Online Research on Plasticizing Process of Starch Under Superimposed Vibration Field

A novel testing machine, integrating plastic vibration processing with molding, based on a multipass rheometer, was used to investigate the effect of the complex force field on plasticization of taro and wheat thermoplastic starch (TPS) melts. Various kinds of continuous vibration fields could be tested by controlling the movement of pistons. A superimposed vibration field, combining the effects of vibration and shear, was obtained by adding a high-frequency low-amplitude oscillation on a low-frequency high-amplitude oscillation. The rheological properties of starch were directly monitored during and after the plasticization process without removing the starch melts out of the testing machine. The apparent viscosity of the TPS melts were obtained for different high-frequency oscillation conditions by monitoring the pressure difference in the cavity. The plasticization preparation time was used to characterize the benefit provided by the superimposed vibration field. The results showed the decrease of the percentage of the average plasticizing preparation time for taro starch was 3.4%, while that for wheat starch was 1.6% compared to single, low-frequency, high-amplitude oscillation. Comparison of the plasticizing preparation time under different vibration frequencies showed that the plasticization was promoted by applying the superposed vibration field, and the effective degree was related to the vibration frequency and starch type. Both TPS exhibited shear-thinning behavior after the plasticization, and samples of both types of starch which were plasticized under higher vibration frequency presented lower apparent viscosities at certain shear rates.     

On the use of a reduced enhanced solid-shell (RESS) element for sheet forming simulations

A recently proposed reduced enhanced solid-shell (RESS) element [Alves de Sousa, R.J., Cardoso, R.P.R., Fontes Valente, R.A., Yoon, J.W., Grácio, J.J., Natal Jorge, R.M., 2005. A new one-point quadrature enhanced assumed strain (EAS) solid-shell element with multiple integration points along thickness: Part I – Geometrically Linear Applications. International Journal for Numerical Methods in Engineering 62, 952–977; Alves de Sousa, R.J., Cardoso, R.P.R., Fontes Valente, R.A., Yoon, J.W., Grácio, J.J., Natal Jorge, R.M., 2006. A new one-point quadrature enhanced assumed strain (EAS) solid-shell element with multiple integration points along thickness: Part II – Nonlinear Applications. International Journal for Numerical Methods in Engineering, 67, 160–188.] is based on the enhanced assumed strain (EAS) method with a one-point quadrature numerical integration scheme. In this work, the RESS element is applied to large-deformation elasto-plastic thin-shell applications, including contact and plastic anisotropy. One of the main advantages of the RESS is its minimum number of enhancing parameters (only one), which when associated with an in-plane reduced integration scheme, circumvents efficiently well-known locking phenomena, leading to a computationally efficient performance when compared to conventional 3D solid elements. It is also worth noting that the element accounts for an arbitrary number of integration points through thickness direction within a single element layer. This capability has proven to be efficient, for instance, for accurately describing springback phenomenon in sheet forming simulations. A physical stabilization procedure is employed in order to correct the element’s rank deficiency. A general elasto-plastic model is also incorporated for the constitutive modelling of sheet forming operations with plastic anisotropy. Several examples including contact, anisotropic plasticity and springback effects are carried out and the results are compared with experimental data.     

Optimal testing for additivity in multiple nonparametric regression

We consider the problem of testing for additivity in the standard multiple nonparametric regression model. We derive optimal (in the minimax sense) non- adaptive and adaptive hypothesis testing procedures for additivity against the composite nonparametric alternative that the response function involves interactions of second or higher orders separated away from zero in L ²([0, 1] ^d )-norm and also possesses some smoothness properties. In order to shed some light on the theoretical results obtained, we carry out a wide simulation study to examine the finite sample performance of the proposed hypothesis testing procedures and compare them with a series of other tests for additivity available in the literature.     

Continuous, large strain, tension/compression testing of sheet material

Modeling sheet metal forming operations requires understanding of the plastic behavior of sheet alloys along non-proportional strain paths. Measurement of hardening under reversed uniaxial loading is of particular interest because of its simplicity of interpretation and its application to material elements drawn over a die radius. However, the compressive strain range attainable with conventional tests of this type is severely limited by buckling. A new method has been developed and optimized employing a simple device, a special specimen geometry, and corrections for friction and off-axis loading. Continuous strain reversal tests have been carried out to compressive strains greater than 0.20 following the guidelines provided for optimizing the test. The breadth of application of the technique has been demonstrated by preliminary tests to reveal the nature of the Bauschinger effect, room-temperature creep, and anelasticity after strain reversals in commercial sheet alloys.     

A simulation-based approach to two-stage stochastic programming with recourse

In this paper we consider stochastic programming problems where the objective function is given as an expected value function. We discuss Monte Carlo simulation based approaches to a numerical solution of such problems. In particular, we discuss in detail and present numerical results for two-stage stochastic programming with recourse where the random data have a continuous (multivariate normal) distribution. We think that the novelty of the numerical approach developed in this paper is twofold. First, various variance reduction techniques are applied in order to enhance the rate of convergence. Successful application of those techniques is what makes the whole approach numerically feasible. Second, a statistical inference is developed and applied to estimation of the error, validation of optimality of a calculated solution and statistically based stopping criteria for an iterative alogrithm. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.Supported by CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), Brasília, Brazil, through a Doctoral Fellowship under grant 200595/93-8.     

Processing and physical property relationships in injection-molded isotactic polypropylene. 1. Mechanical properties

The aim of the research reported in these two articles was to explore the relationship between processing conditions and the physical properties of different grades of isotactic polypropylene injection moldings and propylene/ethylene copolymers. This first article describes the methods and processing conditions used for molding, together with mechanical test results. Both conventional and shear-controlled orientation injection molding (SCORIM) have been employed for the production of moldings. SCORIM is based on the application of specific macroscopic shears to a solidifying melt, which in turn, facilitates enhanced molecular alignment. SCORIM results in more pronounced molecular orientation than conventional injection molding, which is consistent with the substantial increase in Young's modulus of moldings produced by SCORIM. By controlling the processing parameters it is possible to control and enhance the stiffness without loss of tensile strength. An increase of up to four times in impact strength has been achieved with SCORIM as well as a substantial increase in Young's modulus. The conventional injection moldings containing pronounced molecular orientation exhibited impact resistance well below that for the SCORIM moldings. The mechanical tests carried out at 80°C showed that the high-temperature mechanical properties of all the materials, converted into moldings using SCORIM, exhibited substantial enhancement when compared with moldings of the same material converted by conventional injection molding. © 1997 John Wiley & Sons, Inc.     

A Note on the Multivariate Normal Hazard

The ISO* property of noncentrality parameters is derived for the expected value of an ISO* function of independent nonnegative two-parameter compound Poisson random variables and is then applied to unbiasedness of tests and monotonicity of power functions of tests in an order-restricted hypothesis testing problem for the noncentrality parameter. The ISO* property and the Schur convexity are also studied for a class of two-parameter distributions which has the additive property (i.e., is closed under convolution) and contains the one-parameter family with the semigroup property as a special case.     

Experience with wheat flour reference material

The Chemical Section of the National Office of Measures, Hungary (OMH) [1] embarked on the preparation of a wheat sample series as a Certified Reference Material [2] (CRM) in 1992. The practical implementation of the wheat sample series has shown that test- ing laboratories are in great need of easy-to-use flour reference samples to objectively and independently qualify wheat. To fill this need, we have developed a three-term flour reference sample series. The certification process was car-ried out according to ISO recommendations. Investigations of the long-term stability [3] and the application of wheat and flour CRMs are continuing. Wheat is one of the most widely grown crops in Hun- gary and it is one of the major determinative factors in the economy. Its uniform and objective qualification is of outstanding importance. There are well-equipped laborato-ries with sufficient experience to assess wheat flour quality, howev- er, proficiency testing has shown that certified samples need to be used to achieve exact and uniform measuring results. Received: 12 November 1999 Accepted: 16 August 2000     

Nanoporous membranes by cooperative self‐assembly of functionalized SEBS and titania

Sol–gel chemistry was adeptly exploited to fabricate nanoporous membranes by cooperative self‐assembly of modified triblock copolymer (SEBS‐NH₂) and titania network. Reinforcement of the matrix was achieved by hydrolytic condensation of tetraisopropoxytitanate without/with compatiblizing agent (3‐glycidyloxypropyl triethoxysilane), yielding two hybrid systems. Incorporation of different proportions of TiO₂ provoked well‐built variations in morphology of compatiblized SEBS‐NH₂/TiO₂ nanocomposites. At low titania loading, spherical nanoparticles were found well‐dispersed in regimented triblock domains while addition of higher amounts of TiO₂ generated nanoporous membranes by mutual self‐assembling of matrix and the reinforcement. Relative improvement of tensile and thermal properties over uncompatiblized nanocomposites was observed owing to enhanced interfacial interactions. Eventually, a combination of the two phases (17.5 wt. % titania in SEBS‐NH₂) demonstrated ample mechanical reinforcement, thermal and morphological profiles, ensuing robust self‐assembled nanostructures. Forthcoming prospects are envisioned as well. Copyright © 2013 John Wiley & Sons, Ltd.     

超高速摄影仪转镜谐响应的数值与试验分析

对超高速摄影仪转镜进行了谐响应数值分析,得到转镜在正弦周期激励下的幅频响应曲线、应力等值线图。转镜的幅频响应曲线在354 Hz处出现峰值,一阶扭转和二阶弯曲共振带出现了叠加,在1 600 Hz处曲线有细微的波动,转镜在一阶弯曲共振点处的幅频曲线幅值远大于其在1 600 Hz处的幅值,共振点处的等效应力是其匀速运转时的358倍。在转镜试验测试系统上测得的转镜幅频曲线在297 Hz 和355 Hz处均出现了峰值,数值解和实验结果能够很好地吻合。这说明转镜的一阶弯曲固有频率共振带是转镜的危险速度带,一阶弯曲是转镜出现动力学破坏的主要原因。仿真结果与实验结果的一致性表明,利用数值方法预测转镜的设计能否成功克服受迫振动引起的破坏是有效的。