In Situ Processing of Silicon Carbide Layer Structures

A novel route to low-cost processing of silicon carbide (SiC) layer structures is desribed. The processing involves pressureless liquid-phase cosintering of compacted power layers of SiC, containing alumina (Al₂O₃) and yttria (Y₂O₃ sintering additives to yield and yttrium aluminum garnet (YAG) second phase. By adjusting the β:α SiC phase ratios in the individual starting powders, alternate layers with distinctively different microstructures are produced: (i) "homogeneous" microstructures, with fine equiaxed SiC grains, designed for high strength; and (ii) "heterogeneous: microstructures with coarse and elongate SiC grains, designed for high toughness. By virtue of the common SiC and YAG phases, the interlayer interfaces are chemically compatible and strongly bonded. Exploratory Hertzian indetation tests across a bilayer interface confirm the capacity of the tough heterogeneous layer to inhibit potentially dangerous cracks propagating through the homogeneous layer. The potential for application of this novel processing approach to other layer architectures and other ceramic systems is considered.     

Physical,mechanical and thermal properties of cross laminated timber made with coconut wood

European Journal of Wood and Wood Products - The fundamental material properties of coconut wood cross-laminated timber (CLT) were experimentally evaluated with a focus on the effect of the...     

Determination of transfer capability region using boundary tracing method

In electricity markets, transfer capability is a parameter showing the potential of a considered source–sink pair to transfer power. This paper enhances transfer capability monitoring by proposing a method to determine this parameter with respect to a region referred to as the ‘transfer capability region’ (TCR). The boundary of a TCR is traced by using the modified predictor–corrector process on a plane of real and reactive powers. The TCR shows a set of feasible loading points at the sink area. Moreover, the shape of TCR always changes according to the system parameters. This paper also defines the outermost boundary of the TCR when the considered parameters are set to be free. We apply the proposed method to test systems, and then compare to the maximum loading points obtained by the conventional transfer capability calculation. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Contact-Induced Transverse Fractures in Brittle Layers on Soft Substrates: A Study on Silicon Nitride Bilayers

An analysis of transverse cracks induced in brittle coatings on soft substrates by spherical indenters is developed. The transverse cracks are essentially axisymmetric and geometrically conelike, with variant forms dependent on the location of initiation: outer cracks that initiate at the top surface outside the contact and propagate downward; inner cracks that initiate at the coating/substrate interface beneath the contact and propagate upward; intermediate cracks that initiate within the coating and propagate in both directions. Bilayers consisting of hard silicon nitride (coating) on a composite underlayer of silicon nitride with boron nitride platelets (substrate), with strong interfacial bonding to minimize delamination, are used as a model test system for Hertzian testing. Test variables investigated are contact load, coating/substrate elastic-plastic mismatch (controlled by substrate boron nitride content), and coating thickness. Initiation of the transverse coating cracks occurs at lower critical loads, and shifts from the surface to the interface, with increasing elastic-plastic mismatch and decreasing coating thickness. This shift is accompanied by increasing quasi-plasticity in the substrate. Once initiated, the cracks pop in and arrest within the coating, becoming highly stabilized and insensitive to further increases in contact load, or even to coating toughness. A finite element analysis of the stress fields in the loaded layer systems enables a direct correlation between the damage patterns and the stress distributions: between the transverse cracks and the tensile (and compressive) stresses; and between the subsurface yield zones and the shear stresses. Implications of these conclusions concerning the design of coating systems for damage tolerance are discussed.     

Within-tree variability of internal stress generated during drying of rubberwood lumber

The generation of drying stress within the lumber from the trunk of a rubber tree prepared from different locations (radial distance up to 110 mm and height up to 4 m) has been investigated in real-time by using a restoring force measurement on half-split specimens. Drying was performed at constant dry-bulb and wet-bulb temperatures of 90 and 60?°C, respectively. The entire restoring force profiles do not vary significantly with height. In addition, before and after the reversal of stress, the force profiles are largely similar and the maximum negative and positive forces are approximately equal regardless of wood locations within the tree trunk. However in the radial direction, the process of stress reversal consisting of two negative force maxima appears to proceed slower in the inner juvenile wood than in the outer mature wood. Upon water immersion of the specimens for 4 months, the second negative force maximum gradually disappears and the force profiles with a shorter stress reversal period become less sensitive to the wood locations. An examination of the drying curves in the second stage of drying during stress reversal also indicates a slower migration of bound water out of the lumber in the juvenile wood compared to that in the mature wood. The drying is also faster in the water-immersed specimens. It is concluded that variability of the internal stress within the trunk of a rubber tree originated from the role of cell wall amorphous constituents and cell wall extractives on creep property and the movement of bound water within the wood cell wall during drying.     

Crack Suppression in Strongly Bonded Homogeneous/Heterogeneous Laminates: A Study on Glass/Glass-Ceramic Bilayers

A study is made of a glass/glass-ceramic bilayer as a model homogeneous/heterogeneous laminate. The underlying objective is microstructural design of ceramic layer systems with optimum mechanical properties, alternating hard layers, for wear resistance, with tough layers, for fracture resistance. Mica flakes in the glass-ceramic layer inhibit the propagation of well-developed intrusive cracks, by bridging; these same flakes render the structure susceptible to distributed damage, by providing discrete weakness at the microstructural level. A major distinguishing feature of the bilayer design is the incorporation of a strong interface, so that cracks are inhibited by the underlayer rather than deflected between the layers. Vickers and Hertzian indentation tests on specimen cross sections demonstrate the capacity of the glass-ceramic layer to arrest radial and cone cracks penetrating from the adjacent glass layer. Additional Hertzian tests on the outer surfaces of glass layers in a coating/substrate configuration show diffuse damage accumulation in the glass-ceramic substrate layers. This diffuse damage absorbs energy and shields cone cracks in the glass from the applied loading. Implications concerening the design of damage-tolerant laminate structures are discussed.     

Construction material procurement using Internet-based agent system

Conventional material purchasing has some problems related with solicitation process, such as searching for suppliers and obtaining product data information. E-trading portals may reduce the problems; however, new problems occur due to their approaches to build a closed system with their own customers and suppliers. In this research, a decentralized database system equipped with electronic agents for material procurement is proposed. Results showed that this system can be used to assist human purchasers to carry out solicitation in identifying suppliers, searching materials, and preparing purchase orders.