Anisotropy of machine building materials

The results of experimental studies of the anisotropy of elastic and strength characteristics of various structural materials, including pressure worked metals and alloys, laminated fiberglass plastics, and laminated wood plastics, are correlated and classified. Strength criteria under simple and complex stresses are considered as applied to anisotropic materials. Practical application to determining the strength of machine parts and structural materials is discussed

Strength of anisotropic wood and synthetic materials

The possibility of using general formulas for determining the strength of different anisotropic materials is considered, and theoretical formulas are applied and confirmed by results of tests on various nonmetallic materials. Data are cited on the strength of wood, plywood, laminated wood plastics, fiber glass-reinforced plastics and directed polymer films

Stripes, Non-Fermi-Liquid Behavior, and High-Tc Superconductivity

The electronic structure of the high-Tc cuprates is studied in terms of "large-U" and "small-U" orbitals. A striped structure and three types of quasiparticles are obtained, polaron-like "stripons" carrying charge, "svivons" carrying spin, and "quasielectrons" carrying both. The anomalous properties are explained, and specifically the behavior of the resistivity, Hall constant, and thermoelectric power. High-temperature superconductivity results from transitions between pair states of quasielectrons and stripons.Comment: 4 page

Structure and Fracture Visualization of Tilted ABS Specimens Processed via Fused Filament Fabrication Additive Manufacturing

Fused filament fabrication (FFF) technique is one of the most frequently used additive manufacturing (AM) technologies for printing ABS and many other thermoplastic materials. The anisotropy of the mechanical properties of 3D-printed parts manufactured by FFF technology is still of major concern when using this technique. Thus, the component’s orientation, build strategy and printing parameters affect the mechanical properties, and failure mechanisms are of crucial importance. This research aims to partly fill this gap by studying the structure and mechanical behavior of FFF-ABS specimens, and by performing fracture surface analysis by the three-point bend flexural test. A series of tests were conducted to determine the flexural properties of tilted specimens at 0°, 15°, 30°, 45°, 60° and 75° inclination angles relative to the machine platform. The work describes manufacture method of the specimens, experimental procedures, and outcomes from the mechanical and structural characterizations of the FFF-ABS specimens. Overall, two main failure modes were observed for the tested specimens: (1) inter-layer/ inter-raster bond failure (typical for upright specimens) and (2) intra-layer/trans-raster failure (typical for on-edge specimens). A mixed inter-layer/ intra-layer mode was found for the specimens tilted in-between the 15o and 60o range

Mechanical Properties, Structure and Fracture Behavior of Additive Manufactured FFF-ABS Specimens

The Fused Filament Fabrication (FFF) method is one of the most important additive manufacturing (AM) technologies. This technology is used today with various kinds of thermoplastic materials, including ABS. The present study deals with the flexural strength and axial deflection of ABS specimens versus relative density, to observe the influence of build-orientations, build model and microscopic level defects of these properties. In this study, the mechanical and structural characterization of AM-FFF ABS material was studied by CAD modelling of different orientations, three point bending mechanical testing, visual testing, and multifocal light microscopy observation, including fractography analysis. To that end, three different standard building orientations (Flat, On Edge and Upright) were printed, and each was built in two different angle orientations (-45o/+45o and 0°/90o). Based on the three point bending testing results, it was found that the specimen with the highest flexural strength was not necessarily the one with the highest deflection. It was also observed that On Edge 0/+90o orientations showed a relatively larger flexural strength difference in comparison to other building orientations (Flat and Upright). When the mechanical properties achieved from a bending test next to the building platform were compared to the properties far from the building platform, only a slight difference was found, which means that the flexural strength difference results from the building strategy and it is not related to the specific bending surface. Based on fractography observation, there is a major difference in the mechanical properties and fracture surface appearance, when the samples are bent between the layers (Upright orientation) or when the samples are bent through the layers (Flat and On Edge orientation)

Ordered and periodic chaos of the bounded one dimensinal multibarrier potential

Numerical analysis indicates that there exists an unexpected new ordered chaos for the bounded one-dimensional multibarrier potential. For certain values of the number of barriers, repeated identical forms (periods) of the wavepackets result upon passing through the multibarrier potential.Comment: 16 pages, 9 figures, 1 Table. Some former text removed and other introduce

Fused Filament Fabrication Additive Manufacturing: Mechanical Response of Polyethylene Terephthalate Glycol

The additive manufacturing (AM) fused filament fabrication (FFF) technology is widely used today with different kinds of thermoplastic materials, including polyethylene terephthalate glycol (PETG). One of the major problems of parts produced by AM-FFF technology is the anisotropy of their mechanical properties. Therefore, it is very important to understand the effect of build strategy and post-processing on the mechanical properties and failure behavior of the FFF-PETG components. This research aims to examine the influence of 3D-print orientations, post-processing heat treatments and reinforcement of the material with carbon fibers, on the mechanical properties of FFF-PETG specimens. For this purpose, three different standard building orientations, flat, one-edge and upright specimens were printed. Tensile testing was carried out to obtain the mechanical properties of the FFF-PETG specimens for the different 3D-print orientations and post-processing. The specimens were characterized by visual testing, stereo microscopy, and SEM microscopy to examine the fracture surface after tensile test. The upright-melted specimens reached the same tensile strength as the as-printed flat and on-edge orientations specimens. The fracture surface of all three orientations is brittle and it typically starts by a mirror pattern that evolves into cleavage plates

Mechanical Performance, Structure and Fractography of ABS Manufactured by the Fused Filament Fabrication Additive Manufacturing

Fused filament fabrication (FFF) is the most widely used additive manufacturing (AM) technology for printing thermoplastic materials, among them the ABS. A significant problem of 3D-printed parts manufactured by AM-FFF is the anisotropy of their mechanical properties. Thus, it is of great importance to understand the impact of the build strategy of the mechanical properties and failure mechanisms of AM-FFF ABS components. This research aims, at least partly, to fill this gap by studying the structure and mechanical behavior by performing fracture surface analysis of AM-FFF ABS specimens under the three-point bend test. For this purpose, three build orientations (flat, on-edge and upright), each built at 0°/90° and -45°/+45° raster angles and oblique printed samples (0°, 15°, 30°, 45°, 60°, and 75°) built at -45°/+45° raster angles were prepared. The results revealed that the build direction with the lowest density, the flexural modulus of elasticity, flexural strength, and deflection was in the upright direction for both 0°/90° and -45°/+45° raster orientations. Overall, two main failure modes were observed for the tested specimens: (1) inter-layer/inter-raster bond failure, which is the main contributor to failure of all upright samples and (2) intra-layer/trans-raster failure, which is the main contributor to failure of flat and on-edge specimens printed at -45°/+45° raster orientation. The results of the oblique printed samples demonstrate that a single crack initiation can transform into a few inter-laminar and intra-laminar fracture surfaces due to competing stress fields and structural gradients

Electronic Collective Modes and Superconductivity in Layered Conductors

A distinctive feature of layered conductors is the presence of low-energy electronic collective modes of the conduction electrons. This affects the dynamic screening properties of the Coulomb interaction in a layered material. We study the consequences of the existence of these collective modes for superconductivity. General equations for the superconducting order parameter are derived within the strong-coupling phonon-plasmon scheme that account for the screened Coulomb interaction. Specifically, we calculate the superconducting critical temperature Tc taking into account the full temperature, frequency and wave-vector dependence of the dielectric function. We show that low-energy plasmons may contribute constructively to superconductivity. Three classes of layered superconductors are discussed within our model: metal-intercalated halide nitrides, layered organic materials and high-Tc oxides. In particular, we demonstrate that the plasmon contribution (electronic mechanism) is dominant in the first class of layered materials. The theory shows that the description of so-called ``quasi-two-dimensional superconductors'' cannot be reduced to a purely 2D model, as commonly assumed. While the transport properties are strongly anisotropic, it remains essential to take into account the screened interlayer Coulomb interaction to describe the superconducting state of layered materials.Comment: Final version (minor changes) 14 pages, 6 figure