Effects of heat-affected zone peak temperatures on the microstructure and properties of 2090 Al alloy

The influence of the heat-affected zone (HAZ) thermal cycles on the microstructure and mechanical properties of 2090 Al alloy has been investigated. Emphasis is placed on the effects of the HAZ peak temperatures on the T3 and T8 tempered 2090. The HAZ thermal cycles were simulated using a Gleeble, and tensile tests were conducted at 293 and 77 K. The difference in properties between the HAZ and the base metal is primarily caused by the dissolution of strengthening phases. At 578 K, degradation in strength occurs due to dissolution of δ’ phase and, at 773 K, due to dissolution of T₁ phase. The thermal cycle to 648 K leads to an observable growth of T₁ phase, but the volume fraction is too low to be an effective strengthener. As a result, at the 293 K test temperature, the base metal (BM) tempers become irrelevant with the peak temperatures above 578 K, and the ultimate tensile strength (UTS) curves of both the BM-T3 and BM-T8 coincide and follow the same trend up to 853 K. At the 77 K temperature, the strength and elongation of the BM and the thermally cycled specimens in the T3 and T8 tempered conditions follow the trend seen at 293 K and exhibit higher strengths and elongations. Formerly Graduate Student Research Assistant Graduate Student Research     

Investigation of the fracture and fragmentation of explosively driven rings and cylinders

Cylinders and rings fabricated from AerMet^® 100 alloy and AISI 1018 steel have been explosively driven to fragmentation in order to determine the fracture strains for these materials under plane-strain and uniaxial-stress conditions. The phenomena associated with the dynamic expansion and subsequent break up of the cylinders are monitored with high-speed diagnostics. In addition, complementary experiments are performed in which fragments from the explosively driven cylinders are recovered and analyzed to determine the statistical distribution associated with the fragmentation process as well as to determine failure mechanisms. The data are used to determine relevant coefficients for the Hancock–McKenzie (Johnson–Cook) fracture model. Metallurgical analysis of the fragments provides information on damage and failure mechanisms.     

A lumped parameter model of the polymer electrolyte fuel cell

A model of a polymer electrolyte fuel cell (PEFC) is developed that captures dynamic behaviour for control purposes. The model is mathematically simple, but accounts for the essential phenomena that define PEFC performance. In particular, performance depends principally on humidity, temperature and gas pressure in the fuel cell system. To simulate accurately PEFC operation, the effects of water transport, hydration in the membrane, temperature, and mass transport in the fuel cells system are simultaneously coupled in the model. The PEFC model address three physically distinctive fuel cell components, namely, the anode channel, the cathode channel, and the membrane electrode assembly (MEA). The laws of mass and energy conservation are applied to describe each physical component as a control volume. In addition, the MEA model includes a steady-state electrochemical model, which consists of membrane hydration and the stack voltage models.     

Pascal’s triangle-based range-free localization for anisotropic wireless networks

This paper introduces a Pascal’s triangle model to draw the potential locations and their probabilities for a normal node given the hop counts to the anchors according to the extent of detour of the shortest paths. Based on our proposed model, a Pascal’s triangle-based localization (PTL) algorithm using local connectivity information is presented for anisotropic wireless networks with a small number of anchors. The superiority of the PTL algorithm has been validated over the state-of-the-art algorithms through MATLAB simulations. We have shown that compared to the other algorithms, the PTL algorithm achieves higher localization accuracy with even fewer anchors. We have also validated the performance of the PTL algorithm in a real environment.     

Fast Multibit Decision Polar Decoder for Successive-Cancellation List Decoding

Successive-cancellation list (SCL) decoding for polar codes has the disadvantage of high latency owing to serial operations. To improve the latency, several algorithms with additional circuits have been proposed, but the area becomes larger. This paper proposes a fast multibit decision method having-high area efficiency based on the SCL decoding algorithm. First, multiple bits can be determined to reduce clock cycles using new nodes represented by the information bits and frozen bits. We propose the new nodes called the combined nodes and the other node in this paper. The combined nodes that combine redundant operations of the fast-simplified SC (fast-SSC) algorithm can increase area efficiency. The other node with bit patterns other than the node types of the fast-SSC algorithm performs an 8-bit multibit decision to reduce the number of decoding cycles. Latency is further reduced by applying a sphere decoding method to the other node. In addition, a sorter is proposed to reduce the critical path delay. As a large number of path metrics causes sorter delays, the proposed sorter can achieve high throughput with the small area. The proposed (1024, 512) SCL decoder showed negligible performance degradation in the simulation using Matlab and was synthesized using 65 nm CMOS technology. The proposed decoder achieves about 1.3Gbps with the small area. As a result, the area-throughput efficiency is at least 1.4 times higher than the state-of-the-art works over 1 Gbps.

     

New continuous-flow mixed-radix (CFMR) FFT Processor using novel in-place strategy

The paper proposes a new continuous-flow mixed-radix (CFMR) fast Fourier transform (FFT) processor that uses the MR (radix-4/2) algorithm and a novel in-place strategy. The existing in-place strategy supports only a fixed-radix FFT algorithm. In contrast, the proposed in-place strategy can support the MR algorithm, which allows CF FFT computations regardless of the length of FFT. The novel in-place strategy is made by interchanging storage locations of butterfly outputs. The CFMR FFT processor provides the MR algorithm, the in-place strategy, and the CF FFT computations at the same time. The CFMR FFT processor requires only two N-word memories due to the proposed in-place strategy. In addition, it uses one butterfly unit that can perform either one radix-4 butterfly or two radix-2 butterflies. The CFMR FFT processor using the 0.18 /spl mu/m SEC cell library consists of 37,000 gates excluding memories, requires only 640 clock cycles for a 512-point FFT and runs at 100 MHz. Therefore, the CFMR FFT processor can reduce hardware complexity and computation cycles compared with existing FFT processors.     

New Cost-Effective Simplified Euclid’s Algorithm for Reed-Solomon Decoders

This paper proposes a cost-effective simplified Euclid’s (SE) algorithm for Reed-Solomon decoders, which can replace the existing modified Euclid’s (ME) algorithm. The new proposed SE algorithm, using new initial conditions and polynomials, can significantly reduce the computation complexity compared with the existing ME and reformulated inversionless Berlekamp-Massey (RiBM) algorithms, since it has the least number of coefficients in the new initial conditions. Thus, the proposed SE architecture, consisting of only 3t basic cells, has the smallest area among the existing key solver blocks, where t means the error correction capability. In addition, the SE architecture requires only the latency of 2t clock cycles to solve the key equation without initial latency. The proposed RS decoder has been synthesized using the 0.18 μm Samsung cell library, and the gate count of the RS decoder, excluding FIFO memory, is only 40,136 for the (255, 239, 8) RS code.     

The growth of Cu-Sn intermetallics at a pretinned copper-solder interface

This article reports a comparative study of the formation and growth of intermetallic phases at the interface of Cu wetted with a thick solder joint or a thin, pretinned solder layer. The η phase (Cu₆Sn₅) forms when Cu is wet with eutectic solder at temperatures below 400 °C. The intermetallic layer is essentially unaffected by aging at 70 °C for as long as 13 weeks. On aging a eutectic joint at 170 °C, the η-phase intermetallic layer thickens and ε phase (Cu₃Sn) nucleates at the Cu/intermetallic interface and grows to a thickness comparable to that of the η phase, while a Pb-rich boundary layer forms in the solder. The aging behavior of a thin, pretinned eutectic layer is qualitatively different. At 170 °C, the Sn in the eutectic is rapidly consumed to form η-phase intermetallic, which converts to ε phase. The residual Pb withdraws into isolated islands, and the solderability of the surface deteriorates. When the pretinned layer is Pb-rich (95Pb-5Sn), the Sn in the layer is also rapidly converted into η phase, in the form of dendrites penetrating from the intermetallic at the Cu interface and discrete precipitates in the bulk. How ever, the development of the intermetallic largely ceases when the Sn is consumed; ε phase does not form, and the residual Pb remains as an essentially continuous layer, preserving the solderability of the sample. These observations are interpreted in light of the Cu-Sn and Pb-Sn phase diagrams, the temperature of initial wetting, and the relative diffusivities of Cu and Sn in the solder and intermetallic phases. A.J. SUNWOO, Formerly with the Lawrence Berkeley Laboratory, Berkeley, CA,