Modeling of Bolt Joint Behavior of Cast Aluminum Alloy (A380-T5) by Coupling Creep and Plasticity in Finite Element Analysis

Aluminum casting alloys exhibit creep behavior when the materials are exposed to high temperature and load. In this article, the stress- and temperature-dependent creep behavior of a die casting A380-T5 aluminum alloy was simulated using a classical constitutive model. The bolt-load retention behavior of the material was analyzed in a head bolt joint in an aluminum engine under thermal cycle condition using the finite element method. In this simulation, transient thermal analysis was performed first to calculate the metal temperature at the head bolt joint as a function of time during engine thermal cycling. This temperature was then input as the thermal loading in the subsequent structural analysis to calculate its effect on the bolt-load retention. The finite element analysis (FEA) model for the bolt-load retention simulation includes not only the plasticity in all metal components but also the creep properties of head bolt threads in the cast aluminum engine block. The FEA model was validated by good correlation between the predicted head bolt-load loss and the experimental measurement during engine thermal cycling. The simulation results also indicated that creep in the head bolt threads of cast aluminum engine block was mainly responsible for the load loss in the head bolt joint. This article is based on a presentation given in the symposium entitled “Simulation of Aluminum Shape Casting Processing: From Design to Mechanical Properties” which occurred March 12–16, 2006 during the TMS Annual Meeting in San Antonio, Texas under the auspices of the Computational Materials Science and Engineering Committee, the Process Modeling, Analysis and Control Committee, the Solidification Committee, the Mechanical Behavior of Materials Committee, and the Light Metal Division/Aluminum Committee.     

Optimum 4-Transmit-Antenna STBC/SFBC with Angle Feedback and a Near-Optimum 1-Bit Feedback Scheme

A 4-antenna transmit diversity scheme based on space time/frequency block coding (STBC/SFBC) with 1-bit feedback is proposed. We first describe the optimum scheme with angle feedback. We then identify the condition under which choosing between only two choices of angles effectively eliminates the larger between the real and imaginary parts of the interference term. Simulation shows that the 1-bit feedback scheme achieves near-optimum performance.     

Analysis of the Sensitivity of Decision Analysis Results to Errors and Simplifications in Problem Structure: Application to Lake Erie Ecosystem Management

In practical decision analyses, the ldquocurse of dimensionalityrdquo compels one to make simplifying assumptions that can introduce errors into estimates of various indexes that interest decision-makers. These indexes include the expected performance of optimal and suboptimal strategies, the benefit of explicitly considering uncertainty, and the benefit of additional information. This paper quantifies the effects on these indexes of simplifying assumptions, including discretization of the decision space, omission of some decision variables and uncertainties from the decision tree, and disregarding of risk aversion. To reduce errors arising from discretization of the decision space, we use a multidimensional cubic spline to interpolate the performance of alternatives between a few simulated points. A case study analyzes decisions concerning phosphorus loading, fisheries management, and lower trophic research projects in Lake Erie under multiple criteria and ecological uncertainties. Results show that spline-based solutions often yield potentially superior decisions from those based on discretized decision spaces, but that omitting important uncertainties makes more of a difference in this case study's decisions and indexes than simplifying the decision space. On the other hand, incorrect multicriteria weights affect the case study's outcomes more than incorrect probabilities.     

Ultrathin oxide-nitride dielectrics for rugged stacked DRAMcapacitors

Ultrathin dielectric materials that provide high capacitance values are needed for 64- and 256-Mb stacked DRAMs. It is shown that capacitance values as high as 12.3 fF/μm² can be obtained with ultrathin nitride-based layers deposited on rugged polysilicon storage electrodes. These films present the reliability and low leakage current levels required for 3.3-V applications. The nitride thickness, however, cannot be scaled much below 6 nm to avoid the oxidation-punchthrough mechanisms that appear when too-thin films are unable to withstand the reoxidation step     

Image flow segmentation and estimation using displaced spatial gradient

There are two main causes of inaccuracies in estimating image flows using gradient based techniques. One is the erroneous measurement of gradients in brightness and the other is the blurring of motion boundaries which is caused by the smoothness constraint. In the Letter, the gradient measurement error of conventional methods is analysed and a new technique based on this analysis proposed.<>     

A low-power baseband receiver IC for frequency-hopped spreadspectrum communications

A baseband receiver IC which will be incorporated into a low-power frequency-hopped spread spectrum (FH/SS) transceiver for 902-928 MHz ISM band applications is presented. The chip performs noncoherent binary/quaternary frequency shift keying (FSK) demodulation, equal-gain diversity combining of dual antenna branches, and symbol and frequency synchronization. The chip also accommodates variable data rates from 2 to 160 kb/s, programmable hop rates, and tunable bandwidth Loop filters. The core area of the 1-μm CMOS chip is 3.9 mm×3.9 mm with a power consumption of 4.5 mW at 10 MHz from a 3-V supply. A baseband transceiver system utilizing this receiver chip for the prototype handset to demonstrate a point-to-point communication link is also described. Two XILINX FPGA chips were used to implement the remainder of the baseband transceiver functions, including frequency control logic for FSK modulation, acquisition control, data framing, symbol interleaving and deinterleaving, and interface control for data and voice     

Generalized impedance control of robot for assembly tasks requiringcompliant manipulation

To perform assembly tasks requiring compliant manipulation, the robot must follow a motion trajectory and exert an appropriate force profile while making compliant contact with a dynamic environment. For this purpose, a generalized impedance in the task space consisting of a second-order function relating the motion errors and interaction force errors is introduced such that the contact force can be commanded and controlled. With generalized impedance control, the robot can behave with a desired dynamic characteristic when it interacts with the environment. To ensure the success of the assembly, a strategy during task planning which takes into consideration the interrelation between motion and force trajectories as well as contact compliance is introduced. The generalized impedance control method is applied to the prismatic joint of a selective compliance assembly robot arm (SCARA) robot for inserting a printed circuit board (PCB) into an edge connector socket. Depending on the progress of the parts joining operation, various amount of interaction forces are generated which have to be accommodated. It is demonstrated that an assembly strategy which consists of a sequence of carefully planned target impedance can enable the task to be executed in a desirable manner. The effectiveness of this approach is illustrated through experiments by comparing the results with those obtained using a well-established position control scheme as well as the original impedance control method