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.