Very high cycle fatigue properties of crimp and non-crimp carbon fibre reinforced polyphenylene sulfide (CF-PPS)Donnerstag (27.06.2019) 09:45 - 09:48 Uhr
Carbon fiber reinforced polymers find increasing application in very high cycle fatigue (VHCF) loaded structures such as jet engine fan blades or wind turbine blades due to their exceptional lightweight potential and fatigue life performance. During the time in service, these blades can be exposed to more than one billion cycles caused by aerodynamic and gravitational loads. Therefore, a fundamental knowledge of material specific fatigue behavior as well as the underlying mechanisms is mandatory to provide maximum safety while realizing progressive lightweight design. Yet, data on VHCF behavior of fiber reinforced polymers is scarce as the experimental time aspect is critical. For instance, it takes more than 6 years to realize 109 load cycles by using a conventional servohydraulic fatigue setup operated at 5 Hz. To tackle these issues, a unique ultrasonic fatigue testing system for cyclic three-point bending was applied to obtain reliable VHCF data within economically feasible time. Since the mechanical properties of polymer composites are highly dependent on temperature and frequency due to the viscoelastic nature of the matrix, specimen self heating was mitigated by resonance-based testing as well as pulse-pause operation, resulting in an effective testing frequency of approx. 1 kHz. Furthermore, the monitoring of suitable fatigue testing conditions was realized by infrared thermography, high-resolution force measurements and cyclic displacement control via Laser Doppler vibrometry. Within the scope of the presented work outlined above, the damage behavior during very high cycle fatigue of carbon fiber tape and fabric reinforced polyphenylene sulfide with a cross-ply layup was characterized by light optical and scanning electron microscopy during interruptions of constant amplitude tests. The lifetime-oriented results of the VHCF tests up to 109 load cycles as well as the corresponding failure mechanisms of both material variants will be addressed within the poster.