Effect of aminomethoxy silane and olefin block copolymer on rheomechanical and morphological behavior of fly ash-filled polypropylene composites

The design of new composites based on a polypropylene (PP) matrix and filler fly ash particles leads to changes in processability, morphology, and physical properties of the raw thermoplastic. The new materials should combine the processability of common thermoplastics with improved toughness. We have designed more environmentally friendly composites filled with residual ash. To improve composite toughness (one of the principal drawbacks of these PP/ash composites), a new olefin block copolymer (OBC) was included in the filler–matrix interface, and to modify the ash surface, an organosilane was used to enhance interface strength. The present work analyzes the influence of composite formulation on the morphological, mechanical, and rheological properties of the new composites. In terms of rheological properties, modulus and viscosity were enhanced as a function of the amount of filler added. The incorporation of a silane coupling agent into composites brought about beneficial changes in morphology and rheology, related with improved dispersion of ash particles and increased filler–matrix interactions. Finally, when OBC was added to the filler–matrix interface, composite morphology was more homogenous. The best rheological and mechanical properties were obtained when the ratio of OBC to fly ash particles was 1:2.     

High strain-rate modeling of the interfacial effects of dispersed particles in high strength aluminum alloys

The interfacial effects of dispersed particles on the dynamic deformation of high strength aluminum alloys have been investigated using an eigenstrain-based formulation coupled with dislocation-density based crystalline plasticity and a microstructurally based finite element framework. This accounts for the unrelaxed plastic strains associated with the interfacial behavior of dispersed particles, such as Orowan looping. Particle spacing had a significant effect on the distribution of plastic shear slip, with localization occurring between the particles for smaller particle spacing. The eigenstress field associated with larger particles led to longer-range interaction of pressure fields, which can promote void coalescence for nucleated voids at the particle-matrix interface. Grain orientation also had a significant effect on the behavior associated with the particles, with plastic shear slip localizing at the particle-matrix interfaces for low angle grain-boundary (GB) misorientations, and at GBs and GB junctions for high angle GB misorientations.     

陶瓷颗粒增强金属基复合材料的细观强度分析

陶瓷颗粒增强金属基复合材料的失效主要有界面脱粘、增强粒子开裂等新的细观结构损伤机制。为了减小这些不足并对细观失效过程有一个清晰的了解,近来人们对金属基复合材料进行了大量研究,在此基础上,本文用细观力学的方法和损伤模型研究了陶瓷颗粒增强金属基复合材料的强度和损伤失效。为了计算方便,陶瓷颗粒简化为在复合材料中随机分布的椭球形粒子,然后以二相胞元模型计算分析了金属基体、颗粒中的应力应变分布情况,结果表明,基体中应力极不均匀,界面区存在应力集中,并计算了界面弧形裂纹扩展时的能量。最后分别提出了基体,颗粒和界面的失效强度准则,本文结果对于颗粒增强金属基复合材料具有普遍的实用性。     

Elastic and elastic–plastic singular fields around a crack-tip in particulate-reinforced composites with progressive debonding damage

This paper deals with elastic and elastic–plastic singular fields around a crack-tip in particulate-reinforced composites with debonding damage of particle-matrix interface. Numerical analyses are carried out on a crack-tip field in elastic-matrix and elastic–plastic-matrix composites reinforced with elastic particles, using a finite element method developed based on an incremental damage theory of particulate-reinforced composites. A particle volume fraction and interfacial strength between particles and matrix of the composites are parametrically changed. In the elastic-matrix composites, a unique elastic singular field is created on the complete damage zone in the vicinity of a crack-tip in addition to the conventional elastic singular field on the no damage zone. The macroscopic stress level around a crack-tip is reduced by the debonding damage while the microscopic stress level of the matrix remains unchanged. In the elastic–plastic-matrix composites, the damage zone develops in addition to the plastic zone due to matrix plasticity, and both the macroscopic and microscopic stress revels around a crack-tip are reduced by the debonding damage. It is concluded from the numerical results that the toughening due to damage could be expected in the elastic–plastic-matrix composites, while it is questionable in the elastic-matrix composites.     

Linear and non-linear nature of the flow of polypropylene filled with ferrite particles: from low to concentrated composites

The flow behavior of a filled suspension consisting of ferrite particles suspended in a polypropylene matrix with and without the addition of a commercial dispersant (Solplus DP310) was studied. The composites were filled with 10, 20, 30, and 40 vol.%. Both capillary and parallel disk rotational flows were employed. On the one hand, dynamic results confirm general trends found for highly concentrated systems. The higher is the filler level, the lower is the linear viscoelastic domain. When adding the dispersant agent, it was shown a larger linear viscoelastic domain, lower moduli values and thus, lower viscosity. Also, the critical strain, G′ and G′′ showed a power law dependency on the volume fraction. On the other hand, the capillary results showed no dependency of the flow properties on the die. Thus, no slip of the suspension at the wall was observed. Actually, this experimental finding elucidated that the significant decrease on viscosity produced by the addition of the dispersant agent at 40 vol.% is principally due to lubricant effects and not at all to slip contributions. The results also reveal three distinct flow regimes. Low, moderate, and high shear rates lead to different microstructure under flow.     

Dynamic-mechanical properties of interfacially modified glass sphere filled polyethylene

Model composites of spherical glass particles dispersed in a matrix of high density polyethylene were prepared both with and without interfacial modification by an azidofunctional trialkoxysilane. Dynamic mechanical measurements of the composites in the melt state were recorded. The unmodified composites behave as theoretically predicted and the effect of particle—particle interaction at high volume fractions can be measured. The composites with a modified interfacial region have greater shear moduli due to the effect of a region surrounding the particle modified by the silane. The material in this region is largely bound to the glass surface and was examined by Fourier transform infrared spectroscopy after extraction of the bulk matrix. Theoretical calculations are shown to be useful in calculating the mechanical properties and volume fraction of the interfacial region.     

Rheology as a tool for the analysis of the dispersion of carbon filler in polymers

The aim of this work is to validate the use of dynamic oscillatory measurements in the melt to characterize the dispersion of a filler in a matrix after melt blending. Polyethylene oxide (PEO) is used as a polymeric matrix. Active carbon is used as a filler at a constant filler volume content of 26.4%. The melt viscosity of the polymeric matrix is varied by melt blending of two miscible POE and polyethylene glycol (PEG) species having very different molecular weight distributions. This enables to obtain various matrix viscosities and in turn various states of dispersion of the filler that were characterized by optical microscopy and image analysis. Dynamic mechanical measurements in the melt in the terminal zone show a large increase of the moduli associated to the presence of the filler. Comparison with the results of optical microscopy shows that this increase is clearly related to the dispersion. The interparticle distance is likely to be the leading parameter rather than the number of particles. Characterization of the amount of bound polymer shows that the amount of bound polymer is nearly independent of the matrix composition. Futhermore, the composition of the bound layer reflects the matrix composition though PEO is slightly preferentially bound on the active carbon.     

颗粒增强复合材料压缩行为的位错动力学模拟

颗粒增强铜基复合材料因具有极高的强度和弹性模量, 优异的导电、导热性能和抗磨损能力, 被广泛应用于航天航空、汽车、电子工业等领域. 第二相强化是其主要的强化方式, 其通过合金中弥散的微粒阻碍位错运动, 可有效提高金属材料的力学性能, 提高其服役安全. 针对该问题本文采用三维离散位错动力学(three-dimensional discrete dislocation dynamics, 3D-DDD)方法, 对微尺度颗粒增强铜基复合材料进行了微柱压缩模拟, 分析了位错与第二相颗粒交互作用对材料力学响应的影响, 揭示第二相颗粒强化的微观机理. 本研究将第二相颗粒视为位错不可穿透的球形微粒, 采用位错绕过机制模拟颗粒与位错的交互作用过程. 通过调控滑移面相对于第二相颗粒中心的距离发现: 屈服应力和应变硬化率均随距离的增大而减小. 研究也发现Schmid因子越高的滑移系, 屈服应力越低, 后续应变硬化率越低. 多位错与颗粒交互作用的模拟发现, 同一滑移面中位错间的反应和不同滑移系中位错的交互作用可能是导致屈服应力和应变硬化率降低的关键.      

Interfacial effects on the melt state behavior of polyethylene-EPDM-calcium carbonate composites

Dynamic mechanical spectra of various composites of high density polyethylene (PE), ethylene propylene diene rubber (EPDM), and calcium carbonate were obtained at 190°C with a parallel plate instrument. Interfacial effects were found to have a significant influence on the dynamic mechanical behavior of these composites.Composites of calcium carbonate in PE displayed prominent particle—particle interaction effects. This resulted in a greatly enhanced dynamic shear modulusG _d due to the filler addition. Treatment of the calcium carbonate with gamma-aminopropyltriethoxysilane (-APS) or gamma-methacryloxypropyltrimethoxysilane (-MPS) significantly reduced the particle—particle interactions. Solution deposition of EPDM or EPDM grafted with maleic anhydride (EPDM-MA) on the calcium carbonate, before incorporation into a PE composite, also had a significant effect on the composite properties. Comparison of data from composites treated with EPDM vs. EPDM-MA suggested the presence of an interaction between the calcium carbonate surface and the maleic anhydride modification. This conclusion was further supported by solid state proton NMR relaxation model experiments which showed significant immobilization of the EPDM-MA chains on the filler surface. The treatment of calcium carbonate with-APS or-MPS before incorporation into multicomponent polyethylene-rubber-filler composites also had a significant influence on the dynamic mechanical properties of the resultant composites. There is evidence for a reaction between-APS and EPDM-MA during processing on the roll mill.     

Mechanical and structural investigation of isotropic and anisotropic thermoplastic magnetorheological elastomer composites based on poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS)

Novel smart thermoplastic magnetorheological elastomer composites containing micron-sized magnetic carbonyl iron (CI) particles were prepared with a poly(styrene-ethylene-butylene-styrene) (SEBS) triblock copolymer utilized as the thermoplastic matrix rubber, and the structures and properties of the CI-SEBS composites were examined. The CI particles were uniformly dispersed in the composites prepared in the absence of the magnetic field at high temperatures T (>T $_{\rm g}^{\rm S})$ , and this isotropic composite exhibited a larger storage modulus G^?? compared to the SEBS matrix at room temperature (<?<T $_{\rm g}^{\rm S})$ where the EB phase therein was rubbery while the PS phase was in the glassy state. In contrast, the SEBS composite prepared under the magnetic field (with the intensity ???< 2.5?T) at high T (>T $_{\rm g}^{\rm S})$ contained a chain structure of CI particles. This chain structure became longer and better aligned on an increase of ?? up to a saturation of the particle magnetization and on an increase of the time interval of applying the field (that allowed the particles to move and equilibrate their aligned structure). The modulus G^?? of this ??pre-structured?? composite measured for both cases of ?? = 0 and ???> 0 in the direction perpendicular to the chain structure at room temperature was enhanced compared to G^?? of the isotropic composites. This difference of the filler effect (for ???=?0) and the magnetorheological effect (for ???> 0) between the pre-structured and isotropic composites was enhanced when the chain structure of the CI particles in the pre-structured composites became longer and better aligned. A mechanism(s) of this enhancement was discussed in relation to the morphologies (particle distribution) in the composites with the aid of a filler model and a molecular expression of the stress due to magnetically interacting particles.     

Stress-induced interfacial failure in filled polymer melts

We study a dynamic interfacial slip phenomenon in filled polymer melts. When a poly(dimethyl siloxane) melt of weight average molecular weight M _w = 93 700 is mixed with glass beads of diameter up to 45 m, the sample shows some evidence of breakdown of interfacial adhesion between the glass beads and the PDMS matrix at a level of oscillatory stress under which the pure PDMS melt exhibits no decay. The decay of viscoelastic properties with time is essentially independent of the amplitude of shear strain as long as the magnitude of the oscillating stress is sufficiently high. It is suggested that much higher local stress than the apparent applied stress may be generated between the narrowly spaced beads. The interfacial slip was observable because it was measured against a natural length scale d in the filled polymer melts which is the filler size or the inter-filler distance and is much smaller than the dimensions of the flow cell. The decay under high stress and healing of interfacial adhesion upon a large reduction in stress may be related to the de-bonding and reformation of hydrogen bonds between the PDMS chains and the glass bead surfaces.     

Micro-mechanical modelling of strain induced porosity under generally compressive stress states

This paper is concerned with the nucleation and growth of voids in a titanium alloy undergoing high temperature deformations under generally compressive stress states typical of forging processes. A micro-mechanical model for void nucleation has been developed based on a debonding process between primary alpha particles and the beta matrix. The finite element model developed has been used to examine in detail the stress state sensitivity of void nucleation within the particle-matrix system. The results obtained are compared with other phenomenological approaches showing good agreement for most stress states, but giving different results for a range of compressive stress states. A continuum-level representation of the micro-mechanical results has been obtained and implemented into a finite element model. Cylindrical specimen compression tests have been carried out over the strain rate range 0.005-5.0s⁻¹ and temperature range 925–975°C under conditions of high specimen-die friction.Regions of stress triaxiality that are tensile in nature were therefore generated, and the specimens tested to an overall strain of 0.5 were sectioned, polished and etched. The resulting distributions of voids were quantified, and compared with those predicted using the finite element model discussed above. Good quantitative agreement was obtained both in terms of the magnitude of the area fractions of voids and their distributions. The model also captures reasonably well the strain rate and temperature dependence of the voiding. However, the model assumptions of uniform distributions of alpha particles which are all perfectly spherical and with identical interfacial bond strengths are overly simple, and need to be improved.     

纳米Al2O3增强PA6复合材料的摩擦磨损性能研究

利用MMW-1型摩擦磨损试验机考察了纳米Al2O3增强PA6复合材料同45#钢对摩时的摩擦磨损性能,采用扫描电子显微镜观察分析了试样磨损表面形貌.结果表明:纳米Al2O3可以提高PA6的耐磨性能;在小于100 N低载荷下纳米Al2O3填充PA6复合材料的滑动摩擦系数符合粘弹性材料的变化规律;只有当填充量适当时,纳米Al2O3微粒才能有效地增强聚合物基体的抗磨粒磨损性能,并阻碍聚合物基体向偶件磨损表面的粘着转移;纳米Al2O3质量分数为10%的PA6复合材料的抗磨性能最佳.     

一种预测颗粒增强复合材料界面力学性能的新方法

界面在颗粒增强复合材料中起到传递载荷的关键作用, 界面性能对复合材料整体力学行为产生重要影响. 然而由于复合材料内部结构较为复杂, 颗粒与基体间的界面强度和界面断裂韧性难以确定, 尤其是法向与切向界面强度的分别预测缺乏有效方法. 本文以氧化锆颗粒增强聚二甲基硅氧烷(PDMS)复合材料为研究对象, 提出一种预测颗粒增强复合材料界面力学性能的新方法. 首先, 实验获得纯PDMS基体材料及单颗粒填充PDMS试样的单轴拉伸应力$\!-\!$应变曲线, 标定出PDMS基体材料的单轴拉伸超弹性本构关系; 其次, 建立与单颗粒填充试样一致的有限元模型, 选择特定的黏结区模型描述界面力学行为, 通过样品不同阶段拉伸力学响应的实验与数值结果对比, 分别给出颗粒与基体界面的法向强度、切向强度及界面断裂韧性; 进一步应用标定的界面力学参数, 开展不同尺寸及不同数目颗粒填充试样的实验与数值结果比较, 验证界面性能预测结果的合理性. 本文提出的界面力学性能预测方法简便、易操作、精度高, 对定量预测颗粒增强复合材料的力学性能具有一定帮助, 亦对定量预测纤维增强复合材料的界面性能具有一定参考意义.      

Two-fold enhancement in tensile strength of carbon nanotube–carbon fiber hybrid epoxy composites through combination of electrophoretic deposition and alternating electric field

A new carbon nanotube (CNT)–hybridized carbon fiber (CF) was introduced in an attempt to improve interfacial strength between CF and polymeric matrix. Amine-functionalized CNTs was radially deposited on the CF surface through a combination of alternating electric field with electrophoretic deposition process. Radial deposition of CNTs on CF formed a unique porous structure around CF that could significantly increase the interfacial adhesion through interlocking of polymeric matrix. Tensile properties and fatigue life of the reinforced composites were investigated in order to study the effect of interfacial adhesion on mechanical properties of reinforced composites. Results indicate that the radial deposition of CNT on CF can remarkably enhance the compatibility of polymeric matrix with CF. This improvement in compatibility of polymeric matrix with CNT–hybridized CF resulted in considerable enhancement in mechanical properties of composites. The interfacial reinforcing mechanism was explored through fractography of reinforced composites and possible failure modes have been precisely discussed.     

Dependence of nonlinear elasticity on filler size in composite polymer systems

Nanosized filler particles enhance the mechanical properties of polymer composites in a size-dependent fashion. This is puzzling, because classical elasticity is inherently scale-free, and models for the elasticity of composite systems never predict a filler-size dependence. Here, we study the industrially important system of silica-filled rubbers, together with a well-characterized model-filled crosslinked gel and show that at high filler content both the linear and nonlinear elastic properties of these systems exhibit a unique scaling proportional to the cube of the volume fraction divided by the particle size. This remarkable behavior makes it possible to predict the full mechanical response of particle-filled rubbers for small but finite deformations based solely on the rheology of the matrix and the size and modulus of the filler particles.     

Transient network model for a multiphase polymeric fluid

Rheological behaviors of entangled polymer melts filled with rigid solid particles are phenomenologically described based on a Yamamoto type transient network model. Entanglement points are described by one kind of temporary junctions with a lifetime _p . Presence of fillers introduces another kind of network junctions with a lifetime _s , characteristic of adsorption of polymer chains at the filler surface. The degree of compatibility of filler surfaces with the polymer medium is characterized in terms of the adsorption time _s relative to the disentanglement time _p . By incorporating the effects of interfacial slippage into the deformation mechanism of the transient network, one can explain the variation of such rheological functions as shear viscosity with surface treatment of fillers and with molecular weight of the polymer matrix at a given filler volume fraction.     

Influence of the particle size and volume fraction on micro-damage of the composites

The bulk and shear modulus of metal matrix composites with various volume fractions of particles are modified based on the Eshelby’s equivalent inclusion method combined with self-consistent scheme. By introducing the modified modulus, a new model, which can predict the particle size effects on the stress–strain relation under interfacial debonding damage between matrix and particles, is established. The results obtained from the present investigation show a better agreement with the experimental data.     

纳米尺度通道内的界面流体粘性研究

含液微纳米孔隙在自然界中普遍存在,在发展 日趋精密化、微型化的工业中也有着广泛的应用,深刻理解流体在微纳米通道内的物性变化对于相关自然现象以及工业应用具有重要的指导意义.本文基于分子动力学方法,建立了由金属铂板构成的二维纳米尺度通道分子模型,分别考察了受限Lennard-Jones流体和水的物性变化.根据密度、剪切应力...     

改性石墨烯增强聚四氟乙烯摩擦学性能的分子模拟研究

采用分子动力学模拟研究了接枝改性氧化石墨烯对聚四氟乙烯(PTFE)的增强作用与摩擦学性能的影响,首先选用KH550、KH560和KH570三种硅烷偶联剂接枝氧化石墨烯(GO),在填入纯聚四氟乙烯后计算其机械性能与摩擦性能. 对比得出KH560的增强效果最好,杨氏模量和剪切模量分别提高了205%和116%,摩擦系数提高了39.6%. 然后选用聚酰亚胺(PI)接枝氧化石墨烯,对比了接枝改性与物理共混两种方式对增强效果的影响,结果表明接枝改性的增强效果优于物理共混. 最后通过分析界面间相互作用力、结合能、原子相对浓度和原子运动速度等方式揭示了接枝氧化石墨烯对聚四氟乙烯基体的增强机理.