Rababeh, M., Jawad, B., Alwerfalli, D., and Choucair, H., "Fatigue Life Improvement through the “NOVA” Process," SAE Technical Paper 2013-01-1400, 2013, doi:10.4271/2013-01-1400.
The experimental methods focused on utilizing the newly developed NOVA induction heating and hardening manufacturing process as an adapted method to produce high performance engine valve springs. A detailed testing plan was used to evaluate the expected and theorized possibility for fatigue life enhancement. An industry standard statistical analysis method and tools were employed to objectively substantiate the findings. Fatigue cycle testing using NOVA induction-hardened racing valve springs made of ultra-high tensile material were compared to data for springs with traditional heat treatment and those with standard processing.The results were displayed using Wöhler and modified Haigh fatigue life diagrams. The final analysis suggests that NOVA processed springs have a seemingly slight, yet significant benefit in fatigue life of 5 - 7% over springs processed through a competing method. This improvement in fatigue life is a rather precious advantage when considering high performance engine valve springs and could result in up to a 10X improvement in actual spring life, depending on the stress level of the field application.