Delamination Mode I Analysis on Thin Stitch Fiberglass Composite

Area of Science:

• Materials Science
• Mechanical Engineering
• Composite Materials

Background:

• Delamination is a critical failure mode in laminated composites, often initiated by interlaminar matrix cracking.
• Traditional through-thickness reinforcement methods like 3D weaving face industrial adoption challenges due to cost and complexity.
• There is a need for accessible and effective interlaminar reinforcement strategies.

Purpose of the Study:

• To investigate through-thickness stitching as an alternative method for enhancing Mode-I delamination resistance in fiberglass composites.
• To evaluate the impact of different stitch architectures on interlaminar fracture toughness.
• To assess potential trade-offs in mechanical properties due to stitching.

Main Methods:

• Manufacturing of fiberglass composites using an epoxy infusion system and biaxial fabric.
• Introduction of through-thickness stitching with polyethylene threads in varying longitudinal patterns (AV, BV, CV).
• Experimental testing to determine Mode-I interlaminar fracture toughness (G_IC) and microstructural analysis using scanning electron microscopy (SEM).

Main Results:

• Stitching significantly increased Mode-I interlaminar fracture toughness (G_IC) compared to unstitched composites.
• G_IC values increased from 0.0265 kJ/m² (unstitched) to 0.3808, 0.4152, and 0.5192 kJ/m² for AV, BV, and CV stitched samples, respectively.
• SEM revealed localized fiber misalignment (up to 33°) and resin-rich regions in stitched specimens.

Conclusions:

• Through-thickness stitching effectively enhances the Mode-I delamination resistance of fiberglass composites.
• The degree of enhancement is influenced by stitch orientation and spacing.
• While improving delamination resistance, stitching may introduce localized defects affecting other mechanical properties.