PSI - Issue 43

A.D. Nikitin et al. / Procedia Structural Integrity 43 (2023) 53–58 A.D. Nikitin et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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a) d) Fig. 3. The numerical simulation of the torsion crack from defects (a) at the surface, (b) in the bulk at the distance of 1x10 -4 m form surface, (c) in the bulk at the distance of 4x10 -4 m and (d) result of VHCF torsion test on Ti-alloy specimen Nikitin et al. (2016). 4. Conclusion The two-criteria multi regime model is introduced together with the numerical procedure for damage function determination. The model is capable to predict the number of cycles to crack initiation, location of the nucleation site and type of the micro-crack opening. All the parameters for the model can be determined based on uniaxial quasi static tensile and axial fatigue tests. The proposed numerical procedure allows to perform the continuous calculation of fatigue damage accumulation and quasi-crack developing. The model was successfully applied to predict the crack initiation mechanism and crack path in smooth specimens under VHCF pure torsion loading. The proposed approach can be used together with different multiaxial criteria and even extended to three modes crack opening case. The obtained results for the VHCF pure torsion have shown a good qualitative agreement with the experimental results. The model predicted the crack initiation on the plane of maximum shear stress and spontaneous bifurcation to the crack propagation on the plane of maximum normal stress with the changing of the crack opening mechanisms. The model is capable to reconstruct the two types of torsion crack: single Z-type crack and duplex X-type crack. It was shown that duplex type of crack path is more likely for the case of subsurface crack initiation. b) c)

Acknowledgements This work is supported by the Russian Science Foundation, Project № 19 -19-00705. References

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