Key Engineering Materials Vols. 334-335

Abstract: When the KId (dynamic fracture toughness) of the three point bending components is tested on the SHPB device, the signals of reflected waves obtained have been elongated because the end of the incidence pole is generally made by wedge shape. Through the conduction theory based on one dimension stress wave theory, the reflection and transmission phenomena of waves on the surface of the wedge have been analyzed. In the present paper, the loads acting the components have been modified, by removing the stress wave part among incidence and reflection waves reflected by the wedge surface.

Abstract: This study deals with the in-plane Young’s moduli of two-dimensional auxetic cellular materials with negative Poisson’s ratios. The in-plane Young’s moduli of these cellular materials are theoretically analyzed, and calculated from the cell member bending with large deflection. Expressions for the in-plane Young’s moduli of the above-mentioned cellular materials are given by incomplete elliptic integrals. It is found that the in-plane Young’s moduli of two-dimensional cellular materials with negative Poisson’s ratios depend both on the geometry of the cell, and on the induced strain of these cellular materials. The in-plane Young’s moduli are no longer constants at large deformation. But at the limit of small strain, they converge to the results predicted by the small deformation model of flexure.

Abstract: Tensile properties and morphology of poly(ethylene naphthalate)/polyolefin blends and the relationship with the extrusion die size were investigated. Scanning electron micrographs of the blends reveal that the fibre morphology is developed during extrusion through the die. Skin-core morphology has been observed. As die diameter decreases, a droplet-to-fibre transition in morphology increases tensile strength and stiffness. After microfibrillization, up to 100% increase in the tensile stiffness was observed and the tensile strength could increase by one order of magnitude.

Abstract: Mesophase pitch (MPP) has a high carbon yield and excellent graphitizability, compared with commercial coal tar pitch (CTP), which make it suitable for the preparation of C/C composites. In this paper, two MPP were prepared by heat-treatment of two coal tar pitches (CTP and modified coal tar pitch (MCTP)) in the presence of nitrogen. Elemental analysis and FTIR were used to monitor the change of chemical structures of MPP transition from CTP and MCTP. The pyrolysis behaviors of CTP and MCTP were studied by means of thermal analysis (TG and DSC). The morphologies of MPP were inspected by optical microscope. The structures of the MPP were characterized by XRD. The results show that there are more alkyl functional groups existing in CTP and MCTP than in MPP, and MPP has a higher C/H ratio than CTP and MCTP, which indicate MPP formation predominantly polycondense aromatic and release the alkyl functional groups. An endothermic band due to volatilize light compounds around 290 °C, two exothermic peaks at 430°C and 490 °C were characteristic of polymerization reactions, exothermic peaks of MCTP are higher than that of CTP because the former has a higher reaction active for its more alkyl side chain. The optical texture of MPP from CTP is mosaics texture, while from the MCTP is flow domains texture. (002), (101) peaks of graphite occur on XRD patterns, the peaks of MPP from MCTP are higher and narrower than MPP from CTP, which indicates the former is more graphitizability than the latter.

Abstract: Ductile honeycombs under in-plane biaxial loads fail by elastic buckling, plastic yielding and fast fracture of solid cell edges, while brittle honeycombs fail by elastic buckling, brittle rupturing and fast fracture of solid cell edges. In the paper, we aim at summarizing the modeling and theoretical expressions for describing the failure surfaces of honeycombs with non-uniform thickness cell edges under in-plane biaxial loads. Hence, the failure surfaces of ductile honeycombs with plateau borders are generated and found to be dependent on the solid distribution in cell edges and the yielding strengths of solid cell edges. Also, the failure surfaces of brittle honeycombs with plateau borders are significantly affected by the cell-edge modulus of rupture and the solid distribution in cell edges.

Abstract: A series of CuW60Cr15 composites with different Cr particle size ranging from 43μm to147μm in diameter have been prepared by infiltration. The results show that the size of Cr particles plays an important role on the microstructures and the properties of the CuW60Cr15 composite. Fine Cr particle changes not only the size of the isolated CrCu alloy zone but also the structure of the skeletons of the composite obviously. Fine Cr particles increase not only the maximum and the minimum but also the mean value of breakdown voltage. Although the maximum value of chopping currents remains almost constant while Cr particles become finer, the minimum and the mean values of chopping current discernible decrease in the CuW60Cr15 composites. It can be seen from the SEM photos of the composites after arcing that the size and its location of the arc spot determines the chopping current value of the composites.

Abstract: The interfacial structure and interactions of amine-cured epoxy resin (EP) / aluminium oxidie system were investigated in this presentation. The competitive chemisorption of uncured epoxy resin on Al2O3 particles were measured by FTIR and XPS. The interphase structure and the morphology at different depths of the broken-surface of the samples were characterized by XPS and SEM. The results showed that the nitrogenous molecules in the system formed the adsorbed monolayers on the interface based on the coupling interaction of the adsorption and cure. The composition, binding energy and chemical properties of the interphase deviated considerably from that of the bulk.

Abstract: Postbuckling failure behaviors and strength were investigated in compression tests of the hat stiffened composite panels manufactured with different bonding methods and different stiffener section shapes. The skin-stiffener separation loads, separation failure behaviors and final collapse loads were different with respect to bonding methods and stiffener shapes. As the separation failure was initiated early and propagated larger area, collapse loads and structural performance of the panels decreased. The test results showed that the co-curing with or without adhesive film and open type stiffeners were most beneficial for the postbuckling strength.

Abstract: This study examined the dynamic penetration phenomena of high-velocity impact of magnesium alloy
 CFRP (Carbon Fiber Reinforced Plastic) composite. Test materials for investigation are magnesium alloy(AZ31B), the heat-treated magnesium alloy (AZ31B-200°C, AZ31B-300°C, AZ31B-430°C), and carbon/epoxy laminated composite materials with fiber direction [0°]8, [0°/45°]4s, [ 0°/90°]4s, [ 0°/45°/90°]3s and [ 0°/45°/-45°/90°]2s. We used a ballistic range (one-stage light gas gun), and the test specimens were set at 0°obliquity at room temperature. A high-speed camera allowed us to capture and analyzed the dynamic penetration phenomena of the test specimen.

Abstract: This investigation was conducted to study the effect of Al(Cr) content in Cu-Al(Cr) pre-alloyed powders on the distribution of Al2O3(Cr2O3) particles formed by internal oxidation. The results show that the distribution of Al2O3 particles is different with the change of Al content in Cu-Al system. When the Al content is above 1.2wt.%, the Al2O3 particles tend to distribute along the grain boundaries of copper matrix , whereas when the Al content is above 2.0 wt.%, the Al2O3 particles have distributed along the grain boundaries. However, it is interesting to note in Cu-Cr system that most of the formed Cr2O3 particles prefer to distribute in the grain of copper matrix when the Cr content is less than 5wt.%, which is quite different from that of Cu-Al system.