Key Engineering Materials Vols. 334-335

Abstract: The microstructures of Cu-Cr alloys with 2.0-4.2wt%Cr have been studied. Very little dendritic copper was found in supereutectic Cu-Cr alloy containing 2.4wt%Cr. When Cr content reached to 4.2wt%, square-like section Cr fibers other than round fibers were observed besides primary dendritic chromium in the Cu-Cr alloy. The fibrous Cr particles are eutectic chromium phase.

Abstract: This paper proposes a novel atomistic-continuum mechanics (ACM) based on the finite element method (FEM) to investigate the mechanical bulk behavior of atomic-level single crystal silicon under uniaxial tensile loading. The ACM could be reduced efficiently the computational time and maintained the simulation accuracy. A general form of Stillinger-Weber potential function was used for interaction between the silicon atoms in the ACM simulations. Simulation results shows that the Young’s modulus of single crystal silicon were 121.8, 153 and 174.6 GPa along the (100), (110) and (111) crystallographic plane, respectively. These results are in reasonable agreement with the experiment and simulation results reported in the literature.

Abstract: Firstly the tension experiment was undertaken to investigate the mechanic behaviors of the flange repaired composite panels in this paper. Emphases were played on the damage initiation and the failure strength for the repaired composite structure. Then numerical studies were conducted by using finite element method. The effect of geometric non-linearity on the stress-strain response was taken into account through quadrilateral, thick shell elements (S8R). A better agreement with experiment could be obtained when geometric non-linearity was considered. In addition, a user material subroutine (UMAT) was implemented into ABAQUS for studying damage initiation and its progression in the composite structure. Finally, all the predicted strain distributions, damage development and strength of the repaired laminate were compared with experiments. The predictions and experiments were found to be in good agreement.

Abstract: Phase-stepping photoelasticity has been used to study the fragmentation of an E-glass fibre in epoxy resin and examine quantitatively the effect of a transverse matrix crack on the stress transfer at an interphase. Unsized glass fibre was coated by plasma polymerisation with a crosslinked conformal film of 90% acrylic acid and 10% 1,7-octadiene. The micro-mechanical response at the fibre-matrix interphase and in the adjacent matrix has been described in detail using contour maps of fringe order. From these, the interfacial shear stress profiles at fibre-break have been calculated.

Abstract: Spherical alumina powder and dispersant were mixed with distilled and deionized water, and ball milled to make alumina slurry. The slurry was dried in a high magnetic field to make a compact. Subsequently, the compact was cold-isostatic-pressed (CIP) to enhance the homogeneity in particle packing density. Anisotropy of shrinkage during sintering was examined for the alumina compacts in detail. Particle orientation existed in the spherical alumina powder compacts prepared in 10T, and made them shrink anisotropically during sintering. Sintering shrinkage was larger in the direction parallel to magnetic field direction (i.e., the c-axis direction of alumina crystal) than that in its perpendicular direction. The particle orientation structure in the compacts was confirmed with the immersion liquid method of polarized light microscope, and the grain alignment structure in the sintered bodies was also observed with X-ray diffraction, the c-plane was perpendicular to the magnetic field direction. On the other hand, isotropic sintering shrinkage occurred in the spherical alumina powder compacts prepared in 0T, which did not hold the particle orientation. The experimental results indicate that sintering shrinkage of spherical alumina powder compact depends on alumina crystal axis direction. Origin of the sintering shrinkage anisotropy for the spherical alumina powder compacts can be attributed to the particle orientation caused by high magnetic field.

Abstract: The aim of this study is to evaluated the possibility of the in-situ synthesized (TiC+TiB) reinforced titanium matrix composites (TMCs) for the application of structural materials. In-situ synthesis and casting of TMCs were carried out in a vacuum induction melting furnace with Ti and B4C. The synthesized TMCs were characterized using scanning electron microscopy, an electron probe micro-analyzer and transmission electron microscopy, and evaluated through thermodynamic calculations. The spherical TiC plus needle-like and large, many-angled facet TiB reinforced TMCs can be synthesized with Ti and B4C by a melting route.

Abstract: Compressive experiments and finite element method (FEM) have been used to study the mechanical behavior of composite laminate with plies drop-off. A user subroutine has been implemented to ABAQUS to simulate the damage development of the laminate plate. This user subroutine has taken consideration of the mechanical properties degradation according to development of three types of damage. The load-strain curves can agree with each other between experiments and FEM. The detail of damage development of the plies drop-off composite laminate under compressive loading can be described as followed. Matrix cracking damage and fiber-matrix shearing damage occur simultaneously at first, and then fiber buckling damage initiates. Matrix cracking and fiber-matrix shearing are very dangerous to the carrying capacity of laminate and fiber buckling intensifies further this effect. The initiation and development of fiber buckling indicates that laminate loses carrying capacity at all.

Abstract: In this paper the relationship between CAI and compressive design allowables of composite structures were discussed and it was pointed out that traditional CAI values could not reflect the behavior of composite materials to withstand impact adequately and no relationship between CAI values and compressive design allowables existed. Based on the integrity requirements of composite structures, it was pointed out that the evaluation system of composite materials to withstand impact should include both damage resistance and damage tolerance. Large numbers of test data verified that the knee point phenomenon of composite laminates to withstand impact existed. Based on failure mechanisms, it was proposed that the behavior evaluation system of composite systems to withstand impact was based on the properties at the knee point, that is, the maximum capability to keep integrity of the front plies (the maximum contact force) characterizing damage resistance and the threshold of dent depth(or impact energy)~compressive strength(or failure strain) curves characterizing damage tolerance.

Abstract: Iron-hercynite composite was synthesized from Al and Fe3O4 powders by reaction sintering at ~1350oC, or by arc-melting. In reaction sintering, a three-step displacement reaction between Al and Fe3O4 was identified. In arc-melting, we observed that molten iron and hercynite segregated from each other readily. Magnetization of the extracted hercynite from the arc-melted sample was 4 emu/g, smaller than those previously reported, and this can be explained by the variations of the stoichiometric ratio and the degree of inversion of the spinel structure in the hercynite products.