Fatigue behaviour of composite tubes under multiaxial loading

274
Fifth International Conference on Fatigue of Composites
two plies by inserting a Teflon sheet of thickness of 25m. Four delamination cases are considered,
which are [010//906/906/010], [010/906//906/010], [012//04/04/012] and [012/04//04/012], where the symbol “//”
denotes the position of delamination along the through-thickness direction. The distance from the right
end of the delamination to the right end of beam is 200 mm. In our experiments, three kinds of
delamination lengths are employed, i.e., 30 mm, 20 mm and 10 mm, respectively. A circular PZT
actuator (Fujiceramics, C6) is attached on the top surface of the left end of beam using a kind of very
strong adhesive. In this case, the generated waves from the actuator merge into the reflected waves from
the left end of beam directly, and the complex reflection pattern from both ends of the beam can be
avoided. A same PZT sensor is attached on the top surface of the beam between the delamination and
the actuator to pick up the reflected wave from the delamination. The diameter of PZT sensor and
actuator is 10 mm and the thickness is 0.5 mm. Its material properties are: E11=62 GPa, E33=49 GPa,
d33=472 pC/N, and d31=-210 pC/N. A PCI board of wave signal generation (National Instruments, NI
PCI-5411) is used to generate the wave signal, which is amplified by an amplifier
z
Fig. 1. Schematic view of delaminated beam ([010//906/906/010]) with actuator and sensor (S0 mode).
Table 1. Material properties of CFRP beams
E [GPa] G [GPa] [kg/m 3 ]
E11=115
E22=E33=9
G12=G23=G13=3
12=13=0.3
23=0.45
(Krohn-Hite, Model-7500). After the signal is received by the sensor, it is amplified by a charge
amplifier (FEMTO, DLPCA-200), and then sent into an oscilloscope (Tektronix, TDS3034B) for
analysis. Finally, the obtained data from the oscilloscope are processed in a computer. By employing
Hanning window, a signal of 5 cycles and 100 kHz is generated by applying 50 V voltage on the
actuator as follows,
Actuator アクチュエータ(PZT) (PZT) Sensor センサ(P (PZT) ZT) Delamination 擬似はく離(10/11層目)
between
10 th and 11 th plies
x
1005m m mmm
455
320
1600
0.5[1
-cos(2 ft / N)]sin(2 ft), t N / f
Pt () =
0, t N / f
4.8
z
where f is the central frequency in Hz and N is the number of sinusoidal cycles within a pulse.
Here, the propagation speed of S0 Lamb mode is much higher than that of A0 Lamb mode, e.g.,
around 4 times higher in our case. For instance, in our experimental results, before the arrival of
incident A0 Lamb mode at the sensor from the left to the right, the reflected S0 modes from the
delamination and the right end of beam, which travel from the right to the left, already arrive at the
30
200
10
y
(1)