Laser Assisted Processing of Composite Materials and Solar Cells
Inter-Laminar Toughening of Composites for
Wind Turbine Blade Application
A novel process is proposed
for the inter-laminar toughening of continuous fiber reinforced polymer
matrix composites (PMCs). A strong interest exists in enhancing the
toughness of large, tapered laminate composites such as wind turbine blades
fabricated from vacuum assisted resin transfer molding (VARTM). The need to
toughen PMCs arises from the matrix dominated fracture properties between
laminae, resulting in preferential planar fiber/matrix de-bonding (delamination).
The proposed process selectively bonds fiber reinforcement fabrics with a
tough thermoplastic (TP) interleaf prior to VARTM. The method is
particularly beneficial for stress concentration locations such as ply
terminations (drop-offs), free edges, and holes.
To develop a process to form
tough interleaves in a laminate PMC without disrupting the fiber
architecture or degrading its in-plane strength, thorough understanding of
heat transfer, chemical adhesion, polymer inter-diffusion, and bonding
between the interleaf, the fiber reinforcement, and matrix materials is
vital. This process presents significant challenges requiring the
development of predictive capabilities for interleaf morphology and quality
through the modeling of localized thermal and chemical reactions. To fully
understand the effects of reinforcement quality on the delamination behavior
of laminate PMCs, rigorous mechanical testing and characterization is
interleaving of preform laminate composites will be accomplished through hot
melt bonding of select polymers to dry fibers prior to VARTM fabrication.
The selection and characterization of the interleaf material is critical to
enhance fiber and matrix bonding during the hot melt and curing processes.
A ductile TP with a low glass transition temperature (amorphous) and
chemically compatible to epoxy (containing bisphenol-A) is desired to
maximize bonding. Characterization methods including cross sectioning with
optical microscopy and computed tomography will be applied to study the
effects of heating parameters on the interleaf morphology and structure.
The delamination resistance, in both static and fatigue loading conditions
will be tested.