2. EXPERIMENTAL
12 inches wide Carbon–PEEK unidirectional prepregs (Cytec Industries
Inc., USA) were cut and stacked into cross-ply
[0/90]s laminates. The Grade 1 (H: 0.015%, O:
0.18%, N: 0.03%, Fe: 0.2%, C: 0.08%) Ti sheets, supplied by Kobe
Steel, Ltd. (Japan), were 0.5 mm thick after rolling, heating, and
flattening through scratch brushing. The ultimate tensile strength and
modulus of elasticity of Ti are 330 MPa and 83 GPa, respectively.
Prior to lamination, the slimmed Ti alloy sheets were pretreated to
create a strong bonding with APC-2 prepregs. After a series of tensile
tests, surface treatment with a chromic acid anodic method of
electroplating was used. The thickness of the oxide coating film was
approximately 40–80 nm through SEM. The composition of the coating was
determined to contain TiO2 through EDS. The procedure of
making nanoparticle solution was first to dilute nanoparticles in
alcohol (50ml alcohol: 2g SiO2) and stirred uniformly.
Then, SiO2 solution was spread on the prepregs, i.e.,
the interfaces of APC-2 laminate, in a temperature-controlled box to
evaporate the alcohol.
The APC-2 prepregs were sandwiched between the Ti alloy sheets to form
Ti/APC-2 hybrid three-layered laminate. A modified diaphragm curing
process was adopted to cure the hybrid panel and the panel was cut into
samples of 240 (length) × 25 (width) × 1.55 (thickness)
mm3, as shown in Figure 1. The samples were divided
into 12 groups, including neat and nanocomposite laminates with two
inclined crack lengths i.e. 2.0 mm and 3.0 mm, at three angles such as
30°, 45° and 60°. The width of cracks was 0.3 mm according to ASTM
E740-03.
An MTS-810 servohydraulic computer-controlled dynamic material testing
machine was employed to conduct the tensile test and constant stress
amplitude T–T cyclic test with stress ratio = 0.1, frequency = 5 Hz,
and a sinusoidal wave form under a load-controlled mode at room
temperature. A 25-mm MTS-634.11 F-25 extensometer was used to
continuously monitor the strain during the tests.