughened, and glass bead filled polyamide-66 based
resins were considered. The neat polyamide-66 resin provided a baseline and was
able to consistently saturate the fiber bed up to 400µm regardless of
manufacturing conditions. The addition of rubber particles did reduce the
infiltration distances from the base resin by 20% with significant a
significant 50% reduction when the fiber volume fraction reached 0.70. While
the addition of glass particles significantly reduced the infiltration
distances by up to 70% across all manufacturing conditions. The reduction in
flow distance resulted in poor infiltration in thicker fiber beds.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/16655386 |
| Date | 22 November 2021 |
| Creators | Alex M Reichanadter (11422265) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Cost-Effective_Prepreg_Manufacturing_for_High-Volume_Applications/16655386 |
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