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Abstract

In this study, energetic behaviors of polyvinylidene fluoride (PVDF)-coated zirconium (Zr) powders were investigated using thermogravimetric analyzer-differential scanning calorimetry (TGA-DSC). PVDF-coated Zr powder had 1.5 times higher heat flow than ZrO2-passivated Zr powder. PVDF-coated Zr powder had a Zr-F compound formed on its surface by its strong chemical bond. This compound acted as an oxidation-protecting layer, providing an efficient combustion path to inner pure Zr particle while thermal oxidation was progressing at the same time. PVDF coating layers also made thermal reaction start at a lower temperature than ZrO2-passivated Zr powder. It was obtained that the surface PVDF coating layer evaporated at approximately 673 K, but the surface oxide layer fully reacted at approximately 923 K by DSC analysis. Hence, Zr powders showed enhanced energetic properties by the PVDF-coated process.
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Bibliography

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Authors and Affiliations

Won Young Heo
1
ORCID: ORCID
Sung Hwa Bae
2
ORCID: ORCID
Injoon Son
1
ORCID: ORCID

  1. Kyungpook National University, Department of Materials Science and Metallurgical Engineering, Daegu 41566, Republic of Korea
  2. Kyushu University, Department of Materials Process Engineering, Graduate School of Engineering, Fukuoka, Japan
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Abstract

The steam turbine blades of low pressure stages are endangerd by the high-cyclic fatigue due to the combined loading of dynamic stresses by the steam time-variant pressure and the pre-stress from centrifugal forces. Therefore, the importance of their experimental dynamic analysis in the design stage is critical. For laboratory tests of the blades, the piezo actuators placed on the blades, unlike electromagnets placed in the stationary space, give a possibility to excite the flexural vibration of the blades within the bladed disk by time continuous forces independently of the rotor revolutions. In addition, the piezo actuators can be also used to control the vibrations of the blade. Therefore, several dynamic experiments of the clamped model blade equipped with PVDF films were performed for the force description of the piezo foils and their behavior as actuators of the blade vibration. The numerical beam models were used for numerical analysis of the vibration suppression effects both by additional parametric excitation and by active damping. The optimal phase shift of piezo actuator voltage supply was ascertained both for amplitude amplification and suppression. The results contribute to the knowledge of the actuation and active damping of blade vibration by the piezo elements
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Authors and Affiliations

Ludĕk Pešek
Ladislav Půst
Vítĕzslav Bula
Jan Cibulka

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