Modification of the mechanical properties of synthetic fibers by grafting vinyl monomers

Graft polystyrene has been synthesized on polypropylene fibers. The isometric heating curves of the grafted fibers have two maxima. The first is associated with the preserved oriented polypropylene structures, the second with the oriented structures formed directly in the process of polystyrene synthesis. The maximum stress corresponding to the latter maximum is proportional to the amount of polystyrene and the degree of orientation of the starting polypropylene and depends on the mechanical stress in the fiber during the process of polystyrene synthesis.Mekhanika Polimerov, Vol. 3, No. 6, pp. 963–969, 1967     

Polypropylene reinforced with aramid and glass fibers

The effect of the chemical nature of the aramid fibers Phenylone, Terlon, Armos, and SVM on the mechanical, thermophysical, and antifriction properties of reinforced polypropylene was investigated. It was found that the composite filled with SVM fibers based on a stiff-chain polymer has high tensile strength and bending modulus. Reinforcement of polypropylene with Phenylone stiff-chain fibers produces a composite with a high impact viscosity. Organoplastics based on polypropylene and aramid fibers have a low density and friction coefficient and high durability. Reinforcement of polypropylene with aramid (SVM) and glass fibers increases the technological properties of the composites. The glass-filled organoplastics developed can be used in instrument making, radio engineering, and machine building as antifriction and construction materials.Ukrainian State Chemical Technological University, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 106–110, January–February, 1996.     

Interference of stress and vibration relaxation processes in the sound frequency range

An apparatus is described which allows one to study the mutual effect of stress-relaxation processes occurring for various deformations and vibrations of sound frequency. The effect of mechanical stress and stress relaxation is investigated for mechanical dynamical properties in samples of high-pressure polyethylene, isotactic polypropylene, polyamidoester on a base of anilinophthalein, and polyimide obtained by the solid-phase ring formation of polyamidoester. The effect of the supermolecular structure of polypropylene on the nature of the temperature dependence of the loss angle tangent is shown.     

Strengthening of Polypropylene Strips by Orientational Stretching in Liquids

Data on the orientational stretching of polypropylene strips in process liquids serving as plasticizers of polypropylene are presented. Such a stretching allows one to avoid many complications characteristic of stretching in air and to increase the maximum stretch ratio significantly (up to 15). The stretching of strips is accompanied by changes in the crystalline structure of polypropylene and by transformation of the amorphous phase into a crystalline one. It is established that the specific strength of the orientationally stretched strips as a function of stretch ratio has a maximum. This is caused by the competing processes of macromolecule orientation in the stretching direction and the destruction of molecular bonds, which leads to the origination of microdamages in the strip surface layer and to a growing content of amorphous phase. It is shown that the extraction of process liquids from the stretched strips increases their specific strength by 20–30%.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 251–264, March–April, 2005.     

Experimental investigation and approximation of the temperature-dependent stiffness of short-fiber reinforced polymers

In order to predict the effective material properties of a short-fiber reinforced polymer (SFRP), homogenization of elastic properties with the self-consistent (SC) scheme and the interaction direct derivative (IDD) method is performed by means of µCT data describing the microstructure of the composite material. Using dynamic mechanical analysis (DMA), the material properties of both, polypropylene and fiber reinforced polypropylene are investigated by tensile tests under thermal load. The measured storage modulus of the matrix material is used as input parameter for the homogenization scheme. The effective properties of SFRP are compared to experimental results from DMA. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Alkali-silica reaction expansions in high-performance and normal-strength cement grouts reinforced with steel and synthetic fibers

The role of brass-coated steel (BCS), hooked steel (HS), and polypropylene fibers in controlling the expansion and cracking in high-performance and normal-strength cement grouts is investigated. The grouts were prepared using the BCS, HS (from 0 to 2.0 vol.%), or polypropylene (from 0 to 0.30 vol.%) fibers. Standard prisms (25 × 25 × 300 mm³) were cast and cured for 40 days before subjecting to a special treatment to accelerate the alkali-silica reaction (ASR). Expansion measurements were taken for these prisms over an immersion period of up to 98 days, during which the extent of cracking was monitored. The results indicated a significant role of brass-coated and hooked steel fibers at volume fractions of 1.0 and 2.0% and polypropylene fibers at a volume fraction of 0.15% in reducing the expansion due to the ASR. The reduction in expansion of high-performance and normal-strength grouts was also dependent, in addition to the fiber type and content, on the duration of immersion of the grouts in a NaOH solution.Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 1, pp. 121– 130, January–February, 2005.     

Thermal conductivities of polymers at various temperatures and pressures

The authors describe an apparatus and method for investigating the coefficient of thermal conductivity of high-density and low-density polyethylene, polypropylene, polyorthochlorostyrene, and polyparachlorostyrene in relation to temperature and pressure.     

Effect of spherulite dimensions on polypropylene adhesion

The effect of spherulite growth (diameter 25 to 185 µ) on the adhesive properties and density of polypropylene is studied. The adhesive properties are evaluated in terms of adhesive power and adhesion susceptibility. It is shown that, as distinct from the cohesive strength, the strength of adhesive joints in which polypropylene is used as substrate and SKB butadiene elastomer as adhesive increases somewhat with the diameter of the spherulites, while the density of the polypropylene increases linearly. It is suggested that the observed increase in adhesion susceptibility is due to surface development associated with the growth of the spherulites.Mekhanika Polimerov, Vol. 1, No. 3, pp. 3–7, 1965     

Alteration of the mechanical behaviour of polypropylene owing to successive introduction of multiwall carbon nanotubes and stretching

Stretching effects on the morphology of polypropylene/carbon nanotube composites is the focus of this work. The material under investigation was composed of isotactic polypropy lene (iPP) and multiwall car bon nanotubes (MWCNTs) in amount of 0.5 wt.%. The iPP and CNTs were mixed under sonication in a solvent, and the homogenized mixture was melted and pressed. The rectangular plates produced from the material were stretched by a constant load at a fixed temperature in order to obtain extended specimens. The scanning electron microscopy, a thermal gravimetric analysis, and the differential scanning calorimetry were employed to study variations in the structural morphology of the material. A dynamic mechanical analysis showed that the strain-induced crystallization of polypropylene and the possible Stone–Wales transformation of the carbon nanotubes due to stretching improved the mechanical performance of the nanocomposites considered.     

Investigation of the thermophysical properties of polypropylene

The temperature and pressure dependence of the thermophysical properties of isotactic polypropylene has been investigated. The experimental results are presented and discussed.Mekhanika Polimerov, Vol. 2, No. 5, pp. 793–797, 1966     

Creep and failure of polypropylene under low-frequency cyclic loadings

The results of tests on polypropylene specimens under conditions of low-frequency cyclic and static loading are compared. It is shown that as compared with static tests, there is an increase in longevity and a reduction in overall deformation under low-frequency cyclic loadings.     

Investigation of the deformation and failure of polypropylene under indenters of different shapes

In order to study the residual strain distribution in a nontransparent polymer (polypropylene) under identers of various shapes (sphere, cone, cylinder) multilayer colored specimens with a predetermined distribution of the layers were used. By cutting along selected planes it was possible to estimate the residual strains in the interior of the specimen, both qualitatively and quantitatively. By this means we investigated the relations between the reversible and residual strains in polypropylene as a function of the indenter penetration depth and, moreover, the relations between the deformed and failed volumes of polymeric material under indenters of different shapes. It was shown that a change in indenter shape may produce a considerable change (by a factor of 3 or more) in the relations between the penetration, strain propagation, and failure volumes, which should be taken into account both in determining the hardness of polymeric materials by different methods and in selecting the shape of sealing elements.     

混凝土轴拉加卸载随机损伤模型的建立与试验验证

为了分析及深入探讨混凝土在受拉加载及卸载情况下的力学特性,基于随机损伤本构关系提出了一种混凝土轴拉加卸载模型,推导出了混凝土加卸载的应力 应变关系表达式.为了印证理论表达式,进行了混凝土轴向拉伸及加卸载的试验研究,测得了混凝土的材料参数及其相应的轴拉加卸载应力-应变曲线.结合模型的计算结果,对混凝土的轴拉加卸载试验结果进行了对比分析,结果表明:混凝土轴拉加卸载模型能够预测混凝土的极限强度,同时能描述混凝土的强度软化、加载过程中的弹模折减及卸载后的塑性变形.     

细观等效理论预测再生混凝土宏观力学参数北大核心CSCD

预测分析再生混凝土各组分对再生混凝土宏观力学参数的影响是开展再生混凝土基本力学性能的一种方式.为了分析再生混凝土各组分对再生混凝土宏观力学参数的影响,根据再生混凝土的细观结构组成,建立了细观等效模型,利用扭转变形、细观夹杂理论、弹性等效思想和M-T模型方法,推导了由原生骨料、老界面层、老水泥砂浆、新界面层和新水泥砂浆等组成的再生混凝土的宏观力学参数预测模型.预测结果表明,随着再生骨料的取代率增加,水泥砂浆的含量不断增加,再生混凝土孔隙率也随之增大,导致再生混凝土的Poisson比随之增大,弹性模量、剪切模量和体积模量不断降低.模型的预测结果较好地反映了再生混凝土宏观力学参数随再生骨料取代率的增加不断变化的这一趋势,也为再生混凝土宏观力学参数的预测提供了一条简单实用的新方法,有利于再生混凝土基本力学性能的研究分析.     

Investigation of the structure and physicomechanical properties of polypropylene film

The authors have investigated the effect of the dynamic degree of crystallinity, stereoisomeric composition, intrinsic viscosity, and other factors on the nature of the structure formed when polypropylene is made into film and on the physicomechanical properties of the film.Mekhanika Polimerov, Vol. 3, No. 6, pp. 970–976, 1967     

Effect of combined extrusion parameters on mechanical properties of basalt fiber-reinforced plastics based on polypropylene

Basalt fibers are efficient reinforcing fillers for polypropylene because they increase both the mechanical and the tribotechnical properties of composites. Basalt fibers can compete with traditional fillers (glass and asbestos fibers) of polypropylene with respect to technological, economic, and toxic properties. The effect of technological parameters of producing polypropylene-based basalt fiber-reinforced plastics (BFRPs) by combined extrusion on their mechanical properties has been investigated. The extrusion temperature was found to be the main parameter determining the mechanical properties of the BFRPs. With temperature growth from 180 to 240°C, the residual length of the basalt fibers in the composite, as well as the adhesive strength of the polymer-fiber system, increased, while the composite defectiveness decreased. The tensile strength and elastic modulus increased from 35 to 42 MPa and 3.2 to 4.2 GPa, respectively. At the same time, the growth in composite solidity led to its higher brittleness. Thus, a higher temperature of extrusion allows us to produce materials which can be subjected to tensile and bending loads, while the materials produced at a lower temperature of extrusion are impact stable. The effect of the gap size between the extruder body and moving disks on the mechanical properties of the BFRPs is less significant than that of temperature. An increase of the gap size from 2 to 8 mm improves the impregnation quality of the fibers, but the extruder productivity diminishes. The possibility of controling the properties of reinforced polypropylene by varying the technological parameters of combined extrusion is shown. The polypropylene-based BFRPs produced by the proposed method surpass the properties of glass and asbestos fiber-reinforced plastics.Submitted to the 10th International Conference on Mechanics of Composite Materials (Riga, April 20–23, 1998).Ukrainian State University of Chemical Technology, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 6, pp. 845–850, November–December, 1997.     

混凝土搅拌站的选址问题研究

混凝土搅拌站的选址,在施工中占有十分重要的地位.针对混凝土需求随时间不规则变化的情况以及混凝土有效期短等特点,提出了混凝土需求不规则变化的选址模型.该模型把选址与各个时间段的资源配置结合起来确定混凝土搅拌站的位置,在保证需求最大限度得到满足的同时,使选址能够兼顾到尽可能多的需求点,最大化搅拌站的利润.应用该模型和算法成功地解决了一个实际问题,算例验证了模型和算法的有效性.     

高强混凝土立方强度尺寸效应的分析计算

对55组高强混凝土立方强度实测数据作了分析,并给出了计算公式.表明高强混凝土立方强度尺寸效应不同于普通混凝土.     

Helical flow of non-Newtonian polymeric media

The helical flow problem is analyzed with reference to polypropylene. The methods and results of a series of helical flow experiments are described.Topchiev Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 497–505, May–June, 1971.