Radiation-induced grafted UHMW–PE chopped fibers as reinforcing filler in polychloroprene

Ultrahigh molecular weight polyethylene (UHMW-PE) has been grafted with acrylonitrile using gamma radiation. The graft yield of the monomer was controlled by the proper choice of radiation dose and monomer concentration. The grafted chopped fibers were introduced in polychloroprene (CR) rubber mixes in order to improve the interfacial adhesion between fibers and matrix. It has been found that the improvement in the mechanical properties of rubber composites obtained depended markedly on the fiber concentration in the rubber mixture. Scanning electron micrographs showed the presence of a continuous phase of rubber adhered to the surface of grafted fiber. © 1997 John Wiley & Sons, Ltd.     

A Review of Recent Progress in Solid State Fabrication of Composites and Functionally Graded Systems Via Friction Stir Processing

Friction stir processing (FSP) is a rapidly emerging newer solid-state technique for composite fabrication. It involves surface modification which in turn enables successful adaptation of surface properties through plastic deformations in solid state. During initial years of FSP inception, it was primarily employed in development of metal matrix composites of light metal alloys like aluminum. However, recently, it has gained an alluring role in fabrication of composites of various nonferrous and ferrous metal alloys as well as of polymers. In addition to composite fabrication, FSP has evolved as a revolutionary technique in developing functionally graded systems/surfaces (FGS) of metal matrix. This article covers all aspects of FSP in which reinforcement particles are embedded in the base matrix to develop composites and FGS. It presents a critical review on domains of recent developments, effects of different types of reinforcement particles and properties enhancement of composites, and FGS fabrication. In addition to this, various issues, challenges, and future work that demand attention are systematically addressed.     

Is It Better to Forget? Stimulus-Response, Prediction, and the Weight of Past Experience in a Fast-Paced Bargaining Task

Decision makers in dynamic environments such as air traffic control, firefighting, and call center operations adapt in real-time using outcome feedback. Understanding this adaptation is important for influencing and improving the decisions made. Recently, stimulus-response (S-R) learning models have been proposed as explanations for decision makers' adaptation. S-R models hypothesize that decision makers choose an action option based on their anticipation of its success. Decision makers learn by accumulating evidence over action options and combining that evidence with prior expectations. This study examines a standard S-R model and a simple variation of this model, in which past experience may receive an extremely low weight, as explanations for decision makers' adaptation in an evolving Internet-based bargaining environment. In Experiment 1, decision makers are taught to predict behavior in a bargaining task that follows rules that may be the opposite of, congruent to, or unrelated to a second task in which they must choose the deal terms they will offer. Both models provide a good account of the prediction task. However, only the second model, in which decision makers heavily discount all but the most recent past experience, provides a good account of subsequent behavior in the second task. To test whether Experiment 1 artificially related choice behavior and prediction, a second experiment examines both models' predictions concerning the effects of bargaining experience on subsequent prediction. In this study, decision models where long-term experience plays a dominating role do not appear to provide adequate explanations of decision makers' adaptation to their opponent's changing response behavior.     

Behavior of CFRP-confined concrete cylinders with a compressive steel reinforcement

The paper presents results of an experimental investigations carried out to estimate the cooperation between a steel bar reinforcement and round concrete cylinders confined by a carbon-epoxy composite, concerning the increase in the concrete compression strength due the composite wrapping. The steel bar reinforcement with its yield stress considerably increases the bearing capacity of concrete. This also happens above the unconfined concrete strength of specimens. The onset of reinforcement yielding roughly coincides with reaching of the unconfined concrete strength at a compressive strain of ≈0.20%, and therefore it does not produce a change in the tangent modulus of the stress-strain relationships above the limit of linearity. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 3, pp. 293–308, May–June, 2007.     

兵力增援微分对策优化模型及解法

研究了对抗双方的兵力增援问题，建立了兵力增援微分对策优化理论模型及其最优性条件，给出了兵力增援的最优策略。本研究结果对作战方案的制定，评价和作战指挥决策具有理论指导意义。     

Optimal Design of Hole Reinforcements for Composite Structures

In many technical applications like aerospace and automotive structures, holes in thin-walled composite components are necessary for some reason. It easily happens that the presence of a hole results in a detrimental stress concentration in the vicinity of the hole with a strength degradation and premature failure of the structure, respectively. In order to avoid the aforementioned overloading and to achieve a sufficient strength, in practice, a local reinforcement is employed. In the present study, reinforcements by elliptic doublers,as well as doublers adapted to reinforcement requirements in a layerwise manner, are considered. The increasing demands of a low weight and high strength for modern structures lead to the problem of an optimal reinforcement design. For this purpose, an appropriate optimization model is set up, a structural model is developed to describe the mechanical behavior (displacements, stresses, etc.) of such structures, and the techniques of mathematical structural optimization are used to find an optimal design in a systematic manner. In this study, the finite-element method is applied to the structural analysis. Eventually, an appropriate mathematical optimization algorithm is used to approach the desired design optimum in an iterative way. The implemented procedure works with a good reliability and efficiency and yields optimal reinforcement designs which are very useful for direct engineering applications.     

Model for the fracture energy of glassy polymer–polymer interfaces

The increase in the interfacial fracture energy (G_c) with increasing interfacial width (a_i) goes through a transition at a critical value of a_i that is unique to each polymer–polymer system. This transition point does not scale with the bulk entanglement spacing (d_t) for different systems, implying that the role of chain friction in reinforcing these interfaces is more important than previously thought. A theoretical model has been developed to calculate G_c as a function of the interfacial stress transfer due to individual polymer chains. When including the effects of chain friction only, the model reproduces the nonuniversal behavior of G_c with respect to a_i/d_t but yields poor fits for a_i/d_t > 1. The effects of entanglements are then added by calculating the fraction of entangled chains as a function of a_i/d_t. This contribution, although not material specific, matches the qualitative behavior of G_c for large values of a_i/d_t. When both contributions are included in the model, excellent fits are obtained for all data sets. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2377–2386, 2002     

热致液晶高分子与聚碳酸酯原位复合材料的研究

<正> 热致液晶高分子(TLCP)是一种具有高强度、高模量和良好加工性能的新型高分子材料,在流场、温度场和应力场的作用下,易于取向,产生自增强效果.与工程塑料原位(insitu)复合,可以改善工程塑料的流变性能和加工性能,同时还可以提高工程塑料的力学     

In Situ Formation of Particulate Silica in Natural Rubber Matrix by the Sol-Gel Reaction

The sol-gel reaction of tetraethoxysilane was conducted in natural rubber (NR) matrix to obtain NR/in situ silica mixtures. In other words, in situ filling of silica onto NR was conducted. The mixtures were compounded with curing regents, and their viscosities were evaluated. The in situ silica with a coupling agent afforded the lowest viscosity compared not only with a conventional silica (VN-3) but also with a carbon black (HAF). The curing behaviors were most favorable for in situ silica compound. Physical properties of the vulcanizates were also evaluated, and again in situ silica stock gave the best result.     

Morphological,rheological, and mechanical properties of ethylene propylene diene monomer/carboxylated styrene-butadiene rubber/multiwall carbon nanotube nanocomposites

Abstract

A hybrid nanocomposite based on ethylene propylene diene monomer/carboxylated styrene-butadiene rubber (EPDM/XSBR) blend with different concentrations (0–7 phr) of multiwall carbon nanotube (MWCNT) was prepared on a two-roll mill. The role of grafted maleic anhydride (EPDM-g-MA) as compatibilizer and the effect of different concentrations of MWCNT on mechanical properties, morphology, rheological and curing characteristics of nanocomposites were investigated. The curing behavior of the prepared nanocomposites was studied using a rheometer. Also, the microstructure of nanocomposites was observed using TEM. By increasing the MWCNT concentration in the compatible blends, the curing time and scorch time of the blends decreased, while the maximum and minimum torque increased. Failure surface morphology studies showed that the existence of EPDM-g-MAH compatibilizer improved the distribution of MWCNT within the polymer matrix and uniform distribution of MWCNT with a small amount of aggregation was obtained. On the other hand, the presence of MWCNT in the matrix led to a sharper surface of the fracture. Also, mechanical properties such as modulus, tensile strength, hardness, fatigue, resilience and elongation-at-break for compatible EPDM/XSBR nanocomposite showed better results than those for incompatible composite.