Lei Fan

Multi-material structures such as carbon fiber reinforced polymer (CFRP) and epoxy resin are increasingly used in modern power equipment. However, significant differences in their thermophysical properties result in distinct defect thermal responses, which can reduce the reliability of infrared thermography inspections. To address this issue, this study investigates the thermal response mechanisms and quantitative analysis of defects in multi-material power equipment through finite element simulation and experimental validation. Three-dimensional transient heat transfer models containing air voids and heterogeneous insert defects were established using COMSOL Multiphysics for both carbon fiber reinforced polymer and epoxy resin matrices. Pulsed infrared thermography experiments were subsequently conducted to verify the simulation results. The effects of material properties, defect geometry, and cover-layer thickness on thermal response characteristics were systematically analyzed. The results show that thermal diffusivity is the key factor governing defect signal evolution. Carbon fiber reinforced polymer exhibits rapid thermal propagation and early transient responses, whereas epoxy resin produces delayed and slowly increasing thermal signals. Greater defect depth weakens thermal contrast and delays peak response time, while larger defect diameters enhance defect detectability. Increasing cover-layer thickness significantly attenuates defect signals and reduces imaging contrast. Experimental results are in good agreement with simulation predictions, confirming the validity of the proposed models. This work provides a quantitative analysis of defect thermal behavior in multi-material systems and offers a theoretical basis for adaptive infrared thermography inspection and condition assessment of power equipment. It should be noted that this study focuses on mechanistic understanding and parametric analysis rather than on proposing a dedicated quantitative defect-sizing or inversion method.

Multi-material structures such as carbon fiber reinforced polymer (CFRP) and epoxy resin are increasingly used in modern power equipment. However, significant differences in their thermophysical properties result in distinct defect thermal responses, which can reduce the reliability of infrared thermography inspections. To address this issue, this study investigates the thermal response mechanisms and quantitative characterization of defects in multi-material power equipment through finite element simulation and experimental validation. Three-dimensional transient heat transfer models containing air-void and heterogeneous insert defects were established using COMSOL Multiphysics for both CFRP and epoxy resin matrices. Pulsed infrared thermography experiments were subsequently conducted to verify the simulation results. The effects of material properties, defect geometry, and cover-layer thickness on thermal response characteristics were systematically analyzed. The results show that thermal diffusivity is the key factor governing defect signal evolution. CFRP exhibits rapid thermal propagation and early transient responses, whereas epoxy resin produces delayed and slowly increasing thermal signals. Greater defect depth weakens thermal contrast and delays peak response time, while larger defect diameters enhance defect detectability. In-creasing cover-layer thickness significantly attenuates defect signals and reduces imaging contrast. Experimental results are in good agreement with simulation predictions, confirming the validity of the proposed models. This work provides a quantitative understanding of defect thermal behavior in multi-material systems and offers a theoretical basis for adaptive infrared thermography inspection and condition assessment of power equipment.

The alumina doped epoxy resin composites have been widely used to prepare the basin-type insulators in gas-insulated switchgear (GIS). In recent years, the air cavity defects in the basin-type insulators became one of the most common factors to induce GIS faults. Therefore, the development of novel detection techniques for air cavities in epoxy resin composites is of great importance. In this study, multiple epoxy resin samples containing various submillimeter air cavities were prepared. Long pulse thermography (LPT) was employed to detect defects in the epoxy resin composite, and multiple data processing methods were applied to extract the characteristics of the air cavity defects. Quantitative analysis was also used to characterize the detection effectiveness in different thermograms. Experimental results show that derivative thermograms are capable of detecting air cavity defects with a diameter of 0.2 mm at a depth of 1.2 mm. The derivative thermograms can reduce noise and sharpen the defect recognition, exhibiting a high signal-to-noise ratio (SNR). This study also analyzes the impact of the aspect ratio on the detection result, which indicates that the defect with a small aspect ratio is difficult to detect. Based on the infrared thermography technology, this work provides a promising route for defects detection in basin-type insulators.

Porosity is closely related to the corrosion and wear properties of a coating processed by thermal-spraying technology, and the quantitative characterization of porosity is a crucial part of the research on coating structures. The current image analysis method often uses the mechanical polishing method recommended by ISO to measure a coating porosity. This method has been proved to be an effective method for the characterization of oxide coatings. However, due to the significant differences in the physical and chemical properties between aluminum and oxides, this method may not be suitable for aluminum coatings, and a more appropriate approach needs to be explored. In this paper, the effects of three polishing technologies (mechanical polishing, argon-ion-beam polishing, and electrolytic polishing) on the porosity measurement of pure aluminum coatings were compared and studied. The research results showed that the commonly used mechanical polishing method and more advanced argon-ion-beam polishing method could not completely reveal the pore structure because SiC particles would be embedded in the pure aluminum coatings during mechanical polishing, filling large pores. Although electrolytic polishing technology had advantages in revealing the macroporous structure, it would introduce a microporous structure and oxides, which would affect the measurement of the coating porosity. The composite polishing technology (electrolytic polishing + argon-ion-beam polishing) could perfectly reveal the pore structure in the pure-aluminum coating, and the porosity of arc-sprayed aluminum coating was 9.9%, which was close to the macroscopic true value measured using the weighing method of 10.2%.

Slippery liquid-infused porous surfaces (SLIPS) have received growing attention as promising icephobic materials. In this study, SLIPS were prepared on aluminum alloys by combining anodization and infusion of common silicone oil. An SLIPS with low ice-adhesion strength (6 kPa) was obtained by optimizing the anodizing time parameters (10 min). In addition, the frosting process and freezing of water droplets on the as-prepared SLIPS at −10 °C were delayed for 2000 s and 4800 s, respectively. Simultaneously, the as-prepared SLIPS also exhibited excellent anti-icing performance in glaze ice, since the supercooled water drips/ice slipped from the surface. The ice weight of the as-prepared SLIPS was significantly lower than that of the bare aluminum surface and the anti-icing-fluid-coated aluminum surface, which was reduced by 38.2%–63.6% compared with the bare aluminum surface. The ice weight increased with decreased temperature and inclination angle. This work proposes a method suitable for large-area preparation of SLIPS that achieves excellent anti-icing performance and significantly reduces the weight of glaze ice.

In this paper, aluminum coatings were prepared on a steel substrate by thermal spraying, and the corrosion morphology and corrosion resistance of the coating were investigated by salt spray and immersion tests. The results showed that after three months of salt spray tests, the coating still exhibited a surface morphology without significant damage and had good damage tolerance. Further effective protection of the substrate can be achieved by spraying the coating surface with paint. After three months of immersion test, the corrosion rate of samples with thicker coatings was located between 0.002 mm/y and 0.005 mm/y, and only a small amount of corrosion products was observed on the coating surface. The coated samples after salt spray and immersion tests maintained sufficient adhesion (17.07 MPa and 19.25 MPa), and the surface aluminum coating was highly reliable for protection of the steel substrate. In general, the reliability of the coating can be further improved by painting the surface of the thicker Al coating. This provides more ideas for the protection of transmission and transformation equipment.

The dynamic behaviors of water droplets on a slippery surface are significant to practical anti-icing applications. Herein, the impact and sliding behavior of water droplets on lubricant-infused surfaces (LISs) were investigated with a high-speed camera. LISs were prepared by infusing perfluoropolyether oils into anodized porous surfaces. The results show that the maximum spreading diameter and retraction velocity of the impact droplet increased with the We number. For LIS-100, the spreading factor at 2.5 ms increased from 2.00 to 3.88 with We increasing from 30 to 267. Low-viscosity lubricant facilitated the retraction speed and rebound of droplet impact on the surface, while high-viscosity lubricant contributed to the lubricant stability of the LIS. Additionally, high inclination angle (θ) facilitated the rapid shedding of water droplets on the surface. The velocity increased rapidly from 1.04 to 4.66 mm/s with θ increasing from 15° to 45°. The LIS prepared with low-viscosity lubricant had a high sliding velocity, and the sliding velocity of water droplets on LIS-100 was about seven times faster than that on LIS-104. This work reveals the impacting law of water droplets on LISs and provides useful information for the design of LISs under drop impact conditions.