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

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.

Recent Advances in Limiting Fatigue Damage Accumulation Induced by Self-Heating in Polymer–Matrix Composites

“…To be more precise, LCF loads vary typically between 50% and 95% of the ultimate strength of such a composite, leading to high mechanical strains or thermal failure due to the occurrence of the self-heating effect, which may induce macrocracking and premature failure. In addition, LCF tests are typically conducted at a sufficiently low frequency (i.e., 10 Hz or below [13][14][15][16][17][18][19]); otherwise, premature thermal failure will occur before mechanical fatigue failure. From the other perspective, if such a PMC specimen is subjected to a relatively lower level of stress or strain loading, it may experience a higher number of fatigue cycles before its failure, as opposed to low-cycle fatigue failure wherein the specimen's lifetime may be relatively short.…”

“…Testing specimens in the VHCF regime, however, may unfavorably be quite time-consuming and costly, unless the experiments are carried out at a higher frequency level, so as to rationally reduce the time of fatigue experiments of PMCs [31]. This loading frequency may vary from just below 1 Hz up to 20 kHz [16,29,62,63]. Lower frequency levels (normally less than 5 Hz) are primarily implemented for obtaining stresslife (S-N) curves to avoid the hysteresis effect [64], while the accelerated fatigue limit techniques using comparatively high loading frequency [58] as potential candidates have gained a high level of interest.…”

Neural Network Based Determination of the Degree of Fiber Mixing in Hybrid Yarns and Composites

“…This can be achieved in particular by combining conventional fibre composites, which have high stiffness and strength, with metallic materials, which are characterised by their pronounced ductility and an associated higher energy absorption capacity as well as high structural integrity, in a way that meets the requirements [1]. Metal-fibre hybrid materials have been limited to the surface formation of different mono-material yarns at the meso level and layered Fiber Metal Laminates (FML) [2,3]. The layered structure of FML can result in delaminations and composite component failure due to insufficient mixing of individual components [4,5,6,7].…”

Development of multi-material hybrid yarns consisting of steel, glass and polypropylene filaments for fiber hybrid composites

“…2 The hybridization of high-performance fibers with metals has so far been mainly limited to the layerby-layer combination of alternating layers of metal foils and FRPs as fiber-metal laminates (FMLs) [3][4][5][6] and the layered combination of metal and highperformance fibers as hybrid fiber composites. [7][8][9] The focus of the studies was mostly on the effects of the interlayer hybrid ratio and stacking sequence on the mechanical properties of laminated composites. 10,11 However, these hybrid concepts have considerable disadvantages due to complex and cost-intensive manufacturing processes.…”