PSI - Issue 18

Jan Chvojan et al. / Procedia Structural Integrity 18 (2019) 443–448 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Representative tensile characteristic is given in Fig. 3a. Measured strains during tensile tests are shown in Fig. 3b. During the static test, the linear part of tensile characteristics was achieved only up to σ = 4.6 MPa (ε = 80 μmꞏm -1 ). After the first loading cycle due to hardening effect the linear part prolongs up to 8.5 MPa (ε = 190 μmꞏm -1 ). When the strain somehow exceeds this value, the insulator damage will be under low cycle fatigue.

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Fig. 3 (a) tensile characteristics of one tested insulator; (b) stress vs. strain characteristics measured with SG

2.2. Operational tests Five insulators were instrumented with strain gauges (Fig. 4). Two strain gauge pairs (T4, T5) were positioned to the lower internal transversal beam in the brake resistor box (Fig. 4b). Also 3-axis accelerometer was used. Operational tests were performed in Bologna on approximately 100 km traffic lines. Mixed strain time histories from one day test are shown in Fig. 5, divided to part outside and inside the town center. It is obvious that in historical center the insulators are more stressed and obtain more loading circles in comparison with coach operation outside the town.

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Fig. 4 (a) Position of insulators with strain gauges; (b) detail of instrumented insulators #1 and #2

Fig. 5 Comparison of strain time histories outside historical center (first part) and in historical center (second part). The time history in small circle was subsequently used for road simulation on vibration table