Dynamic Flexural Modulus and Low-Velocity Impact Response of Supercomposite^TMLaminates with Vertical Z-Axis Milled Carbon Fiber Reinforcement

In work reported here, the dynamic properties and low-velocity impact response of woven carbon/epoxy laminates incorporating a novel 3D interlaminar reinforcement concept with dense layers of Z-axis oriented milled carbon fiber SupercompositeTM prepregs, are presented. Impulse-frequency response vibration technique is used for non-destructive evaluation of the dynamic flexural modulus (stiffness) and loss factor (intrinsic damping) of woven carbon/epoxy control and SupercompositeTM laminates. Low-velocity punch-shear tests were performed on control and SupercompositeTM laminates according to ASTM D3763 Standard using a drop-weight impact test system. Control panels had all layers of 3K plain woven carbon/epoxy prepregs, with a dense interlaminar reinforcement of milled carbon fibers in Z- direction used in designing the SupercompositeTM laminate—both having same areal density. Impulse-frequency response vibration experiments show that with a 50% replacement of woven carbon fabric in control panel with milled carbon fibers in Z direction dynamic flexural modulus reduced 25% - 30% (loss in stiffness) and damping increased by about the same 25% - 30%. Low-velocity punch-shear tests demonstrated about 25% reduction in energy absorption for SupercompositeTM laminates with the replacement of 50% woven carbon fabric in control panel.

Effect of Fiber Weight Ratio and Fiber Modification on Flexural Properties of Posidonia-Polyester Composites

The main objective of this research is to study the effect of fiber weight ratio and chemical fiber modification on flexural properties of composites reinforced with Posidonia fiber. An unsaturated polyester matrix reinforced with untreated and treated Posidonia fibers was fabricated under various fiber weight ratios. Results showed that the combined chemical treatment provided better mechanical properties of composites in comparison with untreated fiber. The fiber weight ratio influenced the flexural properties of composites. Indeed, a maximum value of flexural modulus was observed for 10% fiber weight ratio for composites reinforced with treated fibers. SEM photographs revealed a different fracture surface between Posidonia fibers reinforced polyester composites.

Flexural rigidity of honeycomb consisting of hexagonal cells

In this study,the flexural rigidity of a honeycomb consisting of regular hexagonal cells is investigated.It is found that the honeycomb bending can not be evaluated by using the equivalent elastic moduli obtained from the in-plane deformation because the moments acting on the inclined cell wall are different for in-plane deformation and bending deformation.Based on the fact that the inclined wall is twisted under the condition of the rotation angle in both connection edges being zero,a theoretical technique for calculating the flexural rigidity of honeycombs is proposed,and the validity of the present analysis is demonstrated by numerical results obtained by BFM.

Effects of freeze-thaw cycles on fracture behavior of epoxy asphalt concrete

According to the winter temperature of Peking,the freeze-thaw（FT） condition in laboratory was determined.Seven groups of epoxy asphalt concrete（EAC） specimen were exposed to different FT cycles.The flexural modulus and fracture energy（G_F） of EAC exposed to different FT cycles were obtained through the 3-point bending test.Meanwhile,the plane strain fracture toughness（K_（IC）） of EAC was obtained through numerical simulation.The results show that the flexural modulus of the FT conditioned EAC samples decreases with the increase of FT cycles.The FT damage of flexural modulus is 60%after 30 FT cycles.Nevertheless,with the increase of FT cycles,the G_F and K_（IC） of EAC decrease first and then increase after 15 FT cycles.

The Effect of Titanium Dioxide and Zinc Oxide Nanoparticles on Some Mechanical Properties of Epoxy Nanocomposites： A Comparative Study

A new type of inorganic-polymer materials of epoxy Titanium Dioxide and Zinc Oxide was prepared. In this work, the mechanical properties of polymer composites reinforced with ceramic nanoparticles were investigated. Three points bending tests demonstrated an enhancement in flexural strength and flexural modulus respectively, compared to the pure epoxy. The reinforcement of nanoparticulate materials was Titanium Dioxide and Zinc Oxide with various weight fraction. Experimental tests results indicated that the composite materials have significantly higher modulus of elasticity than the matrix material. It was found that the enhancement in modulus of elasticity was directly proportional to the weight fraction of reinforcement material, and that Zinc Oxide composites have higher modulus of elasticity than Titanium Dioxide composites with equivalent of weight fraction. The wear results showed that nanoparticles improved the wear resistance of epoxy nanocomposites, the Titanium Dioxide matrix particles could improve the wear resistance of the epoxy more efficiently than Zinc Oxide particles. The fatigue test showed that the fatigue resistance of epoxy Zinc Oxide matrix particles was higher than that of Titanium Dioxide matrix particles.

Flexural Mechanical Properties of Functional Gradient Hydroxyapatite Reinforced Polyetheretherketone Biocomposites

Functional gradient hydroxyapatite reinforced polyetheretherketone is one of the most promising or- thopedic implant biomaterials. In this study, functional gradient hydroxyapatite reinforced polyetheretherketone biocomposites were prepared by layer-by-layer method with the incorporation of hot press molding technology. Studies on the flexural mechanical properties of the functional gradient biocomposites revealed that the flexural stress-stain behavior of the biocomposites presented linear elastic characteristics. The fracture mechanism of the functional gradient biocomposites was predominated by brittle rupture. Furthermore, both flexural strength and break strain of the functional gradient HA/PEEK biocomposites obviously decreased with the rise of the total HA content. The effect of hydroxyapatite concentration difference between adjacent layers （HCDBAL） on the flexural strength obviously relied on the level of HCDBAL and total HA content in the functional gradient HA/PEEK biocomposites. The higher the total HA content in the functional gradient biocomposites is, the less the influence degree of HCDBAL on the flexural strength is. Moreover, total HA content and HCDBAL played synergistic influence on the flexural modulus of the functional gradient HA/PEEK biocomposites.