PSI - Issue 12

A. Castriota et al. / Procedia Structural Integrity 12 (2018) 71–81

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Castriota et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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plane of the spar and the consistency of strain gage measurements.

a

b

Fig. 2: Aeronautical spar equipped with strain gauges (a) and strain gauges map (b).

Subsequently the random fatigue load history has been applied (Step 1). Fatigue load is composed of six types of history loads (flights) that are representative of the real service conditions of the component. Flights are then variously combined to reproduce the load history of 1.5 times the design life of the plane, corresponding to 90000 flights. Fatigue test was carried out at a frequency of 0.5 Hz, which ensures a good tracking of the actuator with respect to the command signal. The acquisition of strain gage data was carried out at a frequency of 10 Hz. If the fatigue failure does not occur, a static test in load control (Step 2) is carried out up to the expected breaking bending load ( ), which is taken as a reference and defined as a normalized static load. is obtained by multiplying among them the ultimate load design (DUL), which represent the maximum design load and the environmental compensation load factor (ECLF), which takes into account environmental factors such as temperature and humidity: = × (1) The loading phase has been divided into 10 steps: the firsts are equal to 0.1 up to 0.8 , the remaining to 0.05 up to . For privacy reasons, all the reported results have been normalized using the maximum load applied in this static test and the maximum strain datum (evaluated in 22A strain-gauge position). The last step (Step 3) is performed only in the case that in Step 2 the static bending failure is not achieved. In this case, the load is applied up to the expected step break load ; once this load threshold is exceeded, increasing loads are continued with a determined application load speed equal to 50 lbf/s (222.4 N/s). For Step 2 and Step 3 the acquisition of strain gage data was carried out at a frequency of 1 Hz.

4. Numerical model

A numerical model was realized with ANSYS Mechanical APDL code to evaluate the correct load application and to determine the load-displacement curve and the bending stiffness of the spar. In this way, it is possible to estimate