PSI - Issue 37

Carl Fällgren et al. / Procedia Structural Integrity 37 (2022) 948–955 Carl Fällgren / Structural Integrity Procedia 00 (2019) 000 – 000

953

6

4.3. Crack propagation life calculation To calculate the crack propagation lives of the specimens, the strip yield model was applied. For the calculations the same weight function as before was used. Crack lengths from 0.25 mm to 3 mm were calculated. Experimental results have shown, that specimen failure (leakage) occurs at smaller crack lengths, cf. Beier et al. (2017). 5. Testing of component-like specimens

Figure 5: Results of pulsating pressure testing of the specimens, h/d = 2.5, at the MFPA.

The component-like specimens shown in Fig. 2 were tested at the MFPA on a high-pressure testing rig. The results are shown in Fig. 6. Testing was performed for all previously described autofrettage grades. The specimens were loaded with pulsating inner pressure with different maximum pressures. For reasons of experimental realisation the lowest pressure was constantly set to 5 MPa, leading to a loading ratio of ≈ 0 . The results for the thicker specimens, h/d = 2.5, are shown in Fig. 6. All results depicted in red are from component-like specimens made of W360. Non-filled markers represent results for non-autofrettaged specimens, half-filled markers represent results for specimens previously subjected to an autofrettage pressure of 850 MPa and fully-drawn markers represent specimens subjected to an autofrettage pressure of 1700 MPa. For comparison, results for specimens with the same geometry made from 42CrMo4, previously subjected to an autofrettage pressure of 850 MPa are shown in blue. The specimens made from 42CrMo4 were fully autofrettaged in that state (cf. Beier et al. (2017)) as the ultimate tensile strength of the material and related to that, the bursting pressure is lower than the value of the steel W360 specimens. All run-outs are marked with an arrow, the number at the arrow indicating the number of specimens tested at the corresponding pressure range. 6. Comparison between calculated and experimentally obtained results As the endurance limit of a component is a value of practical importance, the numerically calculated results are compared to the experimentally obtained endurance limits in Fig. 7 and Fig. 8.