Natural frequencies of composite plates with random material properties using higher-order shear deformation theory

Composites are known to display a considerable amount of scatter in their material properties due to large number of parameters associated with the manufacturing and fabrication processes. In the present work, the material properties have been taken as random variables for accurate prediction of the system behavior. Higher order shear theory including rotatory inertia effects has been accounted for in the system dynamic equations. A first order perturbation technique has been employed to obtain the solution of the governing equations. An approach has been outlined for obtaining closed form expressions for the variances of eigen solutions. The effects of side to thickness ratio and variation in standard deviation of the material properties have been investigated for cross-ply symmetric and anti-symmetric laminates. The mean and standard deviations of the first five natural frequencies have been worked out for laminated rectangular plates with all edges simply supported. The higher order shear deformation theory results have been validated with Monte Carlo simulation results and compared with the results based on classical laminate and first order shear deformation theories.     

A concurrent control architecture for autonomous mobile robots using Asynchronous Production Systems

The quest for efficient real-time response by autonomous robots in hazardous environments necessitates not only fast computational schemes in expert systems but also requires insights on high performance data structures and concurrent algorithms that lead to elegant problem-solving methods in the AI discipline. towards this objective, this paper presents an Asynchronous Production System (APS) of architecture capable of monitoring and processing real-time information.     

Damage Progression Using Speckle-Correlation and High-Speed Imaging for Survivability of Leadfree Packaging Under Shock

Abstract:  In this paper, a methodology to predict failure of electronics under shock and vibration loads has been investigated. Reliability prediction models have been developed using optical feature extraction techniques for 6-leadfree solder alloy systems. Solder alloy systems investigated include, Sn1Ag0.5Cu, Sn3Ag0.5Cu, Sn0.3Ag0.7Cu, Sn0.3Ag0.7Cu0.1Bi, Sn0.2Ag0.7Cu0.1Bi-0.1Ni, 96.5Sn3.5Ag. Previously, Digital Image Correlation (DIC) has been used for measurement of thermally-induced deformation and material characterisation. In this paper, DIC has been used for transient dynamic measurements, and optical feature extraction. Board assemblies have been subjected to shock-impact in various orientations including the zero-degree JEDEC drop and the vertical free-drop. Transient deformation has been measured using both DIC and the strain gages. Measurements have been taken on both the package and the board side of the assemblies. Accuracy of high-speed optical measurement has been compared with that from discrete strain gages. Package architectures examined include-flex ball-grid arrays, tape-array ball-grid arrays, and metal lead-frame packages. Explicit finite-element models have been developed and correlated with experimental data. Three models were developed: smeared property models: Timoshenko-beam models: and explicit sub-models. The potential of damage identification and tracking for various solder alloys has been investigated. Data on the identification of damage proxies for competing failure mechanisms at the copper-to-solder, solder-to-printed circuit board, and copper-to-package substrate has been presented. Design envelopes have been developed based on Statistical Pattern Recognition (SPR). The design-envelope is intended for component integration to ensure survivability in shock and vibration environments at a user-specified confidence level.     

A semiparametric model for compositional data analysis in presence of covariates on the simplex

Compositional data occur as natural realizations of multivariate observations comprising element proportions of some whole quantity. Such observations predominate in disciplines like geology, biology, ecology, economics and chemistry. Due to unit sum constraint on compositional data, specialized statistical methods are required for analyzing these data. Dirichlet distributions were originally used to study compositional data even though this family of distribution is not appropriate (see Aitchison, 1986) because of their extreme independence properties. Aitchison (1982) endeavored to provide a viable alternative to existing methods by employing Logistic Normal distribution to analyze such constrained data. However this family does not include the Dirichlet class and is therefore unable to address the issue of extreme independence. In this paper generalized Liouville family is investigated to model compositional data which includes covariates. This class permits distributions that admit negative or mixed correlation and also contains non-Dirichlet distributions with non-positive correlation and overcomes deficits in the Dirichlet class. Semiparametric Bayesian methods are proposed to estimate the probability density. Predictive distributions are used to assess performance of the model. The methods are illustrated on a real data set.     

Huffman encoding of test sets for sequential circuits

Sequential circuits are hard to test because they contain a large number of internal states that are difficult to control and observe. Scan design is often used to simplify testing; however, scan is not always applicable because of area and performance penalties. Recent advances in sequential circuit testing have led to techniques and tools that provide test sets with high coverage of single stuck-line (SSL) faults for nonscan circuits. However, these test sets contain a large number of patterns and require a tester with considerable pattern depth. We investigate the application of Huffman codes to pattern encoding. This allows the use of low-cost testers that do not require excessive memory. Our method is especially applicable to nonscan and partial-scan embedded core circuits. We demonstrate the feasibility of our approach by applying it to SSL test sets for the ISCAS'89 benchmarks     

Thermal post buckling behavior of rectangular antisymmetric cross-ply composite plates

Summary The thermal post buckling behavior of simply-supported, antisymmetric cross-ply plates with immovable edges is investigated in this paper. For this purpose, a one term approximation for the inplane and transverse displacements is assumed and Rayleigh-Ritz method is used to obtain the equations of equilibrium. The question, whether the true thermal buckling (bifurcation buckling under thermal loads) exists for such plates is also addressed to. The conditions under which the thermal buckling in the classical sense occurs are derived. It is shown that nonlinear bending stiffness for such plates is direction dependent, because of an extra quadratic nonlinear term in addition to the usual cubic nonlinear term in the governing equilibrium equation. Results are presented for various plate configurations.     

The evening news and presidential evaluations.

Examined the effects of TV news accessibility, relevance, and expertise on presidential evaluations in 2 experiments. In each, Ss viewed TV news programs in which the amount of attention given to various national problems was manipulated. In Exp I, 73 undergraduates were divided among 3 conditions defined by level of exposure to stories about energy. Ss viewed 40 mins of news taken from 1979–1980 newscasts before answering questions about President Carter's performance, competence, and integrity. In Exp II, 140 Ss from the community watched newscasts that varied with regard to exposure level to particular national problems. After rating Carter's performance, Ss also completed a political expertise questionnaire. Results show that by drawing attention to certain national problems while ignoring others, TV news programs can define the standards by which presidents are evaluated. As predicted, this effect was greater for evaluations of general performance than for judgments of his competence and integrity, and it was more pronounced among novices than among experts. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Physical aging behavior of high-performance composites

The effect of physical aging on the viscoelastic creep properties of a thermoplastic-toughened cyanate ester resin (Fiberite 954-2) and its IM8/954-2 composites, and a semi-crystalline thermoplastic (Fiberite ITX) and its IM8/ITX composites was investigated. The study was carried out by using dynamic mechanical analysis (DMA) and tensile creep tests. Tests were performed on plain resin, [90 °]_4s, and [± 45 °]_2s composite specimens. Creep tests were conducted up to an aging time of 54 h with the logarithmic aging shift rate, μ, and its dependence on sub-glass transition aging temperature, being determined. The results showed significant physical aging in both material systems. To study the effect of long-term aging on creep behavior, momentary creep tests were conducted on the [± 45 °]_2s composites of both material systems at temperatures between 140 and 200 °C. Master curve plots were drawn from these momentary creep tests using the time/temperature superposition principle (TTSP). Effective time theory (ETT) was then used to modify TTSP and incorporate physical aging effects.     

Hollow spherical nanocapsules of poly(pyrrole) as a promising support for Pt/Ru nanoparticles based catalyst

Poly(pyrrole) hollow spherical nanocapsules (HSNCs-PPy) were prepared and used as an efficient support matrix to PtRu nanoparticles. γ-Radiation was utilized to load PtRu nanoparticles into Ppy-HSNC matrix. The advantageous characteristics of HSNCs-Ppy/PtRu catalyst as a support matrix for loading PtRu catalysts are presented.