Issue 33

M.A. Meggiolaro et alii, Frattura ed Integrità Strutturale, 33 (2015) 368-375; DOI: 10.3221/IGF-ESIS.33.40 369 almost keep all the original reversals. In other words, the racetrack filter condenses the original variable amplitude history into a smoother history, discarding the small amplitude changes that cause negligible fatigue damage [2]. Moreover, the condensed history does not change the order of the significant load events, which is an essential feature to account for plasticity memory effects. Figure 1 : Uniaxial racetrack filter example, showing: (a) the original history; (b) the racetrack defined between the upper and lower fences; (c) the driver path from A to F; and (d) the filtered history. The algorithm of the uniaxial racetrack filter is easier to implement through another physical analogy, a small round peg P that can oscillate inside a slotted plate whose center is the point O, see Fig. 2. The range that the peg can oscillate inside the slot is 2r , the racetrack filter range. Both peg and slot center are initially aligned with point A, as seen in Fig. 2(a). During the path AB, the peg moves up until reaching the upper limit of the slotted plate, which then starts to move up, see Fig. 2(b), where the dark dashed line represents the path of point O. As shown in Fig. 2(c), the following path BCD moves the peg but does not involve any translation of the slotted plate, an indication that the points C and D can be filtered out: peg oscillations alone can be discarded. Then, both paths DE and EF involve slotted plate translations, see Fig. 2(d) and (e), so they must be maintained in the filtered history. After the initial point A, only the peg locations P associated with the end of a translation of the slotted plate are stored in the filtered history. Point B is the peg location at the end of the first slotted plate upward translation, so it is stored. Similarly, points E and F are stored since they are the peg locations at the end of the next downward and upward slotted plate translations. The filtered history is then the path ABEF, as shown in Fig. 2(f), always identical to the path obtained from the original racetrack filter. This amplitude filter is very efficient in practice, since besides small damageless load events it can remove the unavoidable noise e.g. from strain measurements, which can induce much more small reversions than the load itself in the measured signal.