4.2. Fan blades fatigue test
The fatigue tests were carried out in the form of trapezoidal wave with
a loading frequency of 0.04 HZ, as shown in Fig. S3, under normal
temperature and atmospheric conditions. Stress ratio (R =0) was
conducted in all tests. The stress range measured by the test system was
0~5000 Mpa, and the range of rising speed at this
frequency was 0~3000r/min. The actual working condition
of the fan was simulated to the maximum extent. In order to ensure that
each revolving speed range could be accelerated to the specified speed,
the differences of accelerations at different speeds were taken into
account.
Experiments were carried out based on the predicted model, and fatigue
life tests were conducted on fan blades under four different levels of
constant stress. The starting and stopping test was carried out at 1600
rpm firstly, and then the 1800, 2000 and 2200 rpm tests were done. There
were at least four sample fans were used for each set of fatigue life
test. Then, cumulative fatigue tests were carried out at four levels of
1600~2200 speed and at least 4 sample fans were used in
the fatigue life test. In order to discover the generation of fatigue
crack, the response of each critical section and dangerous part was
monitored and observed at different test time during fatigue test. The
fatigue crack propagation was observed and recorded. A crack with a
length of 6mm appears on the surface near the root of the connecting end
of blade and impeller, indicating impeller failure, as shown in Fig. S4.