Application of Ultrasound in Fracture Toughness Measurement of GIS Epoxy Insulators

• Published in: IEEE transactions on instrumentation and measurement 2024-01, Vol.73, p.1-1
• Main Authors: Hao, Yanpeng, Liang, Zhuoyi, Shen, Zikui, Zhang, Yingying, Huangand, Shenglong, Yang, Lin
• Format: Article
• Language: English
• Subjects: <italic xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">G <sub xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">IC; <italic xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">K <sub xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">IC; Acoustics; Al<sub xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">2 O<sub xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">3; Aluminum oxide; Bend tests; Bending; Brittle materials; Composite materials; Crack tips; Cracking (fracturing); Cracks; Destructive testing; Energy release rate; epoxy models; Epoxy resins; Evaluation; Fillers; Fracture toughness; Insulators; Integrated circuits; Longitudinal waves; Modulus of elasticity; Nondestructive testing; Pouring; Product design; Stress intensity factors; Switchgear; Tensile tests; Testing; ultrasonic reflection method; Ultrasonic testing; Ultrasonic variables measurement
• ISSN: 0018-9456; 1557-9662
• DOI: 10.1109/TIM.2024.3375417

The fracture toughness of epoxy composite materials directly impacts the reliability of basin insulators for gas insulated switchgear (GIS), making accurate characterization of this property vital for product design. However, using the conventional mechanical drilling method to prepare three-point bending test specimens for brittle materials inherently creates natural cracks at the top of the artificial cracks, leading to a total crack length that does not meet the required standards and significant test result dispersion. This study proposes a one-piece pouring specimen method to reduce crack length dispersion. Additionally, the ultrasonic reflection method was conducted to estimate the specimen's crack length, considering the potential natural cracks due to epoxy curing and demolding stresses. Ultrasonic longitudinal wave speed was utilized to measure the filler content in the region of interest due to the potential for filler concentration resulting from flow rate differences during pouring. Specimens for measuring fracture toughness were prepared using various epoxy resin models and Al 2 O 3 filler contents. Tensile tests were conducted to determine the modulus of elasticity and Poisson's ratio of the specimens. Additionally, three-point bending tests were carried out to measure the critical load of the fracture. Finally, the critical stress intensity factor ( K IC ) and the critical crack extension energy release rate ( G IC ) were calculated at the crack tip. This research indicates that utilizing ultrasonic non-destructive techniques to measure crack length can aid in evaluating whether the crack length conforms to the standard requirements. Additionally, specimens with cracks produced using molds demonstrated minimal variability in crack length, making fracture toughness measurements in epoxy materials more efficient. By applying non-destructive ultrasonic longitudinal sound speed testing, the number of filler content that affects the fracture toughness of epoxy material can be evaluated beforehand, enabling pre-testing assessments of whether specimens meet filler content prerequisites before moving on to destructive tests. During the evaluation of various epoxy composite materials, the 5531:E-39D(1:1) variant displayed the highest K IC , pointing to superior fracture toughness. Optimally stable epoxy composites were achieved with a 100 phr (parts per hundreds of resin) Al 2 O 3 filler, resulting in the highest K IC value at 206% of that observed i