Fatigue Assessment of Inconel 625 Produced by Directed Energy Deposition from Miniaturized Specimens

In recent years, the industrial application of Inconel 625 has grown significantly. This material is a nickel-base alloy, which is well known for its chemical resistance and mechanical properties, especially in high-temperature environments. The fatigue performance of parts produced via Metallic Additive Manufacturing (MAM) heavily rely on their manufacturing parameters. Therefore, it is important to characterize the properties of alloys produced by a given set of parameters. The present work proposes a methodology for characterization of the mechanical properties of MAM parts, including the material production parametrization by Laser Directed Energy Deposition (DED). The methodology consists of the testing of miniaturized specimens, after their production in DED, supported by a numerical model developed and validated by experimental data for stress calculation. An extensive mechanical characterization, with emphasis on high-cycle fatigue, of Inconel 625 produced via DED is herein discussed. The results obtained using miniaturized specimens were in good agreement with standard-sized specimens, therefore validating the applied methodology even in the case of some plastic effects. Regarding the high-cycle fatigue properties, the samples produced via DED presented good fatigue performance, comparable with other competing Metallic Additive Manufactured (MAMed) and conventionally manufactured materials.

Research on low cycle fatigue life prediction considering average strain

To address the difficult problems in the study of the effect of average strain on fatigue life under low-cycle fatigue loads, the effect of average strain on the low-cycle fatigue life of materials under different strain cycle ratios was discussed based on the framework of damage mechanics and its irreversible thermodynamics. By introducing the Ramberg-Osgood cyclic constitutive equation, a new low-cycle fatigue life prediction method based on the intrinsic damage dissipation theory considering average strain was proposed, which revealed the correlation between low-cycle fatigue strain life , material properties, and average strain. Through the analysis of the low-cycle fatigue test data of five different metal materials, the model parameters of the corresponding materials were obtained. The calculation results indicate that the proposed life prediction method is in good agreement with the test, and a reasonable characterization of the low-cycle fatigue life under the influence of average strain is realized. Comparing calculations with three typical low-cycle fatigue life prediction models, the new method is within two times the error band, and the prediction effect is significantly better than the existing models, which is more suitable for low-cycle fatigue life prediction. The low-cycle fatigue life prediction of different cyclic strain ratios based on the critical region intrinsic damage dissipation power method provides a new idea for the research of low-cycle fatigue life prediction of metallic materials.