Damage assessment through cyclic load-unload tensile tests for ply-level hybrid carbon fiber composites

Abstract

Composite materials are of increasing interest in aircraft and spacecraft structures, and carbon fiber reinforced polymers (CFRP) have emerged as materials meeting quality standards for structural applications in the aircraft industry. Despite their high mechanical properties, CFRPs are associated with high production costs. Building on recent research by the authors, this paper investigates the use of ply-level hybridization to reduce manufacturing costs while maintaining the mechanical performance of the manufactured material. Focusing on the causes of nonlinear response under off-axis tensile loading, the paper involves cyclic load-unload (LU) tensile tests conducted at off-axis angles of 15°, 30°, and 45° to predict mechanical characteristics and damage evolution. Residual strains are directly extracted from load-unload stress-strain responses. Three distinct methods for estimating cycle modulus are employed and compared for damage variable formulation. The research findings reveal dependencies of both the damage variable and residual strains on the off-axis angle. Furthermore, the method used to assess the modulus during cycling loading significantly influences the damage variable estimation. Encouragingly, the hybrid laminates exhibit reduced internal damage and matrix plasticity compared to reference counterparts, indicating a positive effect on the mechanical performances of hybridized CFRPs in addition to the cost reduction.

The effect of printing parameters on the mechanical properties of fiber-reinforced PA6 matrix composites in material extrusion-based additive manufacturing

“…On the other hand, short GF reinforcements are attractive due to their ease of fabrication, high temperature and corrosion resistance, good dimensional stability, lightweight, economical and superior mechanical properties (Curtis et al , 1978; Fu, 1998; Holmström et al , 2020). In this sense, there has been significant interest in the concept of hybridization to address cost-effectiveness while maintaining the expected performance of the material (Casapu et al , 2024; Zuo et al , 2021; Curtis and Browne, 1994; Audibert et al , 2018). Hybrid composites are composites with at least two different types or forms of reinforcing elements (Seydibeyoğlu et al , 2023; Singh et al , 2017) and the use of CF-reinforced composites as hybrids with different reinforcing elements offers various opportunities.…”