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1

Variable surface temperature distribution as a criticality indicator of the self-heating effect in composites

Katunin A.

Advances in Materials Science

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2018

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Vol. 18, nr 1(55)

5--12

EN

Since self-heating effect may significantly intensify structural degradation, it is essential to investigate its criticality, i.e. the temperature value at which fatigue fracture is initiated. In this paper, a new and sensitive criticality indicator based on evaluation of evolution of surface temperature distribution was proposed and experimentally validated. It was shown that comparing to other measurement techniques the presented approach allows for precise evaluation of the critical value of the self-heating temperature. The properly determined critical value may be helpful both during design and operation of elements made of polymers and polymeric composite.

2

Influence of series resistance on thermally induced limitations of SiC Schottky diodes

Janke W., Hapka A.

Elektronika : konstrukcje, technologie, zastosowania

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2011

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Vol. 52, nr 2

163-165

EN

The calculations and measurement results of static DC characteristics of SiC Schottky barrier diodes, including self-heating effect are presented in this paper. In particular, the influence of the value of parasitic series resistance of a diode on the shape of its non-isothermal I-V curves is analyzed. The electro-thermal interactions in a diode working in high-current region may lead to the thermal runaway, therefore the serious limitations of operation conditions exist. The analysis presented by other authors [1-3] show, that the maximum junction temperature (corresponding to the onset of runaway) may be, in some conditions, as low as 110°C, substantially below the generally expected temperature limit of SiC devices. According to the analysis and measurements presented in this paper, the SiC device is able to operate with much higher junction temperature than that predicted in [1-3]. On the other hand, as it is shown, the higher values of series resistance may strongly restrict the values of the diode current ratings, therefore the decrease of series resistance in the manufacturing process is of vital importance.

PL

W artykule zaprezentowano obliczenia oraz pomiary statycznych charakterystyk DC diod Schottky'ego z węglika krzemu, z uwzględnieniem efektu samonagrzewania. Szczególną uwagę poświęcono wpływowi szeregowej rezystancji strat na kształt nieizotermicznych charakterystyk prądowo-napięciowych. Wzajemne oddziaływania elektro-termiczne w diodach pracujących z relatywnie dużymi prądami mogą doprowadzić do efektu określanego jako thermal runaway - czyli niekontrolowanego wzrostu napięcia na pasożytniczej rezystancji elementu. Z tego powodu istnieją poważne ograniczenia wartości zależnych od temperatury parametrów określających warunki pracy elementów (dopuszczalna temperatura pracy, maksymalny prąd przewodzenia). Znajduje się doniesienia [1—3], z których wynika, że maksymalna temperatura pracy elementów z węglika krzemu to 110°C, a przekroczenie tej temperatury może prowadzić do zniszczenia elementu. Wartość 110°C jest stanowczo za niska w odniesieniu do ogólnie oczekiwanych temperatur pracy elementów z węglika krzemu. Wyniki prezentowane w niniejszym opracowaniu wskazują na możliwości bezpiecznej pracy w zakresie temperatur znacznie szerszym niż zakres przewidywany w [1-3]. Z drugiej strony, pokazano że duże wartości szeregowej rezystancji strat mogą poważnie ograniczać zakres prądów dopuszczalnych dla elementów TL węglika krzemu. W związku z tym, dążenie do zmniejszenia udziału rezystancji pasożytniczej w tych elementach jest bardzo istotne.

3

Frequency dependence of the self-heating effect in polymer-based composites

Katunin A., Hufenbach W., Kostka P., Holeczek K.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 41, nr 1-2

9-15

EN

Purpose: The self-heating effect caused by viscous energy dissipation in polymer-based composite structures subjected to harmonic loads is considered to have a great influence on the residual life of the component. The purpose of the conducted investigations is the determination of the dynamic mechanical behaviour of a polymer-based composite material under different excitation frequencies and temperatures. Design/methodology/approach: The dynamic mechanical analysis was employed for measurements of temperature and frequency dependence of the complex rigidity parameters. Obtained loss rigidity curves for different load frequencies enable the determination of the glass-transition temperatures and finally frequency-dependence of the loss rigidity determined on the basis of the kinetic molecular theory and Williams-Landel-Ferry (WLF) hypothesis. Findings: The dependency between glass-transition temperature and excitation frequency has been investigated. The activation energy of the phase transition as well as the temperature dependence of the shift factor was calculated. The glass-transition temperature and constants of WLF equation enable the determination of temperature and frequency dependence of the loss rigidity according to the time-temperature superposition principle. Research limitations/implications: The ranges of temperatures were limited to 30-150 °C and excitation frequencies to 1-200 Hz, the behaviour of the composite material outside these ranges can be estimated based on the theoretical assumptions only. Obtained dependencies are correct only for linearly viscoelastic materials. Practical implications: Obtained dependencies can be useful for estimation of the mechanical and thermal degradation of polymer-based composites and can be subsequently applied for the determination of fatigue, crack growth and residual life of composite structures. Originality/value: The determination of temperature and frequency dependence of the loss rigidity gives an opportunity to obtain the self-heating temperature distribution of the polymer-based composite structures under harmonic loading.