Finally, the last aspect analyzed w next to one of two existing bounds: stick out of contact surface[9,17]. Although it predominate, authors linked crack nucleation site to contact pressure work, crack nucleation site changed from test to test: in a few cases, crack nucleated near stick zones bound (Fig. 9a), in specimens and free region (Fig. 9b). Figure 9 – Examples of crack nucleation sites: stick 3.3. On the device The most advantageous innovation of the ultrasonic device was clearly the possibility of accelerating enormously tests, as presented before. Some other b though. The mechanics of the machine is simple, resulting in easy maintenance and f operators training. Also, settingcomponents of the machine and instruments are fatigue machines. Finally, another great advanta this paper, the choice of fretting amplitude and bulk stress is uncoupled. machines used in several studies[18 On the other hand, a few drawbacks were found alignment problems. The necessity of extremely well polished specimens is inherent to the process, once that superficial problems can trig crack nucleation of geometry – cylinder 100mm long, 4mm diameter more troubling is the necessity of very can see in Fig. 10, nonconformities can be very harmful to tests, once that small deviations in geometry can significantly change fretting displacement (see Fig. 5 to dimensions’ codes). in both properties per deviation percentage in geometry, e.g., 1% of deviati provokes almost 2% of deviation in bulk load and around 0.3% in displacement amplitude. 13th International Conference on Fracture June 16 lly, the last aspect analyzed were the crack initiation sites. Fretting cracks are usually nucleated next to one of two existing bounds: stick-slip zones limit and the limit between slip zone and region Although it is very hard to determine which of these z authors linked crack nucleation site to contact pressure[17]. However, specimens, cracks nucleated in the bound between region under contact of crack nucleation sites: stick-slip zones limit (a) and bound between under contact and free region (b) advantageous innovation of the ultrasonic device was clearly the possibility of accelerating enormously tests, as presented before. Some other benefits -up and operating are easy, except for the alignment process components of the machine and instruments are light and inexpensive when compared to other axial Finally, another great advantage is that, within certain limits, as discussed later in this paper, the choice of fretting amplitude and bulk stress is uncoupled. It used to be a problem in [18-20] in which one factor was dependent on the other. other hand, a few drawbacks were found linked to specimen manufacture The necessity of extremely well polished specimens is inherent to the process, can trig crack nucleation before reaching VHCF cylinder 100mm long, 4mm diameter – can be very time and money consuming. Still more troubling is the necessity of very strict geometric tolerance in manufacture process. As one , nonconformities can be very harmful to tests, once that small deviations in geometry can significantly change fretting displacement amplitude and bulk load at a given position to dimensions’ codes). In this chart, vertical axis represents the percentage of deviation June 16-21, 2013, Beijing, China 7 retting cracks are usually nucleated slip zones limit and the limit between slip zone and region which of these zones will . However, in the present work, crack nucleation site changed from test to test: in a few cases, crack nucleated near stick-slip , cracks nucleated in the bound between region under contact ) and bound between under contact could be pointed out though. The mechanics of the machine is simple, resulting in easy maintenance and facilitating , except for the alignment process. The inexpensive when compared to other axial ge is that, within certain limits, as discussed later in It used to be a problem in in which one factor was dependent on the other. linked to specimen manufacture costs and VHCF. Polishing this kind can be very time and money consuming. Still geometric tolerance in manufacture process. As one d bulk load at a given position In this chart, vertical axis represents the percentage of deviation in both properties per deviation percentage in geometry, e.g., 1% of deviation in diameter D1
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