Metal/Carbon-Fiber Hybrid Composites—Damage Evolution and Monitoring of Isothermal Fatigue at Low and Elevated Temperatures

Bilal Khatri,Frank Balle,Ulf Breuer,Sebastian Schmeer,Jan Rehra

doi:10.3390/jcs6030067

Abstract

Carbon-fiber-reinforced polymers (CFRPs) are the standard lightweight composite material for structural applications in aviation. The addition of metallic fibers to CFRPs to form metal/carbon-fiber hybrid composites (MCFRPs) has been shown to improve the elastic and plastic properties and to enable a non-destructive method for structural health monitoring over the material’s service life. In this paper, the results from the fatigue experiments on these hybrid composites at −55, 25 and 120 °C are discussed. Multidirectional CFRP and MCFRP laminates, fabricated using the autoclave method, were tested and compared under different fatigue loading conditions, while being simultaneously monitored for temperature and electrical resistance. Magnetic phase measurements were additionally carried out for the chosen metastable austenitic steel fibers in the MCFRPs. The results show that the improved ductility of the hybrid composite due to the presence of the steel fibers leads to better performance under fatigue loads and a less-brittle failure behavior. Based on the chemical composition of the metastable austenitic steel fibers, a temperature and plastic deformation-dependent phase transformation was observed, which could potentially lead to a method for non-destructive structural health monitoring of the hybrid composite over its service life.

Highlights

Carbon-fiber-reinforced polymers (CFRP) have, in the last few decades, evolved to become the primary load-bearing material in modern aircraft, comprising over 50 wt.% of the fuselage mass in aircraft, such as the Boeing 787 and the Airbus A350 [1]
The CFRP and metal/carbonfiber hybrid composites (MCFRPs) samples were tested for their monotonic properties at a rate of 50 N/s at –55, 25 and 120 °C
Five CFRP and MCFRP samples were tested at each temperature

Summary

Introduction

Carbon-fiber-reinforced polymers (CFRP) have, in the last few decades, evolved to become the primary load-bearing material in modern aircraft, comprising over 50 wt.% of the fuselage mass in aircraft, such as the Boeing 787 and the Airbus A350 [1]. A number of important aircraft functions, such as lightning-strike protection, grounding, electromagnetic shielding and signal transfer, can only be realized for CFRP-based fuselages by the addition of metallic components, such as copper foils, wires and cables, causing an increase in the process complexity and time. These additional masses do not contribute to the structural properties and are a limiting factor in the cumulative strength-to-density ratio of the fuselage. A comparable level of electrical conductivity to that of aluminum fuselages through modifications of the matrix has far not been attained

Methods

Results

Conclusion