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<p>A fracture toughness is one of the critical parameters for Pyrowear 53 steel which is widely used in planetary gears of aircraft vehicles. Due to a limited volume of planetary gears, it is impossible to directly assess their plain strain fracture toughness K<sub>Ic</sub>. Therefore, the main aim of this study was to determine a formula correlating the plain strain fracture toughness K<sub>Ic</sub> obtained for laboratory compact tension (CT) specimens having a thickness of B = 50&#xa0;mm with smaller specimens (B = 10&#xa0;mm) which can be prepared directly from planetary gears. For this reason, different force-based approaches were utilized considering conditional fracture toughness (K<sub>Q</sub>), size-insensitive conditional fracture toughness (K<sub>Qsi</sub>) and specimen strength ratio (R<sub>sc</sub>) values calculated according to ASTM E399 standard. Four different sizes of CT specimens were analyzed, i.e. B = 50, 25, 16 and 10&#xa0;mm. The K<sub>IC</sub> value obtained for the B = 50&#xa0;mm specimen was 101.7 ± 4.5 MPa m<sup>1/2</sup>, while for the smaller specimen sizes, the K<sub>Q</sub> value gradually decreased from 125.4 ± 10.0 MPa m<sup>1/2</sup> for B = 25&#xa0;mm to 101.1 ± 3.0 and 86.6 ± 1.3 MPa m<sup>1/2</sup> for B = 16 and 10&#xa0;mm, respectively. This trend was opposite to the commonly observed relation that the fracture toughness value increases for smaller specimen size with a higher plain stress region. The specimen size effect observed in the current work resulted from the methodology of determining the K<sub>Q</sub> value based on a force P<sub>Q</sub> defined at a point of 5% deviation from linearity of load-displacement curve. It has been shown that the fracture toughness of the Pyrowear 53 steel specimens exhibiting a rising R curve was more dependent on a ligament size.</p>

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Specimen size effect on fracture toughness of Pyrowear 53 steel for planetary gears

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年11月26日

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  • Kamil Majchrowicz,
  • Barbara Romelczyk-Baishya,
  • Monika Wieczorek-Czarnocka,
  • Krzysztof Raga,
  • Ryszard Filip,
  • Zbigniew Pakieła

摘要

A fracture toughness is one of the critical parameters for Pyrowear 53 steel which is widely used in planetary gears of aircraft vehicles. Due to a limited volume of planetary gears, it is impossible to directly assess their plain strain fracture toughness KIc. Therefore, the main aim of this study was to determine a formula correlating the plain strain fracture toughness KIc obtained for laboratory compact tension (CT) specimens having a thickness of B = 50 mm with smaller specimens (B = 10 mm) which can be prepared directly from planetary gears. For this reason, different force-based approaches were utilized considering conditional fracture toughness (KQ), size-insensitive conditional fracture toughness (KQsi) and specimen strength ratio (Rsc) values calculated according to ASTM E399 standard. Four different sizes of CT specimens were analyzed, i.e. B = 50, 25, 16 and 10 mm. The KIC value obtained for the B = 50 mm specimen was 101.7 ± 4.5 MPa m1/2, while for the smaller specimen sizes, the KQ value gradually decreased from 125.4 ± 10.0 MPa m1/2 for B = 25 mm to 101.1 ± 3.0 and 86.6 ± 1.3 MPa m1/2 for B = 16 and 10 mm, respectively. This trend was opposite to the commonly observed relation that the fracture toughness value increases for smaller specimen size with a higher plain stress region. The specimen size effect observed in the current work resulted from the methodology of determining the KQ value based on a force PQ defined at a point of 5% deviation from linearity of load-displacement curve. It has been shown that the fracture toughness of the Pyrowear 53 steel specimens exhibiting a rising R curve was more dependent on a ligament size.