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Abstract
With the development of modern diesel engines, fuel injection pressure has reached ultra-high levels, with values up to 300 MPa in advanced injector systems. Under such extreme conditions, the injector valve body is subjected to severe cyclic loading, which challenges its structural strength and fatigue life. This study establishes a comprehensive method for evaluating the strength and fatigue performance of the injector valve body through numerical simulation and experimental validation.

1. Introduction
The injector valve body plays a critical role in ensuring precise fuel metering and reliable sealing under ultra-high pressures. However, the combined effects of high stress concentration, cyclic loading, and material degradation increase the risk of fatigue failure. Conventional design approaches are insufficient to guarantee reliability at 300 MPa working pressures. Therefore, a systematic method integrating finite element analysis (FEA), fatigue modeling, and bench testing is required to assess and improve the durability of valve bodies.

2. Strength Analysis
A three-dimensional finite element model of the valve body was developed, incorporating realistic boundary conditions representing injection cycles. The von Mises stress distribution revealed that stress concentration occurred primarily at the valve seat transition and the junction between the valve bore and housing. Structural optimization, such as increasing fillet radii and refining material distribution, was shown to effectively reduce maximum stress by more than 10%.

3. Fatigue Life Evaluation
To evaluate fatigue performance, a stress–life (S–N curve) approach was applied in combination with the Miner’s linear damage accumulation rule. Material properties were derived from high-strength alloy steels commonly used in injector manufacturing. The FEA stress history was mapped to fatigue loading cycles, enabling prediction of fatigue life under repeated 300 MPa injection conditions. Results suggested that without optimization, critical regions may fail after approximately 5×10⁶ cycles, while design modifications extended predicted life beyond 1×10⁷ cycles, meeting durability requirements.

4. Experimental Verification
A high-pressure pulsation test rig was established to replicate actual engine injection conditions. Valve bodies were subjected to cyclic loading at pressures up to 300 MPa, and failure modes were analyzed using scanning electron microscopy (SEM). The observed fatigue cracks originated near stress concentration zones predicted by FEA, confirming the validity of the numerical evaluation method. The experimental results also highlighted the importance of surface finishing and residual compressive stress in improving fatigue resistance.

5. Discussion
The study demonstrates that strength and fatigue evaluation must be conducted simultaneously to ensure valve body reliability. Numerical simulation provides valuable insights into stress distribution, while experimental testing verifies fatigue crack initiation and propagation behavior. Future research may focus on advanced surface treatments, such as shot peening and laser hardening, as well as the use of novel high-strength alloys to further enhance fatigue resistance.

6. Conclusion
A combined numerical–experimental methodology was established for evaluating the strength and fatigue life of injector valve bodies operating under ultra-high pressures of 300 MPa. The results confirm that structural optimization and appropriate material selection can significantly extend component life, providing a reliable basis for the design of next-generation ultra-high-pressure fuel injection systems.