# Shear and Interface Properties for Unidirectional, Woven, and Hybrid M21 Particle-Toughened Composites

## TL;DR

This paper experimentally evaluates the shear and fracture properties of M21 particle-toughened composites to support computational modeling of hybrid laminates.

## Contribution

The study provides the first experimental dataset for hybrid M21 composite interfaces, establishing a benchmark for future simulations.

## Key findings

- Hybrid laminates show high interfacial fracture toughness, especially in woven–woven and unidirectional–woven interfaces.
- Cohesive strength and fracture energy are key parameters governing delamination behavior in simulations.
- Extracted values for each interface type enable accurate modeling of damage initiation and propagation.

## Abstract

The M21 epoxy matrix is a toughened material designed to enhance the fracture resistance of carbon fiber-reinforced polymers (CFRPs). This study presents an experimental characterization of the shear and interlaminar properties required for validating computational damage models of hybrid laminated composite panels manufactured with the M21 material system. In-plane shear behavior was evaluated using ±45 (PM45) tests, while interlaminar fracture properties were characterized through double cantilever beam (DCB) and end-notched flexure (ENF) tests. The results demonstrate that hybrid laminates exhibit high interfacial fracture toughness, with notably increased resistance observed in woven–woven and unidirectional–woven interface pairs. Parametric studies identified cohesive strength and fracture energy as the dominant parameters governing delamination behavior in numerical simulations. Corresponding values were extracted for each interface type, enabling accurate representation of damage initiation and propagation in finite element models. To the authors’ knowledge, this work provides the first experimental dataset for the listed M21-based hybrid unidirectional–woven and woven–woven interfaces, establishing a benchmark for future modeling and simulation of toughened composite structures.