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<p>Fatigue failure in interference fitted joints remains a critical challenge for high-load mechanical assemblies such as down-the-hole drilling bits. While previous studies have demonstrated the beneficial influence of interference fit (IF) on fatigue performance, these investigations are largely restricted to soft alloys and low-cycle fatigue regimes. This study investigates the fatigue life enhancement of interference fits between tungsten carbide and AISI 4340 hardened steel, combining experimental testing, numerical simulations, and fractographic analysis. Fatigue tests were conducted on samples with interference fit levels of 0%, 0.5%, 1%, 1.5%, and 2%. Finite element simulations were conducted in ABAQUS using half-symmetry. The bottom face of the specimen was fixed to represent the fixture support, while symmetry was applied through the specimen mid-plane to reduce computational cost. Fatigue life was estimated using both the Smith–Watson–Topper (SWT) criterion and a user-defined field subroutine for a damage mechanics model. The experimental results revealed a significant improvement in fatigue life due to the presence of IF. Optimal IF level of 1.5% enhanced fatigue life by 245% compared to interference-free samples. However, increasing IF beyond this level slightly reduced fatigue performance, highlighting a trade-off between residual compressive stress benefits and excessive plastic deformation effects. Both numerical approaches predicted the general fatigue life trends, with the damage mechanics model demonstrating superior accuracy, exhibiting a maximum deviation of 14.1% from experimental results compared to 19.7% for the SWT method. Fractographic analysis revealed distinct crack initiation and propagation patterns: interference-free samples exhibited central crack initiation with semi-elliptical growth, while interference fitted samples showed edge-initiated cracks with quarter-elliptical propagation, emphasizing the localized effects of compressive stresses. Finally, a polynomial regression was developed to establish an empirical relationship between IF level and fatigue life.</p> Graphical Abstract <p></p>

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Numerical and experimental insights into fatigue failure of interference fits in AISI 4340 hardened steel and carbide interfaces

  • 期刊论文

  • 发表日期：

    2026年4月12日

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  • Sina Sabbaghi Farshi,
  • Amir Rasti

摘要

Fatigue failure in interference fitted joints remains a critical challenge for high-load mechanical assemblies such as down-the-hole drilling bits. While previous studies have demonstrated the beneficial influence of interference fit (IF) on fatigue performance, these investigations are largely restricted to soft alloys and low-cycle fatigue regimes. This study investigates the fatigue life enhancement of interference fits between tungsten carbide and AISI 4340 hardened steel, combining experimental testing, numerical simulations, and fractographic analysis. Fatigue tests were conducted on samples with interference fit levels of 0%, 0.5%, 1%, 1.5%, and 2%. Finite element simulations were conducted in ABAQUS using half-symmetry. The bottom face of the specimen was fixed to represent the fixture support, while symmetry was applied through the specimen mid-plane to reduce computational cost. Fatigue life was estimated using both the Smith–Watson–Topper (SWT) criterion and a user-defined field subroutine for a damage mechanics model. The experimental results revealed a significant improvement in fatigue life due to the presence of IF. Optimal IF level of 1.5% enhanced fatigue life by 245% compared to interference-free samples. However, increasing IF beyond this level slightly reduced fatigue performance, highlighting a trade-off between residual compressive stress benefits and excessive plastic deformation effects. Both numerical approaches predicted the general fatigue life trends, with the damage mechanics model demonstrating superior accuracy, exhibiting a maximum deviation of 14.1% from experimental results compared to 19.7% for the SWT method. Fractographic analysis revealed distinct crack initiation and propagation patterns: interference-free samples exhibited central crack initiation with semi-elliptical growth, while interference fitted samples showed edge-initiated cracks with quarter-elliptical propagation, emphasizing the localized effects of compressive stresses. Finally, a polynomial regression was developed to establish an empirical relationship between IF level and fatigue life.

Graphical Abstract