Numerical Investigation of Dynamic Buckling of Ultra-DeepWell Tubing Strings Subject to Impact Loading

Abstract

Metallized polypropylene film capacitors (MFCs) undergo dielectric aging under thermal stress, critically affecting operational reliability. To address the insufficient sensitivity of traditional loss-detection methods for early warning, this paper employs frequency-domain dielectric spectroscopy (FDS) to conduct accelerated aging tests on 100 μF automotive-grade MFCs at 120°C. The dielectric loss tangent (tanδ) and capacitance were measured over a wide frequency range (50 Hz–12 kHz). A characteristic frequency of 8100 Hz is identified as an early-warning indicator for thermal aging: while traditional methods detect only 0.7% and 2.5% changes after 360 and 720 h aging respectively, FDS captures 13.68% and 27.5% signal changes at 8100 Hz, reaching 55.5% at capacitor failure (1080 h)—3–8 times more sensitive than conventional approaches. Further analysis reveals frequency-dependent degradation patterns: the low-frequency band reflects increased conductive loss from electrode corrosion, the mid-frequency band shows the most sensitive relaxation loss changes, while high-frequency changes are slower, collectively reflecting progressive aging from interface to bulk. A health index (HI) model integrating multiple spectral features is developed using an improved weighted fusion algorithm, enabling aging state classification into four levels and remaining lifetime prediction with error within 5.6%. This FDSbased tanδ spectral analysis provides a novel approach for MFC lifetime prediction and early aging warning, offering practical significance for enhancing electric drive system reliability in new energy vehicles.OPEN ACCESS Received: 23/10/2025 Accepted: 19/12/2025 Published: 21/09/2026

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