Taurine-Modified Boehmite Nanoparticles for GFRP Wind Turbine Rotor Blade Fatigue Life Enhancement

Advanced nanoparticle-reinforced glass fibre composites represent a promising approach to improving the service life of fatigue-loaded structures such as wind turbine rotor blades. However, processing particle-reinforced resins using advanced infusion techniques is problematic due to, for example, higher viscosity as well as filtering effects. In this work, the effects of boehmite nanoparticles on viscosity, static properties and fatigue life are investigated experimentally. Whereas rheological analysis reveals a significant increase of viscosity in the case of pristine boehmite particles, an additional taurine surface modification of the particles can effectively reduce viscosity increase. As regards mechanical properties, significant improvements of both static as well as fatigue properties are found. The addition of 15 wt.% of boehmite particles increases fatigue life by a maximum of 270% compared to the unmodified fibre-reinforced epoxy. Transmitted light-based investigation of the damage mechanisms shows delayed initiation and smaller growth rates for laminates containing boehmite particles. At the same time, the observed mechanisms and their accumulation along the relative cycle number do not change significantly. In addition, by characterising autonomous heating, the so-called Risitano fatigue limit is determined. The results reveal that with increasing particle content there is an increase in the fatigue limit.

Fatigue life enhancement of NiTi rotary endodontic instruments by progressive reciprocating operation

AIM

To evaluate the effect of reciprocating amplitude and progressive angular increment on fatigue life enhancement of NiTi rotary endodontic instruments.

METHODOLOGY

ProTaper F2 instruments were operated in steel artificial canals with both stationary reciprocating (SR) and progressive reciprocating (PR) motions. The SR motions involved symmetric to and fro reciprocation of ± 180(o) , ± 135(o) , ± 90(o) , ± 60(o) and ± 45(o) . The PR motions were ± 45(o) stationary motion superimposed with angular increments of 7(o) , 11(o) , 22.5(o) or 31(o) whenever an instrument completed 1, 10 or 30 reciprocating cycles (rc). The fatigue lives were compared with those under continuous rotation (CR) and a reciprocating operation with a forward 144(o) and backward 72(o) motion proposed by Yared (2008). The statistical significance of these operating modes on fatigue life was examined using one way anova and post hoc Tukey's tests at P = 0.05. Fractographic analysis was also applied to probe the fracture mechanisms of different rotation motions.

RESULTS

Fatigue life increased with decreasing reciprocating amplitude. Operating in the SR increased fatigue life by 355% over that in the CR. Except for the 22.5(o) increment, all PR motions yielded longer fatigue lives than the SR motion. A progressive reciprocating operation with a ± 45(o) reciprocating amplitude and a + 7(o) progressive angular increment every 10 reciprocating cycles (± 45(o) /10rc/+7(o) ) increased fatigue life by 990% over that in the CR motion. In terms of life enhancement over the CR motion, the larger the curvature the less are the differences between different movements. Single crack initiation sites were found in the CR and SR motions, while three crack initiation sites were typical in the ± 45(o) /10rc/+7(o) motion.

CONCLUSIONS

Fatigue life increased with decreasing reciprocating amplitude in stationary reciprocation. A progressive reciprocating operation with ± 45(o) /10rc/+7(o) motion led to significant fatigue life enhancement and multiple fatigue crack initiation in NiTi endodontic instruments.