The Ti/APC-2 hybrid cross-ply nanocomposite laminates were successfully fabricated by the modified diaphragm curing process. The titanium thin sheets were surface treated by chromic acid anodizing to achieve superior bonding with APC-2 laminates. The nanoparticles SiO2 were uniformly spread on the interfaces of APC-2. The tensile tests at room and elevated temperatures were conducted to obtain the mechanical properties. It is interesting to find a knee point in each stress–strain curve. To predict and verify the feature of knee point the residual stresses and strains were calculated by simple methods. Adopting the residual stress effect and rule of mixtures, the analytical stress–strain curves at elevated temperatures were obtained. The data and mechanisms of the knee point in hybrid laminates were verified and highlighted. The predicted results of ultimate strength, longitudinal stiffness and the knee point are all in very good agreement with the experimental data.
The Ti/AS-4 Carbon Fiber/PEEK (Ti/APC-2) cross-ply nanocomposite laminates were fabricated. The Ti thin sheets were surface treated by anodic oxidation of electroplating to achieve good bonding with APC-2 laminates. Nanoparticles SiO2 were dispersed uniformly on the interfaces of APC-2 with the optimal amount of 1 wt%. The modified diaphragm curing process was adopted to fabricate the hybrid panels. Then, the panels were cut into samples. The centrally notched samples of hole diameter 6mm. First, we obtained the mechanical properties of unnotched samples as base-line data due to tensile and cyclic tests. Then, we performed both tests for the notched samples and found that the ultimate load was reduced 53%, nominal stress 38%, stiffness 3%, and also the fatigue lives compared with unnotched ones. Next, the two-step loading tests, such as high→low and low→high tests, were conducted. The average values of Miner’s sum were less than 1.0 for both two-step tests. The total lives were in the range of 5780~29048 cycles for both tests. That evidently demonstrates the notched samples drastically drop the mechanical properties and lives from high cycle fatigue to low cycle fatigue.
Fiber/metal composites (FMCs) have attracted much attention over twenty years, especially in the applications to aerospace and aeromechanical structures. In addition to their advantages of fiber reinforced composites they also possess superior resistance to cyclic loadings. It is well-known known that conventionally the composite laminates are weak due to out-of-plane loads. Hence, vulnerability against high velocity impact loads is becoming an increasingly critical issue for the design of FMCs in aerospace structures recently. In this study we mainly focus on the theoretical derivations of penetration and perforation in Ti/APC-2 hybrid composite laminates impacted by a hemispherenose cylindrical projectile at high velocities, and verifies the results by numerical simulation, such as finite element method and ANSYS LS DYNA 3D software.Fundamentally, cross-ply [0/90]4s and quasi-isotropic [0/±45/90]2S APC-2 composite laminates are investigated. Then, Ti/APC-2 hybrid laminates are studied as an extensional work based on previous experience. It is quite different from the cases of low velocity impact that the boundary conditions and geometry of laminated plate can be omitted, and the wave propagation model should be used in high velocity impact. Thus, a rectangular composite laminate is analyzed for general purposes. The theoretical process involves first the deformation and failure of face sheets, through-thickness propagation of shock wave into the middle plies of shear failure, fracture of back sheets and perforation finally. Equations of motion for the projectile and effective masses of the face sheets, middle plies and back sheets as shock wave traveling through the whole laminate are derived by using Lagrangian mechanics. The analytical approach is mechanistic involving no detail account of progressive damage due to cracking, delamination and debonding, etc.Analytical predictions of total time of traveling ballistic limit, (perforation of laminate with zero residual velocity), residual velocity, transient deflection and velocities of projectile are determined. They are compared with the results from numerical simulation within acceptable errors. Both methods provide valuable achievements that makes us thoroughly understand the phenomena of high velocity impact in composite laminates.
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