PSI - Issue 12

F. Cianetti et al. / Procedia Structural Integrity 12 (2018) 102–112 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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5

= ∙ { ∙ ∑[ √ ( ) ( ) ⁄ ] = }

(10)

= ∙ [ ⁄ ]

(11) The value is strongly influenced by the number of cycles counted in the window, , and therefore window by window, could vary in value, increasing or decreasing, without, however, meaning that the damage has really increased or decreased. For example, if two windows -th and ( + ) -th generate the same instantaneous damage but the two windows contain different number of cycles and + , two different values of occur for the same damage. To overcome this result and have a value of comparable among the various windows and, therefore, independent of the number of cycles, the value of normalized DES has been defined that is evaluated in the hypothesis of a number of cycles constant for all the windows. In the case of number of cycles constant and equal to equation (11) becomes the following: ̅ = ∙ [ ] − (12) 3. Development of the tool in a control system design environment The evaluation model described in the previous paragraph was then implemented in a computing environment dedicated to the dynamic multidomain simulation of mechanical systems and to the design and verification of control systems (Simulink). Figure 2 shows the model of the fatigue behavior evaluation developed in this environment, capable to be interfaced with any control system in which the input signal represents one of the generic parameters that a multibody model or a real system allows to provide by virtual or real measurement (i.e. acceleration, velocity, displacement, bending moment, stress, strain).

Fig. 2. Simulink model of the proposed damage evaluation tool

All the output parameters described in the previous paragraph and in particular the instantaneous damage, the cumulative damage, the alternating equivalent true and normalized values and, moreover, the mean value and the