PSI - Issue 57

Giovanni M. Teixeira et al. / Procedia Structural Integrity 57 (2024) 670–691 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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TMF tests must have been performed in the absence of oxygen, so that the contribution of oxidation could be evaluated. As running TMF tests in vacuum is not always possible ( and/or viable ) the parameters in equation 53 can not be calibrated in such cases and consequently the contribution of oxidation will be embedded in the other parameters. It is important to bear in mind that the DTMF methodology presented here is based on the fracture mechanics concept of a crack growing from an initial size 0 ( which is related to the concept of intrinsic defects in the material ) up to a final crack . And that means that the number of cycles , , as defined in equation 44, is dependent on the concept of a tolerable crack of size . It is worth reminding that not every crack will propagate to failure, especially under high stress gradients. Some cracks may only propagate until a certain distance and then stop. This is known as the theory of critical distance and is discussed in [24]. So the size can be defined based on the critical distance ( which is a material property ) or based on a particular design criteria. Hydrogen embrittlement [21] and ageing [22] are also phenomena that may contribute to thermomechanical fatigue, although not discussed above. The approach presented here is suitable for low cycle fatigue regime. The presence of high cycle fatigue loads requires especial considerations that are discussed in [23] and [10].

Contact Information The reader is welcome to email giovanni@fastmail.us or giovanni.demorais@3ds.com. References

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