Enhancing Interlaminar Shear Strength in Additively Manufactured Carbon Fiber-Reinforced Thermoplastic Composites Through Microstructural Design

Background

Carbon fiber-reinforced polyetheretherketone (CF-PEEK) composites, produced via material extrusion (ME) 3D printing, offer excellent physical and mechanical properties for aerospace and biomedical applications. However, their layered microstructure from the additive manufacturing process makes them susceptible to interlaminar shear failure.

Objectives

This study investigates the interlaminar shear strength (ILSS) of additively manufactured CF-PEEK composites and unreinforced PEEK. It focuses on the relationship between microstructure, influenced by the mismatch angle between adjacent layers and layer height, and interlaminar shear behavior of CF-PEEK composites.

Method

Short beam shear (SBS) tests are used to evaluate ILSS, with digital image correlation (DIC) capturing in-situ full-field strain fields to observe interlaminar failure mechanisms. Fractographic examinations are also performed to confirm the observed trends.

Results

The experimental findings unveil three key points: (1) An increase in the mismatch angle enhances ILSS, shifting the failure mode from interlaminar shear to bending stress. For pure PEEK, this enhancement can reach 60–70%, while CF-PEEK shows a 30–40% increase. (2) Layer height has contrasting effects: it does not significantly impact ILSS in pure PEEK, but in CF-PEEK composites, a shorter layer height increases ILSS by more than two to three times compared to thicker layers. (3) CF-PEEK composites outperform pure PEEK in ILSS by 40–50% at a layer height of 200 µm. However, this trend reverses at a layer height of 400 µm.

Conclusions

These outcomes suggest the potential for producing PEEK and CF-PEEK composites via ME technique with enhanced ILSS, thereby offering improved structural reliability in their applications.