Cyclic Nano-indentation investigation of Plasticity in Case Hardened Bearing Steels
Demands for performance and reliability of bearings present a challenge for materials and process development in that a knowledge gap exists between the understanding ratcheting mechanisms that lead to crack initiation and mechanical predictions of bearing endurance. Current bearing research suggests the very high cycle fatigue endurance of low-inclusion content bearing steels is dominated by sub-micrometer plasticity and features uncharacterized by standard specifications. This effort investigates whether mechanical measurements on the scale of the sub-micron structures with cyclic nano-indentation relate to bearing steel fatigue performance. Cyclic indentation within the graded microstructures of case hardened steel samples is performed near the typical active fatigue depths in rolling element bearings. With a dynamic mechanical analysis (DMA) technique, differences in elastic losses in the matrix can be discerned between structures. Additionally, these differences in elastic losses resemble the bending fatigue performance and are isolated from residual stress and other variables that cloud fatigue analysis. This method may be utilized in development and optimization of alloys and processing techniques for high cycle and contact fatigue applications.
Bahr, Purdue University.
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