PSI - Issue 5

Miloslav Kepka et al. / Procedia Structural Integrity 5 (2017) 1409–1416

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4 Miloslav Kepka et al. / Structural Integrity Procedia 00 (2017) 000 – 000 According to the standard, the cases with variable-amplitude loads, such as in-service loads, require bi-linear fatigue curves with the transition at the point of = 10 7 cycles. Second fatigue strength exponent is calculated using the formula: 2 = 1+ 2 1 1 . (3) The mean fatigue curve for the structural detail of interest is shown in Fig. 3 and its parameters are given in Table 1.

Fig. 3. Mean fatigue life curve of weld class T.

Table 1. Fatigue characteristics in nCode software description, mean fatigue life curve. Stress range intercept 1 16604 MPa First fatigue strength exponent 1 -0.3333 Fatigue transition point (cycles) 1 10 7 Second fatigue strength exponent 2 -0.2 –ƒ†ƒ”† ””‘” ‘ˆ ‘‰ ˆ 0.2484

2.2. Loading conditions, measured and analyzed stress-time histories

Stress-time histories for a location near the structural detail were recorded with the trolleybus running a 16.2-miles urban route. The hilly test route with a profile typical of San Francisco had varying typical surfaces. The driving modes included brakin g, accelerating, turning and short stops. The measurement involved two “extreme” load conditions: empty and fully-loaded (undamaged) vehicle.