PSI - Issue 7

Dalila Dimaggio et al. / Procedia Structural Integrity 7 (2017) 198–205 D. Dimaggio et al. / Structural Integrity Procedia 00 (2017) 000–000

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Figure 5: (a) Generalized HSV 90% -diagram (b) Basis S-N line for HSV 90% ≥ 30 mm 3 Based on the generalized HSV 90% -diagram (Figure 5(a)) a Basis S-N line for specimens with HSV 90% ≥ 30 mm 3 (un-notched) can be evaluated (Figure 5 (b)). The steps to be followed to get the Basis curve are here described: 1. Medium fatigue regime with k=4.2, normalized endurable stress amplitude σ va,0 =0.75 at N=10 4 cycles; 2. HCF-regime with k*=44.9 (constant value used for all test series after the kneepoint), normalized endurable stress amplitude σ va,0 =0.42 at N=10 6 cycles; 3. Get N k,b and σ k,b of the Basis S-N line as intersection point of the two lines obtained at step 1 and step 2; 4. The Basis S-N line can now be shifted with the support factor n HSV , calculated by the equation (3): ν  = HSV n component HSV with HSV 0 =30mm 3 and ν= -0.05 (3) (4) 6. To get a design S-N line for a fatigue evaluation, the local S-N line has to be shifted to a suitable probability of survival P s. Near-service loading tests (as mentioned in chapter 3.2) have been performed to obtain the parameters for Palmgren Miner linear damage accumulation to get: • a characteristic damage sum D ch and • a “modified” S-N line for damage accumulation (Palmgren-Miner-Modification) for the investigated application. In order to define reliable parameters, different Palmgren-Miner modifications of the axial loaded (R=0) S-N line and different characteristic damage sums D ch have been investigated to get the best Ga β ner line from linear damage accumulation for the VA test results. For this purpose the stress amplitude σ a,b2 of the near service-load block with 10 3 cycles of R=0.7 has to be transformed to a damage equivalent stress amplitude σ a,b2,trans for a stress ratio R σ =0 by using equation (5) that can be derived from equation (1):      0 %, 90 HSV 5. To get the local S-N line with σ k,loc , the following equation (4) has to be used: k b , HSV k loc , n σ σ =

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